Abstract 917: High antitumor activity of the ERK inhibitor SCH722984 against BRAF-mutant, NRAS-mutant and wild-type melanoma cell lines.

Abstract

Abstract MAPK pathway dysregulation via mutations in proteins such as BRAFV600E and NRASQ61 is a key feature in melanomas, leading to constitutive ERK signaling. Currently, there are no FDA-approved targeted therapies effective in vemurafenib-resistant BRAFV600E mutant, NRAS mutant, or wild-type melanoma. The effect of SCH722984, an allosteric inhibitor of ERK 1/2, was determined in a panel of 53 melanoma cell lines, including wild-type, NRAS-mutant and vemurafenib-sensitive and resistant BRAF-mutant melanoma. 54% (13 of 24) of BRAF mutants, including 4 with innate vemurafenib resistance, were sensitive to SCH722984 with an IC50 <1μM. 100% (3 of 3) of BRAF/NRAS double mutants, 71% (10 of 14) of NRAS mutants and 71% (5 of 7) of wild-type melanomas were sensitive. 13% (5 of 24) of BRAF mutants, 14% (2 of 14) of NRAS mutants and 29% (2 of 7) of wild-type melanomas were intermediately sensitive (IC50 1-1.5μM). Among BRAFV600E mutants with in vitro acquired resistance to vemurafenib, those with MAPK pathway reactivation as the mechanism of resistance were sensitive to SCH722984. Combining vemurafenib and SCH722984 in BRAF mutant melanoma was synergistic in a majority of cell lines, resulting in up to 10-fold decrease in the 50% inhibitory concentration (IC50) and with combination indices (CI) below 1. SCH722984 inhibited phosphorylation of RSK, an ERK downstream target. Finally, long term cultures of two BRAFV600E-mutant cell lines sensitive to SCH722984 showed that treatment with SCH722984 alone or in combination with vemurafenib was more potent than vemurafenib alone and resulted in a significant delay in developing acquired resistance. SCH722984 may therefore be clinically applicable as a treatment for non-BRAF mutant melanoma or in BRAF-mutant melanoma with innate or acquired resistance, alone or in combination with BRAF inhibitors. Citation Format: Deborah J. Wong, Lidia Robert, Mohammad S. Atefi, David Foulad, Earl V. Avramis, Begonya Comin-Anduix, Ahmed A. Samatar, Antoni Ribas. High antitumor activity of the ERK inhibitor SCH722984 against BRAF-mutant, NRAS-mutant and wild-type melanoma cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 917. doi:10.1158/1538-7445.AM2013-917