Determining the Mechanisms of Resistance to Drug Combinations and their Fitness Effects in Candida albicans
Year: 2014
Type: dissertation
Abstract: The evolution of drug resistance is occurring rapidly and threatening our arsenal of antimicrobials. This is a poignant issue with antifungals, whose targets are limited due to conservation between fungi and the human host. A promising strategy is to enhance effectiveness of our current antifungals using combination therapy. Adding an inhibitor of one of the key stress response proteins, Hsp90 or calcineurin, to an antifungal azole renders the activity of the azole fungicidal and abrogates azole resistance. However, evidence from clinical isolates indicates that resistance to the drug combination can still arise. Determining the mechanisms of resistance to these drug combinations and their fitness effects will provide information about how resistance can occur and whether it is likely to spread in a population. To address what mechanisms of resistance can arise to drug combinations, I evolved strains of the leading fungal pathogen, Candida albicans, and its genetically tractable relative Saccharomyces cerevisiae, in the presence of an azole and the Hsp90 inhibitor geldanamycin (GdA) or the calcineurin inhibitor FK506. The vast majority of strains (286) went extinct, however, I identified and validated mechanisms of resistance in 13 strains. A variety of resistance mechanisms were found, from well-established resistance mechanisms to novel ones. To address the fitness effects of resistance to an azole in combination with GdA or FK506, I took advantage of these C. albicans in vitro evolved strains and a series of C. albicans clinical isolates that transition to Hsp90- and calcineurin-independent azole resistance. I determined that resistance to the drug combination is often but not universally costly in the absence of drug and in novel, clinically relevant stress environments. Together these results provide a basis for our understanding of key parameters for the evolution of resistance to drug combinations: the variety of mechanisms that encompass resistance, and their fitness costs.
Source: TSpace (University of Toronto)
Author: Jessica A. Hill
Language: English
Subfield: Infectious Diseases
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2760710225