Silk Fibroin Nanoparticle Functionalization with Arg-Gly-Asp Cyclopentapeptide Promotes Active Targeting for Tumor Site-Specific Delivery.

Arg-Gly-Asp (RGD)-based cyclopentapeptides (cRGDs) have a high affinity towards integrin αvß3 and αvß5, 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.

Synthesis of Functionalized 6,5- and 7,5-Azabicycloalkane Amino Acids by Metathesis Reactions.

Azabicyclo[4.3.0]- and [5.3.0]alkanone amino acid derivatives were easily prepared by submitting the same starting dipeptide to a direct ring-closing enyne metathesis or an ethylene-mediated cross-enyne metathesis/ring-closing metathesis, respectively. The reactivity of the newly synthesized 6,5- and 7,5-fused bicyclic scaffolds was then investigated to obtain variously functionalized derivatives with potential applications in the field of peptides/peptidomimetics.

Synthesis of Variously Functionalized Azabicycloalkane Scaffolds by Domino Metathesis Reactions.

7,5-Fused azabicycloalkane scaffolds, carrying a quaternary stereocenter at C3 position of the lactam ring, can act as effective reverse-turn mimics and have proven to be useful intermediates for the preparation of Arg-Gly-Asp (RGD)-based cyclopentapeptides (cRGD) with nanomolar activity as αvß3/αvß5 integrin antagonists. Here, we report the synthesis of new azabicycloalkane scaffolds endowed at the C6 position with a para-substituted phenethyl side chain, which could be exploited to obtain cRGD-based bioconjugates that may find promising applications in anticancer therapy. By performing a domino cross enyne metathesis/ring-closing metathesis (CEYM/RCM) in the presence of styrene derivatives, followed by catalytic hydrogenation of the diene system, we easily converted a dipeptide precursor into the desired C6-functionalized azabicycloalkane scaffolds. The presence of a suitably protected p-amino group on the styrene moiety could be exploited, after deprotection, either to directly conjugate a bioactive compound or to introduce a suitable spacer between the cRGD unit and the bioactive compound.