Chemotherapy and radiation have long been standard treatments for solid tumors such as breast, colon, ovarian, pancreatic, brain and other cancers. However, in addition to causing often-debilitating side effects, these treatments are not always wholly effective, as cancer can return, or come out of remission. One theory behind the cause of relapse is the existence of certain cells present in cancers called “cancer stem cells.”
Cancer stem cells share similar properties with ordinary stem cells, but harbor ulterior motives. Like stem cells, cancer stem cells can self-renew and produce more copies of themselves; they are also thought to produce the cell types that make up a tumor. Cancer stem cells appear to be more resistant to conventional treatments. Though few in number, cancer stem cells can self-replicate over time until a new tumor is formed, and cancer recurs.
California’s stem cell agency, the California Institute for Regenerative Medicine (CIRM), has supported solid tumor researchers that are developing therapies broadly applicable to many types of solid tumor cancers. They have invested more $59 million in this kind of research. These therapies could be used to help treat dozens of different types of cancers.
Cancer cells have high levels of a molecule known as CD47—a “don’t eat me” signal to the immune system. This signal essentially cloaks the cancer cells from being identified and removed by the immune system. The inordinate amounts of CD47 produced by the cancer cells effectively trick the immune system into leaving the cancer cells intact. A group at Stanford, led by Dr. Irving Weissman, developed an antibody that blocks the CD47 signal, thereby masking the “don’t eat me” signal.
“This causes the immune system to attack the cancerous cells, including hopefully the cancer stem cells.”
A team at the University of California, Los Angeles, led by Dr. Dennis Slamon, is currently leading a clinical trial with a similar goal of targeting cancer stem cells. This group is testing a molecule that inhibits a protein called PLK-4 that is enriched in many cancer stem cells. This is first being tested in patients with a variety of advanced cancer types to ensure that it is safe. Dr. Slamon was a pioneer of one of the first therapies for breast cancer, Herceptin, a drug that has helped many patients to date. CIRM is supporting his efforts to succeed again with this therapy.