PT - JOURNAL ARTICLE AU - Yu, Yanbo AU - Liang, Qianwa AU - Liu, Hui AU - Luo, Zonghua AU - Joshi, Sumit AU - Qiu, Lin AU - Gu, Jiwei AU - Tangadanchu, Vijai Kumar Reddy AU - Tu, Zhude TI - <strong>Radiosynthesis and <em>in vivo</em> evaluation of a PET radiotracer for imaging TRPC5 in the brain</strong> DP - 2019 May 01 TA - Journal of Nuclear Medicine PG - 118--118 VI - 60 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/60/supplement_1/118.short 4100 - http://jnm.snmjournals.org/content/60/supplement_1/118.full SO - J Nucl Med2019 May 01; 60 AB - 118Objectives: Transient receptor potential canonical (TRPC) channels constitute a group of TRP superfamily that regulates intracellular Ca2+ concentration. Among them, TRPC5 is a calcium-permeant cation channel that it is widely expressed throughout the brain. TRPC5 plays a crucial role in regulating neuron axon growth and neuronal differentiation. Emerging evidence indicates that targeting TRPC5 has great potential for treating neurological diseases and psychiatric disorders. Recently, HC608 was reported as a potent ligand for TRPC5 with IC50 value of 6.2 nM although it bound with TRPC4 with IC50 value of 32.5 nM. Rodent studies suggested HC608 is very effective for anxiety and depression treating.[3] To investigate the TRPC5 regulate functions for the brain disorders, we radiosynthesized [11C]HC608 and performed initially in vitro and in vivo in rodent to determine if [11C]HC608 could be a suitable PET radiotracer for imaging TRPC5. Methods: The radiosynthesis of [11C]HC608 was accomplished by N-[11C]methylation of its amide precursor with [11C]CH3I under basic condition (K2CO3) in DMF, heated at 90 oC for 5 min, followed by purification using a semi-preparative reverse-phase HPLC column under optimized conditions. The biodistribution study of [11C]HC608 was performed using male Sprague Dawley (SD) rats. Animals were euthanized at 5, 30, 60 min post i.v. injection of [11C]HC608. Tissues of interests were collected, weighed, and counted on an automated Beckman Gamma counter. The uptake of radioactivity was calculated as percentage injected dose per gram (%ID/gram). In vitro autoradiography was conducted on 20µm SD rat brain frozen section. After the section was cut, the slides were incubated with [11C]HC608 (30 µCi/slide) at room temperature for 30 min. For the block study, slides were incubated with [11C]HC608 and 1 µM of HC070, a potent TRPC5 inhibitor with IC50 values of 9.3 and 46.0 nM for TRPC5 and 4, respectively. Following the incubation, the brain slides were washed and then exposed on the Storage Phosphor Screen in an imaging cassette in -20 oC at dark for 3 h. After that, the visualization and quantification of the autoradiographic images were done using Typhoon FLA 7000 scanner (GE). Results: The radiosynthesis of [11C]HC608 was successfully achieved with good radiochemical yield (30-40%), high chemical and radiochemical purity (&gt; 99%), and high specific activity (&gt; 1000 mCi/µmol, decay corrected to EOS). Heart, lung, pancreas, kidney and liver have relative high uptake (&gt;1.5 %ID/gram) at 5 min post injection. The radioactivity was washed out quickly from all tissues except liver; at 60 min, only liver retains 2.22 %ID/gram and all other tissues have &lt;1.0 %ID/gram. The brain uptake (%ID/gram) was 0.51 at 5 min, 0.37 at 30 min, and 0.25 at 60 min. In vitro autoradiography showed the brain uptake of [11C]HC608 is significantly reduced (~60%) in the presence of HC070. Conclusions: Our preliminary biodistribution study suggested that [11C]HC608 is able to penetrate the blood brain barrier and accumulate in the brain sufficiently. In vitro autoradiography results reveals [11C]HC608 specifically binds towards TRPC5. Together, [11C]HC608 has great potential to be a PET tracer for imaging TRPC5 in vivo. Further investigation of [11C]HC608 in different disease models of animal is in progress. Research support: NIH/NINDS&amp;NIA NS075527 and NS103988. References: ADDIN EN.REFLIST [1] Fowler, Melissa A., Kyriaki Sidiropoulou, Emin D. Ozkan, Christopher W. P. PloS One 2007, 2, e573. [2] He Z, Jia C, Feng S, Zhou K, Tai Y, Bai X, Wang Y. J Neurosci, 2012, 32, 9383. [3] Just, S., Chenard, B.L., Ceci, A., Strassmaier, T., Chong, J.A., Blair, N.T., Gallaschun, R.J., del Camino, D., Cantin, S., D’Amours, M. and Eickmeier, C. PloS One 2018, 1, e0191225.