Role of Cyclooxygenase-2 on Intermittent Hypoxia-Induced Lung Tumor Malignancy in a Mouse Model of Sleep Apnea

Noelia Campillo,Paula Naomi Nonaka,Antoni Vilaseca,Jordi Roca-Ferrer,Ramon Farré,David Gozal,César Picado,Marta Torres,Daniel Navajas,Isaac Almendros,Josep Maria Montserrat

doi:10.1038/srep44693

Abstract

An adverse role for obstructive sleep apnea (OSA) in cancer epidemiology and outcomes has recently emerged from clinical and animal studies. In animals, intermittent hypoxia (IH) mimicking OSA promotes tumor malignancy both directly and via host immune alterations. We hypothesized that IH could potentiate cancer aggressiveness through activation of the cyclooxygenase-2 (COX-2) pathway and the concomitant increases in prostaglandin E2 (PGE2). The contribution of the COX-2 in IH-induced enhanced tumor malignancy was assessed using celecoxib as a COX-2 specific inhibitor in a murine model of OSA bearing Lewis lung carcinoma (LLC1) tumors. Exposures to IH accelerated tumor progression with a tumor associated macrophages (TAMs) shift towards a pro-tumoral M2 phenotype. Treatment with celecoxib prevented IH-induced adverse tumor outcomes by inhibiting IH-induced M2 polarization of TAMs. Furthermore, TAMs isolated from IH-exposed mice treated with celecoxib reduced the proliferation of LLC1 naïve cells, while the opposite occurred with placebo-treated IH-exposed mice. Finally, in vitro IH exposures of murine macrophages and LLC1 cells showed that both cell types increased PGE2 release in response to IH. These results suggest a crucial role for the COX-2 signaling pathway in the IH-exacerbated malignant processes, and designate macrophages and lung adenocarcinoma cells, as potential sources of PGE2.

Highlights

Taken together, the intermittent hypoxia (IH)-induced changes on the tumoral immune response would be anticipated to lead to a more tumor-permissive microenvironment, facilitating processes such as tumor growth, invasion, or dissemination, as previously reported[8,9,13]
We found that the IH-induced enhancements of tumor malignancy are mediated, at least in part by the COX-2/prostaglandin E2 (PGE2) signaling pathway
PTGS2 gene and COX-2 protein expression showed a trend toward increases in purified tumor associated macrophages (TAMs) and in tumors isolated from IH-exposed mice in comparison to normoxia, respectively

Summary

Introduction

The IH-induced changes on the tumoral immune response would be anticipated to lead to a more tumor-permissive microenvironment, facilitating processes such as tumor growth, invasion, or dissemination, as previously reported[8,9,13]. Targeting COX-2 activity through nonsteroidal anti-inflammatory drugs (NSAIDs) has been proposed as a potentially promising strategy in the prevention and treatment of cancer[20] In this context, NSAIDs have been widely employed over the last decades in pre-clinical and clinical trials as COX inhibitors, facilitating anti-tumoral host immune responses (mainly through the reduction of the M2-like polarization of TAMs and the infiltration of regulatory cells), and decreasing the incidence and mortality in several types of cancer[21,22]. We used celecoxib (Ce), a well-characterized and specific COX-2 inhibitor, to investigate whether the COX-2/PGE2 signaling pathway participates in the IH-induced exacerbation of malignant processes using a mouse model of OSA bearing Lewis lung carcinoma (LLC1) tumors. We assessed which cell type, namely macrophages or tumor cells, provides the major source of PGE2 in response to IH using a well-established in vitro model

Methods

Results

Conclusion