Abstract IA20: Targeting AMPK signaling in melanoma

Abstract

Abstract Biguanides, such as the diabetes therapeutics metformin and phenformin, have demonstrated anti-tumor activity both in vitro and in vivo. The energy-sensing AMP-activated protein kinase (AMPK) is known to be a major cellular target of biguanides. We have previously reported that AMPK signalling is attenuated by BRAFV600E in melanoma through phosphorylation of LKB1, a major upstream kinase of AMPK. More recently, we have also discovered that BRAF is directly phosphorylated by AMPK, leading to impaired BRAF-KSR1 association and MEK-ERK signalling (Mol Cell, 2013, 52:161). Based on this crosstalk between the AMPK and BRAF signaling pathways, we investigated the anti-tumor effects of combining phenformin with a BRAF inhibitor PLX4720 on the proliferation of BRAF mutated melanoma cells in vitro and on BRAF-driven tumor growth in vivo. Co-treatment of BRAF mutated melanoma cell lines with phenformin and PLX4720 resulted in synergistic inhibition of cell viability, compared to the effects of the single agent alone. Moreover, treatment with phenformin significantly delayed the development of resistance to PLX4720 in cultured melanoma cells. Biochemical analyses showed that phenformin and PLX4720 exerted cooperative effects on inhibiting mTOR signaling and inducing apoptosis. Noticeably, phenformin selectively targeted subpopulations of cells expressing JARID1B, a marker for slow cycling melanoma cells. In contrast, PLX4720 selectively targeted JARID1B negative cells, which represents the majority of cells in the tumors, and spared the JAR1D1B-positive slowing cycling population. Finally, in contrast to their use as single agents, the combination of phenformin and PLX4720 induced tumor regression in both nude mice bearing melanoma xenografts and in a genetically engineered BRAFV600E/PTENnull-driven mouse model of melanoma. These results strongly suggest that significant therapeutic advantage may be achieved by combining AMPK activators such as phenformin with BRAF inhbitors for the treatment of melanoma. Citation Format: Bin Zheng. Targeting AMPK signaling in melanoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Melanoma: From Biology to Therapy; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(14 Suppl):Abstract nr IA20.