Leveraging Vulnerabilities in Copper Trafficking for Synergistic Antifungal Activity

Abstract

Candida albicans is an opportunistic fungal pathogen that causes millions of infections per year, for which more efficacious treatments are needed. Observations that azole antifungals incite C. albicans to adjust a variety of metal-dependent processes led us to hypothesize that vulnerabilities in metallohomeostasis incurred by drug stress could be leveraged by compounds that interrupt metal trafficking. Here, we show that tetrathiomolybdate (TTM), a copper (Cu) chelator that interferes with Cu trafficking and use, inhibits growth of C. albicans on its own and synergizes with select azoles to enhance antifungal activity. Proteomic and biochemical experiments revealed that TTM causes differential expression and stabilization of proteins involved in fermentation and oxidative stress responses in C. albicans. The synergy between TTM and azoles was found to arise from increased expression and stability of the nitric oxide dioxygenase Yhb1, a response driven by the decreased stability and activity incurred by TTM of CuZn superoxide dismutase 1. Addition of imidazole-based antifungals highjacks this stress response by inhibiting Yhb1. This study highlights the centrality of Cu homeostasis as a regulatory hub connecting energy production, oxidative stress management, and overall cellular fitness in ways that can be pharmacologically manipulated to enhance efficacy of existing antifungal agents.