Meyers Nicholas L, Hickling Roger I
Alizyme Therapeutics Limited, Cambridge, UK.
Drugs R D. 2008;9(1):37-63. doi: 10.2165/00126839-200809010-00004.
Renzapride (ATL-1251), a novel benzamide, is currently under clinical development for the treatment of irritable bowel syndrome (IBS). Previous in vitro and in vivo experimental studies have characterized renzapride as a full serotonin 5-HT(4) receptor agonist on the gut and a 5-HT(3) receptor antagonist. Clinical studies have confirmed the therapeutic efficacy, tolerability and safety of renzapride in patients with constipation-predominant IBS. This study set out to characterize the pharmacological profile of renzapride and its potential metabolic products at both 5-HT and other monoamine receptors in the gut.
The affinity of renzapride, its (+) and (-) enantiomers, and its primary metabolite, renzapride N-oxide and its enantiomers, for serotonin receptors was assessed by means of in vitro radioligand binding inhibition studies. After membranes prepared from animal tissue or membranes of cell lines transfected with cloned human receptors had been incubated with radiolabelled ligand with high affinity for a specific receptor, renzapride was added to competitively inhibit this binding. Levels of bound radioligand were measured by filtration and counting of the bound radioactivity. In instances where >50% inhibition of radioligand binding had occurred, the inhibition constant (K(i)) was calculated. Metabolism of renzapride by liver microsomes was assessed by incubating 10 micromol/L renzapride with human liver microsome samples for 60 minutes at 37 degrees C. After the reaction was stopped, the samples were centrifuged and the supernatant analysed for metabolites by high-pressure liquid chromatography (HPLC). The potential inhibitory effects of renzapride on cytochrome P450 (CYP) enzymes were assessed by incubating renzapride at various concentrations over a 1-500 micromol/L concentration range with microsomes genetically engineered to express a single CYP.
Renzapride was selective for serotonergic receptors and, in particular, had high affinity for human 5-HT(3) and guinea-pig 5-HT(4) receptors (K(i) 17 and 477 nm, respectively). Inhibitory properties at 5-HT(2B) receptors were also identified for renzapride, as well as some affinity for 5-HT(2A) and 5-HT(2C) receptors. Renzapride N-oxide and its enantiomers demonstrated much lower affinity for all 5-HT receptors compared with renzapride. Renzapride was metabolized by liver microsomes to a limited extent and there was no significant non-microsomal metabolism of renzapride. Renzapride did not inhibit the major CYP drug-metabolizing enzymes CYP2C9, CYP2D6, CYP1A2, CYP2A6, CYP2C19, CYP2E1 or CYP3A4 at concentrations consistent with use in a clinical setting.
These results confirm and extend earlier studies in animal and human receptors that show renzapride is a potent and generally full 5-HT(4) receptor agonist and 5-HT(3) receptor antagonist. The results reported in the present study indicate that the metabolites of renzapride are minor and are unlikely to contribute to its therapeutic profile or lead to interaction of renzapride with other drugs that inhibit the major drug-metabolizing enzymes in the liver at therapeutic doses. These data contribute to the understanding of the pharmacological actions and metabolic fate of renzapride in vivo.
雷尼必利（ATL - 1251）是一种新型苯甲酰胺，目前正处于治疗肠易激综合征（IBS）的临床开发阶段。以往的体外和体内实验研究已将雷尼必利定性为肠道上的一种完全型5 - 羟色胺（5 - HT）4受体激动剂及5 - HT3受体拮抗剂。临床研究已证实雷尼必利对以便秘为主的肠易激综合征患者具有治疗效果、耐受性及安全性。本研究旨在明确雷尼必利及其潜在代谢产物在肠道中5 - HT及其他单胺受体上的药理学特征。
通过体外放射性配体结合抑制研究评估雷尼必利、其（+）和（-）对映体、其主要代谢产物雷尼必利N - 氧化物及其对映体对5 - 羟色胺受体的亲和力。将动物组织制备的膜或转染了克隆人受体的细胞系膜与对特定受体具有高亲和力的放射性标记配体一起孵育后，加入雷尼必利以竞争性抑制这种结合。通过过滤和对结合放射性的计数来测量结合放射性配体的水平。在放射性配体结合抑制率>50%的情况下，计算抑制常数（K(i)）。通过将10微摩尔/升雷尼必利与人肝微粒体样品在37℃孵育60分钟来评估雷尼必利在肝微粒体中的代谢情况。反应停止后，将样品离心，通过高压液相色谱（HPLC）分析上清液中的代谢产物。通过在1 - 500微摩尔/升浓度范围内以不同浓度孵育雷尼必利与经基因工程改造以表达单一细胞色素P450（CYP）的微粒体，评估雷尼必利对CYP酶的潜在抑制作用。
雷尼必利对5 - 羟色胺能受体具有选择性，尤其对人5 - HT3和豚鼠5 - HT4受体具有高亲和力（K(i)分别为17和477纳米）。还确定了雷尼必利对5 - HT2B受体的抑制特性，以及对5 - HT（2A）和5 - HT（2C）受体的一些亲和力。与雷尼必利相比，雷尼必利N - 氧化物及其对映体对所有5 - HT受体的亲和力要低得多。雷尼必利在肝微粒体中的代谢程度有限，且雷尼必利不存在明显的非微粒体代谢。在与临床应用一致的浓度下，雷尼必利不抑制主要的CYP药物代谢酶CYP2C9、CYP2D6、CYP1A2、CYP2A6、CYP2C19、CYP2E1或CYP3A4。
这些结果证实并扩展了早期在动物和人类受体方面的研究，表明雷尼必利是一种强效且通常为完全型的5 - HT4受体激动剂及5 - HT3受体拮抗剂。本研究报告的结果表明，雷尼必利的代谢产物较少，不太可能对其治疗效果产生影响，也不太可能导致雷尼必利在治疗剂量下与其他抑制肝脏中主要药物代谢酶的药物发生相互作用。这些数据有助于理解雷尼必利在体内的药理作用和代谢命运。
