A small molecule antibiotic platform for selective inhibition of Pseudomonas aeruginosa by targeting folate metabolism

Background

Pseudomonas aeruginosa is a Gram-negative bacterium that is a leading cause of hospital-acquired infections, particularly in immunocompromised patients. Its clinical significance stems from its intrinsic and acquired resistance to a wide range of antibiotics, making infections difficult to treat and contributing to increased morbidity and mortality. A major challenge in the management of P. aeruginosa infections is the lack of effective, selective therapies that can target the pathogen without disrupting the beneficial microbiome. Traditional broad-spectrum antibiotics often lead to collateral damage, such as dysbiosis and secondary infections, underscoring the urgent need for narrow-spectrum agents that can specifically inhibit P. aeruginosa while sparing commensal bacteria.

Current approaches to treating P. aeruginosa infections are hampered by several limitations. Most notably, the bacterium exhibits high resistance to dihydrofolate reductase (DHFR) inhibitors like trimethoprim, which are effective against many other pathogens. This resistance is compounded by P. aeruginosa’s inability to salvage exogenous thymine, a metabolic trait that distinguishes it from most enteric bacteria. Existing DHFR inhibitors fail to achieve sufficient intracellular concentrations in P. aeruginosa due to poor membrane penetration and active efflux by multidrug pumps such as MexAB-OprM. As a result, attempts to exploit the bacterium’s unique metabolic vulnerabilities have been unsuccessful, and there remains a critical gap in the development of selective, effective treatments for P. aeruginosa infections that also preserve the integrity of the host microbiome.

Technology

IRS-143 is a novel small molecule antibiotic specifically engineered to combat Pseudomonas aeruginosa, a major cause of hospital-acquired infections known for its resistance to conventional therapies. Structurally, IRS-143 is a pyrroloquinazolinediamine derivative functionalized with a 2-fluorinated pyridine, which allows it to potently inhibit bacterial dihydrofolate reductase (DHFR) at nanomolar concentrations. The compound is uniquely effective in P. aeruginosa due to its enhanced ability to penetrate bacterial membranes and evade the MexAB-OprM efflux pump, resulting in high intracellular accumulation. IRS-143 disrupts folate metabolism, leading to the build-up of metabolic intermediates and inhibition of bacterial growth. Notably, when administered alongside thymine, IRS-143 selectively targets P. aeruginosa while sparing other bacteria in the microbiome that can salvage thymine, thus minimizing collateral damage to beneficial microbes. The compound also exhibits low mammalian cytotoxicity and demonstrates synergistic antibacterial effects when combined with sulfamethoxazole.

What differentiates IRS-143 is its strategic exploitation of a unique metabolic vulnerability in P. aeruginosa: the bacterium’s inability to salvage exogenous thymine due to the absence of key enzymes. This allows IRS-143, particularly when paired with thymine supplementation, to act as a narrow-spectrum antibiotic—selectively eradicating P. aeruginosa while preserving the broader microbiome. Unlike existing DHFR inhibitors such as trimethoprim, IRS-143 overcomes intrinsic resistance mechanisms by achieving superior intracellular concentrations and avoiding rapid efflux. Resistance to IRS-143, when it does arise, is primarily through overexpression of alternative efflux pumps, but these mutations come with significant fitness and virulence costs, making them rare in clinical settings. The compound’s favorable pharmacokinetic profile, broad activity against resistant strains, and potential for further chemical optimization position it as a promising candidate for targeted therapy against P. aeruginosa, addressing a critical unmet need in infectious disease treatment.

Benefits

• Potent and selective inhibition of Pseudomonas aeruginosa DHFR with nanomolar potency
• Enhanced intracellular accumulation in P. aeruginosa due to improved membrane penetration and reduced efflux susceptibility
• Narrow-spectrum antibacterial activity achieved by thymine supplementation, sparing beneficial microbiome bacteria
• Effective against multidrug-resistant clinical isolates, including strains with high-priority resistance genes
• Synergistic antibacterial effects when combined with sulfamethoxazole, improving therapeutic efficacy
• Low mammalian cytotoxicity and absence of membrane disruption, indicating a favorable safety profile
• Resistance mechanisms reduce bacterial virulence, limiting clinical impact of resistant mutants
• Potential for development as a targeted therapeutic and research tool for studying folate metabolism in P. aeruginosa

Applications

• Targeted P. aeruginosa infection therapy
• Microbiome-sparing hospital antibiotic
• Synergistic combination antibiotic regimens
• Research on bacterial folate metabolism

Additional info

IRS-143 is a pyrroloquinazolinediamine derivative functionalized with 2-fluorinated pyridine that potently inhibits bacterial dihydrofolate reductase. It selectively targets *Pseudomonas aeruginosa* by disrupting folate metabolism while exploiting the pathogen’s inability to salvage exogenous thymine. This molecule achieves high intracellular concentrations through enhanced membrane penetration and reduced efflux susceptibility. When administered with thymine, it preserves the microbiome and demonstrates synergistic efficacy with sulfamethoxazole against multidrug-resistant strains.