The goal of this research is to use radiolabeled engineered peptide scaffolds for development of sensitive ovarian carcinoma diagnostic and therapeutic (theranostic) agents using a matched pair 203Pb/212Pb in vivo ?-particle generator. The high linear energy transfer of a-particle is significantly higher than that of b-particle emittng radionuclides commonly used for therapy. Although the survival rates of early stage ovarian cancer are high, late stage disease is often fatal. The poor prognosis of ovarian cancer results from complicated diagnosis due to a largely asymptomatic disease development, the presence of aggressive metastatic cells, as well as a lack of biomarkers for disease stages. We propose to target the carcinoma-specific Thomsen- Friedenreich (TF) glycoantigen and the ovarian carcinoma biomarker CD44v6, a tumor-specific splice variant of the hyaluronic acid (HA) receptor CD44. CD44v6 glycosylation results in increased HA binding and internalization, leading to a multitude of signaling events. TF disaccharide is displayed on CD44, likely in the cancer-specific v6 region and is associated with invasion and metastasis. It is hypothesized that targeting this TF/CD44v6 glycoepitope will afford the specific localization of a-particle radiation radioactivity to tumors for both imaging and therapy. The targeting vehicle employed will be an engineered derivative of 25 amino acid hepcidin that binds TF/CD44v6 and exhibits optimum in vivo properties compared to antibodies or small peptides, including high in vivo stability and rapid clearance through the kidney, thereby increasing tumor retention and reducing non-target organ radiation. Prolonged bioavailability and minimal exposure to healthy tissues may be further accomplished by delivery of HA to ensure internalization of the TF/CD44v6 peptide.
The specific aims of the proposed research are to 1): select and characterize TF/CD44v6-avid phage display derived peptides;2) bioengineer TF/CD44v6-avid peptide(s) into hepcidin scaffolds and characterize biotinylated and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated forms for their in vitro ovarian cancer cell binding properties;and 3) determine the pharmacokinetics, biodistribution and tumor-targeting ability of both 212Pb and 203Pb-labeled peptide conjugates in vivo in human ovarian carcinoma xenografted mice. The effect of HA treatment on the tumor retention of the radiolabeled hepcidin peptide scaffold will be determined by biodistribution studies. In order to visualize tumor homing, the peptide construct will be labeled with 203Pb for single photon emission computed tomography imaging. The proposed in vivo targeting of ovarian cancers with a-particle labeled peptide scaffolds has wide applicability for the imaging and treatment of ovarian cancer, which is important because early ovarian cancer is often asymptomatic and late stage ovarian cancer is usually fatal. Further, the technology proposed can be applied to target and kill other cancer cells, especially since TF is present on >80% of adenocarcinomas.