Electronic Pulses Could Reduce the Need for High Doses in Gene Therapy Delivery
New technique employs electric pulses to make the human body more receptive to gene therapies.
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While gene therapy has proven to be promising for diseases ranging from cancer to diabetes, the challenge of getting the right dose of genetic material into target cells has caused a bottleneck in the application of such therapies.
In new research published in PLOS ONE, researchers from the University of Wisconsin–Madison have reported on the development of a technique employing electric pulses to make the human body more receptive to certain gene therapies.
We spoke to two of the study authors, Professors Susan Hagness and John Booske, to learn more about the benefits of direct delivery of gene therapy materials, the challenges associated with gene therapy delivery and the use of electronic pulses to encourage uptake of genetic material.
Q: What are the benefits of direct delivery of gene therapy material?
A: Direct delivery may reduce the total dose needed for treatment because it eliminates the attrition of material during circulation through the body and other organs prior to arrival in the targeted tissue/organ (compared to, say, systemic, peripheral injection into a remote blood vessel).
Systemic delivery typically requires large(r) doses to compensate for losses during passage through the circulatory system and other organs. Manufacturing the genetic material delivered via virus vectors is expensive – prohibitively so for many treatments of inherited metabolic diseases (such as hemophilia, diabetes, etc.). Reducing the required dose is critical to practical, affordable treatments.
Direct delivery may also minimize the time the material spends in the circulatory system before uptake in the liver cells. This reduces the likelihood that the immune system will mount an attack on the gene therapy “foreign” material and destroy or inactivate it. The larger doses required with systemic, peripheral injection, along with the associated immunological response (e.g., cytokine storms) present a heightened risk.
Direct delivery is a pathway to reduce the doses required and bypass the immune counter-response, thereby reducing cost and increasing safety.
Q: What are the challenges of gene therapy delivery, and how do these affect patients?
A: The challenges of conventional gene therapy delivery approaches (peripheral injection, e.g., in a remote blood vessel) include the requirements for large doses (to ensure enough of the dose finally arrives at the targeted site and is taken up by the targeted tissue cells) and the risk of immune counter-response to the injection of foreign genetic material.
The former leads to a prohibitively expensive cost of treatment, making it impractical as a widespread treatment option. The latter includes loss of genetic material that may result in ineffective treatment or a dangerous overreaction that can threaten the health of the patient.
Q: How does the application of electronic pulses increase the uptake of gene therapy material into hepatocytes?
A: We are not certain what the specific underlying physical mechanisms are that result in enhanced uptake of the gene therapy material. We have some hypotheses, but no definitive identification of a mechanism currently.
Our findings, reported in the PLOS ONE article, help to rule out some of the possible mechanisms. For example, we know that electric pulses do not modify the genetic material directly before it is absorbed into the cells, and we know that the electric pulses do not modify the culture medium or environment that the cells reside in.
Future experiments are being designed and conducted to pin down the mechanism(s) that are at play. We know that electric pulses induce (nano)pores into the cell membranes, and this effect has been exploited in other investigations to permeabilize the membranes and allow small(er) molecules to be taken up by those cells. However, the larger size of the virus vector (AAV8) capsids used in our experiments lends doubt to the likelihood that this is the mechanism responsible for enhanced uptake in our experiments. It is a subject for further investigation.
Q: What impact could efficient delivery of gene therapies have on patients in the future?
A: Efficient delivery could make many gene therapy cures affordable and safe for a large population of patients. To elaborate, genetic mutation-based metabolic diseases significantly reduce the quality of life for hundreds of millions of people in the world. There are 100s of such diseases, including diabetes, cystic fibrosis, sickle cell anemia and hemophilia. Many of them involve the liver due to its central role in metabolism. Developed countries spend trillions of dollars each year on patient care, with nearly a trillion dollars spent annually on type 1 diabetes (T1D) alone.
Cures for many of these diseases could be attainable if practical, cost-effective methods existed to modify the gene(s) of the liver cells, sufficient to correct the inherited metabolic discrepancy.
Some success with systemic injection gene therapy has been reported, but only in small mammals or with prohibitive costs (~$1 M/treatment in the case of hemophilia). In other words, a famous statement in 1999 by Salk Institute Professor Inder Verma, one of the foremost recognized leaders in gene therapy, still remains relevant today: “There are only three problems in gene therapy: delivery, delivery, delivery.”
Q: What are the next steps in translating this research into clinical trials?
A: Next steps include in vitro investigations of optimal electric pulse parameters and in vivo studies to determine how the phenomenon (which we have observed in vitro) manifests in living tissues. To date, we have only had the opportunity to investigate electric pulsing with a single choice of electric field strength and pulse length, and only with single pulses.
An important question to answer is whether other treatment parameter combinations–i.e., different electric field strengths, different pulse lengths, and/or multiple pulses–produce a stronger effect. Of course, it is important to identify the maximum treatment parameter thresholds above which cell or tissue damage occurs, to ensure that parameter choices are always safely below those thresholds. Meanwhile, our experiments to date were conducted on cells in well culture plates (i.e., in vitro). Although research has shown that cells in vivo (in living tissues) can have similar responses to electric pulsing as cells in vitro, the magnitude of the responses and the parameter values that produce the maximum safe response can be expected to be different. So, experiments with animal models are the next critical step, especially with larger mammals.
Q: Do you have plans to explore the use of electronic pulses in the delivery of gene therapies to other cell types?
A: The potential impact of translating this to clinical practice in liver/hepatocytes has considerable impact value, so that is our primary focus for now. But certainly, expanding the scope of these investigations is of interest in the longer term.
