Scientists have found the Achilles' heel of cells that jump start tumor growth. According to a new study, these "cancer stem cells" reside in blood vessels. Disrupting these vessels, say the researchers, may prove a far more effective cancer therapy than targeting other regions of a tumor.
Cancer biologists once believed that all cells in a tumor were pretty much the same. But in the early 1990s, a team found some interesting characters hanging out with leukemia cells: Instead of rapidly dividing like their million-fold-more-plentiful companions, these outliers grew slowly. And when transplanted to a petri dish, they gave rise to the more common type of leukemia cell. Cancer stem cells are the ultimate source of the tumor, consistently supplying it with new cells. Since then, researchers have discovered other cancer stem cells, including those behind acute myeloma leukemia, two types of brain cancer, and breast cancer. Killing these stem cells should allow researchers to hit a tumor where it hurts, yet chemotherapy has proven ineffective as it tends to kill only rapidly dividing cells.
So neurobiologist Richard Gilbertson at St. Jude Children's Research Hospital in Memphis, Tennessee, and colleagues began looking for a weakness. They started by comparing cancer stem cells to noncancerous neural stem cells. These neural tissue precursors are concentrated in regions rich in blood vessels. The vessels are lined with endothelial cells, which secrete chemical signals that help stem cell survive. Gilbertson's team wondered whether cancer stem cells might require a similar niche.
Sure enough, after examining over 70 human brain tumors, the researchers found that cancer stem cells were frequently located close to tiny vessels called capillaries. When the researchers injected mice with a mix of stem and endothelial cells from human brain tumors, the animals sprouted larger tumors than did mice receiving stem cells alone, the team reports today in Cancer Cell. Drugs that shrunk the capillaries also caused a significant drop in cancer stem cells and consequently put a damper on tumor growth. The same drugs hardly affected the survival of cells in rest of the tumor.
"This study is an excellent example of bringing stem cell insight to cancer," says Robert Wechsler-Reya, a cancer biologist at Duke University Medical Center in Durham, North Carolina. "I think this is going to be the beginning of a really popular approach [to cancer therapy]."