Abstract 3942: Oncogenic BRAF fusion induces MAPK-pathway activation targeted by MEK inhibitor and phosphatidylinositol 3-kinase inhibitor combination treatment in mucosal melanoma

Abstract

Abstract Background: Although remarkable progress has been made in the genomic characterization of cutaneous melanoma, the genetic alterations of primary mucosal melanoma (PMM) remain largely unknown. This study aims to investigate the recurrent mutations in PMM and to characterize the oncogenic potential of the newly identified ZNF767-BRAF fusion as well as its therapeutic implications in PMM. Methods: A total of 46 PMMs underwent exon-capture sequencing of 111 cancer-associated genes to identify somatic non-synonymous mutations, copy number alterations, and structural variations. A cancer cell with a novel ZNF767-BRAF fusion was established from a patient with PMM of the respiratory tract, who was refractory to vemurafenib. To characterize the oncogenic functions of the novel ZNF767-BRAF fusion, we performed western blot, soft agar growth assay and in vivo tumor. The inhibitory effects of vemurafenib, trametinib, buparlisib and LEE011 monotherapy and their combination treatment were measured in vitro and in vivo. Results: Targeted exon-capture sequencing of 46 PMMs revealed a total of 48 somatic non-synonymous mutations in 26 genes. Eight genes harbored recurrent mutations on NRAS (n = 6; 13%) and TP53 (n = 4; 9%) along with BRAF, KIT, MAP3K9, C8A, KRAS, FGFR3 (all observed in two cases; 4%). Of note, a novel ZNF767-BRAF fusion was identified in a PMM of the respiratory tract refractory to vemurafenib treatment. ZNF767-BRAF fusion was validated by Sanger sequencing. We show that ZNF767-BRAF encoded protein promotes the dimerization of RAF and potently activates mitogen-activated protein kinase pathway. The ectopic expression of ZNF767-BRAF fusion induced tumor formation as shown in colony forming assay and tumor xenograft model. The treatment of trametinib inhibited the growth of PMM cells harboring the ZNF767-BRAF fusion but vemurafenib showed no inhibitory effects. Compared with either agent alone, the combination of trametinib and buparlisib showed synergistic antitumor effects in vitro and in vivo. Conclusions: The genomic makeup of PMM is remarkably diverse and distinct from that of cutaneous melanoma. BRAF fusion defines a new molecular subset of PMM and can be therapeutically targetable by the combination of MEK inhibitor and PI3K Inhibitor. Citation Format: Han Sang Kim, Kang Won Jang, Minkyu Jung, Soo Hee Kim, Tae-Min Kim, Byoung Chul Cho. Oncogenic BRAF fusion induces MAPK-pathway activation targeted by MEK inhibitor and phosphatidylinositol 3-kinase inhibitor combination treatment in mucosal melanoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3942. doi:10.1158/1538-7445.AM2015-3942