Triptolide induces caspase-dependent cell death mediated via the mitochondrial pathway in leukemic cells

Abstract

Triptolide, a diterpenoid isolated from the Chinese herb Tripterygium wilfordii Hook.f, has shown antitumor activities in a broad range of solid tumors. Here, we examined its effects on leukemic cells and found that, at 100 nM or less, it potently induced apoptosis in various leukemic cell lines and primary acute myeloid leukemia (AML) blasts. We then attempted to identify its mechanisms of action. Triptolide induced caspasedependent cell death accompanied by a significant decrease in XIAP levels. IntroductionTripterygium wilfordii Hook.f, a member of the Celastraceae family of plants, has been used in Chinese medicine for centuries. Triptolide, a diterpenoid, was first isolated from the plant and structurally characterized in 1972 1 and has been used for the treatment of a variety of autoimmune diseases and as an immunosuppressant in patients with organ and tissue transplantations. [1][2][3][4] Recently, triptolide was shown to have antitumor properties by suppressing the growth and inducing apoptosis of a broad range of human tumor cells. [5][6][7][8][9] Triptolide was also shown to sensitize cells to death induced by various agents, such as Apo2/Trail, TNF-␣, and different chemotherapeutic agents. [10][11][12] However, despite the recognized potent antitumor activity of triptolide, our knowledge regarding its mechanism of action is still limited. So far it is known only that triptolide blocks TNF-␣-mediated induction of c-IAP1 and c-IAP2, and the activation of NFB, 10,13,14 and induces caspase activation. 15,16 Acute myeloid leukemia (AML) is an aggressive hematologic malignancy. Despite major efforts during the past 30 years, limited progress has been made in the treatment of AML. The current primary treatment for AML is chemotherapy, which induces cell death mainly by apoptosis mediated by either the intrinsic mitochondrial or the extrinsic death receptor pathway, both of which lead to caspase activation and cell disintegration. The development of innovative therapies and identification of more effective drugs, therefore, remain high priorities for leukemia research. Because of its antitumor properties, triptolide holds promise as a treatment for leukemia. However, other than recent reports that triptolide induced apoptosis in U937 cells by activating caspase-3 and downregulating XIAP, 16 and that it down-regulated Bcr-Abl expression and induced apoptosis in K562 cells, 17 virtually no work has been done to elucidate the activity and mechanisms of triptolide in leukemia. Through an understanding of the molecular mechanisms that mediate the proapoptotic activity of triptolide, it will be possible to better understand its antileukemic effects and to determine whether it is a candidate for clinical use. In addition, knowing the molecular targets of triptolide and its mechanism of action will enable us to design rational combination therapies that more efficiently eradicate leukemic cells. In the study described here, we examined the effects of triptolide on various leukemic cell lines and primary AML blasts a...

Cancer-specific enhancement of cisplatin-induced cytotoxicity with triptolide through an interaction of inactivated glycogen synthase kinase-3β with p53

“…Although several intracellular pathways such as the modification of nuclear factor-kB, Bcl-2, phosphatidylinositol-3 kinase, cyclins and c-myc have been reported to be responsible for the mechanisms underlying the action of triptolide (Lee et al, 1999;Chang et al, 2001;Jiang et al, 2001;Fidler et al, 2003;Yang et al, 2003;Miyata et al, 2005;Yinjun et al, 2005;Carter et al, 2006;Wan et al, 2006), our results showed that the attenuation of p53-dependent p21 induction was a key mechanism to enhance CDDP-induced cytotoxicity. Several recent studies have demonstrated that p53-dependent p21 induction inhibits the apoptotic response, and p21 attenuation may make genotoxic chemotherapeutic agents more effective by subverting the normal repair process or, more directly, by promoting the apoptotic process through inhibition of p21 interaction with apoptosis signal-regulating kinase 1, which is upstream of JNK (Asada et al, 1999;Gartel and Tyner, 2002;Weiss, 2003).…”

“…Triptolide, a diterpenoid triepoxide derived from the herb tripterygium wilfordii, has been reported to have an antiproliferative effect against a broad spectrum of tumors ( Fidler et al, 2003;Yang et al, 2003;Miyata et al, 2005;Yinjun et al, 2005;Carter et al, 2006;Wan et al, 2006). Its high antiproliferative efficiency is attractive for clinical applications, and phase É clinical trials using PG490-88, a water-soluble prodrug of triptolide, have been already attempted in Europe.…”

“…Its high antiproliferative efficiency is attractive for clinical applications, and phase É clinical trials using PG490-88, a water-soluble prodrug of triptolide, have been already attempted in Europe. However, as Shamon et al (1997) reported using a xenograft model, its narrow therapeutic window would be a problem when used as a single agent, and therefore the benefit of the combination use of triptolide at low concentrations with conventional chemotherapeutic agents such as doxorubicin and CPT-11 has been intended (Fidler et al, 2003;Carter et al, 2006). In this study, we demonstrated the usefulness of triptolide at subtoxic concentrations to enhance CDDP-induced cytotoxicity in urothelial cancer cells with wild-type p53, without synergic toxicity to normal urothelium.…”

“…Although it was considered effective in the treatment of inflammatory or autoimmune disorders by the inhibition of cytokine production Chen et al, 2000;Cibere et al, 2003), triptolide also has an antiproliferative effect for tumor cells in vitro and in vivo (Chang et al, 2001;Jiang et al, 2001;Yang et al, 2003;Fidler et al, 2003;Miyata et al, 2005;Carter et al, 2006;Wan et al, 2006). Among several intracellular pathways suggested to be responsible for the antiproliferative effect of triptolide, the suppression of p21 is one of the most convincing mechanisms (Chang et al, 2001;Fidler et al, 2003) but the details have never been elucidated.…”

Triptolide Inhibits Proliferation and Induces Apoptosis of Human Melanoma A375 Cells

“…Therefore, suppression of cell proliferation and induction of cell apoptosis are potent strategies for tumor intervention. Cell apoptosis can be divided into two pathways: the mitochondria-mediated intrinsic pathway and the death receptor-mediated extrinsic pathway (Carter et al, 2006). When the final steps of consequential signaling cascades take place, apoptotic cells can display a series of morphological alterations such as condensed nulei and cell shrinkage (Thornberry, 1998).…”