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Small cell lung cancer (SCLC) cells express and secrete bombesin-like peptides (BLP) that can activate specific receptors that stimulate the growth of these cells. A murine monoclonal antibody, 2A11, which binds to the BLP, gastrin-releasing peptide with high affinity, has been reported to decrease the growth of SCLC cells in vitro and in athymic nude mice. A Phase I trial in lung cancer patients was performed using multiple doses of 2A11. Thirteen patients with lung cancer received 12 doses of 2A11 antibody three times a week for 4 weeks at one of four dose levels. Serum samples were obtained prior to initiation and before each dose of 2A11 antibody therapy for measurement of 2A11 antibody levels and determination of serum human anti-mouse antibody levels. A pilot imaging evaluation using 111In conjugated 2A11 monoclonal antibody was also performed in the same patients to aid in the study of pharmacokinetics and biodistribution. No toxic reactions were observed, and none of the patients developed detectable human antimouse antibody; however, no objective antitumor responses were observed. The mean trough serum 2A11 levels in patients increased with increasing dose level: 0.26+/-0.2 microg/ml, 6.7+/-6 microg/ml, 71.5+/-60 microg/ml, 248+/-184 microg/ml for dose levels 1 mg/m2, 10 mg/m2, 100 mg/m2, and 250 mg/m2, respectively. At each dose level, sustained detectable serum levels of the monoclonal antibody were achieved. Tumor uptake was noted in 11 of 12 patients who were injected with 111In conjugated 2A11. Because no dose-limiting clinical toxicity was observed, a mathematical model was used to define the recommended Phase II dose of 250 mg/m2. This trial established that repeated doses of monoclonal antibody 2A11 could be given safely to patients, and sustained levels could be achieved for a 4-week schedule. Further evaluation of the antitumor effects of 2A11 is warranted.

Unlabelled: Monoclonal antibodies (MoAb) labeled with 90Y are being used for radioimmunotherapy. Because 90Y is a beta emitter, quantitative information from imaging is suboptimal. With the concept of a "matched pair" of isotopes, 111In is used as a surrogate markerfor90Y. We evaluated the differences in biodistribution between 111In- and 90Y-labeled murine antiTac MoAb directed against the IL-2Ralpha receptor., Methods: The antiTac was conjugated to the 2-(4-isothiocyanatobenzyl)-6-methyl-diethylenetriamine pentaacetic acid (1B4M-DTPA, also known as MX-DTPA). Nine patients with adult T-cell leukemia were treated. Patients received approximately 185 MBq (5 mCi) 111In-labeled antiTac for imaging and 185-555 MBq (5-15 mCi) 90Y-labeled antiTac for therapy. The immunoreactivity of 111In-labeled antiTac was 90%+/-6%, whereas for 90Y-labeled antiTac, it was 74%+/-12%., Results: The differences in blood and plasma kinetics of the two isotopes were small. The area undemeath the blood radioactivity curve was 1.91 percentage+/-0.58 percentage injected dose (%ID) x h/mL for 111In and 1.86%+/-0.64 %ID x h/mL for 90Y. Urinary excretion of 90Y was significantly greater than that of 111In in the first 24 h (P = 0.001), but later, the excretion of 111In was significantly greater (P = 0.001 to P = 0.04). Core biopsies of bone marrow showed a mean of 0.0029+/-0.0012 %ID/g for 111In, whereas the 90Y concentration was 0.0049+/-0.0021 %ID/g. Analyses of activity bound to circulating cells showed concentrations of 500-30,000 molecules of antiTac per cell. When cell-bound activity was corrected for immunoreactive fraction, the ratio of 111In to 90Y in circulating cells was 1.11+/-0.17. Three biopsies of tumor-involved skin showed ratios of 111In to 90Y of 0.7, 0.9 and 1.1., Conclusion: This study shows that differences typically ranging from 10% to 15% exist in the biodistribution between 111In- and 90Y-labeled antiTac. Thus, it appears that 111In can be used as a surrogate marker for 90Y when labeling antiTac with the 1 B4M chelate, although underestimates of the bone marrow radiation dose should be anticipated.

Anti-human serum albumin antibody (Ab) was used as a model antibody. Ab was conjugated with DTPA using cyclic DTPA dianhydride reaction and radiolabeled with 111In. The labeled Ab was purified by affinity chromatography. Size exclusion HPLC of this product showed 62% of 111In bound to monomeric Ab and 38% of the activity bound to antibody oligomers with molecular weights ranging from 300,000 to 450,000. The labeled antibody preparation was injected into the tail vein of rats. The radioactive substances in serum and the supernatant from liver homogenates were analyzed for molecular weight and immunoreactivity. Size exclusion HPLC of the serum samples indicated that the monomeric and dimeric Abs disappeared from the serum at a similar rate over a 48 h period. In addition, a new radioactive substance with an estimated molecular weight of 35,000 appeared in the serum. The immunoreactive fraction of the circulating 111In substances decreased slowly, somewhat proportional to the appearance of the metabolite. On the other hand, the immunoreactivity of the 111In substances in the supernatant from the liver homogenate decreased rapidly and no appreciable immunoreactivity was observed after 48 h. The labeled antibody was catabolized very rapidly in the liver and the major activity in the supernatant was associated with a small molecular weight metabolite which had a HPLC retention time identical to that of DTPA-111In. The second metabolite had an estimated molecular weight of 35,000. No radioactivity was associated with transferrin.

Direct intralymphatic administration of radiolabeled monoclonal antibody in targeting antigen-bearing lymphoma cells in regional lymph nodes of patients with cutaneous T-cell lymphoma was evaluated. Seven consecutive patients undergoing staging lymphangiography received intralymphatic infusions of 111In-T101 to evaluate lymph node involvement. This procedure was accomplished without significant complication. The 111In-T101 rapidly distributed throughout the regional lymphatic compartment and passed into the systemic circulation. Tumor-bearing sites in the inguinal-femoral lymph nodes retained from 0.42 to 4.8% of the injected dose of radiolabeled antibody. Three patients were upstaged to Stage IVA based on tumor involvement found after radiolymphoscintigraphy-directed biopsy of groin lymph nodes, selected because of intense radioactivity by gamma camera imaging. Compared with previously reported s.c. antibody administration, there was a marked reduction in the radioactive exposure of normal tissues at the injection sites in the lower extremities. Direct intralymphatic delivery of 111In-T101 appears to be a feasible, efficient method for delivering therapeutic doses of radiolabeled antibody.

We evaluated the differences in catabolism of 125I, 111In and 90Y-T101 monoclonal antibody (anti-CD5) by peripheral blood mononuclear cells (PBMNC), HUT 102, CCRF-CEM and MOLT-4 cells. All cells showed higher retention of 111In than of 125I. PBMNC showed similar retention of 90Y and 111In. The release of 125I was reduced by using metabolic inhibitors, F(ab')2 of T101, pure lymphocytes or incubating at 4 degrees C. Our findings suggest differences in the intracellular catabolism of the radionuclides.

Serial gamma camera imaging was performed in 11 patients with cutaneous T-cell lymphoma after s.c. injection between the toes of 111In-labeled T101, a pan T-cell monoclonal antibody. Two of the patients also received 111In-labeled 9.2.27, an isotype-matched control monoclonal antibody. Three doses of T101 (0.1, 0.5, and 1.0 mg), coupled with 0.5 mCi 111In, were used to measure lymph node uptake and dose response. A single 0.5-mg (0.5 mCi) dose of 111In-9.2.27 was used as control antibody to assess nonspecific uptake. Low-dose (0.1 mg) T101 administration produced rapid, intense uptake in inguinal-femoral and iliac nodes with minimal uptake in the paraaortic nodes and liver. The 0.5-mg dose and higher produced consistent uptake in all subdiaphragmatic nodes with greatest accumulation of liver activity at the 1.0-mg dose. In the two control studies, the ratio of specific:nonspecific antibody uptake in the inguinal-femoral, iliac, and paraaortic nodes averaged 7.7,5.9, and 1.9 at 48 h, respectively. In another patient, inguinal-femoral node biopsy contained over 2% of the injected dose of 111In-T101 per gram at 7 days. These findings suggest efficient and specific antibody binding in nodes nearest to the injection site, with progressive uptake of remaining antibody in more distant nodes as proximal sites approach saturation. Higher doses increase overflow of unbound antibody into the systemic circulation. There appears to be an optimal s.c. dose of approximately 0.5 mg (0.25 mg/foot) for T101 immunolymphoscintigraphy of subdiaphragmatic lymph nodes in patients with cutaneous T-cell lymphoma.

Eleven patients with metastatic melanoma underwent serial gamma camera imaging and biodistribution measurements after i.v. injection of escalating doses of [111In]9.2.27, an antimelanoma murine monoclonal antibody. Patients received a fixed dose of 1 mg of [111In]9.2.27, with no additional 9.2.27 (five patients), or co-infused with 49 mg (five patients) or 99 mg (one patient) of unlabeled, unconjugated 9.2.27. Higher doses resulted in prolonged blood-pool retention, less uptake in spleen and bone marrow, and appeared to have a positive effect in improving tumor imaging. A dose of 1 mg of 9.2.27 permitted detection of tumors in two of five patients and two of ten lesions, while with greater than or equal to 50 mg, tumors were detected in all patients and in 24 of 32 lesions. Human gamma globulin injected prior to administration of [111In]9.2.27 failed to block the prominent liver, spleen, and bone marrow uptake. No toxicity was observed. These results indicate the feasibility of imaging metastatic melanoma with [111In]9.2.27 and suggest that antibody dose may be a critical determinant of biodistribution and tumor uptake.

A diester linkage was added between monoclonal anti-melanoma antibody 96.5 and a diethylenetriaminepentaacetic acid derivative to test if a tumor-to-blood and -to-organ ratio of the injected antibody in nude mice with human melanoma FEM XII xenografts could be increased by the addition of the readily cleavable linkage. Compared to the 111In-labeled antibody DTPA with a peptide linkage, the diester conjugate cleared much faster from the blood and was retained much less in muscle and normal organs such as liver, spleen and kidney over a 48-hr period. On the other hand, the activity retained in the tumor was larger than or similar to that of the peptide conjugate for this time period. This resulted in a 2.5, 2.1, and 2.6 fold increase in a tumor to blood, to liver and to kidney ratio at 48 hr for the diester conjugate as compared to the peptide conjugate. The whole-body biologic half life of the antibody was 36 hr, three times shorter than the peptide conjugate. The external imaging demonstrated a clearly visible tumor at 4 hr and a lower pool activity at 72 hr for the diester conjugate. The peptide conjugate, however, showed a persistant blood-pool activity at 72 hr. The addition of the diester linkage, therefore may be beneficial for imaging tumors in patients at early time intervals after injection.

We have compared the biodistributions of [131I]B72.3 and 111In-SCN-Bz-DTPA B72.3 monoclonal antibody (MoAb) in patients with metastatic colon cancers. B72.3 is an IgG1 that recognizes a mucin-like colon cancer associated antigen. Eight patients were infused with 3-5 mCi and 0.36-20 mg of 111In-labeled B72.3 prepared with a bifunctional chelate, isothiocyanatobenzyl-DTPA (SCN-Bz-DTPA). The biodistribution was compared with that of 13 patients previously studied as part of a separate trial, with 1-10 mCi and 0.16-1.35 mg of [131I]B72.3. The Beta T1/2 in serum was 63 +/- 5 hr for 111In-SCN-Bz-DTPA B72.3 and 52 +/- 10 hr for [131I]B72.3. Whole-body retention of the 111In (T1/2 = 11.8 days) was significantly longer than for [131I]B72.3 (T1/2 = 3.3 days), p less than 0.000001. The 131I was excreted primarily through the urine. Urinary excretion of 111In was low and gamma camera images confirmed that some 111In was excreted in the bowel. Tumor localization was seen in one of seven evaluable patients receiving 111In-SCN-Bz-DTPA B72.3. Gamma camera images showed that the liver concentrates 111In but not 131I. We conclude that 111In-SCN-Bz-DTPA B72.3 is metabolized in a different manner from the iodinated B72.3. The high concentration and prolonged retention of 111In by the liver interferes with tumor imaging of metastases.