Prostate cancer sufferers offered hope by molecule discovery
Men suffering with currently incurable prostate cancer have been offered hope by the discovery of a molecule that apears to target the tumours.
Published: 8:00PM GMT 28 Dec 2009
The ''monoclonal'' antibody seems to act against the diseas in both its early and advanced stages.
As well as attacking the disease directly, it also helps the immune system to identify and destroy cancer cells.
Tests in mice showed that the antibody, known as F77, wiped out 85% of one type of highly aggressive prostate cancer.
Tumours allowed to grow to a large size were also dramatically reduced in volume.
Each year around 35,000 men in the UK are diagnosed with prostate cancer, and 10,000 die from the disease.
Initially, spreading prostate cancer can be kept under control with therapies that prevent tumour growth being fuelled by androgen male hormones.
But eventually most prostate cancers stop being hormone-sensitive. Few treatment options are then possible and progress of the disease is rapid and lethal.
Up to 45% of patients with local prostate cancer relapse after curative treatments such as surgery and radiotherapy, and their disease begins to spread, or ''metastasise''.
The five-year survival rate for patients with metastatic prostate cancer is only 34%.
Although the new research is at a very early stage, it raises the prospect of an effective treatment for non-hormone-sensitive advanced prostate cancer for the first time.
Writing in the journal Proceedings of the National Academy of Sciences, the US scientists said the F77 antibody showed ''promising potential for diagnosis and treatment of prostate cancer, especially for androgen-independent metastatic prostate cancer''.
The researchers, led by Dr Mark Greene from the University of Pennsylvania School of Medicine in Philadelphia, pointed out that while antibodies were already being used to tackle other diseases such as lymphoma and breast cancer, those suitable for use against prostate cancer were rare.
Two under investigation were both ineffective against many advanced non-hormone-sensitive cancers.
F77 on the other hand targeted the most aggressive cancers and responded to those both sensitive and insensitive to male hormones.
Monoclonal antibodies (mABs) are copies of a single type of immune system protein that can be mass-produced in the laboratory.
Like natural antibodies produced in the body, they help identify and neutralise foreign invaders or other potential sources of danger such as cancer cells.
This is done by latching onto a specific ''enemy'' target molecule, or ''antigen''. In the case of F77, the target is a fatty sugar only found on prostate cancer cell surfaces called PCLA (prostate cancer lipid antigen).
The US scientists found that on its own, F77 induced a degree of ''apoptosis'' - a natural process of cell suicide that helps keep rogue cells in check - in cancer cells.
More importantly, it amplified the immune system's ability to recognise and destroy the cancer.
The antibody was tested on laboratory mice injected with highly aggressive non-hormone responsive human prostate cancer cells known as PC3 cells.
The scientists wrote: ''PC3 tumour growth was completely suppressed in five of six mice in the mAB F77 treatment group.''
''Control'' mice injected with PC3 cells but not treated with F77 all developed tumours that grew to a large size within a month.
Another type of prostate cancer cell, called Du145, was used to study the effect of the antibody on already well-established tumours.
A ''significant reduction'' in tumour growth rate was seen in mice injected with F77. After 10 days, the average size of tumours in treated mice had grown from 30 cubic millimetres to 79.7 cubic millimetres.
In untreated mice they grew to 195.8 cubic millimetres.
Dr Sarah Cant, head of policy and campaigns at The Prostate Cancer Charity, said: ''The researchers behind this early-stage study have identified an antibody that seeks prostate cancer cells and aids their destruction, when grown in the laboratory. The antibody was also capable of inhibiting tumour growth in mice.
''What is potentially significant about this study is that the antibody targets both hormone-sensitive and hormone-insensitive prostate cancer. Many men with advanced prostate cancer, where the disease has spread beyond the prostate gland, are treated with hormone therapy, a treatment to which they can become 'resistant'.
''The study could possibly yield interesting developments, either as a new way of diagnosing prostate cancer, or as a new therapy that could be used to treat early and late stages of the disease, perhaps even when it has spread to the bone.
''It is hoped that the development of this type of therapy will be more specifically targeted than current treatments, meaning that it could be more effective and lead to fewer side-effects.
''An example of this type of therapy that is in current clinical practice is Herceptin for breast cancer. ''We need to remember that this is very early stage research that has only been carried out in cells grown in the laboratory and in mice. Any potential therapy would need to undergo more refinement, and large-scale clinical trials would be needed before it could be proven that this is safe and effective to treat prostate cancer in men. However, the development of any new, targeted treatments or diagnostics is to be welcomed. We will be following the development of this research with interest.''