New drug may target hard-to-treat breast tumours

An experimental drug that makes cancer cells susceptible to a widely used treatment could help women with a hard-to-treat and often more aggressive form of breast cancer, researchers said on Monday.

About a third of women develop so-called estrogen-negative tumours, which means their cancer does not respond to tamoxifen, said Caroline Ford and colleagues at Lund University in Sweden.

But their new drug called Foxy-5 activates the estrogen receptor - a kind of molecular doorway on cells that allows tamoxifen to work, they reported in the Proceedings of the National Academy of Sciences.

“It flips the switch basically,” Ford said in a telephone interview. “It makes breast cancer cells respond to tamoxifen in women who cannot be treated with the drug,” she added. “If you don’t have that molecule you can’t get tamoxifen because there is no target.”

Breast cancer is the leading cause of cancer deaths among women worldwide, according to the American Cancer Society. The group estimates about 465,000 women died of breast cancer globally in 2007, and 1.3 million new cases were diagnosed.

Tamoxifen has been shown to reduce the risk that breast cancer will return after surgery, at least among patients with so-called estrogen-receptor-positive cancer, the most common type. It works by blocking estrogen from causing wild cell growth.

The study of cancer cells in a lab shows the experimental drug may one day offer better options for the third of women who develop estrogen-receptor-negative tumours.

The treatment is not an alternative for a new class of drugs called aromatase inhibitors such as AstraZeneca’s Arimidex, Ford said.

“It is about giving more possibilities to people,” said Ford, adding that another goal is to see whether the drug helps women who develop resistance to tamoxifen.

The researchers, who have filed a patent on the drug and who hope to start trials in humans within five years, studied a gene called Wnt-5a involved in growth and development which has also been linked to some cancers.

They created the drug Foxy-5 to mimic the gene. Like Wnt-5a, Foxy-5 slows the movement of cells. This helps prevent tumours from spreading and turns the estrogen receptor back on so tamoxifen can target the hormone, Ford said.

By Michael Kahn

LONDON (Reuters)