Novel Dual-Acting Therapeutics Against High-Threat K. pneumoniae - SUMMARY Klebsiella pneumoniae (Kp) is a critical public health threat and a leading cause of healthcare-associated infections globally. Increasing prevalence of multidrug-resistant (MDR) Kp, including carbapenem-resistant (CRKp) and extended-spectrum β-lactamase-producing strains (ESBL-Kp), has sharply limited treatment options. Compounding this crisis is the rise of hypervirulent Kp (hvKp) strains, which are now acquiring antimicrobial resistance, resulting in convergent MDR-hypervirulent (MDR-hvKp) strains with increased virulence and drug resistance. These high-threat Kp strains are associated with substantially higher morbidity, mortality, and healthcare costs, highlighting the urgent need for novel, broadly effective therapeutic strategies. Despite this growing threat, the current paradigm in antimicrobial therapeutics remains narrowly focused on bacterial killing and resistance, largely neglecting virulence determinants, particularly those enabling Kp to evade host immune defenses. As resistance escalates and treatment options diminish, there is a critical need for therapies that transcend conventional bactericidal approaches and directly target the underlying biology of virulence. A central virulence factor in Kp is the capsule polysaccharide (CPS), which forms a protective barrier that inhibits phagocytosis, blocks complement activation and antimicrobial peptides, and promotes survival within the host. Despite its central role in pathogenesis, CPS is not targeted by any current antibiotic. While CPS-directed vaccines, monoclonal antibodies, and bacteriophage therapies have shown promise in preclinical studies, their clinical utility remains limited by serotype specificity, poor immunogenicity, and reduced efficacy in immunocompromised patients. To date, no CPS-targeted therapy has achieved clinical approval. This project introduces a first-in-class, dual-acting anti-virulence antibiotic strategy that simultaneously targets Kp virulence and viability. We have developed a novel class of capsule-inhibitory polymyxins (CMXs) that inhibit CPS biosynthesis while exerting direct bactericidal activity. Our preliminary data demonstrate that CMXs: (a) reduce CPS production; (b) disrupt the hypermucoviscosity phenotype; (c) enhance innate immune clearance; (d) exhibit lower cytotoxicity and mutation frequency; and (e) achieve superior in vivo efficacy in a murine sepsis model of MDR-hvKp infection, compared to colistin. Unlike existing therapies constrained by resistance or serotype specificity, CMXs target conserved capsule biosynthesis pathways and promote immune-mediated clearance across both MDR-cKp and hvKp strains, with a reduced likelihood of resistance development. In this proposal, we have three specific aims. We will (1) validate CMX mechanisms of action and resistance pathways, (2) optimize CMX compounds for enhanced potency, spectrum, and safety, and (3) demonstrate in vivo tolerability and efficacy using infection models that reflect both immunocompetent and immunocompromised clinical scenarios. This work will establish a transformative therapeutic strategy to combat the growing threat of MDR and hypervirulent Kp.
