Center for Integrated Molecular Brain Imaging, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark.
J Nucl Med. 2014 Apr;55(4):640-6. doi: 10.2967/jnumed.113.128983. Epub 2014 Feb 24.
The serotonin (5-hydroxytryptamine [5-ΗΤ]) 7 receptor (5-HT7R) is the most recently discovered 5-HT receptor, and its physiologic and possible pathophysiologic roles are not fully elucidated. So far, no suitable 5-HT7R PET radioligand is available, thus limiting the investigation of this receptor in the living brain. Here, we present the radiosynthesis and in vivo evaluation of Cimbi-712 (3-{4-[4-(4-methylphenyl)piperazine-1-yl]butyl}p-1,3-dihydro-2H-indol-2-one) and Cimbi-717 (3-{4-[4-(3-methoxyphenyl)piperazine-1-yl]butyl}-1,3-dihydro-2H-indol-2-one) as selective 5-HT7R PET radioligands in the pig brain. The 5-HT7R distribution in the postmortem pig brain is also assessed.
In vitro autoradiography with the 5-HT7R selective radioligand (3)H-labeled (R)-3-(2-(2-(4-methylpiperidin-1-yl)ethyl)pyrrolidine-1-sulfonyl)phenol (SB-269970) was performed on pig brain sections to establish the 5-HT7R binding distribution. Radiolabeling of 5-HT7R selective compounds was performed in an automated synthesis module in which we conducted either palladium-mediated cross coupling ((11)C-Cimbi-712) or conventional O-methylation ((11)C-Cimbi-717) using (11)C-MeI and (11)C-MeOTf, respectively. After intravenous injection of the radioligands in Danish Landrace pigs, the in vivo brain distribution of the ligands was studied. Specific binding of (11)C-Cimbi-712 and (11)C-Cimbi717 to 5-HT7R was investigated by intravenous administration of SB-269970 before a second PET scan.
High 5-HT7R density was found in the thalamus and cortical regions of the pig brain by autoradiography. The radiosynthesis of both radioligands succeeded after optimization efforts (radiochemical yield, ∼20%-30% at the end of synthesis). Time-activity curves of (11)C-Cimbi-712 and (11)C-Cimbi-717 showed high brain uptake and distribution according to 5-HT7R distribution, but the tracer kinetics of (11)C-Cimbi-717 were faster than (11)C-Cimbi-712. Both radioligands were specific for 5-HT7R, as binding could be blocked by pretreatment with SB-269970 for (11)C-Cimbi-717 in a dose-dependent fashion. For (11)C-Cimbi-717, nondisplaceable binding potentials of 6.4 ± 1.2 (n = 6) were calculated in the thalamus.
Both (11)C-Cimbi-712 and (11)C-Cimbi-717 generated a specific binding in accordance with 5-HT7R distribution and are potential PET radioligands for 5-HT7R. (11)C-Cimbi-717 is the better candidate because of the more reversible tracer kinetics, and this radioligand showed a dose-dependent decline in cerebral binding after receptor blockade. Thus, (11)C-Cimbi-717 is currently the most promising radioligand for investigation of 5-HT7R binding in the living human brain.
血清素（5-羟色胺[5-HT]）7 受体（5-HT7R）是最近发现的 5-HT 受体，其生理和可能的病理生理作用尚未完全阐明。到目前为止，还没有合适的 5-HT7R PET 放射性配体，因此限制了对活脑中该受体的研究。在这里，我们介绍了 Cimbi-712（3-{4-[4-（4-甲基苯基）哌嗪-1-基]丁基}-1,3-二氢-2H-吲哚-2-酮）和 Cimbi-717（3-{4-[4-（3-甲氧基苯基）哌嗪-1-基]丁基}-1,3-二氢-2H-吲哚-2-酮）作为选择性 5-HT7R PET 放射性配体在猪脑中的合成和体内评价。还评估了死后猪脑中 5-HT7R 的分布。
使用 5-HT7R 选择性放射性配体（3）H-标记（R）-3-（2-（2-（4-甲基哌啶-1-基）乙基）吡咯烷-1-磺酰基）苯酚（SB-269970）进行离体放射自显影，以建立 5-HT7R 结合分布。在自动化合成模块中进行了 5-HT7R 选择性化合物的放射性标记，其中我们分别使用（11）C-MeI 和（11）C-MeOTf 进行钯介导的交叉偶联（（11）C-Cimbi-712）或常规 O-甲基化（（11）C-Cimbi-717）。在丹麦兰德瑞斯猪静脉注射放射性配体后，研究了配体在体内的脑分布。通过静脉注射 SB-269970 后，研究了（11）C-Cimbi-712 和（11）C-Cimbi717 与 5-HT7R 的特异性结合。
通过放射自显影在猪脑中发现了高 5-HT7R 密度在丘脑和皮质区域。经过优化努力（放射性化学产率，合成结束时约为 20%-30%），两种放射性配体的合成均取得成功。（11）C-Cimbi-712 和（11）C-Cimbi-717 的时间-活性曲线显示，根据 5-HT7R 分布，脑摄取和分布均较高，但（11）C-Cimbi-717 的示踪剂动力学比（11）C-Cimbi-712 更快。两种放射性配体均为 5-HT7R 的特异性配体，因为（11）C-Cimbi-717 的结合可以被 SB-269970 以剂量依赖性方式阻断。对于（11）C-Cimbi-717，在丘脑计算出的不可置换结合潜能为 6.4±1.2（n=6）。
（11）C-Cimbi-712 和（11）C-Cimbi-717 均与 5-HT7R 分布一致产生特异性结合，并且是 5-HT7R 的潜在 PET 放射性配体。（11）C-Cimbi-717 是更好的候选者，因为其示踪剂动力学更具可逆性，并且这种放射性配体在受体阻断后显示出脑结合的剂量依赖性下降。因此，（11）C-Cimbi-717 是目前研究 5-HT7R 在人类活体大脑中结合的最有前途的放射性配体。
