Thymoquinone enhances the anticancer activity of doxorubicin against adult T-cell leukemia in vitro and in vivo through ROS-dependent mechanisms

Abstract

Aims: Adult T-cell leukemia (ATL) is a mature T-cell neoplasm associated with human T-cell lymphotropic virus (HTLV-1) infection. Major limitations in Doxorubicin (Dox) chemotherapy are tumor resistance and severe drug complications. Here, we combined Thymoquinone (TQ) with low concentrations of Dox and determined anticancer effects against ATL in cell culture and animal model. Main methods: HTLV-1 positive (HuT-102) and HTLV-1 negative (Jurkat) CD4+ malignant T-cell lines were treated with TQ, Dox and combinations. Viability and cell cycle effects were determined by MTT assay and flow cytometry analysis, respectively. Combination effects on mitochondrial membrane potential and generation of reactive oxygen species (ROS) were assessed. Expression levels of key cell death proteins were investigated by western blotting. A mouse xenograft model of ATL in NOD/SCID was used for testing drug effects and tumor tissues were stained for Ki67 and TUNEL. Key findings: TQ and Dox caused greater inhibition of cell viability and increased sub-G1 cells in both cell lines compared to Dox or TQ alone. The combination induced apoptosis by increasing ROS and causing disruption of mitochondrial membrane potential. Pretreatment with N-acetyl cysteine (NAC) or pan caspase inhibitor significantly inhibited the apoptotic response suggesting that cell death is ROS- and caspase-dependent. TQ and Dox combination reduced tumor volume in NOD/SCID mice more significantly than single treatments through enhanced apoptosis without affecting the survival of mice. Significance: Our combination model offers the possibility to use up to twofold lower doses of Dox against ATL while exhibiting the same cancer inhibitory effects. © 2019