Abstract IA10: Kinase-impaired BRAF mutations as predictors of resistance and sensitivity

Abstract

Abstract Non-small cell lung cancer (NSCLC) is a common and rapidly fatal cancer for which targeted therapies have been markedly effective in only about 15% of patients - specifically those with EGFR mutations or EML4-ALK translocations. During a clinical trial of the multi-targeted tyrosine kinase inhibitor dasatinib we identified a patient with stage IV NSCLC who harbored a novel BRAF mutation (Y472C), had a near complete radiographic response to the multitargeted kinase inhibitor dasatinib as sole therapy and remained without active cancer 7 years following treatment. We discovered that Y472CBRAF is a kinase-inactivating BRAF mutation (KIBRAF). BRAF mutations can result in increased or decreased BRAF kinase activity, as well as kinase-neutral mutations, and occur in 8% of NSCLC and many other tumor types. We found that NSCLC cells that harbor KIBRAF undergo senescence when exposed to the dasatinib whereas NSCLC patients and cell lines with wild type BRAF are resistant to dasatinib. Transfection of other NSCLC cells with KIBRAF mutations also increased their dasatinib sensitivity, whereas transfection with an activating BRAF mutation led to their increased dasatinib resistance. NSCLC cells transfected with Y472CBRAF exhibited CRAF, MEK, and ERK activation. Currently there are no well-defined, canonical pathways that explain the observed dasatinib-induced senescence in NSCLC cells with KIBRAF. Dasatinib inhibits the activity of 40 distinct kinase targets and can induce BRAF-CRAF dimerization and CRAF activation in cells with activated RAS or KIBRAF mutations. To investigate the mechanism leading to senescence we performed reverse phase protein arrays to simultaneously examine the expression of 137 proteins and phosphoproteins and gene expression arrays. This approach was limited by the existence of only two NSCLC cell lines with KIBRAF but nonetheless we determined that dasatinib induced DNA damage and subsequently activated DNA repair pathways and the HIPPO signaling pathway only in NSCLC cells with KIBRAF. We are currently conducting a clinical trial for NSCLC patients with KIBRAF mutations to determine the efficacy of dasatinib in these patients prospectively. Citation Format: Faye Johnson, Banibrata Sen, Tuhina Mazumdar, Shaohua Peng, Humam Kadara, Lixia Diao, Lauren Byers. Kinase-impaired BRAF mutations as predictors of resistance and sensitivity. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr IA10.