As a result, Cheresh said, the findings may provide a new strategy for treating cancer. "It means that chemotherapy could be timed appropriately. We could first stabilize the blood vessels, and then come in with chemotherapy drugs that are able to treat the cancer."
Co-author Randall Johnson, Ph.D., professor of biology at UCSD, Cheresh and their colleagues showed in a related paper in the same journal that tumors were more susceptible to drugs after inflammatory cells lost the ability to express VEGF.
"These two papers define a new mechanism of action for VEGF and for anti-angiogenesis drugs," Cheresh said. "It appears that the drugs, in shutting down VEGF activity, are actively maturing blood vessels, causing them to become stable and more normal, as opposed to reducing blood vessels."
VEGF normally promotes the growth of endothelial cells, which in turn helps build new blood vessels in tumors. But tumor blood vessels are built poorly and do a terrible job of carrying blood and oxygen and drugs. Cutting VEGF levels in the tumor in turn increases the activity of cells called pericytes that surround the blood vessels, stabilizing them and making them more susceptible to chemotherapy, Cheresh explained.
Cheresh's group found that receptors for VEGF and another growth-promoting protein, PDGF, form a complex that turns off PDGF and the activity of the blood vessel-support cells. Tumors make too much VEGF in their haste to form blood vessels, which turns on the receptor complex. "When you take away the VEGF, you 'take the foot off of the brake,'" he said, allowing the pericytes to go to work, maturing blood vessels. The same mechanism is at work during wound repair.
Cheresh said that the results show that the host response to the cancer whether or not it is making blood vessel-maturing cells, for example is critical in terms of susceptibility to therapy. "It's not just about the the
|Contact: Steve Benowitz|
University of California - San Diego