BRAF(V600E) is the most common oncogenic mutation in melanoma and leads to constitutive activation of the MAPK pathway, which results in uncontrolled cell growth. Selective BRAF inhibitors such as vemurafenib have been observed to neutralize oncogenic the signaling, inhibit cellular growth, and improve patient outcome. Although these mechanisms of vemurafenib resistance have been reported, few studies focused on how to overcome the resistance. Propranolol, a non-selective β-blocker, was confirmed to involve in multiple anticancer effects. Our previous study also showed propranolol inhibited melanoma by suppressing MAPK and AKT pathways in vitro an in vivo. But its efficacy and mechanism of overcoming vemurafenib still remain unknown in melanoma. Here, we explored the effect of propranolol on the A375, P-8 (patient-derived melanoma cell line) vemurafenib resistance cell line and resistance mice xenografts. Cell viability assay demonstrated that 2μM -20μM vemurafenib couldn’t decrease the proliferation but 24h-120h of incubation of 2μM-200μM propranolol inhibited viability with a concentration and time dependent manner in the two resistance cell line. TUNEL staining showed 24h incubation of 20μM propranolol alone or plus 4μM vemurafeinb obviously increased cell apoptosis. Mice received daily ig. administration of propranolol at the dose of 2 mg/kg alone or plus 10 mg/kg for 21days. The mean tumor volume at day 21 in resistance A375 xenografts was 221.13 ± 7.65mm3vs. 904.12 ± 70.57mm3 vs. 2021 ± 316.24mm3for the propranolol plus vemurafenib, propranolol alone, vemurafenib alone, respectively. Propranolol improved mice survival, 28.6% animal dead in plus group, 57.1% mice dead in the propranolol group, and 71.5% animal dead in vemurafenib at end of treatment. IHC showed propranolol also reduced Ki67 index both in propranolol and plus group when compared with vemurafenib treated mice. Furthermore, RNA sequencing was performed to explore the mechanism of propranolol overcoming the resistance, the data showed propranolol largely reduced mRNA levels of IGF family (IGFBP3, IGFLR1, IGFBP6, IGF2, IGF1R.etc.) but elevated the expressions of innate immune related genes (NKG7, TLR9, NCR3.etc.) in A375-vemr cell line. These results provide a strategy of therapeutic resistance for the clinic, importantly, this study also provide a clue targeting IGF family and regulating innate immune might be a potential strategy to suppress resistance in BRAF inhibitor therapies in melanoma.

Citation Format: Chengfang Zhou, DongYa Shen, WeiLi Wang, Shangchen Xie, Ping Liao, Xiang Chen, Howard L McLeod, Yijing He. Propranolol could overcome BRAF inhibitors resistance by multiple mechanisms in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1186. doi:10.1158/1538-7445.AM2017-1186