Baloxavir Acid-Induced Mitochondrial Toxicity and Cell Cycle Arrest Contribute to Its Adverse Effects.

Baloxavir has emerged as a breakthrough anti-influenza therapy, owing to its single-dose regimen and rapid viral clearance. Nevertheless, clinical adverse effects have been reported, while the underlying cellular mechanisms remain unclear. In this study, we demonstrate that baloxavir acid rapidly induces mitochondrial morphological abnormalities. This mitochondrial dysfunction subsequently initiates a cascade of cellular events, including G0/G1 cell cycle arrest mediated by the downregulation of cyclin D3 and CDK4, and apoptosis via the Bak-caspase-3 pathway. Co-treatment with the antioxidant N-acetylcysteine alleviated baloxavir-induced mitochondrial abnormalities and the decreased expression level of cyclin D3. In contrast, the prodrug baloxavir marboxil exhibited minimal mitochondrial toxicity, underscoring the advantage of the prodrug strategy in reducing adverse effects. Our findings identify mitochondrial impairment as a key mechanism for baloxavir-induced cytotoxicity and provide molecular insights that may help explain its clinical adverse profile.