Altered BRCA1 and BRCA2 responses and mutation of BRCA1 gene in mice exposed chronically and transgenerationally to aqueous extract of betel nut (AEBN)

Genetic and epigenetic instability induced by betel quid associated chemicals

Over the years, betel quid chewing and tobacco use have attracted considerable interest as they are implicated as the most likely causative risk factors of oral and esophageal cancers. Although areca nut use and betel quid chewing may lead to apoptosis, chronic exposure to areca nut and slaked lime may promote pre-malignant and malignant transformation of oral cells. The putative mutagenic and carcinogenic mechanisms may involve endogenous nitrosation of areca and tobacco alkaloids as well as the presence of direct alkylating agents in betel quid and smokeless tobacco. Metabolic activation of carcinogenic N-nitrosamines by phase-I enzymes is required not only to elicit the genotoxicity via the reactive intermediates but also to potentiate the mutagenicity with the sporadic alkylations of nucleotide bases, resulting in the formation of diverse DNA adducts. Persistent DNA adducts provides the impetus for genetic and epigenetic lesions. The genetic and epigenetic factors cumulatively influence the development and progression of disorders such as cancer. Accumulation of numerous genetic and epigenetic aberrations due to long-term betel quid (with or without tobacco) chewing and tobacco use culminates into the development of head and neck cancers. We review recent evidence that supports putative mechanisms for mutagenicity and carcinogenicity of betel quid chewing along with tobacco (smoking and smokeless) use. The detailed molecular mechanisms of the extent of accumulation and patterns of genetic alterations, indicative of the prior exposure to carcinogens and alkylating agents because of BQ chewing and tobacco use, have not yet been elucidated.

Downregulation of ATM and BRCA1 Predicts Poor Outcome in Head and Neck Cancer: Implications for ATM-Targeted Therapy

ATM and BRCA1 are DNA repair genes that play a central role in homologous recombination repair. Alterations of ATM and BRCA1 gene expression are found in cancers, some of which are correlated with treatment response and patient outcome. However, the role of ATM and BRCA1 gene expression in head and neck cancer (HNC) is not well characterized. Here, we examined the prognostic role of ATM and BRCA1 expression in two HNC cohorts with and without betel quid (BQ) exposure. The results showed that the expression of ATM and BRCA1 was downregulated in BQ-associated HNC, as the BQ ingredient arecoline could suppress the expression of both genes. Low expression of either ATM or BRCA1 was correlated with poor overall survival (OS) and was an independent prognostic factor in multivariate analysis (ATM HR: 1.895, p = 0.041; BRCA1 HR: 2.163, p = 0.040). The combination of ATM and BRCA1 expression states further improved on the prediction of OS (HR: 4.195, p = 0.001, both low vs. both high expression). Transcriptomic analysis showed that inhibition of ATM kinase by KU55933 induced apoptosis signaling and potentiated cisplatin-induced cytotoxicity. These data unveil poor prognosis in the HNC patient subgroup with low expression of ATM and BRCA1 and support the notion of ATM-targeted therapy.

Oral submucous fibrosis transforming into squamous cell carcinoma: a prospective study over 31 years in mainland China

OBJECTIVE

Oral submucous fibrosis (OSF) is an oral mucous disease caused by betel quid chewing. It is controversial whether OSF can transform into oral squamous cell carcinoma (OSCC).

MATERIALS AND METHODS

In this prospective study, a group of 567 patients with OSF were enrolled from 1986 to 2017 and followed-up until 2019. The cancerous information was collected and analyzed.

RESULTS

OSF transformed into OSCC in 32 cases (32/567, 5.6%). The patient's age ranged from 20 to 69 years, and the average age was 52 years. The time taken for transformation ranged from 2 to 24 years, the average being 8.6 years. The cancerous transformation occurred in 18 patients (56%) from years 2 to 9, in 13 patients (41%) from years 10-19 and in 1 patient (3%) from 24 years. We analyzed the betel quid chewing habits and found all 32 patients with OSCC-chewed betel quid. Betel quid chewing was most prevalent in patients aged 40-69 years. Sixteen patients had chewed betel quid for 10-19 years (16/32, 50%) and 19 patients (60%) chewed 10-19 slices each day. The OSCC was located in the left or right buccal regions in 23 patients (23/32; 72%) and in the left or right lingual regions in 4 patients (4/32; 12%). Well, moderately and poorly differentiated squamous cell carcinoma was present in 23 patients (23/32; 72%), 4 patients (3/32; 9%), and 5 patients (5/32; 16%), respectively.

CONCLUSION

Our findings supported that OSF is a real oral premalignant disorder.

CLINICAL RELEVANCE

The long duration of the transformation from the OSF to OSCC suggests more frequent examinations and corresponding treatments are necessary for OSF patients.

Downregulation of the DNA Repair Gene DDB2 by Arecoline Is through p53's DNA-Binding Domain and Is Correlated with Poor Outcome of Head and Neck Cancer Patients with Betel Quid Consumption

Arecoline is the principal alkaloid in the areca nut, a component of betel quids (BQs), which are carcinogenic to humans. Epidemiological studies indicate that BQ-chewing contributes to the occurrence of head and neck cancer (HNC). Previously, we have reported that arecoline (0.3 mM) is able to inhibit DNA repair in a p53-dependent pathway, but the underlying mechanism is unclear. Here we demonstrated that arecoline suppressed the expression of DDB2, which is transcriptionally regulated by p53 and is required for nucleotide excision repair (NER). Ectopic expression of DDB2 restored NER activity in arecoline-treated cells, suggesting that DDB2 downregulation was critical for arecoline-mediated NER inhibition. Mechanistically, arecoline inhibited p53-induced DDB2 promoter activity through the DNA-binding but not the transactivation domain of p53. Both NER and DDB2 promoter activities declined in the chronic arecoline-exposed cells, which were consistent with the downregulated DDB2 mRNA in BQ-associated HNC specimens, but not in those of The Cancer Genome Atlas (TCGA) cohort (no BQ exposure). Lower DDB2 mRNA expression was correlated with a poor outcome in HNC patients. These data uncover one of mechanisms underlying arecoline-mediated carcinogenicity through inhibiting p53-regulated DDB2 expression and DNA repair.

Oral submucous fibrosis: An update on pathophysiology of malignant transformation

Oral submucous fibrosis (OSMF) is a potentially malignant condition associated with areca nut chewing. Formerly confined to the Indian subcontinent, it is now often seen in Asian populations of the United Kingdom, USA and other developed countries, and is therefore a serious problem for global health. What makes it more sinister is the malignant transformation rate, which has been reported to be around 7.6% over a 17-year period. In this concise article, we review the current trends in the pathophysiology of malignant transformation of OSMF.

BRCA1 and MDM2 as independent blood-based biomarkers of head and neck cancer

We investigated the role of BRCA1, MDM2, and p53 in the pathogenesis of head and neck cancer (HNC) and evaluated their potential utility as blood-based predictive biomarkers of HNC. Immunostaining of tissue biopsies and whole blood lymphocytes (WBL) of 36 HNC patients were evaluated by immunohistochemistry (IHC) and immunocytochemistry (ICC), respectively. The staining intensities of BRCA1 and MDM2 in matched tissue and blood samples were significantly associated with cancer stage. Furthermore, the cellular levels of BRCA1, MDM2, and p53 were evaluated in peripheral blood lymphocytes (PBL) of 134 HNC patients and 126 controls by slot blotting. Expression levels of all three proteins in PBL of HNC patients varied significantly with respect to those of controls (p < 0.0001) with BRCA1 downregulated to 75 % of control and MDM2 and p53 upregulated to 1.7- and 1.4-fold the control level, respectively. Moreover, positive correlation was observed between expression levels of BRCA1, MDM2, and p53 in matched tissue biopsies-WBL (r s = 0.840, 0.754, and 0.806, respectively), tissue biopsies-PBL (r s = 0.745, 0.736, and 0.776, respectively), and PBL-WBL (r s = 0.709, 0.758, and 0.740, respectively), validating the hypothesis that these proteins may serve as blood-based biomarkers of HNC. Bias-corrected and accelerated (BCa) bootstrap cross-validation estimation of receiver operating characteristics (ROC) analysis established BRCA1 (AUC = 0.726, sensitivity = 89 %, NPV = 82 %) and MDM2 (AUC = 0.827, sensitivity = 85 %, NPV = 81 %) as predictive biomarkers for HNC. In conclusion, this study suggests that BRCA1 and MDM2 play a crucial role in the pathogenesis of HNC and could be used independently as predictive biomarkers for HNC.

Oral submucous fibrosis: review on mechanisms of malignant transformation

Research studies focusing on various aspects of carcinogenesis in the background of fibrosis have advanced significantly in the recent past, allowing us to understand the mechanisms involved in malignant transformation of oral submucous fibrosis (OSF), the most prevalent potentially malignant oral disorder in South Asia. The role of areca nut as a carcinogen has been proven beyond doubt, with a large number of animal studies demonstrating its carcinogenicity, mutagenicity, and genotoxicity. Studies on the molecules implicated in cell cycle regulation, hypoxia, processes leading to DNA double-strand breaks, senescence, and many other pathways related to carcinogenesis have shown ample evidence for the malignant transformation in OSF induced by areca nut. More importantly, the understanding of the mechanisms of malignant transformation may lead to early diagnosis of oral squamous cell carcinoma arising in the background of OSF, which is now considered to constitute a clinicopathologically distinct disease, and the differences are believed to arise from the differential mechanisms of areca nut carcinogenesis. Therefore, the objective of this study is to review the literature on the various mechanisms leading to the malignant transformation of OSF.

Fibrotic Effects of Arecoline N-Oxide in Oral Potentially Malignant Disorders

The metabolites of environmental chemicals play key roles in carcinogenesis. Areca nut is strongly associated with the development of oral potentially malignant disorders (OPMD) or cancer. The main alkaloid in the areca nut is arecoline, which is highly cytotoxic and genotoxic. Arecoline N-oxide, a metabolite of areca nut alkaloids, which has been identified in animal urine, has been shown to induce mutagenicity in bacteria. In this study, it was found that its protein adduct could be detected in oral keratinocytes treated with areca nut extract. Increased collagen expression and severity of squamous hyperplasia were observed in arecoline N-oxide treated mice. In cultured oral fibroblasts, arecoline N-oxide showed stronger effects on the increase of fibrotic related genes including TGF-beta1, S100A4, MMP-9, IL-6, and fibronectin and a decrease of E-cadherin as compared with arecoline. Finally, arecoline N-oxide stimulation effectively increased the DNA damage marker, gamma-H2A.X, both in vitro and in vivo. Taken together, these results indicate that arecoline N-oxide shows a high potential for the induction of OPMD.

Association of betel nut with carcinogenesis: revisit with a clinical perspective

Betel nut (BN), betel quid (BQ) and products derived from them are widely used as a socially endorsed masticatory product. The addictive nature of BN/BQ has resulted in its widespread usage making it the fourth most abused substance by humans. Progressively, several additives, including chewing tobacco, got added to simple BN preparations. This addictive practice has been shown to have strong etiological correlation with human susceptibility to cancer, particularly oral and oropharyngeal cancers.

The PUBMED database was searched to retrieve all relevant published studies in English on BN and BQ, and its association with oral and oropharyngeal cancers. Only complete studies directly dealing with BN/BQ induced carcinogenesis using statistically valid and acceptable sample size were analyzed. Additional relevant information available from other sources was also considered.

This systematic review attempts to put in perspective the consequences of this widespread habit of BN/BQ mastication, practiced by approximately 10% of the world population, on oral cancer with a clinical perspective. BN/BQ mastication seems to be significantly associated with susceptibility to oral and oropharyngeal cancers. Addition of tobacco to BN has been found to only marginally increase the cancer risk. Despite the widespread usage of BN/BQ and its strong association with human susceptibility to cancer, no serious strategy seems to exist to control this habit. The review, therefore, also looks at various preventive efforts being made by governments and highlights the multifaceted intervention strategies required to mitigate and/or control the habit of BN/BQ mastication.