基于PXR/CAR调控血脑屏障上P-糖蛋白的没药甾酮改善脑胶质瘤化疗疗效的作用研究

The expression of P-glycoprotein at the blood-brain barrier plays an important role to cause chemotherapeutic failure of brain glioma. Several studies revealed that pregnane X receptor (PXR) and constitutive androstane receptor (CAR) were involved in the regulation of P-glycoprotein at the blood-brain barrier. Myrrha (moyao) is considered as benefiting Qi and promoting blood circulation, and used for cancer treatment in China. In our previous studies, the results revealed that guggulsterone, the active component of gugulipid, inhibited the expression and function of P-glycoprotein in drug-resistant cancer cells. Recently, we also found that guggulsterone down-regulated the expression and function of P-glycoprotein at the blood-brain barrier. Our pre-experiments showed that guggulsterone increased the sensitivity of brain glioma U118 cells to chemotherapeutic drug through inhibiting PXR, CAR and P-glycoprotein. Based on these findings, we intend to focus on “guggulsterone—PXR/CAR—P-glycoprotein—brain glioma chemotherapy” to undertake the following researches: 1) the regulatory effect of guggulstarone on PXR/CAR at the blood-brain barrier; 2) the modulatory effect of guggulstarone on PXR/CAR-induced MDR1 transcription and P-glycoprotein expression at the blood-brain barrier; 3) the regulatory effect of guggulsterone combined with temozolomide on the proliferation of brain glioma xenograft mouse models. This study will clarify the improving effect of guggulsterone on the chemotherapeutic efficacy of brain glioma through inhibiting PXR/CAR-induced P-glycoprotein expression at the blood-brain barrier.

核受体PXR/CAR调控血脑屏障上P-糖蛋白（P-gp）的表达，是脑胶质瘤化疗失败的重要机制。没药具有理气活血之功效，是常用抗癌中草药；我们前期发现其主要活性成分没药甾酮能抑制肿瘤耐药细胞P-gp表达；近期发现没药甾酮也能抑制血脑屏障上P-gp表达，但机制不清；预实验发现没药甾酮能抑制脑胶质瘤细胞PXR、CAR及P-gp表达，增强化疗敏感性。据此，我们拟围绕“没药甾酮—核受体PXR/CAR—P-gp—脑胶质瘤化疗”这条主线开展以下工作：1）没药甾酮对血脑屏障上PXR/CAR激活的影响；2）没药甾酮对PXR/CAR介导的血脑屏障上MDR1基因转录、P-gp表达和转运功能的调控作用；3）没药甾酮与替莫唑胺联用对人脑胶质瘤细胞原位移植瘤增殖凋亡的影响。项目的完成将明确没药甾酮调控核受体PXR/CAR，抑制血脑屏障上P-gp表达，改善脑胶质瘤化疗疗效的作用及机制；进一步阐明没药的抗癌活性机制。

孕烷X受体（pregnane X receptor, PXR）/组成型雄烷受体（constitutive androstane receptor, CAR）在调控血脑屏障上P-糖蛋白表达中起重要作用。我们体外研究结果表明没药甾酮（Z-guggulsterone）可调控人脑微血管内皮细胞中核受体PXR、CAR、多药耐药基因（multidrug resistance 1, MDR1）和P-糖蛋白表达；进一步研究表明没药甾酮主要通过调控核受体PXR表达，继而下调人脑微血管内皮细胞中MDR1基因转录、P-糖蛋白表达和转运功能；深入研究表明没药甾酮通过下调人脑微血管内皮细胞中蛋白激酶A （protein kinase A，PKA）活性[对蛋白激酶C（protein kinase A，PKC）和蛋白磷酸酶2A（protein phosphatase 2A，PP2A）活性几无影响]和类固醇受体辅助活化因子-1（steroid receptor coactivator-1，SRC-1）表达[对视黄醇X受体（retinoid X receptor α, RXRα）、过氧化物酶体增殖物激活受体γ共激活因子-1α（peroxisome proliferator-activated receptor γ coactivator-1α, PGC-1α)和核受体辅助抑制因子（nuclear receptor corepressor, NCoR）表达几无影响]，阻止PXR与MDR1启动子结合，从而实现对靶基因MDR1转录阻遏。体内研究结果表明没药甾酮不能通过调控核受体PXR表达，继而下调人PXR转基因小鼠脑微血管中MDR1基因转录、P-糖蛋白表达和转运功能；也不能改变化疗药物替莫唑胺体内分布、增加其脑中累积；进一步研究发现没药甾酮可抑制人脑胶质瘤细胞人PXR转基因小鼠原位移植瘤增殖，改善替莫唑胺骨髓抑制，但不能增强替莫唑胺抗脑胶质瘤增殖作用。没药甾酮抗脑胶质瘤作用机制尚需深入研究。