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

A novel mouse model of voluntary stretching and its application in breast cancer research

Background

Stretching exercises such as yoga are recommended for cancer survivors to manage symptoms and promote wellbeing in clinical settings. Although other types of exercise (e.g. running) can reduce the growth of tumors in animal models, the role of stretching on tumor growth remains unclear, and the lack of a preclinical self-stretching model has impeded mechanistic studies on health benefits of stretching. We sought to develop a voluntary stretching animal model to address this research gap and apply it to breast cancer research.

Methods

Using food, water, and enrichment in the home cage as motivators for stretching, a two-week 24/7 behavior monitoring was conducted in a video-based customizable home-cage behavior tracking system, Noldus PhenoTyper, to promote self-stretching in FVB mice. Subsequently, this model was utilized in a comparative study of voluntary stretching and voluntary running on tumor growth and plasma protein profiles in the MET-1 orthotopic mammary tumor FVB mouse model.

Results

The new voluntary stretching model effectively elicited mouse self-stretching in the custom cage setting in the long-term observation and significantly inhibited tumor growth as effectively as voluntary wheel running. Moreover, plasma proteomic analysis demonstrated that voluntary stretch versus voluntary running distinctly impacted systemic protein profiles, possibly linking to different cellular and molecular mechanisms underlying anti-cancer effects and, potentially, exercise-induced benefits in other health conditions.

Conclusion

Our work provides the first preclinical voluntary stretching model, which may be well suited to breast cancer research and a valuable research tool to facilitate investigations of stretching health benefits across various research fields.

Exercise-induced extracellular vesicles in reprogramming energy metabolism in cancer

Cancer is caused by complex interactions between genetic, environmental, and lifestyle factors, making prevention strategies, including exercise, a promising avenue for intervention. Physical activity is associated with reduced cancer incidence and progression and systemic anti-cancer effects, including improved tumor suppression and prolonged survival in preclinical models. Exercise impacts the body's nutrient balance and stimulates the release of several exercise-induced factors into circulation. The mechanisms of how exercise modulates cancer energy metabolism and the tumor microenvironment through systemic effects mediated, in part, by extracellular vesicles (EVs) are still unknown. By transferring bioactive cargo such as miRNAs, proteins and metabolites, exercise-induced EVs may influence cancer cells by altering glycolysis and oxidative phosphorylation, potentially shifting metabolic plasticity - a hallmark of cancer. This short review explores the roles of EVs in cancer as mediators to reprogram cellular energy metabolism through exchanging information inside the tumor microenvironment, influencing immune cells, fibroblast and distant cells. Considering this knowledge, further functional studies into exercise-induced EVs and cellular energy production pathways could inform more specific exercise interventions to enhance cancer therapy and improve patient outcomes.

An integrated framework for the study of exercise across the postdiagnosis cancer continuum

Exercise plays many important roles across the entire cancer continuum that have been described in previous frameworks. These frameworks, however, have generally provided a simplified description of the roles of exercise postdiagnosis. The modern cancer treatment landscape has become complex and often consists of multiple lines of multimodal treatments combined concurrently and/or sequentially and delivered over many months or years. This complexity requires a more multifaceted and targeted approach to the study of exercise after a cancer diagnosis. Here, we propose a new integrated framework-Exercise Across the Postdiagnosis Cancer Continuum (EPiCC)-that highlights the distinct roles of exercise for disease treatment and supportive care from diagnosis until death. We also propose new terminology to clarify the distinct roles of exercise that emerge in the context of the modern cancer treatment landscape. The EPiCC Framework is structured around multiple sequential cancer treatments that highlight six distinct cancer treatment-related time periods for exercise-before treatments, during treatments, between treatments, immediately after successful treatments, during longer term survivorship after successful treatments, and during end of life after unsuccessful treatments. The EPiCC Framework proposes that the specific roles of exercise as a disease treatment and supportive care intervention will vary depending on its positioning within different cancer treatment combinations. As a cancer treatment, exercise may serve as a "priming therapy", primary therapy, neoadjuvant therapy, induction therapy, "bridging therapy", adjuvant therapy, consolidation therapy, maintenance therapy, and/or salvage therapy. As a supportive care intervention, exercise may serve as prehabilitation, intrahabilitation, interhabilitation, rehabilitation, "perihabilitation", health promotion/disease prevention, and/or palliation. To date, exercise has been studied during all of the cancer treatment-related time periods but only in relation to some cancer treatments and combinations. Moreover, fewer studies have examined exercise across multiple cancer treatment-related time periods within any cancer treatment combination. Future research is needed to study exercise as a disease treatment and supportive care intervention within and across the distinct cancer treatment-related time periods contained within different cancer treatment combinations. The aim of the EPiCC Framework is to stimulate a more targeted, integrated, and clinically-informed approach to the study of exercise after a cancer diagnosis.

From sweat to hope: The role of exercise-induced extracellular vesicles in cancer prevention and treatment

The benefits of regular physical exercise on cancer prevention, as well as reducing fatigue, treatment side effects and recurrence, and improving quality of life and overall survival of cancer patients, are increasingly recognised. Initial studies showed that the concentration of extracellular vesicles (EVs) increases during physical activity and that EVs carry biologically active cargo. These EVs are released by blood cells, skeletal muscle and other organs involved in exercise, thus suggesting that EVs may mediate tissue crosstalk during exercise. This possibility triggered a great interest in the study of the roles of EVs in systemic adaptation to exercise and in their potential applications in the prevention and treatment of various diseases, including cancer. This review presents studies exploring the concentration and molecular cargo of EVs released during exercise. Furthermore, we discuss putative stimuli that may trigger EV release from various cell types, the biological functions and the impact of exercise-induced EVs on cancer development and progression. Understanding the interplay between exercise, EVs, and cancer biology may offer insights into novel therapeutic strategies and preventive measures for cancer.

The Influence of Exercise on Cancer Risk, the Tumor Microenvironment and the Treatment of Cancer

There are several modifiable factors that can be targeted to prevent and manage the occurrence and progression of cancer, and maintaining adequate exercise is a crucial one. Regular physical exercise has been shown to be a beneficial strategy in preventing cancer, potentially amplifying the effectiveness of established cancer therapies, alleviating certain cancer-related symptoms, and possibly mitigating side effects resulting from treatment. Nevertheless, the exact mechanisms by which exercise affects tumors, especially its impact on the tumor microenvironment (TME), remain uncertain. This review aims to present an overview of the beneficial effects of exercise in the context of cancer management, followed by a summary of the exercise parameters, especially exercise intensity, that need to be considered when prescribing exercise for cancer patients. Finally, we discuss the influence of exercise on the TME, including its effects on crucial immune cells (e.g., T cells, macrophages, neutrophils, natural killer cells, myeloid-derived suppressor cells, B cells), intratumor angiogenesis, and cancer metabolism. This comprehensive review provides up-to-date scientific evidence on the effects of exercise training on cancer and offers guidance to clinicians for the development of safe and feasible exercise training programs for cancer patients in clinical practice.

Potential involvement of neutrophils on exercise effects in breast cancer malignancy

PURPOSE

This review aimed to comprehensively explore and elucidate multifaceted neutrophils in breast cancer, particularly in the context of physical activity. Neutrophils play a critical role in the tumor microenvironment and systemic immune response, despite their short half-life and terminal differentiation. Through a thorough review of research related to changes in immunity in breast cancer during exercise, this review aims to provide comprehensive insights into immunological changes, especially focusing on neutrophils. Recognizing that much of the existing research has predominantly focused on T cells and nature killer (NK) cells, our review seeks to shift the spotlight toward understanding how exercise affects neutrophils, a less-explored but critical immune response component in breast cancer.

METHODS

This study involved an extensive review of the literature (from 2000 to 2023) using the PubMed, Science Direct, and Google Scholar databases. The keywords chosen for the searches were "immune cells and exercise," "exercise and breast cancer," "tumor microenvironment and neutrophils," and "neutrophils and exercise and breast cancers."

RESULTS

Neutrophils in the tumor microenvironment can exhibit distinct phenotypes and functions. These differences have yielded conflicting results regarding tumor progression. Exercise plays a positive role in breast cancer and alters the immune system. Physical activity can quantitatively and functionally regulate neutrophils under various conditions such as metabolic disruption or senescence.

CONCLUSION

This short communication outlines exercise-induced neutrophil diversification and its role in breast cancer progression, both within and systemically within the tumor microenvironment. Exercise may provide benefits through the potential neutrophil involvement in breast cancer.

Exercise improves the outcome of anticancer treatment with ultrasound-hyperthermia-enhanced nanochemotherapy and autophagy inhibitor

It has been shown that exercise has a direct impact on tumor growth along with functional improvement. Previous studies have shown that exercise decreases the risk of cancer recurrence across various types of cancer. It was indicated that exercise stimulates the immune system to fight cancer. Previous study demonstrated that pulsed-wave ultrasound hyperthermia (pUH) combined with PEGylated liposomal doxorubicin (PLD) and chloroquine (CQ) inhibits 4T1 tumors growth and delays their recurrence. In this study, we investigated if the combinatorial treatment with high-intensity interval training (HIIT) combined with pUH-enhanced PLD delivery and CQ improved the outcome. The mouse experiment composed of three groups, HIIT+PLD+pUH+CQ group, PLD+pUH+CQ group, and the control group. HIIT+PLD+pUH+CQ group received 6 weeks of HIIT (15 min per day, 5 days per week) before 4T1 tumor implantation. Seven days later, they received therapy with PLD (10 mg/kg) + pUH (3 MHz, 50% duty cycle, 0.65 W/cm2, 15min) + CQ (50 mg/kg daily). Results showed that HIIT+PLD+pUH+CQ significantly reduced the tumor volumes and brought about longer survival of tumor-bearing mice than PLD+pUH+CQ did. Blood cell components were analyzed and showed that neutrophil and reticulocytes decreased while lymphocytes increased after exercise.