Evaluation of [18F]fluoroestradiol and ChRERα as a gene expression PET reporter system in rhesus monkey brain

Positron emission tomography (PET) reporter systems are a valuable means of estimating the level of expression of a transgene in vivo. For example, the safety and efficacy of gene therapy approaches to the treatment of neurological and neuropsychiatric disorders could be enhanced via the monitoring of exogenous gene expression levels in the brain. The present study evaluated the ability of a newly developed PET reporter system, [18F]fluoroestradiol, and the estrogen receptor-based PET reporter ChRERα to monitor expression levels of a shRNA designed to suppress choline acetyltransferase (ChAT) expression in rhesus monkey brain. The ChRERα gene and shRNA were delivered together in the same viral vector to monkey striatum. In two monkeys that received injections of viral vector, [18F]fluoroestradiol binding increased by 70% and 86%, respectively, at the target sites compared to pre-injection, demonstrating that ChRERα expression could be visualized in vivo with PET imaging. Postmortem immunohistochemistry confirmed that ChAT expression was significantly suppressed in regions in which [18F]fluoroestradiol uptake was increased. The consistency between PET imaging and immunohistochemical results suggests that [18F] fluoroestradiol and ChRERα can serve as a PET reporter system in rhesus monkey brain for in vivo evaluation of the expression of potential therapeutic agents, such as shRNAs.正电子发射断层扫描（Positron emission tomography, PET）报告系统是评估体内转基因表达水平的可靠工具。例如，通过监测脑内外源基因的表达水平，可优化治疗神经及神经精神疾病的基因疗法的安全性与有效性。本研究评估了新开发的PET报告系统——由[18F]氟雌二醇（[18F]fluoroestradiol）与基于雌激素受体的PET报告分子ChRERα组成——在恒河猴大脑中监测用于抑制胆碱乙酰转移酶（choline acetyltransferase, ChAT）表达的短发夹RNA（short hairpin RNA, shRNA）表达水平的能力。研究中将ChRERα基因与shRNA共同装载至同一病毒载体，并注射至恒河猴纹状体。在两只接受病毒载体注射的恒河猴中，靶位点的[18F]氟雌二醇结合水平较注射前分别升高70%和86%，证实可通过PET成像在体内可视化ChRERα的表达。死后免疫组织化学检测结果证实，在[18F]氟雌二醇摄取升高的脑区，ChAT的表达受到显著抑制。PET成像结果与免疫组织化学结果的一致性表明，[18F]氟雌二醇与ChRERα可作为恒河猴大脑中的PET报告系统，用于体内评估短发夹RNA等潜在治疗剂的表达情况。