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.
Keywords: Apoptosis, Epoxomicin, MG-63, Osteosarcoma, Saos-2, TRAIL, TRAIL-resistance.
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