CancerA run a day keeps the tumour at bay

Exercise=20 protects against cancer. Researchers now understand why

Print edition |=20 Science and technology

Feb=20 27th 2016

AMPLE evidence shows = that=20 exercising regularly reduces the risk of cancer. Similarly, those who = have=20 survived the disease are less likely to see it return if they engage in = lots of=20 physical activity after treatment. All this suggests that such activity = triggers=20 a reaction in the body which somehow thwarts cancer cells, but the = details of=20 the process have remained murky. Now, a team led by Pernille Hojman at=20 Copenhagen University Hospital, in Denmark, has reported in Cell=20 Metabolism that the key to the mystery = is=20 adrenalin.

Dr Hojman began her work by verifying that = exercise truly=20 does have beneficial anti-tumour effects. She and her colleagues gave = some of=20 the mice in their laboratory activity wheels, which the animals could = run around=20 inside as much as they liked. Other mice, meanwhile, were given no = opportunity=20 to exercise beyond moving about inside their cages. The researchers then = induced=20 mice of both sorts to develop one of three types of cancer. Some, they = injected=20 with a substance called diethylnitrosamine, which causes liver cancer. = Others,=20 they injected below the skin with melanoma cells, which then set up shop = where=20 they had been injected. Others still had their tails inoculated with = melanoma=20 cells. In mice, previous experience has shown, this leads to melanomas = forming=20 in the lungs.

Macedonian=20 nationalists storm the parliament to hold on to power

Europea day=20 ago
Donald Trump=E2=80=99s=20 first 100 days

Graphic detaila day ago
America=E2=80=99s=20 economic growth slows to 0.7%

Free exchangea day ago
The=20 correspondence of Nelle Harper Lee and Wayne Flynt

Prosperoa day=20 ago
Liberty of=20 conscience and worship is in decline around the world

Erasmusa day=20 ago
Who builds=20 more houses, the Conservatives or Labour?

Speakers=E2=80=99 Cornera day ago

The results were instructive. While all mice = injected=20 under the skin with melanoma cells developed that cancer, the tumours in = animals=20 which had had access to a running wheel were 61% smaller after six weeks = than=20 were those in mice that had been unable to exercise. A similar reduction = in size=20 (58%) pertained to lung tumours. And, of the mice injected with=20 diethylnitrosamine, only 31% of those with wheels in their enclosures = developed=20 tumours at all=E2=80=94in contrast to a 75% tumour-development rate in = mice lacking=20 access to a wheel.

To try to understand why exercise does this, Dr = Hojman and=20 her team put under a microscope some of the tumours they had induced. = They found=20 that those from well-exercised mice contained more immune cells than = equivalent=20 tumours from inactive animals. Specifically, the former had double the = number of=20 cytotoxic T-cells, which kill off body cells that are damaged, = malfunctioning or=20 infected with viruses. They also had five times more natural killer = cells, a=20 type that sounds the alarm and attracts other immune cells.

In light of these discoveries Dr Hojman repeated = the=20 experiment, this time on mice that had been engineered to lack cytotoxic = T-cells. Again, she found that mice with access to wheels had smaller = tumours.=20 This suggested that the natural killer cells, not the T-cells, were the=20 responsible agents. A third experiment confirmed this. She sabotaged = natural=20 killer cells by giving mice an antibody that eliminated these cells = while=20 leaving the rest of the immune system intact. With the natural killer = cells=20 gone, the tumours of all the mice, regardless of whether or not they = could run=20 in a wheel, grew to the same size.

Dr Hojman knew from past work that epinephrine, = a hormone=20 also commonly known as adrenalin, has the potential to mobilise natural = killer=20 cells. She knew, too, that this hormone=E2=80=99s levels in the blood = rise during=20 periods of physical exertion. That led her to wonder if it is = epinephrine which=20 is behind the cancer-thwarting effects of exercise.

To find out, she ran a fourth experiment, in = which mice=20 induced to have cancer were injected either with epinephrine or with = saline. The=20 hormone performed well, reducing the growth of tumours by 61% in mice = that had=20 no access to a wheel. However, this was not as impressive as the = reduction of=20 74% which the team saw in control mice that got regular exercise. There = was,=20 they concluded, something else involved. And they found it in the form = of=20 interleukin-6.

Levels of this molecule also spike during = exercise=E2=80=94and it,=20 too, helps immune cells home in on tumours. When Dr Hojman and her = colleagues=20 exposed sedentary mice both to epinephrine and to interleukin-6, the = rodents=E2=80=99=20 immune systems attacked the tumours in their bodies as effectively as if = those=20 animals had engaged in regular wheel-runs.

Dr Hojman=E2=80=99s findings, then, suggest that = epinephrine and=20 interleukin-6 could be used as anti-tumour drugs. She is not proposing = that they=20 should be a substitute for exercise in those who are merely = lazy=E2=80=94not least=20 because exercise brings benefits beyond curbing oncogenesis. But people = who are=20 too old or too ill to be active might thus gain exercise=E2=80=99s = anticancer benefits=20 without the need to get sweaty.

View comments

Reuse = this=20 content

CancerA run a day keeps the tumour at bay

Print edition |=20 Science and technology

Latest updates

Macedonian=20 nationalists storm the parliament to hold on to power

Donald Trump=E2=80=99s=20 first 100 days

America=E2=80=99s=20 economic growth slows to 0.7%

The=20 correspondence of Nelle Harper Lee and Wayne Flynt

Liberty of=20 conscience and worship is in decline around the world

Who builds=20 more houses, the Conservatives or Labour?

Climate changeThe Arctic as it is known today is almost = certainly=20 gone

End-of-life careHow to have a better = death

Daily chartDonald Trump=E2=80=99s first 100 = days

LanguageWhy translation platforms cannot replace humans=20

CancerA run a day keeps the tumour at bay

print-edition=20 icon Print edition |=20 Science and technology

Latest updates

Macedonian=20 nationalists storm the parliament to hold on to power

Donald Trump=E2=80=99s=20 first 100 days

America=E2=80=99s=20 economic growth slows to 0.7%

The=20 correspondence of Nelle Harper Lee and Wayne Flynt

Liberty of=20 conscience and worship is in decline around the world

Who builds=20 more houses, the Conservatives or Labour?

Print edition |=20 Science and technology