Alterações genéticas e epigenéticas associadas a neoplasias de cabeça e pescoço

Abstract

Cancer is the leading cause of death worldwide and head and neck malignant neoplasias account for 5% of all new cancer cases in the world. This cancer subtype is the sixth most common form of cancer in Brazil. Specifically, squamous cell carcinoma (SCC) and salivary gland neoplasias (SGNs) account for the majority of reported cases within this subtype. SGNs exhibit a broad spectrum of phenotypic heterogeneity, both within the same tumor as well as when compared to other types of neoplasias. Recently, genetic alterations, including polymorphisms, have been extensively investigated in SCC. The TP53 (Tumor Protein P53) gene is localized to chromosome 17 (17p13.1) and encodes a 53kDa phosphoprotein (P53), which is involved in cell cycle control and associated with a number of neoplasias. Interestingly, a 72 codon single-nucleotide-polymorphism (72 SNP), localized to exon 4 of TP53 is associated with the onset and progression of some types of neoplasia. Hypoxia is an important resistance mechanism for cancer therapy and epigenetic modifications have been shown to be associated with head and neck neoplasias. In fact, miR-210, a miRNA regulated by hypoxia via the hypoxia-inducible factor 1 (HIF-1), is involved in inhibition of apoptosis and increased angiogenesis. Studies have suggested that miR-210 might be a useful biomarker for both diagnosis and prognosis of various neoplasias. Bioinformatics is a powerful tool for the comprehensive evaluation of differential gene expression in tumours. The aim of this dissertation was to evaluate the relationship between expression of the TP53 codon 72 SNP and both the risk of developing HNSCC as well as prognosis in patients with HNSCC. Furthermore, the goal was to determine whether the expression of the hypoxia markers, HIF-1 and miR-210, are altered in benign and malignant SGNs. Finally, through the use of bioinformatics, our aim was to investigate the main processes altered following chemotherapeutic treatment in SGNs. Expression of the TP53 codon 72 SNP in HNSCC and control individuals was evaluated using Polymerase Chain Reaction (PCR), which was followed with a multivariate analysis to determine the odds ratio of HNSCC. Additionally, a Fuzzy C Means Clustering was used to group HSSCC individuals for survival analysis. PCR was also used to evaluate the expression of HIF-1 and miR-210 in 21 samples, including 7 malignant SGNs (33.33%), 7 benign SGNs (33.33%) and 7 control non-neoplastic salivary tissue samples (33.33%). Through the use of bioinformatics, we evaluated the main biological processes regulated by chemotherapy in SGNs. Individuals expressing one arginine of the TP53 codon72 SNP had a greater risk of HNSCC development. However, no association was observed between TP53 codon72 SNP expression and worse HNSCC prognosis. Furthermore, there was no difference in HIF-1 and miR-210 expression in either benign or malignant neoplasias of salivary glands, as compared to control, non-neoplastic salivary glands. Finally, bioinformatic analyses revealed the most robust alterations in processes specifically related to DNA and cellular division in SGNs, as compared to control healthy tissue samples.