Peripheral tumors alter neuroinflammatory responses to lipopolysaccharide in female rats

The role of microglia in 67NR mammary tumor-induced suppression of brain responses to immune challenges in female mice

It is poorly understood how solid peripheral tumors affect brain neuroimmune responses despite the various brain-mediated side effects and higher rates of infection reported in cancer patients. We hypothesized that chronic low-grade peripheral tumor-induced inflammation conditions microglia to drive suppression of neuroinflammatory responses to a subsequent peripheral immune challenge. Here, Balb/c murine mammary tumors attenuated the microglial inflammatory gene expression responses to lipopolysaccharide (LPS) and live Escherichia coli (E. coli) challenges and the fatigue response to an E. coli infection. In contrast, the inflammatory gene expression in response to LPS or a toll-like receptor 2 agonist of Percoll-enriched primary microglia cultures was comparable between tumor-bearing and -free mice, as were the neuroinflammatory and sickness behavioral responses to an intracerebroventricular interleukin (IL)-1β injection. These data led to the hypothesis that Balb/c mammary tumors blunt the neuroinflammatory responses to an immune challenge via a mechanism involving tumor suppression of the peripheral humoral response. Balb/c mammary tumors modestly attenuated select circulating cytokine responses to LPS and E. coli challenges. Further, a second mammary tumor/mouse strain model (E0771 tumors in C57Bl/6 mice) displayed mildly elevated inflammatory responses to an immune challenge. Taken together, these data indicate that tumor-induced suppression of neuroinflammation and sickness behaviors may be driven by a blunted microglial phenotype, partly because of an attenuated peripheral signal to the brain, which may contribute to infection responses and behavioral side effects reported in cancer patients. Finally, these neuroimmune effects likely vary based on tumor type and/or host immune phenotype.

Microglia contribute to mammary tumor-induced neuroinflammation in a female mouse model

Following diagnosis but before treatment, up to 30% of breast cancer patients report behavioral side effects (e.g., anxiety, depression, memory impairment). Our rodent mammary tumor model recapitulates aspects of these behavioral sequelae, as well as elevated circulating and brain inflammatory mediators. Neuroinflammation is a proposed mechanism underlying the etiology of mood disorders and cognitive deficits, and therefore may be contributing to tumor-associated behavioral side effects. The cellular mechanisms by which tumor-induced neuroinflammation occurs remain unknown, making targeted treatment approaches inaccessible. Here, we tested the hypotheses that microglia are the primary cells driving tumor-induced neuroinflammation and behavioral side effects. Young adult female BALB/c mice were induced with a 67NR mammary tumor; tumor-free controls underwent a sham surgery. Mammary tumors increased IBA1+ and GFAP+ staining in the amygdala and hippocampus relative to tumor-free controls. However, tumors did not alter gene expression of Percoll-enriched microglia isolated from the whole brain. While cognitive, social, and anhedonia-like behaviors were not altered in tumor-bearing mice, tumors increased central tendency in the open-field test; microglia depletion did not reverse this effect. Brain region RT-qPCR data indicated that microglia depletion attenuated tumor-induced elevations of neuroinflammatory gene expression in a region- and mediator-specific manner. These results indicate a causal role of microglia in tumor-induced neuroinflammation. This research advances our understanding of the cellular mechanisms underlying tumor-induced neuroinflammation in order to understand how brain responses (e.g., behavior) may be altered with subsequent cancer-related immune challenges.

Heterotopic 4T1 breast cancer transplantation induces hippocampal inflammation and depressive-like behaviors in mice

Cancer and its accompanying treatments can lead to numerous physical and emotional concerns, including subclinical or clinical depression and anxiety, which could significantly impact one's well-being, quality of life, and survival. A large number of studies have elucidated that neuroinflammation is associated with depression. Here, we report the hippocampal pathological changes and depressive behaviors of a heterotopic breast cancer transplantation mouse model; hence, a heterotopic 4T1 breast cancer transplantation mouse model was established. Assessment of cognitive and locomotive functions of the experimental animals was conducted using open- and closed-field tests, including a tail suspension test. Expression levels of monoaminergic system markers, brain-derived neurotrophic factor (BDNF), pro-inflammatory cytokines, and nuclear factor-kappa B (NFκB) in the hippocampus and serum were detected using immunochemistry and western and enzyme-linked immunosorbent assay analysis. A comparison of the differences between model and control animals was performed. As per our findings, 4T1 tumor-bearing mice displayed cancer-related anorexia/cachexia with significant reductions in the travel distance and the total number of squares crossed in the open- and closed-field tests. Additionally, the 4T1 tumor-bearing mice withstood a more extended period of immobility during the tail suspension test. Immunohistochemistry studies revealed reduced levels of serotonin, norepinephrine, and BDNF in the hippocampus and serum. Elevated levels of NFκB and pro-inflammatory cytokines in the hippocampus were also observed. These findings suggest that hippocampal inflammation may have played an important role in the neurological function and depressive behavior in heterotopic 4T1 breast cancer transplantation mice.

Cancer activates microglia to the same extent as chronic stress throughout stress neurocircuitry in a mouse model of breast cancer

The prevalence of stress-related comorbidities is increased approximately 3-fold in cancer patients compared to the general population. There is a scarcity of research focusing on the biological brain changes caused by the cancer due to the assumption that psychological symptoms are solely caused by the stress of a cancer diagnosis. Recent clinical evidence indicates that declines in cognition and increases in mood symptoms occur prior to an individual receiving a cancer diagnosis, suggesting that the cancer itself may play a role in mediating biological brain change. Furthermore, the presence of a tumour may change the brain response to environmental stressors unrelated to a cancer diagnosis. Using a syngeneic, orthotopic mouse model of breast cancer, we compared the impact of mammary tumours and chronic restraint stress on microglial and astrocytic activation throughout stress-relevant neurocircuitry. We also examined whether changes in microglial and astrocytic activation overlapped with changes in chronic neuronal activity. We show that cancer and chronic restraint stress activates microglia to the same magnitude in the same subcortical brain regions, and that this activation correlates with stress coping behaviours. The findings suggest that in some cancer patients, microglia may be activated in brain regions involved in interpreting and responding to psychological distress before they are aware of their diagnosis. In contrast, cancer reduced astrocyte reactivity in two cortical brain regions where there were no clear changes in response to chronic restraint stress. Taken together, it is likely that interventions that aim to improve anxiety and stress in cancer patients by targeting glial responses to cancer would need to be cell-specific; reducing microglial activation and/or stimulating astrocytic activation.

Prior maternal separation stress alters the dendritic complexity of new hippocampal neurons and neuroinflammation in response to an inflammatory stressor in juvenile female rats

Stress during critical periods of neurodevelopment is associated with an increased risk of developing stress-related psychiatric disorders, which are more common in women than men. Hippocampal neurogenesis (the birth of new neurons) is vulnerable to maternal separation (MS) and inflammatory stressors, and emerging evidence suggests that hippocampal neurogenesis is more sensitive to stress in the ventral hippocampus (vHi) than in the dorsal hippocampus (dHi). Although research into the effects of MS stress on hippocampal neurogenesis is well documented in male rodents, the effect in females remains underexplored. Similarly, reports on the impact of inflammatory stressors on hippocampal neurogenesis in females are limited, especially when female bias in the prevalence of stress-related psychiatric disorders begins to emerge. Thus, in this study we investigated the effects of MS followed by an inflammatory stressor (lipopolysaccharide, LPS) in early adolescence on peripheral and hippocampal inflammatory responses and hippocampal neurogenesis in juvenile female rats. We show that MS enhanced an LPS-induced increase in the pro-inflammatory cytokine IL-1β in the vHi but not in the dHi. However, microglial activation was similar following LPS alone or MS alone in both hippocampal regions, while MS prior to LPS reduced microglial activation in both dHi and vHi. The production of new neurons was unaffected by MS and LPS. MS and LPS independently reduced the dendritic complexity of new neurons, and MS exacerbated LPS-induced reductions in the complexity of distal dendrites of new neurons in the vHi but not dHi. These data highlight that MS differentially primes the physiological response to LPS in the juvenile female rat hippocampus.

Sex differences in the behavioral and immune responses of mice to tumor growth and cancer therapy

There is significant variability in the expression of cancer-related fatigue. Understanding the factors that account for this variation provide insight into the underlying mechanisms. One important, but often overlooked, variable is biological sex. While a few clinical studies have indicated that female patients report higher levels of fatigue, these studies are subject to potential socio-culture reporting biases. Only a limited number of preclinical studies have considered sex differences in animal model of fatigue and few have simultaneously considered both disease- and treatment-related factors. The present series of studies was initiated to address the current knowledge gap on the importance of sex differences in cancer-related fatigue. We selected a murine model of human papilloma virus-positive head and neck cancer based on heterotypic injection of the mEERL95 cell line that grows in both male and female mice and responds to a regimen of cisplatin plus irradiation. We also tested the impact of immunotherapy treatment targeting PD1. Voluntary wheel running was used to evaluate fatigue-like behavior. Male mice grew larger tumors than did female mice and showed more severe fatigue-like behavior. We confirmed that the tumor increased the expression of inflammatory cytokines in the liver, but no sex differences were observed. As a trend toward elevated Cd3 mRNA was observed in female mice, we tested the importance of T cells using female Rag2-/- mice. The Rag2-/- female mice had accelerated tumor growth and more severe fatigue-like behavior. In response to cisplatin alone non-tumor-bearing female mice showed a slower recovery of wheel running activity compared to males. However, in response to chemoradiation and anti-PD1 neutralizing antibody, tumor-bearing female mice showed a better tumor response to therapy than male mice, but no significant sex differences were observed for wheel running. These findings point to different mechanisms underlying tumor- and treatment-induced behavioral fatigue and indicate that the sex factor can intervene to modulate the expression of fatigue-like behavior in particular circumstances.

Neuroimmunology of cancer and associated symptomology

Evolutionarily the nervous system and immune cells have evolved to communicate with each other to control inflammation and host responses against injury. Recent findings in neuroimmune communication demonstrate that these mechanisms extend to cancer initiation and progression. Lymphoid structures and tumors, which are often associated with inflammatory infiltrate, are highly innervated by multiple nerve types (e.g. sympathetic, parasympathetic, sensory). Recent preclinical and clinical studies demonstrate that targeting the nervous system could be a therapeutic strategy to promote anti-tumor immunity while simultaneously reducing cancer-associated neurological symptoms, such as chronic pain, fatigue, and cognitive impairment. Sympathetic nerve activity is associated with physiological or psychological stress, which can be induced by tumor development and cancer diagnosis. Targeting the stress response through suppression of sympathetic activity or activation of parasympathetic activity has been shown to drive activation of effector T cells and inhibition of myeloid derived suppressor cells within the tumor. Additionally, there is emerging evidence that sensory nerves may regulate tumor growth and metastasis by promoting or inhibiting immunosuppression in a tumor-type specific manner. Since neural effects are often tumor-type specific, further study is required to optimize clinical therapeutic strategies. This review examines the emerging evidence that neuroimmune communication can regulate anti-tumor immunity as well as contribute to development of cancer-related neurological symptoms.

Mammary tumors suppress aging-induced neuroinflammation in female Balb/c mice

Neuroinflammation confers changes in brain function (i.e., behavior) that are hypothesized to be adaptive in the short-term, but detrimental (e.g., depression, anxiety) if they persist. Both peripheral tumor growth (outside of the brain) and natural aging independently cause neuroinflammation in rodents, which is corroborated by clinical studies. Mammary tumor effects on neuroinflammation and behavior, however, are typically studied in young rodents, whereas most breast cancer patients are middle-aged. Therefore, the existing literature likely underestimates the resulting neuroinflammation that may occur in clinical cancer populations. The present study tested the hypothesis that aging exacerbates mammary tumor-induced neuroinflammation in female mice. Aging (16 months and ovariectomized) increased body and spleen masses, whereas tumors grew faster and increased spleen mass in young mice (12 weeks) only. Tumors (IL-6, IL-10, TNFα, MCP-1, CXCL1, IP-10) and aging (IL-10, IFNγ) independently increased circulating inflammatory markers, although these variables were only significantly additive in one case (TNFα). In contrast to our prediction, the interaction between tumors and aging resulted in reduced mRNA and protein expression of select inflammatory markers in the hippocampus of tumor-bearing aged mice relative to aged controls. These results indicate that tumors reduce inflammatory activation in the brains of aged mice, a deficit that is likely disadvantageous. Further understanding of how aging and cancer interact to affect brain function is necessary to provide clinically-relevant results and identify mechanisms underlying persistent behavioral issues hampering adult cancer patients.

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Tumors grew more slowly in aged mice.

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Tumors and aging independently increased circulating inflammatory markers.

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Tumors reduced mRNA and protein expression of inflammatory markers in the hippocampus in aged mice.

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Reduced inflammatory activation in the brains of aged mice is likely not adaptive.

Cancer and cancer survival modulates brain and behavior in a time-of-day-dependent manner in mice

Improvements in breast cancer therapy/diagnosis have substantially increased the cancer survivor population, although many survivors report persistent mental health issues including fatigue, mood and anxiety disorders, and cognitive impairments. These behavioral symptoms impair quality-of-life and are often associated with increased inflammation. Nocturnal rodent models of cancer are critical to the identification of the neurobiological mechanisms underlying these behavioral changes. Although both behavior and immunity display distinct diurnal patterns, most rodent research in this field is performed during the rodents’ inactive (light) period, which could potentially undermine the conclusions and clinical relevance. Therefore, here we tested the extent to which mammary tumors or tumor resection (“survivors”) in mice affects behavior and neuroinflammation in a nyctohemeral (day versus night)-dependent manner. Indeed, only the dark (active) phase unmasked fatigue-like behavior and altered novel object investigation for both tumor-bearing and -resected mice relative to surgical controls. Several inflammatory markers were expressed in a time-of-day-dependent manner (lower in the dark phase) in the blood and brains of surgical control mice, whereas this temporal pattern was absent (IL-1β, CXCL1, Myd88, Cd4) or reversed (C3) in the respective tissues of tumor-bearing and -resected mice. Taken together, these data indicate that the time of day of assessment significantly modulates various persistent and transient tumor-induced behavioral and immune changes.

Tumor resection ameliorates tumor-induced suppression of neuroinflammatory and behavioral responses to an immune challenge in a cancer survivor model

Breast cancer survivors display altered inflammatory responses to immune challenges relative to cancer-naive controls likely due to previous cancer treatments, stress associated with cancer, and/or tumor physiology. Proper inflammatory responses are necessary for adaptive sickness behaviors (e.g., fatigue, anorexia, and fever) and neuroinflammatory pathways are also implicated in mental health disturbances (e.g., cognitive impairment, depression) suffered by cancer patients and survivors. Rodent cancer models indicate that tumors are sufficient to exacerbate neuroinflammatory responses after an immune challenge, however primary tumors are not usually present in cancer survivors, and the behavioral consequences of these brain changes remain understudied. Therefore, we tested the extent to which mammary tumor resection attenuates tumor-induced neuroinflammation and sickness behavior following an immune challenge (i.p. lipopolysaccharide [LPS] injection) in mice. Tnf-α, Il-1β, and Il-6 mRNA decreased in multiple brain regions of LPS-treated tumor-bearing mice relative to LPS-treated controls; tumor resection attenuated these effects in some cases (but not Tnf-α). Tumors also attenuated sickness behaviors (hypothermia and lethargy) compared to LPS-treated controls. Tumor resection reversed these behavioral consequences, although basal body temperature remained elevated, comparable to tumor-bearing mice. Thus, tumors significantly modulate neuroinflammatory pathways with functional consequences and tumor resection mitigates most, but not all, of these changes.

Sexual activity modulates neuroinflammatory responses in male rats

Immune activity influences reproduction, however, the extent to which mating experience may inversely alter immune pathways is poorly understood. A few studies in humans suggest that mating triggers a circulating immune and hypothalamic-pituitary-adrenal axis response. In male rats, mating experience enhances neuroplasticity and improves cognitive function and affective-like behavior, independent of the physical activity component. Yet, the extent to which mating experience may influence immune responses in the brain remain unexplored. Here, we hypothesized that recent mating experience in male rats increases neuroinflammatory signaling (via lipopolysaccharide [LPS] stimulation, i.p.) and associated sickness behaviors (i.e., food intake, weight loss) relative to sexually-naïve controls. Virgin male rats were exposed to a sexually non-receptive (control) or sexually-receptive female for 30 min for six consecutive days. Immediately following the last mating experience, rats were administered a saline or LPS injection and euthanized four hours later. Mating increased Tnfα responses to LPS in the brain, which positively correlated with LPS-induced weight loss. Mating also increased peripheral corticosterone among saline-treated rats, but this corticosterone response was attenuated in the most proficient copulators (e.g., shortest latencies). Thus, recent mating experience may be a unique modulator of select stimulated inflammatory signals that are relevant to adaptive neuroimmune responses and behavior.

Mammary tumor and mastectomy synergistically promote neuroinflammation in a breast cancer survivor model

Understanding why breast cancer survivors are at an increased risk for cognitive and affective disorders is essential for developing targeted treatment plans and improving quality of life. Microglia priming results in chronic neuroinflammation and can contribute to neuronal degeneration and dysfunction, thereby offering a potential mechanism for altered brain function that persists after tumor removal. This study examined whether mammary tumors alter microglia and augment the inflammatory profile and behavior of mice. To test this, non-metastatic mammary tumor cells (67NR) were injected orthotopically into the mammary glands of BALB/c mice, allowed to grow for 16 days, and then the tumors were removed via mastectomy. Following a 14-day surgical recovery, the mice were challenged with lipopolysaccharide (LPS), and then central and peripheral inflammation, anxiety, and depressive-like behavior were evaluated. Here we show that major central and peripheral inflammatory markers were not altered by tumor growth nor mastectomy surgery alone. However, hippocampal mRNA expression of major proinflammatory cytokines IL-1β and TNFα was increased in tumor removal animals, persisting past surgical recovery. Nonetheless, the immune and behavioral responses following LPS administration were comparable among groups. In sum, these data demonstrate that the combination of tumor and mastectomy promotes neuroinflammation; however, immune challenge did not elucidate this inflammation as maladaptive for the host.

Neuroimmunology of Behavioral Comorbidities Associated With Cancer and Cancer Treatments

Behavioral comorbidities (depression, anxiety, fatigue, cognitive disturbances, and neuropathic pain) are prevalent in cancer patients and survivors. These mental and neurological health issues reduce quality-of-life, which is a significant societal concern given the increasing rates of long-term survival after various cancers. Hypothesized causes of behavioral comorbidities with cancer include tumor biology, stress associated with the cancer experience, and cancer treatments. A relatively recent leading mechanism by which these causes contribute to changes in neurobiology that underlie behavior is inflammation. Indeed, both basic and clinical research indicates that peripheral inflammation leads to central inflammation and behavioral changes in other illness contexts. Given the limitations of assessing neuroimmunology in clinical populations, this review primarily synthesizes evidence of neuroimmune and neuroinflammatory changes due to two components of cancer (tumor biology and cancer treatments) that are associated with altered affective-like or cognitive behaviors in rodents. Specifically, alterations in microglia, neuroinflammation, and immune trafficking to the brain are compiled in models of tumors, chemotherapy, and/or radiation. Evidence-based neuronal mechanisms by which these neuroimmune changes may lead to changes in behavior are proposed. Finally, converging evidence in clinical cancer populations is discussed.

Neuroinflammatory and cognitive consequences of combined radiation and immunotherapy in a novel preclinical model

Background

Cancer patients often report behavioral and cognitive changes following cancer treatment. These effects can be seen in patients who have not yet received treatment or have received only peripheral (non-brain) irradiation. Novel treatments combining radiotherapy (RT) and immunotherapy (IT) demonstrate remarkable efficacy with respect to tumor outcomes by enhancing the proinflammatory environment in the tumor. However, a proinflammatory environment in the brain mediates cognitive impairments in other neurological disorders and may affect brain function in cancer patients receiving these novel treatments. Currently, gaps exist as to whether these treatments impact the brain in individuals with or without tumors and with regard to the underlying mechanisms.

Results

Combined treatment with precision RT and checkpoint inhibitor IT achieved control of tumor growth. However, BALB/c mice receiving combined treatment demonstrated changes in measures of anxiety levels, regardless of tumor status. C57BL/6J mice with tumors demonstrated increased anxiety, except following combined treatment. Object recognition memory was impaired in C57BL/6J mice without tumors following combined treatment. All mice with tumors showed impaired object recognition, except those treated with RT alone. Mice with tumors demonstrated impaired amygdala-dependent cued fear memory, while maintaining hippocampus-dependent context fear memory. These behavioral alterations and cognitive impairments were accompanied by increased microglial activation in mice receiving immunotherapy alone or combined with RT. Finally, based on tumor status, there were significant changes in proinflammatory cytokines (IFN-γ, IL-6, IL-5, IL-2, IL-10) and a growth factor (FGF-basic).

Materials and Methods

Here we test the hypothesis that IT combined with peripheral RT have detrimental behavioral and cognitive effects as a result of an enhanced proinflammatory environment in the brain. BALB/c mice with or without injected hind flank CT26 colorectal carcinoma or C57BL/6J mice with or without Lewis Lung carcinoma were used for all experiments. Checkpoint inhibitor IT, using an anti-CTLA-4 antibody, and precision CT-guided peripheral RT alone and combined were used to closely model clinical treatment. We assessed behavioral and cognitive performance and investigated the immune environment using immunohistochemistry and multiplex assays to analyze proinflammatory mediators.

Conclusions

Although combined treatment achieved tumor growth control, it affected the brain and induced changes in measures of anxiety, cognitive impairments, and neuroinflammation.

Tumor-Associated Fatigue in Cancer Patients Develops Independently of IL1 Signaling

Fatigue is the most common symptom of cancer at diagnosis, yet causes and effective treatments remain elusive. As tumors can be highly inflammatory, it is generally accepted that inflammation mediates cancer-related fatigue. However, evidence to support this assertion is mostly correlational. In this study, we directly tested the hypothesis that fatigue results from propagation of tumor-induced inflammation to the brain and activation of the central proinflammatory cytokine, IL1. The heterotopic syngeneic murine head and neck cancer model (mEER) caused systemic inflammation and increased expression of Il1b in the brain while inducing fatigue-like behaviors characterized by decreased voluntary wheel running and exploratory activity. Expression of Il1b in the brain was not associated with any alterations in motivation, measured by responding in a progressive ratio schedule of food reinforcement, depression-like behaviors, or energy balance. Decreased wheel running occurred prior to Il1b detection in the brain, when systemic inflammation was minimal. Furthermore, mice null for two components of IL1β signaling, the type 1 IL1 receptor or the receptor adapter protein MyD88, were not protected from tumor-induced decreases in wheel running, despite attenuated cytokine action and expression. Behavioral and inflammatory analysis of four additional syngeneic tumor models revealed that tumors can induce fatigue regardless of their systemic or central nervous system inflammatory potential. Together, our results show that brain IL1 signaling is not necessary for tumor-related fatigue, dissociating this type of cancer sequela from systemic cytokine expression.Significance: These findings challenge the current understanding of fatigue in cancer patients, the most common and debilitating sequela associated with malignancy. Cancer Res; 78(3); 695-705. ©2017 AACR.

Euflammation Attenuates Central and Peripheral Inflammation and Cognitive Consequences of an Immune Challenge after Tumor Development

OBJECTIVE

Repeated subthreshold bacterial exposures in rodents cause novel euflammation that attenuates neuroinflammation and sickness behaviors upon subsequent infectious challenges to the host without eliciting illness behavior. The investigation of bacterial exposure effects on brain and behavior is clinically relevant because bacterial-based antitumor treatments are used successfully, but are suboptimal due to their illness side effects. In addition, behavioral consequences (depression, cognitive impairments) to homeostatic challenges that are associated with inflammation are prevalent and reduce the quality of life in cancer patients and survivors. Therefore, this study tested the potential for euflammation to attenuate behavioral consequences of an immune challenge in tumor-bearing mice.

METHODS

Mice with and without oral tumors in their flank underwent the established peripheral euflammatory protocol or vehicle treatment, followed by an acute peripheral immune challenge (lipopolysaccharide [LPS] injection) or PBS. Cognitive function and sickness behavior were assessed after the challenge, and peripheral and central inflammatory responses were measured.

RESULTS

Euflammation reduced LPS-induced peripheral and central inflammation in all mice; however, neuroinflammation was less attenuated in tumor-bearing mice compared with tumor-free controls. LPS-induced lethargy and cognitive impairments were more pronounced among tumor-bearing mice and were effectively attenuated with euflammation. Cognitive changes were independent of brain-derived growth factor gene expression in the hippocampus.

CONCLUSION

These results suggest that induction of euflammation may be useful in alleviating the negative side effects of bacterial-based tumor treatments and in potentially attenuating common behavioral comorbidities associated with cancer or other chronic diseases.

CNS side effects of immune checkpoint inhibitors: preclinical models, genetics and multimodality therapy

Following cancer treatment, patients often report behavioral and cognitive changes. Novel cancer immunotherapeutics have the potential to produce sustained cancer survivorship, meaning patients will live longer with the side effects of treatment. Given the role of inflammatory pathways in mediating behavioral and cognitive impairments seen in cancer, we aim in this review to discuss emerging evidence for the contribution of immune checkpoint blockade to exacerbate these CNS effects. We discuss ongoing studies regarding the ability of immune checkpoint inhibitors to reach the brain and how treatment responses to checkpoint inhibitors may be modulated by genetic factors. We further consider the use of preclinical tumor-models to study the role of tumor status in CNS effects of immune checkpoint inhibitors and multimodality therapy.

Novel rodent model of breast cancer survival with persistent anxiety-like behavior and inflammation

Breast cancer survivors are an expanding population that is troubled by lasting mental health problems, including depression and anxiety. These issues reduce quality-of-life throughout survivorhood. Research indicates that tumor biology, cancer treatments, and stress contribute to these mood disturbances. Although the mechanisms underlying these various causes remain under investigation, neuroinflammation is a leading hypothesis. To date, rodent models of recurrence-free tumor survival for understanding mechanisms by which these behavioral issues persist after cancer are lacking. Here, we test the extent to which potential behavioral symptoms persist after mammary tumor removal in mice (i.e., establishment of a cancer survivor model), while also empirically testing the causal role of tumors in the development of neuroinflammatory-mediated affective-like behaviors. Complete surgical resection of a non-metastatic orthotopic, syngeneic mammary tumor reversed tumor-induced increases of circulating cytokines (IL-6, CXCL1, IL-10) and myeloid-derived cells and modulated neuroinflammatory gene expression (Cd11b, Cxcl1). Multiple anxiety-like behaviors and some central and peripheral immune markers persisted or progressed three weeks after tumor resection. Together, these data indicate that persistent behavioral changes into cancer survivorhood may be due, in part, to changes in immunity that remain even after successful tumor removal. This novel survivor paradigm represents an improvement in modeling prevalent cancer survivorship issues and studying the basic mechanisms by which cancer/cancer treatments influence the brain and behavior.

Neuroimmune mechanisms of behavioral alterations in a syngeneic murine model of human papilloma virus-related head and neck cancer

Patients with cancer often experience a high symptom burden prior to the start of treatment. As disease- and treatment-related neurotoxicities appear to be additive, targeting disease-related symptoms may attenuate overall symptom burden for cancer patients and improve the tolerability of treatment. It has been hypothesized that disease-related symptoms are a consequence of tumor-induced inflammation. We tested this hypothesis using a syngeneic heterotopic murine model of human papilloma virus (HPV)-related head and neck cancer. This model has the advantage of being mildly aggressive and not causing cachexia or weight loss. We previously showed that this tumor leads to increased IL-6, IL-1β, and TNF-α expression in the liver and increased IL-1β expression in the brain. The current study confirmed these features and demonstrated that the tumor itself exhibits high inflammatory cytokine expression (e.g., IL-6, IL-1β, and TNF-α) compared to healthy tissue. While there is a clear relationship between cytokine levels and behavioral deficits in this model, the behavioral changes are surprisingly mild. Therefore, we sought to confirm the relationship between behavior and inflammation by amplifying the effect using a low dose of lipopolysaccharide (LPS, 0.1mg/kg). In tumor-bearing mice LPS induced deficits in nest building, tail suspension, and locomotor activity approximately 24h after LPS. However, these mice did not display an exacerbation of LPS-induced weight loss, anorexia, or anhedonia. Further, while heightened serum IL-6 was observed there was minimal priming of liver or brain cytokine expression. Next we sought to inhibit tumor-induced burrowing deficits by reducing inflammation using minocycline. Minocycline (∼50mg/kg/day in drinking water) was able to attenuate tumor-induced inflammation and burrowing deficits. These data provide evidence in favor of an inflammatory-like mechanism for the behavioral alterations associated with tumor growth in a syngeneic murine model of HPV-related head and neck cancer. However, the inflammatory state and behavioral changes induced by this tumor clearly differ from other forms of inflammation-induced sickness behavior.

Fatigue is associated with inflammation in patients with head and neck cancer before and after intensity-modulated radiation therapy

Patients with head and neck cancer (HNC) receiving intensity-modulated radiation therapy (IMRT) have particularly high rates of fatigue, and pre- and post-radiotherapy fatigue are prognostic factors for pathologic tumor responses and poor survival. Although inflammation has been proposed as one of the potential mechanisms of fatigue in cancer patients, findings have not been consistent, and there is a dearth of longitudinal studies. Accordingly, we conducted a prospective study in 46 HNC patients pre- and one-month post-IMRT. Fatigue was measured by the Multidimensional Fatigue Inventory (MFI)-20 at both time points along with the assessment of peripheral blood inflammatory markers including interleukin (IL)-6, soluble tumor necrosis factor receptor 2, and C-reactive protein (CRP) and gene expression. Generalized estimating equations were used to examine the association between inflammatory markers and fatigue. Gene enrichment analysis using MetaCore software was performed using up-regulated genes that were significantly associated with IMRT and fatigue. Significant associations between fatigue and IL-6 as well as CRP, which were independent of time, were observed. In addition the change in fatigue from pre- to post-IMRT was positively associated with the change in IL-6 and CRP. Analysis of up-regulated gene transcripts as a function of IMRT and fatigue revealed overrepresentation of transcripts related to the defense response and nuclear factor kappa B. In conclusion, our findings support the hypotheses that inflammation is associated with fatigue over time in HNC patients. Future studies on how inflammation contributes to fatigue as well as strategies targeting inflammation to reduce fatigue are warranted.

Sickness behavior induced by cisplatin chemotherapy and radiotherapy in a murine head and neck cancer model is associated with altered mitochondrial gene expression

The present study was undertaken to explore the possible mechanisms of the behavioral alterations that develop in response to cancer and to cancer therapy. For this purpose we used a syngeneic heterotopic mouse model of human papilloma virus (HPV)-related head and neck cancer in which cancer therapy is curative. Mice implanted or not with HPV+ tumor cells were exposed to sham treatment or a regimen of cisplatin and radiotherapy (chemoradiation). Sickness was measured by body weight loss and reduced food intake. Motivation was measured by burrowing, a highly prevalent species specific behavior. Tumor-bearing mice showed a gradual decrease in burrowing over time and increased brain and liver inflammatory cytokine mRNA expression by 28 days post tumor implantation. Chemoradiation administered to healthy mice resulted in a mild decrease in burrowing, body weight, and food intake. Chemoradiation in tumor-bearing mice decreased tumor growth and abrogated liver and brain inflammation, but failed to attenuate burrowing deficits. PCR array analysis of selected hypoxia and mitochondrial genes revealed that both the tumor and chemoradiation altered the expression of genes involved in mitochondrial energy metabolism within the liver and brain and increased expression of genes related to HIF-1α signaling within the brain. The most prominent changes in brain mitochondrial genes were noted in tumor-bearing mice treated with chemoradiation. These findings indicate that targeting mitochondrial dysfunction following cancer and cancer therapy may be a strategy for prevention of cancer-related symptoms.

Pre-treatment effects of peripheral tumors on brain and behavior: neuroinflammatory mechanisms in humans and rodents

Cancer patients suffer high levels of affective and cognitive disturbances, which have been attributed to diagnosis-related distress, impairment of quality of life, and side effects of primary treatment. An inflammatory microenvironment is also a feature of the vast majority of solid tumors. However, the ability of tumor-associated biological processes to affect the central nervous system (CNS) has only recently been explored in the context of symptoms of depression and cognitive disturbances. In this review, we summarize the burgeoning evidence from rodent cancer models that solid tumors alter neurobiological pathways and subsequent behavioral processes with relevance to affective and cognitive disturbances reported in human cancer populations. We consider, in parallel, the evidence from human clinical cancer research demonstrating that affective and cognitive disturbances are common in some malignancies prior to diagnosis and treatment. We further consider the underlying neurobiological pathways, including altered neuroinflammation, tryptophan metabolism, prostaglandin synthesis and associated neuroanatomical changes, that are most strongly implicated in the rodent literature and supported by analogous evidence from human cancer populations. We focus on the implications of these findings for behavioral researchers and clinicians, with particular emphasis on methodological issues and areas of future research.

Cytotoxic chemotherapy increases sleep and sleep fragmentation in non-tumor-bearing mice

Sleep disruption ranks among the most common complaints of breast cancer patients undergoing chemotherapy. Because of the complex interactions among cancer, treatment regimens, and life-history traits, studies to establish a causal link between chemotherapy and sleep disruption are uncommon. To investigate how chemotherapy acutely influences sleep, adult female c57bl/6 mice were ovariectomized and implanted with wireless biotelemetry units. EEG/EMG biopotentials were collected over the course of 3days pre- and post-injection of 13.5mg/kg doxorubicin and 135mg/kg cyclophosphamide or the vehicle. We predicted that cyclophosphamide+doxorubicin would disrupt sleep and increase central proinflammatory cytokine expression in brain areas that govern vigilance states (i.e., hypothalamus and brainstem). The results largely support these predictions; a single chemotherapy injection increased NREM and REM sleep during subsequent active (dark) phases; this induced sleep was fragmented and of low quality. Mice displayed marked increases in low theta (5-7Hz) to high theta (7-10Hz) ratios following chemotherapy treatment, indicating elevated sleep propensity. The effect was strongest during the first dark phase following injection, but mice displayed disrupted sleep for the entire 3-day duration of post-injection sleep recording. Vigilance state timing was not influenced by treatment, suggesting that acute chemotherapy administration alters sleep homeostasis without altering sleep timing. qPCR analysis revealed that disrupted sleep was accompanied by increased IL-6 mRNA expression in the hypothalamus. Together, these data implicate neuroinflammation as a potential contributor to sleep disruption after chemotherapy.