Caffeic Acid Phenethyl Ester (CAPE) May be a Promising Adjuvant Treatment in Gastric Cancer (2007)

Gastric carcinoma is still one of the leading causes of cancer death worldwide, regardless of decreasing incidence in developed countries.1 It is the second most common malignancy among men and the third most common among women in many countries of Latin America and Asia.2 In the last decades, we are evidencing enormous advances in the diagnosis, staging evaluation, and treatment strategies for these patients. Additionally, molecular biology has clarified some of the mechanisms involved in the carcinogenetic process. However, the patient's prognosis is still poor, and even after curative resections (R0), approximately 50% of the patients succumb to recurrent disease during the first 2 years of follow-up.3 Epidemiologic, cross-sectional, and histologic studies have implicated Helicobacter pylori in the pathogenesis of gastric carcinoma through mechanisms that are incompletely understood.4–9 This statement is based on: (1) the epidemiologic association between a high incidence of cancer and a high prevalence of H. pylori4,5,7; (2) the high prevalence of H. pylori infection in patients with gastric cancer8,9; (3) the high prevalence of H. pylori infection in patients with precancerous changes9,10; (4) evolution of an H. pylori-related chronic gastritis into atrophy, intestinal metaplasia, and, eventually, cancer.11 Thus, H. pylori is considered a risk factor for gastric carcinoma, and World Health Organization classified the bacterium as a definite biologic carcinogen. Chronic gastric inflammatory process due to H. pylori seems to be a relevant factor to initiate gastric carcinogenesis, especially in the intestinal type tumors.12,13 So, the molecular mechanisms linking H. pylori infection to the development of gastric carcinoma have become a spotlight research in recent years. Several immune mechanisms of gastric epithelium alterations have been implicated to the H. pylori infection, including (a) gastric epithelial cells are known to express major histocompatibility complex class II antigens14; (b) H. pylori infection induces the expression of intercellular adhesion molecule (ICAM)-1 on gastric epithelial cell lines in vitro15; (c) H. pylori infection increases the levels of messenger RNA (mRNA) expression and, consequently, the protein of proinflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-8.16,17 H. pylori colonization may also activate nuclear factor-kappa B (NF-κB). NF-κB is a ubiquitous transcription factor complex belonging to the Rel multigene family of proteins.18 The most abundant form of NF-κB is the heterodimer of p50 and p65 that are retained in the cytosol by specific inhibitory proteins termed IkB. In most cells, except mature B cells, macrophages, and some neurons, NF-κB complexes are sequestered in the cytoplasm by inhibitory molecules, termed IkBs. Upon stimulation of cells, specific IkBs are degraded, and certain NF-κB factors are stimulated to enter the nucleus, bind its specific cognate DNA site, and subsequently regulate gene transcription.19,20 Activation of NF-κB is pivotal for the inducible expression of the proinflammatory response genes, including cytokines IL-1β, IL-6, IL-8, and TNF-α21 and apoptosis (through Fas-mediated cell death). IL-1 and TNF-α also activate NF-κB to initiate an autoregulatory pathway that is thought to be responsible for increasing the magnitude of the inflammatory response. H. pylori has been shown to induce activation of NF-κB in human gastric cancer cell lines.22,23 Intestinal type gastric carcinoma is strongly associated with high expression of c-myc, cyclin D1, and bcl-xl through NF-κB/p65 activated by H. pylori cagA. Studies have demonstrated that activation of NF-κB by H. pylori requires genes in cag PAI (pathogenicity island).24 CagA protein of H. pylori PAI can be translocated into gastric epithelial cells by a type IV secretion system encoded by cag PAI and is tyrosine phosphorylated. Tyrosine phosphorylated cagA could induce changes in the tyrosine phosphorylation status of distinct cellular proteins and further activates NF-κB. High expression of NF-κB/p65 has been detected in the tissues of H. pylori cagA group with metaplasia, dysplasia, and gastric carcinoma. Some researches showed that tumor cells with activated NF-κB were not sensitive to radio and chemotherapeutic agents, whereas inhibition of NF-κB activity could enhance the radiosensitivity and chemosensitivity of cancer treatment. Activated NF-κB has also been shown to directly stimulate the transcription of genes that encode c-myc and cyclin D1 because a κB binding site is present within the c-myc, and cyclin D1 promoter.25,26 Proliferation induced by c-myc requires the concomitant mutant of p53. In gastric precancerous lesions infected with H. pylori, mutants of p53 were often confirmed.23,27,28 Thus, NF-κB has become a good therapeutic target for gastric cancer and numerous efforts are being made to develop safe NF-κB inhibitors. Among the candidates are natural flavonoids, which constitute a promising class of dietary antioxidants that are found in fruits, vegetables, and tea.29 Among these natural flavonoids, the most hopeful is caffeic acid phenethyl ester (CAPE), which is a phenolic antioxidant structurally related to 3,4-dihydroxycinnamic acid, and can be obtained from propolis, a honey constituent.29 CAPE has been shown to be a safe pharmacologic compound with known anti-inflammatory, immunomodulatory, anticarcinogenic, and antioxidant properties.30 Previous studies have shown that this compound could protect the spinal cord and brain from ischemia reperfusion injury and prevent neurotoxic events caused by excessive inflammatory reaction in brain. CAPE may modify the redox state in transformed fibroblast cells and in leukemic HL-60 cells. In addition, CAPE inhibits the formation of aberrant crypts induced by azoxymethane in vivo, which are relevant to colon carcinogenesis. CAPE has been shown to inhibit induction of preneoplastic lesions or tumors.30–32 Its cancer chemopreventive effects occurs through the inhibition of COX-2 expression and the restoration of disrupted Gap junction intercellular communication in H-ras–transformed, which may be associated in part with the blockade of NF-κB activation.33,34 The current issue of the J Clin Gastroenterol features a paper by Wu et al,35 from Taiwan, that address this topic on the role of H. pylori infection and the mechanisms that may lead to gastric cancer. The paper aims to clarify some of the molecular mechanisms [NF-κB, matrix metalloproteinase-9 (MMP-9), IL-1, and IL-8] involved in the chronic inflammation and carcinogenesis induced by H. pylori, as well as the effects of activated NF-κB inhibitor, CAPE. They have used immunohistochemistry for NF-κB in 90 human gastric cancer specimens and 50 nonmalignant gastric specimens. Electrophoretic mobility shift assays, real time reverse transcription-polymerase chain reaction, and enzyme-linked immunosorbent assay were used to evaluate the responses of human gastric cancer cells subsequent to H. pylori infection and CAPE treatment. Nuclear expression of NF-κB was significantly more frequently observed in gastric cancer tissues than in nonmalignant gastric tissues. H. pylori infection enhanced the activity of NF-κB and the expressions of MMP-9, IL-1β, and IL-8 in gastric adenocarcinoma cell line. However, the augmented responses could be significantly reversed by CAPE treatment. In addition, in vitro studies showed that CAPE inhibits tumor growth and the capacity for invasion. NF-κB activation was associated to increased expression of MMP-9 (a matrix metalloproteinase enzyme that degrade extracellular matrix, facilitating tumor invasion and spread), IL-1β 3, and IL-8. Moreover, NF-κB inhibitors or anti-inflammatory agents such as CAPE might be new adjuvant agent against invasive gastric carcinoma. The authors demonstrated that CAPE not only attenuated the increased MMP-9 expression induced by H. pylori but also inhibited the invasive capacity of gastric cancer cells stimulated by IL-8 (inflammatory response). Therefore, these findings offer an insight into the molecular mechanisms for the anti-inflammatory and immunomodulatory activities of CAPE in relationship to H. pylori infection and other inflammatory diseases or states. Clinical trials on adjuvant therapy with CAPE or other additional gene regulation targets may be advised to augment the disease-free interval and overall survival of the patients.