Mitochondrial DNA mutations in oral squamous cell carcinoma

Saliva as a potential non-invasive liquid biopsy for early and easy diagnosis/prognosis of head and neck cancer

Head and neck squamous cell carcinomas (HNSCCs) are the most devastating diseases in India and southeast Asia. It is a preventable and curable disease if detected early. Tobacco and alcohol consumption are the two major risk-factors but infection of high-risk HPVs are also associated with development of predominantly oral and oropharyngeal carcinomas. Interestingly, unlike cervical cancer, HPV-induced HNSCCs show good prognosis and better survival in contrast, majority of tobacco-associated HPV-ve HNSCCs are highly aggressive with poor clinical outcome. Biomarker analysis in circulatory body-fluids for early cancer diagnosis, prognosis and treatment monitoring are becoming important in clinical practice. Early diagnosis using non-invasive saliva for oral or other diseases plays an important role in successful treatment and better prognosis. Saliva mirrors the body's state of health as it comes into direct contact with oral lesions and needs no trained manpower to collect, making it a suitable bio-fluid of choice for screening. Saliva can be used to detect not only virus, bacteria and other biomarkers but variety of molecular and genetic markers for an early detection, treatment and monitoring cancer and other diseases. The performance of saliva-based diagnostics are reported to be highly (≥95 %) sensitive and specific indicating the test's ability to correctly identify true positive or negative cases. This review focuses on the potentials of saliva in the early detection of not only HPV or other pathogens but also identification of highly reliable gene mutations, oral-microbiomes, metabolites, salivary cytokines, non-coding RNAs and exosomal miRNAs. It also discusses the importance of saliva as a reliable, cost-effective and an easy alternative to invasive procedures.

Prognostic Value of Circulating Mitochondrial DNA in Prostate Cancer and Underlying Mechanism

Circulating DNAs are considered as degraded DNA fragments of approximately 50-200 bp, found in blood plasma, consisting of cell-free mitochondrial and nuclear DNA. Such cell-free DNAs in the blood are found to be altered in different pathological conditions including lupus, heart disease, and malignancies. While nuclear DNAs are being used and being developed as a powerful clinical biomarker in liquid biopsies, mitochondrial DNAs (mtDNAs) are associated with inflammatory conditions including cancer progression. Patients with cancer including prostate cancer are found to have measurable concentrations of mitochondrial DNA in circulation in comparison with healthy controls. The plasma content of mitochondrial DNA is dramatically elevated in both prostate cancer patients and mouse models treated with the chemotherapeutic drug. Cell-free mtDNA, in its oxidized form, induced a pro-inflammatory condition and activates NLRP3-mediated inflammasome formation which causes IL-1β-mediated activation of growth factors. On the other hand, interacting with TLR9, mtDNAs trigger NF-κB-mediated complement C3a positive feedback paracrine loop and activate pro-proliferating signaling through upregulating AKT, ERK, and Bcl2 in the prostate tumor microenvironment. In this review, we discuss the growing evidence supporting cell-free mitochondrial DNA copy number, size, and mutations in mtDNA genes as potential prognostic biomarkers in different cancers and targetable prostate cancer therapeutic candidates impacting stromal-epithelial interactions essential for chemotherapy response.

Effects of tobacco on the DNA of smokers and non-smokers affected by OSCC: systematic review and meta-analysis

Scientific evidence about genetic and molecular changes in oral squamous cell carcinoma (OSCC) among smokers and non-smokers is inconclusive. This systematic review and meta-analysis assessed the effects of tobacco on the DNA of individuals with OSCC based on protein mutations. Electronic searches were conducted on PubMed, Ovid, Web of Science, and Scopus to identify observational studies published up to January/2022. The Joanna Briggs Institute tool was used for the critical appraisal of studies. The certainty of the evidence was evaluated. Twenty-three studies assessing 4,060 individuals (2,967 smokers vs. 1,093 non-smokers) were included in this review. Fifteen groups of proteins/genes were investigated. Analysis of the quality of articles revealed low risk of bias in most studies. The certainty of the evidence was very low. The meta-analysis confirmed no significant difference between smokers and non-smokers with respect to damage to GSTM1 (OR: 0.60; 95%CI: 0.30-1.18), GSTT1 (OR: 1.18; 95%CI:0.49-2.83), hydrolase proteins (Ku70 and Ku80) (OR: 0.74; 95%CI: 0.18-3.05), and transferase proteins (GSTM1, GSTT1, GSTM3) (OR: 0.74; 95%CI: 0.47-1.18). Most of the studies included showed that smokers are more likely to exhibit genetic instability. However, the meta-analysis revealed that smokers do not necessarily have more genetic alterations in the DNA than non-smokers.

The Role of Mitochondrial miRNAs in the Development of Radon-Induced Lung Cancer

MicroRNAs are short, non-coding RNA molecules regulating gene expression by inhibiting the translation of messenger RNA (mRNA) or leading to degradation. The miRNAs are encoded in the nuclear genome and exported to the cytosol. However, miRNAs have been found in mitochondria and are probably derived from mitochondrial DNA. These miRNAs are able to directly regulate mitochondrial genes and mitochondrial activity. Mitochondrial dysfunction is the cause of many diseases, including cancer. In this review, we consider the role of mitochondrial miRNAs in the pathogenesis of lung cancer with particular reference to radon exposure.

Identification of potential candidate genes for lip and oral cavity cancer using network analysis

Lip and oral cavity cancer, which can occur in any part of the mouth, is the 11th most common type of cancer worldwide. The major obstacles to patients' survival are the poor prognosis, lack of specific biomarkers, and expensive therapeutic alternatives. This study aimed to identify the main genes and pathways associated with lip and oral cavity carcinoma using network analysis and to analyze its molecular mechanism and prognostic significance further. In this study, 472 genes causing lip and oral cavity carcinoma were retrieved from the DisGeNET database. A protein-protein interaction network was developed for network analysis using the STRING database. VEGFA, IL6, MAPK3, INS, TNF, MAPK8, MMP9, CXCL8, EGF, and PTGS2 were recognized as network hub genes using the maximum clique centrality algorithm available in cytoHubba, and nine potential drug candidates (ranibizumab, siltuximab, sulindac, pomalidomide, dexrazoxane, endostatin, pamidronic acid, cetuximab, and apricoxib) for lip and oral cavity cancer were identified from the DGIdb database. Gene enrichment analysis was also performed to identify the gene ontology categorization of cellular components, biological processes, molecular functions, and biological pathways. The genes identified in this study could furnish a new understanding of the underlying molecular mechanisms of carcinogenesis and provide more reliable biomarkers for early diagnosis, prognostication, and treatment of lip and oral cavity cancer.

Association Between Mitochondrial DNA Copy Number and Head and Neck Squamous Cell Carcinoma: A Systematic Review and Dose-Response Meta-Analysis

Background

The association between mitochondrial DNA (mtDNA) copy number and head and neck squamous cell carcinoma (HNSCC) risk remains unclear. Therefore, we aimed to evaluate the relationship between mtDNA copy number and HNSCC risk.

Material/Methods

We searched PubMed, Web of Science, and EMBASE until August 2020. Studies that assessed the association between mtDNA copy number and HNSCC as the outcome of interest were included. We performed a 2-class and dose-response meta-analysis to assess the association between cancer risk and mtDNA.

Results

Eight articles (2 cohort studies and 6 case-control studies) with a total of 3913 patients were included in our meta-analysis. The overall results showed that mean mtDNA copy number level from 9 studies was 0.71 higher in patients with cancer than in non-cancer controls (the standardized mean differences (SMD) 0.71, 95% CI: 0.28–1.15, P<0.001). However, when 4 studies were pooled by dichotomizing mtDNA copy number at the median value into high- and low-content groups, no significant association between mtDNA content and overall cancer risk was found (odds ratio (OR)=0.87, 95% CI: 0.52–1.44, P=0.584). Furthermore, we observed a non-linear association from 3 studies between increased mtDNA copy number levels (P for nonlinearity <0.001).

Conclusions

The elevated mtDNA copy number could predict the risk of HNSCC as a biomarker. Moreover, there was non-linear relationship of risk between HNSCC and mtDNA copy number.

Effects of obesity and weight loss on mitochondrial structure and function and implications for colorectal cancer risk

Colorectal cancer (CRC) is the third most common cancer globally. CRC risk is increased by obesity, and by its lifestyle determinants notably physical inactivity and poor nutrition. Obesity results in increased inflammation and oxidative stress which cause genomic damage and contribute to mitochondrial dysregulation and CRC risk. The mitochondrial dysfunction associated with obesity includes abnormal mitochondrial size, morphology and reduced autophagy, mitochondrial biogenesis and expression of key mitochondrial regulators. Although there is strong evidence that increased adiposity increases CRC risk, evidence for the effects of intentional weight loss on CRC risk is much more limited. In model systems, energy depletion leads to enhanced mitochondrial integrity, capacity, function and biogenesis but the effects of obesity and weight loss on mitochondria in the human colon are not known. We are using weight loss following bariatric surgery to investigate the effects of altered adiposity on mitochondrial structure and function in human colonocytes. In summary, there is strong and consistent evidence in model systems and more limited evidence in human subjects that over-feeding and/or obesity result in mitochondrial dysfunction and that weight loss might mitigate or reverse some of these effects.

Mutations in the ND2 Subunit of Mitochondrial Complex I Are Sufficient to Confer Increased Tumorigenic and Metastatic Potential to Cancer Cells

Multiprotein complexes of the mitochondrial electron transport chain form associations to generate supercomplexes. The relationship between tumor cell ability to assemble mitochondrial supercomplexes, tumorigenesis and metastasis has not been studied thoroughly. The mitochondrial and metabolic differences between L929dt cells, which lost matrix attachment and MHC-I expression, and their parental cell line L929, were analyzed. L929dt cells have lower capacity to generate energy through OXPHOS and lower respiratory capacity than parental L929 cells. Most importantly, L929dt cells show defects in mitochondrial supercomplex assembly, especially in those that contain complex I. These defects correlate with mtDNA mutations in L929dt cells at the ND2 subunit of complex I and are accompanied by a glycolytic shift. In addition, L929dt cells show higher in vivo tumorigenic and metastatic potential than the parental cell line. Cybrids with L929dt mitochondria in L929 nuclear background reproduce all L929dt properties, demonstrating that mitochondrial mutations are responsible for the aggressive tumor phenotype. In spite of their higher tumorigenic potential, L929dt or mitochondrial L929dt cybrid cells are sensitive both in vitro and in vivo to the PDK1 inhibitor dichloroacetate, which favors OXPHOS, suggesting benefits for the use of metabolic inhibitors in the treatment of especially aggressive tumors.

Molecular alterations of mitochondrial D-loop in oral leukoplakia

BACKGROUND

Over the years, numerous studies proposed a crucial role of mutations of nuclear DNA in the carcinogenesis process. Of late, many researchers suppose that alterations of mitochondrial DNA should not be excepted from this analysis. Mutational analysis of mitochondrial DNA displayed that mitochondrial D-loop is assessed as a hotspot for molecular alterations in various types of malignant tumors encompassing oral squamous cell carcinoma. Squamous cell carcinoma is believed to emerge through precancerous stages, which might be merely morphologic aspects of cumulative genetic variations.

METHODS

In keeping with this model of molecular tumor progression, this study aimed to investigate the qualitative and quantitative alterations that might occur in mitochondrial D-loop in oral leukoplakia whether dysplastic or not by semiquantitation of a product of the polymerase chain reaction and sequence analyses of mitochondrial D-loop gene.

RESULTS

Statistically significant increases in the mean values of D-loop concentrations were observed across the dysplasia gradient of oral leukoplakia. Sequence analyses revealed the presence of point mutations in both dysplastic and nondysplastic oral leukoplakia but not in normal mucosa.

CONCLUSION

The results of this study suggested that quantitative and qualitative alterations in mitochondrial D-loop could be a promising molecular marker for early detection and progression of the malignancy.

Detection of mitochondrial transfer RNA (mt-tRNA) gene mutations in patients with idiopathic pulmonary fibrosis and sarcoidosis

Mitochondrial reactive oxygen species production may lead to tissue injury associated with two respiratory disorders of unknown origin which are shared by common tissue fibrosis, IPF and sarcoidosis. Sequence analysis of 22 mt-tRNA genes and parts of their flanking genes revealed 32 and 45 mutations in 38/40 IPF and 69/85 sarcoidosis patients respectively. 4 novel mutations were identified. 15/32 and 25/45 mutations were exclusively expressed while 12/32 and 17/45 mutations predominantly occurred in IPF and sarcoidosis group respectively, compared to healthy controls. Novel mutation combinations were solely expressed in disease. Hence, a mitochondrial-mediated pathogenic pathway seems to underlie both entities.

Keratinocyte differentiation induces APOBEC3A, 3B, and mitochondrial DNA hypermutation

Mitochondrial DNA (mtDNA) mutations are found in many types of cancers and suspected to be involved in carcinogenesis, although the mechanism has not been elucidated. In this study, we report that consecutive C-to-T mutations (hypermutations), a unique feature of mutations induced by APOBECs, are found in mtDNA from cervical dysplasia and oropharyngeal cancers. In vitro, we found that APOBEC3A (A3A) and 3B (A3B) expression, as well as mtDNA hypermutation, were induced in a cervical dysplastic cell line W12 when cultured in a differentiating condition. The ectopic expression of A3A or A3B was sufficient to hypermutate mtDNA. Fractionation of W12 cell lysates and immunocytochemical analysis revealed that A3A and A3B could be contained in mitochondrion. These results suggest that mtDNA hypermutation is induced upon keratinocyte differentiation, and shed light on its molecular mechanism, which involves A3s. The possible involvement of mtDNA hypermutations in carcinogenesis is also discussed.

Detection of somatic mutations in the mitochondrial DNA control region D-loop in brain tumors: The first report in Malaysian patients

Although the role of nuclear-encoded gene alterations has been well documented in brain tumor development, the involvement of the mitochondrial genome in brain tumorigenesis has not yet been fully elucidated and remains controversial. The present study aimed to identify mutations in the mitochondrial DNA (mtDNA) control region D-loop in patients with brain tumors in Malaysia. A mutation analysis was performed in which DNA was extracted from paired tumor tissue and blood samples obtained from 49 patients with brain tumors. The D-loop region DNA was amplified using the PCR technique, and genetic data from DNA sequencing analyses were compared with the published revised Cambridge sequence to identify somatic mutations. Among the 49 brain tumor tissue samples evaluated, 25 cases (51%) had somatic mutations of the mtDNA D-loop, with a total of 48 mutations. Novel mutations that had not previously been identified in the D-loop region (176 A-deletion, 476 C>A, 566 C>A and 16405 A-deletion) were also classified. No significant associations between the D-loop mutation status and the clinicopathological parameters were observed. To the best of our knowledge, the current study presents the first evidence of alterations in the mtDNA D-loop regions in the brain tumors of Malaysian patients. These results may provide an overview and data regarding the incidence of mitochondrial genome alterations in Malaysian patients with brain tumors. In addition to nuclear genome aberrations, these specific mitochondrial genome alterations may also be considered as potential cancer biomarkers for the diagnosis and staging of brain cancers.

Impact of somatic mutations in the D-loop of mitochondrial DNA on the survival of oral squamous cell carcinoma patients

Objectives

The aim of this study was to investigate somatic mutations in the D-loop of mitochondrial DNA (mtDNA) and their impact on survival in oral squamous cell carcinoma patients.

Materials and Methods

Surgical specimen confirmed by pathological examination and corresponding non-cancerous tissues were collected from 120 oral squamous cell carcinoma patients. The sequence in the D-loop of mtDNA from non-cancerous tissues was compared with that from paired cancer samples and any sequence differences were recognized as somatic mutations.

Results

Somatic mutations in the D-loop of mtDNA were identified in 75 (62.5%) oral squamous cell carcinoma patients and most of them occurred in the poly-C tract. Although there were no significant differences in demographic and tumor-related features between participants with and without somatic mutation, the mutation group had a better survival rate (5 year disease-specific survival rate: 64.0% vs. 43.0%, P = 0.0266).

Conclusion

Somatic mutation in D-loop of mtDNA was associated with a better survival in oral squamous cell carcinoma patients.

D-loop somatic mutations and ∼5 kb "common" deletion in mitochondrial DNA: important molecular markers to distinguish oral precancer and cancer

Apart from genomic DNA, mutations at mitochondrial DNA (mtDNA) have been hypothesized to play vital roles in cancer development. In this study, ∼5 kb deletion and D-loop mutations in mtDNA and alteration in mtDNA content were investigated in buccal smears from 104 healthy controls and 74 leukoplakia and 117 cancer tissue samples using Taqman-based quantitative assay and re-sequencing. The ∼5 kb deletion in mtDNA was significantly less (9.8 and 10.5 folds, P < 0.0001) in cancer tissues compared to control and leukoplakia tissues, respectively. On the other hand, somatic mutations in D-loop, investigated in 54 controls, 50 leukoplakias and 56 cancer patients, were found to be significantly more in cancer tissues, but not in leukoplakia tissues, compared to control (Z-score = 5.4). MtDNA contents were observed to be significantly more in leukoplakia (2.1 folds, P = 0.004) and cancer (1.6 folds, P = 0.03) tissues compared to control tissues. So, D-loop somatic mutations and ∼5 kb deletion patterns could be used as distinguishing markers between precancer and cancer tissues. This observation further suggests that somatic mutations in D-loop may facilitate carcinogenesis and cancer cells with less ∼5 kb deletion, i.e., intact mtDNA, may become resistant to apoptosis.

Clonality analysis in primary oral squamous cell carcinoma and related lymph-node metastasis revealed by TP53 and mitochondrial DNA next generation sequencing analysis

The chance of developing a neck nodal metastasis after initial treatment of oral squamous cell carcinoma varies from 12.4% to 62%. Despite being the main reason for cancer-related mortality, nodal metastases are still rarely subjected to molecular analyses, and our knowledge of the clonal heterogeneity of multiple lesions within the same patient is limited. The aim of the present study was to evaluate the relationship between primary oral cancer and lymph node metastasis in a series of patients with synchronous and metachronous metastases by 2 clonality tests: mt-DNA and TP53 sequence analysis. The study population consisted of 10 consecutive patients. Data identified in this study demonstrate that our assay based on next-generation analysis of TP53 and mt-DNA is simple, is reliable, allows high throughput, and may be applied to retrospective cases. The combination of mt-DNA and TP53 data analysis helped us to evaluate more precisely and consistently the genetic relationship among different tumor clones.

Additional cytosine inside mitochondrial C-tract D-loop as a progression risk factor in oral precancer cases

INTRODUCTION

Alterations inside Polycytosine tract (C-tract) of mitochondrial DNA (mtDNA) have been described in many different tumor types. The Poly-Cytosine region is located within the mtDNA D-loop region which acts as point of mitochondrial replication origin. A suggested pathogenesis is that it interferes with the replication process of mtDNA which in turn affects the mitochondrial functioning and generates disease.

METHODOLOGY

100 premalignant cases (50 leukoplakia & 50 oral submucous fibrosis) were selected and the mitochondrial DNA were isolated from the lesion tissues and from the blood samples. Polycytosine tract in mtDNA was sequenced by direct capillary sequencing.

RESULTS

40 (25 leukoplakia & 15 oral submucous fibrosis) patients harbored lesions that displayed one additional cytosine after nucleotide thymidine (7CT6C) at nt position 316 in C-tract of mtDNA which were absent in corresponding mtDNA derived from blood samples.

CONCLUSION

Our results show an additional cytosine in the mtDNA at polycytosine site in oral precancer cases. It is postulated that any increase/decrease in the number of cytosine residues in the Poly-Cytosine region may affect the rate of mtDNA replication by impairing the binding of polymerase and other transacting factors. By promoting mitochondrial genomic instability, it may have a central role in the dysregulation of mtDNA functioning, for example alterations in energy metabolism that may promote tumor development. We, therefore, report and propose that this alteration may represent the early development of oral cancer. Further studies with large number of samples are needed in to confirm the role of such mutation in carcinogenesis.

Association between mitochondrial C-tract alteration and tobacco exposure in oral precancer cases

INTRODUCTION

Tobacco exposure is a known risk factor for oral cancer. India is home to oral cancer epidemic chiefly due to the prevalent use of both smoke and smokeless tobacco. To reduce the related morbidity early detection is required. The key to this is detailing molecular events during early precancer stage. Mitochondrion is an important cellular organelle involved in cell metabolism and apoptosis. Mitochondrial dysfunction is thought to be the key event in oncogenesis. Last decade has seen a spurt of reports implicating mitochondrial mutations in oral carcinogenesis. However, there are few reports that study mitochondrial deoxyribonucleic acid (mtDNA) changes in oral precancer. This study aims to understand and link effect of tobacco exposure on mtDNA in oral precancer cases.

SUBJECTS AND METHODS

A total of 100 oral precancer cases of which 50 oral leukoplakia and 50 oral submucous fibrosis were recruited in the study and a detailed questionnaire were filled about the tobacco habits. Their tissue and blood samples were collected. Total genomic DNA was isolated from both sources. Mitochondrial C-tract was amplified and bidirectional sequencing was carried out. Mutations were scored over matched blood DNA.

RESULTS

There was a significant association between the presence of mitochondrial C-tract alteration and duration of tobacco exposure. The probability increased with increasing duration of tobacco consumption. The risk of having this alteration was more in chewers than in smokers.

CONCLUSIONS

Tobacco in both form, chewable and smoke, is oncogenic and causes early changes in mitochondrial genome and chances increases with increasing duration of tobacco consumption.

Mitochondria and the evolutionary roots of cancer

Cancer disease is inherent to, and widespread among, metazoans. Yet, some of the hallmarks of cancer such as uncontrolled cell proliferation, lack of apoptosis, hypoxia, fermentative metabolism and free cell motility (metastasis) are akin to a prokaryotic lifestyle, suggesting a link between cancer disease and evolution. In this hypothesis paper, we propose that cancer cells represent a phenotypic reversion to the earliest stage of eukaryotic evolution. This reversion is triggered by the dysregulation of the mitochondria due to cumulative oxidative damage to mitochondrial and nuclear DNA. As a result, the phenotype of normal, differentiated cells gradually reverts to the phenotype of a facultative anaerobic, heterotrophic cell optimized for survival and proliferation in hypoxic environments. This phenotype matches the phenotype of the last eukaryotic common ancestor (LECA) that resulted from the endosymbiosis between an α-proteobacteria (which later became the mitochondria) and an archaebacteria. As such, the evolution of cancer within one individual can be viewed as a recapitulation of the evolution of the eukaryotic cell from fully differentiated cells to LECA. This evolutionary model of cancer is compatible with the current understanding of the disease, and explains the evolutionary basis for most of the hallmarks of cancer, as well as the link between the disease and aging. It could also open new avenues for treatment directed at reestablishing the synergy between the mitochondria and the cancerous cell.

The mitochondrial genome: a biosensor for early cancer detection?

Mutations in the mitochondrial genome have been reported as biomarkers for the detection of cancer. Hallmarks of cancer development include the accumulation of genetic alterations in the mitochondrial and nuclear genomes. Damage to mitochondria affects energy metabolism, generation of reactive oxygen species, apoptosis, cell growth and other processes that contribute to the neoplastic process. Furthermore, mitochondrial DNA mutations occur frequently in cancer. Little work has been done to link a pathway between mitochondrial mutations and cancer etiology. Volumes of work have been reported on the association of mitochondrial mutations and almost all types of cancer including the use of body fluids for early detection. This review examines the measurement of mitochondrial mutations for the application of detecting human tumor tissue.

Accumulation of mutations over the complete mitochondrial genome in tobacco-related oral cancer from northeast India

Northeast India has one of the world's highest incidences of oral cancer and 90% of them are related to tobacco. We examined the complete mitochondrial genome to determine hot spot mutations in oral cancer. The complete mitochondrial genome was sequenced using PGM™ from 10 patients matched blood and tumour tissue. Overall, 26 somatic mutations were found of which nine mutations in d-loop and 17 mutations in the coding region. The mutations at nucleotide positions 16294, 16325 and 16463 in d-loop and 4136, 13542 and 13869 in coding region are probably an indication to be a hot spot mutation in oral cancer. The knowledge about role, patterns and timing of mitochondrial mutations may serve to be facilitating clinical applications and hot spot mutations may be helpful in assessing cancer risk in tumour.

Association of mitochondrial D-loop mutations with GSTM1 and GSTT1 polymorphisms in oral carcinoma: a case control study from northeast India

OBJECTIVES

Mitochondrial dysfunction is a hallmark of cancer cells. Tobacco consumption in various forms is one of the major risk factors for the development of oral squamous cell carcinoma which makes the mitochondrial DNA susceptible to damage by reactive oxygen species. The GSTT1 and GSTM1 members of the glutathione S-transferase multigene family are candidate carcinogen metabolizing genes. Here we determined the hot spot mutations in the D-loop region and revealing correlation if any, with clinical parameters, along with analysing the genetic polymorphism of GSTT1 and GSTM1 and its susceptibility towards oral cancer.

MATERIALS AND METHODS

To determine the hot spot mutations 25 matched tissue samples of OSCC patients with 25 control subjects were used for PCR and direct sequencing. Analysis for GSTM1 and GSTT1 gene polymorphism was done by multiplex PCR.

RESULTS

Several mutations were found within the D-loop region among which mutations at nt146, nt152 and nt196 are found to be hot spot (P<0.0001, P<0.0001 and P<0.001 respectively). A significant association was found between the numbers of D-loop mutation and GSTM1 (OR=2.03; 95% CI, 1.04-3.96, P=0.003), GSTT1 (OR=1.73; 95% CI, 1.10-2.71, P=0.0027) null genotypes respectively. We observed a significant correlation between the increased number of D-loop mutations with the advancement in tumour stage of the patients (P=0.009, r=0.48).

CONCLUSION

The association of null genotypes and mutations can be used as a possible biomarker for early detection and preventive measure of oral cancer for those habituated to tobacco consumption.

Somatic mitochondrial DNA mutations in human cancers

Mitochondria are ubiquitous organelles in eukaryotic cells principally responsible for regulating cellular energy metabolism, free radical production, and the execution of apoptotic pathways. Abnormal oxidative phosphorylation (OXPHOS) and aerobic metabolism as a result of mitochondrial dysfunction have long been hypothesized to be involved in tumorigenesis. In the past decades, numerous somatic mutations in both the coding and control regions of mitochondrial DNA (mtDNA) have been extensively examined in a broad range of primary human cancers, underscoring that accumulation of mtDNA alterations may be a critical factor in eliciting persistent mitochondrial defects and consequently contributing to cancer initiation and progression. However, the roles of these mtDNA mutations in the carcinogenic process remain largely unknown. This review outlines a wide variety of somatic mtDNA mutations identified in common human malignancies and highlights recent advances in understanding the causal roles of mtDNA variations in neoplastic transformation and tumor progression. In addition, it briefly illustrates how mtDNA alterations activate mitochondria-to-nucleus retrograde signaling so as to modulate the expression of relevant nuclear genes or induce epigenetic changes and promote malignant phenotypes in cancer cells. The present state of our knowledge regarding how mutational changes in the mitochondrial genome could be used as a diagnostic biomarker for early detection of cancer and as a potential target in the development of new therapeutic approaches is also discussed. These findings strongly indicate that mtDNA mutations exert a crucial role in the pathogenic mechanisms of tumor development, but continued investigations are definitely required to further elucidate the functional significance of specific mtDNA mutations in the etiology of human cancers.

The awakening of an advanced malignant cancer: an insult to the mitochondrial genome

BACKGROUND

In only months-to-years a primary cancer can progress to an advanced phenotype that is metastatic and resistant to clinical treatments. As early as the 1900s, it was discovered that the progression of a cancer to the advanced phenotype is often associated with a shift in the metabolic profile of the disease from a state of respiration to anaerobic fermentation - a phenomenon denoted as the Warburg Effect.

SCOPE OF REVIEW

Reports in the literature strongly suggest that the Warburg Effect is generated as a response to a loss in the integrity of the sequence and/or copy number of the mitochondrial genome content within a cancer.

MAJOR CONCLUSIONS

Multiple studies regarding the progression of cancer indicate that mutation, and/or, a flux in the copy number, of the mitochondrial genome content can support the early development of a cancer, until; the mutational load and/or the reduction-to-depletion of the copy number of the mitochondrial genome content induces the progression of the disease to an advanced phenotype.

GENERAL SIGNIFICANCE

Collectively, evidence has revealed that the human cell has incorporated the mitochondrial genome content into a cellular mechanism that, when pathologically actuated, can de(un)differentiate a cancer from the parental tissue of origin into an autonomous disease that disrupts the hierarchical structure-and-function of the human body. This article is part of a Special Issue entitled: Biochemistry of Mitochondria.

Mitochondrial subversion in cancer

Mitochondria control essential cellular activities including generation of ATP via oxidative phosphorylation. Mitochondrial DNA (mtDNA) mutations in the regulatory D-loop region and somatic mtDNA mutations are common in primary human cancers. The biological impact of a given mutation may vary, depending on the nature of the mutation and the proportion of mutant mtDNAs carried by the cell. Identification of mtDNA mutations in precancerous lesions supports their early contribution to cell transformation and cancer progression. Introduction of mtDNA mutations in transformed cells has been associated with increased ROS production and tumor growth. Studies reveal that increased and altered mtDNA plays a role in the development of cancer but further work is required to establish the functional significance of specific mitochondrial mutations in cancer and disease progression. This review offers some insight into the extent of mtDNA mutations, their functional consequences in tumorigenesis, mitochondrial therapeutics, and future clinical application.

Mitochondrial DNA mutations in head and neck cancer are infrequent and lack prognostic utility

Background:

Mitochondrial DNA (mtDNA) mutations occur in head and neck squamous cell carcinoma (HNSCC) and are most frequently detected in the displacement-loop (D-loop) region. The D-loop is considered to be important because it controls mitochondrial gene expression and mtDNA replication. There is currently no evidence that mtDNA mutations can be used as prognostic or predictive biomarkers in HNSCC.

Methods:

We used denaturing high performance liquid chromatography to screen the entire mitochondrial genome of six oral squamous cell carcinoma-derived cell lines and then focused on detecting D-loop abnormalities in 34 HNSCC tissue samples.

Results:

Mitochondrial DNA mutations are not ubiquitous in HNSCC because only half of the cell lines had detectable mtDNA abnormalities following screening of the entire mitochondrial genome and only 18% (6 of 34) of tissue samples had D-loop mutations. There was no correlation between D-loop mutations and determinates of clinical outcome; specifically, tumour stage and the expression of hypoxia-inducible genes included in a highly prognostic hypoxia metagene.

Conclusions:

Taken together, these data suggest that mtDNA D-loop mutations are stochastic events that may not significantly influence the biology of HNSCC and supports the hypothesis that mtDNA mutations in cancer represent bystander genotoxic damage as a consequence of tumour development and progression.

Sequence polymorphisms of mitochondrial D-loop and hepatocellular carcinoma outcome

Accumulation of mutations and single nucleotide polymorphisms (SNPs) in the displacement loop (D-loop) of mitochondrial DNA (mtDNA) might be associated with cancer risk and disease outcome. We investigated the prediction power of D-loop SNPs in hepatocellular carcinoma (HCC) patients. No mutation in these HCC patients has prediction power for post-operational survival, whereas two SNP sites (nucleotides 146 T/C and 150 C/T) were identified by the log-rank test for statistically significant prediction of HCC survival. In an overall multivariate analysis, allele 146 was identified as an independent predictor of HCC outcome. The length of survival of patients with allele 146C was significantly shorter than that of patients with allele 146T (relative risk, 2.781; 95% CI, 1.127-6.859; p=0.026). The analysis of genetic polymorphisms in the mitochondrial D-loop can help identify patient subgroups at high risk of a poor disease outcome.

Proteomics in detection and monitoring of asthma and smoking-related lung diseases

Asthma, chronic obstructive pulmonary disease (COPD) and lung cancer cause extensive mortality and morbidity worldwide. However, the current state-of-the-art diagnosis and management schemes of these diseases are suboptimal as the incidence of asthma has risen by 250% over the last two decades and the 5-year mortality rate of lung cancer remains at 88%. Proteomic analysis is at the frontier of medical research and demonstrates tremendous potential in the early detection, diagnosis and staging, as well as providing novel therapeutic targets for improved management of smoking-related lung diseases. Advances in analytical tools, such as 2D gel electrophoresis, mass spectrometry, protein arrays and improved bioinformatics, allow sensitive and specific biomarker/protein profile discoveries and the infusion of new knowledge towards the molecular basis of lung diseases and their progression. Significant hurdles still stand between these laboratory findings and their applications in clinical practice. One of the challenges is the difficulty in the selection of samples that provide scope into the specific disease entity. Induced sputum, bronchoalveolar lavage, exhaled breath and exhaled breath condensate are methods of sampling airway and lung fluids that can serve as a window to assess the microenvironment of the lungs. With better study design standardization and the implementation of novel technologies to reach the optimal research standard, there is enough reason be optimistic about the future of proteomic research and its clinical implications.

Potential therapeutic benefits of strategies directed to mitochondria

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

The impact of perineural invasion on biochemical outcome after permanent prostate iodine-125 brachytherapy

PURPOSE

Perineural invasion (PNI) in prostate biopsies is associated with increased risk of higher Gleason score and worse pathologic stage. We report the influence of PNI in biochemical no evidence of disease (bNED) survival after (125)I prostate brachytherapy (BT).

METHODS AND MATERIALS

Pathology reports of 700 men with localized prostate cancer who underwent (125)I prostate BT in 1999-2008 were reviewed. The presence or absence of PNI in the biopsy was documented in 339 men. Clinical, treatment, and dosimetric parameters, along with PNI status, were evaluated for bNED survival, defined by "nadir+2" definition.

RESULTS

Of the 339 patients, 87% had favorable risk and 13% intermediate risk. PNI was present in 89 patients (26%). After a median followup of 32 months, there were five biochemical failures (4: +PNI and 1: -PNI), of which one was local failure (+PNI). Actuarial 5-year bNED survival for the entire group was 97.0% (92.9% for +PNI; 99.2% for -PNI). In univariate analysis age, pretreatment prostate-specific antigen, Gleason score 7, and intermediate risk group predicted for worse biochemical outcome, whereas the presence of PNI showed a trend toward significance (p=0.06). Some of the regression algorithms failed to converge because of low event rates.

CONCLUSIONS

We report excellent biochemical control in 339 men treated with (125)I prostate BT. The presence of PNI showed a trend toward significance in predicting 5-year bNED survival but did not impact on local control and should not influence the decision to recommend BT for localized prostate cancer.

Implications of mitochondrial DNA mutations and mitochondrial dysfunction in tumorigenesis

Alterations in oxidative phosphorylation resulting from mitochondrial dysfunction have long been hypothesized to be involved in tumorigenesis. Mitochondria have recently been shown to play an important role in regulating both programmed cell death and cell proliferation. Furthermore, mitochondrial DNA (mtDNA) mutations have been found in various cancer cells. However, the role of these mtDNA mutations in tumorigenesis remains largely unknown. This review focuses on basic mitochondrial genetics, mtDNA mutations and consequential mitochondrial dysfunction associated with cancer. The potential molecular mechanisms, mediating the pathogenesis from mtDNA mutations and mitochondrial dysfunction to tumorigenesis are also discussed.

Mutations in mitochondrial DNA polymerase-gamma promote breast tumorigenesis

Decreased mitochondrial oxidative phosphorylation (OXPHOS) is one of the hallmarks of cancer. To date, the identity of nuclear gene(s) responsible for decreased OXPHOS in tumors remains unknown. It is also unclear whether mutations in nuclear gene(s) responsible for decreased OXPHOS affect tumorigenesis. Polymerase-gamma (POLG) is the only DNA polymerase known to function in human mitochondria. Mutations in POLG are known to cause mitochondrial DNA (mtDNA) depletion and decreased OXPHOS, resulting in mtDNA depletion syndrome in humans. We therefore sequenced all coding exons (2-23) and flanking intron/splice junctions of POLG in breast tumors. We found that the POLG gene was mutated in 63% of breast tumors. We identified a total of 17 mutations across the POLG gene. Mutations were found in all three domains of the POLG protein, including T251I (the exonuclease domain), P587L (the linker region) and E1143G (the polymerase domain). We identified two novel mutations that include one silent (A703A) and one missense (R628Q) mutation in the evolutionarily conserved POLG linker region. In addition, we identified three novel mutations in the intronic region. Our study also revealed that mtDNA was depleted in breast tumors. Consistently, mutant POLG, when expressed in breast cancer cells, induced a depletion of mtDNA, decreased mitochondrial activity, decreased mitochondrial membrane potential, increased levels of reactive oxygen species and increased Matrigel invasion. Together, our study provides the first comprehensive analysis of the POLG gene mutation in human cancer and suggests a function for POLG (1) in decreased OXPHOS in cancers and (2) in promoting tumorigenicity.

Characterization of intracellular superoxide dismutase alterations in premalignant and malignant lesions of the oral cavity: correlation with lymph node metastasis

PURPOSE

The purpose of this study was to characterize changes in the expression of copper-zinc superoxide dismutase (Cu/Zn-SOD) and manganese SOD (Mn-SOD) in oral squamous-cell carcinoma (OSCC).

METHODS

Real-time quantitative reverse transcriptase-polymerase chain reaction analysis of Cu/Zn-SOD and Mn-SOD mRNA expression was carried out in 50 pairs of OSCC tissue specimens and corresponding normal tissues. Mn-SOD protein expression was evaluated further in 65 OSCC tissue samples and 33 oral premalignant lesions (OPLs) using immunohistochemistry.

RESULTS

Significant (P < 0.001) upregulation of Mn-SOD mRNA expression was observed in OSCC tissues compared with the normal tissue counterparts, whereas no significant difference was detected in Cu/Zn-SOD expression. Significant increases in Mn-SOD protein expression were seen in both OPLs (P < 0.001) and OSCC tissue (P < 0.001) together with a high incidence of lymph node metastasis (P = 0.04).

CONCLUSIONS

Our findings suggested that Mn-SOD overexpression is a frequent and early event during oral carcinogenesis and could contribute to aggressive OSCC.

A study of mitochondrial DNA D-loop mutations and p53 status in nonmelanoma skin cancer

BACKGROUND

Mitochondrial DNA (mtDNA) displacement-loop (D-loop) mutations have previously demonstrated potential as smoking-induced biomarkers in oral squamous cell carcinoma (SCC). Additionally, they have been observed in SCC and basal cell carcinoma of nonmelanoma skin cancer (NMSC). However, they have not been examined in the SCC precursor lesions, Bowen disease or actinic keratosis.

OBJECTIVES

Here, we present a novel study of mtDNA D-loop mutations in these two precursors, a rare keratoacanthoma and NMSC (all tumours not related to smoking).

METHODS

We used a polymerase chain reaction and direct sequencing approach. Furthermore, as the tumour suppressor protein p53 has been reported as having a novel role in maintaining mitochondrial genetic stability, we assessed p53 status using immunohistochemistry, evaluating potential association with the presence of mtDNA mutations.

RESULTS

Of 36 tumours, nine (25%) exhibited mutations in the D-loop. In total, 13 base substitutions were observed across all patients: seven (53.8%) were A : T to G : C; two (15.4%) were G : C to T : A; two (15.4%) were G : C to A : T and two (15.4%) were G : C to C : G. Four of the 13 (30.8%) base substitutions were observed at nucleotide 146. We observed abnormal p53 accumulation in over half of the samples analysed (55.5%), suggesting it to be a major part of the carcinogenic process of NMSC; however; there was no association between p53 positivity and the presence of mtDNA mutations (P = 0.47).

CONCLUSIONS

It is unlikely that alteration in p53 status is a contributing factor to mtDNA mutagenesis.

Contamination and sample mix-up can best explain some patterns of mtDNA instabilities in buccal cells and oral squamous cell carcinoma

The study of somatic DNA instabilities constitutes a debatable topic because different causes can lead to seeming DNA alteration patterns between different cells or tissues from the same individual. Carcinogenesis or the action of a particular toxic could generate such patterns, and this is in fact the leitmotif of a number of studies on mitochondrial DNA (mtDNA) instability. Patterns of seeming instabilities could also arise from technical errors at any stage of the analysis (DNA extraction, amplification, mutation screening/sequencing, and documentation). Specifically, inadvertent DNA contamination or sample mixing would yield mosaic variation that could be erroneously interpreted as real mutation differences (instabilities) between tissues from the same individual. From the very beginning, mtDNA studies comparing cancerous to non-cancerous tissues have suffered from such mosaic results. We demonstrate here that the phylogenetic linkage of whole arrays of mtDNA mutations provides strong evidence of artificial recombination in previous studies on buccal cells and oral squamous cell carcinoma.

Mitochondrial DNA instability and metabolic shift in human cancers

A shift in glucose metabolism from oxidative phosphorylation to glycolysis is one of the biochemical hallmarks of tumor cells. Mitochondrial defects have been proposed to play an important role in the initiation and/or progression of various types of cancer. In the past decade, a wide spectrum of mutations and depletion of mtDNA have been identified in human cancers. Moreover, it has been demonstrated that activation of oncogenes or mutation of tumor suppressor genes, such as p53, can lead to the upregulation of glycolytic enzymes or inhibition of the biogenesis or assembly of respiratory enzyme complexes such as cytochrome c oxidase. These findings may explain, at least in part, the well documented phenomena of elevated glucose uptake and mitochondrial defects in cancers. In this article, we review the somatic mtDNA alterations with clinicopathological correlations in human cancers, and their potential roles in tumorigenesis, cancer progression, and metastasis. The signaling pathways involved in the shift from aerobic metabolism to glycolysis in human cancers are also discussed.

Performance of mitochondrial DNA mutations detecting early stage cancer

BACKGROUND

Mutations in the mitochondrial genome (mtgenome) have been associated with cancer and many other disorders. These mutations can be point mutations or deletions, or admixtures (heteroplasmy). The detection of mtDNA mutations in body fluids using resequencing microarrays, which are more sensitive than other sequencing methods, could provide a strategy to measure mutation loads in remote anatomical sites.

METHODS

We determined the mtDNA mutation load in the entire mitochondrial genome of 26 individuals with different early stage cancers (lung, bladder, kidney) and 12 heavy smokers without cancer. MtDNA was sequenced from three matched specimens (blood, tumor and body fluid) from each cancer patient and two matched specimens (blood and sputum) from smokers without cancer. The inherited wildtype sequence in the blood was compared to the sequences present in the tumor and body fluid, detected using the Affymetrix Genechip Human Mitochondrial Resequencing Array 1.0 and supplemented by capillary sequencing for noncoding region.

RESULTS

Using this high-throughput method, 75% of the tumors were found to contain mtDNA mutations, higher than in our previous studies, and 36% of the body fluids from these cancer patients contained mtDNA mutations. Most of the mutations detected were heteroplasmic. A statistically significantly higher heteroplasmy rate occurred in tumor specimens when compared to both body fluid of cancer patients and sputum of controls, and in patient blood compared to blood of controls. Only 2 of the 12 sputum specimens from heavy smokers without cancer (17%) contained mtDNA mutations. Although patient mutations were spread throughout the mtDNA genome in the lung, bladder and kidney series, a statistically significant elevation of tRNA and ND complex mutations was detected in tumors.

CONCLUSION

Our findings indicate comprehensive mtDNA resequencing can be a high-throughput tool for detecting mutations in clinical samples with potential applications for cancer detection, but it is unclear the biological relevance of these detected mitochondrial mutations. Whether the detection of tumor-specific mtDNA mutations in body fluidsy this method will be useful for diagnosis and monitoring applications requires further investigation.

[Mitochondrial DNA mutations in the pathogenesis in the head and neck squamous cell carcinoma]

Data reported until today suggested a pivotal role of nuclear DNA mutations in the process of carcinogenesis. Recently more and more authors claim that disruption of mitochondrial DNA should not be excluded from this analysis. mtDNA have been reported in many cancers of head and neck region. Mitochondrial D-loop has been proven to be mutation hot - spot with majority of mutations in the positions 303 to 315 of poly-C tract. Data show that 37% of patients with premalignant lesions and 62% with carcinoma in situ are positive for mtDNA mutations. Moreover mutations in genes encoding ND2, ND5, COIII, CYTB, and ATP6 were observed in 17% of patients. Mutations in mitochondrial rRNA genes occured in similar number of cases. Neoplastic cells undifferentiation and disease progression is accompanied by multiplication of mtDNA number and increased mtDNA content. mtDNA content corellates with the stage of the disease. mtDNA mutations faciliate cell proliferation and inhibit apoptosis by increasing the production of ractive oxygen species (ROS). Cells harbouring mutated mtDNA have increased proliferation rate, as increased ROS concentration may act as an endogenous growth factor.

Nonsynonymous somatic mitochondrial mutations occur in the majority of cutaneous melanomas

Earlier studies of mitochondrial mutations in melanoma have focused on analysis of selected mitochondrial genes and the displacement loop (D-loop) region using conventional sequencing. In this study we use data from a whole mitochondria-sequencing array, the MitoChip v2.0, to characterize the mutations that are present throughout the mitochondrial genome. The mitochondrial genome of DNA derived from 14 fresh melanoma specimens and two melanoma cell lines, and autologous lymphocytes or immortalized B cells, respectively, were sequenced using the MitoChip v2.0. Paired comparative sequence analysis was carried out to define somatic mutations. Somatic mitochondrial DNA mutations were identified in 12/16 (75%) melanomas, compared with germline lymphocyte DNA. One hundred mutations were present among these 12 melanomas. A disproportionate number of mutations occurred in the D-loop. Furthermore, 9/16 (56.3%) melanomas carried mutations, which resulted in amino acid substitutions in functional genes. In the 10 samples carrying nicotinamide adenine dinucleotide dehydrogenase (ND) complex mutations, multiple mutations were present at a rate significantly greater than the expected frequency based on the size of ND complex genes (P=0.028, Fisher's exact test). Mitochondrial mutation is a frequent occurrence in melanoma. The high rate of missense mutations and the propensity for the ND complex implicate a role for alterations in mitochondrial respiratory function in melanoma carcinogenesis. Mutations of the noncoding D-loop are of unclear significance, but may be associated with alterations in transcription or replication. Further studies are needed to delineate the timing and functional significance of these mutations, and their role in the pathogenesis of this disease.

Molecular mechanisms of head and neck cancer

Despite advances in understanding the underlying genetics, squamous cell carcinoma of the head and neck (SCCHN) remains a major health risk and one of the leading causes of mortality in the world. Current standards of treatment have significantly improved long-term survival rates of patients, but second tumors and metastases still remain the most frequent cause of high mortality in SCCHN patients. A better understanding of the underlying genetic mechanisms of SCCHN tumorigenesis will help in developing better diagnostics and, hence, better cures. In this article we will briefly outline the current state of diagnostics and treatment and our understanding of the molecular causes of SCCHN.

Associations between cigarette smoking and mitochondrial DNA abnormalities in buccal cells

DNA alterations in mitochondria are believed to play a role in carcinogenesis and are found in smoking-related cancers. We sought to replicate earlier findings for the association of smoking with increased mitochondrial DNA (mtDNA) content in buccal cells and further hypothesized that there would be an increased number of somatic mtDNA mutations in smokers. Buccal cells and blood lymphocytes were studied from 42 healthy smokers and 30 non-smokers. Temporal temperature gradient electrophoresis screening and sequencing was used to identify mtDNA mutations. The relative mtDNA content was determined by real-time polymerase chain reaction. Assuming that mtDNA in lymphocytes represents the inherited sequence, it was found that 31% of smokers harbored at least one somatic mtDNA mutation in buccal cells with a total of 39 point mutations and 8 short deletions/insertions. In contrast, only 23% of non-smokers possessed mutations with a total of 10 point mutations and no insertions/deletions detected. mtDNA somatic mutation density was higher in smokers (0.68/10 000 bp per person) than in non-smokers (0.2/10 000 bp per person). There was a statistically significant difference in the pattern of homoplasmy and heteroplasmy mutation changes between smokers and non-smokers. Whereas non-smokers had the most mutations in D-loop region (70%), smokers had mutations in both messenger RNA encoding gene (36%) and D-loop region (49%). The mean ratio of buccal cells to lymphocytes of mtDNA content in smokers was increased (2.81) when compared with non-smokers (0.46). These results indicate that cigarette smoke exposure affects mtDNA in buccal cells of smokers. Additional studies are needed to determine if mitochondrial mutation assays provide new or complementary information for estimating cigarette smoke exposure at the cellular level or as a cancer risk biomarker.

Mitochondrial mutations are a late event in the progression of head and neck squamous cell cancer

PURPOSE

To determine the timing of mitochondrial mutations in the progression of head and neck squamous cell carcinoma.

EXPERIMENTAL DESIGN

Twenty-three mitochondrial mutations were identified in 12 tumors using a high-throughput mitochondrial sequencing array. Areas of adjacent dysplastic and normal epithelium adjacent to tumors were sequenced using conventional methods for the presence of mutations that occurred in the corresponding tumor.

RESULTS

Two of 23 (8.7%) tumor mitochondrial mutations (2 of 12 tumors) were present in both the areas of adjacent dysplasia and normal epithelium. Five of 23 (21.7%) tumor mitochondrial mutations (4 of 12 tumors) were present in areas of adjacent dysplasia. Eleven of 12 tumors contained nonsynonymous mutations that resulted in protein coding alterations. A significant difference (P < 0.01, chi(2)) was found in the incidence of mitochondrial mutation that occurred after development of cancer compared with adjacent areas dysplasia and normal epithelium.

CONCLUSIONS

The majority of mitochondrial mutations occur during or after the transition of preneoplastic epithelium to cancer in head and neck squamous cell carcinoma, indicating that these are a late event in head and neck carcinogenesis.

Application of mitochondrial genome information in cancer epidemiology

Two genomes, nuclear and mitochondrial, exist in humans although information contained in the mitochondrial genome has not been fully utilized in cancer epidemiology. Over the last few years, a variety of approaches have been developed to improve results of conventional cancer screening by detecting molecular markers in different populations. Mitochondrial DNA alterations (mutations, deletions and instability) are emerging as new molecular markers for detecting a variety of cancers in tissue samples and biofluids which can be included in population screening studies. Since mitochondrial genome is small (16.6 kb) and high-throughput assays have been developed for sequencing whole mitochondrial genome, it can be adopted by most of the laboratories conducting epidemiological studies. Applications of mitochondrial DNA markers to identify high risk populations and future challenges are discussed in this article.