Lack of efficacy of two consecutive treatments of radioimmunotherapy with 131I-cG250 in patients with metastasized clear cell renal cell carcinoma.

PURPOSE: A previous activity dose-escalation study using 131I-labeled chimeric monoclonal antibody cG250 in patients with progressive metastatic renal cell carcinoma (RCC) resulted in occasional therapeutic responses. The present study was designed to determine the safety and therapeutic efficacy of two sequential high-dose treatments with 131I-cG250. PATIENTS AND METHODS: Patients (n = 29) with progressive metastatic RCC received a low dose of (131)I-cG250 for assessment of preferential targeting of metastatic lesions, followed by the first radioimmunotherapy (RIT) with 2220 MBq/m2 131I-cG250 (n = 27) 1 week later. If no grade 4 hematologic toxicity was observed, a second low-dose 131I-cG250 (n = 20) was given 3 months later. When blood clearance was not accelerated, a second RIT of 131I-cG250 was administered at an activity-dose of 1110 MBq/m2 (n = 3) or 1665 MBq/m2 (n = 16). Patients were monitored weekly for toxicity, and tumor size was evaluated by computed tomography once every 3 months intervals. RESULTS: The maximum-tolerated dose (MTD) of the second RIT was 1,665 MBq/m2 because of dose-limiting hematological toxicity. Based on an intention-to-treat analysis, after two RIT treatments, the disease stabilized in five of 29 patients, whereas it remained progressive in 14 of 29 patients. Two patients received no RIT, and eight of 29 received only one 131I-cG250 RIT because of grade 4 hematologic toxicity, formation of human antichimeric antibodies, or disease progression. CONCLUSION: In patients with progressive end-stage RCC, the MTD of the second treatment was 75% of the MTD of the first RIT. In the majority of patients, two cycles of 131I-cG250 could be safely administered without severe toxicity. No objective responses were observed, but occasionally two RIT doses resulted in stabilization of previously progressive disease.

Radioimmunotherapy with [131I]cG250 in patients with metastasized renal cell cancer: dosimetric analysis and immunologic response.

PURPOSE: A study was designed to define the therapeutic efficacy, safety, and toxicity of two sequential high-dose treatments of radioimmunotherapy with [131I]cG250 in patients with metastasized renal cell carcinoma. Here, we report the dosimetric analysis and the relationship between the development of a human antichimeric antibody response and altered pharmacokinetics. EXPERIMENTAL DESIGN: Patients (n = 29) with progressive metastatic renal cell carcinoma received a low dose (222 MBq) of [131I]cG250 for dosimetric analysis, followed by the first radioimmunotherapy with 2,220 MBq/m2 [131I]cG250 (n = 27) 1 week later. If no grade 4 hematologic toxicity was observed, a second low dose of [131I]cG250 (n = 20) was given 3 months later. Provided that no accelerated blood clearance was observed, a second radioimmunotherapy of [131I]cG250 was administered at an activity-dose level of 1,110 MBq/m2 (n = 3) or 1,665 MBq/m2 (n = 16). After each administration, whole-body images were obtained and the pharmacokinetics and the development of human antichimeric antibody responses were determined. Radiation-absorbed doses were calculated for whole body, red marrow, organs, and metastases. RESULTS: No correlation was found between hematologic toxicity and radiation-absorbed dose to the whole body or bone marrow, nor administered activity (MBq and MBq/kg). The tumor-absorbed doses varied largely. An inverse relation between tumor size and radiation-absorbed dose was found. Most tumor lesions received <10 Gy, whereas only lesions <5 g absorbed >50 Gy. A relatively high number of patients developed a human antichimeric antibody response (8 of 27) with altered pharmacokinetics, hampering additional radioimmunotherapies in four of these patients. CONCLUSIONS: Dosimetric analysis did not adequately predict the degree of bone marrow toxicity. When human antichimeric antibody developed, the rapid clearance of radioactivity from the blood and body prohibited further treatment. According to the calculated absorbed dose in metastatic lesions, future radioimmunotherapy studies with radiolabeled cG250 should aim at treatment of small-volume disease or treatment in an adjuvant setting.