Capsules containing anti-cancer agents and coated with gold nanoparticles can be melted open in cancer cells using near-infrared lasers and someday this may be done in patients without damaging non-cancerous cells.
So Frank Caruso and his team at the University of Melbourne, Australia, are developing an ingenious way of doing this. Their trick is to enclose the drug in polymer capsules that are peppered with gold nanoparticles and attached to tumour-seeking antibodies.
When injected into the bloodstream, the capsules will concentrate inside tumours. When enough capsules have gathered there, a pulse from a near-infrared laser will melt the gold, which strongly absorbs near-infrared wavelengths. This will rupture the plastic capsules and release their contents.
This packaging is neat because it would prevent the damage that conventional chemotherapy causes to normal cells all over the body while en route to cancer cells.
What is the biggest problem with cancer treatment? Cancer cells are too like normal cells. Therefore it is hard to selectively kill cancer cells. It remains to be seen whether all cancer cells will have enough unique surface proteins to be targettable using antibodies. But for those cancer cells that do present distinct surface antigen patterns an approach like Caruso's to package and selectively deliver toxic compounds (or even gene therapies) to cancer cells is going to be what ends up curing many types of currently uncurable cancers.
Even if some types of cancer cells do not present a single unique antigen this approach could still be used to attack cancer cells. Suppose cancer cells present combinations of antigens that are rarely found in normal cells. A few interdependent chemo agents could be placed in different packages attached to different antibodies. Imagine cancer cells have antigens A, B, and C. Then chemicals X, Y, and Z could be packaged with antibodies aimed at antigens A, B, and C respectively. Then only cells that have all 3 of the targetted antigens on their surfaces that in combination mark them as cancer cells would get all the different types of chemical packages delivered to them. Think of this as analogous to explosives that work only when two or three different chemicals are mixed together. One could create chemical compounds that would act like metaphorical set of anti-cancer explosives. The chemicals would become deadly only when chemicals X, Y, and Z are all released from different packages into the same cell.
Monoclonal antibodies to deliver chemotherapy compounds are already in clinical trials. But Caruso's approach would allow most of the delivery packages to get into cancer cells and then to be released all at once to create a bigger spike in cancer cell killer compounds. Also, Caruso's approach would work better with compounds that would need to detach from their antibody delivery vehicles. Also, in Caruso's approach it seems likely that more chemo molecules could be delivered per antibody.
You can view a slide show and read text of a presentation that Caruso delivered in May 2003 that explains how some of the pieces of this capability were created. That presentation doesn't include the step of using antibodies to deliver capsules. But it does include some interesting bits of information on how the capsules were constructed to be able to be opened by a laser.
Update One problem with this approach is that it may not work well for cancers that have widely metastasized. I came across one report claiming that the near-infrared lasers can penetrate a few millimters of skin or be delivered endoscopically (and the light has to shine for only ten billionths of a second). But what if, for example, one has metastasized cancer to the bone? Lasers therefore seem problematic as activation agents. However, if capsules could be constructed to burst open in response to ultrasound then cancers in brains and other less accessible locations might be reachable with microcapsule chemo delivery vehicles.
|Share |||Randall Parker, 2005 January 10 03:31 PM Biotech Therapies|