Department of Medicine, McGill University Health Centre/Royal Victoria Hospital, Montreal, QC, Canada.
J Neurooncol. 2010 Dec;100(3):345-61. doi: 10.1007/s11060-010-0196-7. Epub 2010 May 14.
The antiproliferative effect of tandem somatostatin receptor (SSTR) activation, epidermal growth factor receptor (EGFR) inhibition, and induction of DNA damage was analyzed using octreotide (OCT), a SSTR agonist, the clinical DNA methylating agent temozolomide (TMZ), Iressa, an EGFR inhibitor, and dual EGFR-DNA targeting agents termed "combi-molecules". Using SSTR-expressing glioma cells harbouring low levels of EGFR (U87MG) or transfected to overexpress EGFR (U87/EGFR) or a variant (U87/EGFRvIII), we showed that Iressa, alone or in combination with the DNA damaging agent TMZ, and combi-molecules RA2 and RA5 inhibited EGF-induced phosphorylation of EGFR in U87MG and more moderately in U87/EGFR and U87/EGFRvIII transfected cells. This translated into equivalent levels of Erk 1/2 inhibition. Activation of SSTRs with OCT did not modulate the effects of the various treatments on Erk 1/2 phosphorylation. Likewise, SSTR activation did not alter TMZ- or DNA-damaging combi-molecules, RA2 and RA5, induced p53 activation nor upregulation. However, SSTR activation significantly shifted TMZ-, RA2- and RA5-induced cell-cycle arrest to earlier phases (i.e., G2/M to late S, late S to S, S to G1). Further analysis showed that apoptosis was not induced. This was in agreement with the fact that p53 activation did not induce Bax upregulation nor did EGFR inhibition promote Bad dephosphorylation. Moreover, enhancement of survivin, an anti-apoptotic protein, expression was observed. The results in toto suggest that the combination of SSTR activation with EGFR inhibition and DNA damage affects cell-cycle progression but a disconnection between the targeted signalling pathways in these brain tumour cells precludes synergistic cell-killing by the triple growth inhibitory events.
采用奥曲肽（OCT）、临床 DNA 甲基化药物替莫唑胺（TMZ）、表皮生长因子受体（EGFR）抑制剂 Iressa 以及称为“组合分子”的双重 EGFR-DNA 靶向剂，分析了串联 somatostatin 受体（SSTR）激活、EGFR 抑制和诱导 DNA 损伤的抗增殖作用。使用表达低水平 EGFR 的 SSTR 阳性神经胶质瘤细胞（U87MG）或转染过表达 EGFR 的细胞（U87/EGFR）或变体（U87/EGFRvIII），我们表明，Iressa 单独或与 DNA 损伤剂 TMZ 以及组合分子 RA2 和 RA5 联合使用，可抑制 U87MG 和 U87/EGFR 和 U87/EGFRvIII 转染细胞中 EGF 诱导的 EGFR 磷酸化。这转化为等效水平的 Erk 1/2 抑制。用 OCT 激活 SSTRs 不会调节各种处理方法对 Erk 1/2 磷酸化的影响。同样，SSTR 激活也不会改变 TMZ 或 DNA 损伤的组合分子 RA2 和 RA5 诱导的 p53 激活或上调。然而，SSTR 激活显著将 TMZ、RA2 和 RA5 诱导的细胞周期阻滞转移到更早的阶段（即 G2/M 到晚期 S、晚期 S 到 S、S 到 G1）。进一步分析表明，未诱导细胞凋亡。这与以下事实一致，即 p53 激活不会诱导 Bax 上调，EGFR 抑制也不会促进 Bad 去磷酸化。此外，观察到抗凋亡蛋白 survivin 的表达增强。总的来说，这些结果表明，SSTR 激活与 EGFR 抑制和 DNA 损伤的联合作用会影响细胞周期进程，但这些脑肿瘤细胞中靶向信号通路之间的脱节阻止了三重生长抑制事件的协同细胞杀伤。
