Differential Distribution of the DNA-PKcs Inhibitor Peposertib Selectively Radiosensitizes Patient-derived Melanoma Brain Metastasis Xenografts.

Radioresistance of melanoma brain metastases limits the clinical utility of conventionally fractionated brain radiation in this disease, and strategies to improve radiation response could have significant clinical impact. The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) is critical for repair of radiation-induced DNA damage, and inhibitors of this kinase can have potent effects on radiation sensitivity. In this study, the radiosensitizing effects of the DNA-PKcs inhibitor peposertib were evaluated in patient-derived xenografts of melanoma brain metastases (M12, M15, M27). In clonogenic survival assays, peposertib augmented radiation-induced killing of M12 cells at concentrations ≥100 nmol/L, and a minimum of 16 hours exposure allowed maximal sensitization. This information was integrated with pharmacokinetic modeling to define an optimal dosing regimen for peposertib of 125 mpk dosed just prior to and 7 hours after irradiation. Using this drug dosing regimen in combination with 2.5 Gy × 5 fractions of radiation, significant prolongation in median survival was observed in M12-eGFP (104%; P = 0.0015) and M15 (50%; P = 0.03), while more limited effects were seen in M27 (16%, P = 0.04). These data support the concept of developing peposertib as a radiosensitizer for brain metastases and provide a paradigm for integrating in vitro and pharmacokinetic data to define an optimal radiosensitizing regimen for potent DNA repair inhibitors.

The selective cyclooxygenase-2 inhibitor NS398 ameliorates cisplatin-induced impairments in mitochondrial and cognitive function.

Chemobrain is a condition that negatively affects cognition in cancer patients undergoing active chemotherapy, as well as following chemotherapy cessation. Chemobrain is also known as chemotherapy-induced cognitive impairment (CICI) and has emerged as a significant medical contingency. There is no therapy to ameliorate this condition, hence identification of novel therapeutic strategies to prevent CICI is of great interest to cancer survivors. Utilizing the platinum-based chemotherapy cisplatin in an investigative approach for CICI, we identified increased expression of cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) in the adult mouse hippocampus, and in human cortical neuron cultures derived from induced pluripotent stem cells (iPSCs). Notably, administration of NS398, a selective COX-2 inhibitor, prevented CICI in vivo without negatively affecting the antitumor efficacy of cisplatin or potentiating tumor growth. Given that dysfunctional mitochondrial bioenergetics plays a prominent role in CICI, we explored the effects of NS398 in cisplatin-induced defects in human cortical mitochondria. We found that cisplatin significantly reduces mitochondrial membrane potential (MMP), increases matrix swelling, causes loss of cristae membrane integrity, impairs ATP production, as well as decreases cell viability and dendrite outgrowth. Pretreatment with NS398 in human cortical neurons attenuated mitochondrial dysfunction caused by cisplatin, while improving cell survival and neurite morphogenesis. These results suggest that aberrant COX-2 inflammatory pathways may contribute in cisplatin-induced mitochondrial damage and cognitive impairments. Therefore, COX-2 signaling may represent a viable therapeutic approach to improve the quality of life for cancer survivors experiencing CICI.

Chemobrain: An accelerated aging process linking adenosine A2A receptor signaling in cancer survivors.

Chemotherapy has a significant positive impact in cancer treatment outcomes, reducing recurrence and mortality. However, many cancer surviving children and adults suffer from aberrant chemotherapy neurotoxic effects on learning, memory, attention, executive functioning, and processing speed. This chemotherapy-induced cognitive impairment (CICI) is referred to as "chemobrain" or "chemofog". While the underlying mechanisms mediating CICI are still unclear, there is strong evidence that chemotherapy accelerates the biological aging process, manifesting as effects which include telomere shortening, epigenetic dysregulation, oxidative stress, mitochondrial defects, impaired neurogenesis, and neuroinflammation, all of which are known to contribute to increased anxiety and neurocognitive decline. Despite the increased prevalence of CICI, there exists a lack of mechanistic understanding by which chemotherapy detrimentally affects cognition in cancer survivors. Moreover, there are no approved therapeutic interventions for this condition. To address this gap in knowledge, this review attempts to identify how adenosine signaling, particularly through the adenosine A2A receptor, can be an essential tool to attenuate accelerated aging phenotypes. Importantly, the adenosine A2A receptor uniquely stands at the crossroads of cancer treatment and improved cognition, given that it is widely known to control tumor induced immunosuppression in the tumor microenvironment, while also posited to be an essential regulator of cognition in neurodegenerative disease. Consequently, we propose that the adenosine A2A receptor may provide a multifaceted therapeutic strategy to enhance anticancer activity, while combating chemotherapy induced cognitive deficits, both which are essential to provide novel therapeutic interventions against accelerated aging in cancer survivors.

Nanotechnology Approaches for Prevention and Treatment of Chemotherapy-Induced Neurotoxicity, Neuropathy, and Cardiomyopathy in Breast and Ovarian Cancer Survivors.

Nanotechnology has emerged as a promising approach for the targeted delivery of therapeutic agents while improving their efficacy and safety. As a result, nanomaterial development for the selective targeting of cancers, with the possibility of treating off-target, detrimental sequelae caused by chemotherapy, is an important area of research. Breast and ovarian cancer are among the most common cancer types in women, and chemotherapy is an essential treatment modality for these diseases. However, chemotherapy-induced neurotoxicity, neuropathy, and cardiomyopathy are common side effects that can affect breast and ovarian cancer survivors quality of life. Therefore, there is an urgent need to develop effective prevention and treatment strategies for these adverse effects. Nanoparticles (NPs) have extreme potential for enhancing therapeutic efficacy but require continued research to elucidate beneficial interventions for women cancer survivors. In short, nanotechnology-based approaches have emerged as promising strategies for preventing and treating chemotherapy-induced neurotoxicity, neuropathy, and cardiomyopathy. NP-based drug delivery systems and therapeutics have shown potential for reducing the side effects of chemotherapeutics while improving drug efficacy. In this article, the latest nanotechnology approaches and their potential for the prevention and treatment of chemotherapy-induced neurotoxicity, neuropathy, and cardiomyopathy in breast and ovarian cancer survivors are discussed.

Adenosine A2A receptor blockade prevents cisplatin-induced impairments in neurogenesis and cognitive function.

Chemotherapy-induced cognitive impairment (CICI) has emerged as a significant medical problem without therapeutic options. Using the platinum-based chemotherapy cisplatin to model CICI, we revealed robust elevations in the adenosine A2A receptor (A2AR) and its downstream effectors, cAMP and CREB, by cisplatin in the adult mouse hippocampus, a critical brain structure for learning and memory. Notably, A2AR inhibition by the Food and Drug Administration-approved A2AR antagonist KW-6002 prevented cisplatin-induced impairments in neural progenitor proliferation and dendrite morphogenesis of adult-born neurons, while improving memory and anxiety-like behavior, without affecting tumor growth or cisplatin's antitumor activity. Collectively, our study identifies A2AR signaling as a key pathway that can be therapeutically targeted to prevent cisplatin-induced cognitive impairments.

Nicotinamide Mononucleotide Prevents Cisplatin-Induced Mitochondrial Defects in Cortical Neurons Derived from Human Induced Pluripotent Stem Cells.

Background: Chemotherapy-induced cognitive impairment (CICI) is a neurotoxic side effect of chemotherapy that has yet to have an effective treatment. Objective: Using cisplatin, a platinum-based chemotherapy together with excitatory cortical neurons derived from human induced pluripotent cells (iPSCs) to model of CICI, our recent study demonstrated that dysregulation of brain NAD+ metabolism contributes to cisplatin-induced impairments in neurogenesis and cognitive function, which was prevented by administration of the NAD+ precursor, nicotinamide mononucleotide (NMN). However, it remains unclear how cisplatin causes neurogenic dysfunction and the mechanism by which NMN prevents cisplatin-induced cognitive impairment. Given that mitochondrial dysfunction is thought to play a prominent role in age-related neurodegenerative disease and chemotherapy-induced neurotoxicity, we sought to explore if NMN prevents chemotherapy-related neurotoxicity by attenuating cisplatin-induced mitochondrial damage. Results: We demonstrate that cisplatin induces neuronal DNA damage, increases generation of mitochondrial reactive oxygen species (ROS) and decreases ATP production, all of which are indicative of oxidative DNA damage and mitochondrial functional defects. Ultrastructural analysis revealed that cisplatin caused loss of cristae membrane integrity and matrix swelling in human cortical neurons. Notably, pretreatment with NMN prevents cisplatin-induced defects in mitochondria of human cortical neurons. Conclusion: Our results suggest that increased mitochondrial oxidative stress and functional defects play key roles in cisplatin-induced neurotoxicity. Thus, NMN may be an effective therapeutic strategy to prevent cisplatin-induced deleterious effects on mitochondria, making this organelle a key factor in amelioration of cisplatin-induced cognitive impairments.

Early stem cell aging in the mature brain.

Stem cell dysfunction drives many age-related disorders. Identifying mechanisms that initially compromise stem cell behavior represent early targets to promote tissue function later in life. Here, we pinpoint multiple factors that disrupt neural stem cell (NSC) behavior in the adult hippocampus. Clonal tracing showed that NSCs exhibit asynchronous depletion by identifying short-term NSCs (ST-NSCs) and long-term NSCs (LT-NSCs). ST-NSCs divide rapidly to generate neurons and deplete in the young brain. Meanwhile, multipotent LT-NSCs are maintained for months but are pushed out of homeostasis by lengthening quiescence. Single-cell transcriptome analysis of deep NSC quiescence revealed several hallmarks of molecular aging in the mature brain and identified tyrosine-protein kinase Abl1 as an NSC aging factor. Treatment with the Abl inhibitor imatinib increased NSC activation without impairing NSC maintenance in the middle-aged brain. Our study indicates that hippocampal NSCs are particularly vulnerable and adaptable to cellular aging.

Hippocampal regenerative medicine: neurogenic implications for addiction and mental disorders.

Psychiatric illness is a prevalent and highly debilitating disorder, and more than 50% of the general population in both middle- and high-income countries experience at least one psychiatric disorder at some point in their lives. As we continue to learn how pervasive psychiatric episodes are in society, we must acknowledge that psychiatric disorders are not solely relegated to a small group of predisposed individuals but rather occur in significant portions of all societal groups. Several distinct brain regions have been implicated in neuropsychiatric disease. These brain regions include corticolimbic structures, which regulate executive function and decision making (e.g., the prefrontal cortex), as well as striatal subregions known to control motivated behavior under normal and stressful conditions. Importantly, the corticolimbic neural circuitry includes the hippocampus, a critical brain structure that sends projections to both the cortex and striatum to coordinate learning, memory, and mood. In this review, we will discuss past and recent discoveries of how neurobiological processes in the hippocampus and corticolimbic structures work in concert to control executive function, memory, and mood in the context of mental disorders.

Nicotinamide Mononucleotide Prevents Cisplatin-Induced Cognitive Impairments.

Chemotherapy-induced cognitive impairment (CICI) is often reported as a neurotoxic side effect of chemotherapy. Although CICI has emerged as a significant medical problem, meaningful treatments are not currently available due to a lack of mechanistic understanding underlying CICI pathophysiology. Using the platinum-based chemotherapy cisplatin as a model for CICI, we show here that cisplatin suppresses nicotinamide adenine dinucleotide (NAD+) levels in the adult female mouse brain in vivo and in human cortical neurons derived from induced pluripotent stem cells in vitro. Increasing NAD+ levels through nicotinamide mononucleotide (NMN) administration prevented cisplatin-induced abnormalities in neural progenitor proliferation, neuronal morphogenesis, and cognitive function without affecting tumor growth and antitumor efficacy of cisplatin. Mechanistically, cisplatin inhibited expression of the NAD+ biosynthesis rate-limiting enzyme nicotinamide phosphoribosyl transferase (Nampt). Selective restoration of Nampt expression in adult-born neurons was sufficient to prevent cisplatin-induced defects in dendrite morphogenesis and memory function. Taken together, our findings suggest that aberrant Nampt-mediated NAD+ metabolic pathways may be a key contributor in cisplatin-induced neurogenic impairments, thus causally leading to memory dysfunction. Therefore, increasing NAD+ levels could represent a promising and safe therapeutic strategy for cisplatin-related neurotoxicity. SIGNIFICANCE: Increasing NAD+ through NMN supplementation offers a potential therapeutic strategy to safely prevent cisplatin-induced cognitive impairments, thus providing hope for improved quality of life in cancer survivors. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/13/3727/F1.large.jpg.

Genetic Inhibition of sFRP3 Prevents Glial Reactivity in a Mouse Model of Accelerated Aging.

PURPOSE: Aging is the most significant risk factor for neurodegenerative disorders that are typified by cognitive deficits. Our recent work utilizing BubR1 hypomorphic (BubR1H/H) mice, an accelerated aging model, has revealed that genetic inhibition of the endogenous Wnt pathway inhibitor secreted frizzled related protein 3 (sFRP3) plays a neuroprotective role. Neuroinflammation has been suggested as a pathological hallmark of age-related neurodegeneration mediating cognitive impairment. However, whether sFRP3 inhibition has a neuroprotective effect on neuroinflammatory gliosis in BubR1H/H mice is unknown. METHODS: To investigate neuroprotection from aging-related neuroinflammation by sFRP3 in vivo, we generated double Bub R1H/H;sfrp3 knockout mice and performed immunohistological analysis with cell type-specific markers for astrocytes (glial fibrillary acidic protein), and microglia (ionized calcium-binding adapter molecule 1). Given that the hippocampus is a brain structure critical for learning and memory, and is uniquely affected in aging-related neurodegeneration, we evaluated morphological changes on astrocytes and microglia via confocal imaging. RESULTS: We demonstrate that BubR1H/H mice exhibit significantly increased levels of astrogliosis and an increased trend of microglial activation in the hilus and molecular layer of the young adult hippocampus, thus suggesting that BubR1 insufficiency accelerates glial reactivity. Importantly, our results further show that genetic inhibition of sFRP3 significantly recovers the astrogliosis and microglial activation observed in BubR1H/H mice, suggesting a critical neuroprotective role for sFRP3 in age-related neuroinflammation. CONCLUSION: Our findings suggest that sFRP3 inhibition may represent a novel therapeutic strategy for neurodegeneration.

Waiting impulsivity during reward seeking increases adult hippocampal neurogenesis in mice.

Impulsivity is defined as a predisposition toward rapid, unplanned reactions in response to internal or external stimuli, often yielding negative consequences. Accordingly, impulsivity is considered a significant risk factor for developing addictive behaviors. The hippocampus is involved in regulating behavioral adaptability and learned behaviors. Consequently, abnormal hippocampal function has been demonstrated to contribute to impulsive and addictive behaviors. Furthermore, differential reinforcement of low rates of behavior (DRL) has shown that the hippocampus is implicated in reward acquisition and impulsivity in humans and rodent models. We have previously shown that impulsive behavior potentiates hippocampal neuroblast proliferation. However, the fate of these precursor cells produced during impulsive reward seeking remains unknown. Here, we demonstrate that DRL-mediated impulsive reward seeking with the 2-choice reaction time task (2-CRTT) increases the number of BrdU labeled cells in the dentate gyrus region of the hippocampus. Importantly, our results also show a significant increase in BrdU+ and NeuN+ colocalized mature newborn neurons in mice exhibiting impulsivity compared to non-impulsive control mice. These results suggest that operant reward seeking during unpredictable schedules of reinforcement contributes to adult hippocampal neurogenesis.

Dysfunctional Mitochondrial Bioenergetics and Synaptic Degeneration in Alzheimer Disease.

Synapses are sites of high energy demand which are dependent on high levels of mitochondrial derived adenosine triphosphate. Mitochondria within synaptic structures are key for maintenance of functional neurotransmission and this critical biological process is modulated by energy metabolism, mitochondrial distribution, mitochondrial trafficking, and cellular synaptic calcium flux. Synapse loss is presumed to be an early yet progressive pathological event in Alzheimer disease (AD), resulting in impaired cognitive function and memory loss which is particularly prevalent at later stages of disease. Supporting evidence from AD patients and animal models suggests that pathological mitochondrial dynamics indeed occurs early and is highly associated with synaptic lesions and degeneration in AD neurons. This review comprehensively highlights recent findings that describe how synaptic mitochondria pathology involves dysfunctional trafficking of this organelle, to maladaptive epigenetic contributions affecting mitochondrial function in AD. We further discuss how these negative, dynamic alterations impact synaptic function associated with AD. Finally, this review explores how antioxidant therapeutic approaches targeting mitochondria in AD can further clinical research and basic science investigations to advance our in-depth understanding of the pathogenesis of AD.

Nearly complete deletion of BubR1 causes microcephaly through shortened mitosis and massive cell death.

BUB-related 1 (BubR1) encoded by Budding Uninhibited by Benzimidazole 1B (BUB1B) is a crucial mitotic checkpoint protein ensuring proper segregation of chromosomes during mitosis. Mutations of BUB1B are responsible for mosaic variegated aneuploidy (MVA), a human congenital disorder characterized by extensive abnormalities in chromosome number. Although microcephaly is a prominent feature of MVA carrying the BUB1B mutation, how BubR1 deficiency disturbs neural progenitor proliferation and neuronal output and leads to microcephaly is unknown. Here we show that conditional loss of BubR1 in mouse cerebral cortex recapitulates microcephaly. BubR1-deficient cortex includes a strikingly reduced number of late-born, but not of early-born, neurons, although BubR1 expression is substantially reduced from an early stage. Importantly, absence of BubR1 decreases the proportion of neural progenitors in mitosis, specifically in metaphase, suggesting shortened mitosis owing to premature chromosome segregation. In the BubR1 mutant, massive apoptotic cell death, which is likely due to the compromised genomic integrity that results from aberrant mitosis, depletes progenitors and neurons during neurogenesis. There is no apparent alteration in centrosome number, spindle formation or primary cilia, suggesting that the major effect of BubR1 deficiency on neural progenitors is to impair the mitotic checkpoint. This finding highlights the importance of the mitotic checkpoint in the pathogenesis of microcephaly. Furthermore, the ependymal cell layer does not form in the conditional knockout, revealing an unrecognized role of BubR1 in assuring the integrity of the ventricular system, which may account for the presence of hydrocephalus in some patients.

sFRP3 inhibition improves age-related cellular changes in BubR1 progeroid mice.

Wnt signaling is a well-known molecular pathway in age-related pathogenesis and therapy of disease. While prior studies have mainly focused on Wnt ligands or Wnt activators, the in vivo functions of naturally secreted Wnt inhibitors are not clear, especially in brain aging. Using BubR1H/H mice as a novel mouse model of accelerated aging, we report that genetic inhibition of sFRP3 restores the reduced body and brain size observed in BubR1H/H mice. Furthermore, sFRP3 inhibition ameliorates hypomyelination in the corpus callosum and rescues neural progenitor proliferation in the hippocampal dentate gyrus of BubR1H/H mice. Taken together, our study identifies sFRP3 as a new molecular factor that cooperates with BubR1 function to regulate brain development, myelination, and hippocampal neurogenesis.

New Roles for Old Glue: Astrocyte Function in Synaptic Plasticity and Neurological Disorders.

Previously believed to solely play a supportive role in the central nervous system, astrocytes are now considered active players in normal brain function. Evidence in recent decades extends their contributions beyond the classically held brain glue role; it's now known that astrocytes act as a unique excitable component with functions extending into local network modulation, synaptic plasticity, and memory formation, and postinjury repair. In this review article, we highlight our growing understanding of astrocyte function and physiology, the increasing role of gliotransmitters in neuron-glia communication, and the role of astrocytes in modulating synaptic plasticity and cognitive function. Owing to the duality of both beneficial and deleterious roles attributed to astrocytes, we also discuss the implications of this new knowledge as it applies to neurological disorders including Alzheimer disease, epilepsy, and schizophrenia.

BubR1 Insufficiency Impairs Affective Behavior and Memory Function in Mice.

PURPOSE: Although aging causes functional declines in cognition, the molecular mechanism underlying these declines remains largely unknown. Recently, the spindle checkpoint kinase budding uninhibited by benzimidazole-related 1 (BubR1) has emerged as a key determinant for age-related pathology in various tissues including brain. However, the neurobehavioral impact of BubR1 has not been explored. In this study, we investigated the role of BubR1 in behavioral function. METHODS: To investigate the neurobiological functions of BubR1 in vivo, we utilized transgenic mice harboring BubR1 hypomorphic alleles (BubR1H/H mice), which produce low amounts of BubR1 protein, as well as mice that have specific knockdown of BubR1 in the adult dentate gyrus. To assess anxiety-like behavior, the above groups were subjected to the elevated plus maze and the light-dark test, in addition to utilizing the tail-suspension and forced-swim test to determine depression-like behavior. We used novel object recognition to test for memory-related function. RESULTS: We found that BubR1H/H mice display several behavioral deficits when compared to wild-type littermates, including increased anxiety in the elevated-plus maze test, depression-like behavior in the tail suspension test, as well as impaired memory function in the novel object recognition test. Similar to BubR1H/H mice, knockdown of BubR1 within the adult dentate gyrus led to increased anxiety-like behavior as well as depression-like behavior, and impaired memory function. CONCLUSION: Our study demonstrates a requirement of BubR1 in maintaining proper affective and memory-related behavioral function. These results suggest that a decline in BubR1 levels with advanced age may be a crucial contributor to age-related hippocampal dysfunction.

Mechano growth factor, a splice variant of IGF-1, promotes neurogenesis in the aging mouse brain.

Mechano growth factor (MGF) is a splice variant of IGF-1 first described in skeletal muscle. MGF induces muscle cell proliferation in response to muscle stress and injury. In control mice we found endogenous expression of MGF in neurogenic areas of the brain and these levels declined with age. To better understand the role of MGF in the brain, we used transgenic mice that constitutively overexpressed MGF from birth. MGF overexpression significantly increased the number of BrdU+ proliferative cells in the dentate gyrus (DG) of the hippocampus and subventricular zone (SVG). Although MGF overexpression increased the overall rate of adult hippocampal neurogenesis at the proliferation stage it did not alter the distribution of neurons at post-mitotic maturation stages. We then used the lac-operon system to conditionally overexpress MGF in the mouse brain beginning at 1, 3 and 12 months with histological and behavioral observation at 24 months of age. With conditional overexpression there was an increase of BrdU+ proliferating cells and BrdU+ differentiated mature neurons in the olfactory bulbs at 24 months when overexpression was induced from 1 and 3 months of age but not when started at 12 months. This was associated with preserved olfactory function. In vitro, MGF increased the size and number of neurospheres harvested from SVZ-derived neural stem cells (NSCs). These findings indicate that MGF overexpression increases the number of neural progenitor cells and promotes neurogenesis but does not alter the distribution of adult newborn neurons at post-mitotic stages. Maintaining youthful levels of MGF may be important in reversing age-related neuronal loss and brain dysfunction.

DISC1 in Astrocytes Influences Adult Neurogenesis and Hippocampus-Dependent Behaviors in Mice.

The functional role of genetic variants in glia in the pathogenesis of psychiatric disorders remains poorly studied. Disrupted-In-Schizophrenia 1 (DISC1), a genetic risk factor implicated in major mental disorders, has been implicated in regulation of astrocyte functions. As both astrocytes and DISC1 influence adult neurogenesis in the dentate gyrus (DG) of the hippocampus, we hypothesized that selective expression of dominant-negative C-terminus-truncated human DISC1 (mutant DISC1) in astrocytes would affect adult hippocampal neurogenesis and hippocampus-dependent behaviors. A series of behavioral tests were performed in mice with or without expression of mutant DISC1 in astrocytes during late postnatal development. In conjunction with behavioral tests, we evaluated adult neurogenesis, including neural progenitor proliferation and dendrite development of newborn neurons in the DG. The ameliorative effects of D-serine on mutant DISC1-associated behaviors and abnormal adult neurogenesis were also examined. Expression of mutant DISC1 in astrocytes decreased neural progenitor proliferation and dendrite growth of newborn neurons, and produced elevated anxiety, attenuated social behaviors, and impaired hippocampus-dependent learning and memory. Chronic treatment with D-serine ameliorated the behavioral alterations and rescued abnormal adult neurogenesis in mutant DISC1 mice. Our findings suggest that psychiatric genetic risk factors expressed in astrocytes could affect adult hippocampal neurogenesis and contribute to aspects of psychiatric disease through abnormal production of D-serine.