Lead optimization of oral DHFR inhibitor for the treatment of multidrug-resistant N. gonorrhoeae infections.

Abstract. The development of new antibiotics for treating N. gonorrhoeae (Ng) is lagging behind the rapid emergence of resistant strains. Ng has developed resistance to all FDA-approved therapies and even to unapproved drugs like gepotidacin and solithromycin. This highlights the scarcity of antimicrobials in clinical development, underscoring the urgent need to discover new antibacterial agents, ideally oral drugs, that can target drug-resistant Ng. This SBIR Phase 2 proposal presents a significant opportunity to develop a narrow-spectrum oral therapeutic for Ng, where existing first-line therapies fail. Our proprietary chemical class targets bacterial dihydrofolate reductase (DHFR) and shows excellent in vitro potency, particularly against MDR Ng clinical isolates. This class also boasts outstanding oral bioavailability, target selectivity, a favorable resistance profile, acceptable toxicity profile, very good pharmacokinetic (PK), and physicochemical/ADME properties. While inactive against other Gram-positive and Gram- negative pathogens, the lead compounds TXA15054 and TXA16126 are potent against multiple Ng strains, including ceftriaxone-resistant strains (WHO-X, WHO-Y, WHO-Z), and azithromycin-, ciprofloxacin-, and tetracycline-resistant CDC isolates, with impressive low MIC values ranging from 0.031 to 0.004 μg/mL. Biochemical and genetic methods have confirmed DHFR as the primary target. TAXIS compounds exhibit negligible activity against human DHFR, with an IC50 selectivity ratio (human/Ng) exceeding 900-fold for both leads. These compounds also have moderate aqueous solubility, high plasma and metabolic stability, and no CYP inhibition. Their cytotoxicity and hERG selective window are several hundred-fold above Ng MICs, indicating a favorable safety profile for clinical use. TXA15054 has excellent PK properties and an oral bioavailability of 85%. Moreover, TXA15054 completely eradicated Ng in a mouse vaginal tract infection model following oral administration, highlighting the importance of this proposal in developing oral therapeutics for drug-resistant Ng infections. This application aims to optimize the lead candidates by addressing three key liabilities: low intrinsic solubility, low therapeutic index, and moderate cytotoxicity. Leveraging insights from early analogs, the multiparametric lead optimization campaign will focus on eliminating these liabilities to produce two preclinical candidates. We believe this SBIR grant will bolster our efforts to deliver a first-line oral treatment for multidrug-resistant Ng infections.