Delivery of healthy proteins directly into human cells to replace malfunctioning proteins, called protein therapy, is considered one of the most direct and safe approaches to treat diseases. Low stability causes the proteins to be frequently broken down and digested by cells' protease enzymes before they reach their target in the body. Also it is very difficult to cross the cell membrane for proteins as the protease will usually digest it. Hence the effectiveness of protein therapy has been limited by low delivery efficiency and the poor stability of proteins. Currently, several protein therapeutics available only act outside of the cell because it's been difficult to deliver the proteins inside the cell. But a new development could change all this. Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have developed a new intracellular delivery platform that uses nanocapsules made up of a single-protein core with a thin polymer shell that can be engineered to either degrade or remain stable based on the cellular environment. The team has been able to use the new technology to stabilize the protein, making it very easy to cross the cell membrane, allowing the protein to function properly once inside the cell.
Nanocapsules are submicroscopic containers composed of an oily or aqueous core, herein a single protein; that is surrounded by a thin, permeable polymer membrane roughly several to tens of nanometers thick. The membranes of the nanocapsules used in the new UCLA delivery method can degrade or remain intact depending on the size of the molecular substrates with which their embedded protein must interact.
Non-degradable nanocapsules are more stable, and small molecular substrates can readily diffuse to the protein embedded inside. The capsule's non-degradable skin meanwhile protects the cargo from protease attacks and stabilizes the protein from other factors, like varying temperatures and pH levels. However, a non-degradable skin may also prevent substrates of larger molecular weight from reaching the embedded protein. In order for the protein to be able to interact with a large substrate, a degradable skin can also be used. When the protein nanocapsule is taken in by the cell, it will stay within the endosome initially. Endosomes generally have lower pH levels than the outside cellular environment; the lower pH triggers the degradation of the polymer skin layer, releasing the protein cargo intracellularly. The team has demonstrated that such skin layers can also be degraded by incorporating components that are sensitive to proteases. This approach will also allow for a more targeted delivery of the proteins.
The new study has shown that multiple proteins can now be delivered to cells with high efficiency and activity but low toxicity, allowing for potential applications in protein therapies, vaccines, cellular imaging, tumor tracking, cancer therapies and even cosmetics. Covering the protein payload with a polymeric shell provides added stability in circulation, where there are plenty of proteases to degrade the naked protein, improving efficacy of delivery. It is also important that to deliver cargo intracellularly and to control the release of the protein cargo by pH or other environmental parameters.
The team hopes the new technology will serve as a delivery platform for any type of protein or protein drug. Though the study, when originally submitted, described the use of the technology with five different proteins, in the short time since, the team has expanded to more than two dozen different proteins.