A multistep radioimmunotherapeutic (RIT) approach, exploiting the combination of a bispecific monoclonal antibody (BsMAb) with 90Y labelled biotinylated long-circulating liposomes was tested as a potential adjuvant treatment for epithelial ovarian carcinomatosis. The BsMAb, with anti-CA 125 and anti-biotin epitopes was used with PEGylated liposomes coated with biotin to deliver the cytotoxic radionuclide 90Y to tumor sites. This approach was used to overcome some of the major obstacles associated with conventional strategies, in particular, to increase the amount of radioactivity delivered to the tumor site compared with conventional monoclonal antibody (MAb) radionuclide delivery. Sequential intraperitoneal administration of the targeting and therapeutic moieties provides the basis for enhanced therapeutic ratio, according to our strategy.

We report here the results of an in vivo therapy using our RIT approach with the Balb/c nude mouse model xenografted with the NIH:OVCAR-3 (CA 125+) human ovarian cancer cell line. An ongoing tumor growth delay/control study in Balb/c mice xenografted intraperitoneally with the NIH:OVCAR-3 cell line indicates a significant delay in onset of tumor and ascites development in treated vs. control populations.