Targeting Glycoprotein NMB With Antibody‐Drug Conjugate, Glembatumumab Vedotin, for the Treatment of Osteosarcoma

Background Cure rates for children and young adults with osteosarcoma have remained stagnant over the past three decades. Targeting glycoprotein non‐metastatic b (GPNMB) with the antibody‐drug conjugate glembatumumab vedotin has improved outcomes for patients with melanoma and breast cancer. The potential utility of targeting GPNMB in osteosarcoma was explored. Methods GPNMB protein expression was evaluated by immunohistochemistry in human osteosarcoma tumor samples and by enzyme‐linked immunosorbent assay (ELISA) in osteosarcoma cell lines. mRNA expression was measured by quantitative PCR in primary osteosarcoma samples and cell lines. Surface GPNMB expression was evaluated by flow cytometry and correlated with in vitro and in vivo cytotoxicity of glembatumumab vedotin. Results Sixty seven human osteosarcoma samples were evaluated by immunohistochemistry, including 12 samples from initial biopsy, 38 samples from definitive surgery, and 17 from the time of disease recurrence. GPNMB was expressed in 92.5% (62/67) of osteosarcoma samples. All primary osteosarcoma samples expressed high levels of GPNMB mRNA. Glembatumumab induced cytotoxic effects in 74% (14/19) of osteosarcoma cell lines, and GPNMB protein levels correlated with glembatumumab in vitro cytotoxicity (r = −0.46, P = 0.04). All osteosarcoma cell lines demonstrated surface GPNMB expression. Conclusions GPNMB is expressed in osteosarcoma and targeting GPNMB with the antibody‐drug conjugate glembatumumab vedotin demonstrates osteosarcoma cytotoxic activity. Clinical trials are indicated to assess the efficacy of targeting GPNMB in patients with osteosarcoma. Pediatr Blood Cancer 2015; 9999:1–7 © 2015 Wiley Periodicals, Inc.