Bacterial signaling systems such as protein kinases and quorum sensing shave become increasingly attractive targets for the development of novel antimicrobial agents in a time of rising antibiotic resistance. The family of bacterial Penicillin-binding-protein And Serine/Threonine kinase-Associated (PASTA) kinases is of particular interest due to the role of these kinases in regulating resistance to β-lactam antibiotics. As such, small-molecule kinase inhibitors that target PASTA kinases may prove beneficial as treatments adjunctive to β-lactam therapy. Despite this interest, only limited progress has been made in identifying functional inhibitors of the PASTA kinases that have both activities against the intact microbe and high kinase specificity. Here, we report the results of a small-molecule screen that identified GSK690693, an imidazopyridine aminofurazan-type kinase inhibitor that increases the sensitivity of the intracellular pathogen Listeria monocytogenes to various β-lactams by inhibiting the PASTA kinase PrkA. GSK690693 potently inhibited PrkA kinase activity biochemically and exhibited significant selectivity for PrkA relative to the Staphylococcus aureusPASTA kinase Stk1. Furthermore, other imidazopyridine aminofurazans could effectively inhibit PrkA and potentiate β-lactam antibiotic activity to varying degrees. The presence of the 2-methyl-3-butyn-2-ol (alkynol) moiety was important for both biochemical and antimicrobial activity. Finally, mutagenesis studies demonstrated residues in the back pocket of the active site are important for GSK690693 selectivity. These data suggest that targeted screens can successfully identify PASTA kinase inhibitors with both biochemical and antimicrobial specificity. Moreover, the imidazopyridine aminofurazans represent a family of PASTA kinase inhibitors that have the potential to be optimized for selective PASTA kinase inhibition.
GSK690693 sensitizes Listeria to β-lactam antibiotics - In a wide variety of important Gram-positive pathogens, PASTA kinases are essential for resistance to β-lactam antibiotics (13, 25, 34). We have previously demonstrated that either genetic deletion or pharmacologic inhibition of the PASTA kinase PrkA with staurosporine sensitizes L. monocytogenes to β-lactams (34). To identify specific (and therefore potentially less toxic) inhibitors of PrkA, we screened 625 small molecule kinase inhibitors from the GlaxoSmithKline Published Kinase Inhibitor Set (PKIS) (37, 38) and Selleck kinase inhibitor libraries against wild-type L. monocytogenes strain 10403s in the presence of a sublethal dose of the β-lactam ceftriaxone (Figure 1A). Sixteen compounds potentiated inhibition of L. monocytogenes growth by ceftriaxone at three standard deviations or more above the mean including the positive control staurosporine. Of these, nine compounds failed to show a dose-response and an additional three showed β-lactam independence in secondary screens.
Reference -
Adam J. Schaenzer, Nathan Wlodarchak, David H. Drewry, Warren E. Rose,… A screen for kinase inhibitors identifies antimicrobial imidazopyridine aminofurazans as specific inhibitors of the Listeria monocytogenes PASTA kinase PrkA, VOLUME 292, ISSUE 41, P17037-17045, OCTOBER 2017
By Ayushi Verma
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