Imperatorin Targets MCL-1 to Sensitize CD133+ Lung Cancer Cells to γδ-T Cell-Mediated Cytotoxicity

CD133+ cancer cells display low sensitivity to anti-cancer treatment; thus, combination treatment with adjuvant drugs is required to improve the efficiency of cancer therapy. The aim of this study was to explore the effect of imperatorin, a linear furanocoumarin compound, on γδ T cell-mediated cytotoxicity against CD133+ lung cancer cells.

CD133+ and CD133- subgroups from A549 and PC9 lung cancer cells were sorted by using flow cytometry. The cytotoxicity of γδ T cells against cancer cells was evaluated by measuring lactate dehydrogenase release. The concentration of tumor necrosis factor-related apoptosis-inducing ligand in the co-culture system was determined by using an enzyme-linked immunosorbent assay. Mitochondrial membrane potential, expression of death receptor 4 (DR4) and DR5 on the cell surface, and rate of apoptosis were measured by flow cytometry. Cytochrome c release and cellular protein expression were detected by western blot analysis.

Compared with CD133- cells, CD133+ cells were resistant to γδ T cell-mediated cytotoxicity. However, imperatorin significantly increased the sensitivity of CD133+ lung cancer cells to γδ T cell treatment in vitro and in vivo. Mechanically, we found that myeloid cell leukemia 1 (MCL-1), an important anti-apoptotic protein belonging to the Bcl-2 family, was overexpressed in CD133+ A549 and PC9 cells compared to their corresponding CD133- cells. Co-treatment with imperatorin and γδ T cells suppressed the expression of MCL-1, and thus promoted the mitochondrial apoptosis mediated by γδ T cells in CD133+ A549 and PC9 lung cancer cells.

Up-regulated MCL-1 in CD133+ lung cancer cells is responsible for their resistance to γδ T cells. Furthermore, the combination of γδ T cells with imperatorin sensitized CD133+ lung cancer cells to γδ T cell-mediated cytotoxicity by targeting MCL-1.