Tests in mice show prosaposin injections reduce tumor growth
MONDAY, June 22 (HealthDay News) -- A protein produced by certain kinds of tumors inhibits the spread of cancer and could potentially be harnessed as a cancer treatment, researchers say.
Currently, there is no approved therapy for inhibiting or treating metastasis -- the migration of cancer cells from the original cancer site to other parts of the body. Metastasis is one of the leading causes of cancer death.
Researchers at Children's Hospital Boston had found previously that metastatic tumors prepare "landing places" for cancer in other organs by secreting certain proteins that encourage tumor growth and attract feeder blood vessels. In the new study, they found that non-metastatic tumors secrete a protein called prosaposin that inhibits metastasis by promoting production of factors that block the growth of blood vessels, according to a news release from the hospital.
Laboratory tests showed that high levels of prosaposin were secreted by non-metastatic, localized prostate and breast tumors but that metastatic tumors secreted very little of the protein. The researchers then added prosaposin to highly metastatic tumor cells and injected them into mice.
Lung metastases in the mice were reduced by 80 percent, lymph node metastases disappeared, and there was a significant increase in survival time, the researchers found.
When prosaposin was injected directly into mice after they'd been injected with tumors cells, there was a large reduction in lung metastases and the mice lived at least 30 percent longer than those who didn't receive prosaposin, the study reported.
Further research revealed that prosaposin stimulated activity of the tumor suppressor p53 in connective tissue (stroma) surrounding the tumor, which then stimulated production of an inhibitor of blood vessel growth in the tumor stroma and in distant cells, according to the study.
"Prosaposin, or derivatives that stimulate p53 activity in a similar manner in the tumor stroma, might be an effective way to inhibit the metastatic process in humans," Randolph S. Watnick, an assistant professor in the Vascular Biology Program at Children's Hospital Boston, said in the news release.
The study appears online in Proceedings of the National Academy of Sciences.
The U.S. National Cancer Institute has more about metastatic cancer.
-- Robert Preidt
SOURCE: Children's Hospital Boston, news release, June 22, 2009
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