Antifolates with Broad Spectrum Antifungal Activity

About This Grant

The effective treatment of invasive fungal infections represents a growing, unmet clinic need that is exacerbated by the development of antimicrobial resistance by major pathogenic strains and the emergence of new species. These infections are often associated with immunocompromised patient populations, such as chemotherapy patients or patients being treated with immunosuppressive therapies for autoimmune or inflammatory disease. These infections also present as secondary infections following illnesses such as infection by SARS-CoV-2, tuberculosis or unmanaged HIV. Although most of these pathogens occur as opportunistic infections in vulnerable patient populations, the recently emerging Candida auris has shown a more infective profile and has been responsible for several outbreaks among immunocompetent patients in the healthcare setting. C. auris, a saprophytic fungus, has emerged only recently as a human pathogen. Other saprophytic fungi, like Aspergillus spp. and Coccidioides spp., are also ubiquitous where inhalation of spores lead to colonization of the respiratory track can lead to serious disease. New therapeutics are desperately needed to address these pathogens. Our lab has been interested using structure-based design to aid the development of novel agents targeting one-carbon metabolism in both prokaryotic and eukaryotic pathogens. In prior work, we developed inhibitors of the fungal dihydrofolate reductase (DHFR) enzymes from opportunistic fungi such as Candida albicans, Candida glabrata and Cryptococcus neoformans. DHFR catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate, a key carrier of one carbon units required for the synthesis of deoxythymidine monophosphate and purines need for genome replication, as well as methionine needed for the recycling of SAM cofactors. These efforts have resulted in the preparation of a library of over 200 antifolates, representing a variety of chemotypes with respect to shape, charge and polarity – parameters we have shown to be important determinants for fungal cell permeation and efflux. Our compound collection can be leveraged to identify leads against other priority pathogens, having already identified compounds with activity against C. auris, Coccidioides immitis (causative agent of Valley fever) and moderate activity against Aspergillus fumigatus. Recently, we were able to obtain high resolution crystal structures of several lead antifolates in complex with C. auris DHFR. In this proposal, we will expand our in-house library and evaluate it against these three pathogens at both the target and organism level to identify important structure activity relationships related to potency, selectivity and spectrum of coverage. Subsequent structure-based design approaches will be directed at the identification of promising candidates for one or more priority fungal pathogens. These compounds will be further developed in the R33 phase through optimization of pharmacokinetics properties and evaluation in animal efficacy models.