A Novel Mitochondrial Inhibitor Blocks MAPK Pathway and Overcomes MAPK Inhibitor Resistance in Melanoma

Abstract

Purpose: The purpose of this study is to determine if inhibition of mitochondrial oxidative phosphorylation (OxPhos) is an effective strategy against MAPK pathway inhibitor (MAPKi)-resistant BRAF-mutant melanomas.Experimental Design: The antimelanoma activity of IACS-010759 (OPi), a novel OxPhos complex I inhibitor, was evaluated in vitro and in vivo. Mechanistic studies and predictors of response were evaluated using molecularly and metabolically stratified melanoma cell lines. 13 C-labeling and targeted metabolomics were used to evaluate the effect of OPi on cellular energy utilization. OxPhos inhibition in vivo was evaluated noninvasively by [ 18 F]-fluoroazomycin arabinoside (FAZA) PET imaging.Results: OPi potently inhibited OxPhos and the in vivo growth of multiple MAPKi-resistant BRAF-mutant melanoma models with high OxPhos at well-tolerated doses. In vivo tumor regression with single-agent OPi treatment correlated with inhibition of both MAPK and mTOR complex I activity. Unexpectedly, antitumor activity was not improved by combined treatment with MAPKi in vitro or in vivo. Signaling and growth-inhibitory effects were mediated by LKB1-AMPK axis, and proportional to AMPK activation. OPi increased glucose incorporation into glycolysis, inhibited glucose and glutamine incorporation into the mitochondrial tricarboxylic acid cycle, and decreased cellular nucleotide and amino acid pools. Early changes in [ 18 F]-FAZA PET uptake in vivo, and the degree of mTORC1 pathway inhibition in vitro, correlated with efficacy.Conclusions: Targeting OxPhos with OPi has significant antitumor activity in MAPKi-resistant, BRAF-mutant melanomas, and merits further clinical investigation as a potential new strategy to overcome intrinsic and acquired resistance to MAPKi in patients.

Inhibition of Oxidative Phosphorylation Reverses Bone Marrow Hypoxia Visualized in Imageable Syngeneic B-ALL Mouse Model

“…Our findings of BM hypoxia reduction by complex I inhibition with IACS-010759 clearly demonstrate the substantial metabolic origin of the BM intratumoral hypoxia. Resolution of measurable hypoxia upon arresting cellular respiration was likewise reported in multiple solid tumor models (38,42,43). The distinct oxidative metabolic requirements of leukemia (AML and recently CML) compared to normal hematopoietic stem cells (HSC) that predominantly utilize glycolysis for energy homeostasis, have been reported previously; and our work for the first time demonstrated a direct link to hypoxic responses.…”

Targeting Mitochondria in Melanoma

“…Several studies showed upregulation of OXPHOS in BRAF inhibitor-resistant melanoma cells, suggesting that targeting mitochondrial respiration could be an effective strategy to overcome MAPK inhibitor resistance [ 13 , 16 , 26 , 50 , 51 ]. In this context, we measured the activity of OXPHOS complexes in isolated mitochondria from vemurafenib-resistant RA375 cells compared to parental A375 cells.…”

“…Therapy resistance is a major clinical challenge and the resistance of melanoma to targeted therapy is accompanied by some distinct changes in cellular metabolism, most notably upregulation of OXPHOS [ 13 , 16 , 26 , 50 , 51 ]. In this context, our analysis of enzymatic activities of OXPHOS complexes shows upregulation of complex IV in a BRAF inhibitor-resistant melanoma cell line.…”

“…However, increasing experimental evidence shows that many subsets of tumor types, such as melanoma, still maintain high levels of mitochondrial energy metabolism despite being glycolytic [ 5 , 6 , 7 , 8 , 9 , 10 ]. Upregulation of OXPHOS in melanoma contributes to tumor invasion, metastasis, and increased resistance to mitogen-activated protein kinase (MAPK) pathway inhibitors, one of the most common anti-melanoma therapies [ 7 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Activating mutations in BRAF and NRAS in the MAPK pathway have been identified in melanomas at frequencies of 50% and 20%, respectively [ 17 , 18 ].…”

“…Taken together, mitochondrial respiration seems to be a causative factor in tumor progression and therapy resistance in melanoma [ 9 , 12 , 15 , 16 ]. Therefore, targeting mitochondrial respiration might offer novel therapeutic strategies against melanoma [ 13 , 16 ]. Various drugs are reported to influence mitochondrial respiration [ 31 ].…”