Chemists working in China have used a native protein to deliver anticancer medicines to tumour cells.

Apoferritin is the iron-free form of ferritin, a naturally-occurring iron-storage protein made from 24 protein subunits. According to Zijian Guo from Nanjing University and his colleagues, ferritin is a promising vehicle for targeted drug delivery. Its protein subunits self-assemble to form a hollow cage into which foreign species, such as drugs, can be accommodated. What is more, ferritin is internalised by some tumours, which is likely to enable targeting to those tissues.

Cisplatin (yellow) is trapped inside apoferritin as its protein subunits unfold and reassemble

Cisplatin and carboplatin are two major platinum-based drugs used in tumour treatment worldwide. Guo's group showed that the drugs could be encapsulated in apoferritin's cavity and tested the drug-loaded proteins' efficacy against rat tumour cells. The cisplatin carrier 'has the potential to exert a cytotoxic effect on tumour cells,' said Guo. It decreases cell viability at concentrations significantly lower than control experiments where the protein is used alone, he explained.

Nicholas Farrell, an expert in platinum antitumour chemistry at Virginia Commonwealth University in Richmond, US, said: 'There has been much interest in formulating and encapsulating platinum-based drugs to enhance their anticancer activity and reduce toxicity. Approaches have included using liposomes and various nanomaterials, a number of which are in clinical trials. The use of a protein such as apoferritin is an innovative and promising contribution to this area.'

Guo suggested that the team's approach could be developed for targeted delivery of other drugs. 'Chemical modification of native proteins is usually needed for efficient drug loading, which undermines their affinity for cellular targets,' he said. 'In our system, the protein remains intact, so its potential recognition nature should not be affected.'

Michael Spencelayh