Gene therapy on film

Researchers have developed ultrathin, nanoscale films composed of DNA and water-soluble polymers that allow controlled release of DNA from surfaces to target treatment in gene therapy.

Prof. David Lynn and his colleagues at the University of Wisconsin School of Medicine and Public Health created the films which can be used to coat implantable medical devices, offering a novel way to route useful genes to exactly where they could do the most good.

Lynn has used the nanoscale films to coat intravascular stents, small metal-mesh cylinders inserted during medical procedures to open blocked arteries. While similar in concept to currently available drug-coated stents, Lynn's devices could offer additional advantages. For example, Lynn hopes to deliver genes that could prevent the growth of smooth muscle tissue into the stents, a process which can re-clog arteries, or that could treat the underlying causes of cardiovascular disease.

When placed in or near a body tissue, the films are designed to degrade and release the DNA. Large strands of DNA cannot normally penetrate cells, so Lynn constructs his films with special polymers designed to bundle the genes into small tight packages that cells can import. Once inside, the genes instruct the cells to make proteins.

The research team creates the films one layer at a time using a dip-coating method, dunking first in one solution, then another. The individual layers are so thin it would take roughly 10,000 of them to equal the thickness of a single sheet of paper.

The researchers alternate layers of DNA with layers of a polymer that is stable when dry but that degrades when exposed to water. Because the polymers carry a positive electric charge that is attractive to DNA, each polymer layer also ‘primes’ the surface to accept the next layer of DNA. While electrostatic forces between the layers keep the film stable in dry, room-temperature conditions, the polymers break down easily in a wet biological environment — like the inside of a patient's body.

Using the layering method, the team can control the amount of DNA by adding more layers, or can even layer multiple ingredients in a specific order. Tweaking the polymer structure slightly can change how quickly the films erode and thus how long cells are exposed to the gene therapy.

The films start to break down when they come into contact with water. ‘The architecture of the film determines the manner in which [DNA] is released,’ Lynn said. In his lab, they have developed some films that fall apart all at once, releasing all the ingredients simultaneously.

More recent designs erode like a bar of soap, with the effect that outer layers are released before inner layers. By placing one gene in the outer layers and another in the inner layers, they can deliver different products sequentially. ‘This kind of control is extremely difficult to achieve using conventional materials,’ Lynn explains.

In addition to delivering DNA from stents, Lynn envisions using these nanoscale films to deliver DNA from other implantable devices. The films also may improve methods for engineering lab-grown tissues, in which precisely controlled delivery of multiple DNA, or protein-based agents, is required to coax cells to develop into functional tissues and organs.