pH-Responsive Isoprenoid-Antimicrobial Peptide conjugates, with Anti-TB activity, forming Polymeric Nanoparticles via Nanoprecipitation.

Tuberculosis (TB) remains a major global health challenge, and although current chemotherapeutic regimens are effective, they are limited by off target toxicity, long treatment duration, and increasing drug resistance. Antimicrobial peptides (AMPs) have emerged as promising therapeutic alternatives, particularly in the context of rising antimicrobial resistance; however, their clinical translation is hindered by significant pharmacokinetic barriers and dose dependent cytotoxicity. This proof of concept study investigates a stimuli responsive polymeric drug conjugate (PDC) system by covalently linking the sesquiterpenoid aldehyde Farnesal (Far) to two linear 20 mer antituberculosis peptides (ATBP1 and ATBP2) through acid cleavable imine (Schiff base) bonds. 1H NMR analysis confirmed imine formation and indicated that steric accessibility of primary amines strongly influences the extent of conjugation, resulting in a low conjugation degree for Far ATBP1 (~5%) and a markedly higher degree for Far ATBP2 (~213.5%). Due to their amphiphilic nature, the conjugates exhibit self assembly behavior; however, nanoprecipitation (NA) using poly(vinyl alcohol) (PVA) as stabilizer produced highly monodisperse polymeric nanoparticles with significantly smaller hydrodynamic diameters compared to self assembled systems. In vitro pH responsive dissociation studies showed that Far ATBP2 NA nanoparticles remained colloidally stable at physiological pH (7.4) but underwent structural disassembly at acidic pH (4.5) via imine hydrolysis—a behavior not observed for Far ATBP1 NA. Finally, MTT assays using human A549 alveolar epithelial cells demonstrated that covalent conjugation substantially reduced peptide and farnesal associated cytotoxicity, attributed to conversion of cationic primary amine groups into imine linkages. Overall, these findings highlight Far ATBP2 NA nanoparticles as a promising biocompatible, pH responsive platform for targeted pulmonary TB therapy.