Cranking Up Cancer Treatments: A Bright Future for Growth Factors
Weiss, Rick, Science News
Cranking Up Cancer Treatments
Like the famous exhortation "Go west, young man," and like the single word "plastics" whispered to Ben in "The Graduate," there's some simple, sage advice going around these days in cancer treatment circles: "growth factors."
Researchers know these naturally occurring molecules by many acronyms, including G-CSF, GM-CSF and EPO. The general public, for the most part, knows little about them. But in the next few years, many cancer specialists say, these biologically active chemicals will spark the first real revolution in oncology since chemotherapy and radiation became commonplace in the 1960s. While the compounds themselves do not cure cancer, they significantly speed the recovery of healthy cells after treatment with traditional cancer therapies.
"Never before have we been presented with a group of compounds for which we can so readily see the application," says Howard Ozer of the University of North Carolina in Chapel Hill.
Growth factors are proteins that regulate the growth and maturation of various cells in the body. Most tantalizing to cancer researchers are the so-called colony stimulating factors (CSFs) and a hormone called erythropoeitin, each of which triggers proliferation of specific cells.
Put simply, colony stimulating factors shift the body's white-blood-cell-making machinery into high gear. They act on progenitors of immune-system cells in the bone marrow, stimulating increased cell production, speedy maturation and quick release into the blood. Various cells in the body make small amounts of CSFs. But with recombinant DNA techniques, scientists now can routinely mass-produce these compounds.
Granulocyte colony stimulating factor (G-CSF) boosts bacteria-gobbling granulocytes -- the most common kind of white cells in blood. Monocyte colony stimulating factor (M-CSF) increases the numbers and activity of two types of aggressive immune cells -- monocytes in the bloodstream and macrophages in body tissues. Granulocyte-macrophage colony stimulating factor (GM-CSF) works on all three cell lineages.
The Food and Drug Administration has yet to approve any CSF for general use. But approval for GM-CSF, the most thoroughly tested, appears "very close," says Jules E. Harris of the Rush Presbyterian St. Lukes Medical Center in Chicago. In San Francisco last month, at the annual meeting of the American Society of Clinical Oncology, researchers reported results of ongoing clinical trials involving CSFs and erythropoeitin, which stimulates production of red blood cells.
"Bone marrow injury is usually the limiting factor for [cancer] chemotherapeutics," says James O. Armitage of the University of Nebraska College of Medicine in Omaha. If doctors use chemotherapy doses low enough to preserve bone marrow function, cancer cells often survive. But higher doses decimate bone marrow along with the cancer cells, leaving patients susceptible to life-threatening infections. Colony stimulating factors show promise as "rescue" compounds to speed recovery of normal, healthy cells after radiation and chemotherapy treatments.
Ongoing studies in Australia, West Germany and the United States indicate that CSFs accelerate bone marrow recovery in patients receiving radiation or chemotherapy. …