Rexahn Pharmaceuticals' Archexin is a string of 20 nucleotides that is complementary to the messenger RNA used to translate the protein kinase B (PKB or AKT) gene into its protein product. By blocking the action of this gene, Rexahn hopes to slow down tumour progression through blocking one pathway of cell proliferation and cell survival.

Antisense drugs have had a difficult time with high profile failures as well as some success stories. However, having already got through Phase I clinical trials with promising results, Rexahn will be hoping Archexin can make it to market as a new treatment for kidney cancer.

Renal cell carcinoma (RCC) is the most common form of kidney cancer, affecting about three in every 10,000 people in the US. It is one of the most difficult cancers to treat because only 20 per cent metastatic RCC tumours respond to standard therapy. The five year survival rate with existing therapies is currently less than 20 per cent.

"We are very pleased to have received [Food and Drug Administration] FDA approval to move this important compound into a Phase II trial for renal cell carcinoma patients, most of whom have limited treatment options," said Dr Chang Ahn, CEO of Rexahn.

"Archexin may someday offer patients a more targeted, less toxic therapeutic approach to cancer treatment."

The company completed the clinical phase of a Phase I clinical trial of Archexin in October 2006. According to Rexahn, the results indicated that fatigue is Archexin's major dose-limiting toxicity, and unlike most anti-cancer drugs, no haematological abnormalities were seen.

Antisense drugs are DNA-like strands of nucleotides that bind to specific areas of mRNA. This section of gene RNA is then degraded and the corresponding protein is never produced. Therefore, any negative effects of the protein are prevented - similarly to small molecule inhibitors. However, as they are made of genetic material, it is thought they highly specific compared to small molecule drugs.

Bayer has a marketed kidney cancer treatment, which they developed in collaboration with Onyx Pharmaceuticals. Nexavar (sorafenib) targets both the RAF/MEK/ERK signalling pathway to inhibit cell proliferation and VEGFR-2/PDGFR-beta to inhibit blood vessel growth in tumours.