Triptolide cooperates with chemotherapy to induce apoptosis in acute myeloid leukemia cells.

OBJECTIVE: Triptolide has shown antitumor activity in a broad range of solid tumors and on leukemic cells in vitro. MATERIALS AND METHODS: The THP1 cell line and primary acute myeloid leukemia (AML) cells were cultured with triptolide alone or in association with AraC or idarubicin in increasing concentrations. Apoptosis was measured by flow cytometry using DiOC6(3) for the cell line and fluorescein isothiocyanateAnnexin-V and CD45 labeling for fresh blast cells. Protein expression was measured by Western blot. Cell cycle distribution of apoptotic cells was measured by flow cytometry. RESULTS: A synergistic effect was observed when triptolide was added to idarubicin or to AraC to induce apoptosis of THP-1 leukemic cells. The triptolide/AraC association was also investigated in vitro on primary blast cells from 25 AML patients. This combination induced significantly higher percentages of apoptosis vs treatment with each drug separately (p<0.005). The IkappaB and X-linked inhibitor of apoptosis protein contents, which were altered by triptolide in idarubicin-treated cells, were not modified in AraC-treated cells. The association of AraC with triptolide increased the number of cells blocked in the S phase and most underwent apoptosis. CONCLUSION: These results suggest that, by modifying the cell cycle kinetics, AraC sensitizes AML cells to apoptosis induced by low concentration triptolide. The in vitro proapoptotic effect of triptolide associated with the antiproliferative activity of AraC warrants further clinical investigation for treatment of AML patients, especially elderly patients for whom low-dose AraC treatment could be improved by the addition of triptolide.

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

To improve conventional chemotherapeutic efficacy, a combination use of traditional medicines is effective but detailed mechanisms have been rarely elucidated. In the this study, we attempted to clarify how triptolide (PG490), an oxygenated diterpene derived from a Chinese herb, enhances the cisplatin (CDDP)-induced cytotoxicity in urothelial cancer cells. Our results showed that a combined CDDP/triptolide therapy induced apoptosis in urothelial cancer cell lines with wild-type p53, but not in those with mutant-type p53 or normal human urothelium. As the mechanism, triptolide suppressed CDDP-induced p53 transcriptional activity, leading to p21 attenuation, which promoted apoptosis via the activation of c-Jun N-terminal kinase (JNK) and Bax. We further demonstrated that the functional regulation of p53 by triptolide was mediated by an intranuclear association of p53 with glycogen synthase kinase-3beta (GSK3beta), which was inactivated by protein kinase C (PKC). This modulation of the PKC-GSK3beta axis by triptolide was observed in a cancer-specific manner. A mouse xenograft model also showed that a combined CDDP/triptolide therapy completely suppressed tumor growth without any side effects. We expect that cancer-specific enhancement of CDDP-induced cytotoxicity with triptolide may effectively overcome the resistance to a CDDP-based conventional chemotherapy as a treatment for urothelial cancer.

Triptolide sensitizes AML cells to TRAIL-induced apoptosis via decrease of XIAP and p53-mediated increase of DR5.

Acute myeloid leukemia (AML) cells are relatively resistant to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL). We previously reported that triptolide, a potent anticancer agent from a Chinese herb, decreases XIAP in leukemic cells. We evaluated the combination of triptolide and TRAIL and found synergistic promotion of apoptosis in AML cells. XIAP-overexpressing U937 cells (U937XIAP) were more resistant to TRAIL than U937neo cells, and inhibition of XIAP with the small-molecule inhibitor 1396-11 enhanced TRAIL-induced apoptosis, implying XIAP as a resistance factor in AML. Furthermore, triptolide increased DR5 levels in OCI-AML3, while the DR5 increase was blunted in p53-knockdown OCI-AML3 and p53-mutated U937 cells, confirming a role for p53 in the regulation of DR5. In support of this finding, disruption of MDM2-p53 binding with subsequent increase in p53 levels by nutlin3a increased DR5 levels and sensitized OCI-AML3 cells to TRAIL. The combination of 1396-11 plus nutlin3a plus TRAIL was more effective than either the 1396-11 and TRAIL or nutlin3a and TRAIL combinations in OCI-AML3 cells, further supporting the role of triptolide as a sensitizer to TRAIL-induced apoptosis in part by independent modulation of XIAP expression and p53 signaling. Thus, the combination of triptolide and TRAIL may provide a novel strategy for treating AML by overcoming critical mechanisms of apoptosis resistance.

Myriaporone 3/4 structure--activity relationship studies define a pharmacophore targeting eukaryotic protein synthesis.

Myriaporones are naturally occurring compounds which structurally resemble the southern hemisphere of the tedanolide family of macrolide antitumor agents. Despite the fact that myriaporone 3/4 represents only a portion of tedanolide, it nonetheless retains much of its biological activity. We show here that like tedanolide, myriaporone 3/4 inhibits protein synthesis and proliferation of mammalian cells with low nanomolar potencies but displays no prokaryotic growth inhibitory effect. Moreover, myriaporone 3/4 displays a very rapid, reversible and p21-independent activity to block S phase progression in mammalian cells. Structure-activity relationship studies revealed that the C18-C19 epoxide and the C14 hydroxymethyl group (tedanolide numbering) of myriaporone 3/4 are required for cell cycle inhibition. These constitute previously unidentified and/or novel pharmacophores for myriaporone 3/4. Our results show that the important biological activities associated with the structurally complex tedanolides are present and can be harnessed in the chemically much simpler myriaporones. This greatly increases the value of the latter as investigative tools for biochemical research as well as for development of potential therapeutics.