TOR kinase inhibition reverses azole resistance in Candida auris by targeting heme biosynthesis

Antimicrobial resistance is a global menace, and multidrug-resistant fungal pathogens pose a serious global health threat. With limited numbers of antifungals available and the emergence of pan-drug-resistant strains, combating fungal infections has become increasingly challenging. Iron homeostasis is known to influence antifungal susceptibility. However, the role of heme, an iron-containing cofactor, in drug resistance remains poorly understood. We investigated the contribution of heme dynamics to acquired azole tolerance and evaluated the therapeutic potential of targeting heme biosynthesis and homeostasis in Candida auris (C. auris). We show that Hemin confers stress-specific protection in C. auris, rescuing growth and biofilm defects caused by Fluconazole (Flc) and the TOR kinase inhibitor Torin2. Transcriptomic analysis revealed that Torin2 in C. auris induces autophagy, represses global translation, and redirects glutamate metabolic flux. Growth complementation assays and quantitative gene expression experiments confirmed that glutamate metabolic flux is redirected towards glutamine biosynthesis via Gln1 activation rather than TCA-cycle participation via Gdh2. This and Hem1 downregulation lead to reduced heme biosynthesis by Torin2. Flc, however, increases heme biosynthesis. Flc binds to the heme moiety of Erg11; hence, increased heme biosynthesis helps buffer Flc. Hemin or 5-ALA supplementation partially rescued growth and restored porphyrin and heme levels. Notably, scavenged heme from Sheep Blood increased MICs for azoles and terbinafine, demonstrating heme-mediated drug tolerance. Importantly, combined Torin2 and Flc treatment reduces growth by downregulating heme exchange and drug efflux, highlighting a potential combinatorial strategy to overcome azole resistance in C. auris. This study highlights the crucial link between the TOR pathway and heme and ergosterol metabolism, which contributes to drug resistance. It proposes targeting heme dynamics as a promising avenue for combination antifungal therapies, potentially improving clinical outcomes against C. auris and other resistant fungal pathogens.