Abstract 730: Efficacy of a novel small molecule MER receptor tyrosine kinase inhibitor in B-RAF wild-type and B-RAF mutant melanoma cell lines

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Metastatic melanoma is the most aggressive cutaneous cancer, with poor prognosis and a median overall survival of less than a year. Current therapies are effective in only a subset of patients, exhibit a variety of side effects, and/or lead to resistance. Previous studies have demonstrated TAM (TYRO3, AXL, MER) receptor tyrosine kinase (TK) expression in melanoma. MER has been implicated in growth and chemoresistance of various cancers, and we and others have demonstrated a potential survival role for MER in melanoma. Our data revealed increasing MER expression in metastatic melanoma compared to primary disease, regardless of B-RAF mutational status. These findings implicate MER as a therapeutic target in melanoma and suggest its utility in patients without B-RAF mutations who currently have limited treatment options. In addition, MER inhibition in combination with B-RAF inhibitors may provide a safer, more effective, and possibly curative treatment for patients with B-RAF mutant melanomas. To this end, we evaluated UNC TKI, a novel, orally bioavailable and potent MER-selective small-molecule tyrosine kinase inhibitor (TKI), in preclinical models of melanoma, both alone and in combination with vemurafenib (a mutant B-RAF TKI). B-RAF wild-type (HMCB) and B-RAF mutant (G361) cell lines were treated with UNC TKI or vehicle. Downstream signaling was evaluated by immunoblotting, and induction of apoptosis was determined by flow cytometry in cells stained with YO-PRO®-1 iodide and propidium iodide. Alternatively, cells were seeded in media containing UNC TKI or vehicle and colony formation was determined. Treatment with UNC TKI induced apoptosis and reduced colony growth in both B-RAF wild-type and B-RAF mutant cell lines, with concentrations as low as 300nM resulting in an almost complete block in colony formation. In addition, MER inhibition reduced activation of downstream pro-survival signaling pathways known to play roles in melanoma, including ERK, AKT, and STAT6. Importantly, combined treatment with UNC TKI and vemurafenib completely abrogated these signaling pathways in a B-RAF mutant cell line and increased apoptosis relative to the single agents, consistent with the idea that MER inhibition may provide additional therapeutic advantage when combined with vemurafenib in patients with B-RAF mutant melanomas. Taken together, these studies validate UNC TKI as a potential treatment for both B-RAF wild-type and B-RAF mutant melanomas and provide data supporting continued development of UNC TKI for treatment of melanoma. Citation Format: Lenka S. Teodorovic, Jacqueline Carrico, Deborah DeRyckere, Weihe Zhang, Xiaodong Wang, Stephen Frye, S. Gail Eckhardt, H. Shelton Earp, Douglas K. Graham. Efficacy of a novel small molecule MER receptor tyrosine kinase inhibitor in B-RAF wild-type and B-RAF mutant melanoma 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 730. doi:10.1158/1538-7445.AM2014-730