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| Human World on Jul 13, 2011

Robert Langer on targeted drug delivery for future medicine

Robert Langer told EarthSky, “You’d like a cancer drug to go to the cancer cell – and to no other cell in the body.”

Robert Langer of M.I.T. helped pioneer targeted drug delivery systems. They are a way of getting drugs to specific parts of the body – even a specific kind of cell. Dr. Langer builds these systems using polymers – long chains of molecules such as those in plastics or rubber – which he engineers at a microscopic scale. He spoke with EarthSky’s Beth Lebwohl about his work and about the future of targeted drug delivery. This podcast is part of the Thanks To Chemistry series, produced in cooperation with the Chemical Heritage Foundation. Generous sponsorship support was provided by the BASF Corporation. Additional production support was provided by The Camille and Henry Dreyfus Foundation, DuPont, and ExxonMobil.

How does targeted drug delivery benefit people?

Let’s say somebody has cancer. You’d like the cancer drug to go right to the target – right to the cancer cell – and to no other cell in the body. That would benefit people because the drug would be a lot more effective. It wouldn’t have the side effects that you get when a drug goes all over the body.

Right now, if you need to take a drug, the drug goes all over the body. That’s why a lot of times, when we take some drugs, we get side effects, sometimes bad effects. Sometimes we get sick to our stomach. Sometimes we get headaches. It all depends on the drug.

You can use targeted drug delivery as long as you know where you want to go in the body. Let’s say you want to try to treat heart disease, and you want it to go to a blood vessel. We’ve done some work on that as well. There are other diseases as well – inflammatory diseases and so forth – but you’d need to have the right targets in the body.

Single polymer chains as recorded using an atomic force microscope (Wikimedia Commons).

You work with polymeric drug delivery systems. What are polymers? Why use polymers to bring drugs to a specific part of the body?

When you hear of things like polyesters, those are polymers. Plastics are polymers, and rubber is also a polymer. Polymers are incredibly versatile. So you can use them, and you can make them into all kinds of shapes and forms, including nanoparticles. It’s their versatility that makes them so helpful.

And what are nanoparticles?

Nanoparticles are tiny little particles – smaller than a micron – much smaller than the width of a human hair. So they’re very, very tiny. But because they’re tiny, they have the ability to get into cells. And so, if you put drugs in them, they may – if you design them correctly – allow the drug to get into the cell you want.

You can also make polymers that are very safe so that they can be good carriers for drugs. We’ve often designed these polymers so that they degrade into things like water and carbon dioxide or things that come out in the urine that are very, very safe.

Here's one example of how targeted drug delivery works. Targeted drug delivery capsules (red) stick to the cancer cells expressing the A33 antigen (blue), while avoiding the cells that don’t express the antigen (green). (NPG Asia Materials)

How does it work? How does a polymer help in developing a targeted drug delivery system?

A polymer at a molecular level is just a really long molecule made up of much smaller molecules. What’s special about it is that you can control all its chemical properties. For example, you might want to adjust the polymer’s degradation rate. Does it degrade fast or slow? If you’re trying to release a drug, you could design the polymer so it might release the drug fast or slow. A third thing that you might want to regulate is its mechanical strength. And all these are possible to do by adjusting the polymer properties.

We basically have worked out new ways to design nanoparticles that you can inject into the body – that can travel around the body for a long time – but ultimately find the tumor or other diseased state. They take the drug right to where you want and not to any of the places where you don’t want it. Or at least they greatly restrict the drug from going to any of the places you don’t want it.

What breakthroughs have occurred in recent years to cause a polymeric drug delivery system to hold so much promise now?

There have been a number of breakthroughs. Some are in materials science, and some are in biology. Examples in materials science are new methods of making nanoparticles of just the size and shape you want.

I understand there is a potential of this technology to deliver drugs straight to our DNA or RNA.

That’s one of the big areas that we’ve looked at – using these nanoparticles to deliver genes or substances that turn genes off. Either turning genes on or turning genes off.

Let me give an example. If somebody had heart disease, they might have a high level of cholesterol. And there are certain genes that you can shut down that will make you have less cholesterol. That’s one of the things we’ve been working on. Or let’s say somebody had cancer, and the cancer cells are starting to invade through other tissues, causing a lot of harm to the patient. We’re working on genes that can prevent that invasion from occurring.

When will we start to see targeted drug delivery systems become commonplace and affordable? Can you give me a timeline?

It’s very hard to know. Personally, I think it’ll take many, many years. I don’t have a timeline, but anytime you develop new medicines it takes a long, long time. The medicine has to go through so many safety trials and human clinical trials. There’s great progress being made, but there’s also a lot of work ahead of us.

Polymer delivery systems are already making a big impact in transdermal patches. They’re in pills. They’re in different implants. They’re in stents. So they’re in a lot of things.

But targeted drug delivery is something that’s more in the future. There are clinical trials with them that have just started. I think in the next five to ten years you’ll see examples where they are being used clinically and having a big impact. At least I hope so.

I understand you can use these systems in other fields, for example, agriculture.

Yes. It’s not so much that you do targeted nanoparticles for agriculture but you do controlled release [using polymers]. For example, if somebody is delivering pesticides to crops, they might just dump them from airplanes. The pesticide all comes at once and might cause bad effects to the land. It might not work as well. It would be much better if you could deliver the pesticide at a relatively steady rate over a long period of time. That’s what controlled release is. It’s delivering things generally at a relatively steady rate over a long period of time. That’s something that we and others have developed some general principles on, which are being applied, for example, in delivering pesticides to crops – and for all kinds of things.

Dr. Robert Langer (NIH)

What’s the most important thing you’d like to tell Earth Sky’s global audience about targeted delivery systems using the long similarly structured chains of molecules known as polymers?

Polymeric drug delivery systems that are targeted really offer new hope for a variety of medical treatments. It’s a way of taking a drug that might normally go throughout the body and not work that well – and maybe cause a lot of side effects – to potentially go right to where you want it, say a cancer cell, and work better on killing that cell and not having the side effects.

Listen to the 90-second and 8-minute podcasts of EarthSky’s interview with Dr. Robert Langer on targeted drug delivery systems at the top of this page. This podcast is part of the Thanks To Chemistry series, produced in cooperation with the Chemical Heritage Foundation. EarthSky is a clear voice for science.

More in the Thanks to Chemistry series: Nina Fedoroff on science for global agricultural challenges