Dr. Alysson R. Muotri, PhD, UC San Diego Professor and director of the stem cell program talks about repurposing an old Hep C drug to kill cells infected with Zika.
Interview conducted by Ivanhoe Broadcast News in March 2018.
What made you think to look at this Hepatitis C drug for Zika?
Dr. Muotri: Okay. Let me step back a moment and just give you the perspective of how we decided to start working on Zika. I’m really from Brazil and my lab here does stem cells work. We use stem cells to recapitulate human neurodevelopment. But by being connected to Brazil I have been seeing all the news and pictures of babies with their dramatic microcephaly symptoms and was wondering what is going on, what is this outbreak? A doctor has made the connection between the birth defect cases born during the outbreak and the Zika virus. These babies all seemed to be positive for the Zika virus. But at the same time this is just a correlation and there were other possible explanations. People were saying, well this might be because of vaccines or because of other drugs or toxins in the environment. We thought it would be really important to prove causation. And this is not something simple; I mean really to prove causation we have to show that the agent that you think is responsible for the disease actually causes the disease. Ethically this is an experiment you cannot do on humans. So we have to take advantage of models. We used two models to show causation. One is a mouse model where we isolate the Zika virus from one of the cases, infected a pregnant mouse and check if the animals were born with birth defects including microcephaly. The other model is a human model, by taking advantage of human pluripotent stem cells. These are stem cells that can be differentiated and specialized in different tissues. We have protocols in the lab to do that for the brain. We can make a brain organoid or a “mini-brain” that we use to recapitulate the key steps of human neurodevelopment. We can also expose those mini brains to the Zika virus, and to our surprise the virus not only infected these cells but kill them in such a fast fashion that at the end of the day what you ended up with cells that are dying, reducing the cortical thickness – a key feature of the microcephalic babies in Brazil. Once the causation was established now we know that the Zika virus has the capacity to lead to birth defects. We thought if we can we use this model to find drugs that might prevent, treat or even cure infected people from the Zika virus. One idea was to look for drugs that already exist and are approved by the FDA so we don’t lose time finding a completely new drug that might have to go through all the steps and clinical trials to be finally approved for the market. By repurposing a drug that already exists we gain time. So, we focused on this class of drugs. And one of them, sofusbuvir, is a drug that was initially approved for Hepatitis C virus. The way we find out that this drug might work or we hypothesized that this drug might work, was by aligning the genome (or the genetic material) from the Hepatitis C virus and the Zika virus. We noticed that they’re from the same family and they share a genomic region that is very similar between those two virus. This is a region in the genome that codes for a polymerase, an enzyme that the viruses uses to replicate themselves inside the cells. Sofusbuvir targets that polymerase. And because they’re very similar, we had hypothesized that the drug could target the Zika polymerase as well. We set up the following experiments: we first infected human mini-brains in our lab, and then start treating them with sofusbuvir, using different concentrations, and doses. We noticed that the treatment was working. The drug could inhibit the viral replication and the brain would develop as normal. That was an In Vitro study. Then we thought about an In Vivo study, by taking advantage of the mouse models we previously developed in the lab. We use adult animals, infected with Zika virus, and then start the drug treatment. We use different mouse models, some animals were immuno suppressed for a more dramatic effect. Once the immunosuppressed mice are in touch with the Zika virus they get really sick and die soon after. But by treating these mice with sofusbuvir right after the infection, we could again reduce the viral particles to the level that we can no longer detect and they did just fine. Next, we used a pregnant animal. And this is to check if we can inhibit or block what we call “vertical transmission”, ie, the virus from the mom that’s infected going to the fetus. We infected these pregnant animals and soon after the infection we started the treatment. We could see a similar result to the immuno suppressed animals – the moms get clean from the virus. There’s no circulating virus in the body and, as a consequence, the fetuses are protected. We collected the brain from those fetuses and we looked for evidence of virus particles and, again, we see none. Thus, we could completely block the viral transmission from mom to fetus. These are very encouraging data because the drug seems to work really nice and it is a drug that’s already available and could be used immediately. It encourages us to move on in to clinical trials. We’re looking for cohorts or populations of people that are infected with the Zika virus to start testing this drug in susceptible human populations.
It will probably be in Brazil because that where there’s a large concentration?
Dr. Muotri: In Brazil it’s definitely one of the biggest targets but there are other countries in Latin America where we start seeing outbreaks as well. One is Columbia, another Ecuador. Those places also have outbreaks and they might benefit by having a clinical trial being done there.
Is there a big book or a website that plots out the Hep C virus and the Zika virus and you can just match them up? How do you do that?
Dr. Muotri: We use computational tools to do this. We have access to the genome of those viruses and then aligned them and look how similar they are.
Did you have to look at them one after the other or the computer does that for you?
Dr. Muotri: The computer does that for us. There’s a bioinformatic colleague here who helps us on that. Moreover, we can recreate the tree dimensional model of these enzymes, together with the polymerase, and we can mimic in silico how the drug will act. You can see that in the same way that the Hepatitis C drug could block the Zika virus polymerase as well. It is our three dimensional models where one can actually visualize how the drug works.
The drug sofusbuvir is currently used for Hep C?
Dr. Muotri: Yes, it’s approved and is a treatment that actually cures you from Hepatitis C; it eliminates the virus from the body.
Stepping back again to the mini brains; is it just a petri dish of cells or you call it a mini brain? What does it look like?
Dr. Muotri: It starts from human pluripotent stem cells, I can show you some pictures or videos. From these cells there’s a recipe that we use. by changing factors in the media that they are floating around. And the cells spontaneously start growing as a 3-D structure. And as the cells grow, they self-organize. This is part of the beauty, the cells do this by themselves. They self-organize in something that resembles the human brain. And as they mature, these cells will start to become more connected to each other, forming networks. There’s a developmental process that you can follow over time. And they mimic what we see during human neurogenesis.
Does it actually look like a brain?
Dr. Muotri: It does not because it is small and we restricted to specific parts of the brain. For example, we focus on the frontal cortex. If you just look for that structure, it looks like the equivalent brain in humans. These mini-brains can grow up to two years and after that cells start dying especially at the center. Because all the nutrients that surround the minibrains goes into the cells by diffusion. After the 3D structure grow so much, and this is about half a centimeter (you can actually see it by naked eye) the cells in the center will start to necrose and eventually die. These 3D structures are not vascularized and there’s no vases going inside and providing for those cells. Although this is something that is a limit at this point, we are working on some protocols that makes them grow a little bit bigger.
What was your reaction when you realized how successful this was to treat the Zika virus?
Dr. Muotri: I think we’re all very excited because we never thought that this drug would work as nicely as it did. As a scientist, I am always very skeptical, creating ways to prove me wrong. We designed experiments to fail, and most of the time they do. Science is about 90% failures. But this situation was quite nice because we could systematically increase the sophistication of the experiments and the results still hold up. It’s a case to celebrate.
How long have you been working on this?
Dr. Muotri: On Zika, since December 2015.
Do you have any idea how soon this might go to human clinical trial?
Dr. Muotri: It all depends on approval by the IRB and we also need to get access to the drug. There’s some negotiation involved. We have the pharmaceutical company who owns the intellectual property for the drug, and we hope that they will offer us to use the drug to test in humans. This might take up to three to four months.
That’s not so bad.
Dr. Muotri: No, no it’s not bad at all. From the beginning of the demonstration of causation, to the finding of a promising drug, and now thinking about the clinical trial, that was within two years. This is fast, this is really fast. We’ve never seen something like that before. That’s why it’s another of those circumstances that’s quite unusual in science.
Do you need FDA approval for this if the trial is going to be in another country?
Dr. Muotri: We need the approval from their own countries to test drugs there.
From Brazil and Columbia?
Dr. Muotri: Yes, we don’t need the involvement from the FDA here.
You guys were the ones to prove causation, the Zika and the Microcephaly?
Dr. Muotri: That’s right, it is a Nature article in 2016.
What haven’t I asked you that you think you would like to get in the story?
Dr. Muotri: I think one of the aspects that I like the most is that the fact that everything was so fast. This is because we have all the technology and stem cell tools in place when the outbreak happened. I keep thinking about what are other situations that we might actually have science ready to go when a new outbreak happens. It boils down to the fact that the human stem cell component is a toolbox that we might use for other things that we’re not anticipating. I never anticipated working on Zika or a viral outbreak in South America and here I am doing this kind of stuff. I think this is an eye opener for the potential of stem cell technology.
END OF INTERVIEW
This information is intended for additional research purposes only. It is not to be used as a prescription or advice from Ivanhoe Broadcast News, Inc. or any medical professional interviewed. Ivanhoe Broadcast News, Inc. assumes no responsibility for the depth or accuracy of physician statements. Procedures or medicines apply to different people and medical factors; always consult your physician on medical matters.
If you would like more information, please contact:
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