In previous entries in this blog I outlined the basics of the project (click here to read more) and expressed my enthusiasm for its potential to control HD (click here to read more). Isis aims to block HD at its genetic root, and, if all goes as planned, the company will be ready to test a drug in humans by late 2010.
On April 9 I visited Isis in Carlsbad, California, to meet the people who are seeking to relieve the suffering of tens of thousands of Huntington’s families and prevent the disease from destroying the brains of people like myself who have tested positive for the defect but not yet shown its most obvious symptoms of shaking limbs and dementia.
A new technology
“We have a technology that prevents the huntingtin protein from being expressed. We showed in cells and animals that we could inhibit mutant huntingtin,” said C. Frank Bennett, Ph.D., senior vice president of research at Isis. “If you don’t express the mutant form of huntingtin, you can abrogate or delay the onset of the disease.”
Isis developed that technology in a feasibility study carried out two years ago for Cure Huntington’s Disease Initiative, Inc. (CHDI), a Los Angeles-based non-profit foundation dedicated exclusively to finding a treatment or cure for HD. Isis demonstrated that it could block the action of the huntingtin gene in mouse and human cells and in actual mouse brains. All humans have two copies of the huntingtin gene, the recipe from which they make huntingtin protein, but in some people one copy of the gene has a mutation that makes a faulty protein, which causes Huntington’s disease. HD is a genetic disease. Children of affected people have a 50 percent chance of inheriting the mutation, and everybody who tests positive for the defect will eventually develop HD.
In October 2007 Isis and CHDI announced the current project, which seeks to control the mutant form of huntingtin in humans. CHDI will provide Isis up to $9.9 million to carry out the various stages of the project over the next three years. CHDI receives support primarily from an anonymous donor (the High Q Foundation) and is also supported by the Huntington’s Disease Society of America and the Hereditary Disease Foundation.
The weapon: big molecules called ‘oligos’
Scientists refer to this approach as “antisense technology.” DNA, the building block of all life, runs our cells by telling them which proteins to make. It does so by sending messages via another molecule called messenger RNA. As encoded by DNA, RNA has a very specific template, somewhat akin to a unique electrical outlet into which only a unique plug can fit. RNA is known as a sense molecule, and Isis manufactures the antisense plugs to control them. These antisense molecules are called oligonucleotides, or oligos.
“Our technology allows one to basically, with a laser-guided missile, target that specific messenger RNA that causes a particular disease and kill it or take it out of the body so that you don’t produce that messenger RNA,” Dr. Bennett explained about the project’s goals. “The result is that you prevent the bad protein from being expressed…. We’re designing oligonucleotides that will bind to the huntingtin messenger RNA, and upon binding to the messenger RNA, prevent it from being translated into a protein product.”
Frank Bennett, Senior Vice President of Research, Isis Pharmaceuticals
Dr. Bennett, who has published more than 90 papers in the field of antisense research and development and has more than 100 issued U.S. patents, likened the manufacture of oligos to playing with Tinkertoys.
Remember that Tinkertoys have circular pieces of wood with holes into which a child puts pencil-like sticks and thus builds a small structure. Isis does the same thing using a complex piece of machinery and produces extremely long molecules. “We do that with chemistry on a machine called an oligonucleotide synthesizer,” he said. Isis can make just a few milligrams of oligos for initial testing and then much larger amounts using much larger machines in order to prepare the oligos for commercial application in partnership with a larger pharmaceutical company.
Fine-tuning the approach
Many researchers are looking at antisense technology for a variety of scientific and medical applications. However, in a field that once had other competitors, Isis is now the only company in the world working with its particular kind of antisense technology, and it has a number of patents for its oligo designs.
Isis’s strength lies in its ability to “measure RNAs in cells,” Dr. Bennett continued. Isis has a room with “rows and rows” of instruments for studying the RNA, “as well as robots that extract the RNAs from cells and put them on machines. We have really industrialized that part of the process.” According to Janet Leeds, Ph.D., CHDI’s director of pre-clinical development, the point person for the Isis project, and a former eight-year employee of Isis, the company has decreased the cost of producing oligos tenfold.
Isis is currently working on fine-tuning the oligo it developed in the feasibility study and has already tested over 200 compounds, said Dr. Leeds. Once the best match is found, it will test the oligo in transgenic mice provided by CHDI. Developed by Dr. William Yang of the University of California, Los Angeles, those mice are engineered so that they have both a normal mouse huntingtin gene and a mutant copy of the human gene. They develop Huntington’s-like symptoms. Isis employs a special clamp known as a stereotactic device to inject drugs into mice at exactly the same spot each time, and it uses other devices to measure the mice’s behavior, muscle strength and coordination, and brain function – all crucial factors in Huntington’s disease.
If mouse tests are successful, Isis will repeat the experiment in monkeys to better assess the safety of the oligo for testing in humans.
“We’re breaking ice in learning how to modulate huntingtin,” Dr. Bennett continued. “Nobody’s had a technology that would allow you to address what is the function of huntingtin in a developed organism. It clearly plays a role in normal physiology. It’s not well understand what that role is, but it seems to be important for some aspects of normal function of neurons as well as other cells in the body. It’s expressed everywhere in the body, not just in the brain.”
Making a safe drug
Now that Isis is close to an oligo, it faces two other huge challenges. First, because the oligo would regulate both normal and mutant huntingtin, Isis and CHDI must determine how much huntingtin should be controlled in order to reduce the effects of the disease, avoid adverse effects, and lessen the chances that gene-positive people start having symptoms. For now the plan is to reduce or “knock down” huntingtin’s action by about 50 percent, said Dr. Leeds.
“That’s no different than any other drug that we use today,” Dr. Bennett said. “Say if you take a drug that lowers your blood pressure. If you’re hypertensive, and are at risk for cardiac dysfunction, because you have high blood pressure, lowering your blood pressure is good. But you don’t want to lower it to zero! All drugs will produce toxicity if you overdose. The animal models will be very instructive for giving us that guidance, because we will be able to lower the normal level of huntingtin as well as mutant huntingtin and cover whatever are the potential adverse effects of that.”
Dr. Leeds added that the Isis scientists could end up discovering that each individual needs a particular molecule to regulate his or her level of huntingtin. But this “personal medicine” approach is not yet feasible.
Getting the remedy into the brain
Secondly, Isis must get the oligo into the brain.
CHDI is banking on Isis’s success in developing the world’s first antisense drug clinical use, Vitravene, which is used to treat an eye disease associated with AIDS. Vitravene is injected directly into the eye. With current technology an oligo for Huntington’s disease cannot be delivered via a pill or injection into the brain, and any medication will have to cross the blood-brain barrier.
In the mouse experiment Isis inserted pumps under the animals’ skin and ran a tube into the brain. For humans, they are considering the use of a hockey puck-sized pump placed in the abdomen, which would pump the drug through a tube carefully inserted into the brain. Dr. Bennett pointed out that people with a number of conditions such as chronic back pain or diabetes already use commercially approved pumps. Doctors can use infrared signals to program the pumps and control the flow of medication and can inject a new supply into the pump through a port just under the skin.
“It’s obviously not ideal, but considering the severity of this disease, it’s well worth the inconvenience that these pumps produce,” Dr. Bennett observed. “Once patients acclimatize to them, they’re really not that bothersome.”
Isis is exploring the possibility of pumping the oligo into the spinal fluid. From there it would diffuse into the brain. This method might use a less invasive pump system.
Dr. Leeds pointed out that CHDI and another company are exploring a third method of delivery: a subcutaneous shot (just under the surface of the skin). A person would receive such a shot about once a month. This technology, however, could be at least a decade off. The longest term goal would be to develop a pill.
Regardless of the method, the patient would have to take the medication for life because of the genetic nature of HD, said Dr. Leeds.
Isis Pharmaceuticals’ unique flavor
Scientists began working with the concept of antisense in the 1970s, and in 2002 they discovered that oligos actually exist in nature and provoke RNA interference (RNAi). Other researchers are seeking ways to use RNAi to treat diseases, including Huntington’s. “Antisense is like a fruit,” Dr. Bennett explained. “We have apples, oranges, and pears. There’s well over a dozen different mechanisms by which you can exploit antisense to modulate gene expression.” For the Huntington’s disease project Isis is employing a particular enzyme involved in the cell’s normal RNA processing, called RNase H.
“We as a company are broadly exploiting all types of antisense,” Dr. Bennett said. “We have a little bit different flavor that we are using for this project, because in our opinion it’s working more efficiently and it’s ready for testing in man today.” The key to understanding the different “flavors,” he added, is to understand that different enzymes block or degrade the RNA in different ways. Whereas RNAi molecules are twice as large as the Isis oligo and do not enter a cell as easily, the Isis product gets into cells without a special formulation.
If all goes as planned, after the monkey study Isis will apply for permission from the U.S. Food and Drug Administration to administer a test in a small group of humans. Following that step the company would seek a partnership with a commercial drug company to run a large-scale clinical trial. Isis will count on CHDI for establishing contact with a larger pharmaceutical company and designing an efficient large clinical trial. The Huntington Study Group’s “Predict HD” program, which tracks the health of people over 18 who have tested positive for HD but not yet developed symptoms, will be an important source of assistance in a large clinical trial, Dr. Leeds said.
The company’s potential
Isis, a publicly traded company which has about 300 employees, will have as many as eight people working on its HD project, including chemists, biologists, specialists in pharmacokinetics (measuring the drug in tissues), toxicologists, and specialists in clinical trial development.
In addition to Vitravene, the company is developing Mipomersen, an antisense drug targeted at people with extremely high cholesterol levels (500 and higher). Known as familial hypercholesterolemia, this condition is similar to Huntington’s disease because of its roots in a genetic defect. It is also possible that the drug could also be used for others with high cholesterol. Dr. Bennett is confident that Mipomersen will reach the marketplace.
Isis has also used an antisense drug to reduce the effects of Lou Gehrig’s disease in test rodents. Isis delivered the drug, ISIS 333611, directly into the rodents’ spinal fluid via an implanted pump. The company is also starting a new project on Parkinson’s disease.
Not a ‘cure,’ but a historic step for science and patients
Like all other scientists, Dr. Bennett hesitates to refer to the potential HD antisense drug as a “cure.” “I don’t think we’ll cure the disease,” he said. “But what I think we may do is benefit the patients so that either we stabilize the disease and they don’t get worse, or we slow the decline…. That would be a fantastic outcome.”
If the CHDI-Isis project is successful, it would be the first time that humanity brought a neurological disorder under control. According to Dr. Bennett, such a result would validate the large investment that science has made in recent years to understand how these diseases come about.
Isis, which began in 1989, has yet to turn a profit but has almost a half billion dollars in the bank for its operating expenses. It expects to have a respectable operating loss of only $15 million for 2008.
“We do this for the patients,” Dr. Bennett said. “These are diseases where there really isn’t much to offer those patients. We’re very motivated to provide therapies for those patients. Ultimately if we help the patients we’ll help the company. I’m paraphrasing – the CEO of Merck actually said this 40 years ago: ‘If you focus on the patients, the rest of it will fall in place.’ I truly believe that.”
(Next time: an at-risk person’s inside look at Isis)