INTRODUCTION T HE DEVELOPMENT OF CANCER is determined by a combination of heredity and envi- ronment. However, the incidence and prog- ress of the disease are most probably depen- dent upon the function of health-promoting genes that produce the correct synthesis of proteins to sustain the viability of cells and maintain or increase the resistance to damage and damage repair processes. Evidence has been accumulating that indicates that regular physical exercise significantly reduces the in- cidence of cancer. The beneficial effect can be as high as 50% for a variety of cancers (10, 15, 29, 31). Chronic physical exercise may de- crease risk by affecting natural immunity, in- cluding the rate of cytokine production, hor- monal changes, and antioxidant defense, or by improving energy balance (5, 6). Oxidative damage to DNA may also under- pin certain cancers, resulting in the loss of function of tumor-suppressor genes and acti- vation of tumor promoting genes with subse- quent malignancy (1, 20). Our recent study led us to suggest that physical exercise could be an active tool against cancer (25). We found that as a result of 9 weeks of swimming 213 1 Laboratory of Exercise Physiology, School of Sport Sciences, Semmelweis University Budapest, and 2 National In- stitute of Oncology, Budapest, Hungary. 3 Tokyo Metropolitan Institute of Gerontology, Tokyo, and 4 Department of Biochemistry, School of Pharmaceutical Sciences, Toho University, Funabashi, Japan. 5 School of Kinesiology, Faculty of Health Science, University of Western Ontario, Canada. Rapid Letter Attenuation of the Development of Murine Solid Leukemia Tumor by Physical Exercise ZSOLT RADAK, 1 DEZSO GAAL, 2 ALBERT W. TAYLOR, 1,5 TAKAO KANEKO, 3 SHUNICHI TAHARA, 3 HIDEKO NAKAMOTO, 4 and SATARO GOTO 4 ABSTRACT The active involvement of physical exercise in the evolution of a variety of cancers is well documented. However, its role in solid leukemia tumor development is essentially unknown. Solid leukemia tumor cells were trans- planted into 21 hybrid BDF1 control mice, exercise-trained mice that did not exercise during leukemia and exer- cise-trained mice that exercised during leukemia. The tumor size of the continuously exercising group was ,50% of that of control and exercise-terminated animals 18 days after the transplantation. The activity of antioxidant en- zymes and the levels of lipid peroxidation and 8-hydroxy-29-deoxyguanosine were not different in the tumors of the three groups. The level of carbonylated proteins was smaller in tumors of continuously exercising animals. The mutant form of cell regulatory protein p53 and vascular endothelial growth factor were present in similar amounts in the tumor cells of each group. On the other hand, the protooncogene Ras and I-kB proteins were pres- ent in higher concentrations in tumors of continuously exercising rats. The present data suggest that exercise dur- ing leukemia attenuates the development of tumors in mice. The selective alteration of regulatory proteins might play a role in the beneficial effects of exercise during leukemia. Antioxid. Redox Signal. 4, 213–219. ANTIOXIDANTS & REDOX SIGNALING Volume 4, Number 1, 2002 © Mary Ann Liebert, Inc.