Long-term exercise training as a modulator of mammary cancer vascularization

Application of infrared thermography in assessing presence and severity of intra-abdominal adhesions

Abdominal surgeries can sometimes lead to the formation of intra-abdominal adhesions, which may result in severe complications. Despite the availability of several diagnostic procedures, thermography has not been used for identifying intra-abdominal adhesions. Therefore, the objective of the current study was to assess abdominal temperature changes in rats with experimentally induced intra-abdominal adhesions. A total of 48 female rats were randomly divided into 4 groups (n = 12 each): Control (Group C), Laparotomy (Group Lap), Peritoneal Button Creation (Group PBC), and Uterus horn (Group UH). Skin temperature of abdominal region was measured before the procedure (T0) and daily thereafter until day 7 (T7). On day 7, all rats were euthanized for macroscopic evaluation, adhesion scoring, histopathological, immunohistochemical and immunofluorescence analyses. Significant differences were observed between Group C and Group PBC and Group UH at T5, while at T6 and T7, there was a difference between Group C and Group Lap, Group PBC, and Group UH in abdominal skin temperature (P < 0.05). The highest level of inflammation, angiogenesis, IL-1β, and VEGF were observed in Group PBC followed by Group UH, Group Lap, and Group C (P < 0.05). There was a significant difference in adhesion formation between Group C and Groups Lap, PBC, and UH (P = 0.02). However, no significant difference was found in adhesion scores between Groups Lap, PBC, and UH (P = 0.25). A significant difference was found in mean abdominal skin temperature between adhesion scores 4 and 0, 1, and 2 (P < 0.05), while no significant difference was observed between adhesion scores 3 and 4 (P > 0.05). In conclusion, the current study suggests that the presence of intra-abdominal adhesions is associated with an increase in abdominal temperature, and this increase is correlates with the severity of adhesion.

Outcomes of physical exercises on initiation, progression, and treatment of breast cancer

The emergence of drug resistance is a substantial obstacle to the effective management of breast cancer, which is the primary cause of cancer-related deaths in women worldwide. To facilitate the development of targeted therapies that can effectively overcome drug resistance, it is crucial to possess a comprehensive comprehension of the molecular mechanisms that underpin resistance to breast cancer treatment. So far, considerable progress has been made in the field of exercise-oncology research and overcome drug resistance, specifically about breast cancer. Evidence has suggested that participation in physical activity is correlated with a decrease in reappearance and fatality rates of breast cancer patients. It has been reported that participation in physical activity can yield favorable outcomes in the prevention, treatment, and post-treatment of breast cancer. An increasing body of empirical evidence suggests that participation in physical activity can alter diverse biological mechanisms, potentially augmenting breast cancer treatments' efficacy. Comparing increased physical activity versus reduced physical activity in breast cancer patients who received chemotherapy, radiotherapy, and surgery supported the significance of exercise in comprehensive care strategies to enhance overall health and treatment efficacy. Furthermore, previous studies have reported that physical activity can enhance the efficacy of breast cancer treatments. This review provides the current literature regarding the influence of physical activity on the occurrence and progression of breast cancer.

Exploiting the therapeutic potential of contracting skeletal muscle-released extracellular vesicles in cancer: Current insights and future directions

The health benefits of exercise training in a cancer setting are increasingly acknowledged; however, the underlying molecular mechanisms remain poorly understood. It has been suggested that extracellular vesicles (EVs) released from contracting skeletal muscles play a key role in mediating the systemic benefits of exercise by transporting bioactive molecules, including myokines. Nevertheless, skeletal muscle-derived vesicles account for only about 5% of plasma EVs, with the immune cells making the largest contribution. Moreover, it remains unclear whether the contribution of skeletal muscle-derived EVs increases after physical exercise or how muscle contraction modulates the secretory activity of other tissues and thus influences the content and profile of circulating EVs. Furthermore, the destination of EVs after exercise is unknown, and it depends on their molecular composition, particularly adhesion proteins. The cargo of EVs is influenced by the training program, with acute training sessions having a greater impact than chronic adaptations. Indeed, there are numerous questions regarding the role of EVs in mediating the effects of exercise, the clarification of which is critical for tailoring exercise training prescriptions and designing exercise mimetics for patients unable to engage in exercise programs. This review critically analyzes the current knowledge on the effects of exercise on the content and molecular composition of circulating EVs and their impact on cancer progression.

Regular Voluntary Running is Associated with Increased Tumor Vascularization and Immune Cell Infiltration and Decreased Tumor Growth in Mice

Tumors present dysfunctional vasculature that limits blood perfusion and hinders immune cells delivery. We aimed to investigate if regular voluntary running promotes tumor vascular remodelling, improves intratumoral immune cells infiltration and inhibits tumor growth. Tumors were induced in C57BL/6 male mice (n=28) by subcutaneous inoculation in the dorsal region with a suspension of RM1 cells (1.5×10⁵ cells/500 µL PBS) and randomly allocated into two groups: sedentary (n=14) and voluntarily exercised on a wheel (n=14). Seven mice from each group were sacrificed 14 and 28 days after cells' inoculation to evaluate tumor weight, microvessel density, vessels' lumen regularity and the intratumoral quantity of NKG2D receptors, CD4⁺and CD8⁺T cells, by immunohistochemistry. The statistical inference was done through a two-way ANOVA. Exercised mice developed smaller tumors at 14 (0.17±0.1 g vs. 0.48±0.2 g, p<0.05) and 28 (0.92±0.7 g vs. 2.09±1.3 g, p<0.05) days, with higher microvessel density (21.20±3.2 vs. 15.86±4.0 vessels/field, p<0.05), more regular vessels' lumen (1.06±0.2 vs. 1.43±0.2, p<0.05), and higher CD8⁺T cells (464.95±48.0 vs. 364.70±49.4 cells/mm², p<0.01), after 28 days. NKG2D expression was higher in exercised mice at 14 (263.27±25.8 cells/mm², p<0.05) and 28 (295.06±56.2 cells/mm², p<0.001) days. Regular voluntary running modulates tumor vasculature, increases immune cells infiltration and attenuates tumor growth, in mice.

Physical Exercise and the Hallmarks of Breast Cancer: A Narrative Review

Growing evidence suggests that, among the different molecular/cellular pathophysiological mechanisms associated with cancer, there are 14 hallmarks that play a major role, including: (i) sustaining proliferative signaling, (ii) evading growth suppressors, (iii) activating invasion and metastasis, (iv) enabling replicative immortality, (v) inducing angiogenesis, (vi) resisting cell death, (vii) reprogramming energy metabolism, (viii) evading immune destruction, (ix) genome instability and mutations, (x) tumor-promoting inflammation, (xi) unlocking phenotypic plasticity, (xii) nonmutational epigenetic reprogramming, (xiii) polymorphic microbiomes, and (xiv) senescent cells. These hallmarks are also associated with the development of breast cancer, which represents the most prevalent tumor type in the world. The present narrative review aims to describe, for the first time, the effects of physical activity/exercise on these hallmarks. In summary, an active lifestyle, and particularly regular physical exercise, provides beneficial effects on all major hallmarks associated with breast cancer, and might therefore help to counteract the progression of the disease or its associated burden.

The effect of aerobic exercise on tumour blood delivery: a systematic review and meta-analysis

PURPOSE

Tumour blood vessels are structurally and functionally abnormal, resulting in areas of hypoxia and heterogeneous blood supply. Aerobic exercise may modulate tumour blood flow and normalise the tumour microenvironment to improve chemotherapy delivery. This systematic review and meta-analysis aimed to evaluate the effect of the aerobic exercise mode on tumour hypoxia, vascularisation and blood flow.

METHODS

Four online databases were searched. Preclinical and clinical randomised controlled trials examining the effects of aerobic exercise training on hypoxia, vascularisation or blood flow in solid tumours were included. The risk of bias was assessed and a meta-analysis performed.

RESULTS

Seventeen preclinical studies and one clinical study met criteria. Eleven studies assessed hypoxia, 15 studies assessed vascularisation and seven evaluated blood flow. There was large variability in measurement methods, tumour types and exercise program designs. The overall risk of bias was unclear in clinical and preclinical studies, owing to poor reporting. There was no significant effect of aerobic exercise on hypoxia (SMD = -0.17; 95% CI = -0.62, 0.28; I2 = 60%), vascularisation (SMD = 0.07; 95% CI = -0.40, 0.55; I2 = 71%) or blood flow (SMD = 0.01; 95% CI = -0.59, 0.61; I2 = 63%).

CONCLUSION

There is heterogeneity in methodology, resulting in evidence that is inconsistent and inconclusive for the effects of aerobic exercise on hypoxia, vascularisation and blood flow. Most evidence of aerobic exercise effects on tumour blood flow is in animal models, with very limited evidence in humans.

Effect of Exercise on Breast Cancer: A Systematic Review and Meta-analysis of Animal Experiments

Objective: Exercise is reported to be beneficial for breast cancer. However, the results seem inconsistent. We conducted this systematic review and meta-analysis of animal experimental studies to fully understand the effect of exercise on breast cancer in animal model.

Methods: We searched databases from inception to April 2022 and manually searched related references to retrieve eligible studies. We screened eligible studies and extracted related data. We assessed the risk of bias and reporting quality using the SYstematic Review Centre for Laboratory animal Experimentation Risk of Bias tool and the Animal Research: Reporting of In Vivo Experiments guidelines 2.0, respectively. We summarized the study characteristics and findings of included studies and conducted meta-analysis with RevMan software. Subgroup analysis and sensitivity analysis were also performed.

Results: We identified 537 potential literatures and included 47 articles for analysis. According to the results of risk of bias assessment, only selective outcome reporting was in low risk of bias. Items of sequence generation, random outcome assessment, and incomplete outcome data were rated as high risk of bias. Most of other items were rated unclear risk of bias. In reporting quality assessment, all included articles reported grouping method and experimental procedures. However, no study provided information of the study protocol registration. Meta-analysis showed that, compared with sedentary lifestyle, exercise reduced more tumor weight (MD = −0.76, 95%CI −0.88 to −0.63, p = 0.85, I² = 0%) and tumor number per animal (MD = −0.61, 95%CI −0.91 to −0.31, p = 0.34, I² = 8%). Exercise decreased more tumor incidence than sedentary lifestyle both in motorized wheel/high-intensity (OR = 0.22, 95%CI 0.11 to 0.46, p = 0.09, I² = 41%) and free wheel/low-intensity treadmill running (OR = 0.45, 95%CI 0.14 to 1.44, p = 0.04, I² = 60%). Sensitivity analysis showed that the results were robust.

Conclusion: Exercise could reduce tumor weight, number of tumors per animal, and incidence of tumor in breast cancer model of mice and rats. However, the risk of bias items and reporting guidelines in preclinical studies should be concerned. Future research should consider standards of conducting and reporting preclinical studies and choose suitable exercise protocol for higher quality evidence of exercise for breast cancer.

Exercise protocols: The gap between preclinical and clinical exercise oncology studies

Introduction

Preclinical studies provide foundational knowledge to develop new effective treatments for use in clinical practice. Similar to clinical exercise oncology studies, it is also important to monitor, identify and/or avoid cancer-induced complications in preclinical (e.g., murine) exercise oncology studies. This may help close the gap between preclinical and clinical exercise oncology studies. The aim of the present mini review is to provide insight into exercise protocol design in preclinical exercise oncology studies in order to close the preclinical-clinical gap. A secondary aim was to examine exercise-responsive outcomes in the preclinical versus clinical setting.

Method

We reviewed animal studies in exercise oncology. A literature search was performed in PubMed/Medline and studies in English were screened.

Results

We found that the majority of preclinical exercise protocols have not been at least tested clinically. We found some evidence that certain outcomes of preclinical studies (e.g., markers of cellular and molecular adaptation) that translate to clinical studies. However, this translation was dependent on the use, by investigators in their study design, of suitable and applicable preclinical exercise protocols.

Conclusions

Cancer and its treatment-induced complications (e.g., fatigue, cardiac atrophy, cachexia, etc.) have largely been ignored in the exercise protocols of preclinical oncology studies. Preclinical exercise oncology studies should consider the limitations of human exercise oncology studies when conducting gap analysis for their study design to increase the probability that findings related to mechanistic adaptations in exercise oncology will be translatable to the clinical setting. By virtue of paying heed to patient compliance and adverse effects, clinical exercise oncology research teams must design relevant, feasible exercise protocols; researchers in preclinical exercise oncology should also take such factors into consideration in order to help bridge the gap between preclinical and clinical studies in exercise oncology.

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Preclinical research provides foundational knowledge for the development of human experimental and clinical studies; however, direct translation of preclinical findings has a low success rate.

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Exercise can provide potent wide-ranging beneficial effects for people with chronic diseases, including cancer.

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A minority of preclinical exercise oncology studies account for cancer-related factors in their experimental design.

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To lessen the preclinical–clinical gap in exercise oncology research, preclinical exercise oncology studies should consider using experimental designs that are based on locomotor activity and/or VO2peak in animals bearing cancer.

The Effects of Physical Exercise on Tumor Vasculature: Systematic Review and Meta-analysis

A wealth of evidence supports an association between physical exercise, decreased tumor growth rate, and reduced risk of cancer mortality. In this context, the tumor vascular microenvironment may play a key role in modulating tumor biologic behavior. The present systematic review and meta-analysis aimed to summarize the evidence regarding the effects of physical exercise on tumor vasculature in pre-clinical studies. We performed a computerized research on the PubMed, Scopus, and EBSCO databases to identify pre-clinical studies that evaluated the effect of physical exercise on tumor vascular outcomes. Mean differences were calculated through a random effects model. The present systematic review included 13 studies involving 373 animals. From these, 11 studies evaluated chronic intratumoral vascular adaptations and 2 studies assessed the acute intratumoral vascular adaptations to physical exercise. The chronic intratumoral vascular adaptations resulted in higher tumor microvessel density in 4 studies, increased tumor perfusion in 2 studies, and reduced intratumoral hypoxia in 3 studies. Quantitatively, regular physical exercise induced an increased tumor vascularization of 2.13 [1.07, 3.20] (p<0.0001). The acute intratumoral vascular adaptations included increased vascular conductance and reduced vascular resistance, which improved tumor perfusion and attenuated intratumoral hypoxia. In pre-clinical studies, physical exercise seems to improve tumor vascularization.

Synergistic Effects of Exercise Training and Vitamin D Supplementation on Mitochondrial Function of Cardiac Tissue, Antioxidant Capacity, and Tumor Growth in Breast Cancer in Bearing-4T1 Mice

Both regular exercise training and vitamin D consumption are beneficial for patients with cancer. The study investigated the effects of interval exercise training (IET) or/and vitamin D supplementation on the gene expression involved in mitochondrial function of heart tissue, tumor size, and total antioxidant capacity (TAC) in breast cancer (BC) model mice. We assigned random 40 female NMRI mice to five equal groups (n = 8); the healthy control group (H.C), cancer control group (Ca.C), cancer with the vitamin D group (Ca.VD), cancer exercise group (Ca.Ex), and cancer exercise along with the vitamin D group (Ca.Ex.VD). Forty-eight hours after treatment, we anesthetized the animals and performed the isolation of heart tissue and blood serum for further studies. The results showed that the lowest mean body weight at the end of the treatments was related to Ca.C (p = 0.001). Vitamin D treatment alone has increased tumor volume growth by approximately 23%; in contrast, co-treatment with exercise and vitamin D inhibited tumor growth in mice (P = 0.001), compared with the cancer control (12%). TAC levels were higher in the group that received both vitamin D and exercise training (Ca.Ex.VD) than in the other treatment groups (Ca.VD and Ca.Ex) (p = 0.001). In cardiac tissue, vitamin D treatment induces an elevation significantly of the mRNA expression of Pgc1-α, Mfn-1, and Drp-1 genes (p = 0.001). The study has shown the overexpression of vitamin D in female mice, and synergistic effects of IET with vitamin D on weight loss controlling, antitumorigenesis, improvement of antioxidant defense, and the modulation of gene expression. The synergistic responses were likely by increasing mitochondrial fusion and TAC to control oxidative stress. We recommended being conducted further studies on mitochondrial dynamics and biogenesis focusing on risk factors of cardiovascular disease (CVD) in patients with BC.

Strategies to Prevent or Remediate Cancer and Treatment-Related Aging

Up to 85% of adult cancer survivors and 99% of adult survivors of childhood cancer live with an accumulation of chronic conditions, frailty, and/or cognitive impairments resulting from cancer and its treatment. Thus, survivors often show an accelerated development of multiple geriatric syndromes and need therapeutic interventions. To advance progress in this area, the National Cancer Institute convened the second of 2 think tanks under the auspices of the Cancer and Accelerated Aging: Advancing Research for Healthy Survivors initiative. Experts assembled to share evidence of promising strategies to prevent, slow, or reverse the aging consequences of cancer and its treatment. The meeting identified research and resource needs, including geroscience-guided clinical trials; comprehensive assessments of functional, cognitive, and psychosocial vulnerabilities to assess and predict age-related outcomes; preclinical and clinical research to determine the optimal dosing for behavioral (eg, diet, exercise) and pharmacologic (eg, senolytic) therapies; health-care delivery research to evaluate the efficacy of integrated cancer care delivery models; optimization of intervention implementation, delivery, and uptake; and patient and provider education on cancer and treatment-related late and long-term adverse effects. Addressing these needs will expand knowledge of aging-related consequences of cancer and cancer treatment and inform strategies to promote healthy aging of cancer survivors.

Obesity and Cancer Metastasis: Molecular and Translational Perspectives

Obesity is a modern health problem that has reached pandemic proportions. It is an established risk factor for carcinogenesis, however, evidence for the contribution of adipose tissue to the metastatic behavior of tumors is also mounting. Over 90% of cancer mortality is attributed to metastasis and metastatic tumor cells must communicate with their microenvironment for survival. Many of the characteristics observed in obese adipose tissue strongly mirror the tumor microenvironment. Thus in the case of prostate, pancreatic and breast cancer and esophageal adenocarcinoma, which are all located in close anatomical proximity to an adipose tissue depot, the adjacent fat provides an ideal microenvironment to enhance tumor growth, progression and metastasis. Adipocytes provide adipokines, fatty acids and other soluble factors to tumor cells whilst immune cells infiltrate the tumor microenvironment. In addition, there are emerging studies on the role of the extracellular vesicles secreted from adipose tissue, and the extracellular matrix itself, as drivers of obesity-induced metastasis. In the present review, we discuss the major mechanisms responsible for the obesity-metastatic link. Furthermore, understanding these complex mechanisms will provide novel therapies to halt the tumor-adipose tissue crosstalk with the ultimate aim of inhibiting tumor progression and metastatic growth.

Role of Regular Physical Exercise in Tumor Vasculature: Favorable Modulator of Tumor Milieu

The tumor vessel network has been investigated as a precursor of an inhospitable tumor microenvironment, including its repercussions in tumor perfusion, oxygenation, interstitial fluid pressure, pH, and immune response. Dysfunctional tumor vasculature leads to the extravasation of blood to the interstitial space, hindering proper perfusion and causing interstitial hypertension. Consequently, the inadequate delivery of oxygen and clearance of by-products of metabolism promote the development of intratumoral hypoxia and acidification, hampering the action of immune cells and resulting in more aggressive tumors. Thus, pharmacological strategies targeting tumor vasculature were developed, but the overall outcome was not satisfactory due to its transient nature and the higher risk of hypoxia and metastasis. Therefore, physical exercise emerged as a potential favorable modulator of tumor vasculature, improving intratumoral vascularization and perfusion. Indeed, it seems that regular exercise practice is associated with lasting tumor vascular maturity, reduced vascular resistance, and increased vascular conductance. Higher vascular conductance reduces intratumoral hypoxia and increases the accessibility of circulating immune cells to the tumor milieu, inhibiting tumor development and improving cancer treatment. The present paper describes the implications of abnormal vasculature on the tumor microenvironment and the underlying mechanisms promoted by regular physical exercise for the re-establishment of more physiological tumor vasculature.

Exercise modulation of tumour perfusion and hypoxia to improve radiotherapy response in prostate cancer

Background

An increasing number of studies indicate that exercise plays an important role in the overall care of prostate cancer (PCa) patients before, during and after treatment. Historically, research has focused on exercise as a modulator of physical function, psychosocial well-being as well as a countermeasure to cancer- and treatment-related adverse effects. However, recent studies reveal that exercise may also directly influence tumour physiology that could beneficially affect the response to radiotherapy.

Methods

In this narrative review, we provide an overview of tumour vascular characteristics that limit the effect of radiation and establish a rationale for exercise as adjunct therapy during PCa radiotherapy. Further, we summarise the existing literature on exercise as a modulator of tumour perfusion and hypoxia and outline potential future research directions.

Results

Preclinical research has shown that exercise can reduce intratumoral hypoxia—a major limiting factor in radiotherapy—by improving tumour perfusion and vascularisation. In addition, preliminary evidence suggests that exercise training can improve radiotherapy treatment outcomes by increasing natural killer cell infiltration in a murine PCa model.

Conclusions

Exercise is a potentially promising adjunct therapy for men with PCa undergoing radiotherapy that may increase its effectiveness. However, exercise-induced tumour radiosensitisation remains to be confirmed in preclinical and clinical trials, as does the optimal exercise prescription to elicit such effects.

Impacts of exercise intervention on various diseases in rats

BACKGROUND

Exercise is considered as an important intervention for treatment and prevention of several diseases, such as osteoarthritis, obesity, hypertension, and Alzheimer's disease. This review summarizes decadal exercise intervention studies with various rat models across 6 major systems to provide a better understanding of the mechanisms behind the effects that exercise brought.

METHODS

PubMed was utilized as the data source. To collect research articles, we used the following terms to create the search: (exercise [Title] OR physical activity [Title] OR training [Title]) AND (rats [Title/Abstract] OR rat [Title/Abstract] OR rattus [Title/Abstract]). To best cover targeted studies, publication dates were limited to "within 11 years." The exercise intervention methods used for different diseases were sorted according to the mode, frequency, and intensity of exercise.

RESULTS

The collected articles were categorized into studies related to 6 systems or disease types: motor system (17 articles), metabolic system (110 articles), cardiocerebral vascular system (171 articles), nervous system (71 articles), urinary system (2 articles), and cancer (21 articles). Our review found that, for different diseases, exercise intervention mostly had a positive effect. However, the most powerful effect was achieved by using a specific mode of exercise that addressed the characteristics of the disease.

CONCLUSION

As a model animal, rats not only provide a convenient resource for studying human diseases but also provide the possibility for exploring the molecular mechanisms of exercise intervention on diseases. This review also aims to provide exercise intervention frameworks and optimal exercise dose recommendations for further human exercise intervention research.

Effect of post-implant exercise on tumour growth rate, perfusion and hypoxia in mice

Preclinical studies have shown a larger inhibition of tumour growth when exercise begins prior to tumour implant (preventative setting) than when training begins after tumour implant (therapeutic setting). However, post-implantation exercise may alter the tumour microenvironment to make it more vulnerable to treatment by increasing tumour perfusion while reducing hypoxia. This has been shown most convincingly in breast and prostate cancer models to date and it is unclear whether other tumour types respond in a similar way. We aimed to determine whether tumour perfusion and hypoxia are altered with exercise in a melanoma model, and compared this with a breast cancer model. We hypothesised that post-implantation exercise would reduce tumour hypoxia and increase perfusion in these two models. Female, 6-10 week old C57BL/6 mice were inoculated with EO771 breast or B16-F10 melanoma tumour cells before randomisation to either exercise or non-exercising control. Exercising mice received a running wheel with a revolution counter. Mice were euthanised when tumours reached maximum ethical size and the tumours assessed for perfusion, hypoxia, blood vessel density and proliferation. We saw an increase in heart to body weight ratio in exercising compared with non-exercising mice (p = 0.0008), indicating that physiological changes occurred with this form of physical activity. However, exercise did not affect vascularity, perfusion, hypoxia or tumour growth rate in either tumour type. In addition, EO771 tumours had a more aggressive phenotype than B16-F10 tumours, as inferred from a higher rate of proliferation (p<0.0001), a higher level of tumour hypoxia (p = 0.0063) and a higher number of CD31+ vessels (p = 0.0005). Our results show that although a physiological training effect was seen with exercise, it did not affect tumour hypoxia, perfusion or growth rate. We suggest that exercise monotherapy is minimally effective and that future preclinical work should focus on the combination of exercise with standard cancer therapies.

The Regulation of the Metastatic Cascade by Physical Activity: A Narrative Review

The purpose of this narrative review is to provide an overview of the currently available knowledge about the mechanisms by which physical activity may affect metastatic development. The search terms exercise [Title/Abstract] AND metastasis [Title/Abstract] returned 222 articles on PUBMED on the 10 February 2019. After careful analysis of the abstracts, a final selection of 24 articles was made. Physical activity regulates the levels of metastatic factors in each of the five steps of the process. Moderate intensity exercise appears to prevent tumor spread around the body, among others, by normalizing angiogenesis, destroying circulating tumor cells, and decreasing endothelial cells permeability. Contrarily, high-intensity exercise seems to favor cancer dissemination, likely through excessive stress, which can be somewhat counteracted by an appropriate warm-up. In conclusion, chronic adaptations to moderate-intensity endurance exercise seem the most effective way to achieve a preventive effect of exercise on metastases. Altogether, the data gathered here reinforce the importance of encouraging cancer patients to perform moderate physical activity several times a week. To limit the undesired events thereof, a good knowledge of the patient's training level is important to establish an adapted exercise training program.

Effects of Exercise on the Tumour Microenvironment

Epidemiological evidence suggests that exercise improves survival in cancer patients. However, much is still unknown regarding the mechanisms of this positive survival effect and there are indications that exercise may not be universally beneficial for cancer patients. The key to understanding in which situations exercise is beneficial may lie in understanding its influence on the tumour microenvironment (TME)-and conversely, the influence of the tumour on physical functioning. The TME consists of a vast multitude of different cell types, mechanical and chemical stressors and humoral factors. The interplay of these different components greatly influences tumour cell characteristics and, subsequently, tumour growth rate and aggression. Exercise exerts whole-body physiological effects and can directly and indirectly affect the TME. In this chapter, we first discuss the possible role of exercise capacity ('fitness') and exercise adaptability on tumour responsiveness to exercise. We summarise how exercise affects aspects of the TME such as tumour perfusion, vascularity, hypoxia (reduced oxygenation) and immunity. Additionally, we discuss the role of myokines and other circulating factors in eliciting these changes in the TME. Finally, we highlight unanswered questions and key areas for future research in exercise oncology and the TME.

Impact of Physical Exercise on Growth and Progression of Cancer in Rodents-A Systematic Review and Meta-Analysis

Background: Physical exercise is suspected to reduce cancer risk and mortality. So far, little is known about the underlying mechanisms. Although limited, murine models represent a promising attempt in order to gain knowledge in this field. Objective: A systematic review and meta-analysis examining various treatment protocols was conducted in order to determine the impact of exercise on tumor growth in rodents. Methods: PubMed, Google scholar and System for information on Gray literature in Europe were screened from inception to October 2017. Risk of bias within individual studies was assessed using the Office of Health Assessment and Translation risk of bias rating tool for human and animal trials. The effect of exercise on tumor growth over and above non-exercise control was pooled using random-effects model. Subgroup analyses were conducted to identify potential moderators. Results: The quality of the included 17 articles ranged between "probably low" and "high risk of bias." A significant reduction in tumor growth in exercising animals compared to controls was detected (Hedges' g = -0.40; 95% CI -0.66 to -0.14, p < 0.01) with between-study heterogeneity (τ² = 0.217, I ² = 70.28%, p < 0.001). The heterogeneity was partially explained by three moderators representing the in-between group differences of "maximum daily exercise" R ² = 33% (p < 0.01), "type of cancer administration" R ² = 28% (p < 0.05), and "training initiation" R ² = 27% (p < 0.05). Conclusion: This meta-analysis suggests that physical exercise leads to reduction of tumor size in rodents. Since "maximum daily exercise" was found to have at least modest impact on tumor growth, more clinical trials investigating dose-response relationships are needed.

The Impact of Exercise Training on Breast Cancer

BACKGROUND/AIM

Physical exercise is increasingly considered by many authors to be a factor reducing the risk of cancer development and premature cancer-related death. Data indicate higher cure rates and longer times of survival in cancer patients who regularly exercise.

MATERIALS AND METHODS

A total of 50 female Sprague-Dawley rats were used in the experiment. Animals at 1 month of age were intraperitoneally injected with N-methyl-N-nitrosourea. Three months following drug administration, rats underwent supervised physical training. The animals were divided into four groups: control untrained group and 3 groups trained with different intensities - i.e. low, moderate and high. Routine histopathological examination of tumors was performed and mitotic activity was assessed by immunohistochemical expression of the Ki-67 antigen.

RESULTS

Ki-67 antigen expression was observed in all analyzed tumors. The increase in Ki-67 antigen expression correlated positively with the increase in training intensity.

CONCLUSION

It can be assumed that low-intensity physical training is safe for patients with breast cancer. However, moderate- and high-intensity training may induce tumor cell proliferation worsening patients' prognosis.

Effects of exercise training on breast cancer metastasis in a rat model

Exercise training is thought to play a protective role against cancer development and metastasis, either by reducing hormonal stimulation of hormone-dependent cancers or by reducing the permeability of vascular walls towards invading metastatic cells. The purpose of this work was to evaluate the role of long-term exercise training in the development and metastasis of breast cancer, in an immune-competent 1-methyl-1-nitrosourea (MNU) induced rat model. A single MNU dose was administered to Sprague-Dawley rats at 50 days of age and the rats were subjected to exercise training on a treadmill at 20 m/min, 60 min/day, 5 days/week for 35 weeks. Exercised animals developed slightly less (2.30 ± 1.42) tumours per animal than sedentary animals (2.55 ± 1.44) and did not develop any metastasis, while two pulmonary metastases were observed in the sedentary group. All primary neoplasms and their metastases were positive for oestrogen (ER) α and progesterone (PR) receptors, indicating high hormonal sensitivity. Interestingly, exercise training increased circulating oestrogen levels, thus suggesting that the mechanism might involve either or both of a protective hormone-independent effect and modulation of tumoural vascularization.

Modulation of mammary tumor vascularization by mast cells: Ultrasonographic and histopathological approaches

AIMS

The inhibition of mast cells' degranulation may be an approach to prevent the formation of new vessels during the mammary carcinogenesis.

MATERIALS AND METHODS

Female Sprague-Dawley rats were randomly divided into five experimental groups. Mammary tumors were induced by intraperitoneal injection of N-methyl-N-nitrosourea (MNU). Animals from group II were treated with ketotifen for 18weeks immediately after the MNU administration, while animals from group III only received the ketotifen after the development of the first mammary tumor. Mammary tumors vascularization was assessed by ultrasonography (Doppler, B Flow and contrast-enhanced ultrasound) and immunohistochemistry (vascular endothelial growth factor-A).

KEY FINDINGS AND SIGNIFICANCE

Similar to what occurs in women with breast cancer, the majority of MNU-induced mammary tumors exhibited a centripetal enhancement order of the contrast agent, clear margin and heterogeneous enhancement. Ultrasonographic and immunohistochemical data suggest that the inhibition of mast cells' degranulation did not change the mammary tumors vascularization.

Experimental mammary carcinogenesis - Rat models

Mammary cancer is one of the most common cancers, victimizing more than half a million of women worldwide every year. Despite all the studies in this field, the current therapeutic approaches are not effective and have several devastating effects for patients. In this way, the need to better understand the mammary cancer biopathology and find effective therapies led to the development of several rodent models over years. With this review, the authors intended to provide the readers with an overview of the rat models used to study mammary carcinogenesis, with a special emphasis on chemically-induced models.

Effects of lifelong exercise training on mammary tumorigenesis induced by MNU in female Sprague-Dawley rats

Breast cancer is the most common malignancy in women worldwide. Several studies have suggested that exercise training may decrease the risk of breast cancer development. This study aimed to evaluate the effects of long-term exercise training on mammary tumorigenesis in an animal model of mammary cancer. Fifty female Sprague-Dawley rats were randomly divided into four groups: MNU sedentary, MNU exercised, control sedentary and control exercised. Animals from MNU groups received an intraperitoneal administration of N-methyl-N-nitrosourea (MNU). Animals were exercised on a treadmill during 35 weeks. When animals were killed, blood samples were collected to determine the hematocrit and to perform the biochemical analysis. Mammary tumors were collected and histologically evaluated; the expression of ERs α and β was evaluated in tumor sections by immunohistochemistry. All survived animals from both MNU groups developed mammary tumors. The number of mammary tumors (p > 0.05) and lesions (p = 0.056) was lower in MNU exercised than in MNU sedentary animals. MNU exercised animals showed lower number of malignant lesions than MNU sedentary animals (p = 0.020). C-reactive protein serum concentration was lower in exercised animals; however, the levels of 17-β estradiol were higher in exercised animals. Tumors from exercised animals exhibited higher expression of ER α than tumors from sedentary animals (p < 0.05). This study analyzes the impact of the longest exercise training protocol on mammary tumorigenesis ever performed. We concluded that the lifelong endurance training has beneficial effects on mammary tumorigenesis in female rats (reduced the inflammation, the number of mammary tumors and lesions, and histological grade of malignancy). Additionally, the mammary tumors from MNU exercised group exhibited higher immunoexpression of ER α that is an indicator of well-differentiated tumors and better response to hormone therapy.