Abstract 3973: Dabrafenib suppresses the growth of BRAF-WT cancers through inhibition of novel targets Nek9 and Cdk16

Abstract

Abstract Although the BRAF inhibitors dabrafenib and vemurafenib have both proven successful against BRAF-mutant melanoma, there seem to be differences in their mechanisms of action. Here, we show that dabrafenib is more effective at inhibiting the growth of NRAS-mutant and KRAS-mutant cancer cell lines than vemurafenib. Using mass spectrometry-based chemical proteomics we identified NEK9 and CDK16 as unique targets of dabrafenib. Both NEK9 and CDK16 were highly expressed in specimens of advanced melanoma, with high expression of both proteins correlating with a worse overall survival. A role for NEK9 in the growth of NRAS and KRAS-mutant cell lines was suggested by siRNA studies in which silencing was associated with decreased proliferation, cell cycle arrest associated with increased p21 expression, inhibition of phospho-CHK1, decreased CDK4 expression and the initiation of a senescence response. Inhibition of CDK4 but not CHK1 recapitulated the effects of NEK9 silencing, indicating this to be the likely mechanism of growth inhibition. We next turned our attention to CDK16 and found that its knockdown inhibited the phosphorylation of the Rb protein at S780 and increased expression of p27. Both of these effects were phenocopied in NRAS and KRAS-mutant cancer cells by dabrafenib but not vemurafenib. Combined silencing of NEK9 and CDK16 were associated with enhanced inhibition of melanoma cell proliferation and a greater induction of cell cycle arrest. In summary, we have identified dabrafenib as a potent inhibitor of NEK9 and CDK16, and suggest that inhibition of these kinases may have activity against cancers that do not harbor BRAF mutations. Citation Format: Manali S. Phadke, Lily Rix, Inna Smalley, Annamarie Bryant, Harshani Lawrence, Braydon Schaible, Ann Chen, Uwe Rix, Keiran Smalley. Dabrafenib suppresses the growth of BRAF-WT cancers through inhibition of novel targets Nek9 and Cdk16 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3973.