Melatonin protects mice from 5-FU hepatotoxicity and improves 5-FU antitumor effects by an apoptotic pathway dependent on cell cycle arrest in A549 human lung cancer cells

Abstract Objectives This study will determine if melatonin (MLT) can be used with 5-fluorouracil (5-FU), an anticancer drug as "adjuvants" to reduce A549 lung cancer cell proliferation and sensitize those cells to 5-FU at lower doses while protecting mice from hepatotoxicity. Methods In vitro, MTT assays assessed cell proliferation, and Annexin-V flow cytometry measured A549 cell apoptosis. RT-qPCR measured apoptotic markers P53, KI67, Bax, Bcl-2, and caspase3; and immunoblotting evaluated cell cycle parameters p21, CDK2, and cyclin E. ELISA biochemical analysis examined liver function, ROS and antioxidant assays, and inflammatory markers, in vivo. Masson's trichome, hematoxylin, and eosin stains examined histopathological changes and fibrosis under a microscope. Key findings MLT combined with 5-FU elevated chemosensitization by decreasing A549 cell proliferation, lowering the IC50, increasing P21, P53, and BAX, decreasing Bcl-2, Ki-67, CDK2, and cyclin E, and inducing apoptosis and cell cycle arrest at G0/G1. After 5-FU (Intraperitoneal (IP))/MLT (oral) co-administration in vivo, all parameters improved and reversed. Liver enzymes (AST and ALT), bilirubin, albumin, total protein, albumin/globulin ratio, ROS, 4HNE, H2O2, and pro-inflammatory cytokines; IL-6, IL-1β, and TNFα declined while antioxidant enzymes like SOD, CAT, GSH, and GPx and IL-10 (anti-inflammatory) increased in combined MLT/5-FU treated groups compared to untreated and 5-FU alone treated groups. Histopathology confirmed these results. Conclusions MLT protected A549 cells from 5-FU-induced hepatotoxicity and enhanced 5-FU's antitumor effect in vitro. These results support MLT/5-FU's benefits, suggesting a more effective lung cancer treatment with fewer hepatotoxicity side effects. That could provide a novel therapeutic strategy for lung cancer.