Ribonucleotide reductase, a novel target for gonorrhea

Abstract

Antibiotic resistant Neisseria gonorrhoeae (Ng) are an emerging public health threat due to increasing numbers of multidrug resistant (MDR) organisms. We identified two novel orally active inhibitors, PTC-847 and PTC-672, that exhibit a narrow spectrum of activity against Ng including MDR isolates. By selecting organisms resistant to the novel inhibitors and sequencing their genomes, we identified a new therapeutic target, the class Ia ribonucleotide reductase (RNR). Activity studies and negative stain electron microscopy of the Ng Ia RNR suggest that these inhibitors potentiate conversion of its active α2β2 state to an inactive α4β4 similar to states first identified with the Escherichia coli (Ec) Ia RNR. Resistance mutations in Ng map to the N-terminal, ATP cone domain of its α subunit and disrupt the interaction with the β subunit required to form the specific quaternary inhibited state. Oral administration of PTC-672 reduces Ng infection in a mouse model and may have therapeutic potential for treatment of Ng that is resistant to current drugs.

Radicals in Biology: Your Life Is in Their Hands

“…Recently, studies with the clinically used nucleoside anticancer therapeutic clofarabine (ClF) , and prospective antibacterials (2-hydroxypyridone derivatives) have proposed that they work by trapping inhibited RNR states (Figure C); evidence suggests that an α6 hexameric state is trapped in the former case and an α4β4 state in the latter case. These two inhibited RNR states have also been shown to occur inside cells. , …”

“…The cone domain architecture is mobile and is also present in many bacterial transcription factors involved in regulation of deoxynucleotide metabolism, although the small-molecule regulators remain unknown . Recently, studies with the clinically used nucleoside anticancer therapeutic clofarabine (ClF) , and prospective antibacterials (2-hydroxypyridone derivatives) have proposed that they work by trapping inhibited RNR states (Figure C); evidence suggests that an α6 hexameric state is trapped in the former case and an α4β4 state in the latter case. These two inhibited RNR states have also been shown to occur inside cells. , …”

“…In the class Ia RNRs, the active state(s) is (are) in dynamic equilibrium with inactive state(s), providing an important mechanism to manage the ratios and amounts of dNTP pools. The recent discovery of a dATP-α4β4 inhibited state in the E. coli RNR and its perturbation by 2-hydroxy­pyridone inhibitors will provide insight about the dynamics of nucleotide-state interconversions and mechanisms of small-molecule perturbations. In the class Ia human RNRs, despite the α,β structural homology with the subunits of E. coli , no high-resolution structures of the metallo­cofactor centers of β2s or any active α/β complexes have been reported.…”

“…Recently, multi-drug-resistant N. gonorrhoeae strains have been shown to be responsive to several 2-hydroxy­pyridone analogs. Their targets appear to be the α4β4 inactive state in vitro, and they show in vivo efficacy in a mouse model . Recent reports of unusual inhibited quaternary structures of class Ia, Ib, and Id RNRs ,− suggest that trapping other RNRs may be possible for obtaining structures for cryo-EM analysis and for guided inhibitor (re)­design.…”

“…These two inhibited RNR states have also been shown to occur inside cells. 29,32 ■ BREAKTHROUGHS ENABLING RADICAL…”