Abstract 732: The impact of aerobic exercise on the tumor microenvironment
Authors: Wiggins Jennifer M. , Lee Jennifer , Rice Lori , Lepler Sharon , Pampo Christine , Siemann Dietmar 
Published: July 2016

Intratumoral hypoxia (pO2 &lt; 10mmHg) is associated with aggressive tumor progression, radiation resistance, suppression of the immune anti-tumor response and poor patient outcome. It is often found in solid tumors, and can constitute a major obstacle to anticancer therapy. The primary cause of abnormal oxygen tensions in tumors is the aberrant tumor vasculature, characterized by tortuous, leaky and immature vessels. A number of intervention strategies designed to overcome tumor hypoxia and improve patient outcome have been investigated including high oxygen content breathing and the use of bioreductive prodrugs, but these have had only moderate success in the clinic.

The goal of the present investigations was to determine whether aerobic exercise could be applied to improve tumor perfusion, oxygenation and the immune anti-tumor response in breast cancer and fibrosarcoma models. Such modulation of the tumor physiology and host environment would be expected to lead to enhanced antitumor efficacy when combined with radiotherapy or chemotherapy.

The effects of mild and moderate intensity treadmill running were studied in mice bearing syngeneic murine mammary carcinomas (4T1 and EMT6) or fibrosarcomas (KHT). The exercise intensities were determined by measuring the anaerobic threshold, which was assessed by measuring the steady rise in blood lactate during an exercise bout. Mice were orthotopically injected with tumor cells and exercise commenced when tumors reached a size of ∼500 mm3 (single) or ∼200 mm3 (repeated bouts). Once size was attained, mice were exposed to either mild (12 m/min) or moderate (18 m/min) intensity exercise. Controls for each treatment consisted of sedentary mice exposed to a stationary treadmill for the equivalent amount of time. At the end of the exercise period tumors were analyzed by histology to assess for physiological changes. Specifically, blood was collected and tumors were harvested, sectioned and evaluated by immunofluorescence. The detection of open blood vessels (Hoechst-33342) was used as an indirect indicator of perfusion and while the hypoxia marker (EF5) was used to determine the level of tumor hypoxia. Both markers were quantified using a Chalkley counter and ImageJ NIH software. In addition, the evaluation of tumor infiltrating immune cells after exercise compared to rest is under active investigation by histological analysis. Furthermore, plasma samples from exercised mice are being tested for immune related cytokines, chemokines and growth factors and compared to those from sedentary controls.

Results to date indicate no difference in tumor growth rate between sedentary and exercising mice. Mild daily bouts of aerobic exercise do not affect the total number of tumor blood vessels but do increase the number of blood vessels that are actively perfused. These findings suggest that exercise may have potential utility in overcoming the aberrant microenvironmental conditions associated in solid tumors with therapeutic resistance.

Citation Format: Jennifer M. Wiggins, Jennifer Lee, Lori Rice, Sharon Lepler, Christine Pampo, Dietmar Siemann. The impact of aerobic exercise on the tumor microenvironment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 732.