Challenges in creating smart drug delivery vehicles
Making liposome bubbles for drug delivery is relatively easy, but keeping them intact through the manufacturing process is difficult. We all know from playing with soap-based bubbles outside on a hot day that they pop easily! Now imagine blowing up bubbles that are 50 to 100 nanometers in diameter and trying to load them with a soluble drug. Just as with the hot summer day bubble analogy, the nanometer scale bubbles pop when you try to force something inside. Now think of what would happen if you tried to freeze dry a bubble. Even if you can get it to stay in the right shape through the freeze drying process, when you add water back again…pop!
Scientists have tried many approaches to stabilizing the liposome bubble shape at the right size so that it can be useful after storage. Some have coated the bubbles with polymers of sugar or proteins. This keeps the structure intact when you re-hydrate the bubbles or load them, but the added layer around the bubble is a big drawback when it comes to delivering its contents.
How our technology overcomes these challenges
Our technology overcomes these stability issues by building an internal scaffold for the bubble made out of DNA. Schematically, it would look like a wheel where the tread is the liposome bubble and the spokes and axis are the DNA. The DNA scaffold keeps the bubble’s shape during initial formation, loading, and storage. What makes this approach even more exciting is that the DNA encodes information, which allows us to add in smart drugs by designing them to link into the liposome scaffold. This means that a DNA scaffold can be loaded with smart drugs before it is capped with a bubble layer.
The scaffold can also bind to other useful things like enzymes, proteins, or aptamers, which are useful for breaking through the barriers of the body and cell. For example, enzymes can be added to loosen the DNA scaffold at certain temperatures in order to make it easier for the liposome to fuse with a cell membrane. Aptamers are very useful DNA chains which can bind to a cell surface much like an antibody. Because aptamers are DNA, they are easy to link in to the exterior of our liposome DNA scaffolds. This makes changing the target cell and tissue for our liposomes far easier than other methods.
Lessons learned from viruses
Enveloped viruses are as old as the cell and have learned a thing or two along the way. These viruses depend on two characteristics to move into the cell: membrane fusion and specific cell affinity. Membrane fusion means that the viruses’ envelop mixes with the cell membrane, releasing all the contents of the virus into the cell at once. Specific cell affinity is determined by what type of cell the virus can grow in. Binding to very specific anchors on the cell’s surface greatly facilitates the viruses’ entry.
Although some have tried viruses as drug delivery vehicles, many problems continue to prevent their widespread use. To learn more about viral delivery problems read our blog post on the topic. Our DNA nanoliposomes have some similar abilities to enveloped viruses, but are completely incapable of replicating or being infectious. The similarities are instead in their size and the ability to use membrane fusion catalysis and cell surface anchoring to deliver their contents into cells. In this way, we retain the benefits of viral delivery physiology without any of the negative ethical, cell specificity, and toxicity concerns.
Since our technology can be built stepwise with multiple layers like an onion, each layer can be used to deliver the underlying liposome contents through a cell or tissue barrier in series. So the outer layer of the bubble gets mixed with the cell’s outer membrane and the second layer of the bubble moves through the cytoplasm to deliver the third and fourth layers through the nuclear membrane. This leaves the contents of liposome floating with the chromosomes.
Hypervariability and adaptability for modern smart drug medicine
One of the greatest benefits of our technology is its ability to be adapted to fit new situations. DNA liposomes are able to target new diseases by tailoring the affinity of the surface tag. Some issues that concerned us in designing DNA liposomes wouldn’t normally be addressable with other delivery models. For example, the insides (cytoplasm) of cells are crowded with large organelles, the cytoskeleton, polysaccharides, nucleic acids, and proteins. This phenomenon, called macromolecular crowding, can be a tricky issue to overcome for the movement of a liposome through the cytoplasm. Our liposomes can be fashioned to use the natural cytoplasmic circulation to facilitate moving to the nucleus without getting stuck somewhere in the crowded cytoplasm. This isn’t possible with any other method.
Immune tolerance is another challenge for delivery models. Quite often a genetic disease treatment will involve a gene that is new to the patient’s immune system. Without first addressing the new gene’s immune status, the immune system can simply wipe out any treated cells before they can benefit from treatment. A classic example of this is in the administration of the CFTR gene in the lungs of cystic fibrosis patients. Without an immune tolerance treatment, the white blood cells of the body attack the CFTR treated lung cells to remove the perceived threat. Our technology would address this issue by creating two separate treatments. The first treatment would present the CFTR gene to the immune system to create lifelong systemic tolerance. The second treatment would then address the gene deficiency. In this case, the CFTR gene would be inserted in the cells that need it.