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). Resistance mutations in Ng map to the N-terminal cone domain of the α subunit, which we show here is involved in forming an inhibited α4β4 state in the presence of the β subunit and allosteric effector dATP. Enzyme assays confirm that PTC-847 and PTC-672 inhibit Ng RNR and reveal that allosteric effector dATP potentiates the inhibitory effect. 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.
Highlights
Increasing resistance to current therapeutics against many pathogenic bacteria (Walsh 2015, Gerasyuto 2018) requires new treatment options with unique mechanism(s) of action
The minimum inhibitory concentrations (MIC) of PTC compounds were determined against six Neisseria gonorrhoeae (Ng) strains (WHO strains, Table 1A) that represent a full range of drug resistant phenotypes relevant to current World HealthOrganization (WHO) gonorrhea treatment guidelines (Unemo 2016), and ten Gram-negative pathogens and normally occurring gut organisms (Table 1B)
The compound PTC-565 representing the [5,6] fused ring structure (Figure 1A) exhibited antibacterial activity against a broad spectrum of Gram-negative pathogens (Table 1A and B); in contrast, PTC-847 and PTC-672 are inactive against the panel of Gram-negative pathogens and normal gut organisms evidenced by MICs ranging from 12.5 to
Summary
Increasing resistance to current therapeutics against many pathogenic bacteria (Walsh 2015, Gerasyuto 2018) requires new treatment options with unique mechanism(s) of action. We reported the discovery of a series of fused indolyl-containing 4-hydroxy-2-pyridones that inhibited bacterial DNA synthesis by targeting mutant DNA topoisomerases (gyrase, topoisomerase IV) and improved in vitro antibacterial activity against a range of fluoroquinolone resistant. The interesting activities of a subset of 4-hydoxy-2-pyridones provided the impetus for synthesis of additional chemotypes with this core (Figure 1) and their evaluation for effectiveness against additional pathogenic strains including Ng and. Organization (WHO) in 2012 (WHO 2012) focused on Ng isolates. They reported seventy eight million Ng infections worldwide with 90% of infections in low and middle income countries. Ng was reported to be the second most prevalent notifiable sexually transmitted infection in the US (CDC 2019a).
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