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Purpose: The use of an α emitter for radioimmunotherapy has potential advantages compared with β emitters. When administered systemically optimal targeting of intact antibodies requires >24 h, therefore limiting the use of short-lived α emitters. This study investigated the biodistribution of bismuth-labeled biotin in A431 tumor-bearing mice pretargeted with antibody B3-streptavidin (B3-SA) and examined the therapeutic efficacy of the α emitter, 213Bi-labeled biotin.Experimental Design: Biotinidase-resistant 7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA)-biotin was radiolabeled with 205,206Bi or 213Bi. Treatment of tumor-bearing mice began by administration of B3-SA (400 μg) to target the tumor sites for 24 h. Then, an agent containing biotin and galactose groups was used to clear the conjugate from the circulation. Four h later, bismuth-radiolabeled DOTA-biotin was given, and biodistribution or therapy was evaluated. Dose escalation treatment from 3.7–74 MBq was performed, and the effects on tumors of different sizes were investigated. Tumor growth, complete blood cell counts, toxicity, and survival were monitored.Results: Radiolabeled biotin cleared rapidly. Rapid tumor uptake resulted in much higher tumor:nontumor targeting ratios than achieved with the directly labeled monoclonal antibody. Dose escalation revealed that 74 MBq caused acute death of mice, whereas 0.37–37 MBq doses inhibited tumor growth and prolonged survival significantly. Evidence of mild hematological toxicity was noted. At therapeutically effective doses renal toxicity was observed.Conclusions: 213Bi-DOTA-biotin, directed by the Pretarget method to tumor-targeted B3-SA, showed a therapeutic effect, although the therapeutic index was low. The source of the toxicity was most likely related to the renal toxicity.

A simplified kiet has been developed for 99mTc protein radiolabeling using an N3S triamide mercaptide bifunctional chelating agent and the preformed chelate approach. The process combined N3S chelating agent, gluconate intermediate transfer agent, stannous reducing agent, and gentisic acid stabilizer into a lyophilized formulation. With sulfur donor atom hemithioacetal protection of the ligand, delta-2,3,5,6-tetrafluorothiophenyl alpha-S-(1-ethoxyethyl)mercaptoacetamido-L-adipoylglycylglycine , optimum 99mTc chelation was achieved in a single step. Subsequent reaction with NR-LU-10 antibody Fab fragment followed by purification via QAE Sephadex anion exchange resin filter afforded 99mTc-N3S-NR-LU-10 Fab conjugate with retained immunoreactivity and effective tumor targeting properties.

Antibodies with their ability to selectivity bind antigens have been of great interest in targeting radiation, drugs and toxins to tumors. Limited success in delivery of radioactivity has been enjoyed with conventional attachment to antibodies. This is due to slow tumor targeting processes and slow disappearance from blood and variable uptake and disappearance from the excretory organs, liver and kidney. Preliminary studies in animal models and patients have shown promise in increasing the tumor to blood exposure ratio by pretargeting antibody followed by small molecule delivery of radioactivity using a molecular capture system. Efficient capture of the small molecule radioactivity carrier by tumor localized antibody and rapid clearance and excretion of the untargeted radioactivity decreases the background problem for imaging and lowers marrow toxicity for radioimmunotherapy. Small peptide ligands that bind to receptor bearing tumors offer similar advantages.

Two peptide analogs of the 37-62 sequence region of the HIV TAT protein bind tightly to the surface of A431 breast carcinoma cells. After conjugation to either of two poorly internalized anti-tumor antibody Fab fragments, the analogs enhanced the in vitro cell surface retention and internalization of the Fab fragments to the level of the whole antibodies. This was at the expense of some binding specificity in the case of 1.6 peptides/NRLU-10 Fab, but not in the case of 1.1 peptides/Fab. Enhanced retention may occur by enhanced bivalent binding of the Fab fragments. The internalized fraction of free peptide, but not of the Fab conjugates, is enhanced by chloroquine. The conjugates which were less specific for tumor cell binding may be useful for enhanced retention/internalization of specifically acting agents, for use at specific sites of injection, or against pre-separated target cell populations, while the more specific conjugate may be of interest for further development.

The Fab fragments of two antitumor monoclonal antibodies, NR-ML-05 and NR-LU-10, have been covalently derivatized with synthetic peptides designed to provide secondary sites of attachment to enhance their retention on tumor cells. Analogs of the peptide "GALA", an amphipathic peptide previously reported to interact with uncharged lipid bilayers, gave antibody conjugates of different molecular weight and bound peptide stoichiometry when attached to Fab fragments using the heterobifunctional cross-linker sulfo-SMCC. This attached peptide enhanced the retention and internalization of Fab fragments of NR-ML-05 on FEMX human melanoma cells, but not of NR-LU-10 on HT-29 human colon carcinoma cells, indicating that this effect might be specific for individual tumor antigen-antibody systems. This peptide appeared to increase nonspecific interactions of the conjugate with antigen-negative cells. Other membrane-active peptides were also tested. None were as effective as the "GALA" analogs. A synthetic ion channel peptide attached to NR-ML-05 Fab exhibited the greatest enhanced internalization of these tested peptides.

The alpha emitter, Bismuth-213, (213Bi) T1/2 = 45 min, obtained from an 225Ac generator, was chelated to DOTA-biotin in high radiochemical yield and specific activity. The radiolabeled product showed good radiochemical stability and was used in preclinical therapy studies using a pretargeting format.

The exchange reactions of S-protected dithiol monoaminemonoamide (MAMA) ligands with Tc(V)-gluconate were investigated. Protection of the mercaptide sulfur atoms with acid, base and metal labile groups permitted complex formation of the MAMA ligands at a range of pHs. In general, the rate of complex formation was faster with the MAMA ligands than with the corresponding diamide dithiol (DADS) ligands. The rate of Tc complex formation depended on the nature of the sulfur protecting groups and on the position of the amine group with respect to the other donor groups in the ligands. Two isomeric ligands showed different mechanisms of complex formation. The isomer which gave the final Tc-dithiolate-MAMA complex in higher yield was shown to form a Tc-thioether-thiol-MAMA complex as an intermediate prior to metal-assisted S-dealkylation. The formation of the Tc-thioether complex intermediate at a lower temperature may account for the enhanced kinetics of chelation compared to the isomer which did not form the intermediate complex.

A novel N2S2-monoamine amide (MAMA) bifunctional chelate was designed and synthesized for labeling of antibodies with Tc-99m. The chelate forms Tc complexes at a range of pH's and shows faster kinetics of complexation than N2S2-diamidedithiol (DADS) ligands. The MAMA chelate contains a carboxyl group for covalent attachment to amino groups on proteins.

Purpose: The therapeutic efficacy of a unique melanoma-targeting peptide conjugated with an in vivo generated α-particle-emitting radionuclide was evaluated in the B16/F1 mouse melanoma animal model. α-Radiation is densely ionizing, resulting in high concentrations of destructive radicals and irreparable DNA double-strand breaks. This high linear energy transfer overcomes radiation-resistant tumor cells and oxygen effects resulting in potentially high therapeutic indices in tumors such as melanoma. Experimental Design: The melanoma targeting peptide, 1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA)-Re(Arg11)CCMSH, was radiolabeled with 212Pb, the parent of 212Bi, which decays via α and β decay. Biodistribution and therapy studies were done in the B16/F1 melanoma-bearing C57 mouse flank tumor model. Results: 212Pb[DOTA]-Re(Arg11)CCMSH exhibited rapid tumor uptake and extended retention coupled with rapid whole body disappearance. Radiation dose delivered to the tumor was estimated to be 61 cGy/μCi 212Pb administered. Treatment of melanoma-bearing mice with 50, 100, and 200 μCi of 212Pb[DOTA]-Re(Arg11)CCMSH extended their mean survival to 22, 28, and 49.8 days, respectively, compared with the 14.6-day mean survival of the placebo control group. Forty-five percent of the mice receiving 200 μCi doses survived the study disease-free. Conclusions: Treatment of B16/F1 murine melanoma–bearing mice with 212Pb[DOTA]-Re(Arg11)CCMSH significantly decreased tumor growth rates resulting in extended mean survival times, and in many cases, complete remission of disease. 212Pb-DOTA-Re(Arg11)CCMSH seems to be a very promising radiopharmaceutical for targeted radionuclide therapy of melanoma.

Pretargeting involves administration of a tumor-targeting monoclonal antibody (mAb) covalently linked to a molecule having a high-affinity binding site for a rapidly distributed radiolabeled effector molecule. The aim of this study was to compare pretargeting to a conventionally labeled antibody for tumor targeting of the intermediate-lived radionuclide (64)Cu, which has shown promise for PET imaging and radioimmunotherapy of cancer.DOTA-biotin (where DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid) and the intact immunoconjugate DOTA-NR-LU-10 were labeled to high specific activities with (64)Cu, and the serum stabilities and target binding capabilities of each agent were assayed in vitro. Nude mice bearing SW1222 human colorectal carcinoma xenografts were administered (64)Cu-DOTA-biotin, with and without pretreatment with the mAb-streptavidin conjugate NR-LU-10/SA and the synthetic clearing agent Biotin-GalNAc(16), or injected with (64)Cu-DOTA-NR-LU-10. Biodistributions of both agents were obtained from 5 min to 48 h after injection.Both (64)Cu-DOTA-biotin and (64)Cu-DOTA-NR-LU-10 were 100% stable in serum in vitro. (64)Cu-DOTA-biotin exhibited98% specific binding to immobilized streptavidin, whereas the immunoreactivity of (64)Cu-DOTA-NR-LU-10 averaged nearly 80%. Biodistributions in SW1222-bearing mice showed that NR-LU-10/SA-pretargeted (64)Cu-DOTA-biotin attained a peak tumor uptake of 18.9 percentage injected dose per gram (%ID/g) at 1 h, with concomitant rapid disappearance from blood and renal excretion. In the absence of pretargeting, (64)Cu-DOTA-biotin had very similar biodistribution and clearance properties, except with extremely low nonspecific tumor uptake. In contrast, (64)Cu-DOTA-NR-LU-10 reached 80.3 %ID/g in tumor tissue, after 48 h, whereas blood clearance was considerably slower than pretargeted (64)Cu-DOTA-biotin. Comparison of the time-activity curves for tumor uptake and blood clearance of pretargeted (64)Cu and the (64)Cu-labeled antibody revealed that the maximum tumor accumulations of radioactivity were similar for each agent, 17.9 percentage injected activity per gram (%IA/g) and 20.7 %IA/g, respectively. However, the tumor-to-blood ratio of areas under the curves was 14 times higher for pretargeted (64)Cu-DOTA-biotin because of the substantial increase in blood clearance of the small effector molecule.The extremely rapid tumor uptake and blood clearance of pretargeted (64)Cu-DOTA-biotin should afford markedly superior PET imaging contrast and therapeutic efficacy, compared with conventionally labeled (64)Cu-DOTA-NR-LU-10. Further comparison of the therapeutic efficacy, toxicity, and dosimetry of these 2 agents is warranted.

Radiolabeled antibodies directed against tumorassociated antigens may be used in the management and treatment of cancer. Radioimmunoscintigraphy (RIS) is an imaging modality that can help determine the location and extent of disease through detection of gamma emitting radionuclides linked to an antibody. Radioimmunotherapy (RIT) is a therapeutic approach that aims to destroy tumor cells via targeted radiation using a tumor-associated antibody radiolabeled with a radionuclide emitting particulate radiation,such as beta or alpha particles.

Current diagnostic imaging procedures are commonly used to view a circumscribed part of the body such as head or thorax. Conventional nuclear medicine imaging procedures such as bone scans may be directed at an organ system, but only recently have single diagnostic imaging procedures become available to search the entire body and all tissues simultaneously for tumor deposits. Antibodies to tumor associated antigens, and ligand-receptor based imaging agents, such as the recently approved somatostatin receptor binding peptide,111 In pentetreotide, offer the opportunity to image tumors directly. Other radiolabeled imaging agents, such as 201 thallium, 99mTc-MIBI and positron emitters such as 18F-fluorodeoxyglucose (FDG) localize in areas of increased cellularity, vascularity or increased metabolism.

We describe here a new method for labelling interleukin-2 (IL-2) in high specific activity with 99mTc for in vivo studies in man. Labelling was performed via a two-step reaction using an N3S bifunctional chelating agent. To optimise the reaction, factors affecting the incorporation of 99mTc into the N3S ligand were studied. The conjugation of the preformed N3S chelate ligand to IL-2 was then similarly optimised. Various strategies for purifying the 99mTc-IL-2 were explored including size-exclusion, ion-exchange, and several modes of reversed-phase chromatography. The radiochemical purity of the purified protein was determined by HPLC, ITLC, TCA precipitation, and SDS-PAGE. The receptor binding capacity of 99mTc-IL-2 was studied. Biodistribution studies in normal mice were performed with 99mTc-IL-2 purified using different techniques or labelled after prolonged storage and compared to 125I-IL-2.

A theoretical comparison was made of radioimmunotherapy (RIT) dosimetry estimates for eight radionuclides ( 90 Y, 105 Rh, 131 I, 153 Sm, 186 Re, 188 Re, 198 Au, 211 At) conjugated to IgG, F(ab′) 2 , and Fab antibody forms. Antibody pharmacokinetics, derived from a nude mouse animal model were combined with appropriate physical data and S values to evaluate absorbed dose to a 0.5 kg centrally located tumor, total body and kidney. Radioimmunoconjugates of F(ab′) 2 with 90 Y, 153 Sm and 186 Re were predicted to be the most promising for RIT.

A monoclonal antibody against the murine T-cell antigen Thy 1.1 was radioiodinated using N -succin-imidyl p -iodobenzoate (PIP) in an attempt to decrease deiodination of the labeled antibody. The biodistribution of the PIP labeled antibody was compared to Iodogen labeled antibody in Thy 1.1 + lymphoma bearing AKR/Cum mice, where the antibody was tumor specific, and AKR/J mice where the antibody reacted with both tumor and normal T-cells. PIP labeling resulted in decreased iodine concentrations in stomach and salivary gland as compared to Iodogen labeling. There was little difference in radioiodine concentrations between the two preparations in tumor, lymphoid tissues or other organs. These results suggest deiodination of intact antibody plays little role in the clearance of radioiodinated anti-Thy 1.1 antibody from tissues.

Orthoiodohippuric (OIH) acid labeled with 131 I is a widely used renal radiopharmaceutical agent and has been the standard radiopharmaceutical agent for the measurement of effective renal plasma flow (EPRF). Limitations to the routine clinical use of 131 I OIH are related to the suboptimal imaging properties of the 131 I radionuclide and its relatively high radiation dose. 123 I has been substituted for 131 I; however, its high cost and short shelf-life have limited its widespread use. Recent work has centered on the development of a new 99m Tc renal tubular function agent, which would use the optimal radionuclidic properties and availability of 99m Tc and combine the clinical information provided by OIH. The search for a suitable 99m Tc renal tubular function agent has focused on the diamide dithiolate (N 2 S 2 ), the paraaminohippuric iminodiacetic acid (PAHIDA), and the triamide mercaptide (N 3 S) donor ligand systems. To date, the most promising 99m Tc tubular function agent is the N 3 S complex: 99m Tc mercaptoacetyltriglycine ( 99m Tc MAG 3 ). Studies in animal models in diuresis, dehydration, acid or base imbalance, ischemia, and renal artery stenosis demonstrate that 99m Tc MAG 3 behaves similarly to 131 I OIH. A simple kit formulation is available that yields the 99m Tc MAG 3 complex in high radiochemical purity. Studies in normal subjects and patients indicate that 99m Tc MAG 3 is an excellent 99m Tc renal tubular agent, but its plasma clearance is only 50% to 60% that of OIH. In an effort to develop an improved 99m Tc renal tubular function agent, changes have been made in the core N 3 S donor ligand system, but to date no agent has been synthesized that is clinically superior to 99m Tc MAG 3 .

Haloaryl compounds are lithiated and thereafter metalated with one of the following organometallic groups: Sn(n--Bu) 3 or SnMe 3 . The resulting aryltin compound can be transmetalated in site-specific reaction with one of the following organometallic groups: HgX, Hg(OAc) 2 , BX 3 , or BZ 2 , wherein X is Cl, Br, or I, and Z is alkyl or alkoxy. The metalated compounds are subsequently radiohalogenated via a demetalation reaction. A functional group suitable for conjugation to protein can be added subsequent or preferably prior to the radiohalogenation. Also compounds of the formula: R 1 --Ar--R 2 , wherein R 1 is either a radiohalogen or any one of the organometallic groups stated above, Ar is aromatic or heteroaromatic ring, and R 2 is a short-chain substituent that does not activate the aromatic ring and that bears a functional group, or a precursor thereof, suitable for conjugation to protein under conditions that preserve the biological activity of the protein. The radiohalogenated small molecules are conjugated to proteins such as monoclonal antibodies for use in diagnosis and therapy.

Haloaryl compounds bearing a defined functional group or precursor are metalated with either Sn(n-Bu)3 or SnMe3. The resulting aryltin compound may be transmetalated in site-specific reaction with one of the following organometallic groups: HgX2, Hg(OAc)2, BX3, or BZ3, wherein X is Cl, Br, or I, and Z is alkyl or alkoxy. The stannylated or otherwise metalated compounds are subsequently radiohalogenated via a demetalation reaction. The Stannylated or otherwise metalated compounds are subsequently radiohalogenated via a demetalation reaction. The functional group is suitable for conjugation to protein and can be present or be added subsequent, but most preferably prior, to the radiohalogenation. Also compounds of the formula: R1 --Ar--R2, wherein R1 is either a radiohalogen or any one of the organometallic groups stated above, Ar is aromatic or heteroaromatic ring, and R2 is a short-chain substituent that does not highly activate the aromatic ring an that bears a functional group suitable for conjugation to protein under conditions that preserve the biological activity of the protein. The radiohalogenated small nolecules are conjugated to proteins such as monoclonal antibodies for use in diagnosis and therapy.

Conditions for blood storage are chosen to assure adequate levels of adenosine triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG). Because of the invasive nature of the techniques, biochemical assays are not routinely used to measure levels of these compounds in stored blood. However, 31P NMR spectroscopy measures phosphorylated intermediates in intact cells and could be used without disruption of the storage pack. We compared levels of ATP and 2,3-DPG measured by 31P spectroscopy and standard enzyme-linked biochemical assays in whole blood (WB) and packed red blood cells (PRBCs) at weekly intervals during a 35-day storage period. NMR demonstrated a marked decrease in 2,3-DPG and an increase in inorganic phosphate after the first week of storage. No significant differences in ATP concentrations were seen in WB during the storage period, but a significant decrease in ATP in PRBCs was documented. There was good agreement in levels of ATP and 2,3-DPG measured by NMR and biochemical techniques. 31P NMR spectroscopy is a noninvasive technique for measuring ATP and 2,3-DPG which has a potential use in quality assurance of stored blood.

Diisopropyl-IDA Tc 99m imaging studies were performed in 11 normal subjects in both the fasting and postprandial states. In 5- to 60-minute analog images obtained in both fasting and postprandial studies, the cardiac blood pool was almost never seen, renal pelvic radioactivity was commonly seen, the extrahepatic biliary tract was always seen, and the left hepatic duct was always more prominent than the right hepatic duct. The biliary tract was visualized by ten minutes in nine of 11 fasting studies and 10 of 11 postprandial studies. The gallbladder was visualized in all eleven fasting studies, but in only four postprandial studies. The gallbladder was visualized in all eleven fasting studies, but in only four postprandial studies (p less than 0.05). The zero- to sixty-minute digital data indicated a greater hepatocyte clearance, an earlier time of peak parenchymal radioactivity, and a faster parenchymal washout in the postprandial studies compared with fasting studies (p less than 0.05). Approximately nine percent of the injected dose was recovered in the urine during the first three hours in fasting and postprandial studies. The normal diisopropyl-IDA Tc 99m study in the fasting and postprandial states is defined; significant differences exist between the two states.

Imaging of diffuse liver disease is traditionally done with Tc-99m-sulfur colloid. The advent of Tc-99m-labeled hepatobiliary agents led the authors to reevaluate the role of Tc-99m-sulfur colloid. A total of 95 paired Tc-99m-diethyl-IDA and Tc-99m-sulfur colloid studies were performed in 61 patients (60 paired studies in liver transplant patients and 35 paired studies patients who had not received liver transplants). The following parameters were visually graded on a five-point scale: Tc-99m-diethyl-IDA clearance and time of appearance of appearance of intestinal activity; and Tc-99m-sulfur colloid liver size, bone marrow activity, splenic size, splenic activity, lung activity. Total serum bilirubin levels were used as the standard measure of liver function. The Tc-99m-diethyl-IDA parameters correlated more highly with total serum bilirubin than did the Tc-99m-sulfur colloid parameters in both the transplant and nontransplant groups. In conclusion, Tc-99m-diethyl-IDA appears to be the preferred radiopharmaceutical for evaluation of hepatocellular function, although both agents may be needed in certain clinical situations.

Animal and preliminary patient data suggest that [ 99 m Tc]parabutyl-IDA might be superior to [ 99 m Tc]diethyl-IDA in imaging the hepatobiliary system in patients with high blood bilirubin levels. A direct clinical comparison between these two agents was made in 14 patients. The total serum bilirubin range was 1.2−50.6 mg/dl (mean = 13.3 mg/dl) and the average time between studies was 2.0 days. Visual evaluation of all 14 paired studies showed [ 99 m Tc]parabutyl-IDA to be superior ( p 99 m Tc]diethyl-IDA was superior ( p p > 0.05) for [ 99 m Tc]diethyl-IDA to demonstrate the intrahepatic ducts better and to show an earlier intestinal arrival time. In the 7 patients who showed evidence of biliary excretion, both agents demonstrated excretion in 6 and only [ 99 m Tc]parabutyl-IDA in I (bilirubin: 50 mg/dl). We conclude that, in general, [ 99 m Tc]para-butyl has no clear advantage over [ 99 m Tc]diethyl-IDA even in patients with elevated bilirubins.

Rhenium and technetium penicillamine complexes have been synthesized by SnCl/sub 2/ reduction of ReO/sub 4//sup -/ or TcO/sub 4//sup -/ in the presence of optically pure or racemic penicillamine. The complexes are characterized by their chromatographic behavior, electronic spectra, fast atom bombardment mass spectra, and variable temperature /sup 1/H NMR spectra. All complexes are six-coordinate in solution, with one tridentate penicillamine, one bidentate penicillamine, and one oxo ligand. The mixed complexes are functional, racemizing by exchange of carboxylates at the sites trans to the oxo ligand. Kinetics of this process were measured by complete line-shape analysis of the NMR spectra, and values for reaction rate constants are reported.

We studied 14 patients having serum creatinines of 1.0 to 12.8 mg/dl with either Tc-99m-N,N'-bis(mercaptoacetyl)-2,3-diaminopropanoate (CO2-DADS) or Tc-99m DTPA, and within 48 hours with the other agent. Analog and digital images of the kidneys and bladder were acquired for 30 minutes after injection and after voiding. The kidney-to-background ratio at 3 minutes for Tc-99m CO2-DADS was 2.01 +/- 0.79 (mean +/- SD) times that for Tc-99m DTPA (P less than 0.001). The parenchymal transit time for Tc-99m CO2-DADS was 1.34 +/- 0.25 (mean +/- SD) times that for Tc-99m DTPA (P less than 0.005). The percent-excreted dose at 30 minutes for Tc-99m CO2-DADS was 2.57 +/- 1.24 (mean +/- SD) times that for Tc-99m DTPA (P less than 0.001). Analog Tc-99m CO2-DADS images showed spatial resolution comparable to that for Tc-99m DTPA. Hepatobiliary excretion was never seen. Tc-99m CO2-DADS appears to be generally superior to Tc-99m DTPA as a renal radiopharmaceutical.

Six healthy individuals and six patients with a wide range of hepatobiliary function abnormalities were studied with Tc-99m-trimethylbromo-IDA; all normal subjects and four of the six patients were also studied with Tc-99m-diisopropyl-IDA. Visual evaluation of analog images demonstrated a greater liver-to-kidney ratio for Tc-99m-trimethylbromo-IDA (p less than 0.01). Sampling for radiopharmaceutical in urine at three hours following injection demonstrated that Tc-99m-trimethylbromo-IDA had a lower renal excretion rate than Tc-99m-diisopropyl-IDA regardless of whether hepatocyte function was normal or abnormal (p less than 0.01). There were no significant differences between the two radiopharmaceuticals in hepatocyte extraction efficiency or hepatic parenchymal transit time. It is concluded that the lower rate of renal excretion and, therefore, greater hepatocyte specificity of Tc-99m-trimethylbromo-IDA justifies expanded clinical trials and may make it the radiopharmaceutical of choice for hepatobiliary imaging.

A series of new ligands and the corresponding technetium-99m chelates based on diamide dimercaptide donor groups were synthesized as derivatives of technetium-99m 1,2-bis(2-thioacetamido)ethane, a complex shown to be excreted by renal tubular secretion. Chelation with 99mTc resulted in single radiochemical products or the expected numbers of stereoisomers. They were purified by high-performance liquid chromatography (HPLC) and evaluated in mice as potential renal tubular function agents. The in vivo properties were sensitive to the presence of functional groups, the positional isomerism of the carboxylate group functionality, and the chelate ring stereochemistry of the ligand. The presence of methyl groups slowed renal transit and decreased renal specificity. Cyclohexyl rings fused to the ethylene bridge of the center chelate ring decreased renal excretion while aromatic rings essentially abolished renal excretion. Slow hepatobiliary clearance was observed as an alternate mode of excretion. Polar groups, such as hydroxyl, carboxylate, and carboxamide, increased renal excretion rates and specificity in a stereochemically dependent manner. 99mTc chelates of 1,3-bis(2-thioacetamido)-2-hydroxypropane, 3,4-bis(2-thioacetamido)butanoate and 1,8-dimercapto-2,7-dioxo-3,6-diazanonanoate were identified as promising new renal radiopharmaceuticals.

The development of monoclonal antibodies of high affinity and selectivity for tumor antigens has supported the development of radiolabeled antibodies for diagnostic localization and targeted delivery of therapeutic radionuclides. Several radionuclide chelating agent systems have been developed for indium-111 and technetium-99m that have shown good sensitivity and specificity for tumor detection in patients. Feasibility for therapy has been shown in animal models and a few patient studies with iodine-131 and yttrium-90. This review covers selection of radionuclides and chemistry of antibody radiolabeling.

Synthesis of methyl 4-tri-n-butylstannylbenzoate (1) was accomplished by reaction of methyl 4-bromobenzoate with hexabutylditin and palladium catalyst. Transmetallation of 1 with mercuric acetate yielded the corresponding arylmercuric acetate 4 which was readily converted to aryl mercuric halides 2a and 2b. Reaction of arylmercuric bromide 2b with diborane or catecholborane produced arylboronic acid 3 in high yield. Iodinations of 1. 2a and 3 were studied using N-chlorosuccinimide/NaI at the 10% and 100% stoichiometric amounts of NaI with Na125I added to monitor the course of the reaction.

Fifteen patients with a wide range of hepatobiliary function were studied with both 99mTc-diethyl-IDA and 99mTc-PIPIDA. In images obtained 5 to 60 minutes after injection, 99mTc-diethyl-IDA was clearly superior with respect to liver/background, hepatic ducts/liver, and small bowel/background ratios. The 99mTc-diethyl-IDA transit time from blood to small intestine averaged 12.2 minutes less than that of 99mTc-PIPIDA. Quantification of relative hepatocyte extraction efficiency indicated that it was 2.15 times higher for 99mTc-diethyl-IDA. Cumulative 3-hour urine collections following injection demonstrated increasing renal excretion of 99mTc-PIPIDA with rising total serum bilirubin levels in a manner quantitatively similar to that determined previously for 99mTc-diethyl-IDA. The authors conclude that 99mTc-diethyl-IDA is superior to 99mTc-PIPIDA for studies of the hepatobiliary system.

A series of 99mTc complexes of naphthalene and naphthalene-like ring systems were evaluated pharmacokinetically as hepatobiliary imaging agents and compared to 131I-rose bengal and 99mTc-N-(2,6-diethylacetanilide)-iminodiacetate in rats and dogs. Although all complexes studied exhibited high specificity for biliary excretion, they varied widely in disappearance rate from blood and in biliary excretion. Complexes with 8-hydroxyquinoline-7-carboxylic acid and hydralazine were relatively lipophilic and were eliminated more slowly than 131I-rose bengal; complexes of iminodiacetic derivatives of naphthalene, N-(2-acetylnaphthyl)iminodiacetic acid and N-(2-naphthylmethyl)iminodiacetic acid were more polar and were eliminated much faster. Renal excretion of the complexes was 5.6% or less except for that of the latter compound (18%). Plasma binding ranged from 51 to 98%.

99mTc - N - (3-bromo-2,4,6-trimethylacetanilide)iminodiacetate (I) and 99mTc-N-pyridoxyl-5-methyl-tryptophan (II) have been described as having optimal properties as hepatobiliary radiopharmaceuticals. This study compared specificity for hepatobiliary excretion, blood disappearance, rates of biliary appearance, and pharmacokinetic parameters including hepatic clearance, volumes of distribution, and mean residence times in normal and sulfobromophthalein-treated rats. The specificity of I was higher as indicated by 94% in the bile at 90 min compared to 91% for II in normal rats and a urine excretion of 0.3% for I compared with 1.9% for II. In sulfobromophthalein-treated animals, urine excretion increases were only to 0.5 and 3.0% for I and II, respectively. In control rats, blood disappearance was similar for both I and II, but II disappeared faster in treated animals. The clearance of II was 70 mL/min/kg in normal and 47 mL/min/kg in treated rats; clearance of I was 51 and 30 mL/min/kg in normal and treated rats, respectively. Volumes of distribution were larger for II. Compound I was superior in specificity while II was superior in clearance and excretion kinetics.

Two phenylsulfonamide fatty acid analogs were synthesized and radioiodinated as potential myocardial imaging agents that might be taken up in the cells and metabolically trapped. The acids, N -11-( p -iodophenylsulfonamide)-undecanoic acid and N -12-( p -iodophenylsulfonamide)-dodecanoic acid, were radioiodinated by exchange with cupric sulfate catalysis. Tissue distribution studies of the radioiodinated acids were performed in mice. Negligible myocardial uptake and rapid renal excretion of the radio-activity was observed with both compounds. The results suggest that the sulfonamide group perturbs the fatty acids to the extent that myocardial uptake is prevented.

Tc-99m-diethyl-IDA imaging demonstrated intrahepatic bile leaks in two patients. The first patient had an intrahepatic abscess associated with a common bile duct stone; he was successfully treated with common duct lithotomy and antibiotics, but without surgical drainage of the intrahepatic abscess. The second patient had bile leakage into an intrahepatic cavitary hematoma after abdominal trauma.

Sixteen patients with biliary atresia and 11 patients with neonatal hepatitis were studied preoperatively with either Tc-99m-diethyl-IDA or TC-99m-diisopropyl-IDA. Two parameters were evaluated: hepatocyte clearance and time to appearance of radioactivity in the intestine. Two observers, using a visual grading system of 1 to 4, gave the 16 patients with biliary atresia a hepatocyte clearance grade of 1.7 +/- 0.6 (mean +/- SD); intestinal radioactivity was not seen through 24 hours. The hepatocyte clearance grade of the 11 patients with neonatal hepatitis was 2.1 +/- 0.9 (mean +/- SD) (p greater than 0.05); intestinal radioactivity was seen in nine of 11 patients (p less than 0.001). Using both parameters, 91% of the patients were classified correctly, 4% were misclassified, and 6% were classified as indeterminate; sensitivity and specificity for biliary atresia were 97% and 82%, respectively. Radionuclide imaging with the newer technetium-99m-labeled hepatobiliary radiopharmaceuticals appears promising for the noninvasive diagnosis of biliary atresia.

A multitude of transitional metal complexes has recently been introduced into clinical practice as hepatobiliary imaging agents; the kinetics of these substances are often poorly understood. To gain better insight into characteristics of these different agents, we measured the extraction efficiency and mean biliary transit time of a variety of iminodiacetate derivatives in the in-situ rat perfused liver. First pass hepatic extraction efficiency averaged 59% for 99mTc N-(p-isopropylacetanilide) iminodiacetate, 73% for 99mTc N-(2,6-diethylacetanilide) iminodiacetate, 74% for 99mTc N-(3-bromo-2,4,6-trimethylacetanilide) iminodiacetate, 90% for 99mTc N-(p-butylacetanilide) iminodiacetate, and 93% for 99mTc N-pyridoxyl-5-methyltryptophan. By comparison, extraction of another organic anionic compound, 131I Rose bengal, was only 12ṁ4%. Mean hepatocyte transit times varied from 2ṁ3 to 7ṁ5 min. Shorter mean transit times were observed for diortho substituted and longer mean transit times for para substituted metal complexes. Radioactivity was quantitatively recovered in bile, and excretion kinetics overall were consistent with data generated in whole animals. These studies demonstrate the value of the in-situ rat perfused liver as a screening tool to characterize hepatobiliary imaging agents.

Since hepatobiliary imaging with 99mTc=labeled iminodiacetic acid derivatives (HIDA) allows relatively separate, sequential measurement of hepatocyte clearance, parenchymal transit, and biliary excretion, these agents should be useful in differentiating intrahepatic cholestasis (IC) from other hepatobiliary disorders. We studied 18 patients with clinical evidence of IC in whom the parenchymal transit time was increased disproportionately to any decrease in hepatocyte clearance. In a second group of 14 patients with hepatocyte disease but without clinical evidence of IC, the average parenchymal transit time was increased less in relation to the average decrease in hepatocyte clearance than in the IC group. In 15 patients with extrahepatic biliary obstruction, the average hepatocyte clearance was disproportionately increased, as in IC, but large-duct obstruction was identified by scintigrams, ultrasound, or computed tomography. These preliminary results suggest that IC can be diagnosed with hepatobiliary imaging.

A series of new ligands and the corresponding technetium-99m chelates based on diamide dimercaptide donor groups were synthesized as derivatives of technetium-99m 1,2-bis(2-thioacetamido)ethane, a complex shown to be excreted by renal tubular secretion. Chelation with 99mTc resulted in single radiochemical products or the expected numbers of stereoisomers. They were purified by high-performance liquid chromatography (HPLC) and evaluated in mice as potential renal tubular function agents. The in vivo properties were sensitive to the presence of functional groups, the positional isomerism of the carboxylate group functionality, and the chelate ring stereochemistry of the ligand. The presence of methyl groups slowed renal transit and decreased renal specificity. Cyclohexyl rings fused to the ethylene bridge of the center chelate ring decreased renal excretion while aromatic rings essentially abolished renal excretion. Slow hepatobiliary clearance was observed as an alternate mode of excretion. Polar groups, such as hydroxyl, carboxylate, and carboxamide, increased renal excretion rates and specificity in a stereochemically dependent manner. 99mTc chelates of 1,3-bis(2-thioacetamido)-2-hydroxypropane, 3,4-bis(2-thioacetamido)butanoate and 1,8-dimercapto-2,7-dioxo-3,6-diazanonanoate were identified as promising new renal radiopharmaceuticals.