JNK/AP-1 activation contributes to tetrandrine resistance in T-cell acute lymphoblastic leukaemia

T-cell acute lymphoblastic leukaemia （T-ALL） is a challenging malignancy with a high relapse rate attributed to drug resistance. Tetrandrine （TET）, a bisbenzylisoquinoline alkaloid extracted from a Chinese herb, is a potential anti-cancer and anti-leukaemic drug. In this study we investigated the mechanisms of TET resistance in T-ALL cells in vitro. Among the four T-ALL cell lines tested, Jurkat and CEM ceils exhibited the lowest and highest resistance to TET with IC50 values at 24 h of 4.31±0.12 and 16.53±3.32 pmol/L, respectively. When treated with TET, the activity of transcription factor activator protein 1 （AP-1） was significantly decreased in Jurkat cells but nearly constant in CEM cells. To avoid cell-specific variation in drug resistance and transcription factor activities, we established a TET-R Jurkat subclone with the estimated IC50 value of 10.90±92 pmol/L by exposing the cells to increasing concentrations of TET. Interestingly, when treated with TET, TET-R Jurkat cells exhibited enhanced AP-1 and NF-κB activity, along with upregulation of c-Jun N-terminal kinase （JNK） and extracellular signal-regulated kinase （ERK） signaling pathways, whereas the expression of P-gp was not altered. Selective inhibition of JNK but not ERK suppressed AP-1 activity and TET resistance in TET-R Jurkat cells and in CEM cells. These results demonstrate that Jurkat cells acquire TET resistance through activation of the JNK/AP-1 pathway but not through P-gp expression. The JNK/AP-1 pathway may be a potential therapeutic target in relapsed T-ALL.