Cyclosporine A revisited: Molecular mechanisms, non-immune physiological pathways, and the architecture of multi-organ toxicities.

Cyclosporine A (CsA) remains a cornerstone immunosuppressant whose discovery transformed transplantation and immune-mediated disease management. Beyond its classical inhibition of the calcineurin-Nuclear Factor of Activated T-cells (NFAT) pathway, recent research has shown that cyclosporine A modulates multiple host physiological pathways, including mitochondrial function, endothelial signaling, and cytoskeletal dynamics. These mechanisms underpin both its therapeutic efficacy and its characteristic toxicities. CsA modulates cyclophilin A (CypA)-dependent processes that influence mitochondrial permeability transition, oxidative stress, and cellular metabolism, linking its molecular actions to renal, cardiovascular, hepatic, and neurological adverse effects. Advances in formulation science, including nanomicellar, liposomal, and kidney-targeted delivery systems, have improved bioavailability and reduced systemic toxicity. Pharmacogenomic insights into CYP3A4/5 and ATP-Binding Cassette Subfamily B Member 1 (ABCB1) polymorphisms now provide a critical framework for emerging personalized dosing strategies that optimize exposure and minimize risk. Emerging applications, such as antiviral therapy, neuroprotection, and antifibrotic interventions, highlight CsA's evolving relevance beyond immunosuppression. Future directions focus on non-immunosuppressive cyclophilin inhibitors, precision pharmacology, and targeted delivery technologies that preserve CsA's beneficial molecular actions while mitigating its limitations. Collectively, these advances expand our understanding of CsA's multi-pathway profile as a mechanistically versatile agent that modulates immune and cellular pathways with relevance to translational therapeutics.