Balanced Phospholipid-Mimicking Amphiphilicity for Curcumin Nanocomplex Formation and Distribution in Three-Dimensional Tumor Spheroids

Curcumin is a promising bioactive compound with anticancer potential; however, its therapeutic application is limited by poor aqueous dispersibility and insufficient distribution within densely packed tumor tissues. Here, we developed a phospholipid-mimicking amphiphilic random copolymer, PMB30W, as an interfacially active nanocarrier to improve curcumin delivery in three-dimensional HepG2 tumor spheroids. PMB30W consists of zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) units and hydrophobic n-butyl methacrylate (BMA) units, providing both hydrated phosphorylcholine functionality and BMA-derived hydrophobicity. PMB30W/CUR formed dispersions with apparent Z-average diameters of 10–13 nm that remained comparable over 1 week and showed high curcumin association efficiencies of 68–76%. In contrast, poly(MPC) (PMPC), which provides phosphorylcholine hydration but lacks hydrophobic BMA units, showed limited curcumin association and larger apparent hydrodynamic diameters. These observations are consistent with a contribution of hydrophobic segments to curcumin association. Confocal fluorescence imaging revealed that PMB30W/CUR exhibited more uniform and extensive distribution throughout HepG2 spheroids than PMPC/CUR and DMSO-dispersed curcumin. This enhanced distribution was maintained under ATP-depletion and low-temperature conditions, suggesting reduced dependence on conventional energy-dependent uptake processes. LDH release assays and cytocompatibility evaluations of curcumin-free polymers indicated that the enhanced spheroid distribution was not attributable to nonspecific biomembrane disruption or intrinsic polymer toxicity. Furthermore, PMB30W/CUR showed enhanced growth inhibition in HepG2 spheroids and induced apoptosis-related molecular responses, including a reduced Bcl-2/Bax expression ratio and increased Caspase-3 expression, supporting the involvement of apoptosis-related signaling in observed growth inhibition. These findings demonstrate that balanced MPC/BMA amphiphilicity is a key molecular design principle linking polymer structure, interfacial properties, three-dimensional distribution, and biological activity, providing a promising strategy for delivering poorly water-soluble bioactive compounds in complex tumor models.