Discovery of Mitochondrial Transcription Inhibitors Active in Pancreatic Cancer Cells

Mitochondrial dysfunction is a hallmark of cancer cells and targeting cancer mitochondria has emerged as a promising anti‐cancer therapy. Previously, we repurposed chlorambucil by conjugating it to a mitochondrial targeting triphenylphosphonium (TPP) group to design Mito‐Chlor, a novel agent that acts on mitochondria DNA (mtDNA). Herein, we show that Mito‐Chlor, but not chlorambucil, inhibits the nascent transcription of mtDNA. Clustering analysis of transcriptomic profile of our Bru‐seq database led to the identification of another mitochondrial transcription inhibitor SQD1, which inhibits the proliferation of MIA PaCa‐2 cells with an IC50 of 1.3 μM. Interestingly, Mito‐Chlor reduces expression of mitochondrial proteins, interferes with mitochondria membrane potential, and impairs oxidative phosphorylation while SQD1 does not. Both compounds increased cellular and mitochondrial reactive oxygen species and stimulated similar signaling pathways in response to oxidative stress. As mitochondrial transcription inhibitors and redox modulators, SQD1 and Mito‐Chlor are promising for the treatment of pancreatic cancer by blocking mitochondrial function. Teamwork: Herein, we show that mitochondria‐targeting chlorambucil, Mito‐Chlor, efficiently inhibits the transcription of mitochondrial DNA. We also report the discovery of a novel mitochondria transcription inhibitor SQD1. These two compounds share a similar genome‐wide transcriptomic profile, and both induce mitochondrial superoxide and similar cell signaling pathways. This study supports targeting mitochondria as an efficient anticancer therapy.