Researchers are creating a "designer" protein that could be effective at treating prostate cancer when other therapies fail.

In laboratory tests, the protein hindered the growth of cancer cells even in conditions where conventional therapies are ineffective.

The researchers, from Imperial College London and the University of Essex, hope to develop the protein into a therapeutic that could be trialled in patients within five years.

The findings are published today in the journal Oncotarget.

Prostate cancer is the most common type of cancer in men. Around 37,000 UK men are diagnosed with the disease each year. Many prostate cancers develop very slowly, but in a small proportion of cases the cancer grows more quickly and spreads to other areas of the body, sometimes proving fatal.

Prostate cancers are only able to grow when they are exposed to male hormones such as testosterone. These hormones bring about their effects by binding to specific receptors. Many existing therapies target these receptors, yet after an average of two years the cancer becomes resistant to treatment. In this phase, hormones continue to drive the growth of cancer cells.

In this new study, the researchers have designed a new protein which blocks the hormone receptors and consequently stops prostate cancer cells from growing in the laboratory. The therapy was successful even in circumstances that lead to the failure of conventional treatments.

Dr Charlotte Bevan, senior author of the study, from the Department of Surgery and Cancer at Imperial College London, said: “Eleven thousand men die from prostate cancer each year in the UK. Existing treatments are good at first but frequently fail after a couple of years. Once the cancer moves to the more aggressive stage, there are few therapies available.

“Our team is seeking to design a new therapy that will help patients once the other ones have failed. There is a lot of research supporting the idea that the androgen receptor continues to drive prostate cancer growth, so we have been investigating novel methods to block this pathway.”

The team is designing a novel therapy by combining two separate proteins to create a hybrid. One half binds to the receptor, whilst the other half blocks the receptor’s activity. The research demonstrates that both of these factors are important in blocking activity, and consequently the growth of the cancer.

“So far, the research has only been carried out in prostate cancer cells in the laboratory.  These proof of principle experiments are really promising, but more work is needed before these therapies are ready for clinical trials” said Dr Greg Brooke, first author of the study, now at the School of Biological Sciences, University of Essex. “The next step is to continue research in cell models to refine the therapy into something that is specific, potent and easy to deliver.

“It’s exciting to think that this research could offer new hope for men with advanced prostate cancer.”

This work was supported by Prostate Cancer UK (formerly Prostate Action), The Martin Harris Research Fellowship, Imperial Innovations and Johnson & Johnson Services Inc., an affiliate of Johnson & Johnson Innovation.

Reference: G.N. Brooke et al. ‘Engineered repressors are potent inhibitors of androgen receptor activity.’ Oncotarget, 17 January 2014.