Preclinical cancer chemoprevention studies using animal model of inflammation-associated colorectal carcinogenesis

Inflammation-Related Carcinogenesis: Lessons from Animal Models to Clinical Aspects

Simple Summary

In multicellular organisms, inflammation is the body’s most primitive and essential protective response against any external agent. Inflammation, however, not only causes various modern diseases such as cardiovascular disorders, neurological disorders, autoimmune diseases, metabolic syndrome, infectious diseases, and cancer but also shortens the healthy life expectancy. This review focuses on the onset of carcinogenesis due to chronic inflammation caused by pathogen infections and inhalation/ingestion of foreign substances. This study summarizes animal models associated with inflammation-related carcinogenesis by organ. By determining factors common to inflammatory carcinogenesis models, we examined strategies for the prevention and treatment of inflammatory carcinogenesis in humans.

Abstract

Inflammation-related carcinogenesis has long been known as one of the carcinogenesis patterns in humans. Common carcinogenic factors are inflammation caused by infection with pathogens or the uptake of foreign substances from the environment into the body. Inflammation-related carcinogenesis as a cause for cancer-related death worldwide accounts for approximately 20%, and the incidence varies widely by continent, country, and even region of the country and can be affected by economic status or development. Many novel approaches are currently available concerning the development of animal models to elucidate inflammation-related carcinogenesis. By learning from the oldest to the latest animal models for each organ, we sought to uncover the essential common causes of inflammation-related carcinogenesis. This review confirmed that a common etiology of organ-specific animal models that mimic human inflammation-related carcinogenesis is prolonged exudation of inflammatory cells. Genotoxicity or epigenetic modifications by inflammatory cells resulted in gene mutations or altered gene expression, respectively. Inflammatory cytokines/growth factors released from inflammatory cells promote cell proliferation and repair tissue injury, and inflammation serves as a “carcinogenic niche”, because these fundamental biological events are common to all types of carcinogenesis, not just inflammation-related carcinogenesis. Since clinical strategies are needed to prevent carcinogenesis, we propose the therapeutic apheresis of inflammatory cells as a means of eliminating fundamental cause of inflammation-related carcinogenesis.

Nuclear receptors: Lipid and hormone sensors with essential roles in the control of cancer development

Nuclear receptors (NRs) are a superfamily of ligand-activated transcription factors that act as biological sensors and use a combination of mechanisms to modulate positively and negatively gene expression in a spatial and temporal manner. The highly orchestrated biological actions of several NRs influence the proliferation, differentiation, and apoptosis of many different cell types. Synthetic ligands for several NRs have been the focus of extensive drug discovery efforts for cancer intervention. This review summarizes the roles in tumour growth and metastasis of several relevant NR family members, namely androgen receptor (AR), estrogen receptor (ER), glucocorticoid receptor (GR), thyroid hormone receptor (TR), retinoic acid receptors (RARs), retinoid X receptors (RXRs), peroxisome proliferator-activated receptors (PPARs), and liver X receptors (LXRs). These studies are key to develop improved therapeutic agents based on novel modes of action with reduced side effects and overcoming resistance.

In vitro cytogenetic toxicity of bezafibrate in human peripheral blood lymphocytes

Bezafibrate (BF) is a peroxisome proliferator-activated receptor (PPAR) agonist used as a lipid-lowering agent to treat both the familial or acquired combined forms of hyperlipidemia. BF is the only available fibrate drug that acts on all PPAR subtypes of α, β, and δ. Although there are studies that indicate a genotoxic potential associated with the use of fibrates, to our knowledge, the genotoxicity of BF in human peripheral blood lymphocytes has not been studied. In the present study, the genotoxic potential of BF was evaluated using chromosome aberration (CA) and micronucleus (MN) assays in peripheral blood lymphocytes of healthy human subjects. In addition, a high performance liquid chromatography (HPLC) method was used to identify and quantitate the drug passage into the cells. Human peripheral blood lymphocytes were exposed to four different concentrations (100, 175, 250 and 325 μg/mL) of BF for 24- and 48-h treatment periods. As shown by HPLC, in spite of significant passage of BF into human peripheral blood lymphocytes in 24- and 48-h treatment periods, BF was not found to increase the CA and MN frequency. On the other hand, exposing cells to BF for 24- and 48-h treatment periods caused significant concentration-dependent decreases in the mitotic index (r = -0.995, p < 0.01 for 24-h; r = -0.992, p < 0.01 for 48-h) and nuclear division index (r = -0.990, p < 0.01 for 24-h; r = -0.981, p < 0.01 for 48-h). Our results suggest that BF has cytotoxic effect on cultured human peripheral blood lymphocytes.

Anti-Oxidant, Pro-Oxidant and Anti-Inflammatory Effects of Unpolished Rice Relevant to Colorectal Cancer

Colorectal cancer (CRC) is a major worldwide health problem owing to its high prevalence and mortality rates. Carcinogenesis in the colon is a multistage and multifactorial process. An imbalance between free radical exposure and anti-oxidant defense systems may leads to oxidative stress and attack of macromolecules which can alter signal transduction pathways and gene expression. Consequently, oxidative damage can lead to cellular dysfunction and contribute to pathophysiological processes in a variety of diseases including CRC. One factor tightly associated with CRC is chronic inflammation, which can be present from the earliest stage of tumor onset. Unpolished rice is an attractive chemoprevention in CRC due to their anti-oxidant and anti-inflammatory activities. The aim of this paper is to review evidence linking oxidative stress and inflammation to CRC and to provide essential background information for understanding future research on oxidative stress and inflammation on CRC. Mechanisms of action of unpolished rice in CRC carcinogenesis are also discussed.

The peroxisome proliferator-activated receptor (PPAR) α agonist fenofibrate suppresses chemically induced lung alveolar proliferative lesions in male obese hyperlipidemic mice

Activation of peroxisome proliferator-activated receptor (PPAR) α disrupts growth-related activities in a variety of human cancers. This study was designed to determine whether fenofibrate, a PPARα agonist, can suppress 4-nitroquinoline 1-oxide (4-NQO)-induced proliferative lesions in the lung of obese hyperlipidemic mice. Male Tsumura Suzuki Obese Diabetic mice were subcutaneously injected with 4-NQO to induce lung proliferative lesions, including adenocarcinomas. They were then fed a diet containing 0.01% or 0.05% fenofibrate for 29 weeks, starting 1 week after 4-NQO administration. At week 30, the incidence and multiplicity (number of lesions/mouse) of pulmonary proliferative lesions were lower in mice treated with 4-NQO and both doses of fenofibrate compared with those in mice treated with 4-NQO alone. The incidence and multiplicity of lesions were significantly lower in mice treated with 4-NQO and 0.05% fenofibrate compared with those in mice treated with 4-NQO alone (p<0.05). Both doses of fenofibrate significantly reduced the proliferative activity of the lesions in 4-NQO-treated mice (p<0.05). Fenofibrate also significantly reduced the serum insulin and insulin-like growth factor (IGF)-1 levels, and decreased the immunohistochemical expression of IGF-1 receptor (IGF-1R), phosphorylated Akt, and phosphorylated Erk1/2 in lung adenocarcinomas. Our results indicate that fenofibrate can prevent the development of 4-NQO-induced proliferative lesions in the lung by modulating the insulin-IGF axis.

Animal models and the tumor microenvironment: studies of tumor-host symbiosis

The contributions of murine models to elucidation of processes central to tumor growth are reviewed. Localized acidosis, increased interstitial pressure, perturbations in structure and function of the extracellular matrix, hypoxia, angiogenesis, and co-optation of the immune response are all phenomena that promote tumor survival and metastasis. The use of animal models is critical to understanding the pathophysiology of these processes and the development of more effective cancer therapies.

A newly synthesized compound, 4'-geranyloxyferulic acid-N(omega)-nitro-L-arginine methyl ester suppresses inflammation-associated colorectal carcinogenesis in male mice

We previously reported the cancer chemopreventive activity of 4'-geranyloxyferulic acid (GOFA, Miyamoto et al., Nutr Cancer 2008; 60:675-84) and a β-cyclodextrin inclusion compound of GOFA (Tanaka et al., Int J Cancer 2010; 126:830-40) in colitis-related colorectal carcinogenesis. In our study, the chemopreventive effects of a newly synthesized GOFA-containing compound, GOFA-N(omega)-nitro-L-arginine methyl ester (L-NAME), which inhibits inducible nitric oxide (iNOS) and cyclooxygenase-2 (COX) enzymes, were investigated using a colitis-associated mouse colorectal carcinogenesis model with azoxymethane (AOM) and dextran sodium sulfate (DSS). The dietary administration of GOFA-L-NAME after the AOM and DSS treatments significantly reduced the multiplicity of adenocarcinomas (inhibition rates: 100 ppm, 84%, p < 0.001; 500 ppm, 94%, p < 0.001) compared with the AOM + DSS group. Dietary GOFA-L-NAME significantly decreased the proliferation (p < 0.001) and increased the apoptosis (p < 0.001) of colonic adenocarcinoma cells. A subsequent short-term experiment revealed that dietary GOFA-L-NAME decreased the mRNA expression of inflammatory enzymes, such as iNOS and COX-2, and proinflammatory cytokines, such as tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and macrophage inflammatory protein (MIP)-2 in the colonic mucosa of mice that received 1.5% DSS in their drinking water for 7 days. Our findings indicate that GOFA-L-NAME is able to inhibit colitis-associated colon carcinogenesis by modulating inflammation, proliferation, apoptosis and the expression of proinflammatory cytokines in mice.

Rodent intestinal epithelial carcinogenesis: pathology and preclinical models

Colon cancer is a major human malignancy that afflicts millions of people throughout the world each year. Genetics and diet play large roles in colon carcinogenesis although chemicals may also contribute. For the past 40 years, scientists have studied experimentally induced intestinal carcinogenesis in rodents in order to elucidate the etiology and mechanisms involved. Comparative histopathology has revealed many similarities of rodent and human intestinal cancers. Comparative molecular pathology has also shown genetic similarities. More recently, genetically engineered mice and inflammatory colon cancer models have been used for investigating mechanisms and potential chemopreventive and treatment modalities. This review will focus on comparative histopathology and nonclinical models.

Dietary Crocin Inhibits Colitis and Colitis-Associated Colorectal Carcinogenesis in Male ICR Mice

A natural carotenoid crocin is contained in saffron and gardenia flowers (crocuses and gardenias) and is used as a food colorant. This study reports the potential inhibitory effects of crocin against inflammation-associated mouse colon carcinogenesis and chemically induced colitis in male ICR mice. In the first experiment, dietary crocin significantly inhibited the development of colonic adenocarcinomas induced by azoxymethane (AOM) and dextran sodium sulfate (DSS) in mice by week 18. Crocin feeding also suppressed the proliferation and immunohistochemical expression of nuclear factor- (NF-) κB but increased the NF-E2-related factor 2 (Nrf2) expression, in adenocarcinoma cells. In the second experiment, dietary feeding with crocin for 4 weeks was able to inhibit DSS-induced colitis and decrease the mRNA expression of tumor necrosis factor α, interleukin- (IL-) 1β, IL-6, interferon γ, NF-κB, cyclooxygenase-2, and inducible nitric oxide synthase in the colorectal mucosa and increased the Nrf2 mRNA expression. Our results suggest that dietary crocin suppresses chemically induced colitis and colitis-related colon carcinogenesis in mice, at least partly by inhibiting inflammation and the mRNA expression of certain proinflammatory cytokines and inducible inflammatory enzymes. Therefore, crocin is a candidate for the prevention of colitis and inflammation-associated colon carcinogenesis.