Department of Clinical Pharmacy and Biopharmaceutics, Graduate School of Medicine, Mie University, Edobashi, Tsu, Mie 514–8507, Japan.
Biol Pharm Bull. 2012;35(1):54-8. doi: 10.1248/bpb.35.54.
The aim of this study was to elucidate the characteristics of the transport of lactone and carboxylate forms of SN-38 (SN-38L and SN-38C, respectively), a metabolite of irinotecan hydrochloride (CPT-11), with the human intestinal epithelial cell line, Caco-2. We examined SN-38L and SN-38C uptake from the apical side into Caco-2, and the effects of various compounds on the uptake of SN-38L. SN-38L and SN-38C in the cells were determined by HPLC with a fluorescence detector. When either SN-38L (0.5 µM) or SN-38C (0.5 µM) was added extracellularly at 37°C, the accumulation of SN-38L into the cells was about 10-fold higher than that of SN-38C, suggesting a dominant role of the lactone form in the uptake of SN-38 into Caco-2. The accumulation of SN-38L in Caco-2 increased time-dependently up to 10 min at 37°C, whereas the accumulation markedly decreased at 4°C. The initial uptake rate of SN-38L approached saturation at high concentrations with Michaelis-Menten constant and 'Hill coefficient,' 2.84±1.00 μM and 2.13±1.14, respectively (mean±S.E.). The accumulation of SN-38L was markedly inhibited by baicalin, an active ingredient of a Chinese herbal medicine, Hange-Shashin-To, as well as CPT-11. The type of inhibition by baicalin was competitive. In contrast, concomitant sulfobromophthalein, taurocholate and estrone 3-sulfate significantly increased SN-38L uptake. These results suggest that apical uptake of SN-38 by Caco-2 is dominantly performed as a lactone form through a specific transporter, which is competitively inhibited by baicalin.
本研究旨在阐明伊立替康盐酸盐（CPT-11）代谢产物 SN-38 的内酯和羧酸盐形式（分别为 SN-38L 和 SN-38C）通过人肠上皮细胞系 Caco-2 的转运特征。我们检测了 SN-38L 和 SN-38C 从顶端侧进入 Caco-2 的摄取情况，并研究了各种化合物对 SN-38L 摄取的影响。细胞内的 SN-38L 和 SN-38C 通过 HPLC 与荧光检测器进行测定。当 37°C 时，细胞外分别添加 0.5μM 的 SN-38L 或 SN-38C 时，SN-38L 向细胞内的积累量约为 SN-38C 的 10 倍，表明内酯形式在 SN-38 进入 Caco-2 中的摄取中起主导作用。在 37°C 下，SN-38L 在 Caco-2 中的积累随时间呈时间依赖性增加，最多可达 10 分钟，而在 4°C 下，积累量明显减少。SN-38L 的初始摄取速率在高浓度下接近饱和，米氏常数和“Hill 系数”分别为 2.84±1.00μM 和 2.13±1.14（平均值±S.E.）。黄芩苷作为一种中药汉方制剂的有效成分，以及 CPT-11，可显著抑制 SN-38L 的积累。黄芩苷的抑制类型为竞争性。相比之下，同时添加磺溴酚酞、牛磺胆酸盐和雌酮 3-硫酸盐可显著增加 SN-38L 的摄取。这些结果表明，Caco-2 通过特定转运体以内酯形式主导 SN-38 的顶端摄取，该转运体被黄芩苷竞争性抑制。
