Genentech, Inc., South San Francisco, California.
Drug Metab Dispos. 2014 Apr;42(4):482-91. doi: 10.1124/dmd.113.055590. Epub 2014 Jan 7.
The study objectives were 1) to test the hypothesis that the lack of P-glycoprotein (P-gp) and the inhibition of breast cancer resistance protein (Bcrp) at the blood-brain barrier after cassette dosing of potent P-gp and Bcrp inhibitors were due to low plasma concentrations of those inhibitors and 2) to examine the effects of P-gp on the unbound brain (C(u,brain)) and cerebrospinal fluid (CSF) concentrations (C(u,CSF)) of P-gp substrates in rats. In vitro inhibition of 11 compounds (amprenavir, citalopram, digoxin, elacridar, imatinib, Ko143 [(3S,6S,12aS)-1,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino[1',2':1,6]pyrido[3,4-b]indole-3-propanoic acid 1,1-dimethylethyl ester], loperamide, prazosin, quinidine, sulfasalazine, and verapamil) on P-gp and Bcrp was examined in P-gp- and Bcrp-expressing Madin-Darby canine kidney cells, respectively. An in vivo study was conducted in wild-type and Mdr1a(-/-) rats after subcutaneous cassette dosing of the 11 compounds at 1-3 mg/kg, and the brain, CSF, and plasma concentrations of these compounds were determined. At the maximal unbound concentrations observed in rats at 1-3 mg/kg, P-gp and Bcrp were not inhibited by a cassette of the 11 compounds. For non-P-gp/Bcrp substrates, similar C(u,brain), C(u,CSF), and unbound plasma concentrations (C(u,plasma)) were observed in wild-type and P-gp knockout rats. For P-gp/Bcrp substrates, C(u,brain) ≤ C(u,CSF) ≤ C(u,plasma) in wild-type rats, but C(u,brain) and C(u,CSF) increased in the P-gp knockout rats and were within 3-fold of C(u,plasma) for six of the seven P-gp substrates. These results indicate that P-gp and Bcrp inhibition at the blood-brain barrier is unlikely in cassette dosing and also suggest that P-gp and Bcrp activity at the blood-CSF barrier is functionally not important in determination of the CSF concentration for their substrates.
1）验证假设，即经组合给药使血脑屏障中的 P-糖蛋白（P-gp）和乳腺癌耐药蛋白（Bcrp）缺失和受到抑制，是由于这些抑制剂在血浆中的浓度较低；2）研究 P-gp 对大鼠脑（C(u,brain)）和脑脊液（CSF）中 P-gp 底物的未结合浓度（C(u,CSF)）的影响。采用体外方法，分别在表达 P-gp 和 Bcrp 的 Madin-Darby 犬肾细胞中检测了 11 种化合物（安普那韦、西酞普兰、地高辛、依利格鲁肽、伊马替尼、Ko143[（3S，6S，12aS）-1，2，3，4，6，7，12，12a-八氢-9-甲氧基-6-（2-甲基丙基）-1，4-二氧代吡嗪[1'，2'：1，6]吡啶并[3，4-b]吲哚-3-丙酸 1，1-二甲基乙酯]、洛哌丁胺、普萘洛尔、奎尼丁、柳氮磺胺吡啶和维拉帕米）对 P-gp 和 Bcrp 的抑制作用。对皮下组合给予这 11 种化合物 1-3mg/kg 的野生型和 Mdr1a(-/-)大鼠进行了体内研究，并测定了这些化合物在脑、CSF 和血浆中的浓度。在 1-3mg/kg 时，大鼠观察到的最大未结合浓度下，组合用药并未抑制 P-gp 和 Bcrp。对于非 P-gp/Bcrp 底物，在野生型和 P-gp 敲除大鼠中观察到相似的 C(u,brain)、C(u,CSF)和未结合血浆浓度（C(u,plasma)）。对于 P-gp/Bcrp 底物，在野生型大鼠中 C(u,brain)≤C(u,CSF)≤C(u,plasma)，但在 P-gp 敲除大鼠中 C(u,brain)和 C(u,CSF)增加，其中 7 种 P-gp 底物中有 6 种的 C(u,brain)和 C(u,CSF)与 C(u,plasma)的比值在 3 倍以内。这些结果表明，在组合给药时血脑屏障中 P-gp 和 Bcrp 的抑制作用不太可能发生，并且还表明，其底物在血-CSF 屏障中 P-gp 和 Bcrp 的活性在确定 CSF 浓度方面功能上并不重要。
