Our second update from the Annual Huntington’s Disease Therapeutics Conference.
Wednesday: huntingtin-lowering drugs
09:03 – This morning’s session is focused on what many scientists consider the most promising approach to HD therapy, “Huntingtin silencing” or huntingtin lowering
09:06 – The idea with Huntingtin silencing is to reduce the creation of the mutant huntingtin protein in cells, using a variety of techniques.
09:06 – For much more on this topic, see: http://en.hdbuzz.net/topic/29
09:07 – Basically, every HD patient has a mutant HD gene. That gene is copied by the cell into a messenger RNA molecule, a working copy of the gene
09:08 – The RNA molecules are used by the cell as templates to create proteins. So: Mutant HD gene -> mutant HD messenger RNA -> mutant HD protein
09:09 – In theory, we could interfere with this chain at any point and have the same effect – reducing the levels of the mutant HD protein.
09:11 – George McAllister, of BioFocus, is leading a project that’s looking for chemicals that reduce levels of mutant huntingtin protein
09:12 – His company is screening a massive number of chemicals: applying them to cells and seeing whether they reduce mutant huntingtin levels
09:15 – New technologies developed over the last few years let BioFocus use real human cells and measure infinitesimal levels of mutant huntingtin
09:32 – BioFocus is screening thousands of molecules, looking for one that reduces mutant huntingtin protein levels without making cells sick
09:35 – This is an interesting approach, they’re looking for chemicals that reduce mutant huntingtin without necessarily knowing how they’re working
09:41 – It’s a cool way to look for drugs that work in ways you might not predict, which is a good way to learn about new approaches to the problem
09:46 – Dean Stamos, of Vertex Pharmaceuticals, addresses the conference on his companie’s efforts to come up with drugs to reduce mutant huntingtin
09:47 – Vertex discovered chemicals that block the activity of a protein called “Hsp90” had the result of reducing mutant huntingtin levels
09:50 – These chemicals turned out to not be good drugs, but could still teach us about how cells get rid of tricky proteins like mutant huntingtin
09:55 – Cells have very sophisticated ways of dealing with proteins, like mutant huntingtin, that don’t fold up correctly.
09:57 – A number of tiny machines called “heat shock proteins” help cells keep all their proteins folded up in the correct shape, even after stress
10:00 – Hsp90 is “heat shock protein 90”, Vertex developed specific molecules to block it, leading to long-term reduction of mutant huntintin
10:01 – For reasons they haven’t specified, Vertex doesn’t feel like these drugs would be good for long-term use
10:06 – Lisa Stanek, Genzyme, is using primates to develop techniques for silencing mutant huntingtin using viral delivery of something called siRNA
10:09 – siRNA’s are ‘small interfering RNA’; short pieces of RNA (a cousin of DNA) that likes to pair up with specific RNA molecules in the cell
10:10 – Once in the cell, siRNA molecules find and destroy the huntingtin messenger RNA molecules, in turn reducing huntingtin protein levels
10:12 – They’re using tiny, harmless, viruses that are good at getting siRNA into brain cells. These viruses are called “adeno-associated viruses”
10:17 – Stanek reminds the audience that treating mouse brains is pretty easy, but human brains are more than 1,000 times larger!
10:18 – To study this, we need to work in animals that have larger brains. Stanek’s team has been working in primates to see how these viruses work
10:21 – Genzyme is conducting careful study of the safety of their viruses in monkeys – if there are any problems we want to catch them now.
10:26 – Trial injections of the viruses Genzyme wants to use for human trials give really impressive spread of the virus throughout the brain!
10:29 – This is exciting, one of the hurdles for this approach in the past was the relatively limited spread of injected virus within the brain
10:31 – Careful observation of injected monkeys revealed no health concerns for a month after they received their brain injections of test virus
11:06 – Next Geoff Nichol from Sangamo Biosciences is giving an update on ‘Zinc Finger’ drugs to reduce production of the mutant huntingtin protein
11:07 – More on zinc finger drugs here http://en.hdbuzz.net/103
11:10 – Zinc finger drugs aim to switch off production of the mutant protein at its source. They stick to the DNA of the gene inside cells
11:10 – After sticking, the mutant protein gene is switched off.
11:11 – What’s more, the zinc finger drugs can switch off the mutant copy of the gene, while leaving the healthy copy alone
11:12 – Leaving the healthy huntingtin gene alone is very appealing because switching it off might cause unwanted side effects – but we don’t know.
11:16 – Sangamo has partnered with Shire Pharmaceutials to develop their zinc finger drugs
11:16 – The zinc finger drug is injected into the brain as a ‘recipe’ carried by a harmless virus.
11:17 – The virus takes up residence in brain cells and the cells themselves become a factory for making the zinc finger drug
11:18 – This means that in theory at least the zinc finger drugs could be a one-shot solution to prevent or slow HD.
11:18 – The flipside of that is that if there are unwanted effects, those will be longlasting too – so it’s important to test these drugs carefully
11:19 – So far, the zinc finger drugs have been tested in several different mouse models of mice and look to be safe and effective.
11:19 – Figuring out how to deliver the drugs safely to the brain is the next big challenge for Sangamo and Shire.
11:21 – A clinical trial of zinc finger drugs is currently in the early planning stages, probably in patients with early symptoms
11:41 – Frank Bennett, of Isis Pharmaceuticals, addresses the conference on his companies efforts with drugs called “antisense oligonucleotides”
11:43 – These “ASO” molecules are another way to destroy specific RNA molecules, helping reduce the levels of a protein we want to get rid of
11:44 – Isis has been working to develop ASO molecules that destroy the huntingtin RNA, and therefore reduce huntingtin protein levels
11:47 – Isis has proven in a large number of animal studies that reducing huntingtin in the brain using ASOs improves HD-like symptoms in mice
11:48 – Isis has experience with these types of molecules – they’ve treated more than 6,000 human patients in 100 clinical studies for other diseases
11:49 – Like many other drugs discussed today, ASOs can’t get into the brain from the blood, so they need to be injected into it somehow
11:51 – To get into the brain, injections can be made at the base of the spine into the spinal fluid, which carries drugs to the brain
11:51 – This approach has been used in multiple human studies conducted by Isis for other diseases, and so far seems safe and effective.
11:52 – In mice treated with ASOs targeting huntingtin, the effect of the drug lasts for months without needing to be re-dosed.
11:56 – Like the other companies here today, Isis has already conducted detailed safety studies in primates
12:02 – As an extra check of their plan for delivery, Isis has done spinal delivery in pigs, who apparently have pretty long spinal cords!
12:05 – Will ASOs work in people? Isis has a program in a disease called Spinal Muscular Atrophy where the drug is being delivered similarly
12:07 – Brain and spinal cord tissue from Spinal Muscular Atrophy patients show that ASOs effectively get into the brain after spinal fluid delivery
12:09 – Though the numbers of patients are small, kids with spinal muscular atrophy treated with Isis' drugs seem to be showing disease improvement
12:11 – Isis is launching a human HD study, starting sometime in the first half of 2015! The drug is called “HTT-Rx”, and the study is focused on safety.
12:13 – This first trial will have the goal of establishing that Htt-Rx delivery to the human brain and spinal cord is safe.
12:15 – What a morning! All these silencing approaches look like very exciting approaches for treating HD, and the technology has really advanced!
12:22 – Doug Macdonald, CHDI, is leading the foundations efforts to look for “biomarkers” for the huntingtin silencing studies. What’s a biomarker?
12:23 – If we silence the huntingtin protein in the brain, how we will know the drugs worked? We can’t very well take brain tissue samples to check
12:24 – So Macdonald is leading efforts to look for other ways to see the effect of silencing drugs in human brains.
12:25 – One way is to measure levels of the huntingtin protein in fluids we can get to, like the spinal fluid. Sampling this is pretty easy.
12:27 – Using rats, CHDI and Isis are testing whether levels of the huntingtin protein in the spinal fluid change after delivery of silencing drugs
12:30 – Data hot off the presses suggests it’s possible that levels of the huntingtin protein in the spinal fluid somewhat mirror brain levels