1. But the relatively new drug nelfinavir may pose a challenge.

2. The most effective of the three, nelfinavir, which impedes the activity of protein-degrading enzymes in the cell, also blocked tumour growth in mice injected with cancer cells.

3. Nelfinavir is now in preliminary clinical trials, which should reveal the dose that can be tolerated by patients with cancer, and how it affects solid tumours in the body.

4. Cancer-causing mutations can also activate the proteasome, so drugs that block protein breakdown, such as nelfinavir, could theoretically halt both diseases.

5. The drugmaker added that the EMS impurities were caused by the manufacturing process of the drug, which is known generically as nelfinavir mesylate.