Effects of nonsteroidal anti-inflammatory drugs on proliferation and on induction of apoptosis in colon cancer cells by a prostaglandin-independent pathway

Nonsteroidal anti-inflammatory drugs (NSAIDs) decrease the incidence of and mortality from colon cancer. We observed that NSAIDs inhibit the proliferation rate, alter the cell cycle distribution, and induce apoptosis in colon cancer cell lines. We evaluated whether the inhibition by NSAIDs of prostaglandin (PG) synthesis is required for their effects on colon cancer cells by studying two human colon cancer cell lines: HCT-15 and HT-29. HCT-15, which lacks cyclooxygenase transcripts, does not produce PGs even when exogenously stimulated, whereas HT-29 produces PGE₂, PGF(2α), and PGI₂. HCT-15 and HT-29 cells, when treated for up to 72 hr with 200 μM sulindac sulfide (an active metabolite of sulindac) or 900 μM piroxicam, showed changes in proliferation, cell cycle phase distribution, and apoptosis. Treatment with PGE₂, PGF(2α), and PGI₂, following a variety of protocols, and at concentrations between 10^-6 and 10^-11 M, failed to reverse the effects of NSAIDs on these three parameters of cell growth. We concluded that NSAIDs inhibit the proliferation rate of the two colon cancer cell lines independent of their ability to inhibit PG synthesis. Thus, alternative mechanisms for their activity on tumor cell growth must be entertained. These observations may be relevant to the mechanism of colon tumor inhibition by NSAIDs.