New self-assembling polyaspartylhydrazide copolymer micelles for anticancer drug delivery

A new amphiphilic copolymer have been synthesized starting from the hydrosoluble polyaspartylhydrazide (PAHy) polymer, by grafting both hydrophilic PEG2000 chains and hydrophobic palmitic acid (C16) moieties on polymer backbone, and the structure of obtained PAHy–PEG2000–C16 copolymer have been characterized by 2D 1H/13C NMR experiments. PAHy–PEG2000–C16 copolymer showed the ability of self-assembling in aqueous media giving a core–shell structure and resulted potentially useful for encapsulating and dissolving hydrophobic drug. The formation of micellar core–shell structure has been investigated by 2D 1H NMR NOESY experiments. The presence of cross-peaks for protons of C16 and PAHy portions, indicated that the two domains are in close proximity forming micelle core. The critical aggregation concentration (CAC) values of PAHy–PEG2000–C16 amphiphilic graft copolymer was determined in water by fluorescence technique, and it was demonstrated that PAHy–PEG2000–C16 micelles are well suited to be micellar vehicle of highly hydrophobic molecules. Therefore, anticancer drug tamoxifen, used as a model hydrophobic molecule, was loaded into PAHy–PEG2000–C16 micelles obtaining an increase of drug solubility of about 3000 times. Transmission electron microscopy (TEM) observations showed the spherical morphology of micelles formed by PAHy–PEG2000–C16 copolymer with a mean diameter of about 30 nm, as confirmed also by dynamic light scattering (DLS) studies. Finally, in vitro cell viability studies were carried out on human breast cancer cells (MCF-7) testing the pharmacological activity of tamoxifen-loaded PAHy–PEG2000–C16 micelles, in comparison with free tamoxifen at different drug concentrations, demonstrating that tamoxifen-loaded PAHy–PEG2000–C16 micelles exhibited a concentration-dependent cytotoxic activity.