A versatile drug screening system was developed to simplify early targeted drug discovery in mice and then translate readily from mice to a dog prostate cancer model that more fully replicates the features of human prostate cancer.
We stably transfected human cDNA of the GRPr bombesin (BBN) receptor subtype to canine Ace-1 prostate cancer cells (Ace-1(huGRPr) ). Expression was examined by (125) I-Tyr(4) -BBN competition, calcium stimulation assay, and fluorescent microscopy. A dual tumor nude mouse xenograft model was developed from Ace-1(CMV) (vector transfected Ace-1) and Ace-1(huGRPr) cells. The model was used to explore the in vivo behavior of two new IRDye800-labeled GRPr binding optical imaging agents: 800-G-Abz4-t-BBN, from a GRPr agonist peptide, and 800-G-Abz4-STAT, from a GRPr antagonist peptide, by imaging the tumor mice and dissected organs.
Both agents bound Ace-1(huGRPr) and PC-3, a known GRPr-expressing human prostate cancer cell line, with 4-13 nM IC50 against (125) I-Tyr(4) -BBN, but did not bind Ace-1(CMV) cells (vector transfected). Binding was blocked by bombesin. Ca(2+) activation assays demonstrated that Ace-1(huGPRr) expressed biologically active GRPr. Both Ace-1 cell lines grew in the flanks of 100% of the nude mice and formed tumors of ∼0.5 cm diameter in 1 week. In vivo imaging of the mice at 800 nm emission showed GRPr+: GRPr- tumor signal brighter by a factor of two at 24 h post IV administration of 10 nmol of the imaging agents. Blood retention (4-8% ID at 1 h) was greater by a factor >10 and cumulative urine accumulation (28-30% at 4 h) was less by a factor 2 compared to a radioactive analog of the t-BBN containing agent, (177) LuAMBA, probably due to binding to blood albumin, which we confirmed in a mouse serum assay.
The dual tumor Ace-1(CMV) /Ace-1(huGRPr) model system provides a rapid test of specific to nonspecific binding of new GRPr avid agents in a model that will extend logically to the known Ace-1 orthotopic canine prostate cancer model. Prostate © 2016 Wiley Periodicals, Inc.
The Prostate. 2016 Mar 04 [Epub ahead of print]
Haiming Ding, Shankaran Kothandaraman, Li Gong, Michelle M Williams, Wessel P Dirksen, Thomas J Rosol, Michael F Tweedle
Department of Radiology, The Wright Center for Innovation in Biomolecular Imaging, The Wexner Medical Center, The Ohio State University, Columbus, Ohio., Department of Radiology, The Wright Center for Innovation in Biomolecular Imaging, The Wexner Medical Center, The Ohio State University, Columbus, Ohio., Department of Radiology, The Wright Center for Innovation in Biomolecular Imaging, The Wexner Medical Center, The Ohio State University, Columbus, Ohio., Department of Radiology, The Wright Center for Innovation in Biomolecular Imaging, The Wexner Medical Center, The Ohio State University, Columbus, Ohio., Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio., Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio., Department of Radiology, The Wright Center for Innovation in Biomolecular Imaging, The Wexner Medical Center, The Ohio State University, Columbus, Ohio.