Inhibitors of an essential M. tuberculosis cytochrome P450 enzyme CYP121

© 2017 Dr. Sunnia RajputTuberculosis (TB) is an infectious disease caused by a rod-shaped mycobacterium called Mycobacterium tuberculosis (Mtb). Since the discovery of streptomycin in the 1940s, several effective anti-TB drugs have been discovered and employed clinically. However, the battle against TB is ongoing with approximately one-third of world’s population estimated to be currently infected with Mtb, with an increased prevalence of multidrug resistant (MDR-TB) and extensively drug resistant (XDR-TB) tuberculosis observed over the last two decades. Thus, there is an on-going need to develop new antimicrobial drugs with novel modes of action. Genome sequencing of Mtb, completed in 1998, revealed the presence of 20 genes encoding cytochrome P450 enzymes (CYPs). One of these CYPs – CYP121A1 – has been shown to be essential for Mtb viability and catalyses a unique reaction involving carbon–carbon bond formation between two tyrosyl side-chains of the cyclodityrosine substrate. This suggests that it may be possible to develop selective inhibitors against CYP121A1 as potential novel anti-Mtb drug leads. During this project, a range of analogues of cyclodityrosine, the natural substrate of CYP121A1, have been synthesized and biochemically analyzed with the aim of defining the binding requirements for the enzyme active site and providing insights into the design of selective inhibitors against CYP121A1. Our analysis shows that modifications at positions 3 and 4 of the tyrosyl aromatic ring are well accommodated within the active site whereas substituents at position-2 are not tolerated. Further, substrate analogue with an iodine at position-3 on the tyrosyl aromatic ring exhibits a 100-fold greater binding affinity compared to the natural substrate. Antimicrobial assays of the substrate analogues including the 3-iodo analogue, show that they are not effective antimicrobial agents (MIC values > 100 μM)