'Cloaked' proteins deliver cancer-killing therapeutics into cells

The "cloaked" proteins can be captured by lipid nanoparticles, which are akin to tiny bubbles of fat. These bubbles are small enough to sneak their hidden cargo into living cells, where the proteins uncloak and exert their therapeutic effect.

The group's paper published in ACS Central Science. The lead author is doctoral student Azmain Alamgir, who works in the labs of the paper's co-senior authors, Chris Alabi, associate professor of chemical and biomolecular engineering, and Matt DeLisa, professor of engineering.

For some drugs to impact a cell's biology, and ultimately treat disease, they need to get inside the cell and reach a specific space. Protein-based therapeutics have many virtues -- they can have more specific effects, with lower toxicity and diminished immune response -- but ease of delivery is not one of them. Proteins are large and cumbersome and don't freely diffuse into cells as easily as small molecules do.

"We had been looking for a clever way to efficiently get our engineered proteins inside of cells, especially in a translational context that would not only work in lab-cultured cells, but that would also be effective and safe in animal models and eventually in humans," DeLisa said.

The researchers had the broad idea of using a bioconjugation approach that would allow the proteins to be loaded into lipid nanoparticles, which form around nucleic acids. A major advantage of this approach was that lipid nanoparticles were a key component in the successful COVID-19 vaccines developed by Pfizer-BioNTech and Moderna.

Those vaccines worked by delivering a payload in the form of messenger RNA, which are nucleic acids. The researchers now would use the same lipid nanoparticle delivery concept -- the same materials even -- but with a protein payload. The trick would be to make proteins look more like nucleic acids.

The researchers found they could accomplish this by "cloaking" the proteins with a negatively charged ion, so they would join with the positively charged lipids electrostatically.

"The crux of our strategy is conceptually very simple," Alamgir said. "We're taking proteins and specifically remodeling their surfaces with negative charges, so they look like nucleic acids and can similarly assemble into nanoparticles when formulated with the characteristic lipids."

The team successfully demonstrated the cloaking method with lysine-reactive sulfonated compounds, killing cancer cells with ribonuclease A and inhibiting tumor signaling with monoclonal immunoglobulin G (IgG) antibodies.