Tykerb Targets Cancer Stem Cells
Drug Curbs Tumor Growth by Wiping Out Cancer Stem Cells
Dec. 17, 2007 (San Antonio) -- For the first time, researchers have shown that a drug, Tykerb, can slash the number of cancer stem cells in women with breast cancer, curbing tumor growth.
The findings are in line with the latest theory of what causes cancer, namely that stem cells hiding within tumors drive their growth. Conventional treatments fail to cure cancer, according to the theory, because they are targeting the wrong cells.
Six weeks of Tykerb treatment slashed the number of breast cancer stem cells by more than half in 30 women studied, and two-thirds were cancer-free after follow-up treatment, says Jenny Chang, MD, of Baylor University in Houston.
At the San Antonio Breast Cancer Symposium here, Chang showed before-and-after photos in which one could see large breast tumors shrinking and, in some cases, all but disappearing after Tykerb treatment.
"This was one of the most important papers at the meeting," Joyce Slingerland, MD, director of the Braman Family Breast Cancer Institute at the University of Miami, tells WebMD. She was not involved with the work.
Stem Cells Fuel Tumor Growth
All stem cells -- regardless of their source -- share some general properties: They can reproduce and make exact copies of themselves, they live longer than ordinary cells, and they can give rise to other cells in our bodies.
Cancer stem calls are a perversion of other adult stem cells. Chang says that fewer than 10% of breast cancer cells have stem cell properties, but that it is this small number that continually reproduce and fuel tumor growth.
In one set of experiments, she took biopsies of breast tissue from 35 women, before and after chemotherapy. The number of cancer stem cells shot up after chemo.
Then, she injected the post-chemo tissue samples into mice with compromised immune systems. Tumors rapidly formed.
Tykerb Targets Cancer Stem Cells
It made sense to try Tykerb. Previous research has shown that the HER2/neu gene, which is associated with aggressive breast cancers, has stem cell properties. Tykerb targets HER2, the protein made by the HER2/neu gene.
The study involved 30 women whose breast tumors had high levels of the HER2 protein. They were given Tykerb for six weeks, followed by 12 weeks of treatment with a chemotherapy drug and Herceptin, which also targets HER2. Then they had surgery.
Examination of tissue samples taken before and after Tykerb treatment showed that the percentage of stem cells in the tissue dropped from 11% to 5%.
Tissue samples taken after surgery showed that 63% of women were cancer free.
"With chemotherapy, we saw an increase in stem cell production and an increase in tumor formation. With Tykerb, we saw the opposite," Chang tells WebMD.
Slingerland likens chemo to taking a shotgun and killing everyone in the room when there are only a few criminals -- the cancer stem cells.
By targeting the stem cells, you increase the chance of curing the cancer while lowering the risk of toxic side effects, she says.
Tykerb is approved to treat women with advanced or metastatic breast cancer whose tumors contain too much of the HER2 protein and who have failed other treatments.