Circadian and melatonin disruption by exposure to light at night drives intrinsic resistance to tamoxifen therapy in breast cancer

Light: An Extrinsic Factor Influencing Animal-based Research

Light is an environmental factor that is extrinsic to animals themselves and that exerts a profound influence on the regulation of circadian, neurohormonal, metabolic, and neurobehavioral systems of all animals, including research animals. These widespread biologic effects of light are mediated by distinct photoreceptors-rods and cones that comprise the conventional visual system and melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) of the nonvisual system that interact with the rods and cones. The rods and cones of the visual system, along with the ipRGCs of the nonvisual system, are species distinct in terms of opsins and opsin concentrations and interact with one another to provide vision and regulate circadian rhythms of neurohormonal and neurobehavioral responses to light. Here, we review a brief history of lighting technologies, the nature of light and circadian rhythms, our present understanding of mammalian photoreception, and current industry practices and standards. We also consider the implications of light for vivarium measurement, production, and technological application and provide simple recommendations on artificial lighting for use by regulatory authorities, lighting manufacturers, designers, engineers, researchers, and research animal care staff that ensure best practices for optimizing animal health and well-being and, ultimately, improving scientific outcomes.

Molecular mechanisms of artificial light at night affecting circadian rhythm disturbance

Artificial light at night (ALAN) pollution has been regarded as a global environmental concern. More than 80% of the global population is exposed to light pollution. Exacerbating this issue, artificially lit outdoor areas are growing by 2.2% per year, while continuously lit areas have brightened by 2.2% each year due to rapid population growth and expanding urbanization. Furthermore, the increasing prevalence of night shift work and smart device usage contributes to the inescapable influence of ALAN. Studies have shown that ALAN can disrupt endogenous biological clocks, resulting in a disturbance of the circadian rhythm, which ultimately affects various physiological functions. Up until now, scholars have studied various disease mechanisms caused by ALAN that may be related to the response of the circadian system to light. This review outlines the molecular mechanisms by which ALAN causes circadian rhythm abnormalities in sleep disorders, endocrine diseases, cardiovascular disease, cancer, immune impairment, depression, anxiety and cognitive impairments.

Melatonin modulates tumor metabolism and mitigates metastasis

INTRODUCTION

Melatonin, originally isolated from the mammalian pineal gland, was subsequently identified in many animal cell types and in plants. While melatonin was discovered to inhibit cancer more than 5 decades ago, its anti-cancer potential has not been fully exploited despite its lack of serious toxicity over a very wide dose range, high safety margin, and its efficacy.

AREAS COVERED

This review elucidates the potential mechanisms by which melatonin interferes with tumor growth and metastasis, including its ability to alter tumor cell metabolism, inhibit epithelial-mesenchymal transition, reverse cancer chemoresistance, function synergistically with conventional cancer-inhibiting drugs while limiting many of their side effects. In contrast to its function as a potent antioxidant in normal cells, it may induce oxidative stress in cancer cells, contributing to its oncostatic actions.

EXPERT OPINION

Considering the large amount of experimental data supporting melatonin's multiple and varied inhibitory effects on numerous cancer types, coupled with the virtual lack of toxicity of this molecule, it has not been thoroughly tested as an anti-cancer agent in clinical trials. There seems to be significant resistance to such investigations, possibly because melatonin is inexpensive and non-patentable, and as a result there would be limited financial gain for its use.

Evaluating Occupant Light Exposure and Usage Patterns in an Inpatient Behavioral Health Unit

OBJECTIVE

To (1) evaluate the use case for tunable lighting in inpatient behavioral health, (2) describe differences in staff lighting exposures between static and tunable lighting conditions using wearable sensors, and (3) document occupant lighting control usage patterns.

BACKGROUND

Tunable lighting fixtures can vary the amount of light and spectral content, so have been offered as a way to address light and health considerations. Before we can understand potential health benefits of tunable lighting, it is helpful to understand how occupant exposures under tunable lighting differ from those under more traditional lighting systems.

METHODS

Tunable lighting benefits and challenges for inpatient behavioral health were carefully detailed during design. Light exposure measurements were recorded at an old site with static fluorescent lighting and a new site with tunable light-emitting diode (LED) lighting. Behavioral health inpatient unit staff participants voluntarily wore a light measurement device to estimate light exposure. At the new site, controls usage data were recorded each time a button was pressed on a lighting control station.

RESULTS

While general observations can be made about the data between sites, there is notable variation at both sites depending on the day and hour. Button press data revealed that occupants used the full capability of the tunable lighting system to support different activities and needs.

CONCLUSION

Understanding the relationship between occupant well-being and light requires a holistic research approach including thoughtful design accounting for real-world constraints, detailed measurement of light exposure, and understanding how occupants interact and make use of new technology.

Role of Melatonin in Cancer: Effect on Clock Genes

The circadian clock is a regulatory system, with a periodicity of approximately 24 h, that generates rhythmic changes in many physiological processes. Increasing evidence links chronodisruption with aberrant functionality in clock gene expression, resulting in multiple diseases, including cancer. In this context, tumor cells have an altered circadian machinery compared to normal cells, which deregulates the cell cycle, repair mechanisms, energy metabolism and other processes. Melatonin is the main hormone produced by the pineal gland, whose production and secretion oscillates in accordance with the light:dark cycle. In addition, melatonin regulates the expression of clock genes, including those in cancer cells, which could play a key role in the numerous oncostatic effects of this hormone. This review aims to describe and clarify the role of clock genes in cancer, as well as the possible mechanisms of the action of melatonin through which it regulates the expression of the tumor's circadian machinery, in order to propose future anti-neoplastic clinical treatments.

Interactions of melatonin with various signaling pathways: implications for cancer therapy

Melatonin is a neuro-hormone with conserved roles in evolution. Initially synthetized as an antioxidant molecule, it has gained prominence as a key molecule in the regulation of the circadian rhythm. Melatonin exerts its effect by binding to cytoplasmic and intra-nuclear receptors, and is able to regulate the expression of key mediators of different signaling pathways. This ability has led scholars to investigate the role of melatonin in reversing the process of carcinogenesis, a process in which many signaling pathways are involved, and regulating these pathways may be of clinical significance. In this review, the role of melatonin in regulating multiple signaling pathways with important roles in cancer progression is discussed, and evidence regarding the beneficence of targeting malignancies with this approach is presented.

Lactic Acidosis in Patients with Solid Cancer

Significance: Cancer-associated tissue-specific lactic acidosis stimulates and mediates tumor invasion and metastasis and is druggable. Rarely, malignancy causes systemic lactic acidosis, the role of which is poorly understood. Recent Advances: The understanding of the role of lactate has shifted dramatically since its discovery. Long recognized as only a waste product, lactate has become known as an alternative metabolism substrate and a secreted nutrient that is exchanged between the tumor and the microenvironment. Tissue-specific lactic acidosis is targeted to improve the host body's anticancer defense and serves as a tool that allows the targeting of anticancer compounds. Systemic lactic acidosis is associated with poor survival. In patients with solid cancer, systemic lactic acidosis is associated with an extremely poor prognosis, as revealed by the analysis of 57 published cases in this study. Although it is considered a pathology worth treating, targeting systemic lactic acidosis in patients with solid cancer is usually inefficient. Critical Issues: Research gaps include simple questions, such as the unknown nuclear pH of the cancer cells and its effects on chemotherapy outcomes, pH sensitivity of glycosylation in cancer cells, in vivo mechanisms of response to acidosis in the absence of lactate, and overinterpretation of in vitro results that were obtained by using cells that were not preadapted to acidic environments. Future Directions: Numerous metabolism-targeting anticancer compounds induce lactatemia, lactic acidosis, or other types of acidosis. Their potential to induce acidic environments is largely overlooked, although the acidosis might contribute to a substantial portion of the observed clinical effects. Antioxid. Redox Signal. 37, 1130-1152.

Pro-Apoptotic and Anti-Migration Properties of a Thiazoline-Containing Platinum(II) Complex in MDA-MB-231 Breast Cancer Cells: The Role of Melatonin as a Synergistic Agent

Triple-negative breast cancer (TNBC) is an aggressive cancer insensitive to hormonal and human epidermal growth factor receptor 2 (HER2)-targeted therapies and has a poor prognosis. Therefore, there is a need for the development of convenient anticancer strategies for the management of TNBC. In this paper, we evaluate the antitumoral potential of a platinum(II) complex coordinated with the ligand 2-(3,5-diphenylpyrazol-1-yl)-2-thiazoline (DPhPzTn), hereafter PtDPhPzTn, against the TNBC cell line MDA-MB-231, and compared its effect with both cisplatin and its less lipophilic counterpart PtPzTn, the latter containing the ligand 2-(pyrazol-1-yl)-2-thiazoline (PzTn). Then, the putative potentiating actions of melatonin, a naturally occurring antioxidant with renowned antitumor properties, on the tumor-killing ability of PtDPhPzTn were also checked in TNBC cells. Our results show that PtDPhPzTn presented enhanced cytotoxicity compared to both the classical drug cisplatin and PtPzTn. In addition, PtDPhPzTn was able to induce apoptosis, being more selective for MDA-MB-231 cells when compared to non-tumor breast epithelial MCF10A cells. Likewise, PtDPhPzTn produced moderate S phase arrest and greatly impaired the migration ability of MDA-MB-231 cells. Most importantly, the co-stimulation of TNBC cells with PtDPhPzTn and melatonin substantially enhanced apoptosis and markedly improved the anti-migratory action compared to PtDPhPzTn alone. Altogether, our findings provide evidence that PtDPhPzTn and melatonin could be potentially applied to breast cancer treatment as powerful synergistic agents.

Melatonin as an oncostatic agent: Review of the modulation of tumor microenvironment and overcoming multidrug resistance

Multi drug resistance (MDR) generally limits the efficacy of chemotherapy in cancer patients and can be categorized into primary or acquired resistance. Melatonin (MLT), a lipophilic hormone released from pineal gland, is a molecule with oncostatic effects. Here, we will briefly review the contribution of different microenvironmental components including fibroblasts, immune and inflammatory cells, stem cells and vascular endothelial cells in tumor initiation, progression and development. Then, the mechanisms by which MLT can potentially affect these elements and regulate drug resistance will be presented. Finally, we will explain how different studies have used novel strategies incorporating MLT to suppress cancer resistance against therapeutics.

Circadian Regulation of Hormonal Timing and the Pathophysiology of Circadian Dysregulation

Circadian rhythms are endogenously generated, daily patterns of behavior and physiology that are essential for optimal health and disease prevention. Disruptions to circadian timing are associated with a host of maladies, including metabolic disease and obesity, diabetes, heart disease, cancer, and mental health disturbances. The circadian timing system is hierarchically organized, with a master circadian clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks throughout the CNS and periphery. The SCN receives light information via a direct retinal pathway, synchronizing the master clock to environmental time. At the cellular level, circadian rhythms are ubiquitous, with rhythms generated by interlocking, autoregulatory transcription-translation feedback loops. At the level of the SCN, tight cellular coupling maintains rhythms even in the absence of environmental input. The SCN, in turn, communicates timing information via the autonomic nervous system and hormonal signaling. This signaling couples individual cellular oscillators at the tissue level in extra-SCN brain loci and the periphery and synchronizes subordinate clocks to external time. In the modern world, circadian disruption is widespread due to limited exposure to sunlight during the day, exposure to artificial light at night, and widespread use of light-emitting electronic devices, likely contributing to an increase in the prevalence, and the progression, of a host of disease states. The present overview focuses on the circadian control of endocrine secretions, the significance of rhythms within key endocrine axes for typical, homeostatic functioning, and implications for health and disease when dysregulated. © 2022 American Physiological Society. Compr Physiol 12: 1-30, 2022.

Circadian Rhythm Disruption Increases Tumor Growth Rate and Accumulation of Myeloid-Derived Suppressor Cells

Circadian rhythm disruption is implicated in the initiation and progression of many diseases, including cancer. External stimuli, such as sunlight, serve to synchronize physiological processes and cellular functions to a 24-h cycle. The immune system is controlled by circadian rhythms, and perturbation of these rhythms can potentially alter the immune response to infections and tumors. The effect of circadian rhythm disruption on the immune response to tumors remains unclear. Specifically, the effects of circadian disruption (CD) on immunosuppressive cell types within the tumor, such as myeloid-derived suppressor cells (MDSCs), are unknown. In this study, a shifting lighting schedule is used to disrupt the circadian rhythm of mice. After acclimation to lighting schedules, mice are inoculated with 4T1 or B16-F10 tumors. Tumor growth is increased in mice housed under circadian disrupting lighting conditions compared to standard lighting conditions. Analysis of immune populations within the spleen and tumor shows an increased accumulation of MDSCs within these tissues, suggesting that MDSC mediated immunosuppression plays a role in the enhanced tumor growth caused by circadian disruption. This paves the way for future studies of the effects of CD on immunosuppression in cancer.

Exposure to artificial light at night: A common link for obesity and cancer?

Exposure to artificial light at night (ALAN) has been associated with disruption of the circadian system, which has been pointed out to have detrimental effects on health. Exposure to outdoor ALAN is very frequent in industrialised countries due to nocturnal light pollution and the relevant involvement of the total workforce in shift work and night work. Ecological and epidemiologic studies highlight the association between exposure to ALAN and several diseases, mainly obesity and cancer. More recently, also indoor ALAN exposure has been investigated. Among several multifactorial mechanisms linking ALAN exposure and health risks, suppression of melatonin secretion plays a pivotal role leading to alterations in circadian rhythm patterns, that are detrimental in terms of appetite regulation, and dysfunctions in metabolic signalling and cell growth in cancer. In addition, gut dysbiosis, inflammation, hypovitaminosis D, imbalance in cytokine secretion and levels are responsible for the multiple relationship linking circadian dysregulation due to ALAN exposure and obesity, and cancer. Therefore, the current manuscript summarises human and basic studies pointing out the impact of ALAN exposure on health, mostly focusing on obesity and cancer. Based on extant evidence, prevention strategies for obesity and cancer should be prompted, targeting exposure to ALAN.

The effect of evening light on circadian-related outcomes: A systematic review

Bright light exposure at night can help workers adapt to their shift schedules, but there has been relatively little research on evening light. We conducted a systematic review of studies that manipulated light exposure in the evening (broadly defined as 16:00-22:00) before real or simulated night shifts. Across the five eligible studies, evening light produced phase delays in melatonin, body temperature, and sleep propensity; it also improved sleep quality, sleep duration, memory, and work performance. There were mixed effects for mood, no changes in sleepiness, and no negative effects. The confidence in these results ranged from moderate for physiological markers of circadian phase delays to very low for mood. Future studies should compare the relative effectiveness and safety of evening versus night-time light exposure. Overall, the benefits of evening light for shift workers are tentative yet promising.

Sleep Disruption and Cancer: Chicken or the Egg?

Sleep is a nearly ubiquitous phenomenon across the phylogenetic tree, highlighting its essential role in ensuring fitness across evolutionary time. Consequently, chronic disruption of the duration, timing, or structure of sleep can cause widespread problems in multiple physiological systems, including those that regulate energy balance, immune function, and cognitive capacity, among others. Many, if not all these systems, become altered throughout the course of cancer initiation, growth, metastatic spread, treatment, and recurrence. Recent work has demonstrated how changes in sleep influence the development of chronic diseases, including cancer, in both humans and animal models. A common finding is that for some cancers (e.g., breast), chronic disruption of sleep/wake states prior to disease onset is associated with an increased risk for cancer development. Additionally, sleep disruption after cancer initiation is often associated with worse outcomes. Recently, evidence suggesting that cancer itself can affect neuronal circuits controlling sleep and wakefulness has accumulated. Patients with cancer often report difficulty falling asleep, difficulty staying asleep, and severe fatigue, during and even years after treatment. In addition to the psychological stress associated with cancer, cancer itself may alter sleep homeostasis through changes to host physiology and via currently undefined mechanisms. Moreover, cancer treatments (e.g., chemotherapy, radiation, hormonal, and surgical) may further worsen sleep problems through complex biological processes yet to be fully understood. This results in a “chicken or the egg” phenomenon, where it is unclear whether sleep disruption promotes cancer or cancer reciprocally disrupts sleep. This review will discuss existing evidence for both hypotheses and present a framework through which the interactions between sleep and cancer can be dissociated and causally investigated.

The potential anti-cancer effects of melatonin on breast cancer

Melatonin is the primary hormone of the pineal gland that is secreted at night. It regulates many physiological functions, including the sleep-wake cycle, gonadal activity, free radical scavenging, immunomodulation, neuro-protection, and cancer progression. The precise functions of melatonin are mediated by guanosine triphosphate (GTP)-binding protein (G-protein) coupled melatonin receptor 1 (MT1) and MT2 receptors. However, nuclear receptors are also associated with melatonin activity. Circadian rhythm disruption, shift work, and light exposure at night hamper melatonin production. Impaired melatonin level promotes various pathophysiological changes, including cancer. In our modern society, breast cancer is a serious problem throughout the world. Several studies have been indicated the link between low levels of melatonin and breast cancer development. Melatonin has oncostatic properties in breast cancer cells. This indolamine advances apoptosis, which arrests the cell cycle and regulates metabolic activity. Moreover, melatonin increases the treatment efficacy of cancer and can be used as an adjuvant with chemotherapeutic agents.

Chronoradiobiology of Breast Cancer: The Time Is Now to Link Circadian Rhythm and Radiation Biology

Circadian disruption has been linked to cancer development, progression, and radiation response. Clinical evidence to date shows that circadian genetic variation and time of treatment affect radiation response and toxicity for women with breast cancer. At the molecular level, there is interplay between circadian clock regulators such as PER1, which mediates ATM and p53-mediated cell cycle gating and apoptosis. These molecular alterations may govern aggressive cancer phenotypes, outcomes, and radiation response. Exploiting the various circadian clock mechanisms may enhance the therapeutic index of radiation by decreasing toxicity, increasing disease control, and improving outcomes. We will review the body’s natural circadian rhythms and clock gene-regulation while exploring preclinical and clinical evidence that implicates chronobiological disruptions in the etiology of breast cancer. We will discuss radiobiological principles and the circadian regulation of DNA damage responses. Lastly, we will present potential rational therapeutic approaches that target circadian pathways to improve outcomes in breast cancer. Understanding the implications of optimal timing in cancer treatment and exploring ways to entrain circadian biology with light, diet, and chronobiological agents like melatonin may provide an avenue for enhancing the therapeutic index of radiotherapy.

A Method for Perfusion of Tissue-Isolated Human Tumor Xenografts in Nude Rats to Investigate the Oncostatic Role of the Physiological Nocturnal Melatonin Signal

The tissue-isolated human tumor perfusion methodology enables the elucidation of physiological melatonin's oncostatic impact on cancer metabolism and physiology. Here we describe an apparatus and surgical technique for perfusing tissue-isolated human tumor xenografts in nude rats in situ that ensures continuous blood flow to and from the tissue. This system and methodology have proven quite successful in examining the receptor-mediated oncostatic effects of the physiological nocturnal melatonin signal on metabolism and physiology in a variety of epithelial and mesenchymal human tumors.

A Method for Growing Tissue-Isolated Human Tumor Xenografts in Nude Rats for Melatonin/Cancer Studies

The tissue-isolated tumor model permits the investigation of melatonin's influence on human tumor growth and metabolism in laboratory rats in vivo. Here we describe a unique surgical technique for implanting and growing human tumor xenografts on a vascular stalk composed of the nude rat epigastric artery and vein that provides a continuous blood supply from a single source to the tissue-isolated tumor while insuring the absence of extraneous vascular connections. A variety of human tumor types may be implanted and grown utilizing this unique model that may provide a plethora of scientific data from a single tumor examined.

Melatonin and Pathological Cell Interactions: Mitochondrial Glucose Processing in Cancer Cells

Melatonin is synthesized in the pineal gland at night. Since melatonin is produced in the mitochondria of all other cells in a non-circadian manner, the amount synthesized by the pineal gland is less than 5% of the total. Melatonin produced in mitochondria influences glucose metabolism in all cells. Many pathological cells adopt aerobic glycolysis (Warburg effect) in which pyruvate is excluded from the mitochondria and remains in the cytosol where it is metabolized to lactate. The entrance of pyruvate into the mitochondria of healthy cells allows it to be irreversibly decarboxylated by pyruvate dehydrogenase (PDH) to acetyl coenzyme A (acetyl-CoA). The exclusion of pyruvate from the mitochondria in pathological cells prevents the generation of acetyl-CoA from pyruvate. This is relevant to mitochondrial melatonin production, as acetyl-CoA is a required co-substrate/co-factor for melatonin synthesis. When PDH is inhibited during aerobic glycolysis or during intracellular hypoxia, the deficiency of acetyl-CoA likely prevents mitochondrial melatonin synthesis. When cells experiencing aerobic glycolysis or hypoxia with a diminished level of acetyl-CoA are supplemented with melatonin or receive it from another endogenous source (pineal-derived), pathological cells convert to a more normal phenotype and support the transport of pyruvate into the mitochondria, thereby re-establishing a healthier mitochondrial metabolic physiology.

Melatonin-A New Prospect in Prostate and Breast Cancer Management

Cancer is a known cause of mortality globally. The management of cancer has been influenced periodically by diverse scientific research for early detection to promote remission and improve quality of life. One of these advancements is the prospect of melatonin (n-acetyl-5-methoxytryptamine) in managing prostate and breast cancers. Melatonin exerts its oncostatic effect by inhibiting angiogenesis, preventing cancer spread and growth, and improving the sensitivity of cancer cells to radiation and chemotherapy in both prostate and breast cancer. This review aims to highlight some of the current studies on melatonin's effect on prostate and breast cancers. We reviewed articles and two randomized controlled trials (RCT) that highlighted the mechanism of melatonin in combating tumorigenesis of these cancers. Articles and RCT studies were obtained by searching PubMed using regular and Medical Subject Heading (MeSH) keyword search strategy. The majority of the articles reviewed supported the use of melatonin in cancer management since inhibition of angiogenesis, cancer proliferation, invasion of normal cells by tumor cells, and improvement in chemotherapeutic and radiation therapy were achieved with its use. In addition, melatonin was also protective against prostate and breast cancers in the general population. Despite the benefits of melatonin in cancer management, most of the studies done were in vivo and in vitro studies, and more studies in human subjects are encouraged to confirm the positive therapeutic use of melatonin.

Roles of circadian clocks in cancer pathogenesis and treatment

Circadian clocks are ubiquitous timing mechanisms that generate approximately 24-h rhythms in cellular and bodily functions across nearly all living species. These internal clock systems enable living organisms to anticipate and respond to daily changes in their environment in a timely manner, optimizing temporal physiology and behaviors. Dysregulation of circadian rhythms by genetic and environmental risk factors increases susceptibility to multiple diseases, particularly cancers. A growing number of studies have revealed dynamic crosstalk between circadian clocks and cancer pathways, providing mechanistic insights into the therapeutic utility of circadian rhythms in cancer treatment. This review will discuss the roles of circadian rhythms in cancer pathogenesis, highlighting the recent advances in chronotherapeutic approaches for improved cancer treatment.

Circadian Rhythms, Disease and Chronotherapy

Circadian clocks are biological timing mechanisms that generate 24-h rhythms of physiology and behavior, exemplified by cycles of sleep/wake, hormone release, and metabolism. The adaptive value of clocks is evident when internal body clocks and daily environmental cycles are mismatched, such as in the case of shift work and jet lag or even mistimed eating, all of which are associated with physiological disruption and disease. Studies with animal and human models have also unraveled an important role of functional circadian clocks in modulating cellular and organismal responses to physiological cues (ex., food intake, exercise), pathological insults (e.g. virus and parasite infections), and medical interventions (e.g. medication). With growing knowledge of the molecular and cellular mechanisms underlying circadian physiology and pathophysiology, it is becoming possible to target circadian rhythms for disease prevention and treatment. In this review, we discuss recent advances in circadian research and the potential for therapeutic applications that take patient circadian rhythms into account in treating disease.

Melatonin Inhibits Osteoclastogenesis and Osteolytic Bone Metastasis: Implications for Osteoporosis

Osteoblasts and osteoclasts are major cellular components in the bone microenvironment and they play a key role in the bone turnover cycle. Many risk factors interfere with this cycle and contribute to bone-wasting diseases that progressively destroy bone and markedly reduce quality of life. Melatonin (N-acetyl-5-methoxy-tryptamine) has demonstrated intriguing therapeutic potential in the bone microenvironment, with reported effects that include the regulation of bone metabolism, acceleration of osteoblastogenesis, inhibition of osteoclastogenesis and the induction of apoptosis in mature osteoclasts, as well as the suppression of osteolytic bone metastasis. This review aims to shed light on molecular and clinical evidence that points to possibilities of melatonin for the treatment of both osteoporosis and osteolytic bone metastasis. It appears that the therapeutic qualities of melatonin supplementation may enable existing antiresorptive osteoporotic drugs to treat osteolytic metastasis.

Role of Melatonin in Breast Carcinoma: Correlation of Expression Patterns of Melatonin-1 Receptor With Estrogen, Progesterone, and HER2 Receptors

Breast carcinoma is a multifaceted-etiology malignancy. The presence of estrogen (ER), progesterone (PR), and HER2 (human epidermal growth factor receptor 2) receptors in breast carcinoma tissue has therapeutic implications. Recent studies indicate that pineal hormone melatonin by its receptor melatonin 1 (MT1) also influences the development and growth of breast cancer cells. The aim of this cross-sectional study was to elucidate the expression pattern of MT1 receptor in relation to estrogen, progesterone, and HER2 receptors in breast carcinoma. Two groups (receptor positive and triple negative) of breast carcinoma were taken. For comparison, normal mammary tissue was used as control. Immunohistochemistry was carried out using anti-melatonin receptor 1A antibody. Membranous/cytoplasmic expression was seen more than the nuclear expression in the cancerous tissue. Positive correlation of the MT1 expression was seen with ER, PR, and HER 2 receptor. Higher MT1 receptor expression was seen in the receptor-positive cases in comparison with triple-negative cases, which might signify melatonin deficiency in the former, leading to reactive increase in cell receptors. No correlation of MT1 expression with Ki67 index or lymph node status in both receptor-positive and triple-negative cases was found. Normal mammary tissue mainly showed cytoplasmic MT1 immunoreactivity of epithelial cells (ducts and acini), myoepithelial cells, and lining epithelium of blood vessels. Receptor-positive cases would, therefore, benefit from the use of melatonin as supporting therapy. This indicates that melatonin receptor status can be used as an independent pathologic indicator to evaluate breast carcinoma tissue, and melatonin receptor status may help to determine treatment protocols.

Exploring the link between chronobiology and drug delivery: effects on cancer therapy

Circadian clock is an impressive timing system responsible for the control of several metabolic, physiological and behavioural processes. Nowadays, the connection between the circadian clock and cancer occurrence and development is consensual. Therefore, the inclusion of circadian timing into cancer therapy may potentially offer a more effective and less toxic approach. This way, chronotherapy has been shown to improve cancer treatment efficacy. Despite this relevant finding, its clinical application is poorly exploited. The conception of novel anticancer drug delivery systems and the combination of chronobiology with nanotechnology may provide a powerful tool to optimize cancer therapy, instigating the incorporation of the circadian timing into clinical practice towards a more personalized drug delivery. This review focuses on the recent advances in the field of cancer chronobiology, on the link between cancer and the disruption of circadian rhythms and on the promising targeted drug nanodelivery approaches aiming the clinical application of cancer chronotherapy.

Metabolic Anti-Cancer Effects of Melatonin: Clinically Relevant Prospects

Metabolic reprogramming characterized by alterations in nutrient uptake and critical molecular pathways associated with cancer cell metabolism represents a fundamental process of malignant transformation. Melatonin (N-acetyl-5-methoxytryptamine) is a hormone secreted by the pineal gland. Melatonin primarily regulates circadian rhythms but also exerts anti-inflammatory, anti-depressant, antioxidant and anti-tumor activities. Concerning cancer metabolism, melatonin displays significant anticancer effects via the regulation of key components of aerobic glycolysis, gluconeogenesis, the pentose phosphate pathway (PPP) and lipid metabolism. Melatonin treatment affects glucose transporter (GLUT) expression, glucose-6-phosphate dehydrogenase (G6PDH) activity, lactate production and other metabolic contributors. Moreover, melatonin modulates critical players in cancer development, such as HIF-1 and p53. Taken together, melatonin has notable anti-cancer effects at malignancy initiation, progression and metastasing. Further investigations of melatonin impacts relevant for cancer metabolism are expected to create innovative approaches supportive for the effective prevention and targeted therapy of cancers.

Part-time cancers and role of melatonin in determining their metabolic phenotype

This brief review describes the association of the endogenous pineal melatonin rhythm with the metabolic flux of solid tumors, particularly breast cancer. It also summarizes new information on the potential mechanisms by which endogenously-produced or exogenously-administered melatonin impacts the metabolic phenotype of cancer cells. The evidence indicates that solid tumors may redirect their metabolic phenotype from the pathological Warburg-type metabolism during the day to the healthier mitochondrial oxidative phosphorylation on a nightly basis. Thus, they function as cancer cells only during the day and as healthier cells at night, that is, they are only part-time cancerous. This switch to oxidative phosphorylation at night causes cancer cells to exhibit a reduced tumor phenotype and less likely to rapidly proliferate or to become invasive or metastatic. Also discussed is the likelihood that some solid tumors are especially aggressive during the day and much less so at night due to the nocturnal rise in melatonin which determines their metabolic state. We further propose that when melatonin is used/tested in clinical trials, a specific treatment paradigm be used that is consistent with the temporal metabolic changes in tumor metabolism. Finally, it seems likely that the concurrent use of melatonin in combination with conventional chemotherapies also would improve cancer treatment outcomes.

Melatonin and its mechanism of action in the female reproductive system and related malignancies

Melatonin (N-acetyl-5-methoxytryptamine), the main product of pineal gland in vertebrates, is well known for its multifunctional role which has great influences on the reproductive system. Recent studies documented that melatonin is a powerful free radical scavenger that affects the reproductive system function and female infertility by MT1 and MT2 receptors. Furthermore, cancer researches indicate the influence of melatonin on the modulation of tumor cell signaling pathways resulting in growth inhibitor of the both in vivo/in vitro models. Cancer adjuvant therapy can also benefit from melatonin through therapeutic impact and decreasing the side effects of radiation and chemotherapy. This article reviews the scientific evidence about the influence of melatonin and its mechanism of action on the fertility potential, physiological alteration, and anticancer efficacy, during experimental and clinical studies.

A novel signature predicts recurrence risk and therapeutic response in breast cancer patients

Acetylserotonin O-methyltransferase (ASMT) is a key enzyme in the synthesis of melatonin. Although melatonin has been shown to exhibit anticancer activity and prevents endocrine resistance in breast cancer, the role of ASMT in breast cancer progression remains unclear. In this retrospective study, we analyzed gene expression profiles in 27 data sets on 7244 patients from 11 countries. We found that ASMT expression was significantly reduced in breast cancer tumors relative to healthy tissue. Among breast cancer patients, those with higher levels of ASMT expression had better relapse-free survival outcomes and longer metastasis-free survival times. Following treatment with tamoxifen, patients with greater ASMT expression experienced longer periods before relapse or distance recurrence. Motivated by these results, we devised an ASMT gene signature that can correctly identify low-risk cases with a sensitivity and specificity of 0.997 and 0.916, respectively. This signature was robustly validated using 23 independent breast cancer mRNA array data sets from different platforms (consisting of 5800 patients) and an RNAseq data set from TCGA (comprising 1096 patients). Intriguingly, patients who are classified as high-risk by the signature benefit from adjuvant chemotherapy, and those with grade II tumors who are classified as low-risk exhibit improved overall survival and distance relapse-free outcomes following endocrine therapy. Together, our findings more clearly elucidate the roles of ASMT, provide strategies for improving the efficacy of tamoxifen treatment and help to identify those patients who may maximally benefit from adjuvant or endocrine therapies.

Melatonin interrupts osteoclast functioning and suppresses tumor-secreted RANKL expression: implications for bone metastases

Cancer-related bone erosion occurs frequently in bone metastasis and is associated with severe complications such as chronic bone pain, fractures, and lower survival rates. In recognition of the fact that the darkness hormone melatonin is capable of regulating bone homeostasis, we explored its therapeutic potential in bone metastasis. We found that melatonin directly reduces osteoclast differentiation, bone resorption activity and promotes apoptosis of mature osteoclasts. We also observed that melatonin inhibits RANKL production in lung and prostate cancer cells by downregulating the p38 MAPK pathway, which in turn prevents cancer-associated osteoclast differentiation. In lung and prostate bone metastasis models, twice-weekly melatonin treatment markedly reduced tumor volumes and numbers of osteolytic lesions. Melatonin also substantially lowered the numbers of TRAP-positive osteoclasts in tibia bone marrow and RANKL expression in tumor tissue. These findings show promise for melatonin in the treatment of bone metastases.

Circadian clock protein CRY1 prevents paclitaxel‑induced senescence of bladder cancer cells by promoting p53 degradation

Bladder cancer is a common tumor type of the urinary system, which has high levels of morbidity and mortality. The first‑line treatment is cisplatin‑based combination chemotherapy, but a significant proportion of patients relapse due to the development of drug resistance. Therapy‑induced senescence can act as a 'back‑up' response to chemotherapy in cancer types that are resistant to apoptosis‑based anticancer therapies. The circadian clock serves an important role in drug resistance and cellular senescence. The aim of the present study was to investigate the regulatory effect of the circadian clock on paclitaxel (PTX)‑induced senescence in cisplatin‑resistant bladder cancer cells. Cisplatin‑resistant bladder cancer cells were established via long‑term cisplatin incubation. PTX induced apparent senescence in bladder cancer cells as demonstrated via SA‑β‑Gal staining, but this was not observed in the cisplatin‑resistant cells. The cisplatin‑resistant cells entered into a quiescent state with prolonged circadian rhythm under acute PTX stress. It was identified that the circadian protein cryptochrome1 (CRY1) accumulated in these quiescent cisplatin‑resistant cells, and that CRY1 knockdown restored PTX‑induced senescence. Mechanistically, CRY1 promoted p53 degradation via increasing the binding of p53 with its ubiquitin E3 ligase MDM2 proto‑oncogene. These data suggested that the accumulated CRY1 in cisplatin‑resistant cells could prevent PTX‑induced senescence by promoting p53 degradation.

Therapeutic targets of cancer drugs: Modulation by melatonin

The biological functions of melatonin range beyond the regulation of the circadian rhythm. With regard to cancer, melatonin's potential to suppress cancer initiation, progression, angiogenesis and metastasis as well as sensitizing malignant cells to conventional chemo- and radiotherapy are among its most interesting effects. The targets at which melatonin initiates its anti-cancer effects are in common with those of a majority of existing anti-cancer agents, giving rise to the notion that this molecule is a pleiotropic agent sharing many features with other antineoplastic drugs in terms of their mechanisms of action. Among these common mechanisms of action are the regulation of several major intracellular pathways including mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK) and protein kinase B (AKT/PKB) signaling. The important mediators affected by melatonin include cyclins, nuclear factor-κB (NF-κB), heat shock proteins (HSPs) and c-Myc, all of which can serve as potential targets for cancer drugs. Melatonin also exerts some of its anti-cancer effects via inducing epigenetic modifications, DNA damage and mitochondrial disruption in malignant cells. The regulation of these mediators by melatonin mitigates tumor growth and invasiveness via modulating their downstream responsive genes, housekeeping enzymes, telomerase reverse transcriptase, apoptotic gene expression, angiogenic factors and structural proteins involved in metastasis. Increasing our knowledge on how melatonin affects its target sites will help find ways of exploiting the beneficial effects of this ubiquitously-acting molecule in cancer therapy. Acknowledging this, here we reviewed the most studied target pathways attributed to the anti-cancer effects of melatonin, highlighting their therapeutic potential.

Light Pollution and Cancer

For many individuals in industrialized nations, the widespread adoption of electric lighting has dramatically affected the circadian organization of physiology and behavior. Although initially assumed to be innocuous, exposure to artificial light at night (ALAN) is associated with several disorders, including increased incidence of cancer, metabolic disorders, and mood disorders. Within this review, we present a brief overview of the molecular circadian clock system and the importance of maintaining fidelity to bright days and dark nights. We describe the interrelation between core clock genes and the cell cycle, as well as the contribution of clock genes to oncogenesis. Next, we review the clinical implications of disrupted circadian rhythms on cancer, followed by a section on the foundational science literature on the effects of light at night and cancer. Finally, we provide some strategies for mitigation of disrupted circadian rhythms to improve health.

Melatonin Can Modulate the Effect of Navitoclax (ABT-737) in HL-60 Cells

Melatonin (N-acetyl-5-methoxytryptamine MEL) is an indolamine that has antioxidant, anti-inflammatory and anti-tumor properties. Moreover, MEL is capable of exhibiting both anti-apoptotic and pro-apoptotic effects. In the normal cells, MEL possesses antioxidant property and has an anti-apoptotic effect, while in the cancer cells it has pro-apoptotic action. We investigated the combined effect of MEL and navitoclax (ABT-737), which promotes cell death, on the activation of proliferation in acute promyelocytic leukemia on a cell model HL-60. The combined effect of these compounds leads to a reduction of the index of mitotic activity. The alterations in the level of anti- and pro-apoptotic proteins such as BclxL, Bclw, Mcl-1, and BAX, membrane potential, Ca²⁺ retention capacity, and ROS production under the combined action of MEL and ABT-737 were performed. We obtained that MEL in combination with ABT-737 decreased Ca²⁺ capacity, dropped membrane potential, increased ROS production, suppressed the expression of anti-apoptotic proteins such as BclxL, Bclw, and Mcl-1, and enhanced the expression of pro-apoptotic BAX. Since, MEL modulates autophagy and endoplasmic reticulum (ER) stress in cancer cells, the combined effect of MEL and ABT-737 on the expression of ER stress and autophagy markers was checked. The combined effect of MEL and ABT-737 (0.2 μM) increased the expression of protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), leading to a decrease in the level of binding immunoglobulin protein (BIP) followed by an increase in the level of C/EBP homologous protein (CHOP). In this condition, the expression of ERO1 decreased, which could lead to a decrease in the level of protein disulfide isomerase (PDI). The obtained data suggested that melatonin has potential usefulness in the treatment of cancer, where it is able to modulate ER stress, autophagy and apoptosis.

Melatonin: A Potential Therapeutic Option for Breast Cancer

Melatonin has significant inhibitory effects in numerous cancers, especially breast cancer. In estrogen receptor (ER)-positive human breast cancer, the oncostatic actions of melatonin are mainly achieved by suppressing ER mRNA expression and ER transcriptional activity via the MT1 receptor. Melatonin also regulates the transactivation of nuclear receptors, estrogen-metabolizing enzymes, and the expression of related genes. Furthermore, melatonin suppresses tumor aerobic glycolysis, critical cell-signaling pathways relevant to cell proliferation, survival, metastasis, and overcomes drug resistance. Studies in animal and human models indicate that disruption of the circadian nocturnal melatonin signal promotes the growth, metabolism, and signaling of human breast cancer, resulting in resistance to hormone therapy and chemotherapy, which may be reversed by melatonin.

Towards an Integral Therapeutic Protocol for Breast Cancer Based upon the New H+-Centered Anticancer Paradigm of the Late Post-Warburg Era

A brand new approach to the understanding of breast cancer (BC) is urgently needed. In this contribution, the etiology, pathogenesis, and treatment of this disease is approached from the new pH-centric anticancer paradigm. Only this unitarian perspective, based upon the hydrogen ion (H+) dynamics of cancer, allows for the understanding and integration of the many dualisms, confusions, and paradoxes of the disease. The new H+-related, wide-ranging model can embrace, from a unique perspective, the many aspects of the disease and, at the same time, therapeutically interfere with most, if not all, of the hallmarks of cancer known to date. The pH-related armamentarium available for the treatment of BC reviewed here may be beneficial for all types and stages of the disease. In this vein, we have attempted a megasynthesis of traditional and new knowledge in the different areas of breast cancer research and treatment based upon the wide-ranging approach afforded by the hydrogen ion dynamics of cancer. The concerted utilization of the pH-related drugs that are available nowadays for the treatment of breast cancer is advanced.

Circadian disruption, melatonin rhythm perturbations and their contributions to chaotic physiology

The aim of this report is to summarize the data documenting the vital nature of well-regulated cellular and organismal circadian rhythms, which are also reflected in a stable melatonin cycle, in supporting optimal health. Cellular fluctuations in physiology exist in most cells of multicellular organisms with their stability relying on the prevailing light:dark cycle, since it regulates, via specialized intrinsically-photoreceptive retinal ganglion cells (ipRGC) and the retinohypothalamic tract, the master circadian oscillator, i.e., the suprachiasmatic nuclei (SCN). The output message of the SCN, as determined by the light:dark cycle, is transferred to peripheral oscillators, so-called slave cellular oscillators, directly via the autonomic nervous system with its limited distribution. and indirectly via the pineal-derived circulating melatonin rhythm, which contacts every cell. Via its regulatory effects on the neuroendocrine system, particularly the hypothalamo-pituitary-adrenal axis, the SCN also has a major influence on the adrenal glucocorticoid rhythm which impacts neurological diseases and psychological behaviors. Moreover, the SCN regulates the circadian production and secretion of melatonin. When the central circadian oscillator is disturbed, such as by light at night, it passes misinformation to all organs in the body. When this occurs the physiology of cells becomes altered and normal cellular functions are compromised. This physiological upheaval is a precursor to pathologies. The deterioration of the SCN/pineal network is often a normal consequence of aging and its related diseases, but in today's societies where manufactured light is becoming progressively more common worldwide, the associated pathologies may also be occurring at an earlier age.

The circadian clock protects against acute radiation-induced dermatitis

Radiation-induced dermatitis is a common occurrence in cancer patients undergoing radiation therapy (RT) and is caused when ionizing radiation (IR) induces DNA strand breaks in skin cells. The wide use of RT in cancer treatments makes it important to minimize RT-induced toxicities including radiodermatitis. This study sought to determine if the circadian clock plays a protective role in minimizing radiodermatitis. We treated mice in control (Day Shift), environmentally-disrupted (Rotating Shift) and genetically-disrupted (Per 1/2-/-) circadian conditions with 6 Gy of IR to the whole body. There was a significantly increased number of radiodermatitis spots on mice with circadian clock disruption compared to control mice. Additionally, circadian clock disrupted mice exhibited reduced protein levels of Bmal1, a phenomenon that sensitized circadian synchronized keratinocytes to IR-induced DNA damage. Furthermore, the skin phenotype results corresponded with significantly reduced body weights and increased genomic DNA damage in blood cells of mice with clock disruption compared to control mice. These findings suggest that the circadian clock plays a protective role in IR-induced DNA damage and skin toxicity, possibly through BMAL1-dependent mechanisms, and potentially impacts RT-associated radiodermatitis in cancer patients.

Molecular Mechanisms Underlying the Circadian Rhythm of Blood Pressure in Normotensive Subjects

PURPOSE OF REVIEW

Blood pressure (BP) follows a circadian rhythm (CR) in normotensive subjects. BP increases in the morning and decreases at night. This review aims at providing an up-to-date overview regarding the molecular mechanisms underlying the circadian regulation of BP.

RECENT FINDINGS

The suprachiasmatic nucleus (SCN) is the regulatory center for CRs. In SCN astrocytes, the phosphorylated glycogen synthase kinase-3β (pGSK-3β) also follows a CR and its expression reaches a maximum in the morning and decreases at night. pGSK-3β induces the β-catenin migration to the nucleus. During the daytime, the nuclear β-catenin increases the expression of the glutamate excitatory amino acid transporter 2 (EAAT2) and glutamine synthetase (GS). In SCN, EAAT2 removes glutamate from the synaptic cleft of glutamatergic neurons and transfers it to the astrocyte cytoplasm where GS converts glutamate into glutamine. Thus, glutamate decreases in the synaptic cleft. This decreases the stimulation of the glutamate receptors AMPA-R and NMDA-R located on glutamatergic post-synaptic neurons. Consequently, activation of NTS is decreased and BP increases. The opposite occurs at night. Despite several studies resulting from animal studies, the circadian regulation of BP appears largely controlled in normotensive subjects by the canonical WNT/β-catenin pathway involving the SCN, astrocytes, and glutamatergic neurons.

Melatonin inhibits Warburg-dependent cancer by redirecting glucose oxidation to the mitochondria: a mechanistic hypothesis

Melatonin has the ability to intervene in the initiation, progression and metastasis of some experimental cancers. A large variety of potential mechanisms have been advanced to describe the metabolic and molecular events associated with melatonin's interactions with cancer cells. There is one metabolic perturbation that is common to a large number of solid tumors and accounts for the ability of cancer cells to actively proliferate, avoid apoptosis, and readily metastasize, i.e., they use cytosolic aerobic glycolysis (the Warburg effect) to rapidly generate the necessary ATP required for the high metabolic demands of the cancer cells. There are several drugs, referred to as glycolytic agents, that cause cancer cells to abandon aerobic glycolysis and shift to the more conventional mitochondrial oxidative phosphorylation for ATP synthesis as in normal cells. In doing so, glycolytic agents also inhibit cancer growth. Herein, we hypothesize that melatonin also functions as an inhibitor of cytosolic glycolysis in cancer cells using mechanisms, i.e., downregulation of the enzyme (pyruvate dehydrogenase kinase) that interferes with the conversion of pyruvate to acetyl CoA in the mitochondria, as do other glycolytic drugs. In doing so, melatonin halts the proliferative activity of cancer cells, reduces their metastatic potential and causes them to more readily undergo apoptosis. This hypothesis is discussed in relation to the previously published reports. Whereas melatonin is synthesized in the mitochondria of normal cells, we hypothesize that this synthetic capability is not present in cancer cell mitochondria because of the depressed acetyl CoA; acetyl CoA is necessary for the rate limiting enzyme in melatonin synthesis, arylalkylamine-N-acetyltransferase. Finally, the ability of melatonin to switch glucose oxidation from the cytosol to the mitochondria also explains how tumors that become resistant to conventional chemotherapies are re-sensitized to the same treatment when melatonin is applied.

Melatonin: an endogenous miraculous indolamine, fights against cancer progression

PURPOSE

Melatonin is an amphipathic indolamine molecule ubiquitously present in all organisms ranging from cyanobacteria to humans. The pineal gland is the site of melatonin synthesis and secretion under the influence of the retinohypothalamic tract. Some extrapineal tissues (skin, lens, gastrointestinal tract, testis, ovary, lymphocytes, and astrocytes) also enable to produce melatonin. Physiologically, melatonin regulates various functions like circadian rhythm, sleep-wake cycle, gonadal activity, redox homeostasis, neuroprotection, immune-modulation, and anticancer effects in the body. Inappropriate melatonin secretion advances the aging process, tumorigenesis, visceral adiposity, etc. METHODS: For the preparation of this review, I had reviewed the literature on the multidimensional activities of melatonin from the NCBI website database PubMed, Springer Nature, Science Direct (Elsevier), Wiley Online ResearchGate, and Google Scholar databases to search relevant articles. Specifically, I focused on the roles and mechanisms of action of melatonin in cancer prevention.

RESULTS

The actions of melatonin are primarily mediated by G-protein coupled MT1 and MT2 receptors; however, several intracellular protein and nuclear receptors can modulate the activity. Normal levels of the melatonin protect the cells from adverse effects including carcinogenesis. Therapeutically, melatonin has chronomedicinal value; it also shows a remarkable anticancer property. The oncostatic action of melatonin is multidimensional, associated with the advancement of apoptosis, the arrest of the cell cycle, inhibition of metastasis, and antioxidant activity.

CONCLUSION

The present review has emphasized the mechanism of the anti-neoplastic activity of melatonin that increases the possibilities of the new approaches in cancer therapy.

A New and Integral Approach to the Etiopathogenesis and Treatment of Breast Cancer Based upon Its Hydrogen Ion Dynamics

Despite all efforts, the treatment of breast cancer (BC) cannot be considered to be a success story. The advances in surgery, chemotherapy and radiotherapy have not been sufficient at all. Indeed, the accumulated experience clearly indicates that new perspectives and non-main stream approaches are needed to better characterize the etiopathogenesis and treatment of this disease. This contribution deals with how the new pH-centric anticancer paradigm plays a fundamental role in reaching a more integral understanding of the etiology, pathogenesis, and treatment of this multifactorial disease. For the first time, the armamentarium available for the treatment of the different types and phases of BC is approached here from a Unitarian perspective-based upon the hydrogen ion dynamics of cancer. The wide-ranged pH-related molecular, biochemical and metabolic model is able to embrace most of the fields and subfields of breast cancer etiopathogenesis and treatment. This single and integrated approach allows advancing towards a unidirectional, concerted and synergistic program of treatment. Further efforts in this line are likely to first improve the therapeutics of each subtype of this tumor and every individual patient in every phase of the disease.

Circadian disruption: What do we actually mean?

The circadian system regulates physiology and behavior. Acute challenges to the system, such as those experienced when traveling across time zones, will eventually result in re-synchronization to local environmental time cues, but this re-synchronization is oftentimes accompanied by adverse short-term consequences. When such challenges are experienced chronically, adaptation may not be achieved, as for example in the case of rotating night shift workers. The transient and chronic disturbance of the circadian system is most frequently referred to as "circadian disruption", but many other terms have been proposed and used to refer to similar situations. It is now beyond doubt that the circadian system contributes to health and disease, emphasizing the need for clear terminology when describing challenges to the circadian system and their consequences. The goal of this review is to provide an overview of the terms used to describe disruption of the circadian system, discuss proposed quantifications of disruption in experimental and observational settings with a focus on human research, and highlight limitations and challenges of currently available tools. For circadian research to advance as a translational science, clear, operationalizable, and scalable quantifications of circadian disruption are key, as they will enable improved assessment and reproducibility of results, ideally ranging from mechanistic settings, including animal research, to large-scale randomized clinical trials.

Periodic Oxaliplatin Administration in Synergy with PER2-Mediated PCNA Transcription Repression Promotes Chronochemotherapeutic Efficacy of OSCC

Developing chemotherapeutic resistance affects clinical outcomes of oxaliplatin treatment on various types of cancer. Thus, it is imperative to explore alternative therapeutic strategies to improve the efficacy of oxaliplatin. Here, it is shown that circadian regulator period 2 (PER2) can potentiate the cytotoxicity of oxaliplatin and boost cell apoptosis by inhibiting DNA adducts repair in human oral squamous cell carcinoma (OSCC) cells. The circadian timing system is closely involved in controling the activity of DNA adducts repair and gives it a 24 h rhythm. The mechanistic dissection clarifies that PER2 can periodically suppress proliferating cell nuclear antigen (PCNA) transcription by pulling down circadian locomotor output cycles kaput-brain and muscle arnt-like 1 heterodimer from PCNA promoter in a CRY1/2-dependent manner, which subsequently impedes oxaliplatin-induced DNA adducts repair. Similarly, PER2 is capable of improving the efficacy of classical DNA-damaging chemotherapeutic agents. The tumor-bearing mouse model displays PER2 can be deployed as an oxaliplatin administration timing biomarker. In summary, it is believed that the chronochemotherapeutic strategy matching PER2 expression rhythm can efficiently improve the oxaliplatin efficacy of OSCC.

Influence of Daytime LED Light Exposure on Circadian Regulatory Dynamics of Metabolism and Physiology in Mice

Light is a potent biologic force that profoundly influences circadian, neuroendocrine, and neurobehavioral regulation in animals. Previously we examined the effects of light-phase exposure of rats to white light-emitting diodes (LED), which emit more light in the blue-appearing portion of the visible spectrum (465 to 485 nm) than do broad-spectrum cool white fluorescent (CWF) light, on the nighttime melatonin amplitude and circadian regulation of metabolism and physiology. In the current studies, we tested the hypothesis that exposure to blue-enriched LED light at day (bLAD), compared with CWF, promotes the circadian regulation of neuroendocrine, metabolic, and physiologic parameters that are associated with optimizing homeostatic regulation of health and wellbeing in 3 mouse strains commonly used in biomedical research (C3H [melatonin-producing], C57BL/6, and BALB/c [melatonin-non-producing]). Compared with male and female mice housed for 12 wk under 12:12-h light:dark (LD) cycles in CWF light, C3H mice in bLAD evinced 6-fold higher peak plasma melatonin levels at the middark phase; in addition, high melatonin levels were prolonged 2 to 3 h into the light phase. C57BL/6 and BALB/c strains did not produce nighttime pineal melatonin. Body growth rates; dietary and water intakes; circadian rhythms of arterial blood corticosterone, insulin, leptin, glucose, and lactic acid; pO₂ and pCO₂; fatty acids; and metabolic indicators (cAMP, DNA, tissue DNA 3H-thymidine incorporation, fat content) in major organ systems were significantly lower and activation of major metabolic signaling pathways (mTOR, GSK3β, and SIRT1) in skeletal muscle and liver were higher only in C3H mice in bLAD compared with CWF. These data show that exposure of C3H mice to bLAD compared with CWF has a marked positive effect on the circadian regulation of neuroendocrine, metabolic, and physiologic parameters associated with the promotion of animal health and wellbeing that may influence scientific outcomes. The absence of enhancement in amelatonic strains suggests hyperproduction of nighttime melatonin may be a key component of the physiology.

Epigenetic inhibition of the tumor suppressor ARHI by light at night-induced circadian melatonin disruption mediates STAT3-driven paclitaxel resistance in breast cancer

Disruption of circadian time structure and suppression of circadian nocturnal melatonin (MLT) production by exposure to dim light at night (dLAN), as occurs with night shift work and/or disturbed sleep-wake cycles, is associated with a significantly increased risk of breast cancer and resistance to tamoxifen and doxorubicin. Melatonin inhibition of human breast cancer chemoresistance involves mechanisms including suppression of tumor metabolism and inhibition of kinases and transcription factors which are often activated in drug-resistant breast cancer. Signal transducer and activator of transcription 3 (STAT3), frequently overexpressed and activated in paclitaxel (PTX)-resistant breast cancer, promotes the expression of DNA methyltransferase one (DNMT1) to epigenetically suppress the transcription of tumor suppressor Aplasia Ras homolog one (ARHI) which can sequester STAT3 in the cytoplasm to block PTX resistance. We demonstrate that breast tumor xenografts in rats exposed to dLAN and circadian MLT disrupted express elevated levels of phosphorylated and acetylated STAT3, increased DNMT1, but reduced sirtuin 1 (SIRT1) and ARHI. Furthermore, MLT and/or SIRT1 administration blocked/reversed interleukin 6 (IL-6)-induced acetylation of STAT3 and its methylation of ARH1 to increase ARH1 mRNA expression in MCF-7 breast cancer cells. Finally, analyses of the I-SPY 1 trial demonstrate that elevated MT₁ receptor expression is significantly correlated with pathologic complete response following neo-adjuvant therapy in breast cancer patients. This is the first study to demonstrate circadian disruption of MLT by dLAN driving intrinsic resistance to PTX via epigenetic mechanisms increasing STAT3 expression and that MLT administration can reestablish sensitivity of breast tumors to PTX and drive tumor regression.

Redox homeostasis in a rodent model of circadian disruption: Effect of melatonin supplementation

Continuous light or dark photoperiods are the leading cause of disruption in the circadian rhythm of day-night cycle. The purpose of this study was to understand the cellular redox balance in a model of circadian disrupted rat model and determine the effect of melatonin supplementation. Young male Wistar rats were randomly divided into five groups (n = 4). Group (I): normal day-night (12 h:12 h) cycle, Group (II): normal rats treated with melatonin, Group (III): rats subjected to continuous light exposure (CLE), Group (IV): CLE rats treated with melatonin, and Group (V) Rats subjected to continuous dark. Melatonin (10 mg/kg) was administered orally at dusk to the Group (II) & (IV). Rats were sacrificed after 10 days of treatment and biomarkers of oxidative stress were evaluated. Results demonstrated significant (p < 0.05) increase of malondialdehyde (MDA), plasma membrane redox system (PMRS), protein carbonyl oxidation (PCO), advanced oxidation protein products (AOPPs), and advanced glycation end products (AGEs) during CLE. A significantly (p < 0.05) decreased level of reduced glutathione (GSH) and ferric reducing antioxidant potential in plasma (FRAP) was also observed during CLE. Treatment with melatonin in CLE rats showed reduced level of MDA, PMRS, PCO, AOPPs and AGEs while GSH and FRAP activity were increased. During continuous dark exposure (CDE) the biomarkers of oxidative stress were attenuated compared to control. Supplementation of melatonin could be a promising strategy to maintain redox homeostasis during prolonged condition of light exposure and other conditions of redox imbalance.

It's About Time: Advances in Understanding the Circadian Regulation of DNA Damage and Repair in Carcinogenesis and Cancer Treatment Outcomes

The circadian rhythm is established by a coordinated network of peripheral clocks interlocked and regulated by a central pacemaker. This network is maintained by the rhythmic expression of core clock genes, which in turn generate oscillatory expression patterns of different sets of target proteins in a tissue-specific manner. Precise regulation of biological processes driven by the body's circadian network in response to periodic changes in the environment determines healthy life. The delicate balance in the cycling of enzymes, metabolites, cofactors, and immune regulators is essential to achieve cellular homeostasis. Disruption of this circadian homeostasis has been linked with the development and progression of various diseases including cancer. Over the years, circadian regulation of drug metabolism and processing has been employed in the treatment of diabetes, hypertension, peptic ulcers, and allergic rhinitis. Although time dictated drug administration was demonstrated many decades ago, its application in cancer treatment is limited due to insufficient mechanistic data supporting experimental results and inconsistency between clinical trials. However, timed administration of anti-cancer drugs is rapidly gaining attention as studies with animal and human models unveil molecular intricacies involved in the circadian control of biological pathways. In this regard, striking a balance between maximizing tumor responsiveness and minimizing side effects is crucial to achieve positive patient outcomes. This review focuses on regulation of the circadian clock in carcinogenesis outcomes through DNA damage and repair mechanisms and its application in therapy with specific emphasis on skin and breast cancers.

Pharmacological, Mechanistic, and Pharmacokinetic Assessment of Novel Melatonin-Tamoxifen Drug Conjugates as Breast Cancer Drugs

Tamoxifen is used to prevent and treat estrogen receptor-positive (ER+) breast cancer (BC); however, its chronic use can increase uterine cancer risk and induce tamoxifen resistance. Novel melatonin-tamoxifen drug conjugates may be promising to treat BC and may help offset the adverse effects of tamoxifen usage alone due to the presence of melatonin. We synthesized and screened five drug conjugates (C2, C4, C5, C9, and C15 linked) for their effects on BC cell (MCF-7, tamoxifen-resistant MCF-7, mouse mammary carcinoma, MDA-MB-231, and BT-549) viability, migration, and binding affinity to melatonin receptor 1 (MT1R) and estrogen receptor 1 (ESR1). C4 and C5 demonstrated the most favorable pharmacological characteristics with respect to binding profiles (affinity for ESR1 and MT1R) and their potency/efficacy to inhibit BC cell viability and migration in four phenotypically diverse invasive ductal BC cell lines. C4 and C5 were further assessed for their actions against tamoxifen-resistant MCF-7 cells and a patient-derived xenograft triple-negative BC cell line (TU-BcX-4IC) and for their mechanisms of action using selective mitogen-activated protein kinase kinase MEK1/2, MEK5, and phosphoinositide 3-kinase (PI3K) inhibitors. C4 and C5 inhibited tamoxifen-resistant MCF-7 cells with equal potency (IC₅₀ = 4-8 μM) and efficacy (∼90% inhibition of viability and migration) but demonstrated increased potency (IC₅₀ = 80-211 μM) and efficacy (∼140% inhibition) to inhibit migration versus cell viability (IC₅₀ = 181-304 mM; efficacy ∼80% inhibition) in TU-BcX-4IC cells. Unique pharmacokinetic profiles were observed, with C4 having greater bioavailability than C5. Further assessment of C4 and C5 demonstrates that they create novel pharmacophores within each BC cell that is context specific and involves MEK1/2/pERK1/2, MEK5/pERK5, PI3K, and nuclear factor κB. These melatonin-tamoxifen drug conjugates show promise as novel anticancer drugs and further preclinical and clinical evaluation is warranted.