Synergistic effects of meloxicam and conventional cytotoxic drugs in human MG-63 osteosarcoma cells. Cyclooxygenase-2 (COX-2) inhibitors have been shown to exert inhibitory effects on many types of malignant tumors and several groups have suggested that COX-2 inhibitors enhance the cytotoxic effects of other anti-cancer agents. We previously reported that meloxicam has an anti-tumorigenic effect on COX-2-expressing osteosarcoma cells. In the current study, we evaluated the synergy between meloxicam and cisplatin (CDDP), doxorubicin (DXR) and 4-hydroperoxy ifosfamide (4OOH-IFM), using the human osteosarcoma cell line, MG-63. Cytotoxicity was determined using 3-(4,5'-dimethylthiazol-2-yl)-2,5'-diphenyltetrazolium bromide (MTT) assays, and isobolographic analysis was used to evaluate any synergy. Apoptotic activity was determined by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL), and by evaluating Bax and Bcl-2 expression levels using real-time RT-PCR and western blotting analysis. Cell cycling was evaluated by flow cytometry. The cytotoxic effects of CDDP and DXR were enhanced synergistically in the presence of meloxicam and were partially due to an increase in apoptosis. By contrast, meloxicam enhanced neither the cytotoxic nor the apoptotic activity of 4OOH-IFM. Combining meloxicam with DXR significantly up-regulated Bax expression, whereas it down-regulated Bcl-2 expression in combination with CDDP. Furthermore, the number of cells in the G2/M phase was significantly increased in DXR-treated samples by the addition of meloxicam, but not in CDDP-treated or 4OOH-IFM-treated samples. These results suggest a potential clinical application of meloxicam in combination with cytotoxic drugs in patients with COX-2-positive osteosarcoma.