Mechanistic role of p38 MAPK in gastric cancer dissemination in a rodent model peritoneal metastasis

Abstract

Peritoneal dissemination is a highly frequent complication of poorly differentiated gastric cancers for which no effective therapies are available. Constitutive activation of mitogen-activated protein kinases (MAPKs) signaling cascades is recognized as a causative factor in the malignant transformation of several carcinoma cell types. In the present study we provide evidence that p38 MAPK inhibition protects against gastric cancer cells dissemination in a mouse model of peritoneal carcinomatosis. Administering mice with ML3403 and SB203580, potent and selective p38 MAPK inhibitors, attenuate the formation of neoplastic foci induced by intraperitoneal inoculation of gastric cancer cells. By gene array analysis we found that such a protective effect correlates with a robust downregulation in the expression of CXC chemokine receptor-4, Fms-related tyrosine kinase 4 (FLT4), the non-receptor spleen tyrosine kinase (SYK) and the collagen α2(IV) (COL4A2) in neoplasic foci. Inhibition of p38 MAPK in vivo increased the sensitivity of tumor cells to cisplatin and associated with a robust downregulation in the expression of the multidrug resistance (MDR)-1, a well defined marker of resistance to chemotherapy. In summary, p38 MAPK inhibition by a small molecule is beneficial in preventing the peritoneal dissemination of poorly differentiated gastric cancer cells by acting at multiple check-points in the process of attachment and diffusion of tumor cells in the peritoneum.

Introduction

MAPKs are serine/threonine kinases activated in response to a variety of external signals (Cuadrado and Nebreda, 2010, Olson and Hallahan, 2004, Wagner and Nebreda, 2009). Three major subclasses of MAPKs, namely, extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK), and p38 have been identified. Various receptor tyrosine kinases, cytokine receptors, G proteins and oncogene products can activate MAPKs. Thus, MAPKs are proposed to be a critical integrator of various signaling transduction systems and involved in various cellular processes including cell proliferation, differentiation, apoptosis, and transformation (Cuadrado and Nebreda, 2010, Olson and Hallahan, 2004, Wagner and Nebreda, 2009).

Constitutive activation of these signaling cascades has been reported as a major causative factor in the malignant transformation of cancer cell lines (Leav et al., 1996, Salh et al., 1999) and is implicated in the carcinogenesis and metastatic potential of human cancers (Huang et al., 2000, Ito et al., 1998, Miki et al., 1999). Thus, there is robust evidence that tumor cell invasion associates with activation of p38 MAPK signaling pathway in cancers of the head and neck, breast, colon (Junttila et al., 2007) and melanoma (Boukerche et al., 2005, Boukerche et al., 2010).

Human scirrhous gastric carcinoma is a diffusely infiltrating type of poorly differentiated gastric carcinoma which, histopathologically, do not form glands, but growth by diffuse infiltration of a broad region of the gastric wall, resulting in fibrous-like thickening of the gastric wall (Dicken et al., 2005) and peritoneal dissemination or distant metastasis to lymph nodes has already occurred in many cases after clinical diagnosis. There are no standard treatments for peritoneal dissemination (Dicken et al., 2005, Yonemura et al., 2007). Peritoneal dissemination occurs frequently even after radical surgery, and is a major factor determining the poor prognosis of patients with scirrhous gastric carcinoma (Dicken et al., 2005, Yonemura et al., 2007). Further systemic chemotherapy tends to have little effect on peritoneal dissemination, because the peritoneal–blood barrier hinders drug distribution throughout the peritoneal cavity (Yonemura et al., 2007). To date, however, the mechanism of peritoneal dissemination of gastric cancer has not yet been fully elucidated. High levels of phospho-p38 MAPK are detected in poorly differentiated gastric cancers in comparison to differentiated cancers (Atsumi et al., 2007, Yokozaki, 2007). It has been suggested that the p38 MAPK signaling may be implicated in the disarrangement of cytoskeletal F-actin filaments and transcriptional suppression of E-cadherin in poorly differentiated gastric cancers. These effects may lead to an irregular cell shape and loss of cell–cell adhesion.

Here, we report that the p38 MAPK pathway plays a mechanistic role in peritoneal dissemination of human gastric cancer cells. By demonstrating that pharmacological inhibition of p38 MAPK prevents metastatic dissemination of gastric cancer cells and have an additive effect in the sensitivity to the chemotherapy, this study suggests that small molecules p38 MAPK inhibitors have anti-cancer potential.