Systemic administration of doxorubicin impairs aversively motivated memory in rats

Senolytic treatment alleviates doxorubicin-induced chemobrain

Doxorubicin (Dox), a widely used treatment for cancer, can result in chemotherapy-induced cognitive impairments (chemobrain). Chemobrain is associated with inflammation and oxidative stress similar to aging. As such, Dox treatment has also been used as a model of aging. However, it is unclear if Dox induces brain changes similar to that observed during aging since Dox does not readily enter the brain. Rather, the mechanism for chemobrain likely involves the induction of peripheral cellular senescence and the release of senescence-associated secretory phenotype (SASP) factors and these SASP factors can enter the brain to disrupt cognition. We examined the effect of Dox on peripheral and brain markers of aging and cognition. In addition, we employed the senolytic, ABT-263, which also has limited access to the brain. The results indicate that plasma SASP factors enter the brain, activating microglia, increasing oxidative stress, and altering gene transcription. In turn, the synaptic function required for memory was reduced in response to altered redox signaling. ABT-263 prevented or limited most of the Dox-induced effects. The results emphasize a link between cognitive decline and the release of SASP factors from peripheral senescent cells and indicate some differences as well as similarities between advanced age and Dox treatment.

Phenyl-2-aminoethyl selenide ameliorates hippocampal long-term potentiation and cognitive deficits following doxorubicin treatment

Chemotherapy-induced memory loss ("chemobrain") can occur following treatment with the widely used chemotherapeutic agent doxorubicin (DOX). However, the mechanisms through which DOX induces cognitive dysfunction are not clear, and there are no commercially available therapies for its treatment or prevention. Therefore, the aim of this study was to determine the therapeutic potential of phenyl-2-aminoethyl selenide (PAESe), an antioxidant drug previously demonstrated to reduce cardiotoxicity associated with DOX treatment, against DOX-induced chemobrain. Four groups of male athymic NCr nude (nu/nu) mice received five weekly tail-vein injections of saline (Control group), 5 mg/kg of DOX (DOX group), 10 mg/kg PAESe (PAESe group), or 5 mg/kg DOX and 10 mg/kg PAESe (DOX+PAESe group). Spatial memory was evaluated using Y-maze and novel object location tasks, while synaptic plasticity was assessed through the measurement of field excitatory postsynaptic potentials from the Schaffer collateral circuit. Western blot analyses were performed to assess hippocampal protein and phosphorylation levels. In this model, DOX impaired synaptic plasticity and memory, and increased phosphorylation of protein kinase B (Akt) and extracellular-regulated kinase (ERK). Co-administration of PAESe reduced Akt and ERK phosphorylation and ameliorated the synaptic and memory deficits associated with DOX treatment.

Targeting ryanodine receptor type 2 to mitigate chemotherapy-induced neurocognitive impairments in mice

Chemotherapy-induced cognitive dysfunction (chemobrain) is an important adverse sequela of chemotherapy. Chemobrain has been identified by the National Cancer Institute as a poorly understood problem for which current management or treatment strategies are limited or ineffective. Here, we show that chemotherapy treatment with doxorubicin (DOX) in a breast cancer mouse model induced protein kinase A (PKA) phosphorylation of the neuronal ryanodine receptor/calcium (Ca2+) channel type 2 (RyR2), RyR2 oxidation, RyR2 nitrosylation, RyR2 calstabin2 depletion, and subsequent RyR2 Ca2+ leakiness. Chemotherapy was furthermore associated with abnormalities in brain glucose metabolism and neurocognitive dysfunction in breast cancer mice. RyR2 leakiness and cognitive dysfunction could be ameliorated by treatment with a small molecule Rycal drug (S107). Chemobrain was also found in noncancer mice treated with DOX or methotrexate and 5-fluorouracil and could be prevented by treatment with S107. Genetic ablation of the RyR2 PKA phosphorylation site (RyR2-S2808A) also prevented the development of chemobrain. Chemotherapy increased brain concentrations of the tumor necrosis factor-α and transforming growth factor-β signaling, suggesting that increased inflammatory signaling might contribute to oxidation-driven biochemical remodeling of RyR2. Proteomics and Gene Ontology analysis indicated that the signaling downstream of chemotherapy-induced leaky RyR2 was linked to the dysregulation of synaptic structure-associated proteins that are involved in neurotransmission. Together, our study points to neuronal Ca2+ dyshomeostasis via leaky RyR2 channels as a potential mechanism contributing to chemobrain, warranting further translational studies.

Chemobrain in Breast Cancer: Mechanisms, Clinical Manifestations, and Potential Interventions

Among the potential adverse effects of breast cancer treatment, chemotherapy-related cognitive impairment (CRCI) has gained increased attention in the past years. In this review, we provide an overview of the literature regarding CRCI in breast cancer, focusing on three main aspects. The first aspect relates to the molecular mechanisms linking individual drugs commonly used to treat breast cancer and CRCI, which include oxidative stress and inflammation, reduced neurogenesis, reduced levels of specific neurotransmitters, alterations in neuronal dendrites and spines, and impairment in myelin production. The second aspect is related to the clinical characteristics of CRCI in patients with breast cancer treated with different drug combinations. Data suggest the incidence rates of CRCI in breast cancer vary considerably, and may affect more than 50% of treated patients. Both chemotherapy regimens with or without anthracyclines have been associated with CRCI manifestations. While cross-sectional studies suggest the presence of symptoms up to 20 years after treatment, longitudinal studies confirm cognitive impairments lasting for at most 4 years after the end of chemotherapy. The third and final aspect is related to possible therapeutic interventions. Although there is still no standard of care to treat CRCI, several pharmacological and non-pharmacological approaches have shown interesting results. In summary, even if cognitive impairments derived from chemotherapy resolve with time, awareness of CRCI is crucial to provide patients with a better understanding of the syndrome and to offer them the best care directed at improving quality of life.

Potential Protective Effect of Coenzyme Q10 on Doxorubicin-Induced Neurotoxicity and Behavioral Disturbances in Rats

The aim of this study was to investigate the potential neuroprotective efficacy of coenzyme Q10 (CoQ10) against doxorubicin (DOX) -induced behavioral disturbances in rats. Female rats were randomly assigned into 4 groups as control, CoQ10, DOX, and DOX plus CoQ10. The CoQ10 groups received CoQ10 (200 mg kg^-1) for 21 days, and the DOX groups received DOX (4 mg kg^-1) on days 7 and 14 of the study. The open field (OF) and elevated plus maze (EPM) tests were performed to assess locomotor activity and anxiety levels. Additionally, malondialdehyde (MDA), and protein carbonyl (PC) levels and acetylcholinesterase (AChE), and glutathione peroxidase (GPx) activities and total antioxidant capacity (TAC) were quantified in brain tissue. DOX administration caused alterations in locomotor activity, and anxiety-like behaviors. Moreover, DOX produced significant elevation in AChE activity . PC level and GPx activity tended to alter with DOX administration. Co-treatment with CoQ10 significantly attenuated DOX-induced behavioral alterations via improving AChE activity in the brain tissue of rats. CoQ10 treatment may be potential for the alleviation of DOX-induced behavioral disturbances. This improvement might be due to the inhibition of AChE activity.

Four decades of chemotherapy-induced cognitive dysfunction: comprehensive review of clinical, animal and in vitro studies, and insights of key initiating events

Cognitive dysfunction has been one of the most reported and studied adverse effects of cancer treatment, but, for many years, it was overlooked by the medical community. Nevertheless, the medical and scientific communities have now recognized that the cognitive deficits caused by chemotherapy have a strong impact on the morbidity of cancer treated patients. In fact, chemotherapy-induced cognitive dysfunction or 'chemobrain'  (also named also chemofog) is at present a well-recognized effect of chemotherapy that could affect up to 78% of treated patients. Nonetheless, its underlying neurotoxic mechanism is still not fully elucidated. Therefore, this work aimed to provide a comprehensive review using PubMed as a database to assess the studies published on the field and, therefore, highlight the clinical manifestations of chemobrain and the putative neurotoxicity mechanisms.In the last two decades, a great number of papers was published on the topic, mainly with clinical observations. Chemotherapy-treated patients showed that the cognitive domains most often impaired were verbal memory, psychomotor function, visual memory, visuospatial and verbal learning, memory function and attention. Chemotherapy alters the brain's metabolism, white and grey matter and functional connectivity of brain areas. Several mechanisms have been proposed to cause chemobrain but increase of proinflammatory cytokines with oxidative stress seem more relevant, not excluding the action on neurotransmission and cellular death or impaired hippocampal neurogenesis. The interplay between these mechanisms and susceptible factors makes the clinical management of chemobrain even more difficult. New studies, mainly referring to the underlying mechanisms of chemobrain and protective measures, are important in the future, as it is expected that chemobrain will have more clinical impact in the coming years, since the number of cancer survivors is steadily increasing.

Animal models of chemotherapy-induced cognitive decline in preclinical drug development

RATIONALE

Chemotherapy-induced cognitive impairment (CICI), chemobrain, and chemofog are the common terms for mental dysfunction in a cancer patient/survivor under the influence of chemotherapeutics. CICI is manifested as short/long term memory problems and delayed mental processing, which interferes with a person's day-to-day activities. Understanding CICI mechanisms help in developing therapeutic interventions that may alleviate the disease condition. Animal models facilitate critical evaluation to elucidate the underlying mechanisms and form an integral part of verifying different treatment hypotheses and strategies.

OBJECTIVES

A methodical evaluation of scientific literature is required to understand cognitive changes associated with the use of chemotherapeutic agents in different preclinical studies. This review mainly emphasizes animal models developed with various chemotherapeutic agents individually and in combination, with their proposed mechanisms contributing to the cognitive dysfunction. This review also points toward the analysis of chemobrain in healthy animals to understand the mechanism of interventions in absence of tumor and in tumor-bearing animals to mimic human cancer conditions to screen potential drug candidates against chemobrain.

RESULTS

Substantial memory deficit as a result of commonly used chemotherapeutic agents was evidenced in healthy and tumor-bearing animals. Spatial and episodic cognitive impairments, alterations in neurotrophins, oxidative and inflammatory markers, and changes in long-term potentiation were commonly observed changes in different animal models irrespective of the chemotherapeutic agent.

CONCLUSION

Dyscognition exists as one of the serious side effects of cancer chemotherapy. Due to differing mechanisms of chemotherapeutic agents with differing tendencies to alter behavioral and biochemical parameters, chemotherapy may present a significant risk in resulting memory impairments in healthy as well as tumor-bearing animals.

Stem cell therapies as a therapeutic option to counter chemo brain: a negative effect of cancer treatment

Chemo brain, a constellation of cognitive deficiencies followed by chemotherapy drugs, used to treat different types of cancers and adversely impacts the quality of life of a cancer survivor. The underlying mechanism of chemo brain remains vague, thus delaying the advancement of efficient treatments. Unfortunately, there is no US FDA approved medicine for chemo brain and often medicines considered for chemo brain are already the ones approved for other diseases. Nevertheless, researches exploring stem cell transplantation in different neurodegenerative diseases demonstrate that cellular transplantation could reverse chemotherapy-induced chemo brain. This review talks about the mechanism behind the cognitive impairments instigated by different chemotherapy drugs used in cancer treatment, and how stem cell therapy could be advantageous to overcome this disease.

Chemotherapy-induced cognitive impairment (CICI): An overview of etiology and pathogenesis

Many cancer patients treated with chemotherapy develop chemotherapy-induced cognitive impairment (CICI), often referred to as chemo-brain, which manifest during or post-treatment with variable degrees, onset and duration thereby affecting the patients' quality of life. Several chemotherapeutic agents have been studied to determine its possible association with cognitive impairment and to fully comprehend their contribution to CICI. A vast number of studies have emerged proposing several candidate underlying mechanisms and etiologies contributing to CICI such as direct neurotoxicity, BBB disruption, decreased hippocampal neurogenesis, white matter abnormalities, secondary neuro-inflammatory response and increased oxidative stress; however, the exact underlying mechanisms are still not well defined. This review summarizes CICI associated with most commonly used chemotherapeutic agents with emphasizes the possible underlying pathogenesis in both animal and clinical studies.

Atomoxetine improves hippocampal cell proliferation but not memory in Doxorubicin-treated adult male rats

Atomoxetine (ATX) is a noradrenaline reuptake inhibitor used to treat Attention deficit hyperactive disorder (ADHD), or improve cognition in normal subjects. Cancer patients treated with systemic adjuvant chemotherapy have described experiencing deterioration in cognition. Doxorubicin (DOX, Adriamycin) is one of the anthracycline families used in chemotherapy, which has a deteriorating effect on both cognition and proliferation. The cognitive effects of ATX require inputs from the hippocampus. The aim of this study was to examine spatial memory and proliferation in the subgranular zone (SGZ) of the DG in adult Lister Hooded rats treated either alone or with a combination of Atomoxetine (30 mg kg⁻¹ day⁻¹, six i.p. doses, one injection every other day) and Doxorubicin (DOX) ( 2 mg kg⁻¹ day⁻¹, six i.p. doses, one injection every other day). Spatial memory was tested using the Novel location recognition (NLR) test, and proliferation of hippocampal cells was quantified using immunohistochemistry for the proliferative marker Ki67. Results showed that ATX treatment has improved the NLR task and increased cell proliferation in the SGZ of the DG, compared with saline‐treated controls. Animals treated with DOX only showed deficits in NLR task, and co‐administration of ATX along with DOX did not improve their performance. DOX chemotherapy caused a significant reduction in the number of proliferating cells in the SGZ of the DG compared with saline‐treated controls. This reduction was reversed by co‐administration of ATX. The above findings suggest that DOX can negatively affect both cell proliferation and memory and ATX co‐administration improves proliferation, but not memory in the adult male rat hippocampus.

Effect of Metformin on Doxorubicin-Induced Memory Dysfunction

Doxorubicin (DOX) is widely used to treat many types of cancer; however, it is associated with chemotherapy-related complications such as cognitive dysfunction, known as chemobrain. Chemobrain affects up to 75% of cancer survivors, and there are currently no available therapeutic options. This study aims to examine whether metformin (MET) can protect against the neurotoxicity caused by DOX treatment. Forty male rats were divided into four groups (10 rats/group): control, DOX, DOX + MET, and MET. Rats treated with DOX received five doses of 4 mg/kg DOX weekly (cumulative dose: 20 mg/kg). For the DOX-MET and MET groups, MET (3 mg/mL) was dissolved in drinking water. Behavioral and glucose tests were performed one day after treatment was completed. We found DOX (4 mg/kg/week, 5 weeks) caused learning and memory impairment in the Y-maze, novel object recognition, and elevated plus maze behavioral tests. MET did not rescue these DOX-induced memory impairments. Neither DOX nor MET nor MET + DOX altered glucose levels following the treatment. In summary, DOX treatment is associated with memory impairment in rats, but MET does not rescue this cognitive dysfunction.

Evaluation of the effects of chemotherapy on brain glucose metabolism in children with Hodgkin's lymphoma

OBJECTIVE

Chemobrain is a recently proposed pathological entity. ¹⁸F-FDG PET/CT can show objective abnormalities to explain brain disorders caused by chemotherapy, although no study has investigated these phenomena in children to date. The main objective of the present study was to examine quantitatively the effects of chemotherapy on brain metabolism in a homogeneous population of children treated for Hodgkin's lymphoma using 18F-FDG PET/CT.

METHODS

In this retrospective study, we included 20 children, newly diagnosed with Hodgkin's lymphoma, who underwent ¹⁸F-FDG PET/CT at initial staging and at least one PET/CT in follow-up. The SPM12 software provided t-maps to show the difference in metabolism between these PET/CTs. The statistical maps were analyzed with xjView software to identify the brain regions associated with the clusters detected.

RESULTS

Altered glucose metabolism was found in the frontal, cingular, and temporoinsular regions after two cycles of chemotherapy. Results in children were compared to a group of 35 adults. For the same statistical threshold, the extent and depth of the metabolic alterations were less in the adult group than in children.

CONCLUSIONS

¹⁸F-FDG PET/CT is useful in providing objective data to explain brain disorders caused by chemotherapy. This could lead to better care and should be compared to neuropsychological test results.

Chemotherapy and cognition: comprehensive review on doxorubicin-induced chemobrain

Chemobrain refers to a common sequela experienced by a substantial subset of cancer patients exposed to chemotherapeutic treatment, a phenomenon that dramatically deteriorates the survivors' quality of life and prevents them from restoring their pre-cancer life. This review is intended to address the current knowledge regarding the mechanisms underlying the pathophysiology of the chemobrain phenomenon, with special focus on the antineoplastic agent ''doxorubicin'', which has been shown to be implicated in strenuous central neurotoxicity despite being-almost entirely-peripherally confined. Moreover, the assessment of the post-chemotherapy cognitive impairment in both human and animal subjects, and the potential pharmacotherapy and behavioral intervention strategies are reviewed.

Characterization and reversal of Doxorubicin-mediated biphasic activation of ERK and persistent excitability in sensory neurons of Aplysia californica

Doxorubicin (DOX), a common chemotherapeutic agent, impairs synaptic plasticity. DOX also causes a persistent increase in basal neuronal excitability, which occludes serotonin-induced enhanced excitability. Therefore, we sought to characterize and reverse DOX-induced physiological changes and modulation of molecules implicated in memory induction using sensory neurons from the marine mollusk Aplysia californica. DOX produced two mechanistically distinct phases of extracellular signal-regulated kinase (ERK) activation, an early and a late phase. Inhibition of MEK (mitogen-activated protein kinase (MAPK)/ERK kinase) after DOX treatment reversed the late ERK activation. MEK inhibition during treatment enhanced the late ERK activation possibly through prolonged downregulation of MAPK phosphatase-1 (MKP-1). Unexpectedly, the late ERK activation negatively correlated with excitability. MEK inhibition during DOX treatment simultaneously enhanced the late activation of ERK and blocked the increase in basal excitability. In summary, we report DOX-mediated biphasic activation of ERK and the reversal of the associated changes in neurons, a potential strategy for reversing the deleterious effects of DOX treatment.

Clearing the fog: a review of the effects of dietary omega-3 fatty acids and added sugars on chemotherapy-induced cognitive deficits

Cancer treatments such as chemotherapy have been an important part of extending survival in women diagnosed with breast cancer. However, chemotherapy can cause potentially toxic side effects in the brain that impair memory, verbal fluency, and processing speed in up to 30% of women treated. Women report that post-chemotherapy cognitive deficits negatively impact quality of life and may last up to ten years after treatment. Mechanisms underlying these cognitive impairments are not fully understood, but emerging evidence suggests that chemotherapy induces structural changes in the brain, produces neuroinflammation, and reduces adult hippocampal neurogenesis. Dietary approaches that modify inflammation and neurogenesis are promising strategies for reducing chemotherapy-induced cognitive deficits in breast cancer survivors. In this review, we describe the cognitive and neuronal side effects associated with commonly used chemotherapy treatments for breast cancer, and we focus on the often opposing actions of omega-3 fatty acids and added sugars on cognitive function, neuroinflammation, and adult hippocampal neurogenesis. Omega-3 fatty acids administered concurrently with doxorubicin chemotherapy have been shown to prevent depressive-like behaviors and reduce neuroinflammation, oxidative stress, and neural apoptosis in rodent models. In contrast, diets high in added sugars may interact with n-3 FAs to diminish their anti-inflammatory activity or act independently to increase neuroinflammation, reduce adult hippocampal neurogenesis, and promote cognitive deficits. We propose that a diet rich in long-chain, marine-derived omega-3 fatty acids and low in added sugars may be an ideal pattern for preventing or alleviating neuroinflammation and oxidative stress, thereby protecting neurons from the toxic effects of chemotherapy. Research testing this hypothesis could lead to the identification of modifiable dietary choices to reduce the long-term impact of chemotherapy on the cognitive functions that are important to quality of life in breast cancer survivors.

Sleep pattern and locomotor activity are impaired by doxorubicin in non-tumor-bearing rats

Purpose

We sought explore the effects of doxorubicin on sleep patterns and locomotor activity. To investigate these effects, two groups were formed: a control group and a Doxorubicin (DOXO) group.

Methods

Sixteen rats were randomly assigned to either the control or DOXO groups. The sleep patterns were examined by polysomnographic recording and locomotor activity was evaluated in an open-field test.

Results

In the light period, the total sleep time and slow wave sleep were decreased, while the wake after sleep onset and arousal were increased in the DOXO group compared with the control group (p<0.05). In the dark period, the total sleep time, arousal, and slow wave sleep were increased, while the wake after sleep onset was decreased in the DOXO group compared with the control group (p<0.05). Moreover, DOXO induced a decrease of crossing and rearing numbers when compared control group (p<0.05).

Conclusions

Therefore, our results suggest that doxorubicin induces sleep pattern impairments and reduction of locomotor activity.

Long-lasting impairments in adult neurogenesis, spatial learning and memory from a standard chemotherapy regimen used to treat breast cancer

The negative impact of chemotherapy on cognitive function in cancer patients has gained increasing attention in the last decade. Whilst the short-term acute effects on cognition are expected following chemotherapy, the persistence of such impairments in the long-term is still in question. This is despite clinical evidence indicating cognitive difficulties may persist well beyond treatment and affect quality of life. In the present study, we assessed the long-term (3 months) cognitive impact of chemotherapy in a mouse model intended to mimic the human female post-menopausal population receiving chemotherapy for breast cancer. Ovariectomized, female, C57BL/6J mice received two doses of Doxorubicin, Cyclophosphamide, and 5-Fluorouracil or saline vehicle (control), separated by one week. During this interval, mice received BrdU injections to label dividing cells. Results indicate a persistent impairment in learning and recall (1h, 24h and 48h) on the Morris water maze, reduced survival and differentiation of new neurons (BrdU+/NeuN+), and a persistent decline in proliferation of new cells (Ki67(+)) in the dentate gyrus. Locomotor activity, motor performance, and anxiety-like behavior were unaffected. We further evaluated the efficacy of a diet enriched in omega-3-fatty acids (DHA+EPA+DPA), in reversing long-term chemotherapy deficits but no rescue was observed. The model described produces long-term cognitive and cellular impairments from chemotherapy that mimic those observed in humans. It could be useful for identifying mechanisms of action and to test further the ability of lifestyle interventions (e.g., diet) for ameliorating chemotherapy-induced cognitive impairments.

Chemotherapy, cognitive impairment and hippocampal toxicity

Cancer therapies can be associated with significant central nervous system (CNS) toxicity. While radiation-induced brain damage has been long recognized both in pediatric and adult cancer patients, CNS toxicity from chemotherapy has only recently been acknowledged. Clinical studies suggest that the most frequent neurotoxic adverse effects associated with chemotherapy include memory and learning deficits, alterations of attention, concentration, processing speed and executive function. Preclinical studies have started to shed light on how chemotherapy targets the CNS both on cellular and molecular levels to disrupt neural function and brain plasticity. Potential mechanisms include direct cellular toxicity, alterations in cellular metabolism, oxidative stress, and induction of pro-inflammatory processes with subsequent disruption of normal cellular and neurological function. Damage to neural progenitor cell populations within germinal zones of the adult CNS has been identified as one of the key mechanisms by which chemotherapy might exert long-lasting and progressive neurotoxic effects. Based on the important role of the hippocampus for maintenance of brain plasticity throughout life, several experimental studies have focused on the study of chemotherapy effects on hippocampal neurogenesis and associated learning and memory. An increasing body of literature from both animal studies and neuroimaging studies in cancer patients suggests a possible relationship between chemotherapy induced hippocampal damage and the spectrum of neurocognitive deficits and mood alterations observed in cancer patients. This review aims to briefly summarize current preclinical and neuroimaging studies that are providing a potential link between the neurotoxic effects of chemotherapy and hippocampal dysfunction, highlighting challenges and future directions in this field of investigation.

The long-term impact of oxaliplatin chemotherapy on rodent cognition and peripheral neuropathy

Chemotherapy treatment is associated with cognitive dysfunction in cancer survivors after treatment completion. The duration of these impairments is unclear. Therefore this paper aims to evaluate the lasting impact of varying doses of the chemotherapy oxaliplatin (OX) on cognition and peripheral neuropathy. In Experiment 1 rats were treated once a week for 3 weeks with either physiological saline (control) or 6 mg/kg OX i.p. and were assessed for peripheral neuropathy, using von Frey filaments, and cognitive function, using novel object and location recognition, up to 2 weeks after treatment completion. For Experiment 2 rats received 3 weekly i.p. injections of either physiological saline (control), 0.6 mg/kg, 2mg/kg or 6 mg/kg OX and assessed for peripheral neuropathy and cognitive function up to 11 months after treatment completion. Systemic OX treatment induced lasting effects on cognitive function at 11 months after treatment, and peripheral neuropathy at 1 month after treatment and these were dose dependent; higher doses of OX resulted in worse cognitive outcomes and more severe peripheral neuropathy.

Redox biology in normal cells and cancer: restoring function of the redox/Fyn/c-Cbl pathway in cancer cells offers new approaches to cancer treatment

This review discusses a unique discovery path starting with novel findings on redox regulation of precursor cell and signaling pathway function and identification of a new mechanism by which relatively small changes in redox status can control entire signaling networks that regulate self-renewal, differentiation, and survival. The pathway central to this work, the redox/Fyn/c-Cbl (RFC) pathway, converts small increases in oxidative status to pan-activation of the c-Cbl ubiquitin ligase, which controls multiple receptors and other proteins of central importance in precursor cell and cancer cell function. Integration of work on the RFC pathway with attempts to understand how treatment with systemic chemotherapy causes neurological problems led to the discovery that glioblastomas (GBMs) and basal-like breast cancers (BLBCs) inhibit c-Cbl function through altered utilization of the cytoskeletal regulators Cool-1/βpix and Cdc42, respectively. Inhibition of these proteins to restore normal c-Cbl function suppresses cancer cell division, increases sensitivity to chemotherapy, disrupts tumor-initiating cell (TIC) activity in GBMs and BLBCs, controls multiple critical TIC regulators, and also allows targeting of non-TICs. Moreover, these manipulations do not increase chemosensitivity or suppress division of nontransformed cells. Restoration of normal c-Cbl function also allows more effective harnessing of estrogen receptor-α (ERα)-independent activities of tamoxifen to activate the RFC pathway and target ERα-negative cancer cells. Our work thus provides a discovery strategy that reveals mechanisms and therapeutic targets that cannot be deduced by standard genetics analyses, which fail to reveal the metabolic information, isoform shifts, protein activation, protein complexes, and protein degradation critical to our discoveries.

Doxorubicin attenuates serotonin-induced long-term synaptic facilitation by phosphorylation of p38 mitogen-activated protein kinase

Doxorubicin (DOX) is an anthracycline used widely for cancer chemotherapy. Its primary mode of action appears to be topoisomerase II inhibition, DNA cleavage, and free radical generation. However, in non-neuronal cells, DOX also inhibits the expression of dual-specificity phosphatases (also referred to as MAPK phosphatases) and thereby inhibits the dephosphorylation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK), two MAPK isoforms important for long-term memory (LTM) formation. Activation of these kinases by DOX in neurons, if present, could have secondary effects on cognitive functions, such as learning and memory. The present study used cultures of rat cortical neurons and sensory neurons (SNs) of Aplysia to examine the effects of DOX on levels of phosphorylated ERK (pERK) and phosphorylated p38 (p-p38) MAPK. In addition, Aplysia neurons were used to examine the effects of DOX on long-term enhanced excitability, long-term synaptic facilitation (LTF), and long-term synaptic depression (LTD). DOX treatment led to elevated levels of pERK and p-p38 MAPK in SNs and cortical neurons. In addition, it increased phosphorylation of the downstream transcriptional repressor cAMP response element-binding protein 2 in SNs. DOX treatment blocked serotonin-induced LTF and enhanced LTD induced by the neuropeptide Phe-Met-Arg-Phe-NH2. The block of LTF appeared to be attributable to overriding inhibitory effects of p-p38 MAPK, because LTF was rescued in the presence of an inhibitor (SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole]) of p38 MAPK. These results suggest that acute application of DOX might impair the formation of LTM via the p38 MAPK pathway.

Neurotoxicity of cancer chemotherapy

There is accumulating clinical evidence that chemotherapeutic agents induce neurological side effects, including memory deficits and mood disorders, in cancer patients who have undergone chemotherapeutic treatments. This review focuses on chemotherapy-induced neurodegeneration and hippocampal dysfunctions and related mechanisms as measured by in vivo and in vitro approaches. These investigations are helpful in determining how best to further explore the causal mechanisms of chemotherapy-induced neurological side effects and in providing direction for the future development of novel optimized chemotherapeutic agents.

Chemotherapy-related cognitive dysfunction: current animal studies and future directions

Cognitive impairment is a potential long-term side effect of adjuvant chemotherapy that can have a major impact on the quality of life of cancer survivors. There is a growing number of preclinical studies addressing this issue, thereby extending our knowledge of the mechanisms underlying chemotherapy-induced neurotoxicity. In this review, we will summarize the recent advances and important findings presented in these studies. Emerging challenges, such as the development of neuroprotective strategies, and the role of the blood-brain barrier on cognitive impairment will be described and future directions in this field of investigation will be outlined.

The short and long term effects of docetaxel chemotherapy on rodent object recognition and spatial reference memory

AIMS

Previous animal studies have examined the potential for cytostatic drugs to induce learning and memory deficits in laboratory animals but, to date, there is no pre-clinical evidence that taxanes have the potential to cause cognitive impairment. Therefore our aim was to explore the short- and long-term cognitive effects of different dosing schedules of the taxane docetaxel (DTX) on laboratory rodents.

MAIN METHODS

Healthy male hooded Wistar rats were treated with DTX (6 mg/kg, 10mg/kg) or physiological saline (control), once a week for 3 weeks (Experiment 1) or once only (10mg/kg; Experiment 2). Cognitive function was assessed using the novel object recognition (NOR) task and spatial water maze (WM) task 1 to 3 weeks after treatment and again 4 months after treatment.

KEY FINDINGS

Shortly after DTX treatment, rats perform poorly on NOR regardless of treatment regimen. Treatment with a single injection of 10mg/kg DTX does not appear to induce sustained deficits in object recognition or peripheral neuropathy.

SIGNIFICANCE

Overall these findings show that treatment with the taxane DTX in the absence of cancer and other anti-cancer treatments causes cognitive impairment in healthy rodents.

Differential expression of cytokines in breast cancer patients receiving different chemotherapies: implications for cognitive impairment research

PURPOSE

Altered levels of cytokines and chemokines may play a role in cancer- and cancer treatment-related cognitive difficulties. In many neurodegenerative diseases, abnormal concentrations of cytokines and chemokines affect neuronal integrity leading to cognitive impairments, but the role of cytokines in chemotherapy-related cognitive difficulties in cancer patients is not well understood. Patients receiving doxorubicin-based (with cyclophosphamide, or cyclophosphamide plus fluorouracil; AC/CAF) chemotherapy or cyclophosphamide, methotrexate, and fluorouracil (CMF) chemotherapy report experiencing cognitive difficulties; because these regimens work by different modes of action, it is possible that they differentially affect cytokine levels.

METHODS

This study examined the relationships between cytokine levels (i.e., IL-6, IL-8, and MCP-1) and type of chemotherapy among 54 early-stage breast cancer patients receiving AC/CAF or CMF. Cytokine levels were assessed at two time-points: prior to on-study chemotherapy cycle 2 (cycle 2) and after two consecutive chemotherapy cycles (prior to on-study cycle 4; cycle 4).

MAIN RESULTS

Analyses of variance using cycle 2 levels as a covariate (ANCOVA) were used to determine differences between chemotherapy groups. Levels of IL-6, IL-8, and MCP-1 increased in the AC/CAF group and decreased in the CMF group; the only significant between-group change was in IL-6 (p < 0.05).

CONCLUSIONS

These results, although preliminary based on the small sample size, suggest that AC/CAF chemotherapy is more cytokine inducing than CMF. Future studies should confirm these results and explore the distinct inflammatory responses elicited by different chemotherapy regimens when assessing cognitive function in cancer patients.

Preserved learning and memory following 5-fluorouracil and cyclophosphamide treatment in rats

Some patients experience enduring cognitive impairment after cancer treatment, a condition termed "chemofog". Animal models allow assessment of chemotherapy effects on learning and memory per se, independent of changes due to cancer itself or associated health consequences such as depression. The present study examined the long-term learning and memory effects of a chemotherapy cocktail used widely in the treatment of breast cancer, consisting of 5-fluorouracil (5FU) and cyclophosphamide (CYP). Eighty 5-month old male F344 rats received contextual and cued fear conditioning before treatment with saline, or a low or high dose drug cocktail (50mg/kg CYP and 75 mg/kg 5FU, or 75 mg/kg CYP and 120 mg/kg 5FU, i.p., respectively) every 30 days for 2 months. After a 2-month, no-drug recovery, both long-term retention and new task acquisition in the water maze and 14-unit T-maze were assessed. Neither dose of the CYP/5FU cocktail impaired retrograde fear memory despite marked toxicity documented by enduring weight loss and 50% mortality at the higher dose. Acquisition in the water maze and Stone maze was also normal relative to controls in rats treated with CYP/5FU. The results contribute to a growing literature suggesting that learning and memory mediated by the hippocampus can be relatively resistant to chemotherapy. Future investigation may need to focus on assessments of processing speed, executive function and attention, and the possible interactive contribution of cancer itself and aging to the post-treatment development of cognitive impairment.

Preserved learning and memory in mice following chemotherapy: 5-Fluorouracil and doxorubicin single agent treatment, doxorubicin-cyclophosphamide combination treatment

Clinical studies suggest that chemotherapy is associated with long-term cognitive impairment in some patients. A number of underlying mechanisms have been proposed, however, the etiology of chemotherapy-related cognitive dysfunction remains relatively unknown. As part of a multifaceted approach, animal models of chemotherapy induced cognitive impairment are being developed. Thus far, the majority of animal studies have utilized rats, however, mice may prove particularly beneficial in studying genetic risk factors for developing chemotherapy induced cognitive impairment. Thus, C57BL/6J mice were treated once a week for three weeks with saline, doxorubicin and cyclophosphamide (D&C), doxorubicin (Dox), or 5-fluorouracil (5-FU). Recent and remote contextual fear conditioning and novel object recognition (NOR) was assessed. Despite significant toxic effects as assessed by weight loss, the chemotherapy treated mice performed as well as control mice on all task. As are some humans, C57BL/6J mice may be resistant to at least some aspects of chemotherapy induced cognitive decline.

Disruption of learning processes by chemotherapeutic agents in childhood survivors of acute lymphoblastic leukemia and preclinical models

OBJECTIVE

With the survival rate of acute lymphoblastic leukemia (ALL) surpassing 90 percent within this decade, new research is emerging in the field of late effects. A review of the research investigating the relationship of treatment regimens for ALL to specific late effect deficits, underlying mechanisms, and possible remediation is warranted to support continued studies.

METHODS

The clinical literature was briefly surveyed to describe the occurrence and topography of late effects, specifically neurocognitive deficits. Additionally, the preclinical literature was reviewed to uncover potential underlying mechanisms of these deficits. The advantages of using rodent models to answer these questions are outlined, as is an assessment of the limited number of rodent models of childhood cancer treatment.

RESULTS

The literature supports that childhood survivors of ALL exhibit academic difficulties and are more likely to be placed in a special education program. Behavioral evidence has highlighted impairments in the areas of attention, working memory, and processing speed, leading to a decrease in full scale IQ. Neurophysiological and preclinical evidence for these deficits has implicated white matter abnormalities and acquired brain damage resulting from specific chemotherapeutic agents commonly used during treatment.

CONCLUSIONS

The exact role of chemotherapeutic agents in learning deficits remains mostly unknown. Recommendations for an improved rodent model of learning deficits in childhood cancer survivors are proposed, along with suggestions for future directions in this area of research, in hopes that forthcoming treatment regimens will reduce or eliminate these types of impairments.