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Background: Radiolabelled antibody targeting of cancer is limited by slow blood clearance. Pretargeting with a non-radiolabelled bispecific monoclonal antibody (bsMAb) followed by a rapidly clearing radiolabelled hapten peptide improves tumour localisation. The primary goals of this first pretargeting study in patients with the anti-CEACAM5 × anti-hapten (HSG) bsMAb, TF2, and the radiolabelled hapten-peptide, IMP288, were to assess optimal pretargeting conditions and safety in patients with metastatic colorectal cancer (CRC)., Methods: Different dose schedules were studied in four cohorts of five patients: (1) shortening the interval between the bsMAb and peptide administration (5 days vs 1 day), (2) escalating the TF2 dose (from 75 to 150 mg), and (3) reducing the peptide dose (from 100 to 25 μg). After confirmation of tumour targeting by (111)In-IMP288, patients were treated with a bsMAb/(177)Lu-IMP288 cycle., Results: Rapid and selective tumour targeting of the radiolabelled peptide was visualised within 1 h, with high tumour-to-tissue ratios (>20 at 24 h). Improved tumour targeting was achieved with a 1-day interval between the administration of the bsMAb and the peptide and with the 25-μg peptide dose. High (177)Lu-IMP288 doses (2.5-7.4 GBq) were well tolerated, with some manageable TF2 infusion reactions, and transient grades 3-4 thrombocytopaenia in 10% of the patients who received (177)Lu-IMP288., Conclusion: This phase I study demonstrates for the first time that pretargeting with bsMAb TF2 and radiolabelled IMP288 in patients with CEA-expressing CRC is feasible and safe. With this pretargeting method, tumours are specifically and rapidly targeted.

This article reviews the development of radioimmunoconjugates as a new class of cancer therapeutics. Numerous conjugates involving different antigen targets, antibody forms, radionuclides and methods of radiochemistry have been studied in the half-century since radioactive antibodies were first used in model systems to selectively target radiation to tumors. Whereas directly conjugated antibodies, fragments and subfragments have shown promise preclinically, the same approaches have not gained success in patients except in radiosensitive hematological neoplasms, or in settings involving minimal or locoregional disease. The separation of tumor targeting from the delivery of the therapeutic radionuclide in a multistep process called pretargeting has the potential to overcome many of the limitations of conventional, or one-step, radioimmunotherapy, with initial preclinical and clinical data showing increased sensitivity, specificity and higher radiation doses delivered. Our particular focus in pretargeting is the use of bispecific, trimeric (three Fab's) constructs made by a new antibody engineering method termed 'dock-and-lock.

Unlabelled: Two radiolabeled antibody products for the treatment of non-Hodgkin's lymphoma have been approved, thus indicating that cancer radioimmunotherapy (RAIT) has finally come of age as a new therapeutic modality, exemplifying the collaboration of multiple disciplines, including immunology, radiochemistry, radiation medicine, medical oncology, and nuclear medicine. Clinical trials are showing usefulness in other hematological neoplasms, but the treatment of solid tumors remains the major challenge, since the doses shown to be effective in hematological tumors are insufficient in the more common epithelial cancers. Nevertheless, use of RAIT in locoregional applications and in the treatment of minimal residual disease have shown promising, Results: There is also optimism that pretargeting procedures, including new molecular constructs and targets, will improve the delivery of radioactivity to tumors with less hematologic toxicity, and thus may become the next generation of RAIT.

A comparison of the therapeutic efficacy of a new bispecific monoclonal antibody (bsMAb)-pretargeting system vs the conventional direct targeting modality was undertaken. A bsMAb was made by coupling the Fab' of a humanized anti-CD20 antibody to the Fab' of a murine antibody directed against the peptide histamine-succinyl-glycine (HSG). The tumor targeting of the bsMAb was separated from the subsequent delivery of the radionuclide-bearing HSG peptide conjugated with (111)In or (90)Y. Nude mice bearing s.c. Ramos human B-cell lymphomas were injected with the bsMAb and then, 48 h later, (111)In/(90)Y-HSG peptide was given. At 3 h postinjection, tumor/blood ratios for pretargeted (111)In-HSG-peptide were similar to that observed with the directly conjugated (111)In-anti-CD20 IgG at its highest level on day 7, but by day 1, tumor/blood ratios were about 10-fold higher than the IgG. Tumors progressed rapidly in animals given 800 microCi of (90)Y-HSG peptide alone, whereas 5/10 animals in the group pretargeted by the anti-CD20 bsMAb were tumor-free 18 weeks later. The antitumor response in animals administered the pretargeted (90)Y-HSG peptide was also significantly superior to treatment with the directly radiolabeled (90)Y-anti-CD20 IgG, whether given as a single injection (P<0.007) or as a divided dose (P=0.016). This bsMAb-pretargeting procedure significantly improves the therapeutic response of targeted radionuclides in non-Hodgkin's lymphoma, warranting further development of this method of radioimmunotherapy.

The use of a divalent effector molecule improves bispecific antibody (bsMAb) pretargeting by enabling the cross-linking of monovalently bound bsMAb on the cell surface, thereby increasing the functional affinity of a bsMAb. In this work, it was determined if a bsMAb with divalency for the primary target antigen would improve bsMAb pretargeting of a divalent hapten. The pretargeting of a (99m)Tc-labeled divalent DTPA-peptide, IMP-192, using a bsMAb prepared by chemically coupling two Fab' fragments, one with monovalent specificity to the primary target antigen, carcinoembryonic antigen (CEA), and to indium-loaded DTPA [DTPA(In)], was compared to two other bsMAbs, both with divalency to CEA. One conjugate used the whole anti-CEA IgG, while the other used the anti-CEA F(ab')(2) fragment to make bsMAbs that had divalency to CEA, but with different molecular weights to affect their pharmacokinetic behavior. The rate of bsMAb blood clearance was a function of molecular weight (IgG x Fab' < F(ab')(2) x Fab' < Fab' x Fab' conjugate). The IgG x Fab' bsMAb conjugate had the highest uptake and longest retention in the tumor. However, when used for pretargeting, the F(ab')(2) x Fab' conjugate allowed for superior tumor accretion of the (99m)Tc-IMP-192 peptide, because its more rapid clearance from the blood enabled early intervention with the radiolabeled peptide when tumor uptake of the bsMAb was at its peak. Excellent peptide targeting was also seen with the Fab' x Fab' conjugate, albeit tumor uptake was lower than with the F(ab')(2) x Fab' conjugate. Because the IgG x Fab' bsMAb cleared from the blood so slowly, when the peptide was given at the time of its maximum tumor accretion, the peptide was captured predominantly by the bsMAb in the blood. Several strategies were explored to reduce the IgG x Fab' bsMAb remaining in the blood to take advantage of its 3-4-fold higher tumor accretion than the other bsMAb conjugates. A number of agents were tested, including those that could clear the bsMAb from the blood (e.g., galactosylated or nongalactosylated anti-id antibody) and those that could block the anti-DTPA(In) binding arm [e.g., DTPA(In), divalent-DTPA(In) peptide, and DTPA coupled to bovine serum albumin (BSA) or IgG]. When clearing agents were given 65 h after the IgG x Fab' conjugate (time of maximum tumor accretion for this bsMAb), (99m)Tc-IMP-192 levels in the blood were significantly reduced, but a majority of the peptide localized in the liver. Increasing the interval between the clearing agent and the time the peptide was given to allow for further processing of the bsMAb-clearing agent complex did not improve targeting. At the dose and level of substitution tested, galacosylated BSA-DTPA(In) was cleared too quickly to be an effective blocking agent, but BSA- and IgG-DTPA(In) conjugates were able to reduce the uptake of the (99m)Tc-IMP-192 in the blood and liver. Tumor/nontumor ratios compared favorably for the radiolabeled peptide using the IgG x Fab'/blocking agent combination and the F(ab')(2) x Fab' (no clearing/blocking agent), and peptide uptake 3 h after the blocking agent even exceeded that of the F(ab')(2) x Fab'. However, this higher level of peptide in the tumor was not sustained over 24 h, and actually decreased to levels lower than that seen with the F(ab')(2) x Fab' by this time. These results demonstrate that divalency of a bsMAb to its primary target antigen can lead to higher tumor accretion by a pretargeted divalent peptide, but that the pharmacokinetic behavior of the bsMAb also needs to be optimized to allow for its clearance from the blood. Otherwise, blocking agents will need to be developed to reduce unwanted peptide uptake in normal tissues.

There is currently no method to cure patients with disseminated colorectal cancer, which is the third leading cancer killer in the Western World. This report shows that the GW-39 intrapulmonary micrometastatic human colonic cancer model in nude mice can be cured with radiolabeled antibodies against carcinoembryonic antigen, and that this approach of radioimmunotherapy is superior to conventional chemotherapy with 5-fluorouracil and leucovorin (5-FU/LV). Monovalent Fab fragments labeled with 131I are superior to intact IgG when survival was evaluated 3, 7, and 14 days after implantation, leading to cures in up to 90% of the mice. Histological results provide support for the differences in therapeutic efficacy observed. Microautoradiography was used to evaluate the intratumoral distribution of each form of antibody. The enhanced tumor control by Fab compared with IgG could be explained in part by the homogeneity of radioantibody distribution of Fab. Biodistribution analysis and initial dose rate calculations for all three forms of antibody also help explain the ability of 131I-labeled Fab to provide better tumor growth control than seen with 131I-labeled IgG. Thus, radioimmunotherapy may be a new modality to treat metastatic disease, particularly when using small antibody fragments.

Unlabelled: This phase I study was initiated to determine the toxicity and therapeutic potential of high-dose 131I-MN-14 F(ab)2 anti-carcinoembryonic antigen monoclonal antibody (MAb) combined with autologous hematopoietic stem cell rescue (AHSCR) in patients with rapidly progressing metastatic medullary thyroid cancer., Methods: Twelve patients were entered into the study. Dose escalation was based on prescribed radiation doses to critical organs (i.e., kidney, lung, and liver). Starting doses were 900 cGy to the kidney and no more than 1200 cGy to the lung and liver, with dose increments of 300 cGy until the maximum tolerable dose is determined. Tumor targeting was assessed by external scintigraphy, toxicity was assessed according to the common toxicity criteria of the National Cancer Institute, and therapy responses were assessed by CT, serum carcinoembryonic antigen, and calcitonin., Results: One patient received 9.95 GBq 131I-MN-14 F(ab)2, for an initial dose of 656 cGy to critical organs, 8 received 900 cGy (8.69-17.98 GBq), and 3 received 1200 cGy (15.17-17.69 GBq). The MAb scans of all patients showed positive findings. Autologous hematopoietic stem cells were given to all patients 1-2 wk after therapy, when the total body radiation exposure was less than 5.2 x 10(-7) C/kg/h. Dose-limiting toxicity, defined as grade 3 or 4 nonhematologic toxicity, was not seen in the patient who received the 656-cGy dose, and only 1 of the 8 patients treated at the 900-cGy dose level had grade 3 toxicity, which was gastrointestinal and reversible. No dose-limiting toxicity was seen in the 3 patients treated at the 1200-cGy dose level. Except for the instance of grade 3 gastrointestinal toxicity, nonhematologic toxicity was relatively mild, with only grade 1 or 2 toxicity observed in 9 patients. No renal toxicity was seen. Of the 12 patients, 1 had partial remission for 1 y, another had a minor response for 3 mo, and 10 had stabilization of disease lasting between 1 and 16 months., Conclusion: The results show the safety of administering high myeloablative doses of 131I-MN-14 F(ab)2 with AHSCR in patients with metastatic medullary thyroid cancer. The antitumor responses in patients with aggressive, rapidly progressing disease are encouraging and warrant further research to optimize the effectiveness of this new treatment.

Both CD22 and CD20 have been used successfully as target molecules for radioimmunotherapy (RAIT) of low-grade B cell non-Hodgkin's lymphoma. Because both CD20 and CD22 are highly expressed relatively early in the course of B cell maturation, and because its expression is maintained up to relatively mature stages, we studied the potential of the humanized anti-CD22 antibody, hLL2, as well as of the chimeric anti-CD20 (chCD20) antibody, rituximab (IDEC-C2B8), for low- or high-dose (myeloablative) RAIT of a broad range of B cell-associated hematological malignancies. A total of 10 patients with chemorefractory malignant neoplasms of B cell origin were studied with diagnostic (n = 5) and/or potentially therapeutic doses (n = 9) of hLL2 (n = 4; 0.5 mg/kg, 8-315 mCi of 131I) or chCD20 (n = 5; 2.5 mg/kg, 15-495 mCi of 131I). The diagnostic doses were given to establish the patients' eligibility for RAIT and to estimate the individual radiation dosimetry. One patient suffered of Waldenström's macroglobulinemia, eight patients had low- (n = 4), intermediate- (n = 2) or high- (n = 2) grade non-Hodgkin's lymphoma, and one patient had a chemorefractory acute lymphatic leukemia, after having failed five heterologous bone marrow or stem cell transplantations. Three of these 10 patients were scheduled for treatment with conventional (30-63 mCi, cumulated doses of up to 90 mCi of 131I) and 7 with potentially myeloablative (225-495 mCi of 131I) activities of 131I-labeled hLL2 or chCD20 (0.5 and 2.5 mg/kg, respectively); homologous (n = 6) or heterologous (n = 1) stem cell support was provided in these cases. Good tumor targeting was observed in all diagnostic as well as posttherapeutic scans of all patients. In myeloablative therapies, the therapeutic activities were calculated based on the diagnostic radiation dosimetry, aiming at lung and kidney doses < or = 20 Gy. Stem cells were reinfused when the whole-body activity retention fell below 20 mCi. In eight assessable patients, five had complete remissions, two experienced partial remissions (corresponding to an overall response rate of 87%), and one (low-dose) patient had progressive disease despite therapy. In the five assessable, actually stem-cell grafted patients, the complete response rate was 100%. Both CD20 and CD22 seem to be suitable target molecules for high-dose RAIT in a broad spectrum of hematological malignancies of B cell origin with a broad range of maturation stages (from acute lymphatic leukemia to Waldenström's macroglobulinemia). The better therapeutic outcome of patients undergoing high-dose, myeloablative RAIT favors this treatment concept over conventional, low-dose regimens.

At the time of surgery, occult metastases (micrometastases) are present in more than 50% of colorectal cancer patients, and the liver is the most frequent site of apparent metastatic disease. Frequently, adjuvant chemotherapy is unable to prevent tumor recurrence. Thus, novel therapeutic strategies are warranted. The aim of this study was to establish a model of human colon cancer metastatic to the liver of nude mice, to assess, in this setting, the therapeutic efficacy of radioimmunotherapy (RAIT) compared to standard chemotherapy and to evaluate, in a Phase I/II trial, the toxicity and therapeutic efficacy of RAIT in colorectal cancer patients with small volume disease metastatic to the liver. Multiple liver metastases of the human colon cancer cell line GW-39 were induced by intrasplenic injection of a 10% tumor cell suspension. Whereas controls were left untreated, therapy was initiated on day 10 or 20 after tumor inoculation with the 131I-labeled, low affinity anticarcinoembryonic antigen (anti-CEA) monoclonal antibody (MAb), F023C5 (Ka = 10(7) liters/mol), or the high-affinity anti-CEA MAb, MN-14 (Ka = 10(9) liters/mol), or chemotherapy (5-fluorouracil/leucovorin (folinic acid) versus irinotecan) at their respective maximum tolerated doses (MTDs). Twelve colorectal cancer patients with small volume disease metastatic to the liver (all lesions < or = 2.5 cm) were entered into a mCi/m2-based Phase I dose escalation study with 131I-labeled humanized version of MN-14, hMN-14. The patients were given single injections, starting at 50 mCi/m2 and escalating in 10-mCi/m2 increments. The MTD was defined as the dose level at which < or = 1 of 6 patients develop grade 4 myelotoxicity. In the mice, untreated controls died from rapidly progressing hepatic metastases at 6-8 weeks after tumor inoculation. The life span of mice treated with 5-fluorouracil/leucovorin was prolonged for only 1-3 weeks, whereas irinotecan led to a 5-8-week prolongation. In contrast, at their respective MTDs, the 131I-labeled low-affinity anti-CEA MAb, F023C5, led to a 20% permanent cure rate, and the high affinity MAb, MN-14, led to an 80% permanent cure rate, when therapy was initiated at 10 days after tumor inoculation. In the 20-day-old tumor stage, although it prolonged life, 131I-F023C5 was unable to achieve cures, whereas 131I-MN-14 was still successful in 20%. Histologically, no remaining viable tumor cells could be demonstrated in these animals surviving > 6 months. In patients, the MTD was reached at 60 mCi/m2 of hMN-14 (at 70 mCi/m2, two of three grade 4 myelotoxicities). Of 11 assessable patients, 2 had partial remissions (corresponding to an objective response rate of 18%), and 5 (45%) had minor/mixed responses or experienced stabilization of previously rapidly progressing disease. These data suggest that in small volume disease, RAIT may be superior to conventional chemotherapy. Antibodies of higher affinity seem to be clearly superior. The clinical response rates in patients with small volume disease are encouraging, being comparable to the response rates of conventional chemotherapeutic regimens but with fewer side effects. Ongoing studies will show whether treatment at the MTD will further improve therapeutic results.

The pharmacokinetics, dosimetry, and immunogenicity of 131I- and (111)In-/90Y-humanized LL2 (hLL2) anti-CD22 monoclonal antibodies were determined in patients with recurrent non-Hodgkin's lymphoma. Fourteen patients received tracer doses of 131I-hLL2 followed 1 week later by therapeutic doses intended to deliver 50-100 cGy to the bone marrow. Another eight patients received (111)In-hLL2 followed by therapy with 90Y-hLL2 also delivering 50 or 100 cGy to the bone marrow. The blood T(1/2) (hours) for the tracer infusions of 131I-hLL2 was 44.2 +/- 10.9 (mean +/- SD) compared with 54.2 +/- 25.0 for the therapy infusions, whereas the values were 70.7 +/- 17.6 for (111)In-hLL2 and 65.8 +/- 15.0 for 90Y-hLL2. The estimated average radiation dose from 131I-hLL2 in tumors >3 cm was 2.4 +/- 1.9 cGy/mCi and was only 0.9-, 1.0-, 1.1-, and 1.0-fold that of the bone marrow, lung, liver, and kidney, respectively. In contrast, the estimated average radiation dose from 90Y-hLL2 in tumors >3 cm was 21.5 +/- 10.0 cGy/mCi and was 3.7-, 2.5-, 1.8-, and 2.5-fold that of the bone marrow, lung, liver, and kidney, respectively. No evidence of significant anti-hLL2 antibodies was seen in any of the patients. Myelosuppression was the only dose-limiting toxicity and was greater in patients who had prior high-dose chemotherapy. Objective tumor responses were seen in 2 of 13 and 2 of 7 patients given 131I-hLL2 or 90Y-hLL2, respectively. In conclusion, 90Y-hLL2 results in a more favorable tumor dosimetry compared with 131I-hLL2. This finding, combined with the initial anti-tumor effects observed, encourage further studies of this agent in therapeutic trials.

Usually, the red marrow (RM) is the first dose-limiting organ in radioimmunotherapy. However, several studies have obtained only poor correlations between the marrow doses and the resulting toxicities. Furthermore, RM doses are mostly not determined directly but are derived from blood doses by assuming a ratio that is, over time for the respective conjugates, more or less constant between blood and marrow activities. The aim of this study was to determine, in a mouse model, this RM:blood activity ratio for various immunoconjugates, to investigate whether there may be differences between complete IgG and its fragments with various labels ((125/131)I versus (111)In, (88/90)Y, or 213Bi), and to analyze, in more detail, factors other than just total dose, such as dose rate or relative biological effectiveness factors, that may influence the resulting myelotoxicity. The maximum tolerated activities (MTAs) and doses (MTDs) of several murine, chimeric, and humanized immunoconjugates as complete IgG or fragments (F(ab)2 and Fab), labeled with beta(-)-emitters (such as 131I or 90Y), Auger electron-emitters (such as 125I or (111)In), or alpha-emitters (such as 213Bi) were determined in nude mice. Blood counts were monitored at weekly intervals; bone marrow transplantation was performed to support the assumption of the RM as dose-limiting. The radiation dosimetry was derived from biodistribution data of the various conjugates, accounting for cross-organ radiation; besides the major organs, the activities in the blood and bone marrow (and bone) were determined over time. Whereas no significant differences were found for the RM:blood ratios between various IgG subtypes, different radiolabels or various time points, differences were found between IgG and bi- or monovalent fragments: typically, the RM:blood ratios were approximately 0.4 for IgG, 0.8 for F(ab')2, and 1.0 for Fab'. Nevertheless, at the respective MTAs, the RM doses differed significantly between the three conjugates: e.g., with 131I-labeled conjugates, the maximum tolerated activities were 260 microCi for IgG, 1200 microCi for F(ab)2, and 3 mCi for Fab, corresponding to blood doses of 17, 9, and 4 Gy, respectively. However, initial dose rates were 10 times higher with Fab as compared to IgG, and still 3 times higher as compared to F(ab)2; interestingly, all three deliver approximately 4 Gy within the first 24 h. The MTDs of all three conjugates were increased by BMT by approximately 30%. Similar observations were made for 90Y-conjugates. Higher RM doses were tolerated with Auger-emitters than with conventional beta(-)-emitters, whereas the MTDs were similar between alpha- and beta(-)-emitters. In accordance to dose rates never exceeding those occurring at the single injection MTA, two subsequent injections of two doses of 80% of the single shot MTA of 131I- or 90Y-labeled Fab' and two doses of 100% of the single shot MTA of 213Bi-labeled Fab' were tolerated without increased lethality, if administered 24-48 h apart. In contrast, reinjection of bivalent conjugates was not possible within 6 weeks. These data suggest that the RM:blood activity ratios differ between IgG and fragments, although there is no anatomical or physiological explanation for this phenomenon at this point. In contrast to the current opinion, indication for a strong influence of the dose rate (or dose per unit time), not only total dose, on the resulting toxicity is provided, whereas the influence of high-linear energy transfer (alpha and Auger/conversion electrons) versus low-linear energy transfer (beta and gamma) type radiation seems to be much lower than expected from previous in vitro data. The lower myelotoxicity of Auger-emitters is probably due to the short path length of their low-energy electrons, which cannot reach the nuclear DNA if the antibody is not internalized into the stem cells of the RM.

Unlabelled: This study was undertaken to determine the factors affecting myelotoxicity after radioimmunotherapy (RAIT) with 131I-labeled anticarcinoembryonic antigen (anti-CEA) monoclonal antibodies (MAbs)., Methods: Ninety-nine patients who received 131I-labeled MN-14 or NP-4 anti-CEA MAbs for the treatment of CEA-producing cancers were assessed for platelet and white blood cell (WBC) toxicity based on the common Radiation Therapy Oncology Group (RTOG) criteria. Univariate and multivariate regression analyses were used to identify the statistically significant factors affecting toxicity among the following variables: red marrow dose, baseline platelet and WBC counts, bone or marrow (or both) metastases, prior chemo- or radiotherapy, timing of prior chemo- or radiotherapy in relation to RAIT, type and number of prior chemotherapeutic regimens, age, sex, antibody form and cancer type., Results: Red marrow dose, baseline platelet or WBC counts and multiple bone or marrow (or both) metastases were the only significant factors affecting hematologic toxicity according to both univariate and multivariate analyses, whereas chemotherapy, 3-6 mo before RAIT, was significant according to multivariate analysis. In this retrospective study, the multivariate regression equations using these four variables provided an exact fit for postRAIT platelet toxicity grade (PltGr) and WBC toxicity grade (WBCGr) in 40% and 46%, respectively, of the 99 patients included in the analysis. Moreover, severe (grade 3 or 4) PltGr and WBCGr could be classified accurately in all cases, whereas nonsevere (grade 0, 1, or 2) PltGr and WBCGr could be classified accurately in all but 6 of 13 cases of grade 2 toxicity, in which a severe toxicity grade was estimated using the regression equations., Conclusion: Red marrow dose, baseline blood counts, multiple bone or marrow (or both) metastases and recent chemotherapy are the most important factors related to hematologic toxicity after RAIT. This study provides a simple model for predicting myelotoxicity with reasonable accuracy in most patients. In addition, the identification of bone or marrow (or both) metastases and recent chemotherapy as significant factors for myelotoxicity may be important in the future design of clinical trials.

Background: Monoclonal antibodies (MAbs) against carcinoembryonic antigen (CEA) have been recognized as targeting agents for medullary thyroid carcinoma (MTC). This Phase I/II study was initiated to determine the safety, maximum tolerated dose (MTD), and therapeutic potential of (131)I-MN-14 F(ab)2 anti-CEA MAb for patients with metastatic MTC., Methods: Fifteen patients were enrolled in this study. Dose escalation was based on estimates of radiation dose to the bone marrow, and the radioactive dose given was determined by a pretherapy diagnostic study in which 8 mCi (0.6-20 mg) of (131)I-MN-14 F(ab)2 was administered 1 week prior to therapy., Results: Three patients received an initial dose of 140 centigray (cGy) to bone marrow, 11 received 180 cGy, and 1 received 220 cGy. Myelosuppression was the only significant treatment-related dose-limiting toxicity (DLT), and the MTD appeared to be 180 cGy to the bone marrow. Human antimouse antibodies (HAMA) developed in 8 patients 2-6 weeks after therapy. Seven patients had a median of 55% reduction of tumor markers. One patient showed a dramatic improvement in the mass effect on the airways caused by 3 tumor lesions in the neck, with a 45% reduction of overall tumor burden. The disease has continued to be radiologically stable in 11 of 12 assessable patients for periods ranging from 3+ to 26+ months., Conclusions: Therapy with (131)I-MN-14 F(ab)2 is well tolerated and shows evidence of biochemical and radiologic antitumor activity. HAMA development suggests that humanized MAbs will be required in trials with repeated dose schedules. Further dose escalation, alone or in combination with other therapy modalities, is indicated for future trials, preferably with humanized anti-CEA MAbs.

90Yttrium-labeled monoclonal antibodies (mAbs) are likely to be important to radioimmunotherapy (RAIT) of a variety of cancers. The goal of this study was to select and evaluate a form of [90Y]mAb suitable for RAIT and determine conditions for high-yield, reproducible radiolabelings. 90Y-Labelings, at 2-40 mCi levels, of cdr-grafted versions of anti-B-cell lymphoma (hLL2) and anti-CEA (hIMMU-14) mAbs were optimized to >90% incorporations using the macrocyclic chelator DOTA as the metal carrier. In in vitro challenge assays, the stability of mAbs labeled with [90Y]DOTA was better than that of the corresponding [90Y]benzyl-DTPA conjugates. The retention of [90Y]DOTA-hLL2 on Raji tumor cells in vitro was similar to that of the same mAb labeled with [90Y]benzyl-DTPA and was about twice as much as with [125I]hLL2, indicating residualization of metalated mAb. Both [90Y]hLL2 conjugates, prepared using DOTA and Bz-DTPA, had similar maximum tolerated doses of 125 muCi in BALB/c mice and showed no discernible chelator-induced immune responses. Animal biodistribution studies in nude mice bearing Ramos human B-cell lymphoma xenografts revealed similar tumor and tissue uptake over a 10 day period, with the exception of bone uptake which was up to 50% lower for [88Y]DOTA-hLL2 compared to [88Y]Bz-DTPA-hLL2 at time points beyond 24 h. With [90Y]DOTA-hLL2 fragments, in vivo animal tumor dosimetries were inferior to those for the IgG, and kidney uptake was relatively high even with D-lysine administration. The ability of [111In]DOTA-hLL2 to accurately predict [90Y]DOTA-hLL2 biodistribution was established. These preclinical findings demonstrate that [90Y]DOTA-(CDR-grafted) mAbs are suitable for examination in clinical RAIT.

Whereas bivalent fragments have been widely used for radio-immunotherapy, no systematic study has been published on the therapeutic performance of monovalent conjugates in vivo. The aim of our study was, therefore, to determine the therapeutic performance of (131)I-labeled Fab as compared to bivalent conjugates and to analyze factors that influence dose-limiting organ toxicity and anti-tumor efficacy. The maximum tolerated doses (MTDs) and dose-limiting organ toxicities of the (131)I-labeled anti-CEA antibody MN-14 [IgG, F(ab')2 and Fab] were determined in nude mice bearing s.c. human colon cancer xenografts. Mice were treated with or without bone marrow transplantation (BMT) or inhibition of the renal accretion of antibody fragments by D-lysine or combinations thereof. Toxicity and tumor growth were monitored. Radiation dosimetry was calculated from biodistribution data. With all 3 (131)I-labeled immunoconjugates [IgG, F(ab')2 and Fab], the red marrow was the only dose-limiting organ; MTDs were 260 microCi for IgG, 1,200 microCi for F(ab')2 and 3 mCi for Fab, corresponding to blood doses of 17 Gy, 9 Gy and 4 Gy, respectively. However, initial dose rates were 10 times higher with Fab as compared to IgG and 3 times higher as compared to F(ab')2. The MTD of all 3 immunoconjugates was increased by BMT by approximately 30%. In accordance with renal doses below 10 Gy, no signs of nephrotoxicity were observed. Despite lower absorbed tumor doses, at equitoxic dosing, Fab fragments were more effective at controlling tumor growth than the respective bivalent fragment or IgG, probably due to higher intratumoral dose rates. Our data indicate that the improved anti-tumor effectiveness of antibody fragments as compared to IgG and the higher myelotoxicity at comparably lower red marrow doses are most likely due to the higher initial dose rates observed with antibody fragments.

Myelosuppression is the dose-limiting side effect of most forms of radioimmunotherapy (RAIT). Long-term leukopenia (4-8 weeks) has been documented from a single maximum tolerated dose (MTD) in experimental mice. Several methods for alleviating RAIT-induced marrow toxicity have been evaluated preclinically, including cytokine intervention, bone marrow transplantation (BMT), and hemoregulatory peptide administration. To improve the therapeutic potential of RAIT, multiple doses of radioantibody must be delivered. Maximizing the frequency of radioantibody administration is desirable. However, little is known about the myelotoxic effects of multiple cycles of RAIT. In the studies presented here we compared the magnitude of myelosuppression, the time of nadir, and the duration of toxicity associated with one or two MTDs of 1-131-MN-14 anti-carcinoembryonic antigen immunoglobulin G (250 microCi) administered to BALB/c mice 49 days apart, the shortest interval possible without producing lethality. Studies were conducted with radioantibody alone or with cytokines (interleukin-1/granulocyte-macrophage colony-stimulating factor), BMT, or Hp5b to determine whether bone marrow became more "brittle" after the first dose. Profiles of myelosuppression and recovery were monitored weekly for 7 weeks after each dose in both granulocyte and lymphocyte populations. The results demonstrated that granulocyte suppression was greater and of longer duration after the second dose of RAIT administered alone, with cytokines, or with BMT, but less severe with Hp5b. For example, in the RAIT + BMT treatment, the second dose resulted in an 87% loss of granulocytes, whereas a 30% loss occurred after the first dose. The nadir of toxicity lasted until days 21 to 28 after the second dose and until day 14 after the first dose. Lymphocyte suppression was of greater duration after the second cycle of RAIT alone or RAIT with BMT, plateauing at <50% of untreated levels between days 28 and 49, but was of shorter duration when RAIT was given with cytokines or Hp5b. The results are discussed in terms of 1) the radiosensitivity of each subpopulation, 2) the effects on progenitors and on stromal cells, 3) the benefits of increasing dose frequency vs. increasing dose intensity, and 4) the possibility of using preclinical data to optimize the frequency of dosing in patient trials.

Unlabelled: The biodistribution, pharmacokinetics and dosimetry of 188Re-labeled MN-14, an IgG anti-carcinoembryonic antigen monoclonal antibody (MAb), were assessed in patients in advanced gastrointestinal cancer. In addition, the dose-limiting toxicity (DLT) and maximum tolerated dose of fractionated doses of this agent were determined., Methods: Eleven patients were administered radioactive doses of directly labeled 188Re-MN-14 IgG, ranging from 20.5 mCi to 161.0 mCi (2.0 mg-4.9 mg). Ten of these patients received two or three MAb infusions, given 3-4 days apart, delivering total doses of 30 mCi/m2-80 mCi/m2. External scintigraphy was used to evaluate the MAb biodistribution, and quantitative external scintigraphic methods were used to determine the organ and tumor radiation doses., Results: The biodistribution studies showed enhanced 188Re-MN-14 uptake in the liver, spleen and kidneys, compared to that of 131I-MN-14. The biological T(1/2) values for 188Re-MN-14 in the blood and whole body (in hours) were 8.2 +/- 4.1 (n = 7) and 107.8 +/- 104.2 (n = 9), respectively (mean +/- s.d.). The radiation absorbed doses (cGy/mCi) delivered to the total body, red marrow, lungs, liver, spleen and kidneys were 0.5 +/- 0.05, 3.6 +/- 1.6, 2.0 +/- 0.8, 5.9 +/- 2.5, 7.1 +/- 1.9 and 8.5 +/- 2.8, respectively. Red marrow suppression was the only DLT observed. The maximum tolerated dose of fractionated doses of 188Re-MN-14 was estimated to be 60 mCi/m2., Conclusion: Despite its relatively increased renal and hepatic uptake, red marrow suppression is the only DLT of 188Re-MN-14. The feasibility of administering relatively high doses of 188Re on a completely outpatient basis may make this agent a preferred candidate for radioimmunotherapy.

Background: Single doses of radioantibody are effective at treating single cells or small clusters of cancer cells. However, large tumor masses require either multiple doses of radioantibody or a multimodal approach to therapy using two or more therapeutic agents. Timing of the second dose in a multiple cycle scheme or the second treatment in a multimodal protocol will depend on recovery from toxicity associated with the first treatment., Methods: BALB/c mice were dosed with a maximal tolerated dose (MTD) of I-131-MN-14 anti-carcinoembryonic antigen immunoglobulin G (IgG) (250 microCi) or F(ab')2 (1.2 mCi). Mice were redosed with the MTD at one of four time points, either Day 28, 35, 42, or 49 after IgG or Day 14, 21, 28, or 35 after F(ab')2. Survival was monitored to determine the earliest time to redose without lethality. Several studies were then performed to identify an accurate measure of true myelorecovery. Mice were bled retroorbitally on the day of the first dose and at weekly intervals thereafter. Total peripheral white blood cell counts, granulocyte counts, and lymphocyte counts were determined for each animal. GR-1hi expression (percentage of positive cells) and mean channel florescence were determined by FACScan analysis of a blood sample incubated with fluorescein isothiocyanate-anti-mouse Ly-6G (GR-1). In other studies, two mice were killed weekly from a group treated with a single MTD of radioantibody. The weights of their spleens and thymus glands were determined. At that time, femoral marrow was collected from these animals and plated in Methocult M3430 methylcellulose medium (Stemcell Technologies, Vancouver, Canada), and total colony-forming cells in culture were determined. Another population of mice was used to assess normal tissue metabolic activity following radioantibody therapy by quantitating the 4-hour utilization of I-125-dUrd., Results: The ability to redose mice with a second MTD of 1-131-IgG or F(ab')2 required 49 days and 35 days, respectively. Granulocyte and lymphocyte counts did not accurately predict myelorecovery from the first dose. Hematopoietic tissue weight, tissue metabolic activity, and marrow colony forming cells all suggested that redosing was possible 1-2 weeks before it could actually be done without lethality. Percent of cells expressing GR-1hi (>60%) and absolute numbers of GR-1hi cells (>1400 cells/mm3) suggested myelorecovery in most animals. A greater degree of accuracy was achieved when trends in GR-1hi expression were noted over 2 or more weeks (i.e., the absolute amount of GR-1hi had to exceed levels in untreated mice, as evidence that the hyperproliferative phase of recovery was complete)., Conclusions: The only approach that accurately predicted the ability to retreat with myelosuppressive therapy without risk of lethality was an increase in GR-1hi-positive cells above untreated levels. Other approaches are currently being investigated, including the expression of proliferation antigens (e.g., proliferating cell nuclear antigen and Ki-67) in both murine and human samples and differentiation antigens (CD33 and CD34) in humans.

Background: Elevated renal uptake and extended retention of radiolabeled antibody fragments and peptides is a problem in the therapeutic application of such agents. However, cationic amino acids have been shown to reduce renal accretion. The aims of the current study were to evaluate whether this methodology would benefit therapy with yttrium 90 (90Y)-labeled antibody fragments (Fab, F(ab)2), to establish the relationship between radiation dosimetry and observed biologic effects, and to compare the antitumor efficacy of antibody fragments with that of whole immunoglobulin (Ig)G., Methods: The maximum tolerated dose (MTD) and the dose-limiting organ toxicity of 90Y-labeled anti-carcinoembryonic antigen (CEA) MN-14 monoclonal antibodies (Fab, F(ab)2, and IgG) were determined in nude mice bearing GW-39 human colon carcinoma xenografts. The mice were treated with or without kidney protection by administration of D-lysine, with or without bone marrow transplantation (BMT), or with combinations of each. Toxicity and tumor growth were monitored at weekly intervals after radioimmunotherapy. Dosimetry was calculated from biodistribution studies using 88Y-labeled antibody. Three different dosimetric models were examined: 1) taking solely self-to-self doses into account, using S factors for 90Y in spheroids from 0.1 to 1 g; 2) correcting for cross-organ radiation; and 3) using actual mouse anatomy as represented by nuclear magnetic resonance imaging with a three-dimensional internal dosimetry package (3D-ID)., Results: The kidney was the first dose-limiting organ with the use of Fab fragments. Acute radiation nephritis occurred at injected activities > or = 325 microCi, and chronic nephrosis at doses > or = 250 microCi. Activities of 200 microCi were tolerated by 100% of the animals (i.e., the MTD). Application of lysine decreased the renal dose by approximately fivefold, facilitating a 25% increase in the MTD (to 250 microCi), because myelotoxicity became dose-limiting despite red marrow doses of less than 5 gray (Gy). By using BMT and lysine, the MTD could be doubled from 200 to 400 microCi, where no biochemical or histologic evidence of renal damage was observed (kidney dose, < or = 40 Gy). With injected activities of > or = 325 microCi without kidney protection, and with a hepatic self-to-self dose of only 4 Gy, rising liver enzymes were observed, which could be explained only by cross-organ radiation from radioactivity in the kidneys (in the immediate neighborhood of the right kidney up to > or = 150 Gy). The MTD of F(ab)2 fragments could be elevated only by a combination of BMT and lysine. With IgG, the bone marrow alone was dose-limiting. Tumor dosimetry correlated well with antitumor effects; Fab was more effective than F(ab)2, which was consistent with its more favorable dosimetry, and it may also be more effective than IgG due to its higher dose rate and more homogenous distribution. Dosimetry Model 1 was insufficient for predicting biologic effects. Model 2 seemed to be more accurate, accounting for interorgan crossfire. However, Model 3 showed an additional substantial contribution to the red bone marrow dose due to crossfire from the abdominal organs., Conclusions: These data show that radiation nephrotoxicity is an important effect of cancer therapy with radiometal-conjugated antibody fragments or peptides. However, this effect can be overcome successfully with the application of cationic amino acids, which substantially increase the anti-tumor efficacy of radiometal-labeled immunoconjugates. For understanding the biologic effects (e.g., liver toxicity) of 90Y in a mouse model, accounting for cross-organ radiation is essential. Further studies with radiometal-conjugated monoclonal antibody fragments and peptides are necessary to determine the MTD, dose-limiting organs, antitumor effectiveness, and nephroprotective effects of cationic amino acids in humans.

Background: Tumor lesions in the millimeter (mm) range may escape detection with nuclear medicine imaging methods (including single photon emission computed tomography [SPECT]) using radiolabeled monoclonal antibodies (MoAbs). We hypothesized that these lesions still could receive a potentially therapeutic radiation absorbed dose, and therefore should be treated, despite the lack of detection., Methods: To simulate this situation, 2-mm beads (0.004 mL) containing approximately 1.15 microCi of iodine-131 (131I) were used. The beads were placed centrally in a 1200-mL liver phantom containing approximately 3 mCi of 131I. The resultant activity concentration on the beads was approximately 288 microCi/mL compared with approximately 2.5 microCi/mL in the phantom, corresponding to a maximum tumor uptake of approximately 0.3% injected dose per gram (%ID/g) if 100 mCi of 131I-labeled immunoglobulin G were administered. The phantom, containing the beads, was imaged by both planar and SPECT techniques at hypothetical Day 1 (time of maximum tumor uptake) and at hypothetical Day 7 to examine the improved target-to-nontarget ratio over time. In addition to imaging the beads, the radiation absorbed dose to the simulated lesions from the beta component emissions of 131I was calculated using absorbed fractions based on Berger's point kernels., Results: Regardless of the conditions used, the beads could not be observed by either planar or SPECT imaging. However, the radiation-absorbed dose to the simulated lesion was calculated to be as high as approximately 6200 centigray (cGy), with an average dose rate of approximately 89.5 cGy/hour., Conclusions: This simulation demonstrates that a relatively high absorbed dose and dose rate can be delivered to mm-sized lesions not observed by conventional nuclear imaging methods, and that these lesions should be considered for radioimmunotherapy with 1311 MoAbs. However, for micrometastases of <1 mm, other radionuclides with shorter path length beta particles than 131I, Auger electrons, or alpha particles should be considered.

Background: Several investigators have reported a considerable variability in the observed hematologic toxicity after radioimmunotherapy (RAIT) with monoclonal antibodies (MoAb) given at similar amounts of radioactivity based on body surface area and/or similar radiation absorbed doses given to the red marrow. The authors investigated various factors potentially affecting hematologic toxicity after RAIT with 131I-labeled anti-carcinoembryonic antigen (CEA) MoAb to identify the statistically significant factors from those commonly perceived clinically to substantially contribute to this toxicity., Methods: Ninety-nine patients who received 131I-labeled anti-CEA MoAb for the treatment of CEA-producing cancers were assessed for platelet and white blood cell toxicity based on the common Radiation Therapy Oncology Group criteria. Multivariate regression analysis was used to identify the statistically significant factors affecting toxicity among the following variables: red marrow dose, baseline platelet and white blood cell counts, bone and/or marrow metastases, prior chemotherapy or radiotherapy, timing of prior chemotherapy or radiotherapy in relationship to RAIT, type and number of prior chemotherapeutic regimens, age, sex, antibody form, and cancer type., Results and Conclusions: Red marrow dose, baseline platelet or white blood cell counts, multiple bone and/or marrow metastases, and chemotherapy 3-6 months before RAIT were the only four significant factors affecting hematologic toxicity according to multivariate analysis. The identification of bone and/or marrow metastases and recent chemotherapy as significant factors for hematologic toxicity could be important in the design of future clinical trials.

In order to optimize radioimmunotherapy (RAIT) as a cancer-treatment modality, it is necessary to select the appropriate radionuclide and antibody carrier. We evaluated the therapeutic potential of a single cycle of Mu-9 anti-CSAp monoclonal antibody (MAb) labeled with 3 different radionuclides, 131I, 90Y and 188Re. Intact antibodies and bivalent fragments with different blood clearance kinetics, normal organ distribution and varying tumor accretion and retention are also evaluated. Efficacy of treatment for large and small tumor burden was assessed in nude mice bearing s.c. GW-39 human colonic-carcinoma xenografts or intrapulmonary micrometastatic GW-39 colonies at the maximal tolerated dose of each agent. The magnitude and duration of myelosuppression associated with each radioantibody was considered by monitoring peripheral blood counts, marrow colony-forming unit activity and hematopoietic tissue weight. Radiation-dose estimates were calculated based on the kinetics of antibody accretion and elimination from tumor and normal tissues, and the results were correlated with tumoricidal activity and dose-limiting toxicity results. These studies, therefore, represent a detailed analysis, in a well-defined experimental tumor system, of several parameters (antibody form, radioisotope, tumor size) influencing the overall outcome of RAIT using equitoxic doses. It was found that myelosuppression is the primary dose-limiting toxicity for all radioantibodies except 90Y-F(ab')2, even though the different agents showed varied organ distribution. In a single-cycle treatment schedule of Mu-9 MAb, the 131I-labeled IgG is the radioimmunoconjugate of choice for the treatment of s.c. and intrapulmonary growth of the GW-39 human colonic-carcinoma xenograft in nude mice.

The goal of our studies was to determine whether administration of IL-1/GM-CSF to mice could reduce radio-antibody-induced myelosuppression and allow either dose escalation of radio-antibody using 131I, 90Y or 188Re conjugated to either intact antibody or bivalent fragments or more frequent dosing with 131I-IgG. Survival, peripheral blood counts, hematopoietic tissue weight and number of marrow CFCs were used to determine the ability to dose-intensify with a single dose or to reduce the spacing between doses. In this report, we show that in the absence of cytokines, 2 cycles of 131I-IgG spaced at 28, 35, 42 and 49 days resulted in 100%, 100%, 40% and 0% lethality, respectively. In contrast, cytokine intervention reduced lethality to 45%, 20%, 0% and 0% at the same time intervals between doses. Thus, the use of cytokines permits at least a 1 week earlier redosing of 131I-IgG. Cytokine intervention also has reduced the magnitude of myelosuppression, as measured by neutropenia and thrombocytopenia, thus permitting intensification of single doses of radio-iodinated intact antibodies, bivalent fragments and 90Y-IgG by at least 30%, 50% and 25%, respectively. However, cytokines were not effective at permitting dose escalation of either 90Y-F(ab')2 or 188Re-IgG. Further optimization of the dose schedule of cytokine administration needs to be explored for these 2 nuclide-antibody forms.

Pretargeting methodologies can produce high tumor:blood ratios, but their role in cancer radioimmunotherapy (RAIT) is uncertain. A pretargeting method was developed using a streptavidin (StAv) conjugate of MN-14 IgG, an anti-carcinoembryonic antigen (CEA) murine monoclonal antibody (mab) as the primary targeting agent, an anti-idiotype antibody (WI2 IgG) as a clearing agent, and DTPA- or DOTA-conjugated biotin as the radiolabeled targeting agent. A variety of reagents and conditions were examined to optimize this method. At 3 h, 111In-DTPA-peptide-biotin tumor uptake was 3.9 +/- 0.8% per gram and tumor:blood ratios were > 11:1. By 24 h, this ratio was 178:1, but tumor accretion declined in accordance with the gradual loss of StAv-MN-14 from the tumor. Tissue retention was highest in the liver and kidneys, but their tumor:organ ratios were > 2:1. Dosimetry predicted that radiolabeled MN-14 alone would deliver higher tumor doses than this pretargeting method. Increasing the specific activity and using DOTA-biotin in place of DTPA increased tumor uptake nearly 2-fold, but analysis of StAv-MN-14's biotin-binding capacity indicated over 90% of the initial biotin-binding sites were blocked within 24 h. Animals fed a biotin-deficient diet had 2-fold higher 111In-DOTA-biotin uptake in the tumor, but higher uptake also was observed in all normal tissues. Although exceptionally adept at achieving high tumor:blood ratios rapidly, the tumor uptake of radiolabeled biotin with this pretargeting method is significantly (p < 0.0001) lower than that with a radiolabeled antibody. Endogenous biotin and enhanced liver and kidney uptake may limit the application of this method to RAIT, especially when evaluating the method in animals, but with strategies to overcome these limitations, this pretargeting method could be an effective therapeutic alternative.

With pretargeting, radioisotope delivery to tumor is decoupled from the long antibody localization process, and this can increase tumor:blood ratios dramatically. Several reagents were prepared for each step of a "two-step" pretargeting method, and their properties were investigated. For pretargeting tumor, streptavidin-monoclonal antibody (StAv-mab) conjugates were prepared by cross-linking sulfo-SMCC-derivatized streptavidin to a free thiol (SH) group on MN-14 [a high-affinity anti-carcinoembryonic antigen (CEA) mab]. Thiolated mabs were generated either by reaction of 2-iminothiolane (2-IT) with mab lysine residues or by reduction of mab disulfide bonds with (2-mercaptoethyl)amine (MEA). Both procedures gave protein-protein conjugates isolated in relatively low yields (20-25%) after preparative size-exclusion (SE) chromatography purification with conservative peak collection. Both StAv-MN-14 conjugates retained their ability to bind to CEA, to an anti-idiotypic antibody to MN-14 (WI2), and to biotin, as demonstrated by SE-HPLC. Two clearing agents, WI2 mab and a biotin-human serum albumin (biotin-HSA) conjugate, were developed to remove excess circulating StAv-MN-14 conjugates in animals. Both clearing proteins were also modified with galactose residues, introduced using an activated thioimidate derivative, to produce clearing agents which would clear rapidly and clear primary mab rapidly. At least 14 galactose residues on WI2 were required to reduce blood levels to 5.9 +/- 0.7% ID/g in 1 h. Faster blood clearance (0.7 +/- 0.2% ID/g) was observed in 1 h using 44 galactose units per WI2. For the delivery of radioisotope to tumor, several biotinylated conjugates consisting of biotin, a linker, and a chelate were prepared. Conjugates showed good in vitro and in vivo stability when D-amino acid peptides were used as linkers, biotin-peptide-DOTA-indium-111 had a slightly longer blood circulation time (0.09 +/- 0.02% ID/g in 1 h) than biotin-peptide-DTPA-indium-111 (0.05 +/- 0.03% ID/g in 1 h) in nude mice. A longer circulation time with the neutral DOTA complex might allow higher tumor uptake.

Unlabelled: The aim of this study was to determine, in a Phase I/II clinical trial, the pharmacokinetics, dosimetry and toxicity, as well as antitumor activity, of the 131I-labeled murine anti-carcinoembryonic antigen (CEA) monoclonal antibody, NP-4 (IgG1 subtype)., Methods: A total of 57 patients with CEA-expressing tumors (29 colorectal, 9 lung, 7 pancreas, 6 breast and 4 medullary thyroid cancer patients), mostly in very advanced stages, were treated. The patients underwent a diagnostic study (1-3 mg of IgG and 8-30 mCi of 131I) to assess tumor targeting and to estimate dosimetry, followed by the therapeutic dose (4-23 mg and 44-268 mCi), based on the radiation dose to the red marrow. Imaging was performed from 4-240 hr postinjection (planar and SPECT). Blood and whole-body clearance were determined; radiation doses were calculated by the Medical Internal Radiation Dose scheme., Results: Red marrow doses ranged from 45 to 706 cGy, and whole-body doses ranged from 31 to 344 cGy. Differences in pharmacokinetics were found between different types of CEA-producing tumors: blood T 1/2 was significantly lower in colorectal cancer when compared to all other tumor types (21.4 +/- 11.1 hr versus 35.8 +/- 13.2 hr, p < 0.01), as was also whole-body t 1/2. Myelotoxicity was dose-limiting, and its severity was related to the types of prior therapy and extent of bone marrow involvement. In patients without prior radiation or chemotherapy, marrow doses as high as 600 cGy were tolerated without evidence of dose-limiting toxicity. No major toxicity to other organs was observed. Tumor doses were inversely related to the tumor mass and ranged between 2 and 218 cGy/mCi. Modest antitumor effects were seen in 12 of 35 assessable patients (1 partial remission, 4 minor/mixed responses and 7 with stabilization of previously rapidly progressing disease)., Conclusion: These results suggest that prior chemotherapy or external beam radiation is an important risk factor for the development of hematological toxicity in radioimmunotherapy and that higher radiation doses may be delivered to tumors of patients without prior therapy compromising the bone marrow reserve. The different and, in the individual cases, unpredictable clearance rates suggest the necessity of dosimetry-based treatment planning rather than mCi/m2 dosing. Small tumors seem to be more suitable for radioimmunotherapy because of their favorable dosimetry, but to achieve better therapeutic results in patients with bulky disease, the application of higher, potentially myeloablative doses is indicated.

LL2 is an anti-CD22 pan-B-cell monoclonal antibody which, when radiolabeled, has a high sensitivity for detecting B-cell, non-Hodgkin's lymphoma (NHL), as well as an antitumor efficacy in therapeutic applications. The aim of this study was to determine whether intracellularly retained radiolabels have an advantage in the diagnosis and therapy of lymphoma with LL2. In vitro studies showed that iodinated LL2 is intracellularly catabolized, with a rapid release of the radioiodine from the cell. In contrast, residualizing radiolabels, such as radioactive metals, are retained intracellularly for substantially longer. In vivo studies were performed using LL2-labeled with radioiodine by a non-residualizing (chloramine-T) or a residualizing method (dilactitol-tyramine, DLT), or with a radioactive metal (111In). The biodistribution of a mixture of 125I (non-residualizing chloramine-T compared to residualizing DLT), 111In-labeled LL2 murine IgG2a or its fragments [F(ab')2, Fab'], as well as its humanized, CDR-grafted form, was studied in nude mice bearing the RL human B-cell NHL cell line. Radiation doses were calculated from the biodistribution data according to the Medical International Radiation Dose scheme to assess the potential advantage for therapeutic applications. At all assay times, tumor uptake was higher with the residualizing labels (i.e., 111In and DLT-125I) than with the non-residualizing iodine label. For example, tumor/blood ratios of 111In-labeled IgG were 3.2-, 3.5- and 2.8-fold higher than for non-residualizing iodinated IgG on days 3, 7 and 14, respectively. Similar results were obtained for DLT-labeled IgG and fragments with residualized radiolabels. Tumor/organ ratios also were higher with residualizing labels. No significant differences in tumor, blood and organ uptake were observed between murine and humanized LL2. The conventionally iodinated anti-CD20 antibody, 1F5, had tumor uptake values comparable to those of iodinated LL2, the uptake of both antibodies being strongly dependent on tumor size. These data suggest that, with internalizing antibodies such as LL2, labeling with intracellularly retained isotopes has an advantage over released ones, which justifies further clinical trials with residualizing 111In-labeled LL2 for diagnosis, and residualizing 131I and 90Y labels for therapy.

Advanced chemotherapy-resistant ovarian cancer has a poor prognosis, thus requiring new therapeutic modalities. A complete clinical remission, using two cycles of 131I-labeled murine MN-14 anti-CEA monoclonal antibody (MAb), given intravenously, is reported in a patient with advanced ovarian cancer refractory to paclitaxel (Taxol) therapy. The patient first received radioimmunotherapy with approximately 74 mCi 131I-MN-14 IgG, followed 4 mo later by a similar dose of radiolabeled MAb. A partial remission was seen by CT 1 mo after the first radioimmunotherapy, and a further objective response was documented after the second radioimmunotherapy. CT scans performed 6 and 11 mo after the second radioimmunotherapy showed stable and minimal residual changes. However, a whole-body PET scan with [18F]fluorodeoxyglucose (FDG-PET) was negative in these regions. The CA-125 also decreased to only 13 U/ml, compared to the baseline value of 7700 U/ml. Based on CT, FDG-PET, serum CA-125 and physical exam, the patient was in complete clinical remission for 8 mo when the CA-125 levels rose. CT also showed a new suspicious lesion, presumably a peritoneal implant. No toxicity was seen after the first injection, and only Grade 1 thrombocytopenia and Grade 2 leukopenia developed after the second injection, both reversing within 6 wk. This is a report of a complete clinical remission with radiolabeled anti-CEA antibodies in a patient with chemotherapy-refractive metastatic ovarian cancer.

The hemoregulatory peptide, pGlu-Glu-Asp-Cys-Lys (pEEDCK or HP5b), has been shown to reversibly inhibit the proliferation of bone-marrow progenitor cells, and has been reported to protect mice from the myelotoxicity associated with ara-C, a chemotherapeutic agent. We undertook to use this reagent to reduce radioimmunotherapy(RAIT)-associated bone-marrow toxicity by suppressing hematopoiesis during the critical period when bone marrow is exposed to radiation. The reported studies optimize the use of HP5b to reduce the duration of neutropenia and thrombocytopenia. We found that 3.6 micrograms/day of HP5b administered through a continuous 7d mini-osmotic pump, together with a bolus dose of 3.6 micrograms 3 hours before the radioantibody dose, gave the best effect, as measured by neutrophil counts on day 28 post RAIT. With sub-lethal doses of RAIT, the period of neutropenia was reduced by 2 weeks, and there appeared to be more rapid recovery of morphologically mature myeloid cells. The peptide, however, does not appear to alleviate the lymphotoxicity associated with RAIT. No adverse effects have been noted from continuous infusions of the peptide. In the past, we reported that cytokines (IL-I/GM-CSF) are not marrow-restorative when given after RAIT. However, an additive effect is observed when HP5b infusions are combined with post-RAIT cytokine administration, suggesting that a significant pool of bone-marrow progenitor cells remains when HP5b is co-administered with RAIT. Thus, HP5b is an alternate approach to reducing myelotoxicity, and may be used in combination with cytokines to further reduce the duration of myelosuppression.

Single and fractionated doses of radioimmunotherapy (RAIT) and standard chemotherapy (0.6 mg 5-FU/day and 0.36 leucovorin/day on days 1-5) result in decreases in vascular permeability (VP) in the GW-39 human colonic xenograft. The effect of a single dose of RAIT (MN-14 anticarcinoembryonic antigen, Mu-9 anticolon-specific antigen, PAM-4 anti-MUC-1, RS-7 and RS-11 antiepithelial glycoprotein labeled with 131I) has also been evaluated in 10 other tumors. Fourteen days after a fixed 1,500-cGy dose of RAIT, 3 colonic tumors (LS174T, HT-29 and MOSER) all exhibited decreases in VP (58, 75 and 70%, respectively). Two colonic (LoVo and GS-7) and 1 breast tumor (MDA-468) did not exhibit any change in VP, and 1 lung (CALU-3), 1 cervical (ME-180), 1 pancreatic (CaPan-1) and 1 breast cancer line (ZR-75) exhibited increases in tumor VP (214, 289, 170 and 139%, respectively). The differences in VP response to RAIT do not appear to be related to the type of tumor, the size of tumor or the antigen being targeted by RAIT. The differences in tumor VP response to RAIT are discussed in terms of the ability to achieve significant tumor accretion of a second dose of radioantibody on a multiple-dosing regimen. We have begun to investigate the mechanism(s) which regulate the varying responses of tumor VP to RAIT by assessing the role that nitric oxide plays. Administration of arginine, a substrate for nitric oxide synthase, results in increases in both baseline and RAIT-modified VP in GW-39 and ME-180 tumors.

A number of radioimmunotherapy (RAIT) trials with iodinated antibodies have shown a high variability in the radiation doses to the thyroid. Therefore, the aim of this study was to evaluate which factors influence these thyroid doses during RAIT with 131iodinated monoclonal anti-carcinoembryonic antigen (CEA) antibodies. Data from 36 patients with CEA-expressing tumours were analysed. The patients underwent RAIT with the 131I-labelled IgG1 anti-CEA antibody, MN-14 (Ka = 10(9) l mol-1) or its F(ab')2 fragment (activity range 45.8-220.0 mCi). The thyroid was blocked with 120 mg iodine (lugol's orSSKI solution) and 400 mg perchlorate per day, starting 1 day prior to the first study. Blood clearance and molecular composition of labelled plasma compounds were determined by blood sampling and size-exclusion high-performance liquid chromatography analysis. The cumulated activities of tissues were determined from daily imaging and blood clearance data. Doses were derived from the MIRD scheme. Thyroid radiation doses showed a high variability, between 1.2 and 37.7 cGy mCi-1 (mean +/- S.D.: 11.1 +/- 8.3 cGy mCi-1), corresponding to absolute doses between 2.5 and 43.6 Gy. However, the maximal iodine uptake in the thyroid was 2.4 +/- 1.9 microCi mCi-1 (range 0.2-10.0 microCi mCi-1), which was less than 1% of the injected activity, indicating that more than 99% of the thyroid was blocked in all cases. No correlation was found between these thyroid doses and conditions leading to an enhanced exposure to free radioiodine, such as unbound I- in the mAb preparation, rapid metabolic breakdown of the labelled antibody due to human anti-mouse antibodies (HAMA), or immune complex formation with circulating antigen. However, a relationship between the thyroid doses and the patients' compliance in taking their Lugol's and perchlorate blocking medications, as well as to a relatively high variability in the biological half-life of the iodine in the thyroid (range from 31.1 h to virtual infinity), is indicated. No rising TSH titres or other signs of (latent) hypothyroidism were seen in these patients during a 2 year follow-up period. Longer follow-up was not possible because of the terminal condition of most of the patients. These data show that thyroid doses in an appropriately blocked individual given a standard, non-myeloablative dose of RAIT, are generally lower than those assumed to be required to cause late hypothyroidism. Even if higher activities are used, potential hypothyroidism may be overcome easily by hormone replacement. Thyroid doses are independent of parameters leading to an enhanced exposure of the thyroid to free radioiodine, suggesting that patient compliance in taking their blocking medication may be the most crucial factor for reducing thyroid doses in RAIT with 131I-labelled antibodies.

Unlabelled: The clinical feasibility of radioimmunotherapy (RIAIT) was assessed in patients with metastatic, carcinoembryonic antigen (CEA)-producing cancers who had minimal residual or small-volume disease (tumor lesions < or = 3 cm in diameter)., Methods: Thirteen cancer patients (8 colorectal, 3 lung, 1 pancreatic and 1 medullary thyroid cancer) received RAIT with 131I-NP-4 F(ab')2 anti-CEA antibody. The radioactive dose given was based on a prescribed radiation dose to the red marrow. Ten of the 13 patients received initial therapeutic doses delivering 150-450 cGy to the red marrow (70-296 mCi) and six patients had more than one therapy infusion., Results: Targeting of all known tumor lesions < 0.5 cm [corrected] in diameter was possible in nine patients and at least one tumor lesion was evident in all patients. Disease stabilization ranging from 3.5 to 7 mo was seen in 6 of the 13 patients who previously had clear evidence of progressive disease. Four of the six patients with disease stabilization received the presumed maximum tolerated dose of 450 cGy to the red marrow. Red marrow suppression was the only observed toxicity and there was a good correlation between the red marrow dose and myelotoxicity. Red marrow doses < or = 250 cGy resulted in < or = grade 2 myelotoxicity and a red marrow dose of 450 cGy resulted in reversible grade 3 or 4 myelotoxicity in 3 of 6 patients. Human anti-mouse antibodies (HAMA) developed in all but one of the six patients who received multiple therapeutic infusions of the antibody., Conclusion: RAIT of patients with small-volume disease is feasible and these patients should be considered for future dose-intensification trials because of their generally poor prognosis.

Unlabelled: This study evaluates the pharmacokinetics, dosimetry, toxicity and therapeutic potential of radiolabeled NP-4 and MN-14 anti-CEA antibodies in medullary thyroid cancer (MTC)., Methods: Eighteen patients with advanced MTC entered exploratory clinical studies with therapeutic doses of 131I-labeled NP-4 and MN-14 murine monoclonal antibodies (MAbs) reactive with carcinoembryonic antigen (CEA). Doses administered ranged from 46 mCi for 131I-MN-14 lgG to 195 mCi for 131I-MN-14 F(ab)2 in patients negative for human anti-mouse antibodies (HAMA)., Results: The radioconjugate blood half-life (T1/2) for the whole lgG was 42.5+/-5.0 hr compared to 18.8+/- 4.1 hr for the bivalent fragments. Tumor doses of 17.5+/-11.0 and 11.4+/-6.3 cGy/mCi were estimated for 131I-MN-14 lgG and F(ab)2, respectively. Tumor/red marrow dose ratios exceeded 3:1 for most lesions. Red marrow doses of up to 350 cGy generally could be delivered with < grade 4 toxicity. Seven of 14 evaluable patients showed evidence of anti-tumor effects lasting up to 26 months, based on physical exam, tumor markers or computed tomography., Conclusion: This study demonstrates that anti-CEA MAbs may be suitable for radioimmunotherapy of metastatic or recurrent MTC.

The aim of this study was to examine factors that may influence the pharmacokinetics, diagnostic accuracy, and dosimetry in radioimmunodetection and radioimmunotherapy with anti-carcinoembryonic antigen (CEA) monoclonal antibodies (mAbs). Data from 275 patients with CEA expressing tumors were analyzed retrospectively. Of these, 69 patients devoid of human antimouse antibody (i.e., 31 colorectal, 9 lung, 7 breast, 4 ovarian, 6 pancreatic, 9 medullary thyroid, 1 gallbladder, and 1 salivary gland cancer, and 1 primary tumor of unknown origin) underwent a low-protein-dose diagnostic study (0.3-2.6 mg of protein; 6.8-28.8 mCi 131I-labeled IgG or fragments), followed within 4 weeks by a high-protein-dose therapy injection (4.0-27.5 mg of protein; 29.8-238.9 mCi). The anti-CEA antibodies NP-4 (Ka=10(8)M-1) and MN-14 (ka=10(9)M-1) were used. Plasma clearance, the molecular composition of radioactivity in the plasma, and the cumulated activity in organs and tumors were determined. Radiation doses were derived from the Medical Internal Radiation Dose scheme. At a low-protein dose and over a similar range of plasma CEA, a significantly higher percentage of MN-14 than of NP-4 was complexed with circulating CEA, consistent with its higher affinity. Complexation was reduced with increasing protein doses. However, the targeting sensitivity was not affected. Profound differences were found in the clearance of the antibody between different types of cancer. Colorectal cancer patients cleared the antibody significantly faster from blood (T1/2=17.6+/-12.6 versus 44.2 +/- 23.7 h) and whole body (t1/2= 53.2 +/- 30.1 versus 114.6+/-59.7 h) than all other tumor types (P <0.001). Consequently, significantly lower red marrow (2.1 +/- 1.0 cGy/mCi versus 4.3 +/- 1.6 cGy/mCi) and whole-body doses (0.5 +/- 0.3 cGy/mCi versus 1.0 +/- 0.4 cGy/mCi) were seen in colorectal cancer patients as compared with other tumor types (P < 0.001). This clearance is probably due to hepatic metabolism of the immune complexes. Clearance rates were especially high in patients with colorectal cancer having large liver metastases and elevated liver enzymes (rapid hepatic clearance with liberation of free I-). In contrast, a disease-stage and plasma CEA-matched cohort of colorectal cancer patients, examined with the 131 I-labeled anti-colon-specific antigen p mAb Mu-9, showed normal murine IgG pharmacokinetics (n=22;3 of them compared intraindividually to MN-14). Only in colorectal cancer patients did complexes between mAb and CEA tend to clear rapidly, whereas Mu-9 had normal kinetics in these patients. This suggests that different CEA-expressing cancer types may produce heterogeneous CEA molecules and that the variability in mAb clearance is due to varying clearance rates of these different circulating CEA subspecies. Disease-related alterations in antibody metabolism are unlikely, given that only anti-CEA antibodies exhibit this phenomenon.

A complementarity-determining region-grafted (humanized) version of MN-14 (hMN-14), a high-affinity, anti-carcinoembryonic antigen (CEA) murine monoclonal antibody (mMAb), was selected from several clones that differed slightly in their framework composition. One clone was selected based on its similar binding affinity to CEA as that observed with mMN-14 MAb and its production yields. Targeting studies, using 131I-labeled humanized MN-14 (hMN-14)/125I-labeled mMN-14 IgG in GW-39 tumor-bearing nude mice, showed excellent tumor uptake and tumor: nontumor ratios, similar to the mMN-14. A pilot clinical imaging trial was initiated to determine the targeting, pharmacokinetics, and dosimetry for 131I-labeled hMN-14 IgG. Nineteen patients with advanced CEA-producing tumors were given 8 to 30 mCi (0.5 to 20.0 mg). Eleven patients also received 131I-labeled mMN-14 IgG for comparison. The biodistribution, tumor targeting, and pharmacokinetic behavior of the hMN-14 was similar to that seen with the mMN-14. The average time required to clear 50% of the radiolabeled hMN-14 from the blood and total body was 32.9 +/- 25.6 h and 109 +/- 73 h, respectively. Patients with elevated plasma CEA (i.e., > 200 ng/ml) had more than 30% of the labeled antibody complexed within 1 h after injection. In some of these patients, increased complexation resulted in enhanced metabolism of the antibody with more rapid clearance from the blood than that seen in patients with lower plasma CEA. The average radiation absorbed dose measured in 20 tumors (average weight, 204 +/- 205 g) in 14 patients was 7.6 +/- 5.3 cGy/mCi. Tumor: nontumor dose ratios were 2.5 +/- 1.6, 9.5 +/- 5.8, and 2.6 +/- 1.8 for the red marrow, total body, and liver, respectively. One patient, with a highly elevated human anti-mouse antibody response from a prior OncoScint study (murine B72.3 IgG), received 3 injections of the hMN-14 without an adverse experience, and showed no evidence of altered biodistribution characteristic of mMAb-human anti-mouse antibody interactions. An antibody response to hMN-14 (HAhMN14) was not detected in patients who received only the hMN-14 (as many as three injections), but in three patients who received two injections of the mMN-14, a HAhMN14 response was detected. With similar, excellent targeting properties as the mMN-14 and the potential for reduced immunogenicity, hMN-14 is an attractive candidate for further clinical imaging and therapy applications.

LL2 is a murine IgG2a anti-CD22 monoclonal antibody found to react with virtually all non-Hodgkin's lymphomas (NHLs). Twenty-one patients with chemotherapy-resistant NHL received nonmyeloablative doses of 131I-labeled LL2 IgG and F(ab')2 ranging from 15 to 343 mCi given in cycles of 15-50 mCi, for up to seven treatment cycles. The cumulative protein dose ranged from 1.1 mg IgG to 157 mg F(ab')2. Seventeen patients were assessable for treatment response, and antitumor effects were seen in five (one complete remission, two partial remissions, and two minor or mixed responses). In addition, one complete response was seen in a patient who received only "diagnostic" doses of 131I-LL2 IgG. Thus, a total of six patients had responses according to the defined response criteria. Three additional patients have been treated with potentially myeloablative doses of 131I-LL2 IgG at a starting dose level of 90 mCi/m2 (100 mg). Two patients were evaluable, and both had partial remissions lasting 8 and 3 months, respectively. Chimeric and complementarity-determining region-grafted LL2 have been developed. Initial clinical studies have shown that these agents have targeting properties similar to the murine LL2 and, therefore, may be suitable alternatives to murine LL2 in the treatment of NHL. LL2 is a promising agent for the treatment of lymphoma, particularly when the maximum tolerated dose is given either with or without autologous bone marrow transplantation.

According to the recommendations of the Dosimetry Task Group of the American Association of Physicists in Medicine, blood-derived estimates of the red marrow (RM) dose from radiolabeled monoclonal antibodies (MAbs) are valid only if the RM is devoid of any specific uptake. There is, therefore, a clear need for an alternative method for estimating the RM dose in patients receiving MAbs that target normal or abnormal (malignant) bone marrow elements. Radiolabeled LL2, an anti-B-cell murine MAb, targets normal B cells and malignant lymphoma cells in the RM. This may result in an increased radiation dose to the RM through neighboring targeted activity. We investigated whether imaging-based estimates of the RM dose, particularly using sacral scintigraphy, correlate with myelotoxicity in non-Hodgkin's lymphoma patients who received 131I-LL2. The sacrum-based RM dose (RMs) was estimated from sacral activity by assuming that 9.9% of the total adult RM is contained in the sacrum. The sacrum was not used if there was focally increased or decreased sacral uptake. Myelotoxicity was assessed based on Radiation Therapy Oncology Group criteria. Twelve of 21 non-Hodgkin's lymphoma patients treated had adequate imaging, dosimetry, and follow-up to evaluate myelotoxicity. Eight of these patients had diffusely increased RM uptake on their MAb scans. The average estimated RMs in the eight patients was 168 +/- 62 cGy (mean +/- SD) with only 50 mCi 131I-LL2. Six of these patients (75%) developed grade 3 or 4 myelotoxicity. In contrast, the average RMs in the four patients who did not have any enhanced uptake on their scans was 71 +/- 30 cGy (P < 0.02). None of these patients developed grade 3 or 4 toxicity. These results suggest that image-based estimates of the RM dose may be predictive of myelotoxicity and should be used in patients with diffuse RM uptake on their scans.

The targeting potential of 131I-labeled NP-4 and MN-14 anti-CEA (carcinoembryonic antigen) monoclonal antibodies (MAbs) was assessed in 19 patients with metastatic medullary thyroid cancer (MTC). Seventeen of these patients also entered pilot radioimmunotherapy studies with nonmyeloablative doses of 131I-anti-CEA MAbs. Tumor targeting was possible in all 19 patients, with an overall lesion sensitivity of 91%. Tumor dosimetry with 131I-MN-14 IgG or F(ab)2 was very favorable, with tumor doses of 14.3 +/- 8.3 cGy/mCi and tumor:red marrow dose ratios exceeding 3:1 for most lesions. Limited antitumor effects lasting up to 26+ months, based on physical exam, tumor markers, computed tomography, or a followup MAb scan, were seen in 5 of 11 assessable patients given relatively low doses of 131I-labeled anti-CEA MAbs. We conclude that anti-CEA MAbs are excellent agents for targeting metastatic MTC. The high tumor uptake of the 131I-anti-CEA antibodies and evidence of tumor response in some patients suggest that radioimmunotherapy with radioiodinated anti-CEA MAbs may be an effective treatment for MTC, particularly when the maximum tolerated dose is given alone or in combination with autologous red marrow or peripheral stem cell support.

Myelosuppressive toxicity is dose-limiting for radioimmunotherapy. We have reported on the use of cytokine intervention (rhIL-1 and rmGM-CSF) to stimulate differentiation of progenitor cells and reduce radioantibody-induced leukopenia and thrombocytopenia (J. Natl. Cancer Inst. 84:399, 1992; Cancer 73:1073, 1994). As an alternative to the use of cytokines, we investigated the effect of syngeneic bone marrow transplantation on the ability to dose-escalate radioantibody. Injection of 10(7) bone marrow cells from a donor mouse 6 to 8 days after a 340- to 360-microCi dose of radioantibody (LD100/28)--a 25 to 30% increase above the maximal tolerated dose--resulted in 100% survival. This observation is associated with a recovery in neutrophil and thrombocyte counts within 21 days of therapy (normal recovery after 275 microCi takes 42 days). None of the mice survived when BMT was done at either 4 or 11 days after radioantibody. Marrow from normal donor mice was more effective than that from cytokine-primed mice whose marrow cells were actively cycling after a 5-day course of IL-1/GM-CSF. The combination of the two myeloprotective approaches, BMT plus a 14-day schedule of IL-1 (2 x 10(3) U/d) and GM-CSF (1 microgram/d) intervention, provided a greater stimulation of peripheral WBC counts than either approach alone; however, further dose escalation under these conditions was not feasible. The 30% intensification in radioantibody dose offers a therapeutic advantage for both bulky disease (GW-39 subcutaneous nude mouse model) and micrometastatic disease (GW-39 intrapulmonary model). In the bulky tumor model, the increase in administered dose resulting from BMT extends the 8-week growth delay observed at 275 microCi 131I-MN-14 IgG by an additional 7 weeks. In the metastatic model, dose intensification increased median animal survival from 15 to 23 weeks. Therefore, by optimizing the use of BMT, a greater therapeutic benefit can be derived from radioantibody therapy in a solid tumor model. This study represents a proof of principle, that BMT can be effective for low-dose-rate therapy as it has been for short-duration intense chemotherapy and radiation therapy. It also highlights several important issues to consider when attempting to apply the method in the clinic.

Localization of radiolabeled antibodies in the perivascular space of tumors resulted in morphological changes in blood vessel structure and physiological changes in tumor vessel function. Vessel diameter decreased by day 14 and was associated with a significant decline in vascular volume (VV). Upon recovery of VV, the basement membrane surrounding the endothelium had thickened. Tumor vascular permeability (VP) decreased within 7 days of treatment and remained suppressed throughout the 42-day observation period of our study. The decline in VP, which could be visualized by fluorescent microscopy of FITC-dextran extravasation, was dose-related and could be quantified at doses as low as 800 cGy. The radioantibody-induced 50-80% decline in tumor VP was observed in 3 human colonic xenografts (GW-39, LSI74T and MOSER). Decreases in VP have been observed for proteins ranging in size from 20 to 150 kDa. Similar effects on VP were noted when low protein doses (10-30 micrograms), which resulted in heterogeneous antibody distribution, were used or with high protein doses (400-750 micrograms), which resulted in more uniform penetration of antibody. If 188Re or 90Y, radiometals with higher beta-energy and longer path lengths, were substituted for 131I, a similar decrease in VP was observed. The radioimmunotherapy (RAIT)-induced decrease in tumor VP resulted in a 90% decline in accretion of a second dose of radioantibody. The 10% of the second dose that was taken up by the tumor targeted many already non-viable tumor regions and some, but not all, viable tumor cell clusters.

Background: The authors recently reported that a 12-day schedule (beginning 3 days before radioantibody treatment) of twice-daily dosing of rH-IL-1 (1 x 10(3) U/dose) and rM-GM-CSF (0.5 micrograms/dose) can reduce the magnitude and duration of radioantibody-induced myelosuppression, thereby permitting a 25-30% increase in the dose of radioantibody that can be administered without the dose proving lethal. In an effort to further reduce toxicity and escalate the tolerated dose, the authors altered the method of administration of cytokines from daily bolus dosing to continuous infusion by implantable osmotic pumps., Methods: A control group of mice was compared to five groups of mice that either did or did not receive a 340 microCi dose of radioantibody, and received no cytokines, cytokines by bolus dosing, or cytokines by continuous infusion. For 4 weeks, peripheral white blood cell and thrombocyte counts and thymus and spleen weights were taken, marrow cell number was monitored, and marrow colony-forming unit activity was evaluated weekly in the untreated control mice and the treated mice., Results: These studies demonstrated that after a dose of radioantibody, continuous dosing of cytokines resulted in higher white blood cell (WBC) and platelet values than if bolus delivery was used (day 7, WBC: 110% vs. 59%; day 14, WBC: 85% vs. 62%; day 21, WBC: 98% vs. 42%; day 7, platelets: 122% vs. 51%; day 14, platelets: 159% vs. 72%; day 21, platelets: 239% vs. 171%). A comparison of bolus versus continuous dosing in the absence of radioantibody indicated that spleen weight increased by 40-60% after continuous infusion of cytokines and by 20-25% after bolus dosing. The 20-30% decrease in thymus weight was similar with both dosing regimens. Colony-forming units (CFUs) in marrow increased from 30-35 in untreated mice to 50-55 in mice given cytokines by bolus injection, and to 150-180 in mice given continuous infusion of cytokines. Spleen CFUs exhibited an insignificant increase after bolus dosing of cytokines but increased almost fourfold after continuous dosing. Peak stimulation of marrow and spleen CFUs occurred 28 days after initiation of cytokine administration (2 weeks after cytokines administration was stopped). The probability of survival for 6 weeks after further dose escalation to 360 microCi I-131-MN-14 immunoglobulin G was 16.4% +/- 8.6% after bolus dosing and 58.1% +/- 11.3% after continuous infusion of cytokines., Conclusions: Although continuous infusion of cytokines proved to be a better method of reducing hematopoietic toxicity, further dose escalation of radioimmunotherapy using the "pump" method of cytokine delivery was not possible. Cytokine intervention by either mode of delivery permits a 25% dose intensification without the dose becoming lethal. Further escalation is not feasible, possibly because of other end organ toxicity.

The therapeutic efficacy of 5-fluorouracil (5-FUra; 0.6 mg/day x 5 days) + leucovorin (LV; 1.8 mg/day x 5 days) and of 131I-labeled MN-14 anticarcinoembryonic antigen IgG (275 microCi single dose) was evaluated in size-matched (0.3-0.7 cm3) s.c. LoVo, HT-29, DLD-1, HCT-15, LS174T, and MOSER, GW-39, and WidR human colonic tumors. These lines express varying amounts of carcinoembryonic antigen and exhibit varying degrees of in vitro responsiveness to 5-FUra. Unlike radioimmunotherapy (RAIT), multiple cycles of chemotherapy were feasible over a 3-week period. However, no therapeutic advantage to a second cycle of 5-FUra/LV administration was found. Therefore, it is reasonable to compare single cycles of both treatment modalities. RAIT was statistically more effective in 5 of 8 tumor lines (LoVo, LS174T, MOSER, WidR, and GW-39). In 1 other line (DLD-1), RAIT was marginally more efficacious, but tumors responded well to both therapies. The lack of a statistical difference between the 2 modalities of treatment may indicate that the efficacy of the 2 treatments is equivalent, or the relatively large variability within the treatment groups may have prevented significance given the number of animals evaluated. RAIT and 5-FUra/LV were equally efficacious in the HT-29 and the HCT-15 tumor lines. Of the 5 xenografts that responded better to RAIT, 3 lines (LS174T, GW-39, and WidR) demonstrated a greater percentage of tumors responding over a 5- to 6-week period. The other 3 lines (LoVo, MOSER, and DLD-1) exhibited a similar percent of tumors responding to both therapies, but a greater growth inhibition in those RAIT-treated tumors that responded. In vitro responsiveness to 5-FUra/LV did not directly correlate with in vivo responsiveness (r2 = -0.664), since LS174T and LoVo tumors, with rapid growth rates (0.05-0.36 cm3/day), were not highly responsive to therapy. Growth inhibition from RAIT also did not correlate with total tumor carcinoembryonic antigen content (r2 = 0.003), an observation that may be due to additional variables, such as accessibility of antigen and innate radiosensitivity of the tumor. RAIT was most effective in the fastest growing tumor lines (LS174T, GW-39, MOSER, WidR, and LoVo). These preclinical results suggest an advantage to radioantibody therapy over one of the most commonly used forms of chemotherapy to treat colorectal cancer. These studies also highlight the need to establish criteria that will enable the selection of therapeutic modalities in patients.

We describe the effects that a concomitant large tumor mass can exert on the therapeutic efficacy of radioimmunotherapy against small tumors, using the nude mouse/GW-39 human colonic cancer model. The tumor uptake 7 days p.i. of i.v.-injected 131I-labeled anti-CEA MAb (NP-4) and anti-CSAp MAb (Mu-9) in small (less than 0.2 g) s.c. GW-39 tumors was approximately 3-fold lower in animals with a concomitant large (greater than 1.0 g) GW-39 tumor than in the absence of a large tumor. An inverse correlation between the mass of the tumor burden and the 131I levels in the blood was observed, indicating that a large tumor mass may act as a sink for the injected radiolabeled antibody. Increasing antibody protein dose did not reverse the reduced uptake in the small s.c. tumors. The therapeutic efficacy of a single 0.25-mCi injection of 131I-labeled anti-CSAp MAb Mu-9 towards intrapulmonary GW-39 metastases was tested in nude mice bearing either small or large GW-39 s.c. tumors. Over 80% of the animals with small s.c. GW-39 tumors survived 18 weeks after tumor transplantation, whereas less than 20% of the animals bearing large s.c. tumors survived past 13 weeks. Dosimetric calculations, based on biodistribution data over time, indicated that the presence of a large s.c. tumor mass may have decreased the radiation dose to the intrapulmonary tumors almost two-fold. However, the radiation dose to the blood was also decreased in the animals with the large tumor burden. Therefore, the animals with larger tumor burden may also have been able to sustain higher doses of the radioantibody. The presence of a large tumor mass can thus affect the biodistribution and therapeutic efficacy of radioiodinated antibodies. We suggest that bulky tumors can adsorb a considerable amount of the injected dose, thereby reducing the total amount of MAb available for binding to the smaller tumors.

Background: In previous studies in a tumor-bearing hamster model, we demonstrated protection and rescue from radioantibody-induced hematopoietic toxicity by treatment with interleukin-1 (IL-1) before or after radioantibody treatment, as well as attenuation of duration of myelosuppression by administration of granulocyte-macrophage colony-stimulating factor (GM-CSF)., Purpose: The purpose of this study was to evaluate the ability of recombinant human IL-1 and recombinant murine GM-CSF to reduce myelosuppression and increase survival of non-tumor-bearing, female BALB/c mice while escalating the maximal tolerated dose (MTD) of radioantibody--the highest dose that results in no deaths., Methods: We administered IL-1 for 7 days at 1 x 10(3) U twice a day and GM-CSF starting on the same day for 12 days at a dose of 0.5 micrograms twice a day, alone or in combination. The doses of iodine 131 (131I)-NP-4 IgG (anti-carcinoembryonic antigen monoclonal antibody) radioantibody used were 270, 340, and 370 microCi; the MTD in mice is 270 microCi. The 12-day schedule of cytokine administration was initiated at various times with respect to the radioantibody dose: on the same day; 6 or 3 days before radioantibody; or 3, 6, or 9 days after radioantibody. Treatment efficacy was measured by survival and white blood cell and platelet counts., Results: A 25% increase to 340 microCi of radioantibody used alone resulted in 100% lethality within 25 days of treatment. The optimal cytokine schedule was a 12-day treatment with the combination of cytokines initiated 3 days before radioantibody. This treatment resulted in 100% survival and significantly reduced the magnitude and duration of hematopoietic toxicity. The increase in radioantibody dose resulted in an 85%-95% decrease in peripheral white blood cells and a 75%-85% reduction in platelets within 14 days of radioantibody administration. Further dose escalation to 370 microCi of radioantibody used alone (37% increase above the MTD) resulted in lethality to 12% of the mice. IL-1 or GM-CSF alone was minimally effective., Conclusions: These studies are the first demonstration that cytokines could be used to reduce radioantibody-induced leukopenia and thrombocytopenia and to escalate the tolerated dose of radioantibody by 25%., Implications: We plan to evaluate the potential therapeutic benefit of a 25% increase in radioantibody dose in a tumor-bearing mouse model.

The haematologic effects of radioimmunotherapy (RAIT) in cancer patients have been studied in order to better understand the aetiology of RAIT-associated myelosuppression. Evaluations were performed on patients treated with 131I-anti-carcinoembryonic antigen (CEA) and 131I-LL2, a monoclonal antibody (MAb) reactive with non-Hodgkin's B-cell lymphoma. Both groups of patients experienced decreases in WBC and platelets. Nadirs were observed 42-51 d post first injection in the lymphoma patients, and 49-66 d post first injection (30-43 d post high-dose therapeutic injection) in the carcinoma patients. Within the WBC population, B cells were the most radiosensitive. The evaluations of the binding of these MAbs to peripheral blood cells and the effect of RAIT on lymphocyte subpopulations indicated a drop of 26-92% in the percentage of B lymphocytes within 1 week following treatment with both 131I-LL2 and 131I-anti-CEA MAbs even though only LL2 binds to B cells. The percentage of T lymphocytes was not affected by the 131I-antibody treatments. These observations suggest that the marked drop in circulating B lymphocytes and platelets after the administration of radioiodinated antibodies is a nonspecific radiation effect, and not necessarily related to the binding of MAb to normal B cells. Thus, among WBCs, B cells are uniquely radiosensitive, and will be unusually affected by antibody-directed internal radiation.

The biodistributions of three 131I-labeled murine monoclonal antibodies, NP-4 and Immu-14 anti(carcinoembryonic antigen), and Mu-9 anti-(colon-specific antigen p), were determined at antibody protein doses varying from 1 microgram to 1000 micrograms in nude mice with small (0.1-0.4 g) GW-39 human colonic cancer xenografts. For each antibody, the percentage of the injected dose per gram of tumor and tumor/nontumor ratios were constant over a wide protein dose range. However, at high protein doses (above 100 micrograms for NP-4 and Immu-14) the percentage of the injected dose per gram of tumor and tumor/nontumor ratios decreased. Assuming that the uptake of a control anti-(alpha-fetoprotein) antibody represents the amount of antibody that accumulates in the tumor nonspecifically (i.e., antigen-independently), it could be shown that for each antibody the amount of antibody protein that accumulates in the tumor specifically, increases linearly with the protein dose, reaching a plateau level at the highest doses tested. The growth inhibition of GW-39 tumor transplants in nude mice treated with 131I-labeled antibody at either low or high antibody protein dose was compared. These experiments indicated that, in this experimental model, enhanced antibody protein dose may decrease the therapeutic efficacy of radioiodinated antibodies. It is suggested that heterogeneous distribution at low protein dose, with intense localization around the blood vessels, may enhance the tumoricidal effect of radioantibodies.