Realigned Transsulfuration Drives BRAF-V600E-targeted Therapy Resistance in Melanoma

BRAF V600E-inhibition effectively treats melanoma, but acquired resistance rapidly develops. Protein expression profiles, mitochondrial energetics, metabolomics and fluxomics data in cell line, xenograft, and patient-derived xenograft systems revealed that concerted reprogramming of metabolic pathways (including glutaminolysis, glycolysis, TCA cycle, electron transport chain [ETC], and transsulfuration), along with an immediate cytoprotective response to drug-induced oxidative stress, underpins drug-tolerant persister cancer cell survival. Realignment of cysteine (Cys) metabolism, in particular an immediate upregulation of cystathionine-γ-lyase (CSE), was vital in persister cells. The oxidative cellular environment, drug-induced elevated cystine uptake and oxidative Cys catabolism, increased intracellular cystine/Cys ratios, thereby favoring cystine as a CSE substrate. This produces persulfides and hydrogen sulfide to protect protein thiols and support elevated energy demand in persister cells. Combining BRAF V600E inhibitors with CSE inhibitors effectively diminished proliferative relapse in culture models and increased progression-free survival of xenografted mice. This, together with induced CSE expression in patient samples under BRAF-V600E-inhibition, reveals an approach to increase BRAF-V600E-targeted therapeutic efficacy.