Celastrol enhances TRAIL‑R2‑mediated apoptosis and cytotoxicity in human renal cell carcinoma cells in caspase‑dependent manner

Celastrol is a triterpene phytochemical known to possess anti‑inflammatory, antioxidant and anticancer properties. The present study investigated the effects of celastrol on tumor necrosis factor‑related apoptosis‑inducing ligand receptor 2 (TRAIL‑R2)‑mediated apoptosis and cytotoxicity in human renal cell carcinoma (RCC) cells when administered in combination with lexatumumab, a human monoclonal agonistic antibody that specifically recognizes TRAIL‑R2. Cytotoxicity was determined by colorimetric assays of cell viability using cell counting kit‑8. The activation of caspases was assessed by quantitative colorimetric assays using caspase‑specific kits. Celastrol significantly enhanced lexatumumab‑induced apoptosis and cytotoxicity in RCC cells. An enhanced effect was also achieved when the duration of treatment with lexatumumab and celastrol was reduced from 24 to 6 h. The expression of TRAIL‑R2 was also remarkably increased by celastrol. Combined treatment with lexatumumab and celastrol significantly triggered activation of the caspase cascade, including caspase‑8, ‑9, ‑6, and ‑3, downstream molecules of death receptors. Furthermore, the cytotoxicity induced by that combination was significantly suppressed by the DR5:Fc chimeric protein, as well as specific inhibitors of caspase‑8, ‑9, ‑6 and ‑3. Taken together, these results indicated that celastrol enhances both TRAIL‑R2‑mediated apoptosis and cytotoxicity by upregulating TRAIL‑R2 and activating the caspase cascade, indicating the possibility of using it in combination with lexatumumab as an innovative therapeutic strategy for treating RCC.