Phase I Radioimmunotherapy of Metastatic Renal Cell Carcinoma with 131I-labeled Chimeric Monoclonal Antibody G250

Clinical tumor targeting studies with chimeric monoclonal antibody G250 (cG250) in renal cell carcinoma (RCC) patients indicated the potential use of this antibody for radioimmunotherapy. Here we report on a phase I activity dose escalation study to determine the safety, the maximum tolerable dose (MTD), and the possible therapeutic potential of 131 I-labeled cG250 in patients with progressive metastatic RCC. All patients ( n = 12) received a diagnostic i.v. infusion of 5 mg of cG250 labeled with 222 MBq of 131 I. If accumulation of the antibody in metastatic lesions was observed, patients were hospitalized and a second, therapeutic, i.v. infusion of 5 mg of cG250 labeled with a high dose of 131I was administered (n = 8). Three patients per dose level were entered, starting at 1665 MBq/m 2 . If no dose-limiting toxicity occurred, the study continued at the next dose level (555 MBq/m 2 increase). Most patients experienced mild nausea without vomiting. No other complaints were reported during hospitalization. In two of two patients who received a dose of 2775 MBq/m 2 , grade IV hematological toxicity was observed, which was defined as dose limiting. Thus, the MTD was set at 2220 MBq/m 2 . In one patient (2220 MBq/m 2 ), stable disease (lasting 3–6 months) was achieved, whereas another patient (2220 MBq/m 2 ) showed a partial response that is ongoing (>9 months). The minor responses observed in this phase I trial in patients with an advanced stage of RCC are encouraging and warrant further study in a phase II setting at the MTD to determine the efficacy of radioimmunotherapy for metastatic RCC.