Histone Methyltransferases as a Target for Lung Cancer Prevention

The evolution of new targeted and chemotherapies for lung cancer, while achieving modest improvement in median survival for advanced lung cancer, offer no clear path to drugs that could make this a chronic disease as seen today for metastatic breast cancer. While smoking cessation reduces mortality, 50% of lung cancer cases are diagnosed in former smokers, necessitating the need for effective preventive agents. Developing lung cancer preventive drugs has also been challenging because of the heterogeneity of this disease with respect to genetic and epigenetic alterations and the lack of a surrogate tissue to noninvasively interrogate intermediate biomarkers of response for therapeutic efficacy. Our group has focused for more than two decades on understanding lung cancer etiology, developing and validating biomarkers for early detection, and assessing efficacy of interventions for therapy and prevention in animal models. The exciting realization that the field of injury extends from the lungs to the nasal epithelium for gene expression changes provides new opportunities to evaluate the effectiveness of novel primary prevention strategies by assessing biomarkers predictive of response in the nasal epithelium. Our tobacco carcinogen-induced in vitro model for transformation of human bronchial epithelial cells (HBECs) has provided key new insights into the earliest steps and targets contributing to pre-malignancy. They include most notably transcriptional repression of microRNAs regulating epithelial to mesenchymal transition and silencing of tumor suppressor genes mediated first by chromatin remodeling catalyzed by either EZH2 and/or G9a, with subsequent dense de novo DNA methylation during progression to malignancy. Epigenetic silencing mediated by chromatin remodeling and cytosine methylation affects hundreds of genes that likely drive initiation and clonal outgrowth of premalignant epithelial cells leading to malignancy. These discoveries and fact that chromatin remodeling can be reversed with non-genotoxic agents (unlike cytosine-DNA methylation which requires treatment with genotoxic cytidine analogs for robust demethylation) offer exciting new opportunities to test preventive interventions focused on inducing the re-expression of these epigenetically regulated genes that in turn, should impede or reverse pre- malignancy. The three integrated specific aims in this application will advance these discoveries by first using the HBEC model to define the effect of modulating the expression of these cancer-associated histone methyltransferases on their gene targets and the transformation process. Second, we will assess whether diet, pharmacologic, and/or specific small molecule inhibitors to EZH2 and G9a can mitigate the transcriptional repression at these gene targets and transformation in vitro and prevent tumor development in vivo. Finally, this work will be translated through a prevention study focused on evaluating whether omega fatty acid supplementation in former smokers can modulate the expression profile in nasal epithelium of EZH2 regulated genes that are altered during transformation of HBECs.