An experimental treatment that uses white blood cells like “Trojan horses” to carry a tumor-busting virus, completely abolished prostate cancer spread after chemo or radiotherapy in mice. The researchers hope clinical trials in human patients with prostate cancer can start in early 2013.

Claire Lewis, a professor at the Department of Oncology in the University of Sheffield, and colleagues, write about their findings in a recent issue of the journal Cancer Research.

Using immune cells to carry viruses to treat cancer is an emerging field. In June 2012, researchers reported discovering how when a cancer-killing virus is injected in the bloodstream it hitches a ride on blood cells and evades attack from the immune system, allowing it to reach cancer tumors, and start destroying cancer cells.

Lewis and her team have also been investigating this approach, and discovered that the challenge is to get enough of the virus deep into the tumor.

After chemotherapy or radiotherapy, the immune system floods the tumor with white blood cells called “macrophages” that mop up the debris caused by the therapy.

Lewis and colleagues found that injecting macrophages carrying a tumor-busting or “oncolytic virus” (OV) into the bloodstream at the exact moment when this surge occurs, they “surf the wave” of white blood cells and inundate the tumor in large numbers.

“… we show that administration of such OV-armed macrophages 48 hours after chemotherapy (docetaxel) or tumor irradiation abolished the post-treatment regrowth of primary prostate tumors in mice, and their spread to the lungs for up to 27 or 40 days respectively,” they write.

The treatment also “significantly increased the lifespan of tumor-bearing mice compared to those given docetaxel or irradiation alone,” they add.

In a statement released last week, Lewis says:

“Our “Trojan horse” can convert a patient’s own white blood cells into tiny tumor-killing machines which fight to prevent tumor regrowth after the end of chemo or radio therapy treatment.”

“This is very empowering for patients who have been undergoing rounds and rounds of chemotherapy or radiotherapy because treatment means it is their own white blood cells doing the work and blasting the cancer,” she explains.

First author Munitta Muthana, from Sheffield’s Department of Infection and Immunity, adds:

“With the initial support of the Yorkshire Cancer Research (YCR) and latterly Prostate Cancer UK, our new therapy has been developed to treat prostate cancer; however, it has the potential to be used to treat patients with any form of cancer.”

Kate Holmes, Head of Research at Prostate Cancer UK describes the study as an “exciting development” in the “Trojan Horse” approach.

“It demonstrates that this innovative method of delivering a tumor-killing virus direct to the cancer site is successful at reducing the development of advanced prostate tumors in mice which have been treated with chemotherapy and radiotherapy.”

“If this treatment goes on to be successful in human trials, it could mark substantial progress in finding better treatments for men with prostate cancer which has spread to the bone, and ensuring the impact of more traditional therapies is maximised,” she adds.

Meanwhile, across the Atlantic in the US, researchers at the Mayo Clinic have discovered that an enzyme called PRSS3, or mesotrypsin, may help drive aggressive prostate cancer. They suggest their finding will lead not only to more effective treatment of advanced prostate cancer, but may also help identify those at high risk for the aggressive form.

Prostate cancer is the most common cancer in men in the UK, where rates have tripled in the last 40 years.

In 2009, about 40,800 men in the UK were diagnosed with the disease, or around 112 a day.

Recent figures from Cancer Research UK predict a man’s risk of developing cancer during his lifetime will rise to one in two by 2027, largely because more people are living longer.

Written by Catharine Paddock PhD