Tauchi T, Shin-ya K, Sashida G, Sumi M, Okabe S, Ohyashiki J H, Ohyashiki K
First Department of Internal Medicine, Tokyo Medical University, Shinjuku-ku, Tokyo, Japan.
Oncogene. 2006 Sep 21;25(42):5719-25. doi: 10.1038/sj.onc.1209577. Epub 2006 May 1.
The telomerase complex is responsible for telomere maintenance and represents a promising neoplasia therapeutic target. Recently, we have demonstrated that treatment with a G-quadruplex-interactive agent, telomestatin reproducibly inhibited telomerase activity in the BCR-ABL-positive leukemic cell lines. In the present study, we investigated the mechanisms of apoptosis induced by telomerase inhibition in acute leukemia. We have found the activation of caspase-3 and poly-(ADP-ribose) polymerase in telomestatin-treated U937 cells (PD20) and dominant-negative DN-hTERT-expressing U937 cells (PD25). Activation of p38 mitogen-activated protein (MAP) kinase and MKK3/6 was also found in telomestatin-treated U937 cells (PD20) and dominant-negative DN-hTERT-expressing U937 cells (PD25); however, activation of JNK and ASK1 was not detected in these cells. To examine the effect of p38 MAP kinase inhibition on growth properties and apoptosis in telomerase-inhibited cells, we cultured DN-hTERT-expressing U937 cells with or without SB203580. Dominant-negative-hTERT-expressing U937 cells stopped proliferation on PD25; however, a significant increase in growth rate was observed in the presence of SB203580. Treatment of SB203580 also reduced the induction of apoptosis in DN-hTERT-expressing U937 cells (PD25). These results suggest that p38 MAP kinase has a critical role for the induction of apoptosis in telomerase-inhibited leukemia cells. Further, we evaluated the effect of telomestatin on the growth of U937 cells in xenograft mouse model. Systemic intraperitoneal administration of telomestatin in U937 xenografts decreased tumor telomerase levels and reduced tumor volumes. Tumor tissue from telomestatin-treated animals exhibited marked apoptosis. None of the mice treated with telomestatin displayed any signs of toxicity. Taken together, these results lay the foundations for a program of drug development to achieve the dual aims of efficacy and selectivity in vivo.
端粒酶复合物负责端粒的维持，是一个很有前景的肿瘤治疗靶点。最近，我们证明了用一种G-四链体相互作用剂端粒抑素处理，可在BCR-ABL阳性白血病细胞系中持续抑制端粒酶活性。在本研究中，我们探讨了急性白血病中端粒酶抑制诱导细胞凋亡的机制。我们发现在经端粒抑素处理的U937细胞（PD20）和表达显性负性DN-hTERT的U937细胞（PD25）中，半胱天冬酶-3和聚（ADP-核糖）聚合酶被激活。在经端粒抑素处理的U937细胞（PD20）和表达显性负性DN-hTERT的U937细胞（PD25）中还发现p38丝裂原活化蛋白（MAP）激酶和MKK3/6被激活；然而，在这些细胞中未检测到JNK和ASK1的激活。为了研究p38 MAP激酶抑制对端粒酶抑制细胞生长特性和细胞凋亡的影响，我们在有或没有SB203580的情况下培养表达DN-hTERT的U937细胞。表达显性负性hTERT的U937细胞在PD25时停止增殖；然而，在存在SB203580的情况下观察到生长速率显著增加。用SB203580处理也减少了表达DN-hTERT的U937细胞（PD25）中细胞凋亡的诱导。这些结果表明，p38 MAP激酶在端粒酶抑制的白血病细胞凋亡诱导中起关键作用。此外，我们评估了端粒抑素对异种移植小鼠模型中U937细胞生长的影响。在U937异种移植瘤中全身腹腔注射端粒抑素可降低肿瘤端粒酶水平并减小肿瘤体积。经端粒抑素处理的动物的肿瘤组织表现出明显的细胞凋亡。用端粒抑素处理的小鼠均未表现出任何毒性迹象。综上所述，这些结果为实现体内疗效和选择性双重目标的药物开发计划奠定了基础。
