Ph.D. candidate Jackson Winter receives fellowship to research CRISPR-Cas9 base-editor therapy for Duchenne Muscular Dystrophy
Bioengineering Ph.D. candidate Jackson Winter has been appointed to the Northwestern University Clinical and Translational Sciences Institute (NUCATS) Multidisciplinary Training Program in Child and Adolescent Health (NUCATS TL1) fellowship program. Winter currently works in Bioengineering Professor Pablo Perez-Pinera's lab where he is developing gene therapies for Duchenne Muscular Dystrophy (DMD), a lethal genetic condition with symptoms that onset in early childhood and that currently has no cure.
DMD is caused by mutations in the dystrophin gene which disrupt the production of the dystrophin protein. This structural protein stabilizes the muscle cell membrane. Without it, muscle cells gradually atrophy throughout the body. Most children with DMD become wheelchair-bound by their teens and the muscle atrophy usually leads to life-threatening complications involving their respiratory and heart functions in their early twenties.
While the genetic cause of DMD is known, this disease is currently incurable. However, some therapies have recently emerged for some genetic disorders, which deliver a replacement gene packaged inside of a virus into the body. A few gene therapies using this strategy have recently gained FDA approval and are promising avenues for treating rare genetic disorders. "What makes DMD particularly challenging is that the dystrophin gene is the largest gene in the genome," said Winter. "There is an intrinsic packaging limitation to what you can load into these viruses that prevents direct delivery of the gene encoding dystrophin."
This is where CRISPR-Cas9 based gene editing can come into play. Instead of delivering the dystrophin gene directly, their lab is seeking to use genome editing tools to modify the gene to treat the disease. One of the main benefits of CRISPR-Cas9 therapy is that it's very targeted. Researchers know where the mutations occur and can use these tools to edit the mutations directly.
While many different mutations in dystrophin may lead to DMD, there are “hot spots” within the gene that large proportions of patients have mutations in. To correct multiple mutations with a single therapeutic, rather than addressing each mutation on a case by case basis, scientists have been using a technique known as exon skipping for several decades.
Exon skipping can be utilized to hide fragments of genes from cells so that they do not utilize that DNA to make a mutated protein. Instead, they just use the healthy DNA. While the FDA has already approved exon skipping drugs, the benefits are only temporary, thus requiring repeated injections throughout the patient’s lifetime, and have a hefty price tag of around $300,000 per year. Winter envisions that they can create a one-time treatment by using gene editing to accomplish permanent exon skipping. "The goal is to restore the expression of dystrophin, do it at a lower cost and make it permanent," said Winter.
Nonetheless, there are some limitations to using CRISPR-Cas9. The original CRISPR-Cas9 technology requires breaking the DNA to make changes during the repair process. But breaking DNA can lead to many unpredictable outcomes including unwanted mutations, translocations or cell death.
Many advances from Perez-Pinera' lab such as their new platform, CRISPR-SKIP, have been iterating on improved versions of a technology called single-base editors which do not require a double-stranded break and are much more predictable and safer. Winter is using CRISPR-SKIP to induce permanent exon skipping in dystrophin and ultimately correct mutations that cause Duchenne muscular dystrophy. Importantly, Winter and his colleagues recently developed a strategy to package these base editors into viral particles which, for the first time, have enabled delivery of the tools directly to live animals and have the potential to be used in patients in the future.
"It's a very long road between when these therapies are invented in labs and when they can be used to treat patients," said Winter. "We need strong collaborations with hospitals, medical schools and investors who can get these types of therapies to the clinic."
NUCATS has the infrastructure to support clinical trials and getting therapies to patients. The opportunity to learn about the clinical and regulatory landscape is a big draw for him. Through the NUCATS program, Winter will be mentored by clinical faculty who are going to expand his horizons as far as the FDA regulatory pathways and drug development process.
Drug development takes a very long time, according to Winter. Nonetheless, he is taking the first steps in that direction by initiating treatment of mouse models of human diseases. He said, "our experiments have already been very promising in cell culture models, we are now looking forward to using our advances to treat the disease in live animals."
In addition to developing treatments for DMD, Winter is also working to treat other diseases such as Parkinson’s while developing improved versions of the gene editing tools his lab uses. While he first joined Perez-Pinera' lab in his junior year as an undergraduate student in the Department of Bioengineering at the University of Illinois at Urbana-Champaign, he is excited to be entering his 6th year under Perez-Pinera’s mentorship. "The lab environment is great, and Pablo is an excellent and very supportive mentor. He has a true vision for innovative research," said Winter.