Exercise delays allogeneic tumor growth and reduces intratumoral inflammation and vascularization

Abstract

This investigation determined whether daily strenuous exercise would alter the progression and regression of an allogeneic lymphoid tumor in mice. We also determined whether exercise would alter the cellular composition and vascularity of the tumor. Female BALB/c mice (age 6-8 wk) were randomly assigned to sedentary control (Con) or daily exercised groups (EXH). EXH mice ran on a treadmill at incremental speeds (20-40 m/min) for 3 h or until fatigue. Each mouse was subcutaneously injected with 20 x 10(6) EL-4 lymphoma cells immediately after the first exercise bout (day 1) and run daily. Tumor volume was measured daily with calipers. In some experiments, mice were euthanized on days 5-10, 12, and 14. Tumors were excised and stained with hematoxylin and eosin or for Factor VIII-associated antigen using immunohistochemistry and analyzed in a blinded fashion under a light microscope. There was no significant treatment main effect found for tumor volumes. Interestingly, a significant treatment x time interaction was found, such that there was a 2-day delay in peak tumor volume and a more rapid tumor regression in EXH. Tumors isolated from Con exhibited significantly higher numbers of apoptotic bodies, blood vessels, macrophages, and neutrophils when compared with EXH. Intratumoral lymphocytes were higher in Con early in tumor growth but higher in EXH at peak tumor size. These data indicate that daily strenuous exercise may influence tumor growth by affecting the microenvironment of the tumor, resulting in a delay in tumor growth and a more rapid regression.

Figures

Fig. 1

A representative hematoxylin and eosin-stained slide (×400 magnification) from a subcutaneous EL-4 tumor from a control mouse. Individual components of the tumor were identified by a blinded observer. a, Lymphocyte; b, blood vessel; c, macrophage (with ingested cellular debris); d, mitotic figure; e, apoptotic body; f, EL-4 cell; g, neutrophil.

Fig. 2

Effects of daily exhaustive exercise on the growth of an EL-4 allogeneic tumor in mice [n = 8 exercise group (EXH) and n = 7 control group (Con)]. Error bars were excluded for clarity. *Two-way repeated-measures ANOVA results revealed a significant treatment × time interaction indicating that the 2 groups exhibited different tumor growth patterns (P < 0.05).

Fig. 3

EL-4 density in tumor cross sections obtained from Con and EXH. There was a significant time main effect and a significant time × treatment interaction, such that Con tumors contained lower densities of EL-4 cells early in development (day 7) but a higher density at day 10. *Significant difference between Con and EXH (P < 0.006).

Fig. 4

Macrophage density in tumor cross sections obtained from Con and EXH. There was a significant time and treatment main effect. *Significant difference between Con and EXH (P < 0.006).

Fig. 5

Neutrophil density in tumor cross sections obtained from Con and EXH. There was a significant time and treatment main effect. *Significant difference between Con and EXH (P < 0.006).

Fig. 6

Lymphocyte density in tumor cross sections obtained from Con and EXH. There was a significant time effect and a time × treatment interaction. *Significant difference between Con and EXH (P < 0.006).

Fig. 7

Visually determined blood-vessel density in tumor cross sections obtained from Con and EXH. There were significant main effects for time and treatment. *Significant difference between Con and EXH (P < 0.006).

Fig. 8

Tumor sections from Con (A) and EXH (B) on day 10 stained with antibody against factor VIII-associated antigen. Arrows indicate factor VIII-associated antigen staining.

Fig. 9

Density of mitotic figures (a marker for cell division) in tumor sections from Con and EXH. There were significant main effects for time, treatment, and their interaction. However, post hoc analysis failed to detect any significant differences between groups on any given day after Bonferroni adjustment.

Fig. 10

Density of apoptotic bodies in tumor sections from Con and EXH. There were significant main effects for time, treatment, and their interaction. *Significant difference between Con and EXH (P < 0.006).

Fig. 11

Necrotic area of tumor sections from Con and EXH. There was a significant time main effect but no treatment or time by treatment interaction. *Significant difference between Con and EXH (P < 0.006).