Inhibition of intestinal carcinogenesis by NSAIDs: complementary action of polyamines
aDepartment of Cell Biology and Anatomy, bBiochemistry & Molecular Biophysics, cCancer Biology Division; Arizona Cancer Center, The University of Arizona, Tucson, AZ, United States
The non-steroidal anti-inflammatory drug (NSAID) sulindac is effective in treating patients with familiar adenomatous polyposis (FAP), an inherited polyposis syndrome, caused by germline mutation of the adenomatous polyposis coli (APC) tumor suppressor gene. Sulindac is under investigation as a colon cancer prevention agent in patients with sporadic colon polyps. The anti-carcinogenic effects of sulindac have been attributed to the induction of apoptosis in colonic mucosa, by both cyclooxigenase-dependent and independent mechanisms. Aims. In the present study, we investigated the mechanism of action of sulindac on antitumor activity against murine tumor model of multiple intestinal neoplasia (Min) mice with genetically altered adenomatous polyposis coli (APC) gene (stop codon 850). Methods. Min animals were obtained by crossing APCMin/APC+ males with B6 females. The presence of the mutant APC allele was detected in the DNA extracted from skin using an allele-specific PCR assay. Treatment of Min mice with non-selective COX-2 inhibitor sulindac (167 ppm in AIN93G diet, Teklad, Inc.) started at 35 days, and continued through 110 days, after birth. Mice were sacrificed at age of 110 days and colon and ileum part of intestinal tract was removed and processed for RNA isolation and polyamine analysis. For tumor counts, intestines were removed and analyzed using a dissecting microscope. Results. Using cDNA microarray analysis, we identified a number of sulindac-inducible genes, including the spermidine/spermine N1-acetyltransferase (SSAT), in human Caco-2 colon cancer derived cells. SSAT is the first enzyme in polyamine catabolism and export. Sulindac (167 ppm) reduced intestinal tumor number, induced intestinal SSAT RNA levels and suppressed putrescine contents. Supplementation of putrescine (1% in drinking water) to Min mice treated with sulindac partially reversed the suppressive effect of this agent on tumor formation. Cell culture studies with HCT116 cells indicated that the induction of SSAT by sulindac occurred in the absence of cyclooxygenase enzyme expression. Sulindac induced the expression the polyamine catabolic enzyme spermidine/spermine acetyltransferase (SSAT) in both small and large intestine independent of the APC mutation. Conclusions. The results identify SSAT induction and suppression of polyamine contents as at least one cyclooxygenase-independent mechanism of sulindac action in the Min mouse model of intestinal carcinogenesis.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 896 (Tumor suppressor genes).