The MEK inhibitor trametinib incurs mitochondrial injury and induces innate immune responses in the mouse heart

→Glu (V600E)-mutated melanoma, but its Food and Drug Administration-approved indications are expanding rapidly. Trm generally is well tolerated, but it can cause dose-limiting cardiomyopathy and heart failure. Here, we characterize a mouse model of Trm cardiotoxicity using complementary in vitro approaches to show that Trm induces mitochondrial dysfunction in cardiomyocytes and some cancer cell types. In vivo, Trm caused contractile dysfunction within 3 days and heart failure within 2 weeks. High-resolution respirometry using isolated cardiac mitochondria revealed that Trm compromises oxidative metabolism, in part, through blunted activity of electron transport system complexes. Trm-mediated mitochondrial injury led to the release of mitochondrial damage-associated molecular patterns including mitochondrial DNA in both mice and humans, triggering activation of canonical innate immune pathways including cGAS-STING. In multiple rodent and human cardiomyocyte platforms, Trm diminished mitochondrial respiratory capacity at nanomolar concentrations, but this lesion was reversed by expression of a phosphomimetic signal transducer and activator of transcription 3-S727 construct. We also found that Trm induced mitochondrial dysfunction in some but not all cancer cell lines, identifying a previously unrecognized effect that could contribute to Trm's anticancer efficacy.