Arg-Gly-Asp (RGD)-based cyclopentapeptides (cRGDs) have a high affinity towards integrin αvβ3 and αvβ5, which are overexpressed by many tumor cells. Here, curcumin-loaded silk fibroin nanoparticles (SFNs) have been functionalized on the surface with cRGD to provide active targeting towards tumor cells; a “click reaction” between the RGD-based cyclopentapeptide carrying an azide group and triple-bond-functionalized nanoparticles has been exploited. Both naked and functionalized SFNs were less than 200 nm in diameter and showed a round-shaped morphology but, after functionalization, SFNs increased in size and protein molecular weight. The functionalization of SFNs’ surfaces with cRGD provided active internalization by cells overexpressing integrin receptors. At the lowest concentration tested (0.01 mg/mL), functionalized SFNs showed more effective uptake with respect to the naked by tumor cells that overexpress integrin receptors (but not for non-overexpressing ones). In contrast, at higher concentrations, the non-specific cell membrane protein–particle interactions are promoted and coupled to specific and target mediated uptake. Visual observations by fluorescence microscopy suggested that SFNs bind to integrin receptors on the cell surface and are then internalized by endocytosis. Overall, SFN functionalization provided in vitro active targeting for site-specific delivery of anticancer drugs, boosting activity and sparing healthy organs.

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 (d₅₀ 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.

Triple negative breast cancer (TNBC) represents one of the most aggressive types of cancer, with a difficult treatment leading to poor prognosis of the disease. Herein we report the synthesis of a custom-made cyclic RGD peptide (cRGD), and its use in decorating liposomes for targeted drug delivery of doxorubicin to TNBC cells overexpressing integrin receptor α_vβ₃. Liposomes carrying dibenzocyclooctine groups on their surface were produced using an optimized large scale microfluidic-assisted approach and subsequently conjugated with cRGD bearing an acyl azide group by means of a click chemistry reaction. This functionalization promotes enhanced cellular uptake via integrin-mediated endocytosis. In vitro assessments confirm enhanced selectivity and cytotoxicity of cRGD-liposomes against triple-negative cancer cells, in addition to dual imaging capabilities by fluorescence and magnetic resonance techniques due to the incorporation of a fluorescent dye and gadolinium complex, respectively. These features support the potential of cRGD-liposomes as a promising platform for targeted drug delivery to specific cancer cell populations, establishing them as viable theranostic agents for precision medicine applications.

Herein we report the preparation of C4‐functionalized proline‐derived azabicycloalkane (Aba) amino acids by exploiting a direct ring closing enyne metathesis reaction of readily accessible dipeptide precursors. The reverse‐turn inducing properties of the newly synthesized constrained dipeptide mimics were assessed by computational studies. Furthermore, the desired Aba derivatives, carrying a synthetically versatile diene moiety, were subjected to post‐functionalization reactions to validate their potential application in peptide/peptidomimetic chemistry and drug discovery.