Cancer Letters

Cancer Letters

Volume 172, Issue 2, 30 October 2001, Pages 111-118
Cancer Letters

Specific inhibition of cyclooxygenase-2 (COX-2) expression by dietary curcumin in HT-29 human colon cancer cells

https://doi.org/10.1016/S0304-3835(01)00655-3Get rights and content

Abstract

Curcumin, a major yellow pigment and active component of turmeric, has been shown to possess anti-inflammatory and anti-cancer activities. Cyclooxygenase (COX)-2 plays an important role in colon carcinogenesis. To investigate the effect of curcumin on COX-2 expression, we treated HT-29 human colon cancer cells with various concentrations of curcumin. Curcumin inhibited the cell growth of HT-29 cells in a concentration- and time-dependent manner. Curcumin markedly inhibited the mRNA and protein expression of COX-2, but not COX-1. These data suggest that a non-toxic concentration of curcumin has a significant effect on the in vitro growth of HT-29 cells, specifically inhibits COX-2 expression, and may have value as a safe chemopreventive agent for colon cancer.

Introduction

Colon cancer is responsible for substantial mortality and morbidity in the Western world. Chemoprevention is a promising strategy because other therapies have not been effective in controlling either the high incidence or low survival rate of gastrointestinal cancers [1]. Recently, emphasis has been focused upon a variety of clinical and basic studies of chemoprevention using naturally occurring substances that are found in normal diets, since they might provide useful strategies to inhibit colon cancer with minimal toxicity [1]. Epidemiological studies suggest that dietary manipulations play an important role in reducing the cancer death rate as much as 90% [2]. Large number of minor food components and chemically related compounds block different stages of the carcinogenic process in animal models and some of these substances partially prevent or delay cancer formation in some high risk human populations [3], [4], [5].

Curcumin (diferuoylmethane) is a major yellow pigment in turmeric (curcuma longa) and is widely used as a spice. Curcumin exhibits a variety of pharmacological effects, and has been reported to have anti-inflammatory [6] and anti-tumor activities [7]. The anticancer properties of curcumin in animals have been demonstrated by the inhibition of tumor initiation induced by benz(a)pyrene and 7,12 dimethyl benz(a)anthracene [8] and tumor promotion induced by phorbol esters on mouse skin and on carcinogen-induced tumorigenesis in the stomach, duodenum and colon of mice [9], [10].

The anti-inflammatory properties of curcumin have recently been attributed, at least in part, to suppression of prostaglandin (PG) synthesis [6], [7]. The conversion of arachidonic acid to PGs is catalyzed by two isoenzymes: the constitutively expressed cyclooxygenase-1(COX-1) [11], [12] and the inducible cyclooxygenase-2 (COX-2) [13], [14]. Both of these enzymes have been shown to be present in colon tumors of rodents and humans [15]. COX-1 is expressed in most tissues that generate PGs during their normal physiological functions, and its expression does not fluctuate in response to stimuli [11], [12]. In contrast, COX-2 expression can be induced by various agents, including inflammatory cytokines, mitogens, reactive oxygen intermediates and many other tumor promoters [13], [14], [16], [17]. Increased expression of COX-2 has been reported in many colorectal tumors and adenocarcinomas [18]. These findings have been substantiated by other studies, where investigators observed markedly elevated levels of COX-2 mRNA and protein in chemical carcinogen induced colonic tumors [15] and in adenomas taken from Min mice [18]. It has also been reported that the overexpression of COX-2 in intestinal epithelium leads to increased carcinogenesis, metastatic potential and angiogenesis [19], [20], [21].

Although the exclusive role of COX-2 in tumor development and progression has yet not been fully elucidated, numerous studies have demonstrated that COX-2 inhibitors can significantly reduce polyp formation and tumor growth in vivo [22]. Recently, Zhang et al. [23] have shown that curcumin inhibits the bile acid and phorbol ester-induced COX-2 expression in gastrointestinal cell lines. They also reported that curcumin can directly inhibit the COX-2 activity. This indicates that like other inhibitors of COX-2, curcumin can also inhibit the expression of COX-2. But, the majority of the COX-2 inhibitors are non-specific such as aspirin and other non-steroidal anti-inflammatory drugs (NASAIDs) [24], [25], [26]. Due to their prolonged use and non-specific inhibition of COX-1, these agents can have severe side effects, such as gastrointestinal ulceration, bleeding, and renal toxicity [26], [27]. In view of all these observations, increased attention has been diverted toward the development of specific COX-2 inhibitors, which might serve as potential non-toxic chemopreventive agents.

The present study was undertaken to investigate the specificity of curcumin in the inhibition of COX-2. This study for the first time showed that curcumin specifically inhibits COX-2 but not COX-1 expression in HT-29 human colon cancer cells.

Section snippets

Materials

The human colon adenocarcinoma cell line HT-29 was obtained from the American Type Culture Collection (ATCC, Rockville, MD). Cell culture reagents were purchased from Life Technologies Inc. (Grand Island, NY). Curcumin was obtained from Sigma Chemical Co., St. Louis, MO., and the stock solution was prepared by dissolving it in dimethyl sulfoxide (Sigma Chemical Co., St. Louis, MO) and stored in a brown bottle at −20°C until used. All other chemicals were purchased from Sigma Chemical Co. (St.

Curcumin inhibits growth of HT-29 cells

The MTT assay was performed to assess the rate of proliferation of HT-29 human colon cancer cells after treatment with varying concentrations of curcumin (0–75 μM) as a function of time (Fig. 1). The resulting growth curves show that curcumin has a concentration- and time-dependent inhibitory effect. The inhibitory effects of curcumin were more pronounced at higher doses, and also after 48 and 72 h of curcumin treatment. Maximum growth inhibitory effects of curcumin were observed at 75 μM

Discussion

The major focus of this study was to investigate the chemopreventive efficacy of curcumin as a possible inhibitor of COX-2 expression using the HT-29 human colon cancer cell model. Selection of curcumin for study as a chemopreventive agent was, in part, based on the evidence that curcumin has an inhibitory effect on arachidonic acid-induced inflammation and on arachidonic acid metabolism through the inhibition of cyclooxygenase and lipooxygenase enzymes in mouse epidermis [6]. Furthermore, it

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    This work was supported in part by a grant ’Complementary Therapies in Medicine’ awarded to D.P.C.

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