Epoxomicin Sensitizes Resistant Osteosarcoma Cells to TRAIL Induced Apoptosis

Osteosarcoma (OS) is the second most common primary malign bone neoplasm after multiple myeloma. Despite systemic chemotherapy, OS may give rise to local recurrences and metastases. Resistance to chemotherapy is not rare and is likely to occur in a high number of patients. Novel therapeutic approaches are required in order to efficiently treat osteosarcoma. Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) and proteasome inhibitors (epoxomicin, MG132, bortezomib) represent new promising approaches in cancer treatment. The aim of our study is to elucidate the effects of epoxomicin alone or in combination with TRAIL in two TRAIL-resistant OS cell lines, Saos-2 and MG-63 namely. We determined the cytotoxic effects of epoxomicin and/or TRAIL on these two types of OS cells using dimethylthiazolyl 2,5 diphenyltetrazolium bromide (MTT) test and measured apoptosis markers such as pro-apoptotic Bax levels and caspase-3, -8, -9 activities. We used TUNEL assay to demonstrate apoptosis. We investigated dose and time dependent survival rates of OS cells and determined LD50 doses of epoxomicin and TRAIL on OS cell viability after 24, 48, and 72 hour incubations. Concurrent incubation with TRAIL and epoxomicin for 24 hour significantly increased caspase-3, caspase-8, caspase-9 activities and Bax protein levels. Our study demonstrated that the combination of TRAIL with epoxomicin enhances apoptosis, and overcomes TRAIL resistance, denoting promising results for OS therapy in the future.