Anticancer agents act, at least in part, by inducing reactive oxygen and nitrogen species (RONS). We examined the redox effect on SW480 and HT-29 colon cancer cells of four anticancer compounds, arsenic trioxide, phosphoaspirin, phosphosulindac, and nitric oxide-donating aspirin (NO-ASA). All compounds inhibited the growth of both cell lines (IC(50), 10-90 micromol/L) and induced RONS detected by a general RONS molecular probe. NO-ASA, which induced at least four individual RONS (NO, H(2)O(2), superoxide anion, and peroxynitirte), induced apoptotic and necrotic cell death that was RONS-mediated (cell death paralleled RONS levels and was abrogated by N-acetyl cysteine but not by diphenylene iodonium, which displayed prooxidant activity and enhanced cell death). Nuclear factor-kappaB and mitogen-activated protein kinases were modulated by RONS. Thioredoxin-1 (Trx-1), an oxidoreductase involved in redox regulation, was heavily oxidized in response to RONS and mediated the growth inhibitory effect of the anticancer agents; knocking-down trx-1 expression by small interfering RNA abrogated cell death induced by them. These compounds also inhibited the activity of Trx reductase that reduces oxidized Trx-1, whereas the Trx reductase inhibitor aurothiomalate synergized with NO-ASA in the induction of cell death. Our findings indicate that the Trx system mediates to a large extent redox-induced cell death in response to anticancer agents. This mechanism of action may be shared by more anticancer agents and deserves further assessment as a candidate mechanism for the pharmacologic control of cancer.