How do cancer cells behave in space?

Cancer is caused by unrestrained division of cells, which in turn is caused by mutated genes. How and why such an uncontrolled cellular proliferation takes place is not fully understood; and this lack of understanding stands in the way of an effective cure.  One intriguing finding about the regulation of cell growth is that gravity, or the lack thereof, has a significant effect on the process. This was the topic of a recent paper by a team of scientists from Denmark and Germany, which was reported by a number of news outlets starting with Popular Science and subsequently by newspapers including the Daily Mail. The cause of excitement was an unusual question – does a trip to space hold the secret to curing cancer?

What did the researchers say?

In their paper in the FASEB (Federation of American Societies for Experimental Biology) journal , the authors note that exposure to micro-gravity environments  (i.e., the kind of weightlessness experienced in space) has a clear effect on the secretion of cytokines, small proteins that are released by cells for the purpose of sending signals to other cells, and on the expression profiles of some types of genes. Cytokines play a key role in many cellular processes associated with cancer, especially cell proliferation, the immune response to tumours, ‘programmed’ cell death, tumor invasion, etc. So, the fact that microgravity environments slow down their secretion is a good thing. Similarly, many genes involved in the regulation of cell proliferation and metastasis (spread of cancer between cells) were ‘differentially’ expressed, i.e., this change in environment had a direct effect on them – in such a way that it slowed down the proliferation of cancerous cells.

How did they figure this out?

The experiment involved some fairly complex machinery, including a way to send some parts of the experiment into outer space! There were two phases really. The first phase, before sending cells to outer space, was to simulate the effect closer to ground, in a plane that is colloquially called the “vomit comet”. If one flies a plane really fast in a steep ascent and quickly reverses direction to come back down, there will be a brief period in between when the passengers will experience weightlessness. For those few seconds, one feels as though one is floating in space. This is what the scientists made their experimental samples do. The cell cultures made several trips in these ‘parabolic flight missions’, getting 30+ instances of weightlessness in a 3 hour period within an Airbus A300. Once they were done with that, it was time to go to space. For this, the lucky few cell cultures hitched a ride on the Shenzhou 8 unmanned space flight experiment, spending about 10 days in space. Once retrieved, the samples were processed using state of the art instrumentation for measuring gene expression and cytokine levels.

How did the media report on this?

The articles in the media focused heavily on the more sensational angles. They boldly declared that the malignant cells were being ‘tamed’. They didn’t quite go as far to argue for ‘orbital health clinics’ (can the NHS actually afford that?!), which is a good thing because actually what has been shown in the research is a rather more preliminary finding than that.

The newspapers couldn’t quite resist some generalisations and simplifications though. The Mail Online stated, “the immune system is suppressed in microgravity”. It doesn’t quite do that, although some processes do helpfully slow down. But, this does raise the important question of how healthy cells fare in these same conditions. Many treatments for cancer, e.g., chemotherapy, are very efficient in killing cancer cells, but also equally efficient at killing healthy cells! This makes therapy difficult. Similarly, it would be problematic if microgravity environments lead to an overall decline in all forms of growth, and not just a targetted effect on cancerous cells.

Also, the sensational headline about antigravity is amusing but misleading. What the cells experienced was really the absence of gravity, and not some other strange physical phenomenon.

What does it mean?

A key takeaway message from these experiments is the utility of studying such diseases in microgravity environments to understanding the underlying dynamics in different environments. For instance, in addition to this Danish study, the Mail refers to other studies at NASA which explore the fact that test cultures in petri dishes could form spatial arrangements in space, akin to what happens inside the body, whereas they end up artificially flat in our laboratories on earth.

That said, there remain many thorny issues with these experiments. For instance, although the parabolic flight missions simulate weightlessness, they require a short burst of hyper-gravity on the way to the few seconds of low-gravity. So, if we really want to understand this aspect of the phenomena, it may be necessary to dedicate more payload space to such experiments in future space missions.

Ma X. et al.“Differential gene expression profile and altered cytokine secretion of thyroid cancer cells in space”. The FASEB Journal, published online, doi: 0.1096/fj.13-243287.