Research that led to the identification of Minocycline
From the November 2011 FAST NewsletterTitle: Approaching clinical trials...."What a long, strange trip it's been"
Author: Edwin J. Weeber, Ph.D.
For those of you who are new to FAST and haven't read previous articles, and/or listened to my anecdotes about my involvement in Angelman syndrome (AS) research, I would like to walk you down the "short path" of where we were a few years ago, and how a basic science approach has forged an unexpected path to the first upcoming clinical trial to test a therapeutic for AS. My sincere hope is that you will see, as I did, the logical progression the research has taken, how it intersected and very much walked hand-in-hand with the mission of FAST. Our progress has allowed us to form a unique perspective for the future of Angelman Syndrome research and hope for Angels everywhere.
An important turning point for Angelman syndrome research in general was the paper Dr. Elgersma and I authored in 2007 entitled "Rescue of neurological deficits in a mouse model for Angelman syndrome by reduction of alpha-CaMKII inhibitory phosphorylation." This paper contained interesting data generated in two different laboratories separated by the Atlantic. However, beyond the face value of the data we presented, was the fact that an enzyme not directly associated with the AS gene (Ube3a) was capable of removing all of the major symptoms in the mouse model of Angelman syndrome. Following the strict definition of a cure (a means of correcting or relieving anything that is troublesome or detrimental), this was a genuine genetic cure of the animal model. This particular method of a cure could never be used for humans with AS, simply because the genetic changes that led to the cure of the mouse model occurred literally before conception. Simply put, the rescued AS mice developed and were born with both the mutation in Ube3a and a mutation in a different gene, CaMKII, which allowed these mice to be born and mature without the symptoms of AS. What this didn't tell us, is whether or not modifying CaMKII in an individual that already had AS would be of benefit so long after the brain had formed and developed. However, it is believed that this enzyme (CaMKII) is not significantly expressed in the human brain until after birth, so the rescue we saw in the mouse model could represent a "cure" after the development of the brain. It is probable that the developmental processes that form the brain in individuals with AS are unaffected and only after birth does the dysfunction begin to manifest. It is important to note that the term "Developmental Disorders" is used for most cognitive childhood disorders, i.e. Fragile X, Rett Syndrome and Autism, and proposes that the disorder is linked with the in utero development of the individual. Think about this: the brain is made up of 100 billion neurons making 3-5 quadrillion synaptic connections in order to function. A genetic or environmental insult to that incredible complexity in connections during the formation of the brain is devastating and irreversible. In other words, there is simply no way to rewire a brain that has been wired incorrectly during development. However, if Angelman Syndrome was not a developmental disorder, and the brain formed correctly, then an effective therapy may be possible.
This revelation is not unique to AS researchers. In fact other laboratories studying Fragile X, Rett Syndrome and Neurofibromotosis-1 were reaching the same conclusions with their own unique mouse models; human disorders associated with cognitive disruption were not necessarily due to developmental disruption in the formation of the brain. Our thoughts in the context of this revelation then turned to a very basic question: Could you rescue the cognitive defects in an adult AS mouse, one that has shown the symptoms of AS throughout life, by simply giving it back the ability to make UBE3A? We recently answered this question. To do this we utilized a viral mediated gene therapy strategy. We made an Adeno-Associated viral (AAV) particle containing the Ube3a gene. By allowing the viral particles to infect regions within the hippocampus and surrounding brain, we were able to deliver the Ube3a gene to hundreds of thousands of neurons in mice with AS. (The hippocampus is a brain structure well known to be involved in learning and memory). After a few weeks we tested the AS mice and found that their ability to learn and remember specific behavioral tests increased dramatically. In fact, we found that the function of the synapses in the hippocampus were almost equal to that of typical mice. The ability to use AAV particles in humans is currently not available and certainly would involve an incredibly invasive procedure. However, as a proof of concept, this research showed convincingly that treatment in the adult mouse model could improve the symptoms of AS. Thus, it should be possible to do the same with human AS patients, and importantly this improvement should be obtainable regardless of age.
This leads us to Compound Three (C-3). The idea for testing FDA approved drugs in the AS mouse was born in FAST as a way to bring a potential therapeutic to use with the greatest speed and efficiency. In light of the success with viral-mediated Ube3a gene therapy described above, this was an exciting proposition, but was a high risk - high payoff experimental approach. This is because the typical scientific approach would be to first identify the target for a drug, then pick the potential drug that would work on that specific target if one existed. We are still unsure of the exact molecular mechanisms underlying Ube3a deficiency and how it causes synaptic disruption. What was working for us is an intimate knowledge of the mouse model, and a collective meeting of some of the best scientific minds associated with FAST to identify compounds that may be useful due to their known mechanisms of action. We also had to determine parameters of duration of treatment, concentrations of the drugs, method of giving the drugs, etc. Most important was that we were confident a change could be detected following rigorous tests of behavior and synaptic function in an effectively treated AS mouse. Various FDA approved drugs, including C-3, were injected into the mice every day for three weeks. We then tested a number of behavioral parameters affected in the AS mouse: activity, motor coordination and motor learning, associative learning and memory, sensory perception, hearing and anxiety. We also tested the ability for creating long-lasting synaptic plasticity (our cellular model for learning and memory). We found that in mice treated with C-3 the motor coordination was nearly identical to typical mice and their ability to learn and remember was increased as well. In addition, we found that the synaptic function in the hippocampus of our treated mice was significantly greater then saline injected mice and equal to that of typical mice. In many aspects, these results were more dramatic than those seen with the gene therapy approach described above! Logic again subscribed that these indications were sufficient to move C-3 to a small clinical trial. We can then use this same scientific method and the rigorous tests and evaluation to determine the efficacy of C-3.
Our laboratory is currently investigating the mechanism by which C-3 can so dramatically affect the AS mouse model in a relatively short period of time. This current research may identify novel targets for other FDA approved drugs, or reveal molecular similarities of AS to other disorders for which a treatment is already available. The future will tell us how effective C-3 is, but the identification of this drug has not made us complacent. With the help of FAST, we are continuing to look for other readily available drugs and compounds that can be "FAST-tracked" for use as a therapeutic. And the long, strange trip continues...
