Phase 1/2 COMPOSE trial tested subcutaneous pegtibatinase in 24 participants with classical homocystinuria; treatment was generally well tolerated and produced rapid, dose-dependent reductions in total plasma homocysteine (tHcy).
0:00Imagine sitting down to dinner. You've got, um, a piece of grilled chicken on your plate or, you know, maybe just a handful of almonds on the side. Right, just a totally normal, healthy meal for most people.
0:10Exactly. But I want you to imagine a reality where eating that exact same food? I mean, eating that normal piece of protein is literally toxic to your body. Yeah, situation where the fundamental building blocks of those foods.
0:23Actually, well, they trigger a massive buildup of toxins in your blood. And it's a buildup so severe that it can cause catastrophic strokes or um, brittle bones or severe vision loss before you even turn 30 years old.
0:36It's terrifying, honestly. Every bite of food becomes a calculated risk. You're navigating a constant daily threat to your vascular and skeletal systems just by trying to nourish yourself. It's wild to think about, but that is the everyday reality for people living with a rare genetic disorder called classical homo system area or HCU.
0:55Which brings us to the mission of today's deep dive. We're looking at a brand new 2025 paper published in genetics and medicine. Right, by lead author, Canfashia Glue, and, you know, a whole team of colleagues.
1:07And this paper covers the compose fees one and two, randomized trial for a new drug called pig Tibetanase. Okay, let's unpack this because we're not just looking at a minor incremental update here. No, not at all.
1:20We are looking at a newly engineered enzyme that has the potential to completely rewrite the rules for these patients. Patients who, honestly, haven't had a new treatment option in over 2 decades. And for you listening, this isn't just a story about a single drug.
1:34It really is a masterclass in how clever bioengineering can bypass the body's broken metabolic machinery. But before we can really understand the cure, we have to understand the machinery that's broken in the 1st place.
1:46Exactly. So HEU is an autosomal recessive disorder. Basically, the body is missing a crucial enzyme called CBS or cystathenine betasynthase. And this CBS enzyme. It has one major job, right? It processes methionine, which is an amino acid found in almost all dietary protein.
2:04Right. So if you think of the methyanine pathway. It's kind of like a plumbing system in a factory. Okay, I like that analogy. So methynine is the water coming in. Yeah, and the CBS enzyme is the main drain that processes everything safely.
2:15So if that main drain is clogged or just missing entirely, the water backs up. And in the human body, that backup is the toxic accumulation of homocystine and methionine. Which is incredibly dangerous.
2:26Elevated total plasma, homocystine, or T-H-A-C actively damages the vascular system. So that's what leads to the blood clots and cardiac arrest. Yes, exactly. Plus, it causes severe osteoporosis, abnormally long limbs and it even degrades the connective tissue in the eyes, causing the lens to dislocate.
2:45Wow, the eye is too. Yeah, it's systemic. The critical danger threshold is 100 micromoles of THEC in the blood. Anything over that is a massive risk. Wait, if we know exactly which enzyme is missing, why haven't we just replaced it before?
2:58It's a great question. I mean, why have standard treatments been stuck in the Dark Ages for over 20 years? Because delivering a functional enzyme that actually survives in the human body is notoriously difficult.
3:10So the current standard of care is basically just damage control. Which involves severe dietary protein restriction, right? Severe restriction, plus these terrible tasting methynine free amino acid formulas and high doses of a supplement called betain.
3:25And reading the paper, it sounds so burdensome that many patients simply cannot comply. They can't. A natural history study showed that even with treatment, many patients' THC levels are still dangerously high, often over 110 micromoles.
3:40So they're still living above that 100 micro mold danger zone. Exactly. This raises an important question. How do we deliver an enzyme that actually works long enough in the body to make a difference? And that failure of dietary restriction leads us directly to the ingenuity of pegged botanes.
3:55Right, because if we can't stop the patient from taking in protein, we have to fix the drain. So what actually is picked bodney? It's a recombinant human CBS enzyme, designed for subcutaneous injection.
4:06Basically, a synthesized version of the missing enzyme. But here's where it gets really interesting. The scientists didn't just copy the natural enzyme perfectly. No, they made 2 brilliant modifications.
4:17Right. First, they truncated it. They remove the C terminal, which is basically like cutting the brakes. Yeah, by removing that regulatory flap, the enzyme is permanently switched on. It's just constantly churning.
4:29And second, they added Peg Moyadies, right. Pedulation. Exactly. Those peg chains give the enzyme a stealth cloak against the immune system. So it stops the body from attacking it as a foreign protein.
4:41Yes, and it dramatically increases its lifespan in the blood, making it too big for the kidneys to filter out quickly. But there's a mind bending part to the drugs design. Natural CBS lives inside tissue cells, right?
4:54Right, in places like the liver and the brain. But picked to bad news stays in the blood plasma. It doesn't go into the tissues at all. Exactly. And that is the core mechanical challenge here. How do you clean the tissues if the drug is just floating in the blood?
5:08Well, to wrap my head around it, I thought of it like putting a heavy duty dehumidifier out in the hallway of a house. Okay, I see where you're going with this. So even though the machine isn't inside the damp bedrooms, which represent the tissues, it dries out the hallway air, the plasma.
5:23Right, it drops the local concentration in the blood to near zero. Exactly. And that creates a gradient that slightly pulls the moisture out from under the bedroom doors. That is exactly how the metabolic sync works.
5:35It draws toxic homocystine out of the tissues to be processed safely in the blood. But a dehumidifier in the hallway is a great theory. Does it actually clear the moisture in a real human body? That's where the composed trial data comes in.
5:47Right. This was 24 participants ranging in age from 12 to 65. Yes, double blind, randomized, and placebo controlled. And it was a dose escalation trial, meaning they safely tested 6 increasing doses, right?
5:59Exactly. They started small to monitor safety before ramping up to therapeutic level. Well, the standout stats from cohorts 5 and 6, which are the highest doses at one. 5 and 2.5 milligrams per kilogram twice weekly are just wild.
6:13The TAC reductions were massive. Yeah, a 57% and 67% relative reduction from baseline. And for anyone listening, what stands out to you here? Well, for me, the most crucial fact is that every single participant on these high doses dropped their THC below the 100 micromole danger zone.
6:33Every single one. It fundamentally changes their risk profile for strokes and bone loss. There was this one specific patient in cohort 6 that just blew my mind. Oh, I know exactly what you're talking about.
6:45Their THE dropped into the normal range like below 15 micromoles. Right. And their methanine actually dropped so low that the doctor had to prescribe them to eat more intact dietary protein. Imagine that.
6:58Being told to eat more normal food after a lifetime of avoiding it. It's a complete paradigm shift for their quality of life. It really is. But what's fascinating here is that the drug didn't just hide the homocystine.
7:08Right. It restarted the whole metabolic engine. Exactly. Other metabolites, likes his dining actually increased. Which proves the pathway was actually functioning again. manufacturing the right downstream products.
7:19It's proof that the factory is running again. It is incredibly easy to get swept up in these miracle results though. It is, but responsible science requires us to look for the catch. Right. So let me play the skeptic here.
7:31Okay, they injected a permanently on genetically modified enzyme into people. Yes they did. What were the side effects? Did the immune system just rebel against it? Looking at the safety data objectively.
7:44It was generally well tolerated. So no massive allergic reactions. Right. No anaphylaxis or severe immune reactions, which is a huge relief. The paper did mention some mild injection site reactions though.
7:55Yeah, that was the most common issue. Localized redness and pain. But I also notice a few participants developed urticaria, you know, hives. Yes, that is an important nuance. A few patients did develop hives.
8:08Doesn't that jeopardize the whole treatment for them? Not necessarily. was actually easily managed. Oh, really? How did they get around it? Patients were premedicated with antihistamines, and the dose was temporarily lowered.
8:19And then they just slowly work their way back up. Exactly. They titrated back up to the target dose without further issues. That's super clever The immune system just sort of got used to it. It developed a tolerance, yeah.
8:31But we do need to outline the scientific limitations here. Right, because it's a small sample size, only 24 people. And a very short, double blind period of only 12 weeks. So we don't really know the long-term clinical outcomes over years of treatment.
8:45We don't. We need to see if it actually prevents vascular damage and bone loss over a decade. But that's what the upcoming phase 3 harmony and ensemble studies are for, right? Yes. They will test this in about 70 patients over a longer period to see if the drug really holds up its promise.
9:01So what does this all mean? It's a huge shift in how we approach the disease. Yeah, pick Tibet news represents a monumental leap for HCU patients. Going from a life of grueling dietary restriction and fear of sudden strokes to something much brighter.
9:15Exactly. The genuine possibility of metabolic normalization and just the simple joy of eating normal food. And if we connect this to the bigger picture. This paper is a beautiful example of molecular medicine.
9:27Understanding a disease at the base, molecular level allows us to engineer highly specific elegant solutions. Like fixing the broken drain by installing a specialized sink in the hallway. Which leaves me with a final lingering question to ponder.
9:42Go for it. If we can successfully create a metabolic sink in the bloodstream to suck out toxins from tissues we can't directly reach, what other untreatable metabolic diseases or even neurodegenerative conditions might be solvable using this exact same indirect dehumidifier approach?
10:00It opens up an entirely new frontier. It really does. Thank you so much for joining us on this deep dive today. Keep exploring, and as always, keep questioning the world around you.
