Department of Clinical Neuroscience, Center for Psychiatry Research, Karolinska Institutet and Stockholm County Council, 17164 Stockholm, Sweden.
Worldwide Research, Development and Medical, Pfizer Inc., Groton, CT 06340, USA.
Molecules. 2023 Jun 7;28(12):4612. doi: 10.3390/molecules28124612.
Muscarinic acetylcholine receptors (mAChR), including M4, draw attention as therapeutic targets for several neurodegenerative diseases including Alzheimer's disease (AD). PET imaging of M4 positive allosteric modulator (PAM) allows qualification of the distribution as well as the expression of this receptor under physiological conditions and thereby helps to assess the receptor occupancy (RO) of a drug candidate. In this study, our aims were (a) to synthesize a novel M4 PAM PET radioligand [11C]PF06885190 (b) to evaluate the brain distribution of [C]PF06885190 in nonhuman primates (NHP) and (c) to analyze its radiometabolites in the blood plasma of NHP. Radiolabeling of [C]PF06885190 was accomplished via N-methylation of the precursor. Six PET measurements were performed using two male cynomolgus monkeys, where three PET measurements were at baseline, two after pretreatment with a selective M4 PAM compound CVL-231 and one after pretreatment with donepezil. The total volume of distribution () of [C]PF06885190 was examined using Logan graphical analysis with arterial input function. Radiometabolites were analyzed in monkey blood plasma using gradient HPLC system. Radiolabeling of [C]PF06885190 was successfully accomplished and the radioligand was found to be stable in the formulation, with radiochemical purity exceeding 99% 1 h after the end of the synthesis. [C]PF06885190 was characterized in the cynomolgus monkey brain where a moderate brain uptake was found at the baseline condition. However, it showed fast wash-out as it dropped to half of the peak at around 10 min. Change of from baseline was around -10% after pretreatment with a M4 PAM, CVL-231. Radiometabolite studies showed relatively fast metabolism. Although sufficient brain uptake of [C]PF06885190 was observed, these data suggest that [C]PF06885190 might have too low specific binding in the NHP brain to be further applied in PET imaging.
毒蕈碱型乙酰胆碱受体（mAChR），包括 M4，作为几种神经退行性疾病（包括阿尔茨海默病（AD））的治疗靶点引起了关注。M4 阳性变构调节剂（PAM）的 PET 成像允许在生理条件下对该受体的分布和表达进行定性，从而有助于评估候选药物的受体占有率（RO）。在这项研究中，我们的目的是：（a）合成一种新型 M4 PAM PET 放射性配体 [11C]PF06885190；（b）评估 [C]PF06885190 在非人类灵长类动物（NHP）中的脑分布；（c）分析其在 NHP 血浆中的放射性代谢产物。通过前体的 N-甲基化完成 [C]PF06885190 的放射性标记。使用两只雄性食蟹猴进行了六次 PET 测量，其中三次 PET 测量在基线时进行，两次在预先用选择性 M4 PAM 化合物 CVL-231 预处理后进行，一次在预先用多奈哌齐预处理后进行。使用带有动脉输入函数的 Logan 图形分析检查 [C]PF06885190 的总分布容积（）。使用梯度 HPLC 系统在猴血浆中分析放射性代谢产物。[C]PF06885190 的放射性标记成功完成，放射性配体在制剂中稳定，合成结束后 1 小时放射性化学纯度超过 99%。在食蟹猴脑中对 [C]PF06885190 进行了表征，在基线条件下发现脑摄取适中。然而，它在大约 10 分钟时迅速下降到峰值的一半，表明其清除速度很快。用 M4 PAM，CVL-231 预处理后，基线的变化约为-10%。放射性代谢产物研究表明其代谢速度相对较快。尽管观察到 [C]PF06885190 的脑摄取足够，但这些数据表明，[C]PF06885190 在 NHP 脑中可能具有太低的特异性结合，无法进一步应用于 PET 成像。
