Project Summary Cūrza is developing a new class of broad-spectrum antibiotics, focused on multidrug-resistant (MDR) Gram- negative pathogens. The CZ-02 program is directed towards inhibitors that bind to a unique site on the bacterial ribosome that is not targeted by approved antibiotics and have not encountered cross-resistance to other antibiotics used clinically. Inspired by a natural product, analogs have been developed that selectively inhibit bacterial protein synthesis, with little effect on mammalian protein synthesis, through a binding interaction with the ribosome at a clinically un-drugged site. The natural product that inspired CZ-02s has multiple metabolic liabilities and lacks activity against Gram-negative pathogens. However, after re-engineering the natural product’s minimum pharmacophore responsible for activity into new chemical matter, the resulting compounds are metabolically stable, exhibit excellent selectivity and potency for bacterial protein synthesis while sparing mammalian ribosomes and are efficacious against MDR pathogens in vitro and in vivo; all while displaying a lack of cytotoxicity toward mammalian cells and avoiding effects on mitochondrial function. The proposed SBIR project will ultimately deliver a new orally administered antibiotic candidate that is potent with broad-spectrum activity and efficacy, focusing on Gram-negative pathogens. This Direct Phase II project will advance the CZ-02 program by the following aims. Aim 1 will pursue parallel paths for oral bioavailability of CZ-02s. One will adopt formulation technologies that have proven successful for other therapeutics to maximizing oral bioavailability for either of 2 late preclinical stage CZ-02s.The second will pursue a medicinal chemistry approach for optimizing physicochemical properties of CZ-02s to impart inherent oral bioavailability to the scaffold. Rigorous microbiological and biochemical evaluation along with profiling of absorption, distribution, metabolism, excretion and toxicity (ADME-Tox) will guide optimization efforts. Aim 2 will use in vivo pharmacokinetic (PK) evaluation to guide optimization along with maximum tolerated dose (MTD) determination to guide in vivo efficacy initially in mouse septicemia models to select lead compounds for evaluation in complicated urinary tract infection (cUTI) models of K. pneumoniae and E. coli (the pathogens most responsible for cUTIs) for down-selection to a single lead candidate. Aim 3 will provide scale-up chemistry to support in vivo studies. Aim 4 has sophisticated PK/pharmacodynamic (PD) profiling to establish the PD driver of efficacy and definition of the optimal dosing regimen in acute pyelonephritis (AP) models. At the culmination of the project, a lead compound will be ready for two species non-GLP toxicology and subsequent IND-enabling studies to ultimately deliver a new antibiotic from a novel class targeting Gram- negative pathogens.