The complex mechanism of antimycobacterial action of 5-fluorouracil
Vinayak Singh1, Miroslav Brecik2, Raju Mukherjee1
1MRC/NHLS/UCT Molecular Mycobacteriology Research Unit & DST/NRF Centre of Excellence for Biomedical TB Research, Institute of Infectious Disease and Molecular Medicine and Division of Medical Microbiology, Faculty of Health Sciences, University of Cape Town, Anzio Road, Observatory 7925, Rondebosch, Cape Town 7700, South Africa.
Abstract:
A combination of chemical genetic and biochemical assays was applied to investigate the mechanism of action of the anticancer drug 5-fluorouracil (5-FU), against Mycobacterium tuberculosis (Mtb). 5-FU resistance was associated with mutations in upp or pyrR. Upp-catalyzed conversion of 5-FU to FUMP was shown to constitute the first step in the mechanism of action, and resistance conferred by nonsynonymous SNPs in pyrR shown to be due to derepression of the pyr operon and rescue from the toxic effects of FUMP and downstream antimetabolites through de novo production of UMP. 5-FU-derived metabolites identified in Mtb were consistent with the observed incorporation of 5-FU into RNA and DNA and the reduced amount of mycolyl arabinogalactan peptidoglycan in 5-FU-treated cells. Conditional depletion of the essential thymidylate synthase ThyX resulted in modest hypersensitivity to 5-FU, implicating inhibition of ThyX by fluorodeoxyuridylate as a further component of the mechanism of antimycobacterial action of this drug.
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