The mechanisms underlying the anti-tumorigenic properties of
cyclooxygenase inhibitors are not well understood. One novel hypothesis is alterations in gene expression. To test this hypothesis
sulindac sulfide, which is used to treat
familial adenomatous polyposis, was selected to detect gene modulation in human colorectal cells at physiological concentrations with microarray analysis. At micromolar concentrations,
sulindac sulfide stimulated apoptosis and inhibited the growth of
colorectal cancer cells on soft
agar.
Sulindac sulfide (10 microm) altered the expression of 65 genes in SW-480
colorectal cancer cells, which express
cyclooxygenase-1 but little
cyclooxygenase-2. A more detailed study of 11 genes revealed that their expression was altered in a time- and dose-dependent manner as measured by real-time RT-PCR. Northern analysis confirmed the expression of 9 of these genes, and Western analysis supported the conclusion that
sulindac sulfide altered the expression of these
proteins.
Cyclooxygenase-deficient HCT-116 cells were more responsive to
sulindac sulfide-induced gene expression than SW-480 cells. However, this response was diminished in HCT-116 cells overexpressing
cyclooxygenase-1 compared with normal HCT-116 cells suggesting the presence of
cyclooxygenase attenuates this response. However,
prostaglandin E2, the main product of
cyclooxygenase, only suppressed the
sulindac sulfide-induced expression of two genes, with little known
biological function while it modulated the expression of two more. The most likely explanation for this finding is the metabolism of
sulindac sulfide to inactive metabolites by the
peroxidase activity of
cyclooxygenase. In conclusion, this is the first report showing
sulindac sulfide, independent of
cyclooxygenase, altered the expression of several genes possibly linked to its anti-tumorigenic and pro-apoptotic activity.