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Exercise starves cancer cells in mice \u2013 and perhaps in humans too<\/p>\n
Alfredas Pliadis\/Xinhua\/Alamy<\/p>\n<\/p>\n
Exercise can slow tumour growth in mice by shifting the body\u2019s metabolism so that muscle cells, rather than cancer cells, take the glucose and grow. A similar process may occur in people.<\/p>\n
It is well known that exercise is linked to a lower risk of cancer<\/a> and that fitter people are more likely to survive it, but the mechanisms behind this are only partly understood. Some of exercise\u2019s influence seems to come via impacts on the community of microbes in our guts<\/a> and through its effects on the immune system<\/a>.<\/p>\n To examine another possible route, Rachel Perry<\/a> at Yale School of Medicine and her colleagues have injected breast cancer cells into 18 mice \u2013 12 of which were fed a diet that caused obesity, which worsens the progression of several types of cancer \u2013 and let half the animals run as much or as little as they wanted on an exercise wheel.<\/p>\n They found that after four weeks, tumours in obese mice that chose to exercise were 60 per cent smaller than those in obese mice that didn\u2019t have access to a working wheel \u2013 and also slightly smaller than those of sedentary mice fed a normal diet. A 30-minute bout of exercise was tied to increased uptake of oxygen and the key energy source glucose in skeletal and cardiac muscles, as well as decreased glucose uptake in tumours.<\/p>\n \u201cThis work reveals that aerobic fitness fundamentally reshapes metabolic competition between muscle and tumours,\u201d says Perry. \u201cImportantly, the exercise intervention was voluntary. We\u2019re not talking about training for a marathon-type exercise, just what the mice wanted to do.\u201d<\/p>\n The researchers analysed gene activity and identified 417 genes in key metabolic pathways in mice that change as a result of exercise, essentially meaning\u00a0the muscle tissues metabolise glucose more and the tumour tissues metabolise it less.<\/p>\n In particular, the researchers say down-regulation in cancer cells of mTOR, a protein involved in cell growth, may be restricting tumour growth.<\/p>\n Perry says that because these metabolic pathways are very similar across mammals, she would expect the phenomenon to extend to people, including those without obesity. Indeed, the researchers say that similar changes in gene activity have been reported in humans with cancer when they exercise.<\/p>\n \u201cIt is another mechanism demonstrating how exercise creates a more cancer-suppressive environment,\u201d says Rob Newton<\/a> at Edith Cowan University in Perth, Australia. \u201cWe need a clinical trial in people, but I really can\u2019t see any reason why you wouldn\u2019t have a similar effect in humans.\u201d<\/p>\n Perry says metabolism happens in all tissues and is affected by both the microbiome and the immune system. \u201cIt\u2019s possible that metabolic alterations could be the missing link between exercise, the microbiome and the immune system, and tumour growth,\u201d she says. \u201cBut I would be shocked if the beneficial effects of exercise weren\u2019t due to multiple mechanisms.\u201d<\/p>\n