TarO-specific inhibitors of wall teichoic acid biosynthesis restore β-lactam efficacy against methicillin-resistant staphylococci

Abstract

The widespread emergence of methicillin-resistant Staphylococcus aureus (MRSA) has dramatically eroded the efficacy of current β-lactam antibiotics and created an urgent need for new treatment options. We report an S. aureus phenotypic screening strategy involving chemical suppression of the growth inhibitory consequences of depleting late-stage wall teichoic acid biosynthesis. This enabled us to identify early-stage pathway-specific inhibitors of wall teichoic acid biosynthesis predicted to be chemically synergistic with β-lactams. We demonstrated by genetic and biochemical means that each of the new chemical series discovered, herein named tarocin A and tarocin B, inhibited the first step in wall teichoic acid biosynthesis (TarO). Tarocins do not have intrinsic bioactivity but rather demonstrated potent bactericidal synergy in combination with broad-spectrum β-lactam antibiotics against diverse clinical isolates of methicillin-resistant staphylococci as well as robust efficacy in a murine infection model of MRSA. Tarocins and other inhibitors of wall teichoic acid biosynthesis may provide a rational strategy to develop Gram-positive bactericidal β-lactam combination agents active against methicillin-resistant staphylococci.

Dual Targeting of Cell Wall Precursors by Teixobactin Leads to Cell Lysis

“…TA plays important roles in bacterial physiology (7,8), and teichoic acid biosynthesis is an important target for antibiotic development (9). Recently, it was shown that inhibition of teichoic acid biosynthesis can restore susceptibility to methicillin in methicillin-resistant Staphylococcus aureus (MRSA) (10).…”

New Structural Templates for Clinically Validated and Novel Targets in Antimicrobial Drug Research and Development

“…It has been demonstrated that the correct localization of PBP4 at the division septum, which is crucial for the resistance mechanism, depends on the presence of wall teichoic acid (WTA) polymers (Scheme 10) (Atilano et al 2010;Brown et al 2012). As WTAs are also responsible for the anchoring of autolysins of the peptidoglycan as discussed above, simultaneous inhibition of WTA du i g the p ese e of β-lactams leads to depleted levels of cross-linked peptidoglycan and to non-viable bacteria, thus circumventing the esista e e ha is to a ds β-lactams and restoring their antibacterial activity against Gram-positive bacteria (Maki et al 1994;Swoboda et al 2011;Farha et al 2013;Wang et al 2013;Sewell and Brown 2014;Lee et al 2016a). …”

“…WTA biosynthesis inhibition is not per se lethal for Gram-positive bacteria. Early stage WTA inhibition can lead to cells showing enhanced sensitivity to certain drugs (see next chapter) (Sewell and Brown 2014;Lee et al 2016a). In contrast, late stage inhibition of membrane-bound WTA precursors is lethal due to accumulation of toxic intermediates and the depletion of cellular pools of bactoprenol phosphate D Elia et al 2006b; Swoboda et al 2011;Brown et al 2013;Wang et al 2013), which is essential for peptidoglycan biosynthesis as discussed above.…”

“…Adapted from (Lee et al 2016a) and (Farha et al 2013) Both compounds lack any intrinsic growth inhibitory activity against MRSA, MRSE, MSSA or several other pathogens. In contrast to tunicamycin A, tarocin A and B show no cytotoxic activity against HeLa cells.…”

“…Recently, researchers at Merck reported a screen of 2.8 million synthetic small molecules for inhibitors of early stage WTA biosynthesis in MRSA. Tarocin A 30 and tarocin B 31 (Scheme 13) were identified as compounds that could suppress TarG inhibition with IC50 s of µM and 6 µM, respectively (Lee et al 2016a). The compounds were subsequently proven to selectively inhibit TarO.…”