Diet-induced obesity does not exacerbate cachexia in male mice bearing Lewis-lung carcinoma tumors.

Cachexia is a muscle-wasting syndrome commonly observed in patients with cancer, which can significantly worsen clinical outcomes. Because of a global rise in obesity, the coexistence of cachexia in obese individuals poses unique challenges, with the impact of excessive adiposity on cachexia severity and underlying pathophysiology not well defined. Understanding the interplay between cachexia and obesity is crucial for improving diagnosis and treatment strategies for these patients; therefore, the present study examined differences in cachexia between lean and obese mice bearing Lewis lung carcinoma (LLC) tumors. Nine-week-old, male C57Bl6J mice were placed on either a chow or a high-fat diet (HFD) for 9 wk. After the diet intervention, mice were inoculated with LLC or vehicle. Markers of cachexia, such as body and muscle loss, were noted in both chow and HFD groups with tumors. Tumor weight of HFD animals was greater than that of chow. LLC tumors reduced gastrocnemius, plantaris, and soleus mass, regardless of diet. The tibialis anterior and plantaris mass and cross-sectional area of type IIb/x fibers in the gastrocnemius were not different between HFD-chow, HFD-tumor, and chow-tumor. Using RNA sequencing (RNA-seq) of the plantaris muscle from chow-tumor and HFD-tumor groups, we identified ∼400 differentially expressed genes. Bioinformatic analysis identified changes in lipid metabolism, mitochondria, bioenergetics, and proteasome degradation. Atrophy was not greater despite larger tumor burden in animals fed an HFD, and RNA-seq data suggests that partial protection is mediated through differences in mitochondrial function and protein degradation, which may serve as future mechanistic targets.NEW & NOTEWORTHY This study provides timely information on the interaction between obesity and cancer cachexia. Lean and obese animals show signs of cachexia with reduced body weight, adipose tissue, and gastrocnemius muscle mass. There was not significant wasting in the tibialis anterior, plantaris, or fast twitch fibers in the gastrocnemius muscle of obese animals with tumors. RNA-seq analysis reveals that obese tumor bearing animals had differential expression of mitochondria- and degradation-related genes, which may direct future studies in mechanistic research.

Tumor-infiltrating nerves functionally alter brain circuits and modulate behavior in a mouse model of head-and-neck cancer.

Cancer patients often experience changes in mental health, prompting an exploration into whether nerves infiltrating tumors contribute to these alterations by impacting brain functions. Using a male mouse model for head and neck cancer, we utilized neuronal tracing techniques and show that tumor-infiltrating nerves indeed connect to distinct brain areas via the ipsilateral trigeminal ganglion. The activation of this neuronal circuitry led to behavioral alterations represented by decreased nest-building, increased latency to eat a cookie, and reduced wheel running. Tumor-infiltrating nociceptor neurons exhibited heightened activity, as indicated by increased calcium mobilization. Correspondingly, the specific brain regions receiving these neural projections showed elevated cFos and delta FosB expression in tumor-bearing mice, alongside markedly intensified calcium responses compared to non-tumor-bearing counterparts. The genetic elimination of nociceptor neurons in tumor-bearing mice led to decreased brain Fos expression and mitigated the behavioral alterations induced by the presence of the tumor. While analgesic treatment successfully restored behaviors involving oral movements to normalcy in tumor-bearing mice, it did not have a similar therapeutic effect on voluntary wheel running. This discrepancy points towards an intricate relationship, where pain is not the exclusive driver of such behavioral shifts. Unraveling the interaction between the tumor, infiltrating nerves, and the brain is pivotal to developing targeted interventions to alleviate the mental health burdens associated with cancer. Significance Statement: Head and neck cancers are infiltrated by sensory nerves which connect to a pre-existing circuit that includes areas in the brain. Neurons within this circuit are altered and mediate modifications in behavior.

Chronic Stress Exacerbates Hyperglycemia-Induced Affective Symptoms in Male Mice.

INTRODUCTION: Among chronically ill populations, affective disorders remain underdiagnosed and undertreated. A high degree of comorbidity exists between diabetes and affective disorders, particularly depression and anxiety. The mechanisms underlying stress-induced affective dysregulation are likely distinct from those induced by diabetes. A direct comparison between stress- and hyperglycemia-induced affective dysregulation could provide insight into distinct mechanistic targets for depression/anxiety associated with these different conditions. METHODS: To this end, the present study used male C57BL/6J mice to compare the independent and combined behavioral and neuroinflammatory effects of two models: (1) unpredictable chronic mild stress and (2) pharmacologically induced hyperglycemia. RESULTS: Streptozotocin-induced hyperglycemia was associated with a set of behavioral changes reflective of the neurovegetative symptoms of depression (i.e., reduced open field activity, reduced grooming, increased immobility in the forced swim task, and decreased marble burying), increased hippocampal Bdnf and Tnf expression, and elevations in frontal cortex Il1b expression. Our chronic stress protocol produced alterations in anxiety-like behavior and decreased frontal cortex Il1b expression. DISCUSSION: While the combination of chronic stress and hyperglycemia produced limited additive effects, their combination exacerbated total symptom burden. Overall, the data indicate that stress and hyperglycemia induce different symptom profiles via distinct mechanisms.

Associative learning contributes to the persistence of fatigue-like behavior in male mice in a model of cancer survivorship.

Persistent fatigue is a debilitating side effect that impacts a significant proportion of cancer survivors for which there is not yet an FDA-approved treatment. While certainly a multi-factorial problem, persistent fatigue could be due, in part, to associations learned during treatment. Therefore, we sought to investigate the role of associative learning in the persistence of fatigue using a preclinical model of cancer survivorship. For this purpose, we used a murine model of human papilloma virus-related head and neck cancer paired with a curative regimen of cisplatin-based chemoradiation in male C57BL/6J mice. Fatigue-like behavior was assessed by measuring variations in voluntary wheel running using a longitudinal design. Treatment robustly decreased voluntary wheel running, and this effect persisted for more than a month posttreatment. However, when wheels were removed during treatment, to minimize treatment-related fatigue, mice showed a more rapid return to baseline running levels. We confirmed that the delayed recovery observed in mice with continual wheel access was not due to increased treatment-related toxicity, in fact running attenuated cisplatin-induced kidney toxicity. Finally, we demonstrated that re-exposure to a treatment-related olfactory cue acutely re-instated fatigue. These data provide the first demonstration that associative processes can modulate the persistence of cancer-related fatigue-like behavior.

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.

Lipopolysaccharide does not alter behavioral response to successive negative contrast in mice.

BACKGROUND: Reduced motivation is one of the main symptomatic features of inflammation-induced depression. However, the exact nature of inflammation-induced alterations in motivation remains to be fully defined. As inflammation has been shown to increase sensitivity to negative stimuli, the present series of experiments was initiated to determine whether systemic inflammation induced by infra-septic doses of lipopolysaccharide (LPS) in mice influences consummatory and instrumental responding to successive negative contrast. METHODS: Successive negative contrast was operationally defined by a shift to a lower value reward than the one mice were trained with. Mice were trained to drink a high sucrose concentration solution and exposed to an acute shift to a lower concentration of sucrose. In another series of experiments, mice were trained to nose poke for chocolate pellets according to a fixed reinforcement schedule 10 (10 nose pokes for the food reinforcement) and exposed to a shift to a lower reward value (decreased number of chocolate pellets or replacement of chocolate pellets by less preferred grain pellets). Lipopolysaccharide (LPS) was administered at the dose of 0.33 1 mg/kg 24 h before the shift. RESULTS: Mice trained to drink a high sucrose concentration responded to the shift in reward value by a reduction in the volume of sucrose consumed and a decrease in lick numbers and bout durations. Mice trained to nose poke for chocolate pellets responded to the shift by alterations in their total number of nose pokes. In both conditions, LPS had no consistent effect on the response to the shift in reward value. CONCLUSIONS: These findings indicate a high variability in the effects of LPS on successive negative contrast and fail to provide evidence in favor of the hypothesis that LPS increases sensitivity to decreases in expected rewards.

Toll-like receptor 4 mediates the development of fatigue in the murine Lewis Lung Carcinoma model independently of activation of macrophages and microglia.

Cancer-related fatigue at the time of tumor diagnosis is commonly attributed to inflammation associated with the disease process. However, we have previously demonstrated that running wheel deficits occur well before increased expression of proinflammatory cytokines in the liver and brain in a murine model of human papilloma virus-related head and neck cancer (mEER). Further, we have demonstrated that genetic deletion of type I interleukin-1 receptor and MyD88 has no effect. In the current investigation we sought to test the generality of this finding by assessing whether there is a role for toll-like receptor (TLR) 4-dependent inflammation in the fatigue-like behavior observed in mice with Lewis Lung Carcinoma (LLC) or mEER tumors. Genetic deletion of TLR4 attenuated tumor-induced elevations in liver pro-inflammatory cytokine expression in both models. However, it only abrogated wheel running deficits in LLC tumor bearing mice. To determine whether TLR4 signaling in the LLC model involves innate immune cells, mice were treated with the colony stimulating factor (CSF)-1 receptor antagonist PLX-5622 before and throughout tumor development to deplete microglia and peripheral macrophages. Administration of PLX-5622 had no protective effect on wheel running deficits in either mEER or LLC tumor models despite effective depletion of microglia and a down regulation of peripheral proinflammatory cytokine expression. These results indicate that the TLR4 signaling that mediates fatigue-like behavior in LLC mice is not dependent upon microglial or peripheral macrophage activation. Based on the literature and our data demonstrating attenuation of ubiquitin proteasome pathway activation in the gastrocnemius muscle of Tlr4-/- mice implanted with LLC cells, we interpret our current findings as indication that skeletal muscle TLR4 signaling may be involved. These results are important in that they add to the evidence that tumor-induced fatigue develops independently from classical neuroinflammation.

Pilot study of neurologic toxicity in mice after proton minibeam therapy.

Proton minibeams (MBs) comprised of parallel planar beamlets were evaluated for their ability to spare healthy brain compared to proton broad beams (BBs). Juvenile mice were given partial brain irradiation of 10 or 30 Gy integral dose using 100 MeV protons configured either as BBs or arrays of 0.3-mm planar MBs spaced 1.0 mm apart on center. Neurologic toxicity was evaluated during an 8-month surveillance: no overt constitutional or neurologic dysfunction was noted for any study animals. Less acute epilation was observed in MB than BB mice. Persistent chronic inflammation was noted along the entire BB path in BB mice whereas inflammation was confined to just within the MB peak regions in MB mice. The potential neurologic sparing, possibly via reduced volume of chronic inflammation, offers a compelling rationale for clinical advancement of this proton technique.

Microglia depletion fails to abrogate inflammation-induced sickness in mice and rats.

BACKGROUND: Production of inflammatory mediators by reactive microglial cells in the brain is generally considered the primary mechanism underlying the development of symptoms of sickness in response to systemic inflammation. METHODS: Depletion of microglia was achieved in C57BL/6 mice by chronic oral administration of PLX5622, a specific antagonist of colony stimulating factor-1 receptor, and in rats by a knock-in model in which the diphtheria toxin receptor was expressed under the control of the endogenous fractalkine receptor (CX3CR1) promoter sequence. After successful microglia depletion, mice and rats were injected with a sickness-inducing dose of lipopolysaccharide according to a 2 (depletion vs. control) × 2 (LPS vs. saline) factorial design. Sickness was measured by body weight loss and decreased locomotor activity in rats and mice, and reduced voluntary wheel running in mice. RESULTS: Chronic administration of PLX5622 in mice and administration of diphtheria toxin to knock-in rats depleted microglia and peripheral tissue macrophages. However, it did not abrogate the inducible expression of proinflammatory cytokines in the brain in response to LPS and even exacerbated it for some of the cytokines. In accordance with these neuroimmune effects, LPS-induced sickness was not abrogated, rather it was exacerbated when measured by running wheel activity in mice. CONCLUSIONS: These findings reveal that the sickness-inducing effects of acute inflammation can develop independently of microglia activation.

Interleukin 6-independent metabolic reprogramming as a driver of cancer-related fatigue.

Fatigue is a common and debilitating symptom of cancer with few effective interventions. Cancer-related fatigue (CRF) is often associated with increases in inflammatory cytokines, however inflammation may not be requisite for this symptom, suggesting other biological mediators also play a role. Because tumors are highly metabolically active and can amplify their energetic toll via effects on distant organs, we sought to determine whether CRF could be explained by metabolic competition exacted by the tumor. We used a highly metabolically active murine E6/E7/hRas model of head and neck cancer for this purpose. Mice with or without tumors were submitted to metabolic constraints in the form of voluntary wheel running or acute overnight fasting and their adaptive behavioral (home cage activity and fasting-induced wheel running) and metabolic responses (blood glucose, ketones, and liver metabolic gene expression) were monitored. We found that the addition of running wheel was necessary to measure activity loss, used as a surrogate for fatigue in this study. Tumor-bearing mice engaged in wheel running showed a decrease in blood glucose levels and an increase in lactate accumulation in the skeletal muscle, consistent with inhibition of the Cori cycle. These changes were associated with gene expression changes in the livers consistent with increased glycolysis and suppressed gluconeogenesis. Fasting also decreased blood glucose in tumor-bearing mice, without impairing glucose or insulin tolerance. Fasting-induced increases in wheel running and ketogenesis were suppressed by tumors, which was again associated with a shift from gluconeogenic to glycolytic metabolism in the liver. Blockade of IL-6 signaling with a neutralizing antibody failed to recover any of the behavioral or metabolic outcomes. Taken together, these data indicate that metabolic competition between the tumor and the rest of the organism is an important component of fatigue and support the hypothesis of a central role for IL-6-independent hepatic metabolic reprogramming in the pathophysiology of CRF.

Inhibition of Indoleamine 2,3 Dioxygenase Does Not Improve Cancer-Related Symptoms in a Murine Model of Human Papilloma Virus-Related Head and Neck Cancer.

The expression of indoleamine 2,3 dioxygenase (IDO) by tumors can contribute to immunotolerance, and IDO induced by inflammation can also increase risk for the development of behavioral alterations. Thus, this study was initiated to determine whether IDO inhibition, intended to facilitate tumor clearance in response to treatment, attenuates behavioral alterations associated with tumor growth and treatment. We used a murine model of human papilloma virus-related head and neck cancer. We confirmed that tumor cells express IDO and expression was increased by radiotherapy. Interestingly, inhibition of IDO activation by the competitive inhibitor 1-methyl tryptophan mildly exacerbated treatment-associated burrowing deficits (burrowing is a sensitive index of sickness in tumor-bearing mice). Genetic deletion of IDO worsened tumor outcomes and had no effect on the behavioral response as by decreased burrowing or reduced voluntary wheel running. In contrast, oral administration of a specific inhibitor of IDO1 provided no apparent benefit on the tumor response to cancer therapy, yet decreased voluntary wheel-running activity independent of treatment. These results indicate that, independent of its potential effect on tumor clearance, inhibition of IDO does not improve cancer-related symptoms.

Lipocalin-2 is dispensable in inflammation-induced sickness and depression-like behavior.

RATIONALE: While the relationship between inflammation and depression is well-established, the molecular mechanisms mediating this relationship remain unclear. RNA sequencing analysis comparing brains of vehicle- and lipopolysaccharide-treated mice revealed LCN2 among the most dysregulated genes. As LCN2 is known to be an important regulator of the immune response to bacterial infection, we investigated its role in the behavioral response to lipopolysaccharide. OBJECTIVE: To explore the role of LCN2 in modulating behavior following lipopolysaccharide administration using wild type (WT) and lcn2-/- mice. METHODS: Using a within-subjects design, mice were treated with 0.33 mg/kg liposaccharide (LPS) and vehicle. Primary outcome measures included body weight, food consumption, voluntary wheel running, sucrose preference, and the tail suspension test. To evaluate the inflammatory response, 1 week later, mice were re-administered either vehicle or LPS and terminated at 6 h. RESULTS: While lcn2-/- mice had increased baseline food consumption and body weight, they showed a pattern of reduced food consumption and weight loss similar to WT mice in response to LPS. WT and lcn2-/- mice both recovered voluntary activity on the fourth day following LPS. LPS induced equivalent reductions in sucrose preference and TST immobility in the WT and lcn2-/- mice. Finally, there were no significant effects of genotype on inflammatory markers. CONCLUSIONS: Our data demonstrate that lcn2 is dispensable for sterile inflammation-induced sickness and depression-like behavior. Specifically, lcn2-/- mice displayed sickness and immobility in the tail suspension test comparable to that of WT mice both in terms of intensity and duration.

Motivational changes that develop in a mouse model of inflammation-induced depression are independent of indoleamine 2,3 dioxygenase.

Despite years of research, our understanding of the mechanisms by which inflammation induces depression is still limited. As clinical data points to a strong association between depression and motivational alterations, we sought to (1) characterize the motivational changes that are associated with inflammation in mice, and (2) determine if they depend on inflammation-induced activation of indoleamine 2,3 dioxygenase-1 (IDO1). Lipopolysaccharide (LPS)-treated or spared nerve injured (SNI) wild type (WT) and Ido1-/- mice underwent behavioral tests of antidepressant activity (e.g., forced swim test) and motivated behavior, including assessment of (1) reward expectancy using a food-related anticipatory activity task, (2) willingness to work for reward using a progressive ratio schedule of food reinforcement, (3) effort allocation using a concurrent choice task, and (4) ability to associate environmental cues with reward using conditioned place preference. LPS- and SNI-induced deficits in behavioral tests of antidepressant activity in WT but not Ido1-/- mice. Further, LPS decreased food related-anticipatory activity, reduced performance in the progressive ratio task, and shifted effort toward the preferred reward in the concurrent choice task. These effects were observed in both WT and Ido1-/- mice. Finally, SNI mice developed a conditioned place preference based on relief from pain in an IDO1-independent manner. These findings demonstrate that the motivational effects of inflammation do not require IDO1. Further, they indicate that the motivational component of inflammation-induced depression is mechanistically distinct from that measured by behavioral tests of antidepressant activity.

Cancer exosomes induce tumor innervation.

Patients with densely innervated tumors suffer with increased metastasis and decreased survival as compared to those with less innervated tumors. We hypothesize that in some tumors, nerves are acquired by a tumor-induced process, called axonogenesis. Here, we use PC12 cells as an in vitro neuronal model, human tumor samples and murine in vivo models to test this hypothesis. When appropriately stimulated, PC12 cells extend processes, called neurites. We show that patient tumors release vesicles, called exosomes, which induce PC12 neurite outgrowth. Using a cancer mouse model, we show that tumors compromised in exosome release are less innervated than controls. Moreover, in vivo pharmacological blockade of exosome release similarly attenuates tumor innervation. We characterize these nerves as sensory in nature and demonstrate that axonogenesis is potentiated by the exosome-packaged axonal guidance molecule, EphrinB1. These findings indicate that tumor released exosomes induce tumor innervation and exosomes containing EphrinB1 potentiate this activity.

Inflammation-induced motivational changes: Perspective gained by evaluating positive and negative valence systems.

Inflammation can profoundly impact motivated behavior, as is the case with inflammation-induced depression. By evaluating objectively measurable basic neurobehavioral processes involved in motivation, recent research indicates that inflammation generally reduces approach motivation and enhances avoidance motivation. Increased effort valuation largely mediates the effects of inflammation on approach motivation. Changes in reward valuation are not uniformly observed in approach motivation. However, inflammation increases the averseness of negative stimuli. Within the context of both approach and avoidance motivation, inflammation appears to enhance the contrast between concurrently presented stimuli. While changes in both approach and avoidance motivation appear to be mediated by midbrain dopaminergic neurotransmission to the ventral striatum, it is unclear if the enhanced contrast is mediated by the same system.

An effort expenditure perspective on cancer-related fatigue.

While fatigue is the most common and debilitating side effect of cancer and cancer treatment it is still poorly understood, partly because it is usually characterized by patient-reported outcomes. As patient-reports are inherently subjective, behavioral correlates of the symptom of fatigue are needed to increase our understanding of the symptom. We focused on motivational effort expenditure as a crucial behavior in cancer-related fatigue, using a validated computerized task contrasting high effort/high reward and low effort/low reward choices under different probabilities of success. Effort expenditure-choices were analyzed in 47 cancer patients differing by their status; current evidence for disease (n = 17) or post-treatment survivors with no evidence for disease (n = 30). In addition, patient-reported fatigue, negative and positive affect, and biomarkers of inflammation were assessed. Patient-reported general and motivational fatigue, negative affect, and plasma concentrations of pro-inflammatory biomarkers were related to higher effort expenditure while positive affect was associated with lower effort expenditure. As all four measures interacted with patient status, exploratory models were computed for patients and survivors separately. These analyses indicated that the effects of fatigue and negative affect were predominantly seen in survivors. In patients still under or shortly post treatment, general fatigue, but not motivational fatigue, was associated with lower effort expenditure but only in the most favorable reward condition. Negative affect did not have an effect. Thus, the effects observed seemed primarily driven by cancer survivors in whom both fatigue and negative affect were associated with higher effort expenditure. These findings are tentatively interpreted to suggest that a tendency to invest more effort despite feelings of fatigue is a vulnerability for developing chronic fatigue. Inflammation and negative affect might contribute to fatigue in some survivors through this effort investment pathway.

The High Costs of Low-Grade Inflammation: Persistent Fatigue as a Consequence of Reduced Cellular-Energy Availability and Non-adaptive Energy Expenditure.

Chronic or persistent fatigue is a common, debilitating symptom of several diseases. Persistent fatigue has been associated with low-grade inflammation in several models of fatigue, including cancer-related fatigue and chronic fatigue syndrome. However, it is unclear how low-grade inflammation leads to the experience of fatigue. We here propose a model of an imbalance in energy availability and energy expenditure as a consequence of low-grade inflammation. In this narrative review, we discuss how chronic low-grade inflammation can lead to reduced cellular-energy availability. Low-grade inflammation induces a metabolic switch from energy-efficient oxidative phosphorylation to fast-acting, but less efficient, aerobic glycolytic energy production; increases reactive oxygen species; and reduces insulin sensitivity. These effects result in reduced glucose availability and, thereby, reduced cellular energy. In addition, emerging evidence suggests that chronic low-grade inflammation is associated with increased willingness to exert effort under specific circumstances. Circadian-rhythm changes and sleep disturbances might mediate the effects of inflammation on cellular-energy availability and non-adaptive energy expenditure. In the second part of the review, we present evidence for these metabolic pathways in models of persistent fatigue, focusing on chronic fatigue syndrome and cancer-related fatigue. Most evidence for reduced cellular-energy availability in relation to fatigue comes from studies on chronic fatigue syndrome. While the mechanistic evidence from the cancer-related fatigue literature is still limited, the sparse results point to reduced cellular-energy availability as well. There is also mounting evidence that behavioral-energy expenditure exceeds the reduced cellular-energy availability in patients with persistent fatigue. This suggests that an inability to adjust energy expenditure to available resources might be one mechanism underlying persistent fatigue.

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 IL1ß 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.

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-1ß, and TNF-α expression in the liver and increased IL-1ß 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-1ß, 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.

Pifithrin-µ Prevents Cisplatin-Induced Chemobrain by Preserving Neuronal Mitochondrial Function.

Cognitive impairment, termed chemobrain, is a common neurotoxicity associated with chemotherapy treatment, affecting an estimated 78% of patients. Prompted by the hypothesis that neuronal mitochondrial dysfunction underlies chemotherapy-induced cognitive impairment (CICI), we explored the efficacy of administering the small-molecule pifithrin (PFT)-µ, an inhibitor of mitochondrial p53 accumulation, in preventing CICI. Male C57BL/6J mice injected with cisplatin ± PFT-µ for two 5-day cycles were assessed for cognitive function using novel object/place recognition and alternation in a Y-maze. Cisplatin impaired performance in the novel object/place recognition and Y-maze tests. PFT-µ treatment prevented CICI and associated cisplatin-induced changes in coherency of myelin basic protein fibers in the cingular cortex and loss of doublecortin+ cells in the subventricular zone and hippocampal dentate gyrus. Mechanistically, cisplatin decreased spare respirator capacity of brain synaptosomes and caused abnormal mitochondrial morphology, which was counteracted by PFT-µ administration. Notably, increased mitochondrial p53 did not lead to cerebral caspase-3 activation or cytochrome-c release. Furthermore, PFT-µ administration did not impair the anticancer efficacy of cisplatin and radiotherapy in tumor-bearing mice. Our results supported the hypothesis that neuronal mitochondrial dysfunction induced by mitochondrial p53 accumulation is an underlying cause of CICI and that PFT-µ may offer a tractable therapeutic strategy to limit this common side-effect of many types of chemotherapy. Cancer Res; 77(3); 742-52. ©2016 AACR.