avb6-directed molecular imaging and therapy



 DESCRIPTION (provided by applicant): The overall goal of this proposal is to further investigate the integrin subtype αvβ6 as a target for molecular imaging and therapy of cancer. The integrin αvβ6 is an epithelial-specific cell surface receptor that is undetectable in healthy adult epithelium but is significantly up-regulated in a wide range of epithelial derived cancers. Previously indicated in pancreatic, ovarian, lung and squamous cell carcinoma, most recent reports indicate the expression of αvβ6 also predicts the transition from DCIS to invasive carcinoma in breast cancer, is indicative of a poor outcome for patients with colon cancers, and promotes osteolysis through the up-regulation of MMP2 in prostate cancer. Overall this makes αvβ6 a significant target for both molecular imaging and therapy. We propose a targeted-peptide based approach to develop both novel αvβ6 specific imaging agents and αvβ6 specific therapies. We will use multimerization approaches to further improve target affinity and albumin binding motifs to improve pharmacokinetic properties of our current αvβ6 targeting peptide PEG28-A20FMDV2 (K16R)-PEG28. All compounds will be screened in vitro and in vivo for affinity and selectivity in ELISA and cell binding studies, their serum stability will be assessed, and the lead compounds taken forward to in vivo imaging studies in tumor-bearing mice based on αvβ6-affinity <5 nM, selectivity >1000 fold, αvβ6 (+) cell binding >50% at 1 h and serum stability >95% after 2 h. The lead compounds, based on murine pharmacokinetics and radiolabeling strategies, will also be investigated in nonhuman primates. We will use PEG28-A20FMDV2 (K16R)-PEG28 as a proof of concept delivery vehicle for two therapeutic strategies: i) D (KLAKLAK) 2 (a pro-apoptotic peptide) and, ii) a micelle-based nanocarrier formulation of paclitaxel (PTX). Efficacy will be assessed in vitro in DX3/mTFL/ITGB6 (αvβ6-positive) and DX3/mTFL (αvβ6-negative) cells prior to in vivo studies in mice. Positron emission tomography (PET) and bioluminescence imaging (BLI) will be used both to track in vivo biodistribution and measure therapeutic efficacy of these targeted therapies. This proposal brings together an interdisciplinary team of investigators with expertise in radiochemistry and molecular imaging (Sutcliffe, PI), biostatistics (Beckett), nonhuman primate imaging (Tarantal), physics and imaging instrumentation (Cherry) and surgical oncology (Bold), with a history of successful collaboration and productive research. This proposal will utilize the state of the art preclinical imaging resources (including nonhuman primate) as well as new radiochemistry and GMP resources to facilitate rapid translation to the clinic.