(686i) Protease-Triggered, Integrin-Targeted Cellular Uptake of Recombinant Protein Micelles

Gao, C. - Presenter, University of Pennsylvania
Hammer, D. A., University of Pennsylvania
Vargo, K. B., University of Pennsylvania
Oleosin is a tri-block structural protein that helps stabilizing oil bodies in plant cells. The wild type oleosin found in sunflower seeds is around 200 amino acids long and has a hydrophobic block in the center, with two hydrophilic arms at the N- and C- termini. This work explores the multiple applications of functionalized oleosin, with the help of molecular biology.

Targeting nano-particles for drug delivery has great potential for improving efficacy and reducing side effects from systemic toxicity. In particular, the RGD motif has been shown to effectively target the αvβ3 receptor, which is overexpressed in breast cancer cell lines. In addition, new developments in the assembly of materials afford the opportunity to expose cryptic targeting domains in tissue-specific microenvironments in which certain proteases are expressed. Here, recombinant oleosin are designed to combine the responsiveness to environmental proteases with specific targeting. Materials made recombinantly allow complete control over amino acid sequence, in which each molecule is identically functionalized. Previously, oleosin, a naturally occurring plant protein that acts as a surfactant, has been engineered to self-assemble into spherical micelles - a useful structure for drug delivery. In order to make oleosins that are locally activated to bind receptors, oleosin is genetically modified to incorporate the integrin-binding motif RGDS just behind a domain cleavable by thrombin. The resulting modified oleosin self-assembles into spherical micelles in aqueous environments, with the RGDS motif protected by the thrombin-cleavable domain. Upon the addition of thrombin, the RGDS is exposed and the binding of the spherical micelles to breast cancer cells is increased 4-fold. The strategy of combining tissue-specific protease cleavable domains with different adhesive domains is modular, wherein numerous different protease/receptor pairs could be combined to optimize targeting in specific diseases. Current work includes incorporating multiple ligand combinations such as PHSRN and RGDS, and enhancing cellular uptake by incorporating cell-penetrating peptides such as Tat-peptide.