Scientists have been looking for better ways to deliver DNA to cells in vivo so that genetic engineering can become effective enough to be used in the clinic. This paper explores several old methodologies as well as one developed by the authors that is an improvement on the efficacy, ease of scale, and likelihood of success in delivering DNA to target cells.
Early methods of delivering DNA to target cells in vivo included a simple lipoplex, a construct made of lipids that could encapsulate a molecule of DNA and deliver it to the cell. However, these early lipoplexes had problems. The immune system would quickly clear them from the body, they were large enough to get stuck in the extracellular matrix (ECM), and they clumped together with anions in various places in the body.
Later methods attempted to use a nucleic acid shell as a delivery system. Nucleic acids are anionic, about 100 nm in diameter, and won’t cause an immune response. This method has shown it has trade-offs, however. Nucleic acid shells are hydrophilic and therefore have a tough time getting across the cell’s membrane.
The scientists of this paper endeavored to assess the main components that a delivery system would need and evaluate the tools that currently exist to see how well they match these needs.
This paper is a meta-analysis that reviews the progress, barriers, and recent solutions to those barriers with regards to delivery of DNA in a nanoparticle to a target cell. As such the main method is one of literature review and not the creation of novel data via experimentation.
Size is crucial to the success, or lack thereof, of delivering a DNA payload to a cell. The scientists determined that the ideal size of a delivery system would be close to, and preferably under, 100 nm in diameter. The best methods at the time of publication used lipids, which help condense the DNA payload down to a very small area.
Charge of the particle is also crucial. While cationic lipid shell helps compact DNA, once they are in vivo, they lose a lot of value due to clumping up. To get around this, the scientists recommend one of four strategies: 1). Covalently attaching molecules to neutralize the cationic lipid outer shell 2). Use titratable cationic lipids, which will be neutral within the body’s typical pH. 3). Use disulfide links that can later be modified to make the lipids neutral, or 4). Use an anionic shell.
Transfection to the cell can be achieved by either using neutral lipids or cholesterol, which the cell will take in via endocytosis. In addition, some targeting ligands were used, though efficacy was questionable when the paper was published.
In addition to the components and make-up of the nanoparticle delivery system, it’s preparation is also critical. Anything that may be used in the drug industry for clinical purposes gains an added benefit if it is easy to produce and can be produced at scale.
The most effective way of creating these particles to date involves using a detergent dialysis. These detergents allow the creation process of the nanoparticles to proceed slowly and reliably while keeping size of the nanoparticle down and success of encapsulation high. In fact, using an ethanol based detergent, scientists have been able to encapsulate large amounts (225 mg of DNA in one day) and with high encapsulation success rate (90% success rate vs 60% success rate with other methods).
According to the authors, “This review of recent progresses on the methods to formulate lipidic NP to encapsulate nucleic acid therapeutics has revealed that steady progress is being made in the development of methods to prepare small diameter lipid particles that stably encapsulate nucleic acids.” (Li, W. 2007). While this definitely represents progress in the field, one technical barrier that still stands in the way of more efficacious treatments involves delivery of the DNA into the nucleus. The material addressed in this summary has solely been in relation to packaging DNA and successfully transfecting the nanoparticle with a high success rate and does not address this hurdle of DNA delivery into the nucleus.
On the other hand, some forms of treatments don’t require DNA to make it all the way into the nucleus, so what has been achieved to date may be enough. Lastly, with the difficulty of the technical problems that lay ahead, the authors suggest that without big pharmaceutical company involvement, progress will be slow.
Li, W., & Szoka, F. C. (2007). Lipid-based Nanoparticles for Nucleic Acid Delivery. Pharmaceutical Research, 24(3), 438-449. doi:10.1007/s11095-006-9180-5
- Acquiring Substantive Knowledge: This paper presents advanced concepts in synthetic biology that assume a lot of background knowledge. It required additional time in researching foundation concepts, such as background research on inflammatory response in relation to charged particles. The presentation of hurdles and successes in overcoming those hurdles proved illuminating.
- Communicating Effectively: This proved to be the most challenging as the content of the paper is extremely dense. Knowing what details to include to make the summary easy to digest without erring on the side of gross generalizations proved difficult. At each turn in the summary, there could have been a greater level of detail added, from more technical analysis to more technical terms. However, at some point in adding granularity, a summary ceases to be a summary and becomes a watered down paraphrasing.