Amy Wong Strilchuk (left) and Dr. Christian Kastrup (right). Image Credit: UBC Michael Smith Laboratories.
Blood clots play a part in many severe health issues, from causing strokes and heart attacks to influencing neurodegenerative diseases like Alzheimer’s. Usually, a patient who develops a clot can dissolve it by taking an anticoagulant drug, but risks the common side effect of excessive bleeding.
A recent study published by the Kastrup Lab at the Centre for Blood Research and Michael Smith Laboratories helps provide a potential solution to this issue through a new approach called siRNA gene therapy.1 We chatted with lead authors Dr. Christian Kastrup (CK) and PhD Candidate Amy Wong Strilchuk (AWS) about their research, and how their findings might help dissolve clots safely.
What was your study about?
CK: We developed a new tool to decrease the activity of Coagulation Factor XIII (FXIII), a blood protein that helps link molecules together to form deadly blood clots. This protein stabilizes clots and makes them more difficult to break down, which can lead to health complications like heart attacks.
After a single injection of silencing RNA (siRNA), delivered using lipid nanoparticles (LNPs), we saw a 90% decrease of FXIII activity for multiple weeks. The decreased activity helped dissolve blood clots more easily without excessive bleeding, which is, unfortunately, a common side effect of current drug therapies.
Research like this gives us a new gene therapy tool to treat all kinds of diseases where FXIII plays a role.
How does siRNA therapy work? How is it different than taking an anticoagulant drug?
AWS: Most anticoagulant drugs indiscriminately inhibit multiple members of the coagulation cascade. This stops the blood clotting process altogether, which means that even minor injuries can put patients at risk of excessive bleeding. The effects of anticoagulants are also more difficult to reverse, because clotting factors from newly transfused blood would still be subject to inhibition by these drugs.
By contrast, our siRNA is delivered into liver cells where most coagulation proteins are made, and stops the synthesis of a specific target – FXIII, in this case – instead of inhibiting the coagulation cascade as a whole. FXIII is not needed for initial clot formation, but rather works downstream to stabilize existing clots, which is why inhibiting it will not pose the same risks of bleeding as other anticoagulants. If the patient suffers a major injury or requires surgery, reversing the siRNA therapy is much easier, since transfusing blood products or FXIII concentrate would immediately supplement the missing protein and help blood return to its normal clotting process.
What is the importance of this research?
CK: In the near term, I think this research is useful to understanding the biochemistry of blood coagulation, as well as the role that blood coagulation plays in inflammation, Alzheimer’s, or other neurodegenerative diseases.
The future goal of this gene therapy approach would look at preventing the causes of stroke, heart attack, and other health complications caused by deadly blood clots. It’s a nice research tool – it has the potential to provide a better and safer therapeutic approach to thrombotic disorders.
What were some techniques you used?
AWS: One of the major techniques we used is thromboelastography (TEG), which measures the stiffness of blood clots over time as they form and lyse, or break down. It provides us with detailed information about different clot characteristics like clot formation rate, overall clot strength, and how easily a clot lyses. In this technique, a sensor is suspended in an oscillating cup that contains a blood sample. The sensor measures the force applied against it by the sample; the force increases as the sample forms a stiffer clot matrix, or decreases as the sample is broken down back into liquid clot lysate.
We also used techniques to identify which proteins were causing changes in these clot characteristics. First, we stimulated the blood to clot, then dissolved the clots using a chemical mixture and analyzed their protein components using a western blot. This allowed us to identify the proteins that were increasing the clots’ resistance to breaking down, and how much their activity depended on FXIII.
What did you find most surprising about the study?
AWS: It’s interesting to see how one injection of the agent we used can have such long-lasting effects. In our study, we see the desired effect for three to five weeks after a single administration — that’s just so different than most therapies out there.
CK: The biggest surprise for me was how effective the siRNA and lipid nanoparticle approach was… This technology was developed at UBC by co-author Dr. Pieter Cullis.
It was one of the first times we used it and I was really surprised at how good it was at ‘knocking down’ or inhibiting the protein that promotes clot stability, thus helping the blood clots break down more easily and safely.
These LNPs are now being used to deliver the leading COVID-19 vaccines, and we’re very happy for Pieter and everyone else who has been championing LNP use.
It’s interesting to see how one injection of the agent we used can have such long-lasting effects. In our study, we see the desired effect for three to five weeks after a single administration — that’s just so different than most therapies out there.
Thank you to Dr. Kastrup and Amy for sharing their work with us! Their research offers a glimpse into how gene therapy can provide a novel approach to safely breaking down blood clots.
We’d also like to acknowledge the many other CBR and UBC collaborators on the study, including: Dr. Ed Conway, Nooshin Safikhan, Jerry Leung, Scott Meixner, Dr. Ed Pryzdial, Dr. Pieter Cullis, Dr. Jayesh Kulkarni, and Dr. Michael Sutherland.
This blog post was adapted from a Tweet thread on Twitter. View the Tweet thread here.
References:
1 Strilchuk AW, Meixner SC, Leung J, et al. Sustained Depletion of FXIII-A by Inducing Acquired FXIII-B Deficiency. Blood (2020) 136 (25):2946-2954. doi: 10.1182/blood.2020004976.