Imatinib-induced apoptosis could be enhanced by Triptolide in Imatinib-resistant chronic myeloid leukemia cell line through down-regulation of HIF-1αand Nrf2

Abstract

BackgroundThe emergence of Imatinib has brought a new era for the treatment of chronic myeloid leukemia. However, resistant to Imatinib might lead to the treatment failure and death of patients. Thus, finding a drug which could enhance the Imatinib-induced apoptosis in vitro could provide the experimental base for the treatment of chronic myeloid leukemia. K562 cell line is a common cell line used in the study of chronic myeloid leukemia while K562/G cell line which is resistant to Imatinib is derived from K562 cell line. AimThis study aims to explore whether low-dose Triptolide(TPL) could enhance the Imatinib-induced apoptosis in K562/G cells and related mechanism. MethodsK562/G cells were subjected to different treatments and thereafter MTT assay, flow cytometry and Western blot or RT-PCR were used to determine IC50, apoptotic status and expression of Nrf2, HIF-1α and their target genes. ResultsTriptolide is highly cytotoxic to K562/G cells in a concentration-dependent manner. To determine the combination effect of TPL and anticancer agents, K562/G cells were exposed to Imatinib(50μM) with or without TPL (25nM) for 24h. The apoptotic cells were determined by PI/Annexin V staining and flow cytometric analysis. Apoptotic ratio of cells treated by Imatinib together with TPL is significantly increased compared to cells treated by Imatinib alone (24.78±1.12 vs. 77.52±7.75, P<0.01). Next, the underlying mechanism was investigated. High expression of Hypoxia-inducible factor-1α (HIF-1α) has been shown to be related with bad clinical outcome in patients while Nrf2 is responsible for chemo-resistanct in cancer cells. Imatinib in combination with TPL could decrease Nrf2 and HIF-1α expression at protein and mRNA levels. Down-stream genes of Nrf2 e.g NQO1, GSR and HO-1 as well as target genes of HIF-1α e.g BNIP3, VEGF and CAIX are also down-regulated at mRNA level. ConclusionTPL could significantly increase the Imatinib-induced apoptotic ratio in K562/G cells through down-regulation of HIF-1α and Nrf2. Disclosures:No relevant conflicts of interest to declare.