Development of an active site inhibitor of Fks1 as a broad spectrum antifungal agent

We propose to develop a mechanistically novel antifungal agent targeting cell wall -1-3-D-glucan biosynthesis (GS) and displaying broad spectrum activity against pathogenic yeasts and molds, including those resistant to existing echinocandins and other standard-of-care (SOC) therapeutics. We present preliminary data demonstrating that the proposed GS inhibitor series: 1) lacks cross-resistance to clinically relevant echinocandin resistant mechanisms, 2) inhibits GS activity by a mechanistically novel mode-of-action (MOA), 3) demonstrates an acceptable in vitro cytotoxicity profile, and 4) offers exceptionally potent and broad-spectrum fungicidal activity across WHO Critical Priority fungal pathogens, including C. albicans, C. auris, and A. fumigatus, as well as some rare molds. Developing the series as a parenterally administered product (e.g., intravenous, IV) aligns its development squarely with the most significant unmet medical need – the hospital setting where life-threatening fungal infections are most prominent. To achieve this goal, we propose the following Specific Aims: Phase 1. Aim 1. Lead Identification. Synthesize up to 50 new analogs and perform SAR according to antifungal potency, spectrum, target engagement, lack of cross resistance to SOC resistance mechanisms, cytotoxicity, pharmacokinetics (PK) and efficacy. Milestone 1. Identify one new analog with demonstrated i) Candida and Aspergillus spectrum and potency > P3105, ii) in vitro GS IC50 < 0.15 ug/mL), iii) no cross-resistance to echinocandin, Ibrexafungerp, or azole-resistant clinical isolates, iv) preliminary in vitro cytotoxicity (human cell cytotoxicity and RBC lysis; IC50 > 128 ug/mL), and v) acceptable PK supporting vi) demonstrated > 2 log reduction in fungal burden in a neutropenic murine infection model of Candidiasis. Phase 2. Aim 2. Lead Optimization. Synthesize > 250 new analogs and optimize activity guided by Fks1 target- based in vitro and whole cell assays, potency and spectrum, parenteral PK, reduced serum binding, cytotoxicity, and efficacy in neutropenic murine Candidiasis and Invasive Aspergillosis (IA) infection models. Milestone 2. Identify 2 compounds demonstrating i) in vitro GS IC50 < 0.05 ug/mL and cross-resistant to P3072 resistant mutants, ii) MIC90 < 1 ug/mL vs Candida spp. and MEC90 < 1 ug/mL vs Aspergillus spp. iii) FOR (<1 x 10-9), iv) therapeutic index (TI) versus human cell lines (TI>128-fold); no red blood cell (RBC) lysis (RBC> 128 ug/mL), v) ppb (< 95%) and no PANLABS off-target activity (IC50>10 uM), vi) PK suitable for IP bid (twice daily) dosing, and vii) successful dose ranging studies to guide dose selection. The top 2 analogs achieving dose dependent efficacy in each infection model (defined as > 3 log reduction in fungal burden versus vehicle control), and overall favorable drug-like properties will be selected as a preclinical candidate (PCC) and back-up. Phase 2. Aim 3. Safety, Metabolism, PK, and Toxicology. Toxicology assessment of the PCC using non-GLP material to conduct initial IND-enabling toxicology studies. Milestone 3: Demonstrate a safe in vivo TI based on the determined NOAEL in Aim 3 and effective efficacy by IP dosing regimen identified in Aim 2.