Target Specificity of ¹⁸⁸Re-labeled B27.1 Monoclonal Antibodies to Ovarian Cancer Cells In Vivo

Abstract

Background: Currently we are exploring a new multistep pretargeting approach involving administration of a bispecific antibody (B27.1 x P54) which has an anti-CA-125 (B27.1) and antibiotin (P54) paratope. It is followed by the administration of radiolabeled biotinylated liposomes to target the ¹⁸⁸Re to the ovarian cancer cells. As a preliminary step to realize this goal, we determined the target specificity of the monoclonal antibodies (B27.1) to the ovarian cancer cells in vivo. Materials and Methods: B27.1 monoclonal antibodies were photoreduced using UV light and incubated with reduced ¹⁸⁸Re for 30 min at 25°C. ¹⁸⁸Re-labeled B27.1 antibodies were purified using size exclusion chromatography. A comparative biodistribution of Re-B27.1 and ¹⁸⁸Re was performed in nude mice xenografted with NIH:OVCAR-3 cells. Results: While free rhenium distributed preferentially into thyroid and stomach with insignificant accumulation in the cancer cells, about 20% of the injected dose of ¹⁸⁸Re-B27.1 was recovered in ascites cells with insignificant localization in other organs four hours after administration. Conclusion: The study validates the affinity of the B27.1 antibodies to the ovarian cancer cells in vivo.