IN VITRO AND IN VIVO EVALUATION OF [ super(64)CU-NOTA-8-AOC-BBN(7-14)NH sub(2)] RADIOPHARMACEUTICAL FOR PET IMAGING OF HUMAN BREAST AND PROSTATE CANCER TUMORS

Introduction: Human prostate and breast cancers are known to express the gastrin-releasing peptide receptor (GRPr) in very high numbers. In this study, a derivative of bombesin (BBN) peptide, an agonist for the GRPr, has been complexed with Cu-64 radionuclide, making the conjugate a potential candidate for positron-emission tomography (PET) imaging and therapy of these human cancers. super(64)Cu-NOTA-8-Aoc-BBN(7-14)NH sub(2) produced high-quality microPET images of GRPR-positive tumors in severely compromised immunodeficient (SCID) mice. Methods: Briefly, the unmetallated conjugate was synthesized by solid-phase peptide synthesis followed by manual conjugation of NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) bifunctional chelating agent. Radiolabeling with Cu-64 radionuclide was performed in buffered, aqueous solution (pH=7-7.5). The radiolabeled conjugate was assayed in vitro and in vivo T-47D (human breast) and PC-3 (human prostate) cell lines in order to determine its specificity and selectivity for the GRPr and its corresponding pharmacokinetic profile. In vivo, multimodal, molecular imaging via microPET/CT and microMRI was performed in tumor-bearing mice models bearing xenografted tumors. Results: The super(64)Cu-NOTA-8-Aoc-BBN(7-14)NH sub(2) targeting vector was determined to specifically localize in GRPr-positive tissues. Accumulation of radioactivity was observed in the tumor in sufficient quantities to allow for identification of tumors in microPET imaging procedures. Uptake and retention of conjugate in T-47D xenografted tumors was determined to be 2.27 plus or minus 0.08%, 1.35 plus or minus 0.14%, and 0.28 plus or minus 0.07% ID/g (Percent Injected Dose Per Gram Tissue) at 1, 4, and 24 h. Uptake and retention of conjugate in PC-3 xenografted tumors was determined to be 3.58 plus or minus 0.70%, 1.64 plus or minus 0.17%, and 1.00 plus or minus 0.19% ID/g at 1, 4, and 24 h, respectively. Conclusion: The super(64)Cu-NOTA-8-Aoc-BBN(7-14)NH sub(2) produced high quality microPET images. The pharmacokinetic profile of this conjugate justifies further preclinical evaluation of this new radiopharmaceutical as a potentially-useful diagnostic agent. Additionally, this new radiopharmaceutical serves as a good reference for modification and optimization of similar agents to maximize tumor uptake and minimize non-target accumulation of radioactivity in collateral tissues.