Hit-to-Lead Identification and Validation of a Triaromatic Pleuromutilin Antibiotic Candidate

Herein, we report the hit-to-lead identification of a
drug-like
pleuromutilin conjugate 16, based on a triaromatic hit
reported in 2020. The lead arose as the clear candidate from a hit-optimization
campaign in which Gram-positive antibacterial activity, solubility,
and P-gp affinity were optimized. Conjugate 16 was extensively
evaluated for its in vitro ADMET performance which,
apart from solubility, was overall on par with lefamulin. This evaluation
included Caco-2 cell permeability, plasma protein binding, hERG inhibition,
cytotoxicity, metabolism in microsomes and CYP3A4, resistance induction,
and time-kill kinetics. Intravenous pharmacokinetics of 16 proved satisfactory in both mice and pigs; however, oral bioavailability
was limited likely due to insufficient solubility. The in
vivo efficacy was evaluated in mice, systemically infected
with Staphylococcus aureus, where 16 showed rapid reduction in blood bacteriaemia. Through our
comprehensive studies, lead 16 has emerged as a highly
promising and safe antibiotic candidate for the treatment of Gram-positive
bacterial infections.