School of Pharmacy, National Taiwan University, No. 1, Sect. 1, Jen-Ai Road, Taipei 100, Taiwan.
Biochem Pharmacol. 2011 May 1;81(9):1136-44. doi: 10.1016/j.bcp.2011.02.013. Epub 2011 Mar 1.
P-glycoprotein (P-gp) overexpression has been demonstrated in many malignancies being a predominant mechanism by which cancer cells develop multidrug resistance. Several categories of P-gp inhibitors have been demonstrated to potentiate anticancer effect induced by cancer chemotherapeutic drugs through competitive inhibition of P-gp pumping activity. Few studies show the agent that selectively acts on P-gp and, by itself, causes cell apoptosis while remain P-gp-deficient cells unaffected. KNG-I-322, a desmosdumotin B derivative, displayed a direct interaction with P-gp and demonstrated selective anti-proliferative and apoptotic activities in P-gp overexpressed Hep3B/VIN other than P-gp-deficient Hep3B cells. KNG-I-322 induced an inhibitory effect on the phosphorylation of mTOR(Ser2448), p70S6K(Thr389) and 4E-BP(Thr37/46) in Hep3B/VIN but not Hep3B cells. The inhibition was fully blocked by the knockdown of P-gp using siRNA techniques. Notably, the P-gp inhibitor, verapamil, also directly interacted with P-gp but significantly diminished KNG-I-322-induced anti-proliferative activity. After the mechanism study, the data showed that KNG-I-322 induced a dramatic down-regulation of GRP78 expression, which was significantly inhibited by verapamil and completely diminished by the knockdown of P-gp. The protein profile analysis of detergent resistant membranes showed that upon the stimulation by KNG-I-322, the level of P-gp expression in non-raft fractions was dramatically increased and, concomitantly, the GRP78 expression was significantly decreased. Taken together, the data suggest that KNG-I-322 induces anticancer activity in Hep3B/VIN cells through a direct interaction with P-gp, leading to the inhibition of mTOR pathways and the induction of GRP78 down-regulation. The data support that KNG-I-322 is a selective anticancer agent against P-gp-overexpressed other than P-gp-deficient cancer cells.
P-糖蛋白（P-gp）过表达已在许多恶性肿瘤中得到证实，是肿瘤细胞产生多药耐药的主要机制之一。已证实几类 P-gp 抑制剂通过竞争性抑制 P-gp 泵的活性，增强抗癌化疗药物的抗癌作用。少数研究表明，某些药物选择性作用于 P-gp，本身就会导致细胞凋亡，而对 P-gp 缺乏的细胞没有影响。KNG-I-322 是一种脱粘蛋白 B 衍生物，与 P-gp 直接相互作用，并在 P-gp 过表达的 Hep3B/VIN 细胞中表现出选择性的抗增殖和凋亡活性，而在 P-gp 缺乏的 Hep3B 细胞中则没有。KNG-I-322 诱导 Hep3B/VIN 细胞中 mTOR（Ser2448）、p70S6K（Thr389）和 4E-BP（Thr37/46）的磷酸化受到抑制，但在 Hep3B 细胞中则没有。用 siRNA 技术敲低 P-gp 可完全阻断这种抑制作用。值得注意的是，P-gp 抑制剂维拉帕米也直接与 P-gp 相互作用，但显著降低了 KNG-I-322 诱导的抗增殖活性。在进行机制研究后，数据显示 KNG-I-322 导致 GRP78 表达明显下调，维拉帕米可显著抑制这种下调，而用 P-gp 敲低则可完全消除下调。去污剂抗性膜的蛋白谱分析显示，在 KNG-I-322 刺激下，非筏蛋白部分的 P-gp 表达水平显著增加，同时 GRP78 表达明显下降。综上所述，数据表明 KNG-I-322 通过与 P-gp 的直接相互作用诱导 Hep3B/VIN 细胞的抗癌活性，导致 mTOR 通路的抑制和 GRP78 的下调。数据表明，KNG-I-322 是一种针对 P-gp 过表达而非 P-gp 缺乏的癌细胞的选择性抗癌药物。
