Awarded joint 2nd prize for Access to Understanding 2013
A mutation that allows cells to grow out of control could also provide a new way to target and destroy cancer cells. This potential Achilles' heel comes from a mutation in a gene called PTEN, which is found in a wide range of cancers.
PTEN is one of many tumour suppressor genes that we have to prevent our cells from growing out of control. If the PTEN gene stops working because of a mutation, it can cause tumours to develop – indeed many tumours have a mutated form of PTEN. However when a door closes, a window opens: the PTEN mutation helps the tumour to grow, but it could also mark it out as a target.
3D-rendered illustration of cancer cells
Shutterstock Image ID: 159517493 Copyright: xrender
Researchers from the Institute of Cancer Research, London, found that switching off another gene known as NLK killed tumour cells that had the PTEN mutation. This makes NLK a good target for drug developers to create a new cancer treatment.
The difficult thing about cancer is that it is made of us – our own cells mutate and grow wildly out control. That means it is unlikely there will ever be a quick fix. Antibiotics work efficiently because bacteria are so different to us that we can develop drugs that target their weaknesses yet barely affect our own cells. But how do you kill something that is the same as you? Current treatments for cancer cause a lot of side-effects in patients because as they try to kill the cancer they also do damage everything else in the body. This is why finding ways to target cancer specifically is so important.
There are several proteins in our cells which we cannot live without, and if the genes responsible for producing those proteins are mutated or switched off the cells die. Targeting these proteins and genes are rarely going to be useful for treatments, as they will kill the patient about as quickly as they kill the cancer. So Alan Ashworth and colleagues set out to find proteins that are not essential in healthy cells, but cells with the PTEN mutation cannot live without. This would pave the way for designing drugs that target the tumour and leave healthy cells alone.
The researchers took samples of tumour cells with and without the mutation, and switched off genes for important proteins that are used for regulating lots of processes in the cell. To do this they used small molecules of RNA (DNA's less famous cousin) which interfere with the processes of specific genes. This is why these molecules are known as small interfering RNA (or siRNA). They block the chain of events that allow a gene to produce a protein, effectively switching it off. By switching off 779 genes individually, they could look for ones where cells with the PTEN mutation died and cells without the mutation survived.
Dividing cancer cells
Shutterstock Image ID: 158445182 Copyright: Juan Gaertner
This is how the researchers discovered the powerful effect of switching off the NLK gene. They are not certain how this works but it appears to protect a protein called FOXO1 that can act as a backup tumour suppressor and cause the cancer cell to die. When PTEN is mutated, the FOXO1 protein becomes vulnerable to a process called phosphorylation, which means it is ejected from the cell nucleus and destroyed. NLK is one of the proteins that phosphorylates FOXO1 and so by switching off the NLK gene, FOXO1 is able to do its job.
This is just the start of a long journey from the lab to (potentially) the hospital. The researchers have shown that targeting NLK is more likely to kill mutated cells than normal cells, but that does not mean it is safe. NLK still has a role to play in healthy cells and preventing it from working is likely to have side-effects, but it could be worthwhile if this approach can kill tumours. The next stage is to develop a drug to stop the NLK protein from working, so that it can be tested further in cells and in living organisms.
This entry describes research published in the following article, selected by Breakthrough breast cancer:
Ana M. Mendes-Pereira, Christopher J. Lord, and Alan Ashworth PLoS One (2012) 7(10) e47249
Access to Understanding entrants are asked to write a plain English summary of a research article. For Access to Understanding 2013 there were 9 articles to choose from, selected by the Europe PMC funders.
The articles are all available from Europe PMC, are free to read and download, and were supported by one or more of the Europe PMC funders.
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