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By Deena Beasley
LOS ANGELES, Mar 13 (Reuters) - A 50-year-old drug given by injection to prevent blood clots may help the body fight the spread of cancerous tumors, according to researchers.
Scientists at the University of California at San Diego said Monday they have evidence that the blood thinning drug heparin limits the ability of certain cancers in mice to metastasize, or spread, by interfering with the ability of cancer cells to travel through the bloodstream.
"These days the primary tumor rarely kills the cancer patient--it is removed by surgery or radiation. It's the spread that kills them," said Dr. Ajit Varki, senior author of the study, which is published in the March 13th issue of the Proceedings of the National Academy of Sciences.
"Heparin has been around for a long time. We were studying heparin's ability to prevent certain cell interactions, which we discovered are involved in the spread of cancer cells," he said.
Heparin is not, however, risk-free. "If you get too much, you can bleed to death. It has to be given under close medical supervision," Varki said.
Animal studies in the 1960s and 1970s showed that heparin--which is given by injection or intravenously--inhibited the spread of cancer. Follow-up human studies focused on the use of oral anticoagulants like Coumadin, which are easier to manage than heparin. However, the pills did not have the same effect and the research stalled.
"Our findings show that the anti-metastatic effect of heparin is not due to its ability to prevent blood clotting, which was previously thought, but rather its blockage of early tumor-platelet interactions in the bloodstream," said Lubor Borsig, a postdoctoral fellow working in Varki's lab.
COULD HELP COLON, PANCREAS, LUNG CANCER PATIENTS
Experimental mice received a single dose of heparin, which lasted only a few hours, yet this early exposure resulted in markedly reduced cancer cell survival and metastasis when the mice were examined several weeks later, the researchers said.
The drug--which has not yet been proven effective for cancer in humans--could be a treatment for patients with cancers of the colon, pancreas, lung, or other types that do not normally live in the bloodstream.
"Blood is a hostile environment for these types of cancer. They can be attacked unless they are able to cloak themselves with platelets. We think heparin blocks the formation of this cloak," Varki explained.
He said the drug may be effective during a very specific timeframe, between the time a patient is diagnosed with cancer and the removal of the primary tumor. "In that interval time--which can be two days or two weeks--we can maybe help patients," the researcher said.
Varki said an accurate estimate of the number of cancer patients who could benefit from heparin can only be determined in clinical trials. "It is only a subset of common cancers that will be helped, but the number of patients could be quite large given the prevalence of these diseases," he said.
Varki said the fact that heparin has been around for so long is an advantage in that regulators would not require extensive safety data, but is it also something of a disadvantage since it is probably not possible to secure a patent--and exclusive marketing rights--for the drug, even for a new use.
"Many companies make heparin. The question is who will step up to the plate," Varki said.
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