Abstract 3984: Elucidating expression patterns of GPNMB and potential anti-tumor effects of the antibody-drug conjugate, glembatumumab vedotin (CDX-011) in human osteosarcoma primary samples and cell lines

Abstract Despite numerous clinical trials to improve outcomes for osteosarcoma treatment, there has been no significant improvement in cure rates over the last three decades. Glycoprotein NMB (GPNMB), also known as osteoactivin, is a transmembrane glycoprotein that is expressed in various normal cell types including osteoclasts and osteoblasts, and plays a role in development and differentiation, respectively. Studies have also shown that GPNMB is highly expressed in cancers including breast cancers and melanomas. CDX-011 is an antibody-drug conjugate that targets the GPNMB protein. A human monoclonal antibody glembatumumab is linked to monomethyl auristatin E, an antimitotic agent. Recent studies have shown the drug is effective in treating patients with metastatic triple- negative GPNMB-expressing breast cancer, and melanoma. The pediatric preclinical testing program (PPTP) has recently shown the drug is efficacious in xenograft models of osteosarcoma. In this study, we explore the feasibility of GPNMB as a target for antibody-mediated therapy in osteosarcoma and assess the anti-tumor effects of CDX-011. Since CDX-011 activity appears to correlate with GPNMB protein expression, a cohort of osteosarcoma tissue sections from patients at the time of initial biopsy, definitive surgery, and recurrence was stained immunohistochemically to determine the presence or absence of GPNMB protein. The majority of samples show positive staining suggesting further that osteosarcoma might be a candidate for CDX-011 treatment. Flow cytometry was performed on human osteosarcoma xenografts and cell lines to determine the surface expression level of GPNMB prior to treatment with CDX-011. Of the 9 cell lines studied, 5 lines showed high surface expression of GPNMB protein. Cytotoxicity assays were performed on the same 9 cell lines representing both high and low GPNMB surface expression patterns to determine the in vitro effectiveness of CDX-011 in osteosarcoma cell lines and its correlation with GPNMB expression. IC50 on those cell lines ranged from 3.5- 56 µM. Three out of 5 cell lines, which showed high GPNMB surface expression pattern, demonstrated lower IC50 (3- 14 µM) compared to the others. These findings suggest that CDX-011 may be a potential targeted treatment in osteosarcoma patients with elevated GPNMB expression patterns. In addition, further studies are ongoing, including quantitative PCR for GPNMB gene expression, and ELISA to further validate expression of GPNMB protein to better understand the mechanism of CDX-011 in osteosarcoma. Citation Format: Sajida Piperdi, Vicky Kuo, Amy Park, Michael Roth, Richard Gorlick. Elucidating expression patterns of GPNMB and potential anti-tumor effects of the antibody-drug conjugate, glembatumumab vedotin (CDX-011) in human osteosarcoma primary samples and cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3984. doi:10.1158/1538-7445.AM2014-3984