Melatonin protects against long-term doxorubicin-induced cardiotoxicity in a preclinical model of childhood cancer survivors

Cardiovascular disease is the leading cause of early mortality among childhood cancer survivors. Most of these patients receive anthracyclines, particularly doxorubicin (DOX), due to its high efficacy against solid tumors and hematological malignancies. However, DOX is associated with long-term cardiac toxicity, including delayed cardiac dysfunction and irreversible heart failure, making survivorship care a growing concern. A proposed mechanism of long-term doxorubicin-induced cardiotoxicity (DOXIC) is the accumulation of DOX in cardiomyocyte mitochondria, which increases free radical production, promotes oxidative stress, and progressively impairs cardiac function. We hypothesized that melatonin (aMT), a mitochondria-targeted antioxidant, could prevent DOXIC. Melatonin has demonstrated safety at high doses and can enhance chemotherapy efficacy. This study evaluated the cardioprotective effects of aMT in a mouse model mimicking childhood cancer survivorship. Wild-type mice received DOX from 3 to 5 weeks of age and were assessed at 12 months. aMT was administered during DOX treatment and continued for one month afterward. Experimental groups included: (1) Vehicle, (2) DOX, and (3) DOX + aMT. Cardiac function, mitochondrial structure and function, and gene expression were evaluated using echocardiography, TEM, high-resolution respirometry and mRNA sequencing. Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis (IPA) were used for transcriptomic analysis. Melatonin preserved cardiac function both during and long after DOX exposure and protected mitochondrial ultrastructure and function. GSEA showed that aMT upregulated genes related to cardiac development, contractility, action potential, sarcomere structure, and energy metabolism. IPA further revealed that aMT suppressed pathways involved in heart disease, among them cardiomyopathy, myocardial dysfunction and hypertrophy of left ventricle, apoptosis and organismal death, while enhancing those linked to cardiac contractility, cell viability and survival, microtubule organization, and DNA repair. These findings provide the first evidence that melatonin can prevent long-term DOXIC, supporting its potential as a cardioprotective agent for childhood cancer survivors.