Department of Molecular and Clinical Pharmacology , University of Liverpool , Liverpool L69 3GL , U.K.
Department of Molecular and Clinical Cancer Medicine , University of Liverpool , Liverpool L69 3BX , U.K.
Mol Pharm. 2018 Aug 6;15(8):3557-3572. doi: 10.1021/acs.molpharmaceut.8b00547. Epub 2018 Jul 10.
The weak base antipsychotic clozapine is the most effective medication for treating refractory schizophrenia. The brain-to-plasma concentration of unbound clozapine is greater than unity, indicating transporter-mediated uptake, which has been insufficiently studied. This is important, because it could have a significant impact on clozapine's efficacy, drug-drug interaction, and safety profile. A major limitation of clozapine's use is the risk of clozapine-induced agranulocytosis/granulocytopenia (CIAG), which is a rare but severe hematological adverse drug reaction. We first studied the uptake of clozapine into human brain endothelial cells (hCMEC/D3). Clozapine uptake into cells was consistent with a carrier-mediated process, which was time-dependent and saturable ( V = 3299 pmol/million cells/min, K = 35.9 μM). The chemical inhibitors lamotrigine, quetiapine, olanzapine, prazosin, verapamil, indatraline, and chlorpromazine reduced the uptake of clozapine by up to 95%. This could in part explain the in vivo interactions observed in rodents or humans for these compounds. An extensive set of studies utilizing transporter-overexpressing cell lines and siRNA-mediated transporter knockdown in hCMEC/D3 cells showed that clozapine was not a substrate of OCT1 (SLC22A1), OCT3 (SLC22A3), OCTN1 (SLC22A4), OCTN2 (SLC22A5), ENT1 (SLC29A1), ENT2 (SLC29A2), and ENT4/PMAT (SLC29A4). In a recent genome-wide analysis, the hepatic uptake transporters SLCO1B1 (OATP1B1) and SLCO1B3 (OATP1B3) were identified as additional candidate transporters. We therefore also investigated clozapine transport into OATP1B-transfected cells and found that clozapine was neither a substrate nor an inhibitor of OATP1B1 and OATP1B3. In summary, we have identified a carrier-mediated process for clozapine uptake into brain, which may be partly responsible for clozapine's high unbound accumulation in the brain and its drug-drug interaction profile. Cellular clozapine uptake is independent from currently known drug transporters, and thus, molecular identification of the clozapine transporter will help to understand clozapine's efficacy and safety profile.
弱碱性抗精神病药氯氮平是治疗难治性精神分裂症最有效的药物。未结合的氯氮平在脑和血浆中的浓度大于 1，表明存在转运体介导的摄取，而这一过程尚未得到充分研究。这很重要，因为它可能对氯氮平的疗效、药物相互作用和安全性有重大影响。氯氮平使用的一个主要限制是氯氮平引起的粒细胞缺乏症/粒细胞减少症（CIAG）的风险，这是一种罕见但严重的血液药物不良反应。我们首先研究了氯氮平进入人脑血管内皮细胞（hCMEC/D3）的摄取情况。氯氮平进入细胞的摄取符合载体介导的过程，该过程具有时间依赖性和饱和性（ V = 3299 pmol/百万细胞/分钟， K = 35.9 μM）。化学抑制剂拉莫三嗪、喹硫平、奥氮平、普萘洛尔、维拉帕米、吲哚拉明和氯丙嗪可使氯氮平的摄取减少多达 95%。这在一定程度上可以解释在啮齿动物或人体内观察到的这些化合物的体内相互作用。利用过表达转运体的细胞系和 hCMEC/D3 细胞中的 siRNA 介导的转运体敲低进行的广泛研究表明，氯氮平不是 OCT1（SLC22A1）、OCT3（SLC22A3）、OCTN1（SLC22A4）、OCTN2（SLC22A5）、ENT1（SLC29A1）、ENT2（SLC29A2）和 ENT4/PMAT（SLC29A4）的底物。在最近的全基因组分析中，鉴定出肝摄取转运体 SLCO1B1（OATP1B1）和 SLCO1B3（OATP1B3）为额外的候选转运体。因此，我们还研究了氯氮平进入 OATP1B 转染细胞的转运情况，发现氯氮平既不是 OATP1B1 和 OATP1B3 的底物，也不是其抑制剂。总之，我们已经确定了脑内氯氮平摄取的载体介导过程，这可能部分解释了氯氮平在脑中的高未结合浓度及其药物相互作用模式。细胞内氯氮平摄取与目前已知的药物转运体无关，因此，氯氮平转运体的分子鉴定将有助于了解氯氮平的疗效和安全性。
