The Enhancement Of Oridonin By VPA On Inducing Apoptosis Of HL-60 Cells

BackgroundAcute promyelocytic leukemia(APL) accounts for approximately 5% to 10% of acute myeloid leukemia(AML). It is identified as a distinct entity among the AML by its consistent chromosomal translocation t(l5;17) with corresponding PML-RARA and RARA-PML fusion genes. The induction of differentiation and apoptosis are optimal strategies in biotherapy methods of leukemia. Since the introduction of all-trans retinoic acid(ATRA) in the treatment and optimization of the ATRA-based regimens, the CR rate was raised up to 90% to 95% and 5-year disease free survival(DFS) to 74%. The use of arsenic trioxide(ATO) since early 1990 s further improved the clinical outcome of refractory or relapsed as well as newly diagnosed APL. Otherwise, so far only ATRA alone, or combined with ATO, could induce CR in most of patients with APL by inducing terminal differentiation, and they do not work on the types of patients with AML. In addition, side effects and drug resistance were also the limitations of the treatment of patients with APL. Therefore, scientists begin to explore some new techniques or drugs to induce differentiation of leukemia cells. The combination of traditional Chinese medicine and western medicine is an ideal choice to treat patients with AML. In the present study, the synergistic effect of low concentration of oridonin(ORI) plus histone deacetylase inhibitor(HDACi) VPA on HL60 cells was detected.ORI is a diterpenoid compound isolated from the Chinese medicinal herb Isodon rubescens, and possesses a variety of biological effects such as anti-inflammatory functions,antiviral functions and immunoregulatory, etc. In recent reports, ORI has been demonstrated to be an effective antitumor agent with significant effects on some malignancies of different pathological types, included acute lenkmia.HDACi could increase the acetylation level of histone as well as some non-histone proteins, and tightly control in the cells because they are involved in vital processes such as cell cycle progression, differentiation, and apoptosis. Valproic acid(VPA), a well-tolerated agent for neurological disorders, has already been demonstrated to have induce apoptosis or differentiation of leukemia cells either alone or in combination with other anti-leukemic agents. Thereby, we assumed that oridonin in conjunction with VPA may get even more encouraging synergistic effect than that of each of them alone, which was not reported so far. The results indicated that combination of oridonin plus VPA really could induce synergistic effect on inducing apoptosis of HL-60 cells.ObjectiveOridonin(ORI) obtained from the traditional Chinese herbal medicine rabdosia rubescens exerts potent antitumor activities in cancer cells. Valproic acid(VPA), as a potent histone deacetylase inhibitor(HDACi), possesses significant antileukemic activitites. But no research shows the anti-leukemic effect of oridonin cotreated with VPA.MethodsIn this study, we demonstrated that oridonin in combination with VPA synergistically inhibited the proliferation of HL-60 cells.ResultsIn the present study, the anti-proliferation effects of oridonin on acute promyelocytic leukemia HL60 cells and its mechanisms were studied in vitro. HL60 cells were treated with different concentrations of oridonin plus VPA. Cell growth inhibition, apoptosis and related pathways were assessed by MTT assay, RT-PCR as well as flow cytometry(FCM) and western blot analysis. It was demonstrated that oridonin in combination with VPA synergistically inhibited the proliferation of HL-60 cells. The combination of ORI and VPA could trigger obvious apoptosis through the intrinsic pathway, which was contributed to the down-regulation of Bcl-2/Bax ratio,mitochondrial instability and caspase-9 activation,as well as through the extrinsic pathway by triggering Fas/Fas L and caspase-8 activation. Furthermore, MAPK pathway was also involved in inducing apoptosis of HL60 cells by combination of ORI and VPA. Furthermore, the combination of ORI and VPA in vivo also could remarkably prolong survival time or decreased the xenograft tumor size.ConclusionsTaken together, oridonin may serve as a potential anti-leukemia reagent, the novel combination of oridonin plus VPA combination showed a synergistic effect and may be a promising method for treatment of APL.