The increased expression of gonadotropin releasing hormone receptor (GnRH-R) in brain has been strongly linked to Alzheimer disease. Therefore, the development of radiolabeled imaging agents for GnRH-R is relevant for early diagnosis of Alzheimer disease. We have recently disclosed the discovery of two promising compounds displaying nanomolar-range affinity for the GnRH-R. In the present study, a preclinical evaluation of the compound properties was performed to evaluate their potential as single photon emission computed tomography (SPECT) radiotracers for imaging the GnRH-receptor. The compounds were assessed in vitro by performing serum stability analysis by human and rat serum, metabolic profiling by human liver microsomes, and exploratory rat brain autoradiography. The investigated compounds displayed satisfactory stability against human, rat serum, and liver microsomal metabolism, which favors their potential as SPECT-imaging agents. Additionally, we identified and quantified the formation rate of the metabolites by fragmentation of up to five mass spectrometric stages. The GnRH-R rat brain specificity of these compounds was tested in competition with a known ligand for the receptor and the in vitro autoradiography confirmed that compounds 3 and 4 binds to rat GnRH-R in different rat brain regions.
大脑中
促性腺激素释放激素受体(GnRH-R)表达的增加与阿尔茨海默病密切相关。因此,开发 GnRH-R 放射性标记显像剂对于阿尔茨海默病的早期诊断具有重要意义。我们最近发现了两种有前景的化合物,它们对 GnRH-R 具有纳摩尔范围的亲和力。在本研究中,对化合物特性进行了临床前评估,以评估它们作为单光子发射计算机断层扫描 (
SPECT) 放射性示踪剂用于 GnRH 受体成像的潜力。通过对人和大鼠血清进行血清稳定性分析、通过人肝微粒体进行代谢分析以及探索性大鼠脑放射自显影,对这些化合物进行了体外评估。研究的化合物对人、大鼠血清和肝微粒体代谢表现出令人满意的稳定性,这有利于它们作为
SPECT 成像剂的潜力。此外,我们通过多达五个质谱阶段的碎片鉴定并量化了代谢物的形成率。这些化合物的 GnRH-R 大鼠脑特异性通过与受体的已知
配体竞争进行测试,体外放射自显影证实化合物 3 和 4 与大鼠不同脑区的 GnRH-R 结合。