Abstract 69: Anti-podocalyxin cancer-specific monoclonal antibody: preclinical study

Abstract Background: Podocalyxin, a CD34-related sialomucin, is expressed in many tumors including colorectal cancers, breast cancers, mesothelial tumors, and brain tumors. Overexpression of podocalyxin has been reported to be an independent predictor of progression, metastasis, and poor outcome. However, PODXL is known to be highly expressed in normal cells including many epithelial cells and endothelial cells; therefore, podocalyxin could not be a target of antibody therapy. Although many monoclonal antibodies (mAbs) against podocalyxin have been established, they bind to both cancer and normal cells. We recently established a novel technology for developing cancer-specific mAbs (CasMabs), which could target only cancer cells although those membrane proteins are highly expressed in both cancer and normal cells. Methods: We first produced a podocalyxin-expressing glioblastoma cell line. We purified human podocalyxin using PA-tag, and immunized mice with those proteins. CasMabs were screened using flow cytometry against podocalyxin-expressing cancer cells and podocalyxin-expressing normal cells. The cancer specificity was confirmed using immunohistochemistry against breast cancer tissues. Furthermore, a human-mouse chimeric anti-podocalyxin mAb was produced. Antibody-dependent cellular cytotoxicity (ADCC) was investigated in vitro using glioblastoma cells as target cells and human NK cells as effector cells. The in vivo efficacy was evaluated using xenograft models of podocalyxin-expressing cell lines. Furthermore, we investigated the toxicity of chPcMab-6 using cynomolgus monkey. Results: A cancer-specific anti-podocalyxin mAb (clone: PcMab-6; mouse IgG1, kappa) was established. PcMab-6 reacted with podocalyxin-expressing many cancer cell lines including brain tumors, malignant mesotheliomas, colon cancers, and pancreatic cancers whereas it did not bind to vascular endothelial cells in flow cytometry. Furthermore, PcMab-6 reacted only with podocalyxin-expressing cancer cells, not with VECs in breast cancer tissues using immunohistochemistry. Furthermore, we produced chPcMab-6, a human-mouse chimeric mAb of PcMab-6, which also reacts with only podocalyxin-expressing cancer cells. ChPcMab-6 possesses ADCC activity in vitro and antitumor effect in vivo. Single injection of chPcMab-6 induced no clinical abnormality in male cynomolgus monkey (2 mg/kg and 20 mg/kg) . In addition, abnormal values were not observed in hematologic test, urine analysis, and measurement of serum inflammatory cytokines. Tissue disorders were not found in histology and relative organ weight on postmortem examination. Conclusion: ChPcMab-6, a cancer-specific human-mouse chimeric anti-podocalyxin mAb could be useful for targeting podocalyxin in cancer, although podocalyxin is highly expressed in many normal cells. Citation Format: Shinji Yamada. Anti-podocalyxin cancer-specific monoclonal antibody: preclinical study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 69. doi:10.1158/1538-7445.AM2017-69