Deficient double-strand break repair in oral squamous cell carcinoma cell lines

Harnessing the role of epigenetic histone modification in targeting head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most prevalent form of cancer worldwide. Despite advancements made in treatment strategies, the fatality rate of HNSCC is very high. An accumulating body of evidence suggests that epigenetic modification of histones plays an influential role in the development and progression of the disease. In this review we discuss the role of epigenetic modifications in HNSCC and the inter-relationships of human papillomavirus oncoproteins and histone-modifying agents. Further, we explore the possibility of identifying these modifications as biomarkers for their use as drugs in treatment strategies.

Molecular landscape of head and neck cancer and implications for therapy

Head and neck squamous cell carcinomas (HNSCC) arising from the oral cavity, pharynx, and larynx constitute the 6^th most common human cancer. Human papillomavirus (HPV)-positive tumours are distinct from HPV-negative counterparts, with HPV status affording clear clinical utility, prognostic benefit and better treatment outcomes. In contrast to their HPV-positive counterparts, HPV-negative tumours are characterized by high mutational load and chromosomal aberrations, with varying copy number alteration (CNA) profiles. HNSCC are distinct tumours at the chromosomal, gene and expression levels, with additional insight gained from immune profiling. Based on mutational analyses, HNSCC are categorized as HPV-positive, HPV-negative CNA-silent, and HPV-negative CNA-high tumours. Furthermore, gene expression profiling segregates these tumours into atypical, classical, basal, and mesenchymal, with clear differences observed between tumours of the oral cavity, oropharynx, hypopharynx and larynx. Additional immune profiling further classifies tumours as either immune-active or immune-exhausted. The clinical utility and impact of these tumour molecular subtypes however remains to be determined. HNSCC harbor high levels of somatic mutations. They display loss at 3p and 18q and gain at 3q and 8q, with mutations in CDKN2A, TP53, CCND1, EGFR, PIK3CA, PTEN, NOTCH1, NSD1, FAT1, AJUBA and KMT2D. Important pathways include the p53 and RB pathways which are involved in cell cycle control and are frequently lost in HPV-negative tumours, the WNT-β-catenin pathway related to the mesenchymal subtype and smoking etiology, and the PI3K pathway which includes the most common genetic alteration in HPV-positive HNSCC. Understanding the mutational, genomic and transcriptomic landscape of HNSCC has leveraged better therapeutic approaches to manage this group of diseases, and it is hoped that additional insight into the molecular subtypes of HNSCC and its specific subsites will further drive improved strategies to stratify and treat patients with this debilitating disease.

Exome sequencing of oral leukoplakia and oral squamous cell carcinoma implicates DNA damage repair gene defects in malignant transformation

OBJECTIVES

To map the genomic pathways of patients with oral leukoplakia (OLK) which transformed to cancer (progressive) and those which did not (non-progressive), and to compare their exomic profiles.

MATERIALS AND METHODS

Whole exome sequencing was performed on 42 sequential samples from five progressive and eight non-progressive patients. Association of genomic variant frequencies with progression or lesion severity were analysed by non-parametric tests (Kruskal-Wallis and Mann-Whitney-Wilcoxon) and multivariate sparse partial least squares discriminant analysis (sPLS-DA). Enrichment analysis was used to characterise the effect of mutations upon biological pathways. Confirmatory studies used qPCR and immunohistochemistry.

RESULTS

Using sPLS-DA, the variant frequency of a small number of genes could be used to classify the samples based on lesion severity or progressive status. Enrichment analysis showed that DNA damage repair gene related pathways were highly impacted in lesions which progressed to cancer. Multivariate analysis of a set of 148 DNA damage repair genes could be used to classify progressive lesions using mutation frequency. BRCA1, BRCA2 and other double strand break (DSB) repair Fanconi anaemia (FA)/BRCA pathway genes were prominent contributors to this classification.

CONCLUSION

Patients with progressive and non-progressive OLK can be differentiated using the frequency of exomic variants, particularly in DNA damage repair pathway genes. To our knowledge, this is the first report of FA/BRCA (DSB) pathway involvement in malignant transformation of OLK to oral squamous cell carcinoma (OSCC).

Oral leukoplakia remains a challenging condition

Crispian Scully had many interests in the realm of oral diseases. But oral leukoplakia was one that piqued his curiosity when he was still an academic neophyte and remained a topic which he studied throughout his enormously productive career. It is easy to understand why. While the clinical manifestations of oral leukoplakia are common, we still do not fully understand why one version of the condition is benign, while another, similar in appearance, progresses to a malignancy. The diagnosis of oral leukoplakia is based on expert clinical and histopathological examamination. Management and treatment of leukoplakia remain challenging especially for large lesions and the proliferative subtype. This review aims to provide a general overview on leukoplakia, explore current challenges in its diagnosis and management and discuss the opportunities to better understand the condition.

Transcriptome changes induced in vitro by alcohol-containing mouthwashes in normal and dysplastic oral keratinocytes

BACKGROUND

The role of alcohol-containing mouthwash as a risk factor for the development of oral cancer is a subject of conflicting epidemiological evidence in the literature despite alcohol being a recognised carcinogen. The aim of this study was to use in vitro models to investigate mechanistic and global gene expression effects of exposure to alcohol-containing mouthwash.

METHODS

Two brands of alcohol-containing mouthwash and their alcohol-free counterparts were used to treat two oral cell lines derived from normal (OKF6-TERT) and dysplastic (DOK) tissues. Genotoxicity was determined by Comet assay. RNA-seq was performed using the Ion Torrent platform. Bioinformatics analysis used R/Bioconductor packages with differential expression using DEseq2. Pathway enrichment analysis used EnrichR with the WikiPathways and Kegg databases.

RESULTS

Both cell lines displayed dose-dependent DNA damage in response to acute exposure to ethanol and alcohol-containing mouthwashes as well as alcohol-free mouthwashes reconstituted with ethanol as shown by Comet assay. The transcriptomic effects of alcohol-containing mouthwash exposure were more complex with significant differential gene expression ranging from >2000 genes in dysplastic (DOK) cells to <100 genes in normal (OKF6-TERT) cells. Pathway enrichment analysis in DOK cells revealed alcohol-containing mouthwashes showed common features between the two brands used including DNA damage response as well as cancer-associated pathways. In OKF6-TERT cells, the most significantly enriched pathways involved inflammatory signalling.

CONCLUSIONS

Alcohol-containing mouthwashes are genotoxic in vitro to normal and dysplastic oral keratinocytes and induce widespread changes in gene expression. Dysplastic cells are more susceptible to the transcriptomic effects of mouthwash.