Blockage of Cholinergic Signaling via Muscarinic Acetylcholine Receptor 3 Inhibits Tumor Growth in Human Colorectal Adenocarcinoma

SIMPLE SUMMARY: Darifenacin is a selective muscarinic acetylcholine receptor 3 (M3R) antagonist in clinical use for benign bladder disorders. Here, the effects of M3R blockage by darifenacin on human colon adenocarcinoma cells are analyzed in vitro and in vivo. M3R expression was found in the majority of clinical colorectal cancer samples, making it attractive for drug targeting. In mice, darifenacin inhibited orthotopic and metastatic tumor xenograft growth. In vitro analyses on colon carcinoma cell lines showed that M3R targeting counteracts acetylcholine-induced p38, ERK1/2 and Akt signaling, and disrupts MMP-1 expression and tumor cell invasion. Our data suggest that targeting cholinergic signaling by darifenacin may be beneficial in the treatment of colorectal cancer. ABSTRACT: Cholinergic signaling via the muscarinic M3 acetylcholine receptor (M3R) is involved in the development and progression of colorectal cancer (CRC). The present study aimed to analyze the blocking of M3R signaling in CRC using darifenacin, a selective M3R antagonist. Darifenacin effects were studied on HT-29 and SW480 CRC cells using MTT and BrdU assays, Western blotting and real time RT-PCR. In vivo, blocking of M3R was assessed in an orthotopic CRC xenograft BALB/c(nu/nu) mouse model. M3R expression in clinical tumor specimens was studied by immunohistochemistry on a tissue microarray of 585 CRC patients. In vitro, darifenacin decreased tumor cell survival and proliferation in a dose-dependent manner. Acetylcholine-induced p38, ERK1/2 and Akt signaling, and MMP-1 mRNA expression were decreased by darifenacin, as well as matrigel invasion of tumor cells. In mice, darifenacin reduced primary tumor volume and weight (p < 0.05), as well as liver metastases, compared to controls. High expression scores of M3R were found on 89.2% of clinical CRC samples and correlated with infiltrative tumor border and non-mucinous histology (p < 0.05). In conclusion, darifenacin inhibited components of tumor growth and progression in vitro and reduced tumor growth in vivo. Its target, M3R, was expressed on the majority of CRC. Thus, repurposing darifenacin may be an attractive addition to systemic tumor therapy in CRC patients expressing M3R.