Repurposing Etoposide for Caries Prevention: In Vivo Efficacy and In Vitro Inhibition of Streptococcus mutans Virulence

Introduction and Aims Despite established preventive measures, dental caries remains highly prevalent, highlighting the need for novel anticaries agents. Drug repurposing offers a promising approach to identifying such candidates. Etoposide (ETO), a clinically approved anticancer agent with reported antibacterial activity, has not been evaluated for anticaries potential in vivo . Methods In vitro antibacterial and antibiofilm assays characterized the effects of ETO on Streptococcus mutans ( S. mutans ) growth and biofilm formation. Virulence-associated phenotypes, including extracellular polysaccharide production, bacterial adhesion, and acidogenicity, were subsequently quantified. Virulence-associated gene expression was analysed by reverse transcription quantitative PCR (RT-qPCR), and safety was assessed via cytotoxicity assays in oral and immune cell lines. An S. mutans -infected rat caries model was then established to validate in vivo anticaries efficacy, with sodium fluoride as a positive control. Histological examination was performed to assess local tissue safety. Results Topical ETO reduced Keyes scores at the enamel (E), superficial dentin (Ds), and moderate dentin (Dm) levels by 17.0%, 45.3%, and 47.1%, respectively, compared with the negative control (all p < .05). In vitro , ETO suppressed biofilm formation and acidogenicity in a concentration-dependent manner. Scanning electron microscopy (SEM) demonstrated altered biofilm architecture at sub-minimum inhibitory concentrations (sub-MIC). Genes involved in extracellular polysaccharide synthesis, acidogenicity, and biofilm development were significantly downregulated at sub-MIC concentrations. Cell viability exceeded 70% across all tested oral and immune cell lines, and no histopathological changes were detected in vivo . Conclusion This study provides preclinical evidence supporting the repositioning of ETO as a promising candidate anticaries agent. Clinical Relevance These findings support the development of anticaries strategies targeting S. mutans growth and virulence and highlight drug repurposing as a potential approach for expanding the armamentarium of caries prevention.