Novel polymeric nanoparticles for intracellular delivery of peptide Cargos: antitumor efficacy of the BCL-2 conversion peptide NuBCP-9.

The preclinical development of peptidyl drugs for cancer treatment is hampered by their poor pharmacologic properties and cell penetrative capabilities in vivo. In this study, we report a nanoparticle-based formulation that overcomes these limitations, illustrating their utility in studies of the anticancer peptide NuBCP-9, which converts BCL-2 from a cell protector to a cell killer. NuBCP-9 was encapsulated in polymeric nanoparticles composed of a polyethylene glycol (PEG)-modified polylactic acid (PLA) diblock copolymer (NuBCP-9/PLA-PEG) or PEG-polypropylene glycol-PEG-modified PLA-tetrablock copolymer (NuBCP-9/PLA-PEG-PPG-PEG). We found that peptide encapsulation was enhanced by increasing the PEG chain length in the block copolymers. NuBCP-9 release from the nanoparticles was controlled by both PEG chain length and the PLA molecular weight, permitting time-release over sustained periods. Treatment of human cancer cells with these nanoparticles in vitro triggered apoptosis by NuBCP-9-mediated mechanism, with a potency similar to NuBCP-9 linked to a cell-penetrating poly-Arg peptide. Strikingly, in vivo administration of NuBCP-9/nanoparticles triggered complete regressions in the Ehrlich syngeneic mouse model of solid tumor. Our results illustrate an effective method for sustained delivery of anticancer peptides, highlighting the superior qualities of the novel PLA-PEG-PPG-PEG tetrablock copolymer formulation as a tool to target intracellular proteins.