Abstract B23: Mutant NRAS regulates glycolysis in melanoma through ERK, mTOR and the MYC/HIF1α/MondoA network of transcriptional regulators

Abstract

Abstract Background/Aims: After BRAF, NRAS is the most commonly mutated oncogene in melanoma. However therapies targeting NRAS remain elusive. Recent investigations have demonstrated that mutated RAS can increase glycolytic metabolism in cancer cells, and our previous work has elucidated a role for glycolysis in the sensitivity of BRAF-mutant melanoma cells to inactivation of BRAF(1). This study aims to identify the molecular pathways controlling glycolysis in NRAS-mutant melanoma in the context of therapeutic targeting of critical oncogenic pathways. Methods: A panel of NRAS and BRAF-mutant melanoma cell lines were screened for changes in viability and glycolysis following treatment with a panel of small molecule inhibitors targeting the MAPK and PI3K pathways. Glycolytic responses of melanoma cells, following MEK, ERK, selective-PI3K, AKT, mTOR or combined PI3K/mTOR inhibition (alone or in combination), were investigated by assessing cell proliferation, glucose uptake, lactate production, and known transcriptional regulators of glycolysis. Results: In NRAS-mutant melanoma, MEK and ERK inhibition resulted in a reduction in lactate production, and similar responses were observed following treatment with mTORC1/2 and PI3K/mTOR inhibitors but not AKT or selective PI3K inhibitors. Treatment with MEK or ERK inhibitors resulted in a consistent reduction in glucose uptake, with a more modest effect being observed following combined PI3K/mTOR inhibition. Treatment with a combination of MEK or ERK inhibitor with either an mTORC1/2 or PI3K/mTOR inhibitor, resulted in synergy with respect to a reduction in cell proliferation. However, synergy was not demonstrated when lactate production and glucose uptake were assessed indicating that inhibition of MEK or ERK was sufficient to inhibit glycolysis in NRAS-mutant cells. Notably, treatment with these inhibitors also resulted in altered expression of transcriptional regulators of glycolysis (reduced MYC and HIF1α, increased TXNIP protein expression via MondoA), similar to that seen in BRAF-mutant melanoma cells. The role of each individual transcriptional regulator of glycolysis in the response of NRAS-mutant cells to MEK/ERK inhibition is under investigation. Conclusion: NRAS-mutant melanoma cells demonstrate a similar glycolytic phenotype to BRAF-mutant melanoma cells, with MAPK pathway or mTOR inhibition resulting in decreased lactate production, glucose uptake and modulation of the MYC/HIF1α/MondoA network of transcriptional regulators of glycolysis. These findings identify the mechanism of oncogene-driven glycolysis in NRAS-mutant melanoma, and open new possibilities for targeting glycolysis as a therapeutic target in the treatment of patients with NRAS-mutant melanoma.