Nitric oxide-releasing nonsteroidal anti-inflammatory drugs (NO-
NSAID) are promising
chemoprevention agents; unlike conventional
NSAIDs, they seem free of appreciable adverse effects, while they retain beneficial activities of their parent compounds. Their effect on colon
carcinogenesis using
carcinoma formation as an end point is unknown. We assessed the chemopreventive properties of
NO-indomethacin (
NCX 530) and
NO-aspirin (
NCX 4016) against
azoxymethane-induced
colon cancer. Seven-week-old male F344 rats were fed control diet, and 1 week later, rats received two weekly s.c.
injections of
azoxymethane (15 mg/kg
body weight). Two weeks after
azoxymethane treatment, rats (48 per group) were fed experimental diets containing
NO-indomethacin (0, 40, or 80 ppm), or
NO-aspirin (1,500 or 3,000 ppm), representing 40% and 80% of the maximum tolerated dose. All rats were killed 48 weeks after
azoxymethane treatment and assessed for colon
tumor efficacy and molecular changes in colonic
tumors and normally appearing colonic mucosa of different dietary groups. Our results suggest that
NO-indomethacin at 40 and 80 ppm and
NO-aspirin at 3,000 ppm significantly suppressed both
tumor incidence (P < 0.01) and multiplicity (P < 0.001). The degree of inhibition was more pronounced with
NO-indomethacin at both dose levels (72% and 76% inhibition) than with
NO-aspirin (43% and 67%).
NO-indomethacin at 40 and 80 ppm and
NO-aspirin at 3,000 ppm significantly inhibited the colon
tumors' (P < 0.01 to P < 0.001) total
cyclooxygenase (COX), including COX-2 activity (52-75% inhibition) and formation of
prostaglandin E2 (
PGE2),
PGF2alpha, and 6-keto-PGF1alpha, and TxB2 from
arachidonic acid (53-77% inhibition).
Nitric oxide synthase 2 (NOS-2) activity and
beta-catenin expression were suppressed in animals given NO-
NSAID. In colonic crypts and
tumors of animals fed these two NO-
NSAIDs, there was a significant decrease in
proliferating cell nuclear antigen labeling when compared with animals fed the control diet. The results of this study provide strong evidence that NO-
NSAIDs possess strong inhibitory effect against colon
carcinogenesis; their effect is associated with suppression of COX and NOS-2 activities and
beta-catenin levels in colon
tumors. These results pave the way for the rational design of human clinical trials.