Evaluation of in vitro and in vivo antifungal activities of a deuterated tetrazole-based CYP51 inhibitor.

Invasive fungal infections represent a significant global health threat, and increasing prevalence of azole-resistant fungal pathogens has severely undermined the efficacy of current antifungal therapies. Tetrazole-based CYP51 inhibitors have recently emerged as promising next-generation antifungal agents, largely due to their reduced potential for drug-drug interactions. In our previous study, tetrazole compound 15, containing a pyrazole side chain, exhibited potent in vitro antifungal activity but suffered from poor metabolic stability, potentially limiting its in vivo efficacy. To address this metabolic vulnerability, we employed a benzylic deuteration strategy to modify compound 15, resulting in the deuterated analogue CN-15D. In vitro antifungal susceptibility testing demonstrated that CN-15D maintained potent activity against a panel of clinical fungal isolates, with minimum inhibitory concentration values ranging from <0.004 to 2 μg/mL and showed potent activity against recombinant S. cerevisiae strains expressing fungal CYP51 enzymes. Notably, deuterium substitution led to a marked improvement in metabolic stability, with an approximately 4-fold extension of the half-life of CN-15D in a microsome metabolic assay. In vivo efficacy evaluation using a Galleria mellonella infection model revealed that CN-15D conferred survival benefits comparable to those of compound 15 and fluconazole. Furthermore, CN-15D exhibited low cytotoxicity and low hERG inhibition, indicating a favorable safety profile. Collectively, these findings support further investigation of the deuterated tetrazole CN-15D as a promising antifungal agent.