Abstract
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Objectives: To prepare a novel radiolabeled TSPO ligand CB86 targeting agent 99Tcm-DTPA-CB86 and evaluate its biological properties.
Methods: DPTA-CB86 was prepared by coupling with a bifunctional chelating agent, and then labeled with 99Tcm to obtain 99Tcm-DTPA-CB86. The labeling efficiency, radiochemical purity, and stability were determined in vitro. In vitro cellular uptake and efflux were performed on RAW264.7 macrophage cells. Biodistribution and micro SPECT/CT imaging were investigated on Freund’s Adjuvant-Induced Left Arthritis in mice. SPSS 18.0 analysis software was used to conduct a t-test for the data that fit the normal distribution and homogeneity of variance. Results The labeling yields and radiochemical purity of 99Tcm-DTPA-CB86 were (95.86 ± 2.45) % and (97.45 ± 0.69) %, respectively. 99Tcm-DTPA-CB86 displayed good stability, which the radiochemical purity was more than > 90%, in PBS solution at 4 h. It also exhibited high specific TSPO binging in RAW264.7 macrophage cells in vitro. The highest uptake ratio was (36.45 ± 2.18) % at 3 h after incubation, and decreased significantly [(10.43 ± 2.01)%] after adding excessive unlabeled DTPA-CB86. The difference was significant (t = 6.217, P < 0.05) (Fig.1). The cell efflux study showed that 99Tcm-DTPA-CB86 has good cell retention by RAW264.7 cells, with only about 13.99 % (decreased from(33.31 ± 2.34)% to(19.32 ± 2.01)% of total input radioactivity) of 99Tcm-DTPA-CB86 efflux observed during 4.5 h to 8 h incubation (Fig.2). Biodistribution and MicroSPECT/CT imaging demonstrated uptake of 99Tcm-DTPA-CB86 in the left arthritic ankles was significantly increased compared with contralateral normal ankles (Fig.3). Uptake in the arthritic ankles could be largely blocked by an excess of DTPA-CB86 (Fig.4). Conclusion 99Tcm-DTPA-CB86 can be readily synthesized, clearly visualized arthritis and exhibited low background, suggesting its potential as a novel promising molecular probe targeting TSPO for arthritic SPECT imaging. [Key words] Translocator protein; Arthritis; Isotope labeling; Technetium radioisotope; Tomography, emission-computed, single-photon; Tomography, X-ray computed
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