Cancer Science Institute of Singapore, National University of Singapore, Singapore, Singapore.
Cancer Biol Ther. 2012 Jan 1;13(1):34-42. doi: 10.4161/cbt.13.1.18437.
Phosphoinositide-3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitors are an emerging class of anti-cancer agents. Here, we tested the hypothesis that the dual PI3K/mTOR inhibitor, PI103, could synergize with the chemotherapeutic agent, 5-fluorouracil (5-FU) by inhibiting E2F1, thymidylate synthase (TS) and enhancing DNA damage. Drug combination effects were assessed in gastric cancer cells using the median-effect equation. The specific effects of inhibition of E2F1 and PIK3CA were examined by siRNA, and mTOR by rapamycin exposure. Protein expression and apoptosis pre- and post-treatment was measured using standard methods. PI103 and 5-FU was synergistic in 3/5 gastric cancer cell lines tested. Synergy was associated with PI3KCA mutation, reduced TS and E2F1 protein levels, increased H2AX phosphorylation and apoptosis. E2F1 siRNA enhanced sensitivity to 5-FU only in cells displaying synergy. Excess thymidine exposure converted synergism to antagonism in all cells. Inhibition of PI3K and mTOR alone enhanced 5-FU cytotoxicity in only 2/3 cell lines that displayed synergy each. In AGS cells, PI3K inhibition alone enhanced 5-FU sensitivity as much as dual PI3K/mTOR inhibition. In HGC27 cells, dual inhibition increased 5-FU sensitivity more than single PI3K or mTOR inhibition. Combined PI103 and 5-FU treatment reduced in vivo tumor growth more than treatment with single agents. PI3K/mTOR inhibitors can enhance 5-FU cytotoxicity in vitro and in vivo, especially in PIK3CA mutant tumor cells. Dual, rather than single, PI3K/mTOR inhibitors may combine better with 5-FU due to cellular heterogeneity in sensitivity to PI3K and mTOR inhibition.
磷酸肌醇 3-激酶（PI3K）和哺乳动物雷帕霉素靶蛋白（mTOR）抑制剂是一类新兴的抗癌药物。在这里，我们通过抑制 E2F1、胸苷酸合成酶（TS）和增强 DNA 损伤，检验了双重 PI3K/mTOR 抑制剂 PI103 与化疗药物 5-氟尿嘧啶（5-FU）协同作用的假设。使用中值效应方程在胃癌细胞中评估药物组合效应。通过 siRNA 抑制 E2F1 和 PIK3CA，通过雷帕霉素暴露抑制 mTOR，检测特定抑制作用。使用标准方法测量治疗前后的蛋白表达和细胞凋亡。在 5 种胃癌细胞系中，PI103 和 5-FU 具有协同作用。协同作用与 PI3KCA 突变、TS 和 E2F1 蛋白水平降低、H2AX 磷酸化和细胞凋亡增加有关。只有在显示协同作用的细胞中，E2F1 siRNA 增强对 5-FU 的敏感性。在所有细胞中，过量胸苷暴露将协同作用转化为拮抗作用。单独抑制 PI3K 和 mTOR 仅在 3/3 显示协同作用的细胞系中增强 5-FU 的细胞毒性。在 AGS 细胞中，单独抑制 PI3K 增强 5-FU 敏感性的程度与双重 PI3K/mTOR 抑制相同。在 HGC27 细胞中，与单独抑制 PI3K 或 mTOR 相比，双重抑制增加了 5-FU 的敏感性。联合 PI103 和 5-FU 治疗比单独使用单一药物治疗更能减少体内肿瘤生长。PI3K/mTOR 抑制剂可增强体外和体内 5-FU 的细胞毒性，尤其是在 PIK3CA 突变肿瘤细胞中。由于对 PI3K 和 mTOR 抑制的敏感性存在细胞异质性，双重而非单一的 PI3K/mTOR 抑制剂可能与 5-FU 更好地结合。
