In the news
6 Sep 2008
11 October 2007
Nobel prize 'knockout mice' research already superseded by ‘switching off’ human genes in the test tube
Gene targeting research in mice, which was recently1 awarded the Nobel Prize for Medicine, is already an outdated technique which is being superseded by cutting-edge non-animal technology, says the Dr Hadwen Trust.
The technique developed by scientists Mario Capecchi, Oliver Smithies and Briton Martin Evans2 is called gene targeting. It involves silencing or ‘knocking out’ specific genes in mice to identify their function in the hope of gaining insight into human diseases3.
However, the Dr Hadwen Trust4 warns that targeted gene disruption in mice is already out-dated. It is time consuming, has low efficiency, can cause substantial suffering to animals and is of questionable relevance to human physiology. Ironically, GM mouse research in cystic fibrosis (the specialist area of the British Nobel recipient) has performed particularly poorly.
By contrast, modern non-animal techniques being funded by the charity, are already superseding much out-dated knockout mice work and offering far greater relevancy to many human disease.
Says Nicky Gordon, Dr Hadwen Trust:
“Despite much optimistic hype, many scientists are now recognising that mouse ‘models’ don’t represent a gold standard because human genes and mouse genes can have unexpectedly different functions. It can never be safely assumed that results from gene targeting in mice can applied to a human disease, and often the dissimilarity is startling. It is ironic that just as the Nobel Prize is being awarded, the very technique it highlights is already being superseded by methods more directly applicable to humans because they avoid the unnecessary distraction of animal experiments.
In selecting discoveries based on animal research, the Nobel Committee risks falling into the trap of assuming that GM animal research is going to be valid and predictive for humans, which in so many cases it is proved not to be. If researchers had not focused so much attention on GM mice and instead helped to develop relevant methods based on human genes, who knows what greater progress we might have made in the fight against disease.”
Knockout mice – how it works
To produce GM mice, researchers have to genetically modify mouse stem cells when they are still an embryo and observe what happens as the mouse develops. As this will be species specific, researchers concurrently use highly controversial human embryonic stem cells to see if the equivalent gene has the same effect. It is at this stage that all too often researchers find that the GM mouse experiments have not been relevant to humans.
Lack of applicability to humans – some examples:
1. Only recently, researchers from the US and Canada studying heart disease found that, although their gene-mutated mice5 showed an improvement in heart function, human patients with a mutation in the equivalent gene show such severely reduced heart function that two patients with the mutation required a heart transplant before they reached the age of 30yrs6 .
2. A gene called “Large tumour suppressor 2” was known to prevent tumour development in people, yet it didn’t have that effect in mice. The mice with this gene knocked-out (so that tumour suppression would be switched off) still did not develop cancer.
3. The “klotho” gene in humans is known to be involved in coronary artery disease and heart disease. But this wasn’t the case in the knockout mice. Mice with the klotho gene knocked out were very small and sickly and died prematurely at 9 or 10 weeks of age, but they did not suffer any heart problems.
4. In cystic fibrosis (CF) research, mouse ‘models’ have delayed research and could have held up the search for a treatment for the disease. Mice with mutations in the equivalent gene that is at fault in CF patients are being used to study the condition, but often do not suffer from any lung disease, which is fatal in 95% of human patients.
Non-animal ‘RNA interference’ technology – how it works
The Dr Hadwen Trust is funding a range of projects at leading British Universities using an established technique called RNA interference, that looks set to have the potential to completely replace the use of GM knockout mice. The research works by targeting and silencing human genes in human cells and tissue. Unlike the traditional method, this new technique can use any cell from the human body and so doesn’t rely on the use of controversial embryonic stem cells. The ability to inactivate selected genes in human cells in the test tube could have a dramatic impact on biomedical research, not least because it studies the correct gene in the right animal (humans) instead of the wrong gene in the wrong animal (mice).
RNAi is an established and proven technique, but this is the first time it has been applied to replace the use of GM mice. The Dr Hadwen Trust is funding research at the University of York, Kings College London and Manchester University to develop this technique. The charity, which combines vital human disease research with the development of new techniques to replace animal experiments, has identified the replacement of transgenic animals as a key strategic priority. Recent years have seen a rapid rise in the number of genetically modified animals used in experiments. Over 1 million procedures were conducted on transgenic animals in the UK alone in 2006, representing 34% of all procedures. An additional 327,000 procedures were conducted on animals with a harmful genetic defect7.
NOTES
1 8 October 2007
2 Professor Capecchi at the University of Utah; Sir Martin Evans at the University of Cardiff; Professor Smithies of the University of North Carolina at Chapel Hill.
3 More than 10,000 mice genes (approximately half of the total) have so far been ‘knocked out’, and more than 500 different mouse ‘models’ of human disorders have been developed.
4 The Dr Hadwen Trust is the UK’s leading medical research charity that funds and promotes exclusively non-animal techniques to replace animal experiments. Our vital work benefits humans with the development of more relevant and reliable science whilst also benefiting laboratory animals. We believe that excellence in medical research can and should be pursued without animal experiments.
5 Odom, D.T. et al (2007) Tissue-specific transcriptional regulation has diverged significantly between human and mouse. Nature Genetics, 39(6):730-32
6 Haghighi, K. et al (2003) Human phospholamban null results in lethal dilated cardiomyopathy revealing a critical difference between mouse and human. The Journal of Clinical Investigation, 111: 869-876
7 Statistics of Scientific Procedures on Living Animals – Great Britain, 2006, released in a summary, on the Home Office website on 23 July 2007. The complete document is available at http://scienceandresearch.homeoffice.gov.uk/animal-research/publications-and-reference/statistics/?version=2
