Mitochondrial Amount Determines Doxorubicin‐Induced Cardiotoxicity in Cardiomyocytes

Abstract Doxorubicin, an anthracycline commonly used for treating cancer patients, is known for its cardiotoxic side‐effects. Although dose‐dependent, but susceptibility remains variable among patients, and childhood‐exposure‐adult‐onset remains challenging. Besides topoisomerase toxicity, Doxorubicin is also toxic to the mitochondria yet the underlying late onset mechanism remains elusive. Here, it is observed that the mitochondrial copy number in PBMCs of patients treated with anthracycline chemotherapy is negatively correlated with the change in plasma BNP levels after treatment. Isogenic hiPSC‐CMs are generated with high, norm, and low mitochondrial copy numbers using mitochondrial transplantation and the YFP‐Parkin system. Remarkably, lower mitochondria copy number translates to lower IC₅₀, suggesting increased susceptibility. Mitochondria supplementation by intramyocardial injection prevents doxorubicin induced heart failure. Mechanistically, doxorubicin treatment leads to mPTP opening and mitochondrial DNA (mtDNA) leakage. This mtDNA leakage event activates the cGAS‐STING pathway and drives inflammation and myocardial senescence. Cardiomyocyte‐specific knockout of Sting (Myh6‐Cre/Sting^flox/flox; Sting^CKO) and over expression of mitochondrial tagged DNase1 in mice partially rescue doxorubicin‐induced cardiac dysfunction. In conclusion, the work establishes a negative correlation between cardiomyocyte mitochondrial copy number and doxorubicin toxicity. Molecularly, it is demonstrated that mtDNA leakage activates cGAS‐STING pathway and accelerates myocardial dysfunction. These insights offer new co‐administration strategies for cancer patients.