As you may know, I co-founded Repair Biotechnologies, a company presently focused on developing an approach to rapidly reverse the cholesterol content of atherosclerotic lesions, a goal that is impossible to achieve using the existing panoply of treatments for atherosclerosis. We use gene therapy techniques to provide cells with the ability to safely break down excess cholesterol, enabling the removal of pathological levels of intracellular cholesterol and localized deposits of extracellular cholesterol that characterize conditions such as atherosclerosis (in blood vessel walls) and NASH (in the liver). Atherosclerosis is an important consequence of aging: the structural weakness and narrowing in blood vessels caused by the growth of cholesterol-laden lesions is the cause of death for a quarter of humanity. Closer to half of humanity were cancer somehow removed from the human condition.
The Foresight Institute runs salons these days, and publishes a range of interesting presentations from people in the biotechnology, molecular nanotechnology, and artificial general intelligence fields. Earlier this year, the Foresight Institute staff were kind enough to invite me to present on the work taking place at Repair Biotechnologies, and the understanding of atherosclerosis that informs that work.
I titled the presentation "Atherosclerosis, the As Yet Undefeated Monster" in part as a reaction to a certain type of conversation that recurs when talking to venture capitalists. Many biotech investors, and others too, seem to think that atherosclerosis is a solved problem, and therefore a poor choice of field in which to see a return by supporting the development of new approaches. Many of the best-selling small molecule drugs are statins that have been deployed for decades to treat atherosclerosis by lowering LDL cholesterol in the bloodstream. Physicians reflexively prescribe statins to older individuals. Everyday people obsess about their blood cholesterol levels. New LDL cholesterol lowering drugs that employ modern technologies such as monoclonal antibodies and siRNA are being approved for use on an ongoing basis.
Yet in this environment of decades of ever more attention given to the reduction of LDL cholesterol levels in the bloodstream, atherosclerosis still kills a quarter of humanity. Atherosclerosis is very far removed from being a solved problem! There is an enormous unmet need and ongoing mortality, on a par with the global burden of cancer.
LDL cholesterol reduction as a basis for therapy can lower late life mortality by 20% at most, with many large, robust clinical trials failing to obtain even that degree of benefit. It just isn't the right mechanism if the goal to produce a cure. It doesn't matter how efficiently a therapy reduces LDL cholesterol in the bloodstream, that 20% mortality reduction appears to be a ceiling. PCSK9 inhibitors do no better than statins when it comes to lowered mortality following control of LDL cholesterol, despite being a much more modern and capable technology. I feel that perhaps the research and development community has been encouraged in its near monomaniacal fixation on lowering LDL cholesterol by the discovery of human gene variants (in PCSK9, ANGPTL3, and so forth) that result in lower LDL cholesterol and up to 50% lower cardiovascular mortality. But that result is obtained due to a full lifetime of lowered LDL cholesterol. Therapies built on those discoveries cannot match that outcome.
Atherosclerotic lesions grow over time at a pace that is influenced by LDL cholesterol levels, by the pace at which cholesterol arrives from the bloodstream to a lesion. Reducing that pace via LDL cholesterol lowering therapy cannot reverse established lesions, or even stop them from further growth and eventual rupture, however. Once a lesion is established, the more important mechanism is the dysfunction of the macrophage cells responsible for clearing cholesterol from blood vessel walls. Those cells are overwhelmed, become inflammatory, attract more macrophages, and die, adding their mass to the lesion. The lesion becomes a macrophage graveyard.
To actually reverse atherosclerotic lesions, to actually produce a treatment that could legitimately be called a cure for atherosclerosis, one needs to protect the function of macrophages in the hostile, inflammatory, cholesterol-laden atherosclerotic plaques. If macrophages can be made invulnerable to excess cholesterol, and other harms such as oxidized LDL particles, then given enough time they will do their jobs and repair the blood vessel wall. That is our goal at Repair Biotechnologies, to make a real and meaningful inroad towards that goal.
So why are macrophages not able to do their job later in life? We need to understand cholesterol transport first. Cholesterol isn't created or destroyed in near all cells, it is rather ingested and excreted. Cells don't break down or get rid of the cholesterol they don't want locally, they hand it off to other cells and parts of the system when they no longer need it. Cholesterol is created in the liver, gets stuck onto LDL particles and goes into the bloodstream, gets stuck in a blood vessel wall, macrophages eat it and then throw it back into the bloodstream to attach to the HDL particles that flow back into the liver. LDL and HDL particles do pretty much the same work when you're young and old, it's the macrophages that stop doing their job. So why exactly do they stop doing their job? Due to a variety of issues - namely systemic inflammation, systemic oxidative stress, and too much cholesterol, although the last is probably not the worst of those three. What this leads to is a feedback loop. Your plaque is a macrophage graveyard, and the signaling of that draws in even more macrophages trying to fix the problem. That is the underlying cause of atherosclerosis.
As you are aware, there's an entire research community and pharmaceutical industry focused only on lowering LDL cholesterol - taking that part of cholesterol transport from the liver to the rest of your body and turning it down. This probably helps a little, since you're reducing oxidized LDL and altered cholesterols, you end up with less altered cholesterol in the plaques, so you're giving macrophages a little bit more breathing room. But it doesn't work to a great enough degree, even if you reduce LDL cholesterol to 10-20% of what is normal in humans, you won't get rid of the plaques, you won't reverse it.
What are the alternatives? Let's start with those that don't work. I mentioned that systemic inflammation is one of the problems leading to atherosclerosis. But if you reduce inflammation systemically, studies suggest you get about the same benefit to mortality as you would get from lowering LDL cholesterol. Which doesn't mean that somebody cannot come up with a way that could do this in a better and more targeted fashion, but the tools available for control of systemic inflammation are really blunt right now.
The second alternative sounds much better, if limited to mice. Reverse cholesterol transport is the pathway wherein a macrophage sucks up cholesterol and hands it off to HDL particles in the bloodstream. There are a number of genes involved in this - macrophages use ABCA1 to hand off cholesterol to the HDL particle initially and then ABCG1 helps add more cholesterol to the particle. Then the particle heads to the liver and is excreted and ejected from the body. Anything you do in mice to make one or more parts of this system work better, it all works great - up to 50% reversal of plaque lipid content in some cases. But every time it was tried in humans, it failed - there's a whole list of clinical trials over the last 20 years that tried and failed. That tells us that we don't understand something very important about the way in which cholesterol transport is rate-limited in its different steps in humans vs in mice.
So our approach is to make macrophages resilient to the environment in old tissues. There have been a number of people trying this, some of it hasn't made it very far, some of it is interesting, and sometimes there is overlap between those two. There is a recent paper with a hypothesis of effect they showed is that if you target lysosomes in macrophages with antioxidants, it prevents the oxidized LDL particles from messing things up, and therefore more macrophages are doing their job - reversing the plaque by 50% in a mouse model. It's entirely possible their hypothesis is wrong and delivering antioxidants is improving something else in the picture, but it's certainly a result that self-experimenters should pay attention to because these antioxidants are easily available.
Secondly there is the Underdog Pharmaceuticals approach - sequestration of 7-ketocholesterol, which is a highly toxic altered cholesterol, thought to play a big role in atherosclerosis. Lastly there is our approach - engineering macrophages to give the ability to degrade excess cholesterol, whether or not it is altered. The company is named Repair, since I believe that if you're going to address aging and you can't point to something you are actually repairing - a form of damage or dysfunction, where you can clearly say that you are fixing this - then you might not be doing the right thing.
In summary, what we're doing is allowing macrophages to degrade cholesterol and then stepwise approaching the various atherosclerotic conditions in order of number of patients. So starting with an orphan condition - homozygous familial hypercholesterolemia, then you go into larger patient groups as you gain experience doing this. Unlike most therapies, we can actually apply ourselves to any form of atherosclerosis, whether or not it has a genetic cause, we don't care how you got plaques, we just break them down. We've demonstrated AAV delivery of our cholesterol degrading protein - has a very large effect of 48% reversal of plaque lipids in a month, which is large in the scheme of things as compared to other approaches.
Our goal is to produce a universal macrophage cell therapy. As I said, atherosclerosis is basically the encounter of an aged macrophage with cholesterol, at which point you get a lot of cell death and cholesterol-based plaque. If you overwhelm the existing systems of normal macrophages with excess cholesterol, they can't do anything with it and bbecome pathological foam cells - they don't have an way to deal with that level of cholesterol. So with that picture in mind, the whole spectrum of LDL lowering cholesterol drugs really only lowers that input to the problem. And they can't lower it more than a little, because the macrophage is in the plaque, not in the bloodstream, and the plaque is packed full of cholesterol and toxic horrible nastiness, so you're not really getting a lot of boost from lowering the input from bloodstream. The problem is the plaque that's sitting there. You can't reverse it by undertaking this LDL lowering approach, you still have macrophages exposed to excess cholesterol and becoming pathological foam cells as a result.
And the pathological foam cells leading to your plaque brings us to this point, one that has to be made to a lot of people, unfortunately. Your risk of death is not due to LDL cholesterol, it's due how much plaque you have. It's exactly how much plaque you have and how much high risk plaque - the soft plaque laden with cholesterol. That determines your mortality. LDL cholesterol, while widely accepted as a surrogate marker, is not the cause of your death. That's why different people can have different levels of cholesterol in their bloodstream and have quite divergent mortality rates.
The point of the exercise is to figure out what we should do differently - and that is making macrophages invulnerable to the plaque-based environment as best as we can. Our idea of "as best we can" is to give a macrophage the capability to break down cholesterol safely in situ. I should say that this is not a trivial thing to do, because a cell is basically an enormous lump of cholesterol - our body uses cholesterols everywhere in the cell membrane. The reason why we never evolved to break down cholesterol when it's harming us is probably because our cells have cholesterol everywhere. So you couldn't evolve something that just chews cholesterol whenever it sees it. And that's why delivering things like the known cyclodextrins that bind to cholesterol is not quite simple either, because the first thing that will happen if you dump a bunch of cyclodextrins into somebody is that their blood turns to mush, because it will consume all your blood cells by hooking all the cholesterol out of cell walls.
So the objective is a safe way of breaking down cholesterol, but only the excess cholesterol, which is what we achieve by putting in these specific mechanisms into the cells we're working with. We can demonstrate that by putting these mechanisms into any old cell, and the output is exactly the same - we get a catabolite that is safe and more soluble, and quickly leaves the cell, departing into the bloodstream where it is gotten rid of. What this means is that we can take macrophages and give them the ability to express our cholesterol degrading proteins, and then if you dump cholesterol on those cells they remain competent and able to ingest cholesterol and dispose of it - that's what you want in your plaque.
So going forward, we take induced pluripotent stem cells (iPSCs) from mice or humans, the lines are then disrupted in certain ways to make them universal (you get rid of the surface markers that make them recognizable - a very important technology that leads to off the shelf lines of universal cells, you can look at recent reports from Sana Biotechnology, of the delivery of universal iPSCs to primates, for example). We then differentiate iPSCs into macrophages that express cholesterol degrading proteins, and this is the way we produce a cost effective cell therapy. We've injected mice with the first of these cells over the last month or so and we should have initial data by the end of the year.
And then what we do with this is a stepwise approach through the orphan indication of homozygous familial hypercholesterolemia with very few patients and a much easier FDA process, then to the heterozygous familial hypercholesterolemia indication with more patients, and then to the large high risk subpopulations of atherosclerosis, possibly tens of millions of patients at the end of the day. These are all people who will have medical imaging carried out to show the presence of high-risk, cholesterol-laden plaques. Ultimately we think you can take the lion's share of death - of that 27% by atherosclerotic diseases - and use technology such as ours to remove that cause of death from the human condition. How long is it going to take? Who knows, but the most high-risk population is where we start.