Preclinical Evaluation of a Novel 99mTc-Labeled CB86 for Rheumatoid Arthritis Imaging

摘要

Early diagnosis and therapy are crucial to control disease progression optimally and achieve a good prognosis in rheumatoid arthritis (RA). Previous study showed that a technetium-99m (~(99m)Tc)-labeled TSPO ligand (~(99m)Tc-CB256 [2-(8-(2-(bis(pyridin-2-yl)methyl)amino)acetamido)-2-(4-chlorophenyl)H -imidazo[1,2-a ]pyridin-3-yl)-N ,N -dipropylacetamide] composed of a translocator protein (TSPO) ligand CB86 [[2-(4-chlorophenyl)-8-amino-imidazo[1,2-a ]-pyridin-3-yl]-N ,N -di-n -propylacetamide] and di-(2-picolyl)amine, a bifunctional chelate agent, was used to image a TSPO-rich cancer cell in vitro ; however, few ~(99m)Tc-CB256 in vivo evaluation has been reported so far probably due to the cytotoxicity of CB256 (ca . 75 times more than analogous CB86). Herein, we describe a novel TSPO targeting radiopharmaceutical consisting of CB86 and diethylenetriaminepentaacetic acid (DTPA), a conventional bifunctional chelating ligand in clinical trials used to prepare ~(99m)Tc-labeled CB86, and its evaluation as a ~(99m)Tc-single-photon emission computed tomography (SPECT) probe. The radiosynthesis and characterization of ~(99m)Tc-DPTA-CB86 including hydrophilicity and stability tests were determined. Additionally, the binding affinity and specificity of ~(99m)Tc-DTPA-CB86 to TSPO were evaluated using RAW264.7 macrophage cells. Biodistribution and ~(99m)Tc-SPECT studies were conducted on rheumatoid arthritis (RA) rat models after the injection of ~(99m)Tc-DTPA-CB86 with or without co-injection of unlabeled DTPA-CB86. The radiosynthesis of ~(99m)Tc-DTPA-CB86 was completed successfully with the labeling yields and radiochemical purity of 95.86 ± 2.45 and 97.45 ± 0.69%, respectively. The probe displayed good stability in vitro and binding specificity to RAW264.7 macrophage cells. In the biodistribution studies, ~(99m)Tc-DTPA-CB86 exhibited rapid inflammatory ankle accumulation. At 180 min after administration, ~(99m)Tc-DTPA-CB86 uptakes of the left inflammatory ankle were 2.35 ± 0.10 percentage of the injected radioactivity per gram of tissue (% ID/g), significantly higher than those of the normal tissues. ~(99m)Tc-SPECT imaging studies revealed that ~(99m)Tc-DTPA-CB86 could clearly identify the left inflammatory ankle with good contrast at 30–180 min after injection. Therefore, ~(99m)Tc-DTPA-CB86 may be a promising probe for arthritis ~(99m)Tc-SPECT imaging.