Architecture-driven optimization of nanocarriers for pH-responsive drug delivery

Purpose: pH-responsive drug delivery systems, which enable site-specific drug release and reduce systemic toxicity, offer a promising strategy to exploit the acidic tumor microenvironment. We previously demonstrated the effectiveness of poly(ethylene glycol)-poly[(benzyl-L-aspartate)-co-(N-(3-aminopropyl)imidazole-L-aspartamide)] (PEG-PABI) as a pH-sensitive nanocarrier for anticancer therapy. The purpose of this study is to optimize PEG-PABI for enhanced pH-sensitive targeting and controlled drug release under acidic conditions. Methods: To optimize this design, we synthesized two structural variants of PEG-PABI, namely, linear PEG-PABI (AB type, 5 and 10 kDa) and branched PEG-(PABI)₂ (AB₂ type, 10 kDa), where two PABI arms are conjugated to a single PEG backbone, by tuning the polymer architecture and molecular weight. All PABI variants were investigated using molecular dynamics simulations. Results: The simulations revealed that extended PABI chains enhanced intermolecular interactions and improved nanoparticle stability. The branched PEG-(PABI)₂, which mimics phospholipid amphiphilicity, showed superior colloidal stability. All variants maintained their pH responsiveness, thereby enabling drug release under acidic conditions. Doxorubicin-loaded nanocarriers showed efficient drug encapsulation and potent anticancer effects both in vitro and in vivo. Among these nanocarriers, the branched PEG-(PABI)₂ displayed the most favorable performance, with enhanced colloidal stability, efficient endosomal escape, and increased tumor accumulation. Conclusion: Overall, the PEG-PABI system maintained strong pH responsiveness. Notably, the structure of branched PEG-(PABI)₂ resembles that of polymersomes, with dual PABI arms and a central PEG mimicking amphiphilic bilayers. These findings highlight the promise of branched PEG-(PABI)₂ as an advanced system for pH-sensitive and tumor-specific drug delivery.