Encapsulation of Combretastatin A-4 in Sub-10 nm unimer micelles to improve its aqueous stability and anticancer activity

Combretastatin A-4 (CA-4), a potentially potent anticancer agent with poor aqueous solubility and chemical instability, poses significant challenges for clinical translation. In this study, we report the encapsulation of CA-4 in sub-10 nm unimer micelles (UMs) derived from amphiphilic random copolymers of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and perfluoroalkyl acrylate (FA), synthesized via ARGET-ATRP. These copolymers self-fold in aqueous media to form compact single-chain nanoparticles that efficiently encapsulate CA-4, achieving encapsulation efficiencies up to 95 % at 19:1 copolymer/drug weight ratio. The resulting nanocarriers significantly enhanced the solubility and stability of CA-4 in phosphate-buffered saline over two months, while preserving its cis-configuration and biological activity. Drug release profiles demonstrated controlled diffusion and appeared to be influenced by copolymer composition, i.e. the hydrophilic/hydrophobic balance. Fluorescently labeled UMs were readily internalized by cancer cells within minutes, supporting their potential as ultrasmall, responsive drug nanocarriers. In vitro cytotoxicity studies demonstrated that encapsulated CA-4 maintained similar potency compared to the free drug against MIA PaCa-2 (IC50 = 4.9 ± 0.6 nM vs. 3.3 ± 1.4 nM) and A2780 (IC50 = 2.7 ± 0.6 nM vs. 2.0 ± 0.5 nM) cancer cell lines, while showing enhanced activity in A375 melanoma cells (IC50 = 4.8 ± 0.7 nM vs. 8.1 ± 1.3 nM).