Targeting the epigenome for the treatment of thoracic malignancies

Antitumour effect of valproic acid against salivary gland cancer in vitro and in vivo

Salivary gland cancer (SGC) has a comparatively poor prognosis and is prone to frequent recurrence and metastases. Therefore, the development of more effective chemotherapy against SGC is desirable. The aim of the present study was to investigate the antitumour effects of valproic acid (VPA) against SGC in vitro and in vivo. Two human SGC cell lines (HSY and HSG cells) were used in the present study. The effects of VPA on the proliferation of SGC cells in vitro were assessed by MTT assay. Cancer cells treated with VPA were subjected to cell cycle analysis by flow cytometry. In addition, the expression levels of p21 and p27 were examined by real-time RT-PCR to identify the mechanisms of the antitumour effect of VPA on SGC. The effects of VPA on cancer growth in vivo were evaluated in a xenograft model. VPA inhibited the proliferation of SGC cells in a dose-dependent manner in vitro. Degenerated cancer cells were observed at high concentrations of VPA. In the cell cycle analysis, VPA induced cell-growth inhibition and G1 arrest of cell cycle progression in both cancer cell lines in a time- and dose-dependent manner. VPA markedly upregulated the mRNA expression levels of both p21 and p27 in both SGC cell lines in a time-dependent manner. In the xenograft model experiment, VPA treatment markedly inhibited the growth of salivary gland tumours when compared with the growth of the untreated controls. VPA may be a valuable drug in the development of better therapeutic regimens for SGC.

Epigenetic modulation enhances the therapeutic effect of anti-IL-13R(alpha)2 antibody in human mesothelioma xenografts

PURPOSE

The interleukin-13 receptor α2 (IL-13Rα2) is expressed by a variety of human malignant cells. Here, we have examined the constitutive surface expression and the epigenetic regulation of IL-13Rα2 by human mesothelioma. We have also investigated the therapeutic effect of the DNA methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) and anti-IL-13Rα2 monoclonal antibody on mesothelioma xenografts.

EXPERIMENTAL DESIGN

Cell surface expression of IL-13Rα2 by various lung carcinomas was analyzed using flow cytometry. Therapeutic effects of anti-IL-13Rα2 and 5-aza-dC were investigated using antibody-dependent cellular cytotoxicity and proliferation assays and by monitoring the survival of mesothelioma-bearing mice.

RESULTS

We found that human malignant mesotheliomas expressed surface IL-13Rα2 on their surface and that it was upregulated by treatment with 5-aza-dC. This augmented expression of IL-13Rα2 resulted in growth inhibition of the mesothelioma cells when cocultured with anti-IL-13Rα2 and effector cells, such as splenocytes and peritoneal exudate cells. The growth inhibition of mesothelioma cells was mediated by IFN-γ that was only detected in the supernatant when effector cells were exposed to 5-aza-dC-treated tumors in the presence of anti-IL-13Rα2. Compared with the control or either regimen alone, in vivo administration of anti-IL-13Rα2 in combination with 5-aza-dC significantly prolonged the survival of mice with mesothelioma xenografts.

CONCLUSIONS

These observations indicate a promising role for IL-13Rα2 as a target for antibody treatment in malignant mesothelioma, and, in combination with epigenetic regulation by a DNA methylation inhibitor, suggest the potential for a novel strategy to enhance therapeutic potency.

Reduced expression of IRF7 in nasal epithelial cells from smokers after infection with influenza

Smokers are more susceptible to respiratory viral infections, including influenza virus, but the mechanisms mediating this effect are unknown. To determine how epithelial cells contribute to the enhanced susceptibility seen in smokers, we established an in vitro model of differentiated nasal epithelial cells (NECs) from smokers, which showed enhanced mucin expression. The NECs from smokers responded to influenza infection with greater cytotoxicity, release of interleukin-6, and viral shedding than NECs from nonsmokers. Focusing on type I interferon (IFN) expression, we observed that influenza-infected NECs from smokers produced significantly less IFN-alpha than NECs from nonsmokers. Similarly, the expression of IRF7, a key transcription factor controlling the expression of IFN-alpha, was significantly decreased in influenza-infected and IFN-beta-stimulated NECs from smokers. Furthermore, our data indicate that the DNA methylation of the IRF7 gene and expression of the DNA (cytosine-5-)-methyltransferase 1 was enhanced in NECs from smokers. To confirm these findings in vivo, we initiated a study in which smoking and nonsmoking healthy volunteers were inoculated nasally with the live-attenuated influenza virus (LAIV) vaccine, and nasal biopsies were obtained before and after the administration of LAIV. The LAIV-induced expression of IRF7 was lower in the nasal epithelium from smokers, supporting our in vitro observations. These data demonstrate that infection with influenza results in the reduced expression of transcription factor IRF7 in NECs from smokers, and that these effects may be mediated by an epigenetic modification of the IRF7 gene, thus providing a potential mechanism rendering smokers more susceptible to respiratory virus infections.

Conserved responses to trichostatin A in rodent lungs exposed to endotoxin or stretch

Histone deacetylase (HDAC) isoenzymes have been suggested as possible drug targets in pulmonary cancer and in inflammatory lung diseases such as asthma and COPD. Whether HDAC inhibition is pro- or anti-inflammatory is under debate. To further examine this clinically relevant paradigm, we analyzed 8 genes that are upregulated by two pro-inflammatory stimuli, i.e. endotoxin and mechanical stress (overventilation), in isolated rat and mouse lungs, respectively. We studied the effect of the HDAC inhibitor trichostatin A (TSA) under control conditions, in response to endotoxin and overventilation, and on the effects of the steroid dexamethasone. TSA affected gene expression largely independent of the stimulus (endotoxin, overventilation) and the species (rat, mouse) leading to upregulation of some genes (Tnf, Cxcl2) and downregulation of others (Cxcl10, Timp1, Selp, Il6). At the protein level, TSA reduced the stimulated release of TNF, MIP-2alpha and IL-6, indicating that TSA may affect protein translation independent from gene transcription. In general, the anti-inflammatory effects of TSA on gene expression and protein release were additive to that of dexamethasone, suggesting that both drugs employ different mechanisms. We conclude that pro-inflammatory stimuli induce distinct sets of genes that are regulated by HDAC in a diverse, but consistent manner across two rodent species. The present findings together with previous in vivo studies suggest that the effect of HDAC inhibition in the intact lung is in part anti-inflammatory.