Therapeutic Effect of α-Emitting 224Ra-Labeled Calcium Carbonate Microparticles in Mice with Intraperitoneal Ovarian Cancer12

BACKGROUND Ovarian cancer patients with chemotherapy-resistant residual microscopic disease in the peritoneal cavity have a considerable need for new treatment options. Alpha-emitting radionuclides injected intraperitoneally may be an attractive therapeutic option in this situation as they are highly cytotoxic, while their short range in tissues can spare surrounding radiosensitive organs in the abdomen. Herein we evaluate the therapeutic efficacy of a novel α-emitting compound specifically designed for intracavitary radiation therapy. METHODS The α-emitter 224Ra was absorbed on calcium carbonate microparticles. Immunodeficient, athymic nude mice with human ovarian cancer cells growing intraperitoneally were treated with different activity levels of 224Ra-microparticles. Tumor growth, survival, and tolerance of the treatment were assessed. Two tumor models based on the cell lines, ES-2 and SKOV3-luc, with different growth patterns were studied. RESULTS In both models, intraperitoneal treatment with 224Ra-microparticles gave significant antitumor effect with either considerably reduced tumor volume or a survival benefit. An advantageous discovery was that only a few kilobecquerels per mouse were needed to yield therapeutic effects. The treatment was well tolerated up to a dose of 1000 kBq/kg with no signs of acute or subacute toxicity observed. CONCLUSIONS Intraperitoneal α-therapy with 224Ra-microparticles demonstrated a significant potential for treatment of peritoneal micrometastases in ovarian carcinoma.