Credit: © 2008 Wiley

The development of nanocarriers to deliver drugs — in particular, for treating cancer — to specific cells in the body is the subject of intense research. The ability of viruses to target and kill cells has inspired the design of many drug-delivery systems, but none of these have been able to match the targeting capabilities of viruses, or their ability to move on to a new cell once the previous cell has been destroyed.

Now, You Han Bae and co-workers1 at the University of Utah and the Catholic University of Korea have developed a nanogel that is able to mimic viral properties much better than previous systems. The nanogel consists of a hydrophobic polymer core that contains histidine units, and two layers of hydrophilic shell — polyethylene glycol and bovine serum albumin. The bovine serum albumin shell is functionalized with folate ligands, which can bind to the folate receptors that are present on many tumours. The core is loaded with a model anticancer drug.

The nanogel is pH sensitive — swelling when the pH reaches about 6.4 (owing to protonation of the histidine units) and then shrinking again at higher pH. When the nanogel enters a cancer cell it swells because the pH value inside the cell is slightly lower than that outside, and this swelling causes some of the drugs inside the nanogel to be released. Moreover, the nanogels can move on to other cells where the process can be repeated to release more drugs.