Locoreginal radioimmunotherapy with 186Re-labeled monoclonal antibody in treating small peritoneal carcinomatosis of colon cancer in mice in comparison with 131I-counterpart.

The efficacy of locoregional radioimmunotherapy (RIT) in treating peritoneal tumors of colon cancer of <2 mm in diameter was examined at maximum tolerated doses, focusing the comparison between 186Re and 131I labeled to an anti-colorectal cancer IgG1. Estimated radiation doses to tumors were considerably higher with 186Re-RIT than with 131I-RIT. The advantage of 186Re-RIT decreased with decreasing tumor size, but 186Re-RIT delivered 1.6-times higher radiation to tumors of 1 mm. Consequently, 186Re-RIT attained better survival of mice than 131I-RIT or chemotherapy with 5-fluorouracil did. Therefore, locoregional 186Re-RIT may be an option in an adjuvant setting of colon cancer with high risk of peritoneal dissemination.

Feasibility of 186Re-radioimmunotherapy for treatment in an adjuvant setting of colon cancer.

PURPOSE: (186)Re displays abundant intermediate energy beta emission, and possesses an appropriate physical half-life of 3.7 days. We compared the efficacy of radioimmunotherapy (RIT) with an anti-colorectal cancer monoclonal IgG1, (186)Re-A7, with that of RIT employing (131)I in a mouse liver metastasis model. METHODS: Liver metastases were established by intrasplenic injection of LS180 human colon cancer cells. Based on the results of toxicity assessment with escalated administration doses, 21 MBq (186)Re-A7 and 7 MBq (131)I-A7 were chosen as maximum tolerated doses. In the first experiment, mice underwent RIT at 2 weeks when metastases attain a diameter of several millimeters, and were killed 2 weeks later to assess metastatic burden in the liver. In the second experiment, RIT was conducted at 1 week when metastases of several hundred micrometers in diameter were observed, and survival of mice was examined. RESULTS: (186)Re-A7 RIT inhibited the growth of liver metastases better than (131)I-A7 RIT ( P<0.02). Furthermore, (186)Re-A7 RIT induced better improvement in survival of mice than (131)I-A7 RIT ( P<0.002). (186)Re-A7 RIT caused slightly more severe myelotoxicity in mice, but they eventually recovered. Radiation dose estimation demonstrated a significant advantage of (186)Re-A7 RIT over (131)I-A7 RIT. CONCLUSION: These results support the use of RIT with (186)Re-MAb in an adjuvant setting in cases involving minimal disease.

Benefits of combined radioimmunotherapy and anti-angiogenic therapy in a liver metastasis model of human colon cancer cells.

The combined use of anti-angiogenic therapy (AT) and radioimmunotherapy (RIT) may improve the therapeutic outcome in patients with cancer lesions. This hypothesis is based on the ability of AT to suppress tumour endothelial compartments and the direct action of RIT against tumour cells. We previously confirmed this hypothesis in an established subcutaneous xenograft model of colon cancer. The purpose of the current investigation was to determine the benefit of this combination within a liver metastasis model, which mimics treatment of minimal disease in an adjuvant setting. Liver metastases were established in nude mice by intrasplenic inoculation of LS180 colon cancer cells; following such inoculation, metastases of <1 mm in diameter can be observed at 1 week and these lesions can attain a size of several millimetres at 2 weeks. Daily AT with 2-methoxyoestradiol (2-ME), 75 mg/kg, was initiated at 1 week. RIT with 7 MBq of (131)I-A7, an IgG1 anti-colorectal monoclonal antibody, was conducted at 2 weeks. RIT employing an irrelevant IgG1, (131)I-HPMS-1, was implemented for comparison. The weight of liver metastases was measured 4 weeks after cell inoculation. The effect of AT on (131)I-A7 accumulation in metastases was also observed. Toxicity of treatment was monitored by blood cell counts. Monotherapy with 2-ME AT or (131)I-A7 RIT significantly suppressed metastasis growth ( P<0.0001): metastasis weight was 5.96+/-0.87 g in non-treated controls, 2.67+/-1.89 g in cases receiving AT and 0.85+/-0.68 g in those receiving (131)I-A7 RIT. Combination of AT and (131)I-A7 RIT more effectively suppressed the growth to 0.28+/-0.32 g ( P<0.05 vs RIT alone). The effect of (131)I-HPMS-1 RIT, which suppressed metastasis growth to 2.25+/-0.88 g, was significant in comparison with the control ( P<0.0001); however, the combination of AT and (131)I-HPMS-1 RIT (which suppressed growth to 1.41+/-0.68 g) was far less effective than the combination of AT and (131)I-A7 RIT. AT did not decrease (131)I-A7 accumulation in metastases. AT did not affect RIT myelotoxicity. The results of this study demonstrating the combined effects of AT and (131)I-A7 RIT in a small metastasis model indicate that such combination therapy may be suitable for the treatment of minimal disease.