Herbal Medicines Showing Synergistic Effects with Tumor Necrosis Factor‑Related Apoptosis‑Inducing Ligand (TRAIL) against A549 TRAIL‑resistant Lung Cancer Cells: A Screening Study

Background: Tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL) is a cytokine that activates apoptosis through death receptors on the cell surface and is regarded as a potential anticancer agent. However, many cancer cells are resistant to TRAIL‑induced apoptosis. Objective: The aim is to identify the herbal medicines that could help overcome resistance in TRAIL‑resistant lung cancer cells. Materials and Methods; TRAIL‑resistant A549 cells and 13 herbal medicines with known apoptosis‑related anticancer effects were used in this study: Clematidis Radix, Corydalis Tuber Rhizoma, Paeoniae Radix Rubra, Corni Fructus, Curcumae longae Rhizoma (CLR), Moutan Cortex, Salviae miltiorrhizae Radix, Phellodendri Cortex, Farfarae Flos, Paeoniae Radix Alba, Angelicae gigantis Radix, Coptidis Rhizoma (CR), and Taraxaci Herba. Cytotoxic effects were investigated after a 48‑h incubation, using an 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyl tetrazolium bromide assay, to identify the herbal medicines with the most potent synergistic effects with TRAIL. Results: The majority of the 13 medicines exhibited concentration‑dependent cytotoxicity against A549 cells. Among them, CR and CLR showed the most potent cytotoxic effects, based on the IC50. We then investigated the use of these two medicines in combination with TRAIL and identified synergistic cytotoxic effects against TRAIL‑resistant A549 cells. Conclusion: Synergistic cytotoxic effects of the combination of TRAIL and herbal medicines, in particular, CR and CLR, were confirmed in A549 cells. Therefore, CR and CLR showed potential to be used as candidates to overcome TRAIL resistance. Future studies to identify their underlying mechanism of action are required.