Ole Tietz1, Alison Marshall1, Cody Bergman1, Melinda Wuest1, Frank Wuest2. 1. Department of Oncology, University of Alberta, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada. 2. Department of Oncology, University of Alberta, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada; Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G 2H1, Canada. Electronic address: wuest@ualberta.ca.
Abstract
INTRODUCTION: Non-invasive imaging of COX-2 in cancer represents a powerful tool for assessing COX-2-mediated effects on chemoprevention and radiosensitization using potent and selective COX-2 inhibitors as an emerging class of anticancer drugs. Careful assessment of the pharmacokinetic profile of radiolabeled COX-2 inhibitors is of crucial importance for the development of suitable radiotracers for COX-2 imaging in vivo. The delicate balance between the selection of typical COX-2 pharmacophores and the resulting physicochemical characteristics of the COX-2 inhibitor represents a formidable challenge for the search of radiolabeled COX-2 imaging agents. Several pyrimidine-based COX-2 inhibitors demonstrated favorable in vitro and in vivo COX-2 imaging properties in various COX-2 expressing cancer cell lines. Here, we describe a comparative radiopharmacological study of three 18F-labeled COX-2 inhibitors based on a pyrimidine scaffold. The objective of this study was to investigate how subtle structural alterations influence the pharmacokinetic profile of lead compound [18F]1a ([18F]Pyricoxib) to afford 18F-labeled pyrimidine-based COX-2 inhibitors with improved COX-2 imaging properties in vivo. METHODS: Radiosynthesis of radiotracers was accomplished through reaction with 4-[18F]fluorobenzyl amine on a methyl-sulfone labeling precursor ([18F]1a and [18F]2a) or late-stage radiofluorination using a iodyl-containing labeling precursor ([18F]3a). Radiopharmacological profile of 18F-labeled pyrimidine-based COX-2 inhibitors [18F]1a, [18F]2a and [18F]3a was studied in COX-2-expressing human HCA-7 colorectal cancer cell line, including cellular uptake studies in HCA-7 cells and dynamic PET imaging studies in HCA-7 xenografts. RESULTS: Cellular uptake of radiotracers [18F]2a and [18F]3a in HCA-7 cells was 450% and 300% radioactivity/mg protein, respectively, after 90 min incubation, compared to 600% radioactivity/mg protein for radiotracer [18F]1a. Dynamic PET imaging studies revealed a tumor SUV of 0.53 ([18F]2a) and 0.54 ([18F]3a) after 60 min p.i. with a tumor-to-muscle ratio of ~1. Tumor SUV for [18F]1a (60 min p.i.) was 0.76 and a tumor-to-muscle ratio of ~1.5. Pyricoxib analogues [18F]2a and [18F]3a showed distinct pharmacokinetic profiles in comparison to lead compound [18F]1a with a significantly improved lung clearance pattern. Replacing the 4-[18F]fluorobenzyl amine motif in radiotracer [18F]1a with a 4-[18F]fluorobenzyl alcohol motif in radiotracer [18F]3a resulted in re-routing of the metabolic pathway as demonstrated by a more rapid liver clearance and higher initial kidney uptake and more rapid kidney clearance compared to radiotracers [18F]1a and [18F]2a. Moreover, radiotracer [18F]3a displayed favorable rapid brain uptake and retention. CONCLUSION: The radiopharmacological profile of three 18F-labeled COX-2 inhibitors based on a pyrimidine scaffold were evaluated in COX-2 expressing human colorectal cancer cell line HCA-7 and HCA-7 xenografts in mice. Despite the overall structural similarity and comparable COX-2 inhibitory potency of all three radiotracers, subtle structural alterations led to significantly different in vitro and in vivo metabolic profiles. ADVANCES IN KNOWLEDGE: Among all tested pyrimidine-based 18F-labeled COX-2 inhibitors, lead compound [18F]1a remains the most suitable radiotracer for assessing COX-2 expression in vivo. Radiotracer [18F]3a showed significantly improved first pass pulmonary passage in comparison to radiotracer [18F]1a and might represents a promising lead compound for the development of radiotracers for PET imaging of COX-2 in neuroinflammation.
INTRODUCTION: Non-invasive imaging of COX-2 in cancer represents a powerful tool for assessing COX-2-mediated effects on chemoprevention and radiosensitization using potent and selective COX-2 inhibitors as an emerging class of anticancer drugs. Careful assessment of the pharmacokinetic profile of radiolabeled COX-2 inhibitors is of crucial importance for the development of suitable radiotracers for COX-2 imaging in vivo. The delicate balance between the selection of typical COX-2 pharmacophores and the resulting physicochemical characteristics of the COX-2 inhibitor represents a formidable challenge for the search of radiolabeled COX-2 imaging agents. Several pyrimidine-based COX-2 inhibitors demonstrated favorable in vitro and in vivo COX-2 imaging properties in various COX-2 expressing cancer cell lines. Here, we describe a comparative radiopharmacological study of three 18F-labeled COX-2 inhibitors based on a pyrimidine scaffold. The objective of this study was to investigate how subtle structural alterations influence the pharmacokinetic profile of lead compound [18F]1a ([18F]Pyricoxib) to afford 18F-labeled pyrimidine-based COX-2 inhibitors with improved COX-2 imaging properties in vivo. METHODS: Radiosynthesis of radiotracers was accomplished through reaction with 4-[18F]fluorobenzyl amine on a methyl-sulfone labeling precursor ([18F]1a and [18F]2a) or late-stage radiofluorination using a iodyl-containing labeling precursor ([18F]3a). Radiopharmacological profile of 18F-labeled pyrimidine-based COX-2 inhibitors [18F]1a, [18F]2a and [18F]3a was studied in COX-2-expressing human HCA-7 colorectal cancer cell line, including cellular uptake studies in HCA-7 cells and dynamic PET imaging studies in HCA-7 xenografts. RESULTS: Cellular uptake of radiotracers [18F]2a and [18F]3a in HCA-7 cells was 450% and 300% radioactivity/mg protein, respectively, after 90 min incubation, compared to 600% radioactivity/mg protein for radiotracer [18F]1a. Dynamic PET imaging studies revealed a tumor SUV of 0.53 ([18F]2a) and 0.54 ([18F]3a) after 60 min p.i. with a tumor-to-muscle ratio of ~1. Tumor SUV for [18F]1a (60 min p.i.) was 0.76 and a tumor-to-muscle ratio of ~1.5. Pyricoxib analogues [18F]2a and [18F]3a showed distinct pharmacokinetic profiles in comparison to lead compound [18F]1a with a significantly improved lung clearance pattern. Replacing the 4-[18F]fluorobenzyl amine motif in radiotracer [18F]1a with a 4-[18F]fluorobenzyl alcohol motif in radiotracer [18F]3a resulted in re-routing of the metabolic pathway as demonstrated by a more rapid liver clearance and higher initial kidney uptake and more rapid kidney clearance compared to radiotracers [18F]1a and [18F]2a. Moreover, radiotracer [18F]3a displayed favorable rapid brain uptake and retention. CONCLUSION: The radiopharmacological profile of three 18F-labeled COX-2 inhibitors based on a pyrimidine scaffold were evaluated in COX-2 expressing humancolorectal cancer cell line HCA-7 and HCA-7 xenografts in mice. Despite the overall structural similarity and comparable COX-2 inhibitory potency of all three radiotracers, subtle structural alterations led to significantly different in vitro and in vivo metabolic profiles. ADVANCES IN KNOWLEDGE: Among all tested pyrimidine-based 18F-labeled COX-2 inhibitors, lead compound [18F]1a remains the most suitable radiotracer for assessing COX-2 expression in vivo. Radiotracer [18F]3a showed significantly improved first pass pulmonary passage in comparison to radiotracer [18F]1a and might represents a promising lead compound for the development of radiotracers for PET imaging of COX-2 in neuroinflammation.
Authors: Freimut D Juengling; Frank Wuest; Sanjay Kalra; Federica Agosta; Ralf Schirrmacher; Alexander Thiel; Wolfgang Thaiss; Hans-Peter Müller; Jan Kassubek Journal: Front Neurol Date: 2022-08-17 Impact factor: 4.086