Department of Pediatrics, College of Medicine, University of Kentucky, Lexington, KY 40536, USA.
Toxicon. 2010 Apr 1;55(4):827-37. doi: 10.1016/j.toxicon.2009.11.019. Epub 2009 Nov 24.
Solute transporters that are selectively expressed on tumor cell membranes could be targeted with small molecule toxins that are selective substrates for these transporters. HeLa cells transfected to express the solute transporter OATP1B1 are exquisitely sensitive in vitro to microcystin LR (MCLR) and its analogs, and undergo rapid morphologic changes after exposure to MCLR. Immunoblot analyses revealed HSP27 phosphorylation increased prior to the rapid MCLR-induced morphologic changes. However, transfection of OATP1B1-expressing cells with HSP27 dominant negative mutants did not reverse MCLR toxicity. Although the MAP kinase p38 inhibitor SB202190 partially reversed MCLR cytotoxicity, the control molecule, SB202474, had similar effects. Unexpectedly, both SB202190 and SB202474 inhibited OATP1B1 uptake activity, indicating an alternative explanation for cytotoxicity reversal that did not involve p38 MAP kinase. Similarly, although the potassium chloride co-transporter (KCC) inhibitor (dihydro-indenyl)oxyalkanoic acid (DIOA), and the anti-oxidant, N-acetyl cysteine (NAC) both reversed MCLR cytotoxicity, both were also found to be unexpected OATP1B1 transport inhibitors. Therefore, the mechanism of MCLR-induced cytotoxicity is obscured by the inhibition of OATP1B1 uptake activity by MAP kinase inhibitors, DIOA, and NAC. Finally, growth of OATP1B1-expressing HeLa xenografts was inhibited by MCLR, suggesting that MCLR structural analogs selected for a broader therapeutic index could target OATP-expressing tumors.
选择性表达在肿瘤细胞膜上的溶质转运体可以作为小分子毒素的靶点，这些毒素是这些转运体的选择性底物。转染表达溶质转运体 OATP1B1 的 HeLa 细胞在体外对微囊藻毒素 LR（MCLR）及其类似物非常敏感，并且在暴露于 MCLR 后迅速发生形态变化。免疫印迹分析显示 HSP27 磷酸化在快速 MCLR 诱导的形态变化之前增加。然而，用 HSP27 显性负突变体转染表达 OATP1B1 的细胞并没有逆转 MCLR 毒性。尽管 MAP 激酶 p38 抑制剂 SB202190 部分逆转了 MCLR 的细胞毒性，但对照分子 SB202474 也具有相似的作用。出乎意料的是，SB202190 和 SB202474 均抑制了 OATP1B1 的摄取活性，表明细胞毒性逆转的另一种解释不涉及 p38 MAP 激酶。同样，尽管钾氯离子共转运体（KCC）抑制剂（二氢-茚基）氧基烷酸（DIOA）和抗氧化剂 N-乙酰半胱氨酸（NAC）均逆转了 MCLR 的细胞毒性，但它们也被发现是意外的 OATP1B1 转运抑制剂。因此，MAP 激酶抑制剂、DIOA 和 NAC 抑制 OATP1B1 摄取活性掩盖了 MCLR 诱导的细胞毒性的机制。最后，MCLR 抑制了表达 OATP1B1 的 HeLa 异种移植物的生长，这表明选择具有更宽治疗指数的 MCLR 结构类似物可以靶向表达 OATP 的肿瘤。
