Effects of combination chemoprevention on markers of cell turnover and agent action in colorectal mucosal tissue from patients in a Phase III trial of difluoromethylornithine and sulindac for prevention of colon polyp recurrence

CN21-04

Ornithine decarboxylase (ODC) is the first enzyme in polyamine synthesis and is a target of the MYC gene. MYC is regulated by the adenomatous polyposis coli (APC) tumor suppressor gene in intestinal and colonic epithelial cells in humans and rodents (1). Non-steroidal anti-inflammatory drugs (NSAIDS) influence arachidonic acid metabolism in part by inhibiting the activities of cyclooxygenase 1 (COX1) and/or cyclooxygenase 2 (COX2), but NSAIDS also activate polyamine catabolism and export via COX-independent mechanisms (2, 3). Difluoromethylornithine (DFMO) is an irreversible inhibitor of ODC, which has been developed as a cancer chemopreventive agent (4). DFMO or any of several NSAIDS alone reduces colon carcinogenesis in rodent models, and the combination of DFMO and NSAIDS acts at least synergistically in both rodent and human cell models of colonic neoplasia (1). A polymorphism affecting ODC expression has been associated with risk of polyp recurrence in humans with prior polyps, especially in individuals taking aspirin (5, 6), which further supports the rationale for combination chemoprevention with agents acting to suppress polyamine synthesis and/or activate polyamine catabolism and export.
 A Phase III trial of combination DFMO (500 mg/day) and the NSAID sulindac (150 mg/day) versus placebo for three years for prevention of colon polyps was conducted in patients with prior sporadic polyps. Three hundred and seventy-five patients were randomized and stratified for aspirin usage in the trial. The treatment dramatically reduced the recurrence of total and advanced polyps, independent of aspirin. Treatment was associated with a statistically significant decrease in polyamine contents in apparently normal colorectal mucosa. Aspirin use was associated with a decrease in levels of prostaglandin E2 (PGE2) in normal colorectal biopsies at baseline. However, treatment with DFMO and sulindac was not associated a statistically significant further decrease in colorectal mucosal PGE2 in this trial. Measures of apoptosis and proliferation in apparently normal colorectal mucosa were unaffected by the treatment.
 These data indicate that colorectal mucosal polyamine contents are markers of treatment effects mediated by the combination of DFMO and sulindac. Colorectal mucosal PGE2 levels, however, were not associated with treatment in this study. Measures of cell turnover (proliferation and apoptosis) in apparently normal colonic mucosa were not associated with treatment and its effects on polyp recurrence. The measures of colorectal biopsy polyamine and PGE2 levels support the hypothesis that combination DFMO and sulindac are acting to reduce tissue levels of the polyamines in a manner associated with a dramatic reduction in recurrence of neoplastic colon polyps.
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