thromboxane-b2 and Colorectal-Neoplasms

Aspirin may reduce the risk of colorectal neoplasia at doses similar to those recommended for the prevention of cardiovascular disease. Thus, we aimed to address whether enhanced platelet activation, as assessed by the measurement of the urinary excretion of 11-dehydro-TXB(2) (a major enzymatic metabolite of TXB(2)), occurs in patients with colorectal cancer. In 10 patients with colorectal cancer, the urinary excretion of 11-dehydro-TXB(2) was significantly higher than in 10 controls, matched for sex, age and cardiovascular risk factors [1001(205-5571) versus 409(113-984) pg/mg creatinine, respectively, median (range), P<0.05]. The administration of aspirin 50 mg daily for 5 consecutive days to colorectal cancer patients caused a cumulative inhibition of platelet cyclooxygenase (COX)-1 activity either ex vivo, as assessed by the measurement of serum TXB(2) levels, or in vivo, as assessed by urinary 11-dehydro-TXB(2) excretion. In conclusion, enhanced platelet activation occurs in colorectal cancer patients. Permanent inactivation of platelet COX-1 by low-dose aspirin might restore anti-tumor reactivity.

Topics: Aged; Aspirin; Biomarkers; Colorectal Neoplasms; Cyclooxygenase 1; Cyclooxygenase Inhibitors; Female; Humans; Male; Membrane Proteins; Middle Aged; Platelet Activation; Platelet Aggregation Inhibitors; Prostaglandin-Endoperoxide Synthases; Thromboxane B2

Regular use of nonsteroidal anti-inflammatory drugs is associated with a significantly lower incidence of several types of cancer, particularly those affecting the gastrointestinal tract. However, the propensity of these drugs to cause ulcers and bleeding in the stomach and small intestine limits their utility for chemoprevention of cancer. In the present study, we evaluated the effectiveness of a novel hydrogen sulfide-releasing derivative of naproxen in reducing the incidence of pre-cancerous lesions (aberrant crypt foci) in mice treated with the carcinogen azoxymethane. Weekly administration of azoxymethane over a 4-week period resulted in formation of an average of ∼50 aberrant crypt foci in the colon. Twice-daily treatment with naproxen at high doses significantly reduced the number of aberrant crypt foci. However, a significantly greater effect was observed with ATB-346 (H2S-releasing naproxen) and it was also effective at much lower doses, where naproxen was ineffective. The H2S-releasing moiety of ATB-346 did not significantly affect the number of aberrant crypt foci, suggesting that both the inhibition of cyclooxygenase activity and release of H2S were necessary for the enhanced chemopreventative effect. ATB-346 suppressed colonic prostaglandin synthesis and whole blood thromboxane synthesis as effectively as naproxen, but did not induce any gastrointestinal injury. These results demonstrate that ATB-346 exerts superior chemopreventive effects to those of naproxen, while sparing the gastrointestinal tract of the injury normally associated with use of the parent drug. ATB-346 may therefore be an attractive agent for chemoprevention of colon cancer, and possibly of cancers in other tissues.

Topics: Aberrant Crypt Foci; Animals; Anti-Inflammatory Agents, Non-Steroidal; Azoxymethane; Colon; Colorectal Neoplasms; Dinoprostone; Male; Mice; Naproxen; Protective Agents; Rats; Thromboxane B2

The induced synthesis of bioactive prostanoids downstream of cyclooxygenase-2 (COX-2) and prostaglandin H(2) (PGH(2)) exerts a critical event in colorectal carcinogenesis. Here we demonstrate that APC(Min/+) mice with genetic deletion of microsomal prostaglandin E synthase-1 (mPGES-1), which catalyses the terminal conversion of PGH(2) into PGE(2), surprisingly develop more and generally larger intestinal tumors than do mPGES-1 wild type littermates (mean number of tumors/intestine 80 vs. 38, p<0.0005, mean tumor diameter 1.64 vs. 1.12 mm, p<0.0005). No deviation regarding the expression of other PGE(2) related enzymes (COX-1, COX-2, mPGES-2, cPGES, and 15-PGDH) or receptors (EP1-4) was obvious among the mPGES-1 deficient mice. PGE(2) levels were suppressed in tumors of mPGES-1 deficient animals, but the concentrations of other PGH(2) derived prostanoids were generally enhanced, being most prominent for TxA(2) and PGD(2). Thus, we hypothesise that a redirected synthesis towards other lipid mediators might (over)compensate for loss of mPGES-1/PGE(2) during intestinal tumorigenesis. Nevertheless, our results question the suitability for mPGES-1 targeting therapy in the treatment or prevention of colorectal cancer.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Cell Transformation, Neoplastic; Colorectal Neoplasms; Dinoprostone; Female; Gene Deletion; Intramolecular Oxidoreductases; Male; Mice; Mice, Mutant Strains; Prostaglandin-E Synthases; RNA, Messenger; Thromboxane B2