This study tests antisense oligonucleotides (ASOs) targeting Prnp in wild‑type mice infected with RML prions and shows that sequence‑specific PrP lowering by bolus i.c.v. ASO dosing delays disease and extends survival, even when given near clinical onset.
0:00Welcome to Base by Base, the papercast that brings genomics to you wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. Yes thank you for tuning in. This is the 2nd of 2 episodes dedicated to Lido Sousa, the Brazilian Aviation Communicator behind the channel, AVONZ Musicas, Airplanes, and Music, who shared publicly in August 2026 that he had been diagnosed with Kritzfeldt Jakub disease.
0:24In our previous episode, we looked at a genetic silencing approach now entering its 1st human trial. Today, we go back to the study that opened this whole field. The experiment that 1st showed in living animals that lowering pryon protein after symptoms have already begun can still change the course of the disease.
0:42Right. It's such a critical piece of the puzzle. So we're asking one massive question today. Once a prion disease has actually started, you know, once it's taken hold, is it definitively too late? Yeah, and historically, I mean, for decades, for any rapidly progressive neurological condition like this, the medical consensus was just a devastating yet.
1:01It was always assumed to be too late. The narrative is just this steady, unstoppable decline. Like a runaway train or something. Exactly. But the research we're unpacking today. It completely reframes that assumption.
1:14It asks if we can intercept a fatal brain disease that has already, you know, breached the walls and started causing severe structural damage. And before we get into how they actually tested this, we need to talk about who did the testing.
1:26Because this wasn't just a small side project, right? Oh no, not at all. The collaboration behind this work is a huge part of why it's so robust. So we're talking about a combined effort from the NIIed Rocky Mountain Laboratories, which was led by Byron Coffey, along with the broad institute team of Sonia Velab and Eric Minikl, and Iona's Pharmaceuticals.
1:46So that's government, academia, and industry all teaming up. Yeah, it's a rare and really powerful thing to see those 3 pillars converging on a single, highly focused goal. And this specific paper, from 2019, it literally became the scientific foundation on which all the current genetic silencing trials in this space were built.
2:07Wow. Okay, so to understand what they pulled off. Let's establish what we're actually fighting here. Prand disease is uh, it's terrifyingly unique. I always kind of explain it using a zombie analogy. Oh I like that.
2:18Yeah, so in our bodies, we naturally produce this normal cellular protein called PRP. It's just hanging out mostly in the central nervous system, anchored to the cell membranes. It's just a normal guy.
2:29Right, Minding its own business. Exactly. But in Prion disease, one of those normal PRP proteins misfolds. It twists into this dangerous rogue shape. Yeah, PRPSE. Right. And that rogue protein acts like a zombie.
2:43So it bumps into a normal PRP protein, binds to it, and basically bites it, forcing that normal protein to misfold as well. So then you have 2 zombies. And then four, and then eight. Right. It triggers this relentless exponential chain reaction.
2:57They clump together, form these toxic aggregates, and ultimately cause massive neuronal death. The molecular mechanism is truly that insidious. And what's really challenging is how this chain reaction even starts in the real world.
3:09We generally classify pryan diseases into 3 etiologies. Okay, what are they? First, you have the acquired form, which is incredibly rare today. That's when someone is exposed to external prions, like through contaminated surgical instruments or historically eating infected meat, which led to variant CJD.
3:27Right, the mad cow era. Exactly. Second, there are genetic forms. This is where a specific inherited mutation in the PRNP gene makes a person's normal PRP protein unstable. So it's highly susceptible to just spontaneously misfolding on its own.
3:43But those two, acquired and genetic. That's not most people, right? No, the vast majority, roughly 85% of human cases, are entirely sporadic. 85%. Yeah, there's no genetic mutation from a parent, no exposure to contaminated material.
3:57It's just this incredibly unlucky biological event where a single wild type protein randomly misfolds and kicks off the whole fatal cascade. That is so scary. Just a random roll of the biological dice.
4:09It is, but here is the critical thing, regardless of whether it's acquired genetic or sporadic, the underlying vulnerability of the disease remains exactly the same. Meaning the disease still needs normal proteins to convert.
4:20Exactly. The prying contagion relies entirely on the body's own continuous production of normal PRP protein. It needs fuel. So, okay, if the disease is completely dependent on our own biology supplying the fuel, the obvious question is, uh, can we just turn off the tap?
4:38Like if we stop making normal PRP, does the disease halt? But wait, don't we need that protein? I mean, our brains are full of it. You'd think so, right. It's a very logical concern, but genetics has actually heavily validated this therapeutic hypothesis.
4:52Decades of research show that the normal PRP protein is surprisingly dispensable. Dispensable. We can just live without it. Yeah. Scientists have engineered knockout animals, mice, goats, cattle that completely lack the prion gene.
5:05They produce 0 PRP, and they are perfectly healthy. Wait, really? A whole cow with no PRP. Yep. They develop normally. Their neurological function is fine, normal lifespans. And we even have robust genomic data from human populations showing individuals who carry loss of function variants.
5:19So people walking around right now. Yes, essentially they have one copy of their prion gene turned off, so they produce half the normal amount of the protein, and they are totally healthy. No neurological deficits whatsoever.
5:30Oh, wow. So we're manufacturing this protein, but our central nervous system doesn't strictly need it to survive. That makes PRP like the perfect drug target, doesn't it? It's an unusually good target, yes.
5:43Because the protein is dispensable, but the disease absolutely requires it. So if we eliminate it, the disease stops spreading, and the patient doesn't suffer some catastrophic side effect from losing the protein.
5:55That's the theory, exactly. Which brings us to the actual tool this 2019 team used to try and turn off that tap. Anti-sense oliga nucleotides or ASOs. Now, for those cracking along, we know that DNA transcribes into Messenger RNA, and that RNA is then translated into a protein.
6:12The goal here isn't to alter the DNA itself, right? We're trying to intercept that RNA message before the PRP protein can even be built. Precisely. ASOs are basically the synthetic, single stranded strings of nucleic acids.
6:25They are designed with a specific sequence that is perfectly complementary to the target messenger RNA. In this case the MRNA for the PRP protein. Sounds like a matching puzzle piece. Yes. When the ASO enters the cell, it seeks out and binds directly to that target MRNA.
6:43This forms a DNA RNA heteroduplex. A heteroduplex, just a hybrid molecule. And this hybrid acts like a flair for the cell's native immune system. It triggers an enzyme called Arna's H1. Okay. And that enzyme recognizes this abnormal double stranded structure and just cleaves the ONA strand.
7:02It destroys the instructions before the ribosome can ever translate it into the prian protein. Oh, that's brilliant. So the drug doesn't just block the RNA. It actually recruits the cell's own cleanup crew to shred the blueprint.
7:12Exactly. a highly efficient mechanism. But, and I have to push back a bit on the timeline here, because we've known about ASOs for a while, right? And RNA interference technologies like Serno, we've known for decades that PRP is the required fuel.
7:25So why wasn't this solved like 15 years ago. What were the historical roadblocks that made this specific 2019 paper such a big deal? Well, earlier researchers were practically flying blind. They ran into a massive wall of methodological and chemical limitations, like you mentioned Cerna, small interfering RNA.
7:45It struggled immensely with central nervous system delivery. Because the brain is hard to get into. Exactly. Brain tissue is notoriously difficult to penetrate. Surname molecules just could not achieve widespread distribution.
7:58They'd stay completely localized near the injection site. Oh, so they'd only treat like one tiny spot in the brain. Right, which isn't helpful for a disease spreading everywhere. ASO is offered away forward because they can be chemically modified by altering the sugar backbone of the nucleotides.
8:12Scientists made ASOs highly stable in the cerber spinal fluid. So they wouldn't just get immediately chewed up by enzymes. Precisely. But even with those chemical modifications. The early ASO experiments in prion disease were plagued by major unresolved issues.
8:27Yeah, looking at the background, there were 3 major historical hurdles that stood out to me. And this 2019 team set out to explicitly solve them, right? Yes So the 1st was mechanism and anguity. Like, past studies would give these early generation compounds to mice.
8:42They'd see a slight extension in survival, but they had no idea why. Like, was the drug actually triggering Arnie's H2 lower the RNA or was it just physically sticking to the misfolded prions? Right. That physical sticking is what we call an aptimeric effect.
8:56Prayons are notoriously sticky proteins, and nucleic acids can sometimes bind to them nonspecifically. Like molecular glue. Exactly. And if a drug is just acting like glue, temporarily slowing down the aggregation, that is not a reliable or scalable pharmacological mechanism.
9:12Definitively targeted genetic silencing, not just random chemical interference. Okay, so that was hurdle one. And even when they tried to figure that out, they hit the 2nd massive hurdle, delivery toxicity.
9:23Oh, this was a huge problem. The old studies relied on continuous intraventricular infusion, meaning they were surgically implanting these tiny osmotic pumps into the brains of the mice. To drip the drug in constantly.
9:37But the pumps themselves were so harsh, they caused so much tissue damage in necrosis, that half the mice were dying from the complications of the delivery system long before the pryan disease even killed them.
9:49Which naturally leads to the 3rd and really the most clinically devastating hurdle. Because the delivery method was so toxic, and the early drugs weren't optimized, researchers could only show a survival benefit if they treated the animals immediately, sometimes literally the day after they were infected.
10:05Whoa, day one. Yeah. The mice simply wouldn't live long enough to test late stage efficacy. So they could never answer the most important clinical question, which is, does this drug work after the disease is already deeply established?
10:17And that is the crucial question for human patients, because, going back to what you said earlier, 85% of human cases are sporadic, people have absolutely no idea they are developing prion disease until the cognitive and motor symptoms show up.
10:31By the time a patient gets a diagnosis, the neurological fire is already raging. Exactly. So to finally overcome these failures, the 2019 team designed this radically different, highly controlled methodology, they infected their mouse cohorts, inter-cerebrally, with a very specific aggressive strain of prions known as the RML strain.
10:50Right, the Rocky Mountain Lab strain. It's a very standard, well characterized model. And to solve that delivery toxicity issue, they entirely abandon the continuous osmotic pumps. Thank goodness. Yeah.
11:02Instead, they used bolus intracerbro ventricular injections, or ICV doses. Meaning just a shot. Yes, spaced out, single injections of the ASO delivered directly into the fluid filled ventricles of the brain.
11:15It's a rapid delivery of a concentrated dose, relying on the chemical stability of the modern ASO to just circulate naturally through the cerebrospinal fluid and permeate the tissue over time. So much less invasive.
11:26And they engineered 2 active ASOs for this experiment. Let's call them active ASO1 and active ASO2. They targeted different regions of the mouse, PRMP gene, I assume, to make sure the effects weren't just a fluke of one specific sequence.
11:42Exactly. But the most brilliant part of their methodology, I think, was the inclusion of a control ASO. Yes, the scrambled one. Right. This control molecule had the exact same chemical modifications, the same altered sugar backbone, but they scrambled the nucleotite sequence, so it didn't match any RNA transcript in the mouse genome.
12:01It was just gibberish. Basically, yeah. And the control ASO was the ultimate test for that 1st historical hurdle, mechanism ambiguity. Because if the scrambled ASO also extended survival, it would mean the therapeutic effect was just that Apomeric sticky interaction.
12:17Right. I mean, the chemistry itself was just gumming up the works, not actually silencing the gene. Right. But if only the active ASOs work. The mechanism was definitively RNA lowering. Okay, so let's look at the actual experiment phases.
12:29The 1st was the prophylactic arm, designed to test pure prevention. They gave these bullus injections every 60 to 90 days, starting 14 days before the mice were even infected. Yes. And the numbers from this prophylactic arm are absolutely staggering.
12:43By continuously suppressing the normal PRP protein, before the infection could take hold, the active ASOs delayed the onset of clinical signs by up to 99%. It's incredible. And they extended all cause survival, which measures how long the animals lived overall, by 61% to 98% compared to the saline treated control mice.
13:0498%. That's basically doubling their lifespan. It is. In the context of a universally fatal, rapidly progressive neurodegenerative model, nearly doubling the lifespan of an infected animal is just a monumental biological achievement.
13:17And what about the scramble control ASO? It did absolutely nothing. I don't think they are. Zero. The mice treated with the control ASO progressed and succumbed to the RML Prians at the exact same furious rate as the mice given a placebo saline injection.
13:31Which is exactly the definitive proof they needed. Yes. It confirmed, without a shadow of a doubt. that the survival extension was driven entirely by the targeted lowering of PRPRNA. Not by any random chemical stickiness.
13:45They proved the mechanism was sound. And by using the bolus injections, they proved the delivery method was vastly safer than the old pumps. But, as incredible as that prophylactic arm is, it still represents a best case scenario.
13:58It's treating the fire before the match is even struck. Right. The true holy grail of this paper is the delayed treatment arm. What happens when the house is already burning down? So they took a cohort of mice and waited a full 120 days post infection before giving a single treatment.
14:13And just to give contacts on that timeline. These RML infected mice typically only survive about 160 days in total. Yeah, that's important to understand. Treating at 120 days means intervening when the disease has already run 75% of its terminal course.
14:27At 120 days post-infection, these mice are on the absolute precipice of frank clinical signs. The neuropathology is already severe. If you look at the brain tissue of amounts at this stage, you observe extreme spongiform vaculation.
14:40Sponger forms. So literally like a sponge. Exactly. The toxic prion aggregates cause the neurons to die and leave behind these microscopic holes, turning the intricate architecture of the brain into a sponge-like texture.
14:52And alongside that, the brain is undergoing massive astrogiosis. What's that? Astrocytes are the support cells of the brain, and they become hyper-reactive in this desperate inflammatory response to the widespread neuronal injury.
15:05The tissue is heavily burdened with misfolded PRP deposits. It's a brain in the midst of a catastrophic structural collapse. And they took these heavily compromised mice at 120 days and gave them a single bolus injection of active ASO1.
15:19Yes. And the results here are the most clinically vital data points in the entire study. That single late stage injection extended survival by 55%. It's astounding. to put raw numbers on it. These mice lived an average of 87 days longer than their saline treated counterparts.
15:35They took an actively dying brain and pushed back the inevitable by nearly 3 months from one isolated intervention. It is a profound finding because it absolutely shatters the assumption that late stage treatment is completely futile.
15:47But we do need to look at the nuances of the data. The researchers were incredibly transparent about a specific limitation in this delayed treatment arm. Right. I noticed that too, with active ASO too.
15:59Yes. While ASO1 produced that massive 55% survival extension, active ASO2 actually proved to be highly toxic at the 120 day mark. Oh, wow. Yeah. The mice given ASO2 at this late stage experienced a sudden severe clinical decline and died within days of the injection.
16:17Wait, but ASO 2 worked beautifully in the prophylactic arm. Why would it be lethal at 120 days? It's a sobering reality of pharmacology. The ASOs utilized in this study were early proof of concept tool compounds.
16:29They were not polished, highly optimized drugs ready for the clinic. But more importantly, it underscores how fragile a deeply damaged central nervous system truly is. So a healthy brain, or a brain very early in the infection, can tolerate the chemical stress of the drug, but a brain riddled with microscopic holes just can't handle it.
16:47Exactly. The tolerability profile of any drug completely changes when the target organ is actively failing. And building on that, we must state plainly that these are results in a mouse model. An extension of survival in a mouse, even a dramatic 87 day extension, is not a cure.
17:04Right, extending survival is not the same as cure or reversal. Right. The ASO therapy slows down the progression by starving the disease of its fuel, but it does not reverse the damage already done. It cannot bring dead neurons back to life.
17:17It's buying critical time, but it's not rebuilding the house. No it's not. So how do we trace the line from a 55% survival extension in a mouse to actual human medicine. Like, what did this 2019 paper ultimately provide for researchers trying to design a clinical trial today?
17:34It provided a massive foundation. First, because the control ASO proved the mechanism is unequivocally RNA lowering, we now have a viable biomarker. In human trials for neurodegenerative diseases, it is notoriously hard to measure if a drug is actually working inside the brain.
17:49But with this mechanism, researchers don't have to guess, they can perform a lumbar puncture and measure the concentration of normal PRP in a patient's cerebra spinal fluid. Oh, so if the normal PRP levels drop, they know definitively that the drug is hitting its target.
18:05Exactly. Having a direct, measurable biomarker is a huge advantage. And the 2nd thing is the delivery method itself. By proving that bowl is dosing works, they validated a highly translational approach.
18:16In humans, this translates to periodic lumbar punctures spinal taps every few months, rather than needing invasive hardware implanted in the skull. Which we already do for other therapies, right? Yes, this exact method is used to deliver life-saving ASO therapies for other severe conditions like spinal muscular atrophy.
18:35And this research was the direct catalyst that led to ION 717, an advanced anti-sense drug developed by IONIS that successfully transitioned into human testing. In fact, in 2026, the pride profile trial for Iowa 777 was reopened with an additional dosing cohort.
18:51But we have to be exceptionally clear here. Preliminary safety data in a clinical trial. is exactly that preliminary safety data. It does not establish efficacy. As of right now, no PRP lowering drug has yet been shown to help human patients.
19:05Right. No drug has shown it can alter the disease course in humans yet. We are very much still in the testing phase. And the success of any future therapies relies almost entirely on the speed of clinical diagnostics.
19:17Because every day matters. Every single day, even if an ASO can alter the disease course at late stages. Every day of lost neurons in a human patient is completely irreplaceable. The 2019 paper implicitly highlights the absolute necessity of rapid diagnostics, specifically pointing to the RTQIC essay.
19:37Right, RTQIC. That's the test that can detect misfolded prions in human spinal fluid with incredible sensitivity. Yes. But for it to matter, neurologists have to know to look for prior disease much earlier.
19:48When a patient presents with sudden rapidly progressive dementia, the RTQYIC assay needs to be deployed immediately, not as a last resort. So the therapeutic window is the most critical variable. And really, that's the central insight of this whole deep dive.
20:02To summarize it in just a couple sentences. Prion diseases are ruthless and fast, but this research proved that the window after symptom onset may not be completely closed, intercepting the disease by knocking down its genetic fuel can still significantly alter the course, even when pathology has already begun.
20:19It cracked open a door that the medical field assumed had been permanently shut for decades. Which leaves me with a lingering thought that extends far beyond just prion disease. If we can engineer a sequence specific molecular interceptor to turn off a single protein.
20:34If we can halt one of the most aggressive, untreatable, fatal brain diseases simply by starving it of its genetic fuel, what other fatal, untreatable diseases hiding in our DNA are just waiting for the right RNA switch to be flipped off?
20:48The exact question driving the bleeding edge of genomic medicine today. We closed this pair of episodes where we began with Lido Sousa. To the investigators and sponsors running prion disease trials at Ionis, at the Broad Institute, and at the centers collaborating with them.
21:02There is a patient in Brazil on a waiting list, and a community following your work with real attention. We know that trial enrollment is decided by protocol criteria and clinical judgment, not by public appeals, and we are not asking anyone to set those aside.
21:16We are asking that access outside the United States be kept in view as these programs expand, because prime disease does not respect borders, and neither should the search for a treatment. To listeners.
21:27The CGD Foundation supports patients and families worldwide, and the trials discussed in these 2 episodes are registered publicly on clinicaltrials.gov, Lito Obregado. This pair of episodes is for you.
21:39This episode was based on an open access article under the CCBY 4.0 license. You can find a direct link to the paper and the license in our episode description. If you enjoy this, follow or subscribe in your podcast app and leave a 5 star rating.
21:52If you'd like to support our work, use the link in the description. Now stay with us, foe.
