Cyclooxygenase-2 (COX-2) inhibitors exert antitumor activity via COX-2-dependent and independent pathways. We wished to evaluate the antitumor activity of
meloxicam, a preferential
COX-2 inhibitor, in
osteosarcoma, the most common primary malignant bone
tumor, and determine whether its antitumor effect is COX-2-dependent. COX-2 expression in the
osteosarcoma cell lines MG-63, HOS and U2-OS was determined by real-time RT-PCR and western blotting. Subsequently, the inhibitory effects of
meloxicam on
osteosarcoma cell growth and invasiveness were assayed by
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and
matrigel invasion assays, respectively. Apoptotic activity was evaluated by terminal
deoxynucleotidyltransferase-mediated dUTP nick end labeling staining and semi-quantification of Bax and Bcl-2 expression by real time RT-PCR and western blotting. Prostaglandin-E(2) (
PGE(2)) production in the presence and absence of
meloxicam was analyzed by
enzyme immunoassay, and to determine whether the effects of
meloxicam are COX-2-dependent or independent,
PGE(2) was added to see if it reversed the effects of
meloxicam. In addition, the effects of
meloxicam on
tumor growth and
metastasis were evaluated in an in vivo mouse model using grafted LM-8 mouse
osteosarcoma cells, together with immunohistochemical analysis for
vascular endothelial growth factor in lung metastatic lesion.
Meloxicam inhibited
PGE(2) production, proliferation and invasiveness especially in MG-63 cells, which express relatively high levels of COX-2. Only high concentrations of
meloxicam caused apoptosis and upregulated Bax
mRNA and
protein in MG-63 cell culture. In contrast,
meloxicam did not induce apoptosis in HOS and U2-OS cells, expressing relatively low levels of COX-2. Exogenous
PGE(2) reduced the effects of
meloxicam on cell viability and invasiveness, but not its effect on Bax
mRNA. In vivo, high doses of
meloxicam suppressed LM-8
tumor growth and lung
metastasis.
Meloxicam, may have both COX-2-dependent and independent inhibitory actions on
osteosarcoma. Its effects are more prominent in
osteosarcoma cells that have relatively high levels of COX-2.