Thymoquinone synergizes with arsenic and interferon alpha to target human T-cell leukemia/lymphoma

Aims: To reduce the dose of arsenic used against human T-cell leukemia/lymphoma and to sensitize cells to drug treatment, we combined arsenic/interferon-alpha (As/IFN-alpha) with thymoquinone (TQ) in HTLV-I positive (HuT-102 and C91) and HTLV-1 negative (CEM and Jurkat) cell lines. Main methods: Cells were treated with TQ, As/IFN-alpha and combinations. Trypan blue and flow cytometry were used to investigate viability and cell cycle effects. Annexin-V staining, rhodamine assay and western blotting were used to determine apoptosis induction and changes in protein expression. Efficacy of single drugs and combinations were tested in adult T-cell leukemia (HuT-102) mouse xenograft model. Keyfindings: TQ/As/IFN-alpha led to a more pronounced and synergistic time-dependent inhibitory effect on HTLV-I positive cells in comparison to As/IFN-alpha. While As/IFN-alpha combination was not effective against CEM or Jurkat cells, the triple combination TQ/As/IFN-alpha sensitized these two cell lines and led to a pronounced time-dependent inhibition of cell viability. TQ/As/IFN-alpha significantly induced apoptosis in all four cell lines and disrupted the mitochondrial membrane potential. Apoptosis was confirmed by the cleavage of caspase 3 and poly (ADP ribose) polymerase (PARP), downregulation of Bcl-2 and XIAP and upregulation of Bax. TQ alone or in combination activated p53 in HTLV-1 positive cell lines. Strikingly, TQ/As/IFN-alpha resulted in a pronounced significant decrease in tumor volume in HuT-102 xenograft mouse model, as compared to separate treatments or double combination therapy. Significance: Our results suggest a strong potential for TQ to enhance the drug targeting effects of the standard clinical drugs As and IFN-alpha against CD4 + malignant T-cells.