Effective inhibitors of the essential kinase PknB and their potential as anti-mycobacterial agents

Abstract

SummaryPknB is an essential serine/threonine kinase of Mycobacterium tuberculosis with possible roles in a number of signalling pathways involved in cell division and metabolism. We screened a library of >50,000 compounds for inhibitors of the in vitro phosphorylation of GarA (Rv1827) by PknB and identified a number of inhibitors. A program of synthetic medicinal chemistry was subsequently conducted around one class of inhibitors and was successful in generating ATP competitive inhibitors with potency in the nanomolar range. Compounds in this class showed cross-reactivity with the related M. tuberculosis kinase, PknF, but not with PknG in an in vitro autophosphorylation assay. These synthesised inhibitors were able to prevent the growth of M. tuberculosis in an Alamar blue assay and in an intracellular model of infection, but only in the micromolar range. We attempted to determine if cell wall permeability was an explanation for the discrepancy between the potent in vitro compared with relatively poor in vivo activity, but found no evidence that the activity of the inhibitors could be improved by weakening the cell wall. Despite a number of drug discovery efforts attempting to develop inhibitors against PknB, it is yet to be reported that any such inhibitors prevent mycobacterial growth at submicromolar concentrations.

Selective Pharmacologic Inhibition of a PASTA Kinase Increases Listeria monocytogenes Susceptibility to β-Lactam Antibiotics

“…While antibiotic resistance in the model pathogen L. monocytogenes is not a burgeoning issue, we believe that these data act as a proof of principle that specificity in the targeting of bacterial PASTA eSTKs is possible. Prior to our work, pharmacologic inhibitors that target the M. tuberculosis kinase PknB have also been identified, although their development as potential therapeutic agents is still a work in progress (16)(17)(18). Inhibitors of other bacterial PASTA kinases that work in a ␤-lactam-synergistic manner remain to be identified.…”

“…While the substrates and function of the PASTA kinases are incompletely defined, they appear to have various functions in different organisms, ranging from playing a role in biofilm formation (Streptococcus mutans) to being essential in some organisms (M. tuberculosis) (14,15). As such, pharmacologic inhibition of PASTA kinases has been preliminarily pursued as a novel antimicrobial therapeutic strategy against the M. tuberculosis kinase PknB (16)(17)(18). Deletion of Stk1, the PASTA kinase in S. aureus, reverses the methicillin-resistant phenotype in MRSA (19,20).…”

The Mycobacterial Cell Envelope--Lipids

“…Several chemical scaffolds (Vertex Pharmaceuticals Inc.) (Magnet et al 2010;Danilenko et al 2011;Lougheed et al 2011;Chapman et al 2012) 1996; Pitarque et al 2008;Dhiman et al 2011). Whether Mtb requires phosphatidylglycerol, CL, PS, and PE for growth is at present not known.…”

Structure based de novo design of IspD inhibitors as anti-tubercular agents

“…It helps in analyzing the active site of the receptor and to derive the key interaction sites, which were further used for designing of new molecules based on the seed structure using grow strategy. From the literature source we found most of the anti-tubercular agents to be less potent against whole cells when compared to that against the purified protein in vivo [16]. This difference in activity might be due to the cell wall permeability factor in the whole cells.…”