Development of a novel PET imaging agent for prostate cancer

DESCRIPTION (provided by applicant): PSMA is an important biomarker for prostate cancer prognosis and an appropriate target for therapy due to its restricted expression mainly on late-stage, androgen-independent and metastatic prostate cancer cells. While currently there is only one clinical PSMA targeted agent for SPECT imaging (the antibody-based Prostascint ), high-affinity small-molecule inhibitors to PSMA have not been fully exploited for targeting and imaging prostate cancer. The overall objective of this application is to optimize a novel imaging probe for the in vivo detection of PSMA positive prostate tumors. Our central hypothesis for the proposed work is that an F-18 labeled irreversible inhibitor to PSMA coupled with PET scan could be used for prostate cancer staging as well as localization of lymph and bone metastasis. The rationale for undertaking the proposed research is that optimized F-18 labeled PSMA imaging constructs will serve as the foundation for a clinically relevant imaging modality for the diagnosis and post-treatment assessment of prostate cancer. This labeling needs to be in a chemistry that is readily available to the growing number of hospitals with cyclotrons and PET scanners. Additionally, demonstrating the effectiveness of our prostate tumor imaging probes in vivo and safety in animal models will serve as initial steps for the subsequent development of a radiotherapeutic agent for clinical use. The PIs will test the central hypothesis and accomplish the overall objective of this application by pursuing the following specific aims: Phase I 1) optimize the nucleophilic 18F labeling of CTT-54; 2) chemical/biochemical evaluation of lead compounds from AIM 1. Phase II Aims: 1) In vivo evaluation of selected PET tracers produced by Phase I and In vivo testing of lead compound for safety and pharmacokinetics Milestones include: labeling of CTT-54 with 1) an overall yield of 40%, high specific activity (gt500 Ci/mmole), stability of gt90% for up to 6 hours, 2) targeting of prostate cancer in mouse xenograft model and 3) a safety profile that will support filing an IND. The proposed work is expected to yield the following outcomes. First, a labeling chemistry that can be used in any one of the 277 PET centers in the United States. Secondly, a safety profile of the labeled lead compound that would support an investigation new drug application with the FDA. The high- affinity small-molecule targeting platform upon which our lead compound is based is unique compared to other targeting molecules because it has demonstrated irreversible binding to the prostate tumor biomarker PSMA. These unique characteristics make this compound is a more attractive targeting platform for prostate tumor binding with enhanced translational potential. It is expected that the proposed work will result in optimized prostate cancer imaging agents, which is important because better detection agents are essential for assisting clinicians in staging prostate cancer, developing personalized therapy, and monitoring treatment. PUBLIC HEALTH RELEVANCE: The overall goal of this application is to develop a novel clinically relevant diagnostic for prostate cancer that capitalizes on the potency and specific affinity of small-molecule inhibitors to PSMA. The overall objectives of this application are to further the development our primary PSMA inhibitor, CTT-54 by optimizing the 18F-labeling chemistry, demonstrating PET imaging of prostate cancer in animal models systems, and initiate toxicology studies in support of clinical trials. The preliminary data presented demonstrates that a small molecule inhibitor of PSMA can target and image prostate cancer when coupled to a radionuclide tracer.