2518. Lead optimization on 26-membered thiopeptide antibiotics and identification of pre-clinical candidates against Clostridioides difficile and Staphylococcus aureus for impetigo

BACKGROUND: Thiopeptides are structurally complex natural products that exert potent antimicrobial activity against Gram-positive pathogens by inhibiting bacterial protein synthesis. However, there has not been any attempt to conduct extensive medicinal chemistry campaign on these natural products, due to their chemical complexity. The advent of efficient syntheses of thiopeptides led us to identify promising pre-clinical candidates: AJ-024 against Clostridioides difficile and AJ-147 against Staphylococcus aureus for the indication of impetigo. METHODS: AJ-024 was screened against extensively classified C. difficile clinical isolates. Its time-kill kinetics and in vivo mouse efficacy were investigated against hypervirulent C. difficile ribotype 027. Metagenomic sequencing (16S rRNA) was performed to examine AJ-024's impact on gut microbiome. Similarly, AJ-147 was screened against methicillin-resistant S. aureus clinical isolates. Its time-kill kinetics, as well as its in vivo SSTI model were investigated. Pro-inflammatory cytokines were measured. Pharmacokinetic studies of these two agents, as well as their ADME properties and toxicity have also been investigated. RESULTS: AJ-024 has potent antibacterial activity, along with rapid bactericidal action against C. difficile ribotype 027 resulting in 99.99% reduction in 4X MIC in 3 hours. No recurrence was observed in the mouse in vivo model and this was corroborated by our 16S rRNA sequencing data. AJ-024 exerts minimal impact on beneficial gut-microbiome. AJ-147 exhibited a potent antibacterial activity against mupirocin resistant S. aureus. In vivo efficacy in a SSTI model revealed that AJ-147 is x1,000 more active than mupirocin. AJ-147 downregulates pro-inflammatory cytokines, such as IL-1ß and IL-6, that might elicit beneficial host immune response. Impact of AJ-024 on gut microbiome [Figure: see text] Investigation of AJ-024's impact on gut microbiome through 16s rRNA sequencing In vivo efficacy of AJ-147 in SSTI model [Figure: see text] AJ-147 compares favorably to mupirocin and downregulates pro-inflammatory cytokines CONCLUSION: Our medicinal chemistry campaign on thiopeptide antibiotics have led us to identify two preclinical candidates, AJ-024 and AJ-147. These two agents possess distinctive advantages compared to the first-line of treatments for each indication. Efforts are being directed to the completion of IND-enabling studies. DISCLOSURES: Hee-Jong Hwang, PhD, A&J Science: Stocks/Bonds|KHIDI: Grant/Research Support Young-Jin Son, A&J Science: Employee of A&J Science|A&J Science: Ownership Interest|KHIDI: Grant/Research Support Dahyun Kim, n/a, A&J Science: Employee of A&J Science Jusuk Lee, Ph.D., A&J Science: Employee of A&J Science Clovis Shyaka, n/a, A&J Science: Employee of A&J Science