Two New RSRT-Funded Projects That Use a Novel Approach to Deliver Genetic Medicine to the Brain

For over a decade, Jiangbing Zhou, a professor of neurosurgery and biomedical engineering at Yale University School of Medicine, has been investigating how to deliver medicines to the brain. His interests started with creating better therapies for hard-to-treat brain cancers like glioblastoma, and then expanded to neurogenetic diseases, such as Angelman syndrome. Two years ago, through a conference focused on Angelman syndrome, he connected with Monica. “Monica is always searching for new ideas and new solutions for Rett syndrome,” said Zhou. “She was there to see if any of the approaches being used for Angelman could be used for treating Rett. And that was the spark for what became two new projects aimed at curing Rett syndrome, supported through RSRT.”

Monica was impressed by Zhou’s expertise in the delivery of genetic medicines to the brain, so she connected Zhou with RSRT researcher Guoping Feng, MIT, who is developing base editing therapeutics for Rett, and Shawn Liu, Columbia, an expert in epigenetic editing. The three together with Yong-Hui Jiang, also from Yale, are now co-investigators on the new projects.

The new projects — which have received $1.6 million in funding from RSRT — use a novel delivery method combined with base editing and epigenome editing, respectively, to treat Rett syndrome at the DNA level.

Base editing is a version of CRISPR-based genome editing. Conventional CRISPR editing creates a double-stranded break in DNA at a specific location. When the break is repaired, researchers have the opportunity to make changes to the DNA at the break site. Base editing uses CRISPR’s remarkable ability to target a specific genomic site to make small changes to DNA without double-stranded breaks, thereby improving the safety of the treatment. Base editing is typically used to change just a single DNA letter at a particular location, like correcting a typo.

The other treatment approach focuses on epigenome editing. The MECP2 gene is located on the X chromosome. Girls and women have two copies of the X chromosome in each cell, but only one copy in any given cell is active. The other is “silenced.” Which copy is active and which copy is silenced is random on a cell-to-cell basis. The goal of epigenome editing for Rett syndrome is to activate the silenced MECP2 gene so that cells will have the normal level of functional MECP2. This approach has the potential to be effective for treating individuals with any MECP2 mutation.

"We are eager to do the research and create better options for individuals with Rett syndrome.”

-Jiangbing Zhou

As genomic technologies improve, effectively getting them to the brain remains a key challenge. Genetic medicines typically consist of two components: delivery and cargo. The cargo is the active treatment component, like CRISPR-Cas9 for DNA editing or ADAR for RNA editing. The delivery component gets the cargo into the right cells.

The gold standard for delivery is specialized viruses which have a natural ability to get into human cells. Researchers can harness this ability, while engineering viruses to deliver genomic medicine as their cargo. Viruses have successfully been used to deliver gene therapy and genome-editing treatments, like Zolgensma for SMA1. But they also have their drawbacks: viral delivery can trigger immune reactions in patients, and because of this, a patient can only be treated with one virally delivered medicine in their lifetime. The size of a cargo viruses can deliver is also limited, which presents a challenge for some genetic medicines. Manufacturing viruses is also complicated and expensive, which can drive up the price of therapies. Viral delivery may involve additional risk of off-target effects due to prolonged expression of the editing machinery. Over the past several years, researchers have delved into creating and refining nonviral delivery methods to overcome these limits. Zhou and collaborators are working on a unique delivery method for nonviral delivery.

“Most approaches to delivery are physically too large to cross the blood-brain barrier or to diffuse well through the brain,” says Zhou. “So, we are creating specialized approaches specifically for the brain.”

As part of recent work funded through the NIH, Zhou developed a new technology for delivering ribonucleoproteins, or RNPs, like CRISPR-Cas9 to the brain. Their Stimuli-Responsive Traceless Engineering Platform (STEP) technology comprises a library of thousands of chemical molecules, each approximately 2 kDa in size. These molecules can attach to a RNP and facilitate its entry into a cell. Engineering with STEP doesn’t significantly increase the RNP size. Demonstrated in mouse models, STEP-RNPs have a remarkable ability to diffuse within the brain when delivered into the spinal fluid (intrathecally) or injected directly into the brain. They even have some ability to cross the blood-brain barrier when delivered intravenously. Zhou aims to further develop the technology for use in Rett.

“Right now, we are working on manufacturing high-quality RNPs that can perform the base editing or epi editing in cells. The next step will be to screen our library of STEP molecules to see which are most effective with these RNPs. After that, we’ll start working with the molecules in mouse models of Rett syndrome,” says Zhou. These models were previously developed by other researchers through RSRT funding.

"We’re really excited about these two projects. They simply wouldn’t exist without RSRT’s support or Monica’s enthusiasm."

-Jiangbing Zhou