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

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.

The BRAF Inhibitor Vemurafenib Activates Mitochondrial Metabolism and Inhibits Hyperpolarized Pyruvate–Lactate Exchange in BRAF-Mutant Human Melanoma Cells

“…These findings indicate that, in addition to downregulation of glycolytic metabolism, BRAF inhibition alters glycine, myo-inositol, and lipid metabolism, inducing a metabolic shift that is able to maintain cellular energetic status probably by means of activating compensatory pathways, for example, OxPhos (16). Indeed, we observed increased ROS production (to a similar extent as in previous publications; ref.…”

“…BRAF inhibitor treatment has previously been shown to reactivate mitochondrial OxPhos, leading to increased reactive oxygen species (ROS) levels (13). We thus assessed ROS in WM266.4 cells following exposure to vemurafenib and found that, consistent with a previous report (16), BRAF inhibition in BRAF V600D WM266.4 cells for 24 hours led to a concentration-dependent increase in ROS production (up to 197.8% AE 62.8% of controls; P ¼ 0.03), indicating that OxPhos may also be increased in our cells ( Supplementary Fig. S3).…”

“…We and others have shown that inhibition of BRAF-MEK-ERK signaling in BRAF-mutant melanoma models activates mitochondrial metabolism and decreases lactate production through inhibition of HK2 and glucose transporter expression downstream of CMYC and HIF1a (14)(15)(16)32). In this study, we sought to characterize the downstream alterations in metabolic pathways and fluxes triggered by BRAF inhibition and evaluate their significance for drug antiproliferative activity and potential as noninvasive biomarkers of response to treatment.…”

“…We and others have also shown that inhibitors of MEK and BRAF reverse this metabolic phenotype by attenuating the glycolytic activity of BRAF-mutant human melanoma cells (14,15) and reactivating mitochondrial oxidative phosphorylation (OxPhos; ref. 16) linked to reduced expression of hexokinase 2 (HK2) and glucose transporters 1 and 3, following the downregulation of CMYC (14) and HIF1a (15) downstream of the ERK1/2 pathway. Indeed, reduced uptake of the radioactive glucose analogue 2 […”

Differential contribution of the mitochondrial translation pathway to the survival of diffuse large B-cell lymphoma subsets

“…Second, select targeting of OxPhostype survival mechanisms may have broader implications for resistance mechanisms that enable tumors to escape inhibition of canonical growth factor signaling, including those initiated by BCR, RAS, and BRAF signaling pathways. 7,52,53 Notably, tigecycline is FDA-approved and is being actively developed for its potential therapeutic benefits in several diseases. 54 Our findings warrant investigation of the therapeutic utility of tigecycline and other inhibitors of the mitochondrial translation pathway in DLBCL and other OxPhos-dependent tumors.…”