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

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.

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.

Tumour brain: Pretreatment cognitive and affective disorders caused by peripheral cancers

People that develop extracranial cancers often display co-morbid neurological disorders, such as anxiety, depression and cognitive impairment, even before commencement of chemotherapy. This suggests bidirectional crosstalk between non-CNS tumours and the brain, which can regulate peripheral tumour growth. However, the reciprocal neurological effects of tumour progression on brain homeostasis are not well understood. Here, we review brain regions involved in regulating peripheral tumour development and how they, in turn, are adversely affected by advancing tumour burden. Tumour-induced activation of the immune system, blood-brain barrier breakdown and chronic neuroinflammation can lead to circadian rhythm dysfunction, sleep disturbances, aberrant glucocorticoid production, decreased hippocampal neurogenesis and dysregulation of neural network activity, resulting in depression and memory impairments. Given that cancer-related cognitive impairment diminishes patient quality of life, reduces adherence to chemotherapy and worsens cancer prognosis, it is essential that more research is focused at understanding how peripheral tumours affect brain homeostasis.

Biology of iatrogenic sexual dysfunction in men and women survivors of cancer

Sexual dysfunction (SD) is widely reported by cancer survivors. However, this is an issue underestimated by doctors and the contribution of anticancer therapies for the development of SD in cancer survivors is understudied and poorly understood. Sexual function involves the activation of a neurovascular system that leads to penile erection in males and clitoral engorgement in females. Anticancer therapies can cause damage to the neurovascular circuit responsible for normal sexual function and thus, individual or combined therapies could play a role in the development of SD in all types of cancer survivors and not only those affected by genital cancers. In this review, the pathophysiology of SD and possible mechanisms underlying SD induced by anticancer therapies will be discussed. The effects of chemotherapy, radiotherapy and surgical interventions on the vasculature and nerves as well as their effects on sex hormones and inflammatory processes could link the biological effects of these interventions with SD. In conclusion, this review reports evidence that, despite psychological aspects and the disease itself, anticancer therapies are able to induce direct and indirect effects in males and females that could lead to SD in cancer survivors even after the end of the treatment.

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.