A team of scientists at Rice University, led by Dr. Junghae Suh, published a report in ACS Nano describing the engineered “tunable protease-activatable virus nanonodes” they want to use for gene delivery to treat cancer and other diseases.
The design focuses on two proteases shown to be elevated at tumor sites that can be used to release adeno-associated viruses (AAVs) only in the presence of cancer cells, relieving normal cells of the treatment burden. “If we were just looking for one protease, it might be at the cancer site, but it could also be somewhere else in your body where you have inflammation. This could lead to undesirable side effects,” said Dr. Suh in a news release. “By requiring two different proteases – let’s say protease A and protease B – to open the locked virus, we may achieve higher delivery specificity since the chance of having both proteases elevated at a site becomes smaller”.
AAVs are attractive for gene therapy because they are benign relative to other viral gene delivery methods. Most other laboratories target AAVs to specific cell types based on a particular receptor that is over-expressed by target cells.
Dr. Suh want to take a different approach, and says that “we were looking for other types of biomarkers beyond cellular receptors present at disease sites. In breast cancer, for example, it’s known the tumor cells oversecrete extracellular proteases, but perhaps more important are the infiltrating immune cells that migrate into the tumor microenvironment and start dumping out a whole bunch of proteases as well.”
The team integrated peptides into the capsids of self-assembling AAVs to act as a lock preventing premature AAV release. These peptides, which can be designed to be cleaved by any number of proteases, are the substrates for the proteases expressed by tumor cells. Once the peptides are cleaved, the AAVs are free to bind to the tumor cells and lead to cell destruction through downstream effects. “So that’s what we’re going after to do targeted delivery. Our basic idea is to create viruses that, in the locked configuration, can’t do anything. They’re inert… these viruses unlock, bind to the cells and deliver payloads that will either kill the cells for cancer therapy or deliver genes that can fix them for other disease applications,” explained Dr. Suh.
These other disease applications may include stroke, Parkinson’s disease, Alzheimer’s disease, and heart disease, as the afflicted tissues in each case have been found to express high levels of proteases. Molecular-imaging can be used to detect what type and how much of each protease is expressed by cells in the diseased tissue. “With that information, we would be able to pick a virus device from our panel of engineered variants that has the right properties to target that disease site,” said Dr. Suh. “That’s where we want to go.”
Ultimately, the study furthers the field of gene targeting. “To increase the specificity of virus unlocking, you can imagine creating viruses that require many more keys to open. For example, you may need both proteases A and B as well as a cellular receptor to unlock the virus. The work reported here is a good first step toward this goal,” concluded Dr. Suh.
Other authors from Rice University include alumni Justin Judd and Abhinav Tiwari; graduate students Michelle Ho, Eric Gomez and Christopher Dempsey; associate professor of bioengineering Oleg Igoshin; and associate professor of biochemistry and cell biology Jonathan Silberg. They collaborated with faculty Kim Van Vliet and Mavis Agbandje-McKenna at University of Florida. Funding was provided by the National Science Foundation, the National Institutes of Health, the American Heart Association and the Cancer Prevention and Research Institute of Texas.