Development of a mechanistically novel synergistic adjuvant to partner with polymyxin antibiotics

Acinetobacter baumannii (Ab) and related spp. cause severe nosocomial pneumonia, wound, blood, and urinary tract infections, with mortality rates ranging from 25-75%. The emergence of multidrug-resistant (MDR) Ab isolates has made it difficult to treat with most standard-of-care antibiotics. Carbapenems have served as the preferred therapy to treat Ab infections, however, over 50% of infections are now carbapenem-resistant Ab (CRAB). Consequently, the WHO and CDC have classified CRAB as a PRIORITY-1 CRITICAL and URGENT threat pathogen. Polymyxin B (PMB) and colistin have become the antibiotics of last resort to treat CRAB despite their low therapeutic index due to potential nephrotoxicity. To address this unmet medical need, we aim to develop an effective combination agent comprising a polymyxin potentiator and an efficacious, mechanistically novel antibiotic, medinamycin (MedM). MedM is unaffected by clinically relevant modes of antibiotic resistance, exhibits low FOR and provides robust synergistic bactericidal activity against Ab, including colistin-resistant, MDR, and CRAB isolates, and is predicted to be a safe and effective antibiotic to permit lower effective doses of PMB, thereby reducing adverse effects. Aim 1 (Phase 1) Validate the feasibility of developing semisynthetic MedM analogs effective in combination with PMB and/or SPR741 against polymyxinR Ab. Improve MedM bioprocess to deliver >1 g for Aim 1 studies. Demonstrate chemical tractability. Develop the structure activity relationship (SAR) of new analogs using MOA, FOR, microbiological activity, and cytotoxicity assays. Demonstrate in vivo efficacy of a MedM analog + PMB against a PMBR Ab isolate in murine bacteremia infection model. Aim 2 (Phase 2) Complete bioprocess optimization and conduct a semisynthetic lead optimization with the goal of identifying MedM analogs with improved potency and/or drug like properties. Increase reliable production levels of MedM to >250 mg/L using 20L bioreactors, eventually producing 30 g of MedM. Using this material, prepare up to 150 semisynthetic analogs in an iterative fashion according to emerging SAR. Measure Ab MIC for all compounds, and for select compounds evaluate synergistic inhibitory concentration with potential polymyxin partners, in vitro tox and ADME, FOR, kill curves, PK and MIC90 to select polymyxin partner and analogs to advance to in vivo testing in Aim 3. Aim 3 (Phase 2) In vivo characterization of MedM analogs in combination with selected potentiator in relevant mouse models of Ab infection to identify lead series of combination product. Test efficacy of superior MedM analogs + polymyxin potentiator against a PMBR Ab clinical isolate in a mouse peritonitis infection model, followed by a deep thigh and neutropenic mouse lung infection model. In each study, demonstrate that a MedM analog provides statistically significant efficacy (P < 0.05) if combined with polymyxin at a sub-efficacious dose to identify lead MedM series for combination product. Dose fractionation studies will also be performed.