Delineating chromatin-related gene expression signatures as a function of HNSCC progression

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Summary Oral squamous cell carcinoma (OSCC), the most common subtype of head and neck carcinoma (HNSCC), has very few targeted therapies available and poor overall survival. Novel strategies based on the high-throughput analyses offer new hope for improved risk assessment, early cancer detection, therapeutic intervention and tumor surveillance, but the impact of these strategies has been limited by an incomplete understanding of the biology of oral cancer, particularly in its early developmental stages. Like other solid malignancies, OSCCs begin as pre-neoplastic cellular proliferation that are driven by the serial acquisition of genetic and epigenetic alterations. Nearly 20% of patients with OSCC harbor multiple pre-malignant lesions showing signs of dysplasia, often visually identified as leukoplakia or erythroplakia. As some of these lesions evolve to malignant neoplasms, they represent intermediate steps in OSCC progression. This multi-step process from normal epithelium to early premalignant change to carcinoma in situ (CIS) and fully invasive carcinoma, provides a rational framework for studying molecular alterations underlying the OSCC progression. However, relatively few oncogenic mutations critical to the development of OSCC are currently recognized, impeding discovery of novel targeted therapeutics. Moreover, mutations alone are insufficient to explain the broad spectrum of gene expression changes that characterize OSCC. Whole-genome distribution of enhancers, the functional elements of the chromatin, is associated with the development of multiple solid malignancies, and mediates widespread genomic changes including expression of known cancer driver genes. Although it is becoming apparent that enhancers are the critical regulators of their target genes, and enhancer genomic elements are rapidly emerging as potent targets for anti-cancer therapeutics, the association between chromatin modifications and gene expression patterns in OSCC is not yet defined, and no comprehensive molecular information is available in oral pre-neoplastic lesions. This project will use novel bioinformatics and experimental approaches to test the central hypothesis that transcriptional changes, which arise during OSCC carcinogenesis, are enabled by dynamic chromatin alterations. Our integrated analysis will couple the gene expression and methylation landscape with a corresponding evaluation of the cancer- specific enhancer phenotype throughout the continuum of OSCC progression. Characterizing the timing and manner by which gene expression alterations coincide with markers of chromatin organization in sequentially progressive lesions within the oral cavity (e.g. mild dysplasia, moderate dysplasia, severe dysplasia/CIS, and invasive OSCC) will yield the first comprehensive epigenetic map of HNSCC evolution, and will define the key epigenetically regulated genes that drive OSCC carcinogenesis. Furthermore, evaluating their biological and clinical relevance may open up a fertile avenue for developing novel intervention strategies targeting these genes at various developmental stages of HNSCC.