Metabolic resistance to the inhibition of mitochondrial transcription revealed by CRISPR-Cas9 screen

Cancer cells depend on mitochondria to sustain their increased metabolic need and mitochondria therefore constitute possible targets for cancer treatment. We recently developed small-molecule inhibitors of mitochondrial transcription (IMTs) that selectively impair mitochondrial gene expression. IMTs have potent antitumor properties in vitro and in vivo, without affecting normal tissues. Because therapy-induced resistance is a major constraint to successful cancer therapy, we investigated mechanisms conferring resistance to IMTs. We employed a CRISPR-Cas9 whole genome screen to determine pathways conferring resistance to acute IMT1 treatment. Loss of genes belonging to VHL and mTORC1 pathways caused resistance to acute IMT1 treatment and the relevance of these pathways was confirmed by chemical modulation. We also generated cells resistant to chronic IMT treatment to understand responses to persistent mitochondrial gene expression impairment. We report that IMT1-acquired resistance occurs through a compensatory increase of mtDNA expression and cellular metabolites. We found that TFAM downregulation and inhibition of mitochondrial translation impaired survival of resistant cells. The identified susceptibility and resistance mechanisms to IMTs may be relevant for different types of mitochondria-targeted therapies.