There’s a good review in Nature Reviews: Cancer (with free access) about the ways in which nanotechnology could help the fight against cancer – Cancer Nanotechnology: Opportunities and Challenges . The article, by Ohio State University’s Mauro Ferrari, concentrates on two themes – how nanotechnologies can help diagnose and monitor cancer, and how it could lead to more effective targeting and delivery of anti-cancer agents to tumours.
The extent to which we urgently need better ways of wrapping up therapeutic molecules and getting them safely to their targets is highlighted by a striking figure that the article quotes – if you inject monoclonal antibodies and monitor how many of these molecules get to a target within an organ, the fraction is less than 0.01%. The rest are wasted, which is bad news if these molecules are expensive and difficult to make, and even worse news if, like many anti-cancer drugs, they are highly toxic. How can we make sure that every one of these drug molecules get to where they are needed? One answer is to stuff them into a nanovector, a nanoscale particle that protects the enclosed drug molecules and delivers them to where they are needed. The simplest example of this approach uses a liposome – a bag made from a lipid bilayer. Liposome encapsulated anti-cancer drugs are now clinically used in the treatment of Karposi’s sarcoma and breast and ovarian cancers. But lots of work remains to make nanovectors that are more robust, more resistant to non-specific protein adsorption, and above all which are specifically targeted to the cells they need to reach. Such specific targeting could be achieved by coating the nanovectors with antibodies with specific molecular recognition properties for groups on the surface of the cancer cells. The article cites one cautionary tale that illustrates that this is all more complicated than it looks – a recent simulation suggests that it is possible to get a situation in which targeting a drug precisely to a tumour can make the situation worse, by causing the tumour to break up. It may be necessary not just to target the drug carriers to a tumour, but to make sure that the spatial distribution of the drug through the tumour is right.
The future will probably see complex nanovectors engineered to perform multiple functions, protecting the drugs, getting them through all the barriers and pitfalls that lie between the point at which the drug is administered and the part of the body where it is needed, and releasing them at their target. The recently FDA approved breast cancer drug, Abraxane, is an advance in the right direction; one can think of it as a nanovector that combines two functions. The core of the nanovector consists of a nanoparticulate form of the drug itself; dispersing it so finely dispenses with the need for toxic solvents. And bound to the drug nanoparticle are protein molecules which help the nanoparticles get across the cells that line blood vessels. It’s clear that as more and more functions are designed into nanovectors, there’s a huge amount of scope for increases in drug effectiveness, increases that could amount to orders of magnitude.
