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Collaboration May Help Uncover Treatments for Rare Neurologic Disease

Sung-Wook Jang and robot

NCATS researcher Sung-Wook Jang stands next to the high-throughput screening robotic system used to identify potential treatments for Charcot-Marie-Tooth disease.

A research collaboration including scientists from NCATS and the University of Wisconsin–Madison, helped identify three promising molecular compounds from a collection of approved drugs to pursue as potential treatments for Charcot-Marie-Tooth disease (CMT), a genetic neurological disease for which there are no current treatments.

The nonprofit CMT Association initiated and supported the university research, and findings were reported on July 20, 2012, in the ACS Chemical Biology journal. The research team screened nearly 3,000 approved and investigational drugs from the NCATS Pharmaceutical Collection, in a laboratory test, or assay, for CMT. Identifying an already approved drug that possibly is effective for another disease can have many advantages over developing a medicine from the start, including shortening the time it may take to apply for human clinical trials.

"These findings demonstrate what can be accomplished when a disease foundation and the academic researchers it funds work with the therapeutic development experts at NCATS to translate basic research findings into the first steps of developing a drug," said Christopher P. Austin, former director of the NCATS Division of Pre-Clinical Innovation. "At NCATS, we plan to form more successful collaborations like this one in the future."

Each of us has a dozen genes or so that exist in more or fewer copies than normal in our genome. Called copy number variations, these genetic differences result from duplications and deletions of genes and can result in the production of too much or too little of a gene product such as a protein in a cell. A common form of CMT, called CMT disease type 1A (CMT1A), occurs from such a copy number variation, and other research has linked copy number variants to diseases, including breast cancer, Parkinson’s disease and Alzheimer’s disease.

In CMT1A, a gene called peripheral myelin protein 22 (PMP22) occurs in multiple copies. As a result, excess PMP22 protein builds up in cells in the peripheral nervous system, disrupting proper nerve conduction and contributing to slow progressive degeneration of the muscles in the foot, lower leg, hand and forearm, and a mild loss of sensation in the limbs, fingers and toes.

In search of compounds that inhibit the excess production of PMP22, the researchers collaborated to develop a novel assay, incorporating a regulatory element of the PMP22 gene that leads to its overexpression and subsequently contributes to CMT1A.

In 2009, Sung-Wook Jang, the first author of the ACS Chemical Biology CMT study, joined the laboratory of NCATS investigator James Inglese, a chemical biologist with expertise in assay development and high-throughput screening, to work on the project. Jang, supported by the CMT Association, was a recent graduate student who trained with John Svaren, one of the paper’s authors, at the University of Wisconsin, Madison.

Jang led the validation of the CMT1A assays. He also screened NCATS’ pharmaceutical collection in the assay and confirmed the findings in secondary tests.

"Our decision to bring in Sung-Wook to champion this project enabled him to leverage his prior expertise in CMT and make rapid advances in the program," said Inglese. "Sung-Wook’s understanding of the underlying biology of CMT transitioned well to his training at NCATS in assay development, screening and data analysis. It is a model that we plan to use in the future and one that would benefit other disease organizations seeking to establish translational research programs."

For the CMT1A assay, the researchers prepared two cell lines that each contained a unique reporter that would indicate to researchers those drugs that were targeting the PMP22 regulatory element. Only drugs registering in both cell lines were considered by researchers to have the desired effect. Jang used a technique called RNA silencing to demonstrate that the activity of the regulatory element from PMP22 could be reduced when factors critical to PMP22 expression were depleted from the cell. This increased the researchers’ confidence that the assay design was faithful to the biology of CMT, and enabled them to identify three medications fenretinide, ovlanil and bortezomib that substantially decreased PMP22 expression.

The authors recommend that the assay strategy used successfully for CMT1A may be useful for other rare diseases caused by gene copy number variations, leading to improved monitoring of disease regulatory pathways in cells and identifying compounds to explore as potential treatments. They caution, though, that developing these findings into a treatment for CMT1A patients still could be an uphill climb and is prone to failures along the way ─ similar to any other therapeutic development effort.

Further research still must demonstrate the effectiveness of such compounds in animal models and humans. For example, as a direct follow-up from the study, European collaborators funded by CMTA have begun to test proteasome inhibitors such as bortezomib, one of the drugs that decreased PMP22 expression, in a rat model of CMT in Europe.

In addition, the CMT Association now is expanding the subtypes of CMT for researchers to study as part of the collaboration. The association also aims to create a human model system of CMT1A using induced pluripotent stem cells, a type of adult stem cell. And, researchers in Inglese’s laboratory at NCATS are utilizing new techniques to build next-generation assays for CMT1A that more accurately assess active compounds; they also are identifying other targets in the genome that may affect PMP22 expression.

"The CMT Association’s Strategy to Accelerate Research (STAR) will continue to fund projects that contribute to our ultimate goal of a finding a first treatment for CMT," said Pat Livney, CMT Association chief executive officer. "I am confident the association, together with the dedicated world class scientific team led by Drs. Inglese and Svaren, is delivering the state-of-the-art results that will prove successful."

 

Posted July 2012