Scientists in the UK have found a way to target cancer with gold.

David Russell and co-workers at the University of East Anglia have designed a system that delivers a light sensitive drug to cancer cells. The system uses gold nanoparticles, to which the drug and another organic molecule, called a phase transfer agent, can be bound. This drug-nanoparticle complex can be used to kill cancer cells in a process called photodynamic therapy (PDT).
 
PDT is an established cancer treatment that is available in several countries. It uses the combination of a photoactive drug (a photosensitiser) and light.  When stimulated by visible light the drug damages the target cancer cells, leaving healthy tissue unharmed. 

Russell's system used a cancer drug based on a phthalocyanine molecule. These molecules are more specific to cancer tissue than others commonly used in PDT. However, this type of drug is not water soluble, making it more difficult to deliver it to target sites, said Russell. Using a phase transfer agent can help overcome this problem by making the drug-nanoparticle complex soluble in water, he explained. 

On irradiating with red light, the phthalocyanine drug produces an active form of oxygen, singlet oxygen, which is toxic to cells. The group found that the drug-nanoparticle complexes produced 50 per cent more singlet oxygen than the drug alone. 

Russell showed that the drug-nanoparticle complexes were taken up by cervical cancer cells in vitro. These cancer cells then died by apoptosis, or cell suicide. 'While our results are very encouraging, the next key phase of the work is to take the in vitro study to the in vivo environment. To do this we are collaborating with a PDT group in Padova,' said Russell. 

David Phillips, a PDT expert from Imperial College London, UK, said, 'This is a very useful, novel means of getting photosensitisers into cells, and in this case, the use of the gold nanoparticles enhances the singlet oxygen yield, so is a real bonus.' Phillips suggests that, although there will be several factors to consider, the delivery system 'promises well for future applications in vivo.' 

Katherine Vickers