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Matrix metalloproteinases (MMPs) and cyclooxygenase-2 (COX-2) are expressed in both sporadic and familial adenomatous colonic polyps and tumours and have been independently shown to play causal roles in intestinal tumour formation in mouse models of colon cancer. The apparent roles of these enzymes in intestinal tumorigenesis led us to examine, in the Min mouse model of colon cancer, if selective COX-2 and MMP inhibitors provide additive or synergistic therapeutic benefits in intestinal tumour prevention. The broad-spectrum MMP inhibitor (A-177430; MMPI) and the selective COX-2 inhibitor (A-285969; COX-2I) both showed dose-dependent inhibition of the number of adenomas in Min mice. Using suboptimal doses, the MMPI reduced tumour multiplicity by 32%, the COX-2I by 48% and, both agents in combination resulted in a 67% decrease compared to control demonstrating a cooperative effect on intestinal tumorigenesis. Apoptosis, proliferation, and angiogenesis were assayed in tumors from each treatment group. These agents in combination allowed for a lowered dosage to be administered to achieve significant biological effects. Clinically, this could potentially reduce side effects associated with currently used MMP and COX-2 inhibitors. Together, these compounds could represent an easily tolerated chemopreventive approach.

Both the matrix metalloproteinase matrilysin and the prostaglandin H synthase cyclooxygenase-2 (Cox-2), are thought to play key roles in colorectal carcinogenesis. These enzymes are overexpressed in 85-90% of human colorectal cancers. Furthermore, mice carrying an adenomatous polyposis coli germline mutation that are also nullizygous for either matrilysin or Cox-2 display a significant reduction in tumor multiplicity. To determine if there is a direct link between matrilysin and Cox-2, their expression was characterized in two mouse models of intestinal carcinogenesis and in human colorectal tumor samples. Both matrilysin and Cox-2 expression was increased in the mouse models and in the human colorectal cancers; however, immunohistochemistry and in situ hybridization indicated that their localization within the tumors was different. In the mouse models, Cox-2 was expressed in the superficial stroma, whereas matrilysin expression was localized exclusively to the neoplastic epithelium. In contrast, in human colorectal cancers, both Cox-2 and matrilysin were expressed in the neoplastic epithelium. Although over 80% of the specimens expressed both matrilysin and Cox-2, the levels and localization of matrilysin and Cox-2 expression were distinct. Cox-2 expression was strongest in well-differentiated areas, and matrilysin immunostaining was strongest in the more dysplastic and invasive regions of the tumor. These results indicate that these two important modulators of colorectal tumorigenesis are differentially expressed and imply that the therapeutic benefit may be improved by combination therapy utilizing selective Cox-2 and matrilysin inhibitors.

Cyclooxygenase (COX), the key regulatory enzyme for prostaglandin synthesis is transcribed from two distinct genes. COX-1 is expressed constitutively in most tissues, and COX-2 is induced by a wide variety of stimuli and was initially identified as an immediate-early growth response gene. In addition, COX-2 expression is markedly increased in 85-90% of human colorectal adenocarcinomas, whereas COX-1 levels remain unchanged. Several epidemiological studies have reported a 40-50% reduction in the risk of developing colorectal cancer in persons who chronically take such nonsteroidal anti-inflammatory drugs (NSAIDs) as aspirin, which are classic inhibitors of cyclooxygenase. Genetic evidence also supports a role for COX-2, since mice null for COX-2 have an 86% reduction in tumor multiplicity in a background containing a mutated APC allele. These results strongly suggest that COX-2 contributes to the development of intestinal tumors and that inhibition of COX is chemo-preventative.