Doxorubicin sensitizes human tumor cells to NK cell- and T-cell-mediated killing by augmented TRAIL receptor signaling

Doxorubicin (DOX) is an anthracycline antibiotic that is widely used to treat different types of malignancy. In this study, it was studied whether DOX could be used to render tumor cells susceptible to apoptosis by NK and T cells. Pretreatment with subapoptotic doses of DOX sensitized tumor cell lines of various histotypes to both NK and T cells resulting in a 3.7 to 32.7% increase in lysis (2.5 mean fold increase, p<0.0001) and a 2.9 to 14.2% increase in lysis (3.0 mean-fold increase, p<0.05), respectively. The sensitizing effect of the drug was primarily dependent on the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/TRAIL-receptor signaling, but not on Fas-ligand, perforin, NKG2D or DNAM-1. The central role of the TRAIL signaling pathway was further supported by an increased expression of TRAIL-R2 on DOX-treated tumor cells and by downregulation of cellular FLICE inhibitory protein, the inhibitors of death receptor-mediated apoptosis. Compared to untreated cells, pretreatment of tumor cells with DOX showed increased processing and activation of caspase-8 on coculture with NK or T cells. The significance of this treatment strategy was confirmed using a xenogeneic tumor-bearing mouse model. Tumor progression was delayed in mice that received either NK cells (p<0.05) or T cells (p<0.0001) following DOX treatment compared to mice receiving either cell type alone. Moreover, combined infusion of both NK and T cells following DOX treatment not only delayed tumor progression but also significantly improved the long-term survival (p<0.01). Based on these findings, it was proposed that DOX can be used to improve the efficacy of adoptive cell therapy in patients with cancer. What's new? Doxorubicin is widely deployed against a variety of cancers. This study asked whether doxorubicin could make tumor cells more vulnerable to death at the hands of immune cells. The authors treated tumor cell lines with the drug, then unleashed NK and T-cells on them. The immune cells were better able to destroy the pre-treated cells, thanks to a boost to the TRAIL-signaling pathway. Thus a combination therapy, using doxorubicin to prep the tumors for assault by adoptively transferred NK cells and T cells, could improve existing treatment methods.