Fisetin reduces the resistance of MOLT-4 and K562 cells to TRAIL-induced apoptosis through upregulation of TRAIL receptors.

TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that is capable of apoptosis induction selectively in tumor cells. Although TRAIL has been harnessed in numerous clinical trials, resistance to TRAIL-induced apoptosis is a major challenge ahead of this therapy in various cancer models as well as in leukemia. Since histone deacetylases (HDACs) are known to affect drug resistance in malignant cells, the present study aimed to evaluate the potential of fisetin for sensitization of MOLT-4 and K-562 leukemic cells to TRAIL-induced apoptosis. The MOLT-4 and K-562 cells were treated with increasing concentrations of fisetin and its impact on the growth inhibition and apoptosis induction of TRAIL were evaluated by MTT and Annexin V/7-AAD assays. The impact of fisetin on the mRNA and protein expression levels of apoptosis regulatory genes such as BIRC2/c-IAP1, CFLAR/cFLIP, CASP3, CASP7, CASPP9, TNFRSF10A/DR4, TNFRSF10B/DR5, and BID were examined by PCR array, qRT-PCR, and flow cytometry. Pre-treatment of MOLT-4 and K-562 cells with fisetin reduced the IC50 of TRAIL in growth inhibition along with an improvement in apoptosis induction by TRAIL. The expression of the BIRC2 gene encoding antiapoptotic protein c-IAP1 downregulated in the fisetin-treated cells while the expressions of TNFRSF10A and TNFRSF10B encoding TRAIL death receptors increased. Fisetin demonstrated a potential for alleviating the TRAIL resistance by modulating the apoptosis regulatory factors and improving the expressions of TRAIL receptors that could facilitate the application of TRAIL in cancer therapies.