An antidepressant from the Fifties could treat prostate cancer and reduce side-effects of other treatments.

Results of a small trial suggest that the drug phenelzine, which treats depression (by altering levels of brain chemicals that regulate mood) can shrink tumours in men whose prostate cancer has returned.

Phenelzine had fewer side-effects than conventional hormone therapy, which treats the cancer by reducing levels of testosterone — the hormone fuels the growth of cancerous cells.

Phenelzine is a type of drug called an MAO inhibitor, which treats depression by stopping an enzyme called monoamine oxidase from breaking down serotonin and dopamine, the ‘feel-good’ brain chemicals [File photo]

Prostate cancer is the most common cancer in British men, with around 48,500 new cases annually. It claims 11,700 lives a year. Surgery (to remove the prostate gland) or radiotherapy are the main treatments.

The disease recurs in about 15,000 cases a year and those affected are usually given hormone pills or injections to block the production of testosterone.

This is very effective at halting the cancer but can cause severe side-effects including hot flushes, fatigue, impotence, loss of muscle and thinning bones. Now research suggests giving phenelzine alongside hormone therapy reduces these side-effects.

Phenelzine is a type of drug called an MAO inhibitor, which treats depression by stopping an enzyme called monoamine oxidase from breaking down serotonin and dopamine, the ‘feel-good’ brain chemicals.

MAO inhibitors were the first antidepressants to be introduced, 70 years ago, but are no longer in common use, partly because they can interact with other drugs.

But as well as having a role in depression, the monoamine oxidase enzyme is also known to help prostate cancer cells grow.

Giving phenelzine interrupts the signals that testosterone sends to cancer cells, prompting them to grow. 

However, unlike hormone therapy, it does not block the production of testosterone and so avoids its unpleasant side-effects.

Researchers at the University of Southern California, in the U.S., gave phenelzine to 20 men whose prostate cancer had returned after surgery, in doses similar to those used for treating depression (60mg to 90mg).

Taken twice a day for 12 weeks, the antidepressant cut levels of the prostate specific antigen (PSA) protein in 55 per cent of the men (measuring levels of PSA enables doctors to monitor the progress of prostate cancer).

PSA levels in five men dropped by at least 30 per cent and in one they reduced by 74 per cent. Some participants experienced side-effects including a dry mouth, fatigue and mild dizziness, reported the journal Prostate Cancer and Prostatic Diseases.

The team say that giving the drug could mean lower doses of hormone therapy are needed, which would reduce severe side-effects from a lack of testosterone — or the drug could be used first, cutting the time men spend on hormone treatment.

Professor Nicholas James, a team leader in prostate and bladder cancer research at the Institute of Cancer Research, in London, says that finding a new use for existing medicines is a speedy way of introducing new treatments. 

‘It would be attractive to me as a clinician and to my patients to have treatments that delay their starting hormone therapy,’ he says. 

‘This definitely merits further research.’

Source: Dailymail