Characterization Of A New Antibody That Reacts With A Tumor-Specific Variant Of Ceacam-5 And Ceacam-6

Introduction: h16C3 is a humanized monoclonal antibody being developed as a novel biological treatment for several types of solid tumor. By mass spectroscopy identification and target validation research, we determined that h16C3 appears to recognize a variant form of CEACAM-5 and CEACAM-6, molecules with a well-known association to cancer. Here we show the pre-clinical activities of this new mAb which shows great potential as a therapeutic agent to treat solid tumors. Methods: The 16C3 antibody was selected from hundreds of hybridoma clones generated from mice immunized with semi-purified membrane-associated proteins derived from biologically screened, pooled human allogeneic colon cancer tissues. In vitro assays and in vivo studies were performed to characterize the potential of h16C3 as a therapeutic modality for solid tumors that express the variant CEACAM antigens. Results: Here we show that unlike most modalities targeting the CEACAM molecules, h16C3 reacts with variant CEACAM-5/6 expressed specifically by human tumor tissues as follows: 98% of human colorectal tumor tissues, 80% of pancreatic tumor tissues, 76% of lung tumor tissues, 43% of uterus tumor tissues, and 29% of breast tumor tissues stained positively with h16C3. Importantly, h16C3 did not cross-react significantly with normal human tissues, except for occasional, weak binding to certain GI tract tissues, which may indicate a pre-malignant state. We showed further that the h16C3 antibody exhibits cell-specific binding and ADCC activity against human colorectal and pancreatic tumor cells, but not against antigen-negative control tumor cell lines. In vivo, the anti-tumor efficacy of h16C3 was tested using pre-established subcutaneous human tumor xenograft models. The data showed significant anti-tumor action compared to control treated mice, including some complete tumor regressions. The bio-distribution of radiolabeled h16C3 in mice with pre-established human tumors exhibited specific accumulation of h16C3 at the tumor site, with little or no binding or accumulation in several major organ systems. Conclusions: The pre-clinical studies of h16C3 to date indicate that it has significant, specific anti-tumor potency, and suggest that it may have clinical activity in cancer patients whose tumor expresses the variant CEACAM-5/6 epitope. The therapeutic humanized 16C3 antibody is being developed for testing in a Phase I clinical trial. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4582. doi:10.1158/1538-7445.AM2011-4582