Relative of smallpox virus may be effective against breast cancer

A relative of the smallpox virus may be an effective weapon against one of the deadliest forms of breast cancer, research has shown.

Laboratory tests showed that more than 90% of triple negative breast cancer (TNBC) cells treated with the vaccinia virus were destroyed within four days.

In mice with the disease, one strain of the virus cleared 60% of tumours while the extent of those left was dramatically reduced.

Vaccinia virus is best known as the basis of the vaccine that eradicated smallpox. Although closely related to the variola virus that causes smallpox, it is generally harmless to humans.

TNBC is difficult to treat because it lacks three types of molecular “receptor” that can be targeted by existing hormonal and antibody treatments.

The disease mostly occurs in younger women and is responsible for 10% to 20% of all breast cancer cases.

TBNC tends to be aggressive and often recurs after chemotherapy. The virus targets a signalling protein that tumours use to promote the formation of blood vessels that support their growth.

TNBC has high levels of the protein, known as vascular endothelial growth factor.

The lead researcher, Dr Sepideh Gholami, from Stanford University in California, US, said: “The reason we used the vaccinia virus is that it is a member of the smallpox family, and, as we know, smallpox vaccine has been given to millions of people to eradicate smallpox.

“So we thought it would be safer and more promising in terms of a clinical trial and actual application.”

The findings were presented at the American College of Surgeons’ Annual Clinical Congress in Chicago. Exposing mice with TNBC tumours to the virus led to “extensive destruction” of the cancer over a period of three weeks, said the scientists.

As well as infecting and breaking down cancer cells, the virus also blocked the growth of tumour blood vessels. Ultrasound imaging revealed a “significant reduction” in blood flow to tumours.

The network of blood vessels supplying tumours with nutrients and oxygen shrank to half its normal size in treated animals. The next step will be to design a clinical trial and assess the safety of the virus in patients, Dr Gholami said.