Cells in blood may help cancers spread

CHICAGO (Reuters) - Normal cells in the blood that play a role in healing wounds may also be creating the right conditions for cancer cells to spread, U.S. researchers said on Tuesday.

They said fibrocytes, blood cells derived from bone marrow, could explain how healthy cells become habitats for cancer.

"Cancer cells do not enter healthy tissue easily. We know that," Dr. Hendrik van Deventer of the University of North Carolina at Chapel Hill, whose research appears in the American Journal of Pathology, said in a telephone interview.

"There has been sort of this movement to look for the cells that help prepare distant tissue to accept metastasis," he said, referring to the process in which cancer spreads to other parts of the body.

"We don't know what that cell is," van Deventer said, but he said that cell might be a fibrocyte.

"It has characteristics that make it a nice cancer metastasis-promoting cell," van Deventer said.

Van Deventer began to suspect fibrocytes when he was working with mice that were genetically engineered to lack the cell receptor CCR5, a cellular doorway that helps control the migration of cells through the body. CCR5 is the same entry point used by the human immunodeficiency virus, which causes AIDS, to get inside immune cells.

These genetically altered mice, which also had the skin cancer melanoma, tended to get fewer metastatic tumors than normal mice with melanoma. Van Deventer's team methodically injected these altered mice with various types of cells from normal mice to try to make them form more tumors.

"We tried that with a bunch of different cells. The one that worked is this fibrocyte," he said.

When van Deventer injected the mice with 60,000 of the cells, the rate of metastases nearly doubled. "That's a big effect for a relatively small number of cells," van Deventer said in a statement.

In healthy humans, fibrocytes travel through the bloodstream to injured areas, where they produce changes that are good for wounds. Van Deventer suspects these changes may help cancer grow.

In his experiments, van Deventer noticed that mice injected with fibrocytes started making matrix metallopeptidase 9, or MMP-9, an enzyme that is known to promote cancer.

While not proven, the study at least points to a likely candidate, van Deventer said.

If fibrocytes are involved, he said there may already be a potential treatment. Van Deventer said there are drugs that block the MMP-9 enzyme.

"The problem is the side effects were awful. They have been abandoned," he said.

But since the MMP enzyme works in conjunction with CCR5, he thinks they might be able to develop a drug that blocks both, allowing doctors to reduce the dose of the MMP-9 blocker.

"The combination of the drugs could be used at lower doses and have the same effect, and you wouldn't have as many side effects," he said.

(Editing by Will Dunham)