Many of the most longstanding and effective cancer therapeutic drugs are excellent at killing tumour cells by exploiting their characteristic rapid growth. However, this means that they also affect other proliferating cells such as hair follicles and those lining the digestive system, giving rise to some unpleasant side-effects. One way to overcome this has been to develop specific molecules that only target cancer cells. These therapies have certainly been nothing less than revolutionary (think imatinib, immunotherapy, and many more), but innovative new ways to target cancer cells are still needed. This has given rise to an opportunity to turn the issue on its head; it’s time to think about how to get there. Is there a way we can deliver drugs to cancer cells and not their more normal neighbours?
We now know that cancer cells have a wide range of unusual features: many are surrounded by the crab-like blood vessels from which they acquired their name, and they can be especially leaky, with poor waste drainage (enhanced permeability and retention, or EPR). There are several ways to exploit these features. One strategy is to package chemotherapy drugs into nanoparticles coated with special substances to target them to cell membranes. Here they are engulfed by tumour cells, allowing the drug to build up inside. The first successful nanoparticle therapy contains paclitaxel, a longstanding potent chemotherapy drug, bundled into a nanoparticle and coated with albumin and is FDA and EMA approved for breast, lung, and pancreatic cancer. Moreover, nanoparticle carriers are only one type of packaging material; others include carbon nanotubes, complex polymers, and liposomes (to name a few), which offer novel specific methods to deliver drugs to tumours and have already led to numerous clinical trials worldwide. Clearly, this is an exciting and rapidly advancing therapeutic area and at least five liposomal drugs have already been launched.
These are also exciting advances for the wider medical community, as the concept can be applied to many other diseases. It demonstrates how expanding biological understanding, coupled with advances in the manipulation of chemical structure, is giving rise to increasingly smart, multidisciplinary ways to combat disease.