Search

Serological analysis of the specificity of blood group Lewis-Y (Ley) monoclonal antibodies (mAbs) against natural and synthetic Ley determinants reveals that Ley mAbs against synthetic Ley determinants display strong reactivity with synthetic Ley and weak reactivity with natural Ley-expressing cells, while those against natural Ley determinants react well with both the Ley-expressing cells. The mAbs against natural Ley were IgG3 or IgM while those against synthetic Ley were IgG2a, IgG2b or IgG1. IgG3 mAb is highly specific for Ley and displays strong reactivity with cytotoxic tests and rosetting assay using natural Ley.

Unlabelled: This trial was performed to determine the maximum tolerated whole-body radiation-absorbed dose of fractionated (131)I-cG250., Methods: This was a phase 1 dose escalation trial. Dose escalation refers here to the escalation of average whole-body absorbed dose. Fifteen patients with measurable metastatic renal cancer were studied. For each treatment cycle, patients initially received a "scout" administration consisting of 5 mg of cG250 antibody labeled with 185 MBq (5 mCi) of (131)I. Whole-body and serum activity was measured for 1 wk, and a simple pharmacokinetic model was fitted to the measured data. The pharmacokinetic model was used to calculate the required activities, administered in a fractionated pattern with 2-3 d between fractions, projected to deliver the prescribed whole-body absorbed dose. The initial cohort of 3 patients was prescribed an average whole-body absorbed dose of 0.50 Gy. In subsequent cohorts this was increased in 0.25-Gy increments. The first fraction in each cycle was 1,110 MBq (30 mCi) of (131)I conjugated to 5 mg of antibody. Subsequent fractions consisted of variable activities depending on the patient-specific whole-body clearance rates and the times between fractions. Patients without evidence of disease progression were retreated after recovery from toxicity if there was no evidence of altered pharmacokinetics or serum human antichimeric antibody titers, for a total of no more than 3 treatments., Results: For the initial treatment course, the pharmacokinetics of the scout dose accurately predicted the pharmacokinetics of fractionated (131)I-cG250 therapy. In 2 patients, altered clearance accurately predicted development of human antichimeric antibody. Targeting to known disease >or= 2 cm in diameter was noted in all patients. Dose-limiting toxicity was hematopoietic, and the maximum tolerated dose per cycle was 0.75 Gy., Conclusion: Measurements of whole-body and serum clearance of cG250 antibody can be used to accurately predict the clearance of subsequent administrations, thus enabling rational treatment planning. An additional practical benefit of real-time pharmacokinetic monitoring is that therapy can be altered dynamically to reduce toxic side effects. However, there was no evidence for fractionation-induced sparing of the hematopoietic system in this study.

In antibody-directed enzyme-prodrug therapy (ADEPT), antibody-enzyme conjugates specifically activate non-toxic prodrugs in tumour tissue. The A33 cognate antigen is a promising target for immunotherapy of gastrointestinal cancers. We have explored A33-based ADEPT with carboxypeptidase A (CPA) and the prodrug, methotrexate-phenylalanine (MTX-Phe). In A33-positive SW1222 cells, the toxicity of MTX-Phe was about 3 logarithms lower compared to MTX. Preincubation with a huA33 antibody-CPA conjugate (huA33-CPA), but not with an isotypic control conjugate, rendered MTX-Phe equally toxic to MTX. No toxicity was observed in mice receiving MTX-Phe in 8-fold the LD50 of MTX. Nude mice bearing A33-positive SW1222 colon carcinoma xenografts were injected intravenously (IV) with 125I-labeled huA33-CPA. The conjugate localised to the tumour with a maximum from 6-24 h. Pre-treating these mice with excess A33 substantially reduced subsequent conjugate uptake, demonstrating immunologic specificity of tumour-uptake. Total tumour uptake and ratios of tumour over blood or normal tissues, however, were lower than with unconjugated A33. This may explain in part why no significant tumour responses were observed in xenografted mice. In summary, our results demonstrate in principle the feasibility of A33-based enzyme targeting, but they call for small recombinant antibody-enzyme constructs to facilitate tumour penetration and clearance from the bloodstream.

Purpose: The purpose of this research was to determine the safety, immunogenicity, pharmacokinetics, biodistribution, and tumor uptake of repeat infusions of a complementarity-determining region grafted humanized antibody (sibrotuzumab) directed against human fibroblast activation protein (FAP)., Experimental Design: A Phase I open-label dose escalation study was conducted in patients with cancers epidemiologically known to be FAP positive. Patients were entered into one of four dosage tiers of 5, 10, 25, or 50 mg/m(2) sibrotuzumab, administered weekly for 12 weeks, with trace labeling with 8-10 mCi of (131)I in weeks 1, 5, and 9., Results: A total of 26 patients were entered into the trial (15 males and 11 females; mean age, 59.9 years; age range, 41-81 years). Twenty patients had colorectal carcinoma, and 6 patients had non-small cell lung cancer. A total of 218 infusions of sibrotuzumab were administered during the first 12 weeks of the study, with 24 patients being evaluable. One patient received an additional 96 infusions on continued-use phase for a total of 108 infusions over a 2-year period, and 1 patient received an additional 6 infusions on continued use. There were no objective tumor responses. Only one episode of dose-limiting toxicity was observed. Therefore, a maximum tolerated dose was not reached. Treatment-related adverse events were observed in 6 patients during the infusional monitoring period. Four of the 6 patients, 3 of whom had associated positive serum human antihuman antibody, were removed from the study because of clinical immune responses. Gamma camera images of [(131)I]sibrotuzumab demonstrated no normal organ uptake of sibrotuzumab, with tumor uptake evident within 24-48 h after infusion. Analysis of pharmacokinetics demonstrated a similar mean terminal t(1/2) of 1.4-2.6 days at the 5, 10, and 25 mg/m(2) dose levels, and with a longer mean t(1/2) of 4.9 days at the 50 mg/m(2) dose level., Conclusion: Repeat infusions of the humanized anti-FAP antibody sibrotuzumab can be administered safely to patients with advanced FAP-positive cancer.

Purpose: In previous studies, humanized A33 (huA33) demonstrated modest antitumor activity in chemotherapy-resistant colorectal cancer patients. In addition, unexpected major tumor responses were observed in patients treated with a specific chemotherapy regimen [carmustine, vincristine, fluorouracil, and streptozocin (BOF-Strep)] administered after huA33 protocols. We designed the present Phase I, open label, cohort, dose-escalation study of huA33 and a fixed dose of BOF-Strep to (a) determine the maximum tolerated dose of huA33 immunotherapy administered with chemotherapy, (b) determine whether chemotherapy modifies huA33 immunogenicity, and (c) develop preliminary information regarding antitumor activity., Experimental Design: Stage IV fluorouracil/leucovorin and irinotecan-refractory colorectal cancer patients (n = 16) received escalating weekly doses of huA33 (5-40 mg/m(2)) with BOF-Strep chemotherapy., Results: Four patients requiring radiotherapy or surgery were removed early. Of 12 evaluable patients, grade 3 and 4 neutropenia (n = 2) and grade 3 thrombocytopenia (n = 1) were observed. Seven of 12 (58.3%) patients developed anti-huA33 activity. Three patients had radiographic partial responses for 7.5, 5.5, and 14 months with greater than 85% decline in serum carcinoembryonic antigen levels. One mixed response (4.5 months with a serum carcinoembryonic antigen decline of 38%) was also observed., Conclusions: huA33 can be safely combined with BOF-Strep chemotherapy. The present report provides compelling evidence supporting our previous observations of major antitumor activity with the combination of huA33 and BOF-Strep chemotherapy. huA33 is still immunogenic when administered with chemotherapy. Future studies to evaluate the immunogenicity of new huA33 antibodies and identify which drugs in the BOF-Strep regimen are critical for enhanced antitumor efficacy are planned.

Purpose: Humanized A33 (huA33; IgG1) monoclonal antibody detects a determinant expressed by 95% of colorectal cancers and can activate immune cytolytic mechanisms. The present study was designed to (a) define the toxicities and maximum tolerated dose of huA33 and (b) determine huA33 immunogenicity., Experimental Design: Patients (n = 11) with advanced chemotherapy-resistant colorectal cancer received 4-week cycles of huA33 at 10, 25, or 50 mg/m(2)/week. Serum samples were analyzed using biosensor technology for evidence of human antihuman antibody (HAHA) response., Results: Eight of 11 patients developed a HAHA response. Significant toxicity was limited to four patients who developed high HAHA titers. In two of these cases, infusion-related reactions such as fevers, rigors, facial flushing, and changes in blood pressure were observed, whereas in the other two cases, toxicity consisted of skin rash, fever, or myalgia. Of three patients who remained HAHA negative, one achieved a radiographic partial response, with reduction of serum carcinoembryonic antigen from 80 to 3 ng/ml. Four patients had radiographic evidence of stable disease (2, 4, 6, and 12 months), with significant reductions (>25%) in serum carcinoembryonic antigen levels in two cases., Conclusions: The complementarity-determining region-grafted huA33 antibody is immunogenic in the majority of colon cancer patients (73%). HAHA activity can be measured reproducibly and quantitatively by BIACORE analysis. Whereas the huA33 construct tested here may be too immunogenic for further clinical development, the antitumor effects observed in the absence of antibody-mediated toxicity and in this heavily pretreated patient population warrant clinical testing of other IgG1 humanized versions of A33 antibody.