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Experimenting with zinc fingers on rabbits and patients


Experiments with zinc fingers: 'The mouse ear model'
Aaron Klug Scientist
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Now I'll return to Sangamo, as I said Sangamo made zinc fingers against VEGF but by this time RNAi. RNAi interference appeared on the scene and that's pretty powerful in stopping gene development. It doesn't always work, sometimes you have to try four, five times with different sequences. It doesn't seem to have that specificity that zinc fingers can produce but you can make RNAi pretty cheaply. You can use a whole range of RNAis. So that's good at repressing genes but what they can't do is switch on a gene. So I think a lot of the work that Sangamo is doing is activating genes and so to activate a gene or to manipulate a gene, there's straight forward... you make a zinc finger to target the right region and you fuse it to some kind of affected domain. Affected domain can be an activation domain, it can be a nuclease domain. I wrote this in '94 that is to chop up the gene, the nuclease, to make... in fact to disable a gene. And in fact, I did make one with an Israeli group which didn't work out. Somebody wrote to me they wanted to knock out a tomato virus and this is a lady called Dina Raveh and we sent her three fingers, for the particular target, but the nuclease domain she had chosen still had a certain amount of DNA binding, it wasn't a pure catalytic domain, so it bound to other places... she had minor cuts elsewhere so if you tried to use this, switch off the virus, it would be... it would start making cuts in the host, because you see it's not too fussy. So this illustrates the point about having high specificity. And having a pure nuclease domain. Now I'll talk later about the nuclease domain because that is what led to what's now called gene correction, or gene editing. But that will be the punch line.

I'll come back to VEGF. So VEGF, as I said, in a normal production of vasculature the first thing to do is produce capillaries. Capillaries have to grow and so on and then you start making arteries, there's a whole set of genes after VEGF, there's angiopoietin and many others. Now the... so Sangamo showed that you could switch on VEGF, we know obviously, but pretty nicely with three zinc fingers or six zinc fingers, but the point of it was that the... you had to do it in an animal. This was one that had been done in cell lines, in human kidney cell lines. And so they did it and they decided that they would... where you need to switch on the vasculature now the real target, and I don't mean to make a pun, is the heart because people had been trying for quite a time how to grow new blood vessels for people that had coronary disease, so you make new blood vessels and there were various people trying stem cell, putting stem cells in to the heart because supposedly they'll turn into blood cells under the right conditions. Some people are actually injecting, I don't know how they do this, this is in monkeys, but now starting it in humans, apparently you can do this, you can get ethical approval, injecting VEGF into hearts of people who have serious heart disease. It's probably something of a last resort so apparently, it's permitted ethically. But what this a rather late stage to do this in, so the... but there is a disease which isn't as debilitating as coronary disease, it's called peripheral arterial obstructive disease, it leads to a condition called claudication where the people have great pains in their legs mostly because the arteries are blocked, they're furred up and so there are treatments for it, or pills that people can take to reduce it and so on. But the obvious target would be to try to grow new arteries.

So Sangamo started, together with... collaborating with various academical laboratories, a program to see if they could grow new vasculature in patients with peripheral arterial obstructive disease. Sometimes it's called PAD, peripheral arterial disease, sometimes obstructive is left out, the British do, one is PAD the other is PAOD, but they then to say PAD, of which there are 8 million patients in the United States. Now this will be a costly business. So Sangamo, this is the way things work in biotechnology, we try to make about $22 million on a company called Edwards Life Sciences to start... they've done the basics, which I'll describe in a moment, to start doing... applying for the clinical trials in such patients of whom I have said there were 8 million. So the way you proceed is this, this is interesting because it's my first... I'm on the scientific advisory board, it's one of my first encounters with the progress of a drug to trials. Cambridge anti-body technology we haven't talked about, I have watched that as well, so I do have some experience but this was the first time with the zinc fingers. So what they do, the first thing you do is there's a model called 'the mouse ear model', the ear of a mouse is pretty transparent, you can see it by eye with a low power microscope or a low power lens, you can see the blood vessels. Now, as I said, VEGF, this is obviously a target other people have been trying, obviously wanting to do things in the heart and also perhaps in the limbs. So the... what companies had done had been to patent the different splicing isoforms of VEGF and they tried them one at a time. This is all in the literature and they do grow, you can see in the ear of a mouse very easy to see the new capillaries. You can look at the mouse, you can do the... you simply inject the plasmid of DNA into the... then miraculously the DNA gets into the nucleus, this is standard stuff now. You can help it on its way with a retrovirus, in fact plasma injection or by lipo infection, it's actually pretty efficient, as I said. Nowadays there's a thing called the MAXA which gives you 70% success in many places. So you can see the new blood vessels develop.

Born in Lithuania, Aaron Klug (1926-2018) was a British chemist and biophysicist. He was awarded the Nobel Prize in Chemistry in 1982 for developments in electron microscopy and his work on complexes of nucleic acids and proteins. He studied crystallography at the University of Cape Town before moving to England, completing his doctorate in 1953 at Trinity College, Cambridge. In 1981, he was awarded the Louisa Gross Horwitz Prize from Columbia University. His long and influential career led to a knighthood in 1988. He was also elected President of the Royal Society, and served there from 1995-2000.

Listeners: Ken Holmes John Finch

Kenneth Holmes was born in London in 1934 and attended schools in Chiswick. He obtained his BA at St Johns College, Cambridge. He obtained his PhD at Birkbeck College, London working on the structure of tobacco mosaic virus with Rosalind Franklin and Aaron Klug. After a post-doc at Childrens' Hospital, Boston, where he started to work on muscle structure, he joined to the newly opened Laboratory of Molecular Biology in Cambridge where he stayed for six years. He worked with Aaron Klug on virus structure and with Hugh Huxley on muscle. He then moved to Heidelberg to open the Department of Biophysics at the Max Planck Institute for Medical Research where he remained as director until his retirement. During this time he completed the structure of tobacco mosaic virus and solved the structures of a number of protein molecules including the structure of the muscle protein actin and the actin filament. Recently he has worked on the molecular mechanism of muscle contraction. He also initiated the use of synchrotron radiation as a source for X-ray diffraction and founded the EMBL outstation at DESY Hamburg. He was elected to the Royal Society in 1981 and is a member of a number of scientific academies.

John Finch is a retired member of staff of the Medical Research Council Laboratory of Molecular Biology in Cambridge, UK. He began research as a PhD student of Rosalind Franklin's at Birkbeck College, London in 1955 studying the structure of small viruses by x-ray diffraction. He came to Cambridge as part of Aaron Klug's team in 1962 and has continued with the structural study of viruses and other nucleoproteins such as chromatin, using both x-rays and electron microscopy.

Tags: Sangamo Therapeutics, Edwards Life Sciences, Dina Raveh

Duration: 7 minutes, 12 seconds

Date story recorded: July 2005

Date story went live: 24 January 2008