C-end rule peptide-guided niosomes for prostate cancer cell targeting

The use of nanoformulations in drug delivery has a significant impact to increase the drug therapeutic efficacy and improve their safety in anticancer treatments. Non-ionic surfactant vesicles (NSVs), or niosomes, are a class of nanocarriers that are low-cost, physiochemical stable, and represent a promising alternative to liposomes. Tumor-penetrating C-end Rule (CendR) peptides, that target neuropilin-1 (NRP-1), a cell surface receptor commonly overexpressed on solid tumor cells, are widely used for precise delivery of diagnostic and therapeutic nanoparticles to malignant lesions. In this study, we investigated the impact of NSV functionalization with prototypic CendR peptide RPARPAR (abbr. RPAR) on NRP-1-dependent targeting of prostate cancer cells. Doxorubicin (DOX)-loaded NSVs, with or without RPAR conjugation, were prepared, physicochemical charac-terized, and finally tested for NRP-1 binding in human primary prostate carcinoma-1 and prostate carcinoma epithelial cell lines (PPC-1 and 22Rv1, respectively) that are NRP-1 positive, and melanoma (M21) cells that are NRP-1 negative. We demonstrated that the cellular uptake of RPAR-NSVs was NRP-1-dependent and the uptake rate of RPAR-NSVs was ca. ten times higher than un-targeted NSVs in PPC-1 cells; while no significant differ-ences, between targeted and un-targeted nanocarriers, were obtained in M21 cell line. These data were further confirmed by using NRP-1 CendR-binding pocket-blocking (mAb7E8) antibody, which significantly inhibited the internalization of RPAR-NSVs in PPC-1 cells from ca. 80%-3%. The resulting data obtained of cytotoxic studies agreed the uptake results, thus showing a significant increase of cytotoxic effect for RPAR-NSVs@DOX in PPC-1 and 22Rv1 cells compared to NSVs@DOX. These results provide a proof of concept that the conjugation of CendR peptides on the surface of NSVs can increase the specific targeting of nanoparticles in NRP-1 positive cells, thus improving the therapeutic efficacy of resulting targeted nanocarriers for cancer treatment. Our results have important implications for the development of more efficient and selective cancer therapies and support further in vivo studies by using more complex targeting peptides, such as iRGD or other CendR peptides, that are also targeting primary recruitment receptors (i.e. integrins) and are then proteolytically activated into CendR pep-tides in the tumor microenvironment.