Murine Colon Epithelial Cell Proliferation and Neoplasia Muscarinic Receptors Attenuates

Colon epithelial cells express and most colon cancers overexpress M3 muscarinic receptors (M3R). In human colon cancer cells, post-M3R signaling stimulates proliferation. To explore the importance of M3R expression in vivo , we used the azoxymethane-induced colon neoplasia model. Mice treated with weekly i.p. injection of saline [10 wild-type (WT) mice] or azoxymethane (22 WT and 16 M3R / mice) for 6 weeks were euthanized at 20 weeks. At week 20, azoxymethane-treated WT mice weighed f16% more than M3R / mice (33.4 grams F 1.0 grams versus 27.9 grams F 0.5 grams; mean F SE, P < 0.001). In azoxymethane-treated M3R / mice, cell proliferation (BrdUrd staining) was reduced 43% compared with azoxymethane-treated WT mice (P < 0.05). Whereas control mice (both WT and M3R / ) had no colon tumors, azoxymethane-treated WT mice had 5.3 F 0.5 tumors per animal. Strikingly, azoxymethane-treated M3R / mice had only 3.2 F 0.3 tumors per mouse (P < 0.05), a 40% reduction. Tumor volume in azoxymethane-treated M3R / mice was reduced 60% compared with azoxymethane-treated WT mice (8.1 mm F 1.5 mm versus 20.3 mm F 4.1 mm; P < 0.05). Compared with WT, fewer M3R / mice had adenomas (6% versus 36%; P = 0.05), and M3R / mice had fewer adenocarcinomas per mouse (0.6 F 0.1 versus 1.7 F 0.4; P < 0.05). Eleven of 22 WT but no M3R / mice had multiple adenocarcinomas (P < 0.001). Compared with WT, azoxymethanetreated M3R-deficient mice have attenuated epithelial cell proliferation, tumor number, and size. M3R and post-M3R signaling are novel therapeutic targets for colon cancer. [Cancer Res 2008;68(10):3573–8]