cRGD-Functionalized Silk Fibroin Nanoparticles: A Strategy for Cancer Treatment with a Potent Unselective Naphthalene Diimide Derivative

SIMPLE SUMMARY: For many types of cancer, chemotherapy is still widely used, but it can cause serious side effects because it kills all rapidly growing cells, not just the cancerous ones. In this paper, a nanoparticle-based drug delivery system has been designed to selectively deliver a highly cytotoxic drug to tumor cells. The nanoparticles, obtained from a protein called silk fibroin, have been loaded with a naphthalene diimide derivative, namely NDI-1, which kills cells by affecting their DNA. The surface of the silk fibroin nanoparticles has been decorated with cyclopentapeptides incorporating the Arg-Gly-Asp sequence (cRGDs) to specifically target the tumor cells, thus reducing the harm to healthy cells and minimizing side effects. ABSTRACT: Developing drug delivery systems to target cytotoxic drugs directly into tumor cells is still a compelling need with regard to reducing side effects and improving the efficacy of cancer chemotherapy. In this work, silk fibroin nanoparticles (SFNs) have been designed to load a previously described cytotoxic compound (NDI-1) that disrupts the cell cycle by specifically interacting with non-canonical secondary structures of DNA. SFNs were then functionalized on their surface with cyclic pentapeptides incorporating the Arg-Gly-Asp sequence (cRGDs) to provide active targeting toward glioma cell lines that abundantly express ανβ3 and ανβ5 integrin receptors. Cytotoxicity and selective targeting were assessed by in vitro tests on human glioma cell lines U373 (highly-expressing integrin subunits) and D384 cell lines (low-expressing integrin subunits in comparison to U373). SFNs were of nanometric size (d(50) less than 100 nm), round shaped with a smooth surface, and with a negative surface charge; overall, these characteristics made them very likely to be taken up by cells. The active NDI-1 was loaded into SFNs with high encapsulation efficiency and was not released before the internalization and degradation by cells. Functionalization with cRGDs provided selectivity in cell uptake and thus cytotoxicity, with a significantly higher cytotoxic effect of NDI-1 delivered by cRGD-SFNs on U373 cells than on D384 cells. This manuscript provides an in vitro proof-of-concept of cRGD-silk fibroin nanoparticles’ active site-specific targeting of tumors, paving the way for further in vivo efficacy tests.