Thermally Triggered Multivalent Targeting of Tumors

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DESCRIPTION (provided by applicant): The overall objective of the proposed research is to demonstrate the feasibility of a new tumor selective targeting approach - thermally triggered polyvalent targeting - that provides external control of affinity targeting to enhance the selective delivery of anticancer drugs to the tumor vasculature. This overall objective is motivated by the rationale that there is an urgent need for improved therapy of primary tumors, especially for tumors of the brain, pancreas, ovary and colon, where mortality is typically caused by the inability of therapy to control the primary tumor. The central hypothesis of the proposed research is that thermally triggered polyvalent targeting will: (1) enhance accumulation of the drug payload in solid tumors; (2) limit drug exposure in normal tissues; and (3) improve tumor therapy. In the proposed research, a thermally responsive polypeptide will be synthesized that self-assembles into a nanoscale structure - a polypeptide micelle with a diameter of ~60 nm - only within a tumor that is mildly heated (~42¿C) by externally focused hyperthermia. These polypeptide micelles are designed to present multiple copies of a tumor endothelial specific targeting ligand on the exterior - corona - of the micelle. The polyvalent presentation of targeting ligands only in the tumor will increase its avidity and therefore selectively deliver the anticancer therapeutics to the tumor vasculature while sparing normal tissues. The modulation of both affinity and size at the nanoscale is a unique feature of these engineered nanostructures, and is the key to their performance. The thermally triggered micelle forming system consists of elastin-like polypeptides (ELPs) in an AB diblock architecture. ELPs are thermally responsive biopolymers that undergo a thermally triggered hydrophilic-hydrophobic phase transition above their transition temperature (Tt). A diblock ELP copolymer (ELPBC) will incorporate a vascular targeting ligand (L) at the end of its hydrophilic block and will be conjugated at the hydrophobic end to 211 Astatine (211At), a radionuclide which emits highly potent, short penetration a-particles. L-ELPBC-211At conjugates will self-assemble into polyvalent micelles at 40¿C in heated tumors and target the tumor endothelium by a greater thermally triggered avidity of the micelle to tumor endothelium, leading to ablation of tumor vasculature. Thee significance of the proposed research is that it will be, to our knowledge, the first attempt to harness