Tumor circulating DNA profiling in xenografted mice exposed to intermittent hypoxia

A review of obstructive sleep apnea and lung cancer: epidemiology, pathogenesis, and therapeutic options

Despite undeniable advances in modern medicine, lung cancer still has high morbidity and mortality rates. Lung cancer is preventable and treatable, and it is important to identify new risk factors for lung cancer, especially those that can be treated or reversed. Obstructive sleep apnea (OSA) is a very common sleep-breathing disorder that is grossly underestimated in clinical practice. It can cause, exacerbate, and worsen adverse outcomes, including death and various diseases, but its relationship with lung cancer is unclear. A possible causal relationship between OSA and the onset and progression of lung cancer has been established biologically. The pathophysiological processes associated with OSA, such as sleep fragmentation, intermittent hypoxia, and increased sympathetic nervous excitation, may affect normal neuroendocrine regulation, impair immune function (especially innate and cellular immunity), and ultimately contribute to the occurrence of lung cancer, accelerate progression, and induce treatment resistance. OSA may be a contributor to but a preventable cause of the progression of lung cancer. However, whether this effect exists independently of other risk factors is unclear. Therefore, by reviewing the literature on the epidemiology, pathogenesis, and treatment of lung cancer and OSA, we hope to understand the relationships between the two and promote the interdisciplinary exchange of ideas between basic medicine, clinical medicine, respiratory medicine, sleep medicine, and oncology.

Mutated TP53 in Circulating Tumor DNA as a Risk Level Biomarker in Head and Neck Squamous Cell Carcinoma Patients

Circulating tumor DNA (ctDNA) has been suggested as a surrogate biomarker for early detection of cancer recurrence. We aimed to explore the utility of ctDNA as a noninvasive prognostic biomarker in newly diagnosed head and neck squamous cell carcinoma (HNSCC) patients. Seventy HNSCC specimens were analysed for the detection of TP53 genetic alterations utilizing next-generation sequencing (NGS). TP53 mutations were revealed in 55 (79%). Upon detection of a significant TP53 mutation, circulating cell-free DNA was scrutinized for the presence of the tumor-specific mutation. ctDNA was identified at a minimal allele frequency of 0.08% in 21 out of 30 processed plasma samples. Detectable ctDNA correlated with regional spread (N stage ≥ 1, p = 0.011) and poorer 5-year progression-free survival (20%, 95% CI 10.9 to 28.9, p = 0.034). The high-risk worst pattern of invasion (WPOI grade 4-5) and deep invasion were frequently found in patients whose ctDNA was detected (p = 0.087 and p = 0.072, respectively). Detecting mutated TP53 ctDNA was associated with poor progression-free survival and regional metastases, indicating its potential role as a prognostic biomarker. However, ctDNA detectability in early-stage disease and the mechanisms modulating its release into the bloodstream must be further elucidated.

Potential Pathophysiological Pathways in the Complex Relationships between OSA and Cancer

Several epidemiological and clinical studies have suggested a relationship between obstructive sleep apnea (OSA) and a higher incidence or severity of cancer. This relationship appears to be dependent on a myriad of factors. These include non-modifiable factors, such as age and gender; and modifiable or preventable factors, such as specific comorbidities (especially obesity), the use of particular treatments, and, above all, the histological type or location of the cancer. Heterogeneity in the relationship between OSA and cancer is also related to the influences of intermittent hypoxemia (a hallmark feature of OSA), among others, on metabolism and the microenvironment of different types of tumoral cells. The hypoxia inducible transcription factor (HIF-1α), a molecule activated and expressed in situations of hypoxemia, seems to be key to enabling a variety of pathophysiological mechanisms that are becoming increasingly better recognized. These mechanisms appear to be operationally involved via alterations in different cellular functions (mainly involving the immune system) and molecular functions, and by inducing modifications in the microbiome. This, in turn, may individually or collectively increase the risk of cancer, which is then, further modulated by the genetic susceptibility of the individual. Here, we provide an updated and brief review of the different pathophysiological pathways that have been identified and could explain the relationship between OSA and cancer. We also identify future challenges that need to be overcome in this intriguing field of research.

Circulating tumor nucleic acids: biology, release mechanisms, and clinical relevance

BACKGROUND

Despite advances in early detection and therapies, cancer is still one of the most common causes of death worldwide. Since each tumor is unique, there is a need to implement personalized care and develop robust tools for monitoring treatment response to assess drug efficacy and prevent disease relapse.

MAIN BODY

Recent developments in liquid biopsies have enabled real-time noninvasive monitoring of tumor burden through the detection of molecules shed by tumors in the blood. These molecules include circulating tumor nucleic acids (ctNAs), comprising cell-free DNA or RNA molecules passively and/or actively released from tumor cells. Often highlighted for their diagnostic, predictive, and prognostic potential, these biomarkers possess valuable information about tumor characteristics and evolution. While circulating tumor DNA (ctDNA) has been in the spotlight for the last decade, less is known about circulating tumor RNA (ctRNA). There are unanswered questions about why some tumors shed high amounts of ctNAs while others have undetectable levels. Also, there are gaps in our understanding of associations between tumor evolution and ctNA characteristics and shedding kinetics. In this review, we summarize current knowledge about ctNA biology and release mechanisms and put this information into the context of tumor evolution and clinical utility.

CONCLUSIONS

A deeper understanding of the biology of ctDNA and ctRNA may inform the use of liquid biopsies in personalized medicine to improve cancer patient outcomes.

Advances in Molecular Pathology of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a common syndrome that features a complex etiology and set of mechanisms. Here we summarized the molecular pathogenesis of OSA, especially the prospective mechanism of upper? airway dilator fatigue and the current breakthroughs. Additionally, we also introduced the molecular mechanism of OSA in terms of related studies on the main signaling pathways and epigenetics alterations, such as microRNA, long non-coding RNA, and DNA methylation. We also reviewed small molecular compounds, which are potential targets for gene regulations in the future, that are involved in the regulation of OSA. This review will be beneficial to point the way for OSA research within the next decade.

Hypoxia-Nitric Oxide Axis and the Associated Damage Molecular Pattern in Cutaneous Melanoma

Hypoxia was intensively studied in cancer during the last few decades, being considered a characteristic of the tumor microenvironment. The aim of the study was to evaluate the capacity of tumor cells to adapt to the stress generated by limited oxygen tissue in cutaneous melanoma. We developed a case-control prospective study that included 52 patients with cutaneous melanoma and 35 healthy subjects. We focused on identifying and monitoring hypoxia, the dynamic of nitric oxide (NO) serum metabolites and posttranslational metabolic disorders induced by NO signaling according to the clinical, biological and tumoral characteristics of the melanoma patients. Our study showed high levels of hypoxia-inducible factor-1a (HIF-1a) and hypoxia-inducible factor-2a (HIF-2a) in the melanoma patients. Hypoxia-inducible factors (HIFs) control the capacity of tumor cells to adapt to low levels of oxygen. Hypoxia regulated the nitric oxide synthase (NOS) expression and activity. In the cutaneous melanoma patients, disorders in NO metabolism were detected. The serum levels of the NO metabolites were significantly higher in the melanoma patients. NO signaling influenced the tumor microenvironment by modulating tumoral proliferation and sustaining immune suppression. Maintaining NO homeostasis in the hypoxic tumoral microenvironment could be considered a future therapeutic target in cutaneous melanoma.

Comprehensive Analysis of N6-Methyladenosine Regulators in the Subcluster Classification and Drug Candidates Prediction of Severe Obstructive Sleep Apnea

Background: Obstructive sleep apnea (OSA) is the most common type of sleep apnea that impacts the development or progression of many other disorders. Abnormal expression of N6-methyladenosine (m6A) RNA modification regulators have been found relating to a variety of human diseases. However, it is not yet known if m6A regulators are involved in the occurrence and development of OSA. Herein, we aim to explore the impact of m6A modification in severe OSA.

Methods: We detected the differentially expressed m6A regulators in severe OSA microarray dataset GSE135917. The least absolute shrinkage and selection operator (LASSO) and support vector machines (SVM) were used to identify the severe OSA-related m6A regulators. Receiver operating characteristic (ROC) curves were performed to screen and verify the diagnostic markers. Consensus clustering algorithm was used to identify m6A patterns. And then, we explored the character of immune microenvironment, molecular functionals, protein-protein interaction networks and miRNA-TF coregulatory networks for each subcluster. Finally, the Connectivity Map (CMap) tools were used to tailor customized treatment strategies for different severe OSA subclusters. An independent dataset GSE38792 was used for validation.

Results: We found that HNRNPA2B1, KIAA1429, ALKBH5, YTHDF2, FMR1, IGF2BP1 and IGF2BP3 were dysregulated in severe OSA patients. Among them, IGF2BP3 has a high diagnostic value in both independent datasets. Furthermore, severe OSA patients can be accurately classified into three m6A patterns (subcluster1, subcluster2, subcluster3). The immune response in subcluster3 was more active because it has high M0 Macrophages and M2 Macrophages infiltration and up-regulated human leukocyte antigens (HLAs) expression. Functional analysis showed that representative genes for each subcluster in severe OSA were assigned to histone methyltransferase, ATP synthesis coupled electron transport, virus replication, RNA catabolic, multiple neurodegeneration diseases pathway, et al. Moreover, our finding demonstrated cyclooxygenase inhibitors, several of adrenergic receptor antagonists and histamine receptor antagonists might have a therapeutic effect on severe OSA.

Conclusion: Our study presents an overview of the expression pattern and crucial role of m6A regulators in severe OSA, which may provide critical insights for future research and help guide appropriate prevention and treatment options.

On the Relationship between Diabetes and Obstructive Sleep Apnea: Evolution and Epigenetics

This review offers an overview of the relationship between diabetes, obstructive sleep apnea (OSA), obesity, and heart disease. It then addresses evidence that the traditional understanding of this relationship is incomplete or misleading. In the process, there is a brief discussion of the evolutionary rationale for the development and retention of OSA in light of blood sugar dysregulation, as an adaptive mechanism in response to environmental stressors, followed by a brief overview of the general concepts of epigenetics. Finally, this paper presents the results of a literature search on the epigenetic marks and changes in gene expression found in OSA and diabetes. (While some of these marks will also correlate with obesity and heart disease, that is beyond the scope of this project). We conclude with an exploration of alternative explanations for the etiology of these interlinking diseases.

Clinical Applications of Liquid Biopsy in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common malignant tumor with high mortality and poor prognosis in the world. The low rate of early diagnosis, as well as the high risk of postoperative metastasis and recurrence, led to the poor clinical prognosis of HCC patients. Currently, it mainly depends on serum markers, imaging examination, and tissue biopsy to diagnose and determine the recurrence and metastasis of HCC after treatments. Nevertheless, the accuracy and sensitivity of serum markers and imaging for early HCC diagnosis are suboptimal. Tissue biopsy, containing limited tissue samples, is insufficient to reveal comprehensive tumor biology information and is inappropriate to monitor dynamic tumor progression due to its invasiveness. Thus, low invasive diagnostic methods and novel biomarkers with high sensitivity and reliability must be found to improve HCC detection and prediction. As a non-invasive, dynamic, and repeatable detection method, “liquid biopsy”, has attracted much attention to early diagnosis and monitoring of treatment response, which promotes the progress of precision medicine. This review summarizes the clinical applications of liquid biopsy in HCC, including circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), and exosome in early diagnosis, prognostic evaluation, disease monitoring, and guiding personalized treatment.

Blood, Toil, and Taxoteres: Biological Determinates of Treatment-Induce ctDNA Dynamics for Interpreting Tumor Response

Collection and analysis of circulating tumor DNA (ctDNA) is one of the few methods of liquid biopsy that measures generalizable and tumor specific molecules, and is one of the most promising approaches in assessing the effectiveness of cancer care. Clinical assays that utilize ctDNA are commercially available for the identification of actionable mutations prior to treatment and to assess minimal residual disease after treatment. There is currently no clinical ctDNA assay specifically intended to monitor disease response during treatment, partially due to the complex challenge of understanding the biological sources of ctDNA and the underlying principles that govern its release. Although studies have shown pre- and post-treatment ctDNA levels can be prognostic, there is evidence that early, on-treatment changes in ctDNA levels are more accurate in predicting response. Yet, these results also vary widely among cohorts, cancer type, and treatment, likely due to the driving biology of tumor cell proliferation, cell death, and ctDNA clearance kinetics. To realize the full potential of ctDNA monitoring in cancer care, we may need to reorient our thinking toward the fundamental biological underpinnings of ctDNA release and dissemination from merely seeking convenient clinical correlates.

Hypoxia in Lung Cancer Management: A Translational Approach

Simple Summary

Hypoxia is a common feature of lung cancers. Nonetheless, no guidelines have been established to integrate hypoxia-associated biomarkers in patient management. Here, we discuss the current knowledge and provide translational novel considerations regarding its clinical detection and targeting to improve the outcome of patients with non-small-cell lung carcinoma of all stages.

Abstract

Lung cancer represents the first cause of death by cancer worldwide and remains a challenging public health issue. Hypoxia, as a relevant biomarker, has raised high expectations for clinical practice. Here, we review clinical and pathological features related to hypoxic lung tumours. Secondly, we expound on the main current techniques to evaluate hypoxic status in NSCLC focusing on positive emission tomography. We present existing alternative experimental approaches such as the examination of circulating markers and highlight the interest in non-invasive markers. Finally, we evaluate the relevance of investigating hypoxia in lung cancer management as a companion biomarker at various lung cancer stages. Hypoxia could support the identification of patients with higher risks of NSCLC. Moreover, the presence of hypoxia in treated tumours could help clinicians predict a worse prognosis for patients with resected NSCLC and may help identify patients who would benefit potentially from adjuvant therapies. Globally, the large quantity of translational data incites experimental and clinical studies to implement the characterisation of hypoxia in clinical NSCLC management.

Epigenetics of obstructive sleep apnea syndrome: a systematic review

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is a chronic and widely prevalent disease, associated with multiple health disorders. Current diagnostic strategies for OSA are limited due to cost, time, and access. Epigenetic signatures offer insight into the relationships between disease and environment and could play a significant role in developing both diagnostic and therapeutic tools for OSA. In the current study, a systematic literature search was conducted to investigate the existing evidence of OSA-associated epigenetic modifications.

METHODS

A systematic literature search was performed using electronic academic databases including PubMed, CINAHL, Scopus, Embase, EBM Reviews, and Web of Science. However, the current study focused on screening for original, English language articles pertaining to OSA and associated epigenetic mechanisms. To produce unbiased results, screening was performed independently by authors.

RESULTS

We identified 2,944 publications in our systematic search. Among them, 65 research articles were related to OSA-associated differential gene expression, genetic variation, and epigenetic modifications. Although these 65 articles were considered for full manuscript review, only twelve articles met the criteria of OSA-associated epigenetic modifications in humans and animal models. Human subjects with OSA had unique epigenetic changes compared to healthy controls, and, interestingly, epigenetic signatures were commonly identified in genes associated with metabolic and inflammatory pathways.

CONCLUSIONS

Although the available studies are limited, this research provides novel insights for development of epigenetic markers for the diagnosis and treatment of OSA. Thorough genome wide investigations will be required to develop cost-effective, robust biomarkers for the identification of OSA among children and adults. Here, we offer a study design for such efforts.

Sleep Apnoea Adverse Effects on Cancer: True, False, or Too Many Confounders?

Obstructive sleep apnoea (OSA) is a prevalent disorder associated with increased cardiovascular, metabolic and neurocognitive morbidity. Recently, an increasing number of basic, clinical and epidemiological reports have suggested that OSA may also increase the risk of cancer, and adversely impact cancer progression and outcomes. This hypothesis is convincingly supported by biological evidence linking certain solid tumours and hypoxia, as well as by experimental studies involving cell and animal models testing the effects of intermittent hypoxia and sleep fragmentation that characterize OSA. However, the clinical and epidemiological studies do not conclusively confirm that OSA adversely affects cancer, even if they hold true for specific cancers such as melanoma. It is likely that the inconclusive studies reflect that they were not specifically designed to test the hypothesis or because of the heterogeneity of the relationship of OSA with different cancer types or even sub-types. This review critically focusses on the extant basic, clinical, and epidemiological evidence while formulating proposed directions on how the field may move forward.

Hypoxia differently modulates the release of mitochondrial and nuclear DNA

BACKGROUND

We investigated the influence of hypoxia on the concentration of mitochondrial and nuclear cell-free DNA (McfDNA and NcfDNA, respectively).

METHOD

By an ultra-sensitive quantitative PCR-based assay, McfDNA and NcfDNA were measured in the supernatants of different colorectal cell lines, and in the plasma of C57/Bl6 mice engrafted with TC1 tumour cells, in normoxic or hypoxic conditions.

RESULTS

Our data when setting cell culture conditions highlighted the higher stability of McfDNA as compared to NcfDNA and revealed that cancer cells released amounts of nuclear DNA equivalent to the mass of a chromosome over a 6-h duration of incubation. In cell model, hypoxia induced a great increase in NcfDNA and McfDNA concentrations within the first 24 h. After this period, cfDNA total concentrations remained stable in hypoxia consecutive to a decrease of nuclear DNA release, and noteworthy, to a complete inhibition of daily mitochondrial DNA release. In TC1-engrafted mice submitted to intermittent hypoxia, plasma NcfDNA levels are much higher than in mice bred in normoxia, unlike plasma McfDNA concentration that is not impacted by hypoxia.

CONCLUSION

This study suggests that hypoxia negatively modulates nuclear and, particularly, mitochondrial DNA releases in long-term hypoxia, and revealed that the underlying mechanisms are differently regulated.

ALKBH5-m6A-FOXM1 signaling axis promotes proliferation and invasion of lung adenocarcinoma cells under intermittent hypoxia

Obstructive sleep apnea (OSA) is closely associated with cancer progression and cancer-related mortality. N6-methyladenosine (m⁶A) is involved in the process of intermittent hypoxia (IH) promoting tumor progression. However, it is unclear how m⁶A regulates the development of lung adenocarcinoma under IH. In this study, we found that ALKBH5 was elevated in lung adenocarcinoma cells and subcutaneous tumors in mice under IH, which was associated with decreased m⁶A levels in these cells and tissues. Next, we knocked out ALKBH5 in a human lung adenocarcinoma cell line under IH, and we found that the proliferation and invasion of these cells were significantly inhibited. Mechanistic analysis showed that under IH, knockout of ALKBH5 in lung adenocarcinoma cells upregulated the level of m⁶A in Forkhead box M1 (FOXM1) mRNA and decreased the translation efficiency of FOXM1 mRNA, resulting in downregulation of the FOXM1 protein. The FOXM1 protein is elevated in lung adenocarcinoma cells and subcutaneous tumor tissues of mice under IH. By knocking out FOXM1 in lung adenocarcinoma cells under IH, proliferation and invasion of these cells were inhibited, and overexpression of FOXM1 partially restored the inhibition of growth and invasion of lung adenocarcinoma cells due to ALKBH5 knockout. Collectively, our findings demonstrate that the m⁶A demethylase ALKBH5 affects the proliferation and invasion of lung adenocarcinoma cells under IH by downregulating m⁶A modification on FOXM1 mRNA and by promoting FOXM1 expression.

Liquid biopsy in hepatocellular carcinoma: circulating tumor cells and circulating tumor DNA

Hepatocellular carcinoma (HCC) is one of the most common cancers and a leading cause of death worldwide. Due to latent liver disease, late diagnosis, and nonresponse to systemic treatments, surgical resection and/or biopsy specimens are still generally considered as the gold standard by clinicians for clinical decision-making until now. Since the conventional tissue biopsy is invasive and contains small tissue samples, it is unable to represent tumor heterogeneity or monitor dynamic tumor progression. Therefore, it is imperative to find a new less invasive or noninvasive diagnostic strategy to detect HCC at an early stage and to monitor HCC recurrence. Over the past years, a new diagnostic concept known as “liquid biopsy” has emerged with substantial attention. Liquid biopsy is noninvasive and allows repeated analyses to monitor tumor recurrence, metastasis or treatment responses in real time. With the advanced development of new molecular techniques, HCC circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) detection have achieved interesting and encouraging results. In this review, we focus on the clinical applications of CTCs and ctDNA as key components of liquid biopsy in HCC patients.

Epigenetics: A Potential Mechanism Involved in the Pathogenesis of Various Adverse Consequences of Obstructive Sleep Apnea

Epigenetics is defined as the heritable phenotypic changes which do not involve alterations in the DNA sequence, including histone modifications, non-coding RNAs, and DNA methylation. Recently, much attention has been paid to the role of hypoxia-mediated epigenetic regulation in cancer, pulmonary hypertension, adaptation to high altitude, and cardiorenal disease. In contrast to sustained hypoxia, chronic intermittent hypoxia with re-oxygenation (IHR) plays a major role in the pathogenesis of various adverse consequences of obstructive sleep apnea (OSA), resembling ischemia re-perfusion injury. Nevertheless, the role of epigenetics in the pathogenesis of OSA is currently underexplored. This review proposes that epigenetic processes are involved in the development of various adverse consequences of OSA by influencing adaptive potential and phenotypic variability under conditions of chronic IHR. Improved understanding of the interaction between genetic and environmental factors through epigenetic regulations holds great value to give deeper insight into the mechanisms underlying IHR-related low-grade inflammation, oxidative stress, and sympathetic hyperactivity, and clarify their implications for biomedical research.

Intermittent hypoxia promotes melanoma lung metastasis via oxidative stress and inflammation responses in a mouse model of obstructive sleep apnea

Background

Recently, increased tumor incidence and cancer-related mortality have been reported among patients with obstructive sleep apnea (OSA). Intermittent hypoxia (IH), the hallmark feature of OSA, contributes to the metastasis of tumors. However, the molecular mechanisms by which tumor metastasis is accelerated by OSA-like IH remain to be elucidated.

Methods

C57BL/6 J male mice were subjected to intravenous injection of B16F10 melanoma cells before receiving IH treatment. Then, the animals were randomly distributed into three groups (n = 8 each): normoxia (N) group, IH group, and antioxidant tempol group (IHT, exposed to IH after treatment with tempol). After the mice were sacrificed, the number and weight of lung metastatic colonies were assessed. The lung tissues with tumor metastasis were analyzed for markers of oxidative stress and inflammation and for HIF-1α using western blotting and real-time PCR (qRT-PCR). The level of reactive oxygen species (ROS) in B16F10 cell was also assessed after N, IH and IH with tempol treatments.

Results

Compared with normoxia, IH significantly increased the number and weight of mouse lung metastatic colonies. Treatment of B16F10 cells with IH significantly enhanced ROS generation. Lung tissues with tumor metastasis provided evidence of increased oxidative stress, as assessed by p22^phox and SOD mRNA levels and the NRF2 protein level, as well as increased inflammation, as assessed by TNF-α and IL-6 mRNA levels and the NF-κB P65 protein level. HIF-1α protein levels were increased in response to IH treatment. Tempol, an important antioxidant, ameliorated IH-induced melanoma lung metastasis in mice and reduced oxidative stress and inflammation responses.

Conclusions

These results support the hypothesis that oxidative stress and inflammation responses play an important role in the pathogenesis of OSA-like IH-induced melanoma lung metastasis in mice. Antioxidant intervention provides a novel strategy for the prevention and treatment of cancer in OSA populations.

Development of a Method to Implement Whole-Genome Bisulfite Sequencing of cfDNA from Cancer Patients and a Mouse Tumor Model

The goal of this study was to develop a method for whole genome cell-free DNA (cfDNA) methylation analysis in humans and mice with the ultimate goal to facilitate the identification of tumor derived DNA methylation changes in the blood. Plasma or serum from patients with pancreatic neuroendocrine tumors or lung cancer, and plasma from a murine model of pancreatic adenocarcinoma was used to develop a protocol for cfDNA isolation, library preparation and whole-genome bisulfite sequencing of ultra low quantities of cfDNA, including tumor-specific DNA. The protocol developed produced high quality libraries consistently generating a conversion rate >98% that will be applicable for the analysis of human and mouse plasma or serum to detect tumor-derived changes in DNA methylation.

DNA Methylation in Pediatric Obstructive Sleep Apnea: An Overview of Preliminary Findings

Obstructive sleep apnea (OSA) is characterized by phenotypic variations, which can be partly attributed to specific gene polymorphisms. Recent studies have focused on the role of epigenetic mechanisms in order to permit a more precise perception about clinical phenotyping and targeted therapies. The aim of this review was to synthesize the current state of knowledge on the relation between DNA methylation patterns and the development of pediatric OSA, in light of the apparent limited literature in the field. We performed an electronic search in PubMed, EMBASE, and Google Scholar databases, including all types of articles written in English until January 2017. Literature was apparently scarce; only 2 studies on pediatric populations and 3 animal studies were identified. Forkhead Box P3 (FOXP3) DNA methylation levels were associated with inflammatory biomarkers and serum lipids. Hypermethylation of the core promoter region of endothelial Nitric Oxide Synthase (eNOS) gene in OSA children were related with decreased eNOS expression. Additionally, increased expression of genes encoding pro-oxidant enzymes and decreased expression of genes encoding anti-oxidant enzymes suggested that disturbances in oxygen homeostasis throughout neonatal period predetermined increased hypoxic sensing in adulthood. In conclusion, epigenetic modifications may be crucial in pediatric sleep disorders to enable in-depth understanding of genotype-phenotype interactions and lead to risk assessment. Epigenome-wide association studies are urgently needed to validate certain epigenetic alterations as reliable, novel biomarkers for the molecular prognosis and diagnosis of OSA patients with high risk of end-organ morbidity.

Intermittent hypoxia and cancer: Undesirable bed partners?

The deleterious effects of intermittent hypoxia (IH) on cancer biology have been primarily evaluated in the context of the aberrant circulation observed in solid tumors which results in recurrent intra-tumoral episodic hypoxia. From those studies, IH has been linked to an accelerated tumor progression, metastasis and resistance to therapies. More recently, the role of IH in cancer has also been studied in the context of obstructive sleep apnea (OSA), since IH is a hallmark characteristic of this condition. Such recent studies are undoubtedly adding more information regarding the role of IH on tumor malignancy. In terms of the IH patterns associated with OSA, this altered oxygenation paradigm has been recently proposed as a determinant factor in fostering cancer incidence and progression from both in vitro and in vivo experimental models. Here, we summarize all the available evidence to date linking IH effects on several types of cancer.

Origins, structures, and functions of circulating DNA in oncology

While various clinical applications especially in oncology are now in progress such as diagnosis, prognosis, therapy monitoring, or patient follow-up, the determination of structural characteristics of cell-free circulating DNA (cirDNA) are still being researched. Nevertheless, some specific structures have been identified and cirDNA has been shown to be composed of many “kinds.” This structural description goes hand-in-hand with the mechanisms of its origins such as apoptosis, necrosis, active release, phagocytosis, and exocytose. There are multiple structural forms of cirDNA depending upon the mechanism of release: particulate structures (exosomes, microparticles, apoptotic bodies) or macromolecular structures (nucleosomes, virtosomes/proteolipidonucleic acid complexes, DNA traps, links with serum proteins or to the cell-free membrane parts). In addition, cirDNA concerns both nuclear and/or mitochondrial DNA with both species exhibiting different structural characteristics that potentially reveal different forms of biological stability or diagnostic significance. This review focuses on the origins, structures and functional aspects that are paradoxically less well described in the literature while numerous reviews are directed to the clinical application of cirDNA. Differentiation of the various structures and better knowledge of the fate of cirDNA would considerably expand the diagnostic power of cirDNA analysis especially with regard to the patient follow-up enlarging the scope of personalized medicine. A better understanding of the subsequent fate of cirDNA would also help in deciphering its functional aspects such as their capacity for either genometastasis or their pro-inflammatory and immunological effects.

Sleep and Breathing … and Cancer?

Sleep, like eating and breathing, is an essential part of the daily life cycle. Although the science is still emerging, sleep plays an important role in immune, cardiovascular, and neurocognitive function. Despite its great importance, nearly 40% of U.S. adults experience problems with sleep ranging from insufficient total sleep time, trouble initiating or maintaining sleep (Insomnia), circadian rhythm disorders, sleep-related movement disorders, and sleep-related breathing disorders such as obstructive sleep apnea (OSA). Herein, we discuss new evidence that suggests that sleep may also affect carcinogenesis. Specifically, we review recent epidemiologic data suggesting links between cancer and OSA. As OSA is a common, underdiagnosed, and undertreated condition, this has public health implications. Intriguing animal model data support a link between cancer and sleep/OSA, although mechanisms are not yet clear. Leaders in the fields of sleep medicine, pulmonology, and oncology recently met to review and discuss these data, as well as to outline future directions of study. We propose a multidisciplinary, three-pronged approach to studying the associations between cancer and sleep, utilizing mutually interactive epidemiologic studies, preclinical models, and early-phase clinical trials. Cancer Prev Res; 9(11); 821-7. ©2016 AACR.

Obstructive sleep apnea and cancer: effects of intermittent hypoxia?

Obstructive sleep apnea (OSA) is a common disorder characterized by pauses in regular breathing. Apneic episodes lead to recurrent hypoxemia-reoxygenation cycles with concomitant cellular intermittent hypoxia. Studies suggest that intermittent hypoxia in OSA may influence tumorigenesis. This review presents recent articles on the potential role of OSA in cancer development. Relevant research has focused on: molecular pathways mediating the influence of intermittent hypoxia on tumor physiology, animal and epidemiological human studies linking OSA and cancer. Current data relating OSA to risk of neoplastic disease remain scarce, but recent studies reveal the potential for a strong relation. More work is, therefore, needed on the impact of OSA on many cancer-related aspects. Results may offer enlightenment for improved cancer diagnosis and treatment.

Obstructive sleep apnea and cancer: Epidemiologic links and theoretical biological constructs

Sleep disorders have emerged as highly prevalent conditions in the last 50-75 y. Along with improved understanding of such disorders, the realization that perturbations in sleep architecture and continuity may initiate, exacerbate or modulate the phenotypic expression of multiple diseases including cancer has gained increased attention. Furthermore, the intermittent hypoxia that is attendant to sleep disordered breathing, has recently been implicated in increased incidence and more adverse prognosis of cancer. The unifying conceptual framework linking these associations proposes that increased sympathetic activity and/or alterations in immune function, particularly affecting innate immune cellular populations, underlie the deleterious effects of sleep disorders on tumor biology. In this review, the epidemiological evidence linking disrupted sleep and intermittent hypoxia to oncological outcomes, and the potential biological underpinnings of such associations as illustrated by experimental murine models will be critically appraised. The overarching conclusion appears supportive in the formulation of an hypothetical framework, in which fragmented sleep and intermittent hypoxia may promote changes in multiple signalosomes and transcription factors that can not only initiate malignant transformation, but will also alter the tumor microenvironment, disrupt immunosurveillance, and thus hasten tumor proliferation and increase local and metastatic invasion. Future bench-based experimental studies as well as carefully conducted and controlled clinical epidemiological studies appear justified for further exploration of these hypotheses.

Microarray-based analysis of plasma cirDNA epigenetic modification profiling in xenografted mice exposed to intermittent hypoxia

Intermittent hypoxia (IH) during sleep is one of the major abnormalities occurring in patients suffering from obstructive sleep apnea (OSA), a highly prevalent disorder affecting 6-15% of the general population, particularly among obese people. IH has been proposed as a major determinant of oncogenetically-related processes such as tumor growth, invasion and metastasis. During the growth and expansion of tumors, fragmented DNA is released into the bloodstream and enters the circulation. Circulating tumor DNA (cirDNA) conserves the genetic and epigenetic profiles from the tumor of origin and can be isolated from the plasma fraction. Here we report a microarray-based epigenetic profiling of cirDNA isolated from blood samples of mice engrafted with TC1 epithelial lung cancer cells and controls, which were exposed to IH during sleep (XenoIH group, n = 3) or control conditions, (i.e., room air (RA); XenoRA group, n = 3) conditions. To prepare the targets for microarray hybridization, we applied a previously developed method that enriches the modified fraction of the cirDNA without amplification of genomic DNA. Regions of differential cirDNA modification between the two groups were identified by hybridizing the enriched fractions for each sample to Affymetrix GeneChip Human Promoter Arrays 1.0R. Microarray raw and processed data were deposited in NCBI's Gene Expression Omnibus (GEO) database (accession number: GSE61070).