Kinase-Impaired BRAF Mutations in Lung Cancer Confer Sensitivity to Dasatinib

Abstract

During a clinical trial of the tyrosine kinase inhibitor dasatinib for advanced non–small cell lung cancer (NSCLC) one patient responded dramatically and remains cancer-free 4 years later. A comprehensive analysis of his tumor revealed a previously undescribed, kinase inactivating BRAF mutation (Y472CBRAF); no inactivating BRAF mutations were found in the non-responding tumors taken from other patients. Cells transfected with Y472CBRAF exhibited CRAF, MEK, and ERK activation – characteristics identical to signaling changes that occur with previously known kinase inactivating BRAF mutants. Dasatinib selectively induced senescence in NSCLC cells with inactivating BRAF mutations. Transfection of other NSCLC cells with these BRAF mutations also increased these cells’ dasatinib sensitivity, whereas transfection with an activating BRAF mutation led to their increased dasatinib resistance. The sensitivity induced by Y472CBRAF was reversed by the introduction of a BRAF mutation that impairs RAF dimerization. Dasatinib inhibited CRAF modestly, but concurrently induced RAF dimerization resulting in ERK activation in NSCLC cells with kinase inactivating BRAF mutations. The sensitivity of NSCLC with kinase impaired BRAF to dasatinib suggested synthetic lethality of BRAF and a dasatinib target. Inhibiting BRAF in NSCLC cells expressing wild-type BRAF likewise enhanced these cells’ dasatinib sensitivity. Thus, the patient’s BRAF mutation was likely responsible for his tumor’s marked response to dasatinib, suggesting that tumors bearing kinase impaired BRAF mutations may be exquisitely sensitive to dasatinib. Moreover, the potential synthetic lethality of combination therapy including dasatinib and BRAF inhibitors may lead to additional therapeutic options against cancers with wild-type BRAF.

Cancer gene profiling in non-small cell lung cancers reveals activating mutations in JAK2 and JAK3 with therapeutic implications

“…The rest of the seven mutations in EGFR have unknown functional significance. BRAF is mutated in 34 patients: 19 (2.0%, 19/ 932) are activating mutations with vemurafenib [8,9] or dabrafenib (with or without MEK inhibitor trametinib) [10,11] as treatment options; nine (1.0%, 9/932) mutations impaired BRAF functions and the patients may respond to dasatinib [24]; the remaining six mutations have unknown functional consequences. Exon 20 insertion in HER2 (ERBB2) is identified in 16 (1.7%, 16/932) patients and available targeted agents include trastuzumab or afatinib [17,18].…”

Targeted sequencing of refractory myeloma reveals a high incidence of mutations in CRBN and Ras pathway genes

“…[1][2][3][4] We observed 9 BRAF-mutated patients (18%), with 4 (8%) having the mutation at known activating and druggable site p.Val600Glu. 31,32 In 4 patients, kinase-inhibiting BRAF mutations were identified, known to paradoxically activate the MAPK pathway via c-RAF (Gly466Val, 33 Gly469Arg, 34 and Asp594Asn 35 [present in 2 patients]). Two patients showed additional activating mutations in NRAS and KRAS, respectively, and 1 patient harbored 2 BRAF mutations (Lys499Asn and Glu695Lys) (supplemental Table 2).…”

It takes two to tango – signalling by dimeric Raf kinases

“…This B-Raf 5 mutation enhances B-Raf:Raf-1 heterodimerization, which in cooperation with dasatinib treatment induces apoptosis in cancer cells. 61 Raf inhibitors also induce robust association of KSR1 or KSR2 with B-Raf, which in contrast to inhibitor-induced B-Raf:Raf-1 10 heterodimerization is not dependent on activated Ras. 62 Furthermore, in tumours driven by B-RafV600E treatment with Raf inhibitors induces preferential binding of B-RafV600E to KSR1, but little B-RafV600E:Raf-1 heterodimerization.…”