Abstract 1305: Identification of signal transduction kinases inhibited by pan-RAF inhibitor belvarafenib using FRET imaging technique

The mitogen-activated protein kinase (MAPK) pathway plays an important role for the survival and proliferation of tumor cells. For example, the activation of the MAPK pathway due to mutations in BRAF, NRAS and KRAS kinases is known to be the causes of various solid tumors and hematologic malignancies. Accordingly, there is a strong need for effective therapeutic drugs for treating cancers caused by genetic mutation of BRAF, NRAS or KRAS. Belvarafenib (HM95573 or GDC5573), currently in Phase 1 clinical trials, is a selective and orally bioavailable pan-RAF kinase inhibitor. When biochemically assayed for hundreds of kinases, Belvarafenib showed selectivity toward RAF family kinases, including strong inhibition activities for BRAF WT, BRAF mutants and CRAF. Previously, we reported that Belvarafenib strongly inhibits the growth of cancer cell lines with BRAF, NRAS or KRAS mutations and also shows excellent anticancer efficacy in animal models using the corresponding cancer cells. In this study, employing fluorescence resonance energy transfer (FRET) imaging, we examined which protein kinases involved in signal transduction are regulated by Belvarafenib and investigated the mechanism of action for the regulation in typical cancer cells harboring BRAF, NRAS or KRAS mutations such as A375 (melamona), SK-MEL-30 (Kwmelamona), HCT116 (CRC), and Calu-6 (NSCLC). Among the various protein kinases that can be involved in signal transduction, we identified with time-lapse FRET imaging that the phosphorylation of ERK, AKT and S6K are inhibited after the treatment of Belvarafenib in the above cancer cells of BRAF, NRAS or KRAS mutations. Of note, BRAF mutant selective inhibitors, Vemurafenib and Dabrafenib were not active in cancer cells of NRAS or KRAS mutations. These results correlate with the in vitro and in vivo anticancer activity in cancer cells of BRAF, NRAS or KRAS mutations. In conclusion, unlike Vemurafenib and Dabrafenib, the pan-RAF inhibitor Belvarafenib could be effective for treating the cancer caused by NRAS or KRAS mutations, as well as BRAF mutations. Citation Format: Dong-Jun Bae, Sang-Yeob Kim, JooYun Byun, InHwan Bae, YoungGil Ahn, YoungHoon Kim, Kwee Hyun Suh. Identification of signal transduction kinases inhibited by pan-RAF inhibitor belvarafenib using FRET imaging technique [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1305.