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ObjectiveLabeled oxidation-specific antibodies (Ox-AB) detect, quantify, and noninvasively image lipid-rich atherosclerotic lesions. However, it is unknown whether Ox-AB detect plaque stabilization.Methods and resultsThe aortic uptake of intravenously injected 125I-MDA2 (Ox-AB to malondialdehyde [MDA]-low-density lipoprotein [LDL]) was quantitated in: (1) LDL receptor-/- mice with established atherosclerosis continued on Western diet (Progression) or switched to chow (Regression) or chow+vitamins E and C (Regression-VIT) for 6 months; and (2) Watanabe rabbits (3- to 57-months old) with naturally evolved atherosclerotic lesions. In mice, the Progression group had more extensive atherosclerosis, higher 125I-MDA2 uptake, high concordance of Sudan (lipid)-staining and 125I-MDA2 uptake, and stronger oxidized LDL (OxLDL) and macrophage immunostaining than both Regression groups. In contrast, the Regression groups showed Sudan-positive lesions with focally diminished 125I-MDA2 uptake, which coincided with reduced OxLDL and macrophages but more smooth muscle cells (SMCs) and collagen. In rabbits, areas of increased 125I-MDA2 uptake were associated with high Sudan concordance and strong immunostaining for OxLDL and macrophages. Interestingly, advanced lesions with focally diminished 125I-MDA2 uptake showed stronger immunostaining for SMCs and collagen, particularly at the fibrous cap.ConclusionsOx-AB uptake is focally diminished in plaques displaying accepted features of plaque stability. Imaging techniques to detect the presence and depletion of OxLDL may be useful in assessing plaque stabilization.

ObjectiveLabeled oxidation-specific antibodies (Ox-AB) detect, quantify, and noninvasively image lipid-rich atherosclerotic lesions. However, it is unknown whether Ox-AB detect plaque stabilization.Methods and resultsThe aortic uptake of intravenously injected 125I-MDA2 (Ox-AB to malondialdehyde [MDA]-low-density lipoprotein [LDL]) was quantitated in: (1) LDL receptor-/- mice with established atherosclerosis continued on Western diet (Progression) or switched to chow (Regression) or chow+vitamins E and C (Regression-VIT) for 6 months; and (2) Watanabe rabbits (3- to 57-months old) with naturally evolved atherosclerotic lesions. In mice, the Progression group had more extensive atherosclerosis, higher 125I-MDA2 uptake, high concordance of Sudan (lipid)-staining and 125I-MDA2 uptake, and stronger oxidized LDL (OxLDL) and macrophage immunostaining than both Regression groups. In contrast, the Regression groups showed Sudan-positive lesions with focally diminished 125I-MDA2 uptake, which coincided with reduced OxLDL and macrophages but more smooth muscle cells (SMCs) and collagen. In rabbits, areas of increased 125I-MDA2 uptake were associated with high Sudan concordance and strong immunostaining for OxLDL and macrophages. Interestingly, advanced lesions with focally diminished 125I-MDA2 uptake showed stronger immunostaining for SMCs and collagen, particularly at the fibrous cap.ConclusionsOx-AB uptake is focally diminished in plaques displaying accepted features of plaque stability. Imaging techniques to detect the presence and depletion of OxLDL may be useful in assessing plaque stabilization.

The goal of this research is to develop stable radioimmunoconjugates (RICs) of an anti-HER 2/neu antibodies (MoAbs) for imaging and therapy in an animal model bearing human breast tumors. Pharmacy-grade Herceptin and an anti-HER2/neu antibody were conjugated with a DTPA linker. InCl(3)111 and YCl(3)90 were labeled to MoAb-CHX-A"-DTPA according to the procedure of Clarke et al. (Cancer Res 60: 4804, 2000). Binding capacity of RICs was tested with human cancer cell lines MCF-7, HCC-1954, BT-474 and SKBR-3., The original document contains color images. All DTIC reproductions will be in black and white.

In functional dyspepsia, abnormal intragastric distribution of a test meal has been identified but has never been correlated to any symptom pattern. The aim of this study was to compare the intragastric distribution of a meal between functional dyspepsia patients and controls, and to correlate distribution with symptom patterns, using scintigraphic gastric emptying studies. In forty patients with functional dyspepsia and 29 healthy volunteers, scintigraphic planar images were obtained immediately after ingestion of a mixed radiolabelled test meal and every 20 min for 2 h. The images of the stomach were divided into proximal and distal compartments. The mean intragastric distribution was similar in patients and controls. Over the whole test, 18 (45%) and 20 (50%) patients had a distal redistribution of the solid and liquid phase of the meal, respectively, while proximal retention of these phases was found in 13 (33%) and 9 (23%) patients. Early satiety was associated with early distal redistribution of the liquid phase and fullness was associated with late proximal retention. This study shows similar intragastric distribution of a test meal in health and functional dyspepsia. Within the patient group, an association between abnormal intragastric distribution patterns and symptom profiles was found, which might be related to different pathophysiological mechanisms.

The goal of this research is to develop stable radioimmunoconjugates (RICs) of and-HER2/neu antibodies (MoAbs) for imaging and therapy in an animal model bearing human breast tumors. Pharmacy-grade Herceptin and an and-HER2/neu antibody were conjugated with a DTPA linker. (111)nCl3 and (90)YCI3 were labeled to MoAb-CHX-A"-DTPA according to the procedure of Clarke et al. (Cancer Res 60: 4804, 2000). Binding capacity of RICs was tested with human cancer cell lines MCF-7, HCC-1954, BT-474 and SKBR- 3.

The diagnosis of recurrent ovarian carcinoma is usually determined at surgical re-exploration since the main non-invasive diagnostic tests have low accuracy. It would be desirable to have a high accuracy non-invasive diagnostic procedure. With this aim, we have assessed the utility of three-step immunoscintigraphy. Thirty patients were intravenously injected with biotinylated monoclonal antibodies MOv18 and B72.3, followed by avidin-streptavidin injection and finally by 111In-biotin. Tumour recurrences were imaged 2 h post radioactivity injection. All patients underwent surgical re-exploration 3-4 days after immunoscintigraphy; the presence of tumour in the area of immunoscintigraphic uptake was evaluated in the biopsied material. Twenty-one patients studied were true-positive, five were true-negative, four were false-positive and none was false-negative. The diagnostic accuracy, positive predictive value and negative predictive value were 87%, 84% and 100% respectively. If these findings are confirmed in a larger number of patients, we expect immunoscintigraphy to be introduced as a cost-effective procedure in the follow-up of patients who have received surgery for ovarian carcinoma, since it promises to reliably identify patients who do not require surgical re-exploration, and guide biopsies when they are indicated.

The aim of this study was to assess the possible quantification of vertebral residual bone marrow content relative to the bone marrow content of a non-irradiated vertebra. This method is based on the vertebral count activity, measured using radioimmune bone marrow scintigraphy. First, however, we had to evaluate intra- and inter-observer variability. In three patients who underwent radioimmune bone marrow scintigraphy, two independent observers measured the count density in 51 (15 lumbar and 36 thoracic) vertebrae using a manually drawn region of interest. To evaluate intra- and inter-observer variability, we calculated the means and standard deviations of the differences between measurements. Bland-Altman plots were drawn for all vertebrae as well as for three subgroups of vertebrae (the upper thoracic spine, D1-D6; the lower thoracic spine, D7-D12; and the lumber spine, L1-L5). For all vertebrae, the mean (+/- S.D.) difference, expressed as a percentage of the overall mean, was -0.44 +/- 3.3% for observer 1 and -0.3 +/- 2.1% for observer 2 for intra-observer variability; inter-observer variability varied from 0.55 +/- 3.9% to 1.28 +/- 3.7%. On the Bland-Altman plots, the data points were evenly distributed above and below the 0-line and the linear regression equations matched the line of equality almost perfectly. This pattern was observed for all the vertebrae as well as for the subgroups of vertebrae. In conclusion, our results show that the intra- and inter-observer variabilities are not great, confirming that this technique is simple and robust and can be used for further quantification of bone marrow content in the axial skeleton.

The in vivo post-targeting of tumor by means of anti-carcinoembryonic-antigen (CEA) monoclonal antibodies (MAbs) and the avidin-biotin three-step system was tested by immunoscintigraphy and radioimmunoguided surgery (RIGS) in six patients with primary or recurrent rectal cancer. The patients were preoperatively injected with 1 mg of FO23C5 (anti-CEA) and/or B72.3 anti-tumor-associated glycoprotein (TAG-72) biotinylated MAb; after 24 hours, 1 mg of avidin was administered, and, after a further 24 hours, biotin labeled to Indium-111 (In111) was injected. Preoperative imaging was obtained by means of a gamma camera, and a portable gamma-detecting probe (Neoprobe 1000) was intraoperatively used to count tumor and surrounding normal tissue. Eight tumor sites were localized in the six patients. Four lesions were identified preoperatively and six intraoperatively with a mean tumor-to-normal-tissue (T/NT) ratio of 1:8. This method allowed preoperative scintigraphy and intraoperative radioimmunodetection to be performed with a single radioactive compound injection of biotin labeled to In111 within few days before surgery

The use of a cocktail of monoclonal antibodies in intraoperative radioimmunodetection of colorectal tumour has been evaluated in 14 patients. Eight patients had primary and six recurrent colorectal cancer. Three different monoclonal antibodies were used included B72.3, recognizing TAG72 antigen, FO23C3 and FO23C5 directed against two epitopes of CEA. The antibodies were labeled with 125I. During surgery the radioactive emission of tumour and normal tissue was evaluated by a gamma detecting probe. Ten patients showed positive intraoperative results and in particular 6 (75%) of the 8 patients with primary tumour and 4 (67%) of the 6 patients with recurrence, with a mean tumour to normal tissue ratio of 2.2. Intraoperative radioimmunodetection was instrumental in modifying the therapeutic approach in two patients with recurrent cancer but in none of the patients with a primary presentation. Immunohistochemical analysis, to evaluate TAG72 and CEA antigen expression, was performed in 13 cases. CEA antigen was expressed in 8/13 cases and TAG72 in 5/13. Thus the sensitivity was 38.5% and 61.5% with B72.3 and anti-CEA monoclonal antibodies respectively, while in combination the sensitivity was 71.4%. The use of a cocktail of different antibodies improved the sensitivity of intraoperative radioimmunodetection of colorectal tumours, when compared with a single antibody injection. This approach might improve the clinical use of radioimmunodetection.

To evaluate the use of pretargeted immunoscintigraphy (ISG) in the diagnosis and follow-up of patients with medullary thyroid carcinoma (MTC), we studied 25 patients with histologically proven disease; ISG was repeated after surgery in two patients. The antibody, either an anticarcinoembryonic antigen (CEA) or an antichromogranin A (CgA) biotinylated monoclonal antibody (MAb) or a cocktail of the two biotinylated MAbs was first injected. After 24 h, avidin was administrated i.v., followed by 111In-labelled biotin 24 h later. Fifty-two lesions were visualised. Six primary tumours, diagnosed by increased calcitonin levels, were all correctly diagnosed; 47 recurrences, also suspected by blood tumour markers, were detected and confirmed by cytology or histology. In one case, single photon emission tomography allowed the detection of small lymph nodes with a diameter of 4-7 mm. These lesions, not judged neoplastic by ultrasound, were confirmed to be neoplastic by fine needle aspiration. Pretargeted ISG correctly localises primary tumours and recurrences in MTC patients, when the only marker of relapse is serum elevation of calcitonin. With this three-step pretargeting method, cocktails of potentially useful MAbs can be used, avoiding false-negative studies that may occur when CEA or CgA are not expressed

The detection of chromogranins (Cg) by immunohistochemistry and serology represents a new in vitro diagnostic tool for endocrine tumours. We have recently reported on the feasibility of targeting chromogranin A (CgA) for in vivo detection of pituitary adenomas by immunoscintigraphy (ISG). The scintigraphic procedure, based on an anti-CgA monoclonal antibody and on the avidin-biotin three-step method (Cg-3S-ISG), was evaluated on a group of 29 consecutive patients with known or suspected endocrine tumours other than pituitary adenomas, i.e. medullary thyroid carcinoma, carcinoid, insulinoma and parathormone- or ACTH-producing tumours. Primary tumours (10) and recurrences (16) were visualised in 26 patients, whereas conventional imaging techniques (planar radiography, computerised tomography, magnetic resonance imaging and ultrasonography) failed to detect the tumour sites in ten of the same (Cg-3S-ISG-positive) patients. Therefore, these preliminary results indicate that Cg-3S-ISG, the first immunological method able to detect endocrine tumours in vivo, has a higher diagnostic accuracy than conventional imaging techniques (93.1% compared with 65.5%)

SPECT radioimmunoscintigraphy with Tc-99m-labeled anti-melanoma monoclonal antibodies (MAbs) 225.28S is being used to detect uveal melanoma. Recently, pretargeting methods have been described to reduce background activity and perform imaging in a shorter time interval. Methods: We compared the three-step pretargeting method with conventional radioimmunoscintigraphy in 15 patients with a clinical and laboratory diagnosis of uveal lesion. High-resolution SPECT radioimmunoscintigraphy was performed in all patients with directly labeled MAbs and, 1 wk later, with the three-step pretargeting technique. Eleven patients underwent eye enucleation and specimens of uveal melanoma were available for histology, whereas four patients underwent conservative therapy. The percent injected dose (%ID) delivered to the tumor and the tumor-to-background ratio were calculated. Results: In all three-step radioimmunoscintigraphy studies, there was a reduction of nonspecific nasopharyngeal background. The three-step radioimmunoscintigraphy tumor-to-nontumor ratio was 3.1 +/- 1.3 versus 1.5 +/- 0.5 of conventional radioimmunoscintigraphy, while the percent injected dose on the tumor was similar for the two methods (4.4 +/- 3.0 versus 3.8 +/- 2.8) x 10(-3). Conclusion: Improved SPECT imaging with the three-step radioimmunoscintigraphy results from reduced background and from higher counting statistics due to reduction of time interval between radiotracer administration and imaging, whereas the absolute amount of tracer delivered to the tumor by the two methods is comparable

The intraoperative detection of tumors by means of a gamma-ray detector that recognized radiolabelled monoclonal antibodies (MoAbs) on tumour cell surfaces has been shown to be feasible and clinically useful. The technology is called the Radioimmunoguided Surgery (RIGS) system. We have been working with this system for five years and in this paper we report our experience using different radiolabelled MoAbs and methods in terms of clinical utility in patients with primary or recurrent colorectal cancer. In the first part of the experience we injected with the MoAb B72.3 a group of 66 patients with primary (36) or recurrent (30) cancer introducing for 7 out of 66 a variation of the method to try to overcome some limits of the original procedure. With the new method, based on the avidin-biotin binding, it is possible to use anti-Cea MoAbs and to reduce the preoperative waiting time, injecting biotinylated MoAbs and avidin. In the second part of the experience, a second group of 15 patients with primary (12) and recurrent (3) cancer was injected with biotinylated MoAbs FO23C5 (anti-Cea) while in a third group of 16 patients, 6 with primary and 10 with recurrent cancer a cocktail of antibodies was used. During surgery a probe (NEOPROBE) was used to count obvious tumor, surrounding normal tissue and to scan the abdomen for areas of increased radioactivity. In the first group of patients tumour was localized by probe in 18/36 (50%) cases of primary cancer and in 24 out of 30 recurrences (80%). In the second group tumour was localized in 8/12 (67%) primary cancers and in 2 out of 3 (67%) recurrences. In the last group primary tumours were localized in 5/6 (83%) patients and recurrent cancer in 7/10 (70%). The method altered the surgical procedure in 2 out of 36 primary tumours (6%) and in 8 out of 30 recurrences (27%) injected with the B72.3. In the group of 15 patients injected with the anti-Cea the method changed the surgical strategy in 2/12 (16%) primaries and in 1 out

Radiolabeled monoclonal antibodies (MAbs) have been reported to allow tumor intraoperative detection by means of a gamma-detecting probe. The technology is called the Radioimmunoguided Surgery (RIGS) system. The main inconveniences of the method are 1) the long interval needed for clearance of unattached MAbs from the patient's body, between the injection of the MAb and surgery, and 2) the low sensitivity of current MAbs used in detecting small tumors. We describe a new method to overcome these inconveniences using biotinylated MAbs and avidin in order to obtain a rapid blood clearance of the radiolabeled MAbs both anticarcinoembryonic antigen and antitumor-associated glycoprotein-72 MAbs.

The imaging of cerebral gliomas with radiolabelled monoclonal antibodies (MoAbs) has been previously reported. However, previous studies have been hampered by the drawback of a low tumour to non-tumour ratio. In order to overcome this problem we have developed a three-step pre-targeting method using the avidin-biotin system. The rationale of this technique consists in vivo labelling of biotinylated MoAbs targeted onto tumour deposits, when most of the unbound antibodies have been cleared from the bloodstream as avidin-bound complexes. The anti-tenascin MoAb BC2, specific for the majority of gliomas, was biotinylated and 1 mg was administered i.v. in 20 patients with histologically documented cerebral lesions. After 24-36 h, 5 mg avidin was injected i.v. followed 24 h later by a third i.v. injection of 0.2 mg PnAO-biotin labelled with 15-20 mCi technetium-99m. No evidence of toxicity was observed. Whole-body biodistribution was measured at 20 min, 3 h and 5 h post-injection. [99mTc]PnAO-biotin had a fast blood clearance and was primarily excreted through the biliary system. A dedicated single-photon emission tomography system was used to acquire brain tomographic images 1-2 h after the administration of [99mTc]PnAO-biotin. Tumours were detected in 15/18 glioma patients with a tumour to non-tumour ratio of up 14:1. This three-step method, based on the sequential administration of anti-tenascin MoAb BC2, avidin and [99mTc]PnAO-biotin, can support computed tomography or magnetic resonance imaging for the diagnosis and follow-up of patients with glioma. Further studies are required to evaluate the potential of this technique for therapeutic application.

One of the limitations of intraoperative tumor detection with radiolabeled monoclonal antibody (Mab), by means of a gamma-detecting probe (GDP), is the long time interval needed between Mab injection and surgery to obtain low blood-pool activity. Such an interval can be shortened considerably, exploiting the high affinity between avidin and biotin. Methods: Twenty patients with colorectal cancer were injected with 1 mg of biotinylated I-125 monoclonal antibodies followed, 48 hr later, by a chase of cold avidin. During surgery, the GDP was used to detect radioactive emissions from the tumor and normal tissue. Tumor tissue samples were analyzed in vitro by immunohistochemical tests for the presence of tumor antigens and in vivo antibody localization. Results: At the time of surgery (average 7 days postinjection), the mean value of circulating radioactivity was 6% +/- 3% of the injected dose. Of 20 patients studied, tumors were localized in 13 cases (65%). Subclinical tumors were detected in 3 patients (15%). Conclusion: The use of I-125-labeled biotinylated Mabs followed by avidin as a chase enhances the applicability and effectiveness of radioimmunoguided surgery technology and will allow the use of radioisotopes with a shorter half-life than I-125

Several problems still limit the full use of the diagnostic potential of immunoscintigraphy (IS) with technetium-99m labelled monoclonal antibodies (MoAbs) 225-28S directed to high molecular weight melanoma associated antigen (HMW-MAA). The principal problem is the unfavourable ratio of tumour to non-tumour activity (T/nT), due to the poor tumour uptake and the high aspecific uptake of the tissue surrounding the tumour. Recently, it was demonstrated that using the tumour pretargeting technique based on the injection of monoclonal antibody and the avidin/biotin system (three step immunoscintigraphy), an improvement in the T/nT ratio can be obtained in patients with carcinoembryonic antigen secreting tumours. The aim of this study was to compare the diagnostic sensitivity of traditional immunoscintigraphy with that of three step immunoscintigraphy in seven patients with uveal melanoma. All the patients underwent immunoscintigraphy with MoAb 225.28S radiolabelled with technetium-99m, and a three step immunoscintigraphy 1 week later. No patients demonstrated immediate toxic effects after receiving the reagents, no matter which of the two methods was used. The traditional immunoscintigraphy had a diagnostic sensitivity of 71.4%, diagnosing five out of seven melanomas tested. The three step study detected all the melanomas examined (7/7) with a diagnostic sensitivity of 100% and showed a drastic reduction in background. The preliminary results confirm the feasibility of visualising the uveal melanoma and show that the three step immunoscintigraphy is more diagnostically sensitive than traditional immunoscintigraphy, particularly in small lesions

Background. Radioimmunoguided surgery (RIGS) by means of radiolabeled monoclonal antibodies and a probe has been reported to be useful in recognizing subclinical tumor deposits during operation. Aim of this study was to understand the limits of this technique and to access the potential diagnostic use of RIGS in colorectal cancer surgery. Methods. Monoclonal antibody B72.3 reacting with TAG 72 antigen, labeled with iodine, 125, was injected in 32 patients with primary tumors and in 22 patients with recurrent colorectal cancer. One hundred thirty-three suspected tumor sites were evaluated during operation by means of probe and resected with immunohistochemistry as control. Results. Primary tumor sites were localized by RIGS in 60% of cases, and recurrent sites were localized in 82% of cases. There was a significant correlation both for primary (p<0.001) and recurrent (p<0.001) tumor sites between intraoperative RIGS findings and TAG 72 tumor antigen expression. Results obtained with the probe were instrumental in modifying the surgical approach in six (27%) of 22 patients with recurrences, allowing the removal of tumor masses that would otherwise have been overlooked. Conclusions. The results of RIGS seems to be encouraging in terms of clinical use. The potential high diagnostic resolution appears to improve surgical ablation of colorectal cancer, especially in patients with recurrent cancer or suspected recurrent tumors who have negative results for intraabdominal disease by all other roentgenographic criteria with rising carcinoembryonic antigen or TAG 72 antigen levels

For various pituitary adenomas, it has been demonstrated that somatostatin receptor can be present. Pilot studies have shown that radio-indium labeled pentetreotide allows very good scintigraphic localization of somatostatin receptor-bearing cell masses. Recently, the presence of CgA in pituitary adenomas has also been demonstrated. MAb A11, raised against CgA, has been successfully used with a three-step ISG for the diagnosis of neuroendocrine tumors. Therefore the combined use of three-step ISG with MAb A11 and radiolabeled somatostatin can be useful in the diagnosis of pituitary adenomas. Twelve patients, 5 secreting (group A) and 7 nonsecreting (group B) pituitary adenomas, were enrolled in the study. All patients underwent three-step ISG, and, 2 wk later, scintigraphy with 111In-labeled pentetreotide (Octreoscan). Three-step ISG consisted of i.v. injection of 1 mg of biotinylated MAb A11 (first step), followed by 10 mg of avidin (second step) and [99mTc]PnAO-biotin (third step). Tomographic imaging were acquired for three-step ISG and Octreoscan at 2 and 4 h after radiotracer injection, respectively. The results are the following: 2 patients of group A (secreting tumors) had a positive three-step ISG, whereas all the patients but one of the same group had a positive pentetreotide study; all the patients of group B (nonsecreting tumors) had a positive three-step ISG and 4 had a positive pentetreotide scintigraphy. These data suggest the utility of the combined use of these techniques for a better diagnosis of pituitary adenomas.

An integrated approach to existing methods of extracting biodistribution data, pharmacokinetics and radiation absorbed dose estimates from serial scintigraphic images is described. This approach employs a single computer-generated user interface to reformat planar scans into a standard file type, align conjugate (anterior and posterior) images, draw regions of interest {(ROIs)} over selected organs and lesions and generate count data for anterior and posterior views and calculated geometric means. Using standard correction methods, the fraction injected activity is obtained for all {ROIs} and total body. This methodology has been applied to the analysis of {indium-III-labelled} breast-cancer-directed antibodies and technetium-90m-labelled {CEA-specific} antibody fragments in non-small-cell lung cancer. It is anticipated that this approach will be useful for evaluating the dosimetry of other radiolabelled monoclonal antibodies, as well as other radiopharmaceuticals.}, QC 20111107

Radiolabelled MoAbs have been used in both the diagnosis and the treatment of a variety of tumors. Recently, a three-step tumor pre-targeting strategy has been proposed to overcome one of the major limiting factors in radioimmunodetection: the low tumor-to-background ratio. We evaluated this pre-targeting protocol in 10 patients diagnosed as having pulmonary carcinoma. One milligram of biotinylated anti-CEA MoAb (FO23C5) was administered i.v. (1st step); 24 hours later 5 mg of avidin was injected i.v. (2nd step) followed by 100-500 ng of 111In-biotin (5 mCi) the day after (3rd step). Imaging was performed using single photon emission tomography (SPET). No toxicity and no adverse reactions were observed. Tumor was detected in 8 out of 10 patients. Mediastinal metastases were also localised in 2 out of 3 patients, and adrenal gland recurrency in 1 out of 2 patients. The tumor/background (normal lung), heart, liver and spine ratios were respectively 2.0, 1.0, 1.3 and 4.1 at 90 minutes post-injection. These preliminary data show that the three-step pretargeting method is safe and allows SPECT tumor localization soon after the injection of the radiolabel. In the future, the use of MoAbs with higher specificity could result in improved tumor-targeting, and in the possibility of lung cancer radioimmunotherapy.

Diagnosis and experimental therapy of cancer have been performed with encouraging results using radiolabelled monoclonal antibodies. However, the high background due to non-specific uptake by normal tissue and blood is a major drawback in antibody-guided tumor detection. Various strategies have been proposed to overcome this problem, such as computed background subtraction, use of a second antibody, and local delivery. An antibody is a slow "bullet" for tumor targeting, since in many lesions it requires two or three days to accumulate. The use of fragments such as F(ab')2 or Fab, which display a faster blood clearance than whole antibody, improves tumor localization to a sufficient extent (hours) to allow the use of the most suitable radionuclides, e.g. 99m-Tc. In therapeutic applications we are still far away from the optimal condition in terms of the absolute amount of radioactivity delivered to the tumor. The high specificity of antibodies could be exploited at its best by delaying the delivery of the label to a time when the ratio tumor-bound to non-tumor-bound antibody has reached its maximum value. To obtain this goal, the label should display a fast clearance and should be captured by the antibody already targeted onto tumor cells. These considerations have led to strategies of tumor pretargeting where antibody and label are administered separately. One of these strategies, based on the avidin-biotin system, has already been used extensively for several years in immunohistochemistry and in ELISA. Due to the flexibility of this system, several alternative protocols are possible.(ABSTRACT TRUNCATED AT 250 WORDS)

A new method for intraperitoneal tumour targetting in ovarian cancer using biotinylated monoclonal antibodies (MoAb) and radioactive streptavidin is described. Fifteen patients with histologically documented ovarian carcinoma were injected intraperitoneally with 2 mg of biotinylated MoAb MOv18, followed 3-5 days later by 100-150 micrograms of indium-111 streptavidin, at the specific activity of 280-370 MBq/mg in 500 ml of normal saline. No toxicity was observed. Tumours were imaged from 2 to 48 h after radioactivity injection by recording both planar and single photon emission tomography (SPET) data. All patients underwent surgery 1-8 days later (mean 3 days) after scanning. The resected tumour and normal tissue radioactivity were measured. On the day of surgery, the tumour to normal tissue ratio was 9:1 (range 3:1-30:1) and 45:1 (range 12:1-120:1) for intra- and extraperitoneal samples, respectively. The mean tumor to blood ratio was 14:1 (range 4:1-30:1). The injected dose (i.d.) per gram of tumour was 0.112 (range 0.01-0.3) for recurrences and 0.05 for primary tumour (range 0.005-0.2). Over 24-48 h 14% i.d. (range 8-18% i.d.) was found in the urine, 14% i.d. (range 6-29% i.d.) in the blood and 63% i.d. (range 56-70% i.d.) was still in the peritoneal cavity. These preliminary clinical data suggest that this two-step strategy may be superior to the conventional approach (radiolabelled antibodies) for intraperitoneal radioimmunolocalization and radioimmunotherapy of ovarian cancer.

To evaluate the usefulness of structural and biochemical imaging techniques for the diagnosis of uveal melanoma, 12 patients with choroidal melanoma were examined. Magnetic resonance imaging was used in 11 of 12 patients, as one had a metal prosthesis. All the subjects underwent single photon planar scintigraphy (SPPS) and single photon emission computed tomography (SPECT) using the 99mTc-labeled F(ab')2 of the anti-melanoma monoclonal antibody 225.28S ([99mTc]MoAb) and positron emission tomography (PET) using [18F]fluorodeoxyglucose ([18F]FDG). Magnetic resonance identified 6 of 11 melanotic lesions (definite melanomas) and 4 of 11 hypomelanotic lesions (probable melanomas), whereas in one case it was inconclusive. [99mTc]MoAb uptake was observed in 5 of 12 lesions using SPPS and 8 of 12 lesions using SPECT. [18F]FDG uptake was observed in 3 of 12 lesions by PET. These results demonstrate that both MR and radioimmunoscintigraphy are sensitive techniques for the diagnosis of choroidal melanomas and suggest that the detection of melanomas by MR, SPPS, and SPECT is largely dependent upon their size. The validity of these conclusions was verified in four subjects in whom the diagnosis was based on MR and/or SPECT findings only and confirmed by histology. The finding that only some of the uveal melanomas of larger size are visualized based on [18F]FDG uptake suggests that melanomas can have either high or low glucose consumption

We describe a method to postlabel, in vivo, biotinylated monoclonal antibodies pretargeted onto tumor deposits when most of the non-tumor-bound antibodies have already been cleared as avidin-bound complexes. The application of this principle to tumor detection by immunoscintigraphy was tested in 20 patients with histologically documented cancer and increased circulating carcinoembryonic antigen levels. One mg of biotinylated anti-carcinoembryonic antigen monoclonal antibody (FO23C5) was administered i.v. (first step). After 3 days, 4-6 mg of cold avidin were injected i.v. (second step), followed 48 h later by 0.2-0.3 mg of a biotin derivative labeled with 111In (2-3 mCi) (third step). No evidence of toxicity was observed. Whole body radioactivity distribution was measured in five patients at various intervals postinjection by the conjugate counting technique. Tumors and metastases were detected in 18 of 19 patients (the remaining patient was a true negative) within 3 h after administration of 111In-biotin by planar or single photon emission tomography imaging. At the time of imaging, tumor/blood pool ratio was 5.5 +/- 3.2, and tumor/liver ratio was 6.7 +/- 3.9. Blood clearance of 111In-biotin was multiexponential, with the fast component having a t1/2 of 5 +/- 3 min. Urinary excretion of radioactivity over 3 h was 63.5 +/- 4.9% of the injected dose. Radioactivity at 3 h was 6.5 +/- 1.8% in blood, 1.6 +/- 0.3% in the kidney, and 2.4 +/- 0.6% in the liver. This approach represents an improvement in immunoscintigraphic techniques for tumor localization. The potential use for radioimmunotherapy is discussed.

A major inconvenience of intraoperative tumor detection with radiolabeled monoclonal antibody (MoAb) by means of a probe is the long interval needed between the injection of MoAb and surgery (at least 20 days). We describe a new method which entails injection of 125I-labeled biotinylated monoclonal antibodies and cold avidin in order to obtain a rapid blood clearance of the radiotracer. The first clinical application of this protocol has been carried out in a colon cancer patient operated on six days after the administration of 125I-labeled biotinylated MoAb and cold avidin, with an optimal tumor-to-normal tissue ratio and with 90% of the circulating radioactivity cleared in two days.