Persistent cyclooxygenase-2 inhibition downregulates NF-{kappa}B, resulting in chronic intestinal inflammation in the min/+ mouse model of colon tumorigenesis.

Cyclooxygenase-2 (COX-2) inhibition prevents adenoma formation in humans and mouse models of colon cancer. The selective COX-2 inhibitor celecoxib reduces COX-2 and prostaglandin E(2) (PGE(2)) expression and adenomas in the intestine of Min/+ mice after treatment for several weeks, but prolonged treatment increases PGE(2) production, resulting in drug-resistant tumor formation and transforming growth factor beta (TGFbeta)-dependent intestinal fibrosis. In this study, we examined pathways that regulate COX-2 expression and suppress chronic intestinal inflammation. We show that NF-kappaB signaling was inhibited in the ileum of Min/+ mice receiving long-term treatment with celecoxib. This effect was associated with inhibition of TGFbeta-associated kinase-1 and IkappaB kinase alpha/beta activities and reduced expression of the Toll-like receptor (TLR) 2 and TLR4 that enhance colonic barrier function. Additionally, we observed reduced activities of protein kinases c-Jun NH(2)-terminal kinase 1 and protein kinase A and transcription factor cyclic AMP-responsive element binding protein, regulators of COX-2 expression, which cross-talk with NF-kappaB. In ileum subjected to long-term celecoxib treatment, we noted relatively higher expression of COX-2, vascular endothelial growth factor, and interleukin-1beta in Paneth cells, whereas NF-kappaB and COX-2 were more strongly expressed by an expanded population of stromal myofibroblasts. Our findings argue that celecoxib resistance is an acquired adaptation to changes in the crypt microenvironment that is associated with chronic intestinal inflammation and impaired acute wound-healing responsiveness.

Chronic cyclooxygenase-2 inhibition promotes myofibroblast-associated intestinal fibrosis.

Anti-inflammatory drugs prevent intestinal tumor formation, an activity related to their ability to inhibit inflammatory pathway signaling in the target tissue. We previously showed that treatment of Min/(+) mice with the selective cyclooxygenase-2 (COX-2) inhibitor celecoxib induced rapid tumor regression; however, drug-resistant tumors appeared with long-term treatment. In this study, we investigated whole-tissue changes in inflammatory signaling by studying constituents of the tissue stroma and extracellular matrix. We found that celecoxib resistance was associated with changes in factors regulating autocrine transforming growth factor-beta (TGFbeta) signaling. Chronic drug treatment expanded the population of bone marrow-derived CD34(+) vimentin(+) alphaSMA(-) myofibroblast precursors and alphaSMA(+) vimentin(+) F4/80(-) myofibroblasts in the lamina propria and submucosa, providing a source of increased TGFbeta and COX-2 expression. Membrane constituents regulating TGFbeta availability, including syndecan-1 and heparanase-1, were also modified by chronic treatment in a manner promoting increased TGFbeta signaling. Finally, long-term celecoxib treatment induced tissue fibrosis, as indicated by increased expression of collagen, fibronectin, and laminin in the basement membrane. We conclude that chronic COX-2 inhibition alters TGFbeta signaling in the intestinal mucosa, producing conditions consistent with chronic inflammation.

Microsatellite instability predicts improved response to adjuvant therapy with irinotecan, fluorouracil, and leucovorin in stage III colon cancer: Cancer and Leukemia Group B Protocol 89803.

PURPOSE: Colon cancers exhibiting DNA mismatch repair (MMR) defects demonstrate distinct clinical and pathologic features, including better prognosis and reduced response to fluorouracil (FU) -based chemotherapy. This prospective study investigated adjuvant chemotherapy containing FU and irinotecan in patients with MMR deficient (MMR-D) colon cancers. PATIENTS AND METHODS: Cancer and Leukemia Group B 89803 randomly assigned 1,264 patients with stage III colon cancer to postoperative weekly bolus FU/leucovorin (LV) or weekly bolus irinotecan, FU, and LV (IFL). The primary end point was overall survival; disease-free survival (DFS) was a secondary end point. Tumor expression of the MMR proteins, MLH1 and MSH2, was determined by immunohistochemistry (IHC). DNA microsatellite instability was also assessed using a panel of mono- and dinucleotide markers. Tumors with MMR defects were those demonstrating loss of MMR protein expression (MMR-D) and/or microsatellite instability high (MSI-H) genotype. RESULTS: Of 723 tumor cases examined by genotyping and IHC, 96 (13.3%) were MMR-D/MSI-H. Genotyping results were consistent with IHC in 702 cases (97.1%). IFL-treated patients with MMR-D/MSI-H tumors showed improved 5-year DFS as compared with those with mismatch repair intact tumors (0.76; 95% CI, 0.64 to 0.88 v 0.59; 95% CI, 0.53 to 0.64; P = .03). This relationship was not observed among patients treated with FU/LV. A trend toward longer DFS was observed in IFL-treated patients with MMR-D/MSI-H tumors as compared with those receiving FU/LV (0.57; 95% CI, 0.42 to 0.71 v 0.76; 95% CI, 0.64 to 0.88; P = .07; hazard ratio interaction between tumor status and treatment, 0.51; likelihood ratio P = .117). CONCLUSION: Loss of tumor MMR function may predict improved outcome in patients treated with the IFL regimen as compared with those receiving FU/LV.