A selective low-dose cisplatin strategy enabled by melatonin and cannabinoids for targeting osteosarcoma and...

Therapeutic management of osteosarcoma and chondrosarcoma is limited by cisplatin (CP)-associated systemic toxicity and acquired chemoresistance. Strategies enabling effective dose reduction while maintaining antitumor activity are urgently required. This study investigated whether melatonin (MEL) and cannabinoids (CBD, THC) enhance CP efficacy through synergistic, multi-target mechanisms in osteosarcoma (MG63, Saos2) and chondrosarcoma (SW1353) cells, with normal fibroblast (FL) and osteoblast (HC) cells as controls. Cytotoxicity and antiproliferative effects were evaluated using MTT and LDH assays. Drug interactions were quantified via combination index (CI) and dose-reduction index (DRI) analyses. Apoptotic mechanisms were assessed by Casp3, Casp8, Casp9, and Bax gene expression, DNA fragmentation, DAPI nuclear staining, and Rhodamine-123-based mitochondrial membrane potential analysis. Anti-migratory and anti-invasive effects were examined using wound-healing and invasion assays. Molecular docking was performed to predict interactions with COX-2, MMPs, ADAMTS-5, and MAPK pathway proteins. Combination regimens, particularly THC + CP + MEL, and CP + MEL, demonstrated strong synergism (CI < 1) in SW1353 and Saos2 cells, enabling up to a 2.77 - 4.38-fold reduction in CP dose. Synergistic treatments significantly upregulated apoptotic markers and induced selective DNA fragmentation, chromatin condensation, and mitochondrial depolarization in cancer cells, while normal cells showed minimal alterations. Cannabinoids markedly suppressed migration and invasion, effects further enhanced in combination treatments. Docking analyses supported high-affinity multi-target interactions consistent with the observed biological responses. Collectively, melatonin enhances cannabinoid-mediated chemosensitization to cisplatin through selective, pro-apoptotic and anti-invasive mechanisms, supporting a low-dose, multi-target combinatorial strategy for bone sarcoma therapy.