Molecular targeting of protein arginine deiminases to suppress colitis and prevent colon cancer.

Xiangli Cui,Corey P Causey,Erin E Witalison,Lorne J Hofseth,Paul R Thompson

doi:10.18632/oncotarget.5937

Abstract

Ulcerative colitis (UC) is a chronic disease, in which the lining of the colon becomes inflamed and develops ulcers leading to abdominal pain, diarrhea, and rectal bleeding. The extent of these symptoms depends on disease severity. The protein arginine deiminase (PAD) family of enzymes converts peptidyl-Arginine to peptidyl-Citrulline through citrullination. PADs are dysregulated, with abnormal citrullination in many diseases, including UC and colorectal cancer (CRC). We have developed the small molecule, pan-PAD inhibitor, Chlor-amidine (Cl-amidine), with multiple goals, including treating UC and preventing CRC. Building off our recent results showing that: 1) Cl-amidine suppresses colitis in vivo in a dextran sulfate sodium (DSS) mouse model; and 2) Cl-amidine induces microRNA (miR)-16 in vitro causing cell cycle arrest, we tested the hypothesis that Cl-amidine can prevent tumorigenesis and that miR-16 induction, by Cl-amidine, may be involved in vivo. Consistent with our hypothesis, we present evidence that Cl-amidine, delivered in the drinking water, prevents colon tumorigenesis in our mouse model of colitis-associated CRC where mice are given carcinogenic azoxymethane (AOM), followed by multiple cycles of 2% DSS to induce colitis. To begin identifying mechanisms, we examined the effects of Cl-amidine on miR-16. Results show miR-16 suppression during the colitis-to-cancer sequence in colon epithelial cells, which was rescued by drinking Cl-amidine. Likewise, Ki67 and cellular proliferation targets of miR-16 (Cyclins D1 and E1) were suppressed by Cl-amidine. The decrease in cell proliferation markers and increase in tumor suppressor miRNA expression potentially define a mechanism of how Cl-amidine is suppressing tumorigenesis in vivo.

Highlights

Ulcerative colitis (UC) is a chronic, relapsing inflammatory bowel disease that affects millions of people worldwide and causes symptoms of abdominal pain, diarrhea, and rectal bleeding
Since the citrullination of proteins involved in apoptosis facilitates the process of apoptosis [18,19,20,21], the higher dose of Cl-amidine may be inhibiting the citrullination necessary for the progression of apoptosis and aiding in the development of tumors, accounting for the increased tumor incidence
We provide evidence that Cl-amidine, a small molecule inhibitor of protein arginine deiminase (PAD), administered to mice in drinking water suppresses colitis (Figure 1) and tumorigenesis (Figure 2; Table 1)

Summary

Introduction

Ulcerative colitis (UC) is a chronic, relapsing inflammatory bowel disease that affects millions of people worldwide and causes symptoms of abdominal pain, diarrhea, and rectal bleeding. Due to the chronic inflammatory state of UC, which causes cyclical oxidative stress and leads to DNA damage, patients with UC are at a higher risk of developing colorectal cancer (CRC). The probability of developing CRC increases yearly once UC develops, with up to an approximate 20% incidence after 30 years [1, 2]. Current treatment options help to treat the symptoms, prevent flares, and heal the damaged colon; the treatment outcomes are often marginal, patients become refractory, and there are dangerous adverse side effects. We continue to investigate novel therapies showing reduced toxicity and more substantial efficacy in treating UC and preventing CRC.

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