NO-donating aspirin inhibits both the expression and catalytic activity of inducible nitric oxide synthase in HT-29 human colon cancer cells

Biochem Pharmacol. 2005 Oct 1;70(7):993-1000. doi: 10.1016/j.bcp.2005.06.027.


Nitric oxide-releasing aspirin (NO-ASA) is emerging as a potentially important chemopreventive agent against colon cancer. We examined in HT-29 human colon adenocarcinoma cells the effect of NO-ASA on the inducible form of nitric oxide synthase (NOS2), an enzyme implicated in colon carcinogenesis. NO-ASA inhibited in a time- and concentration-dependent manner the expression of NOS2 up to 70% compared to control (IC50 for this effect = 46 microM). NO-ASA also decreased the corresponding steady-state mRNA levels and this reduction preceded the reduction of protein levels by at least 6 h. NO-ASA also reduced the enzymatic activity of NOS2, as determined by a direct enzyme assay (maximal reduction = 80%) and by determining the accumulation of NO in the culture medium (IC50 for this effect = 36 microM). These effects of NO-ASA on NOS2 were paralleled by inhibition in cell growth (IC50 = 8.5 microM). These findings indicate that NO-ASA profoundly inhibits both the expression and enzymatic activity of NOS2 and suggest that these effects may represent an important mechanism for the colon cancer chemopreventive effect of NO-ASA.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenocarcinoma / enzymology*
  • Adenocarcinoma / pathology
  • Aspirin / pharmacology*
  • Base Sequence
  • Catalysis
  • Colonic Neoplasms / enzymology*
  • Colonic Neoplasms / pathology
  • DNA Primers
  • HT29 Cells
  • Humans
  • Nitric Oxide Donors / pharmacology*
  • Nitric Oxide Synthase / antagonists & inhibitors*
  • Nitric Oxide Synthase / genetics
  • Nitric Oxide Synthase / metabolism
  • Nitric Oxide Synthase Type II
  • RNA, Messenger / genetics


  • DNA Primers
  • Nitric Oxide Donors
  • RNA, Messenger
  • NOS2 protein, human
  • Nitric Oxide Synthase
  • Nitric Oxide Synthase Type II
  • Aspirin