Science Interviews

Mothership for Nanotechnology

Ben - I caught up with Professor Michael Sailor from the University of California at San Diego, another person enjoying the sun while we're in the snow, to find out how you can convince such tiny particles to be your drug deliverers.

Michael - To get a material to deliver a drug one of the themes that we've been developing is so-called mothership for nanotechnology. We build a nanostructure that's fairly large. It's still a nanostructure but it's large enough to hold a smaller component inside it. What will make these porous silicon-based nanostructures that can contain a drug. One of the really favourite projects right now, a really exciting one that I have going on is working with a guy named bill Freeman who's at the Jacob Retina Centre here at UC San Diego. He sees patients every day with a disease called macular degeneration. That's a disease of the eye, typically age-related. One of the main causes of blindness in older folks. There are no drugs available that you can give to a patient as a pill and have it get through the stomach and make it to the eye. So they unfortunately have to take their patients and stick a needle in their eye with the drug. The problem with that is there's a chance of infection and once you put the drug in the eye typically these kinds of drugs will only last for a month or two before they're all gone and then the patient has to come back in and be injected again. Bill approached me with this problem and he said the only way we can keep the drug in the patient's eye for a therapeutically useful time is to massively overdose them. We have to inject a lot of drug in the eye. If we put a high dose in the patient's very susceptible to problems. There's probability of strokes and other complications that come from having too high a concentration of drug. He knew we were working on these little nanoparticles that had pores in them. He said can you put the drug inside those structures, lock it up in there, keep it away from the body, sequester it until it's needed and then have it leach out slowly? So the level of drug concentration in the body is much lower – still above the therapeutic level so it's treating the disease but not so high that it does any damage. What we are now developing are materials that can stay in the eye – at least in the rabbit eye for eight months.

Ben - How does it avoid the processes that usually recycle the fluid in the eye and would usually take away the drug that they'd put in there.

Michael - If you had a material that you're putting into the eye and it stayed there even after its effective time was done after it's already delivered its drug then it eventually ends up you're going to start occluding the vision. A real key thing for that was to have these materials definitely dissolve away into nothing. It has to dissolve away slow enough that the drug locked inside is delivered in a fairly smooth and slow fashion.

Ben - This should mean that people suffering from AMD would at least have one nanoparticle administered every six months rather than an injection of an excess of drug every month.

Michael - Well, we still have to put a lot of drug in the eye so it wouldn't be one nanoparticle. We would be injecting large quantities of nanoparticles: roughly the same volume that the doctor now injects into a patient. They key thing is that when that drug goes in to the 100microlitre injection that's going into the eye it's not all instantly available. Some of it is locked away and it's releasing over a much slower time period.

Ben - When do you expect that the people will be queuing up for their clinics to have their nanoparticle injections?

Michael - That's a really tough question. We would like to get into the clinic within a year. We're at the stage right now where we're doing experiments with rabbits. As you know with any material; nanomatrials in particular we want to be very careful we're not doing more harm than good. The problems that may come up, infections, longer-term issues – do materials really degrade away to nothing, are they getting eliminated completely? There's a lot of work that still needs to be done. One of the real challenges here with the nanomaterial is even if you think it's harmless and I'm sitting here saying these are made of silicon dioxide or iron oxide and that's a material the body can accept and degrade smoothly there are great examples of nanomaterials that are made of things that are completely harmless that are really nasty. For instance, carbon nanotubes do not degrade in the body at all. Unless your body can eliminate them somehow if it gets stuck somewhere it's there forever. If you look at asbestos, the chemical composition of it is quite harmless itself: aluminium, oxygen and some iron initially so kind of the same sort of constituents that we're talking about here. Why is that particular alumino-silicate, that asbestos mineral so harmful? Because it's in a nanostructure that doesn't degrade it's actually quite harmful. Even though its elemental components are not toxic when that material gets into the body and lungs in particular for asbestos it sits there and doesn't go away. The body can't dissolve it and so those fibres will stay lodged in the lungs, make lesions and cause problems. That's a real moral to the story of nanomaterials. It's not good enough to just say the elements are harmless. You've got to know that the material itself will go away.

February 2009