Mitochondrial oxidative stress is the achille's heel of melanoma cells resistant to Braf-mutant inhibitor

Paola Corazao-Rozas,Camille Scalbert,Pierre Guerreschi,Stéphane Balayssac,Guillaume Garçon,Manel Jendoubi,Ariel Savina,Pierre Formstecher,Myriam Malet-Martino,Jérome Kluza,Aurélie Jonneaux,Stephane Rocchi,Fanny André,Laurent Mortier,Philippe Marchetti

doi:10.18632/oncotarget.1420

Abstract

Vemurafenib/PLX4032, a selective inhibitor of mutant BRAFV600E, constitutes a paradigm shift in melanoma therapy. Unfortunately, acquired resistance, which unavoidably occurs, represents one major limitation to clinical responses. Recent studies have highlighted that vemurafenib activated oxidative metabolism in BRAFV600E melanomas expressing PGC1α. However, the oxidative state of melanoma resistant to BRAF inhibitors is unknown. We established representative in vitro and in vivo models of human melanoma resistant to vemurafenib including primary specimens derived from melanoma patients. Firstly, our study reveals that vemurafenib increased mitochondrial respiration and ROS production in BRAFV600E melanoma cell lines regardless the expression of PGC1α. Secondly, melanoma cells that have acquired resistance to vemurafenib displayed intrinsically high rates of mitochondrial respiration associated with elevated mitochondrial oxidative stress irrespective of the presence of vemurafenib. Thirdly, the elevated ROS level rendered vemurafenib-resistant melanoma cells prone to cell death induced by pro-oxidants including the clinical trial drug, elesclomol. Based on these observations, we propose that the mitochondrial oxidative signature of resistant melanoma constitutes a novel opportunity to overcome resistance to BRAF inhibition.

Highlights

Activating mutations in BRAF, such as BRAFV600E can lead to aberrant MAPK signalling and proliferation in human tumors including melanoma, papillary thyroid carcinoma, and gastrointestinal stromal tumor [1,2,3]
Mitochondrial superoxide detected with MitoSOX reagent was significantly increased in BRAFV600E mutant melanoma cell lines after vemurafenib exposure, an effect largely prevented by pretreatment with the antioxidants VitC and VitE (Fig. 1C)
Our results indicate that BRAF inhibitors can increase mitochondrial metabolism through a PGC1α independent mechanism

Summary

Introduction

Activating mutations in BRAF, such as BRAFV600E can lead to aberrant MAPK signalling and proliferation in human tumors including melanoma, papillary thyroid carcinoma, and gastrointestinal stromal tumor [1,2,3]. MEK inhibitors have been unsuccessful both in preclinical models and in patients with resistance to BRAF inhibitors [10] suggesting that other compensatory pathways would be involved and, to date, no effective therapy that circumvents melanoma resistant to BRAF inhibitors is available. These observations highlight urgent need to find new therapeutic strategies to overcome resistance to BRAF inhibitors

Methods

Results

Conclusion