Melanoma cells release dysfunctional mitochondria to the tumor microenvironment and circulation in association with tumor progression

Recent evidence establishes that melanoma cells actively uptake mitochondria from stromal cells; however, the mitochondrial release in a physiological context remains unstudied. Here, we show that melanoma cells release dysfunctional mitochondria into the extracellular space through a predominantly non-vesicular route. Using melanocyte Melan-a and melanoma B16-F1 and B16-F10 cell lines, we observed increased extracellular mitochondrial release in malignant cells. Electron microscopy revealed these mitochondria lacked cristae and were primarily free organelles. Membrane potential analysis confirmed their dysfunctional state. Mitophagy analysis using mtKeima showed that, under oxidative stress, melanoma cells failed to activate canonical mitophagy and instead upregulated mitochondrial release as an alternative MQC mechanism. Western blot analysis revealed a fission-biased mitochondrial network in melanoma cells, with elevated phospho-DRP1/DRP1 ratio, and a tendency to reduce MFN1 and OPA1. Together with PINK1/ATG7 downregulation and BNIP3/NIX upregulation, suggest a secretory mitophagy phenotype. Tumor-derived mitochondria were detected in both the tumor microenvironment and plasma of melanoma-bearing mice, with extracellular mitochondria levels correlating with tumor burden. Plasma from melanoma patients exhibited elevated levels of TOMM20⁺ mitochondria compared to healthy donors. Transcriptomic analysis of The Cancer Genome Atlas melanoma cohort revealed that high expression of MQC-related genes DRP1 and BNIP3L was associated with worse prognosis. Collectively, our findings uncover a tumor-intrinsic, non-canonical MQC pathway that releases dysfunctional mitochondria. This mechanism establishes a new paradigm of tumor-host systemic communication, wherein circulating tumor-derived mitochondria might actively influence disease progression. These findings open avenues for developing non-invasive biomarkers and therapeutic strategies targeting mitochondrial release.