Tiny capsules offer an alternative to the viral administration of gene therapy

New genetic code modification tools offer new treatments for inherited diseases, some cancers and even persistent viral infections. But the typical method of administering gene therapies to specific tissues in the body can be complicated and cause disturbing side effects.

Researchers at the University of Wisconsin-Madison have solved many of these problems by bundling a gene editing payload into a tiny, customizable synthetic nanocapsule. They described the delivery system and its cargo today (9 September 2019) in the newspaper Nature Nanotechnology.

"To edit a gene in a cell, the editing tool must be integrated into the cell in a safe and efficient manner," says Shaoqin "Sarah" Gong, professor of biomedical engineering and researcher at the Institute of Discovery of Wisconsin at UW-Madison. . His laboratory specializes in the design and construction of nanoscale administration systems for targeted therapy.

"Editing the wrong tissue in the body after the injection of gene therapies is a source of serious concern," says Krishanu Saha, also a professor of biomedical engineering at UW-Madison and co-chair of the steering committee of a national consortium on the genome edition, with support of 190 million US dollars. National Institutes of Health. "If the reproductive organs are inadvertently modified, the patient will transmit the gene modifications to their children and to each subsequent generation."

Most of the genomic changes are done with viral vectors, according to Gong. Viruses have billions of years of experience in cell invasion and co-opting of their own machines to make new copies of the virus. In gene therapy, viruses can be modified to transport genome editing machines rather than their own viral genes into cells. The editing machines can then modify the cell's DNA to, for example, correct a problem in the genetic code that causes or contributes to the disease.

"Viral vectors are attractive because they can be very effective, but they are also associated with a number of safety issues, including unwanted immune responses," Gong said.

New cell targets may also require laborious modifications of viral vectors, and the manufacture of tailored viral vectors can be complicated.

"It is very difficult, if not impossible, to customize many viral vectors for distribution in a specific cell or tissue of the body," says Saha.

Gong's laboratory has covered a payload in gene therapy, namely a version of the CRISPR-Cas9 gene editing tool with the RNA guide designed in Saha's lab, with a thin polymer shell, allowing to obtain a capsule of about 25 nanometers in diameter. The surface of the nanocapsule can be decorated with functional groups such as peptides that give the nanoparticles the ability to target certain types of cells.

The nanocapsule remains intact outside the cells – in the blood, for example – to collapse inside the target cell when it is triggered by a molecule called glutathione. The released payload then moves to the kernel to edit the cell's DNA. Nanocapsules should reduce unplanned genetic changes because of their short life span in the cytoplasm of a cell.

This project is a collaboration involving the UW-Madison skills in chemistry, engineering, biology and medicine. Bikash R. Pattnaik, professor of Pediatrics and Ophthalmology, and Masatoshi Suzuki, professor of Comparative Biosciences, and their teams have tried to demonstrate gene editing in the eyes of the mouse and skeletal muscles, respectively , using nanocapsules.

Since the nanocapsules can be lyophilized, they can be conveniently purified, stored and transported in powder form, while providing sufficient flexibility for assay control. The researchers, from the Wisconsin Alumni Research Foundation, have a patent pending on nanoparticles.

"The small size, superior stability, versatility of the surface modification and the high editing efficiency of nanocapsules make it a promising platform for many types of gene therapy," says Gong.

The team aims to further optimize nanocapsules in ongoing research for effective brain and eye editing.