Cyclooxygenase-2 (COX-2) inhibition can inhibit UVB-induced
carcinogenesis in the skin. We have shown that COX-2 is overexpressed in UVB-induced
squamous cell carcinomas (SCCs).
Celecoxib, a specific inhibitor of COX-2, blocks UVB-induced
papillomas and
carcinomas in murine skin. However, as
COX-2 inhibitors of this type are associated with an increased risk of adverse cardiovascular events, we decided to study
nimesulide, a different class of
COX-2 inhibitor, an N-arylmethanesulfonamide derivative not known to have these untoward effects. To assess the antitumor-promoting effects of
nimesulide, 90 mice were equally divided into three groups. Group I animals received no test agent or UVB and served as age-matched controls; group II animals were irradiated with UVB (180 mJ cm(-2), twice weekly for 35 weeks) and group III animals received 300 p.p.m.
nimesulide in
drinking water and were irradiated with UVB as described for group-II.
Nimesulide treatment reduced the growth of UVB-induced
tumors both in terms of
tumor number and
tumor volume. By weeks 25, 30 and 35, the
tumor numbers in the
nimesulide-treated group were 79%, 49% and 53% less than the number occurring in UVB-treated animals whereas
tumor volume was reduced 69%, 54% and 53%, respectively, compared to the UVB-irradiated control group.
Nimesulide also inhibited the malignant progression of SCCs. The reduction in
tumorigenesis was paralleled by a decrease in
cell cycle regulatory proteins (
cyclins A, B1, D1, E, CDK2/4/6) and the antiapoptotic
protein (Bcl2); concomitantly there was an increase in proapoptotic markers,
poly (ADP-ribose) polymerase (PARP) and
caspase-3.
Nimesulide also decreased
ornithine decarboxylase expression and the nuclear accumulation of
nuclear factor kappa B transcriptionally active
protein complexes. These results show that alternative classes of
COX-2 inhibitors may likely be efficacious as
cancer chemopreventive agents and may have an improved therapeutic index.