Using animal models of human breast and prostate cancers, the researchers found that injections of the neurotransmitter dopamine can improve blood flow to tumors and improve delivery of an anticancer drug, doubling the amount of the drug in tumors and increasing its effectiveness. The increasedblood flow also raised tumor oxygen levels, a condition that typically improves the effectiveness of both chemotherapy and radiation therapy.
The study also found that dopamine plays an important role in maintaining the structure of normal blood vessels, and that it does this by working through the D2 dopamine receptor, which is present in normal blood-vessel cells called endothelial cells and pericytes. Dopamine was absent in tumor blood-vessel cells.
The findings are published online in the Proceedings of the National Academy of Sciences.
"Our study indicates a use for dopamine in the treatment of cancer and perhaps other disorders in which normalizing abnormal and dysfunctional blood vessels might improve therapeutic responses," says principal investigator Dr. Sujit Basu, associate professor of pathology and a researcher in the OSUCCC -- James Experimental Therapeutics Program.
"Since dopamine and related agents are already used in the clinic for other disorders, these comparatively inexpensive drugs might be applied to the treatment of cancer to increase the therapeutic responses of chemotherapy and radiotherapy," he says.
The blood vessels that develop inside tumors are structurally abnormal, chaotic and leaky and do a poor job of supplying blood to the tumor, Basu notes. This hinders the delivery of chemotherapeutic agents, and it leaves tumors oxygen deprived. This oxygen deprivation makes tumor cells resistant to chemotherapy and radiation.
Basu and his colleagues found that the dopamine treatment normalizes the structure of abnormal tumor blood vessels, indicating an important role for a neurotransmitter in the remodeling of blood vessels. Other key findings include the following:
"Overall, our findings suggest that the normalization of tumor blood vessels using the neurotransmitter dopamine might be an important approach for improving therapeutic efficacy in the treatment of cancer patients," Basu says.
Funding from the National Cancer Institute, U.S. Department of Defense Grant mainly supported this research; a grant from the American Heart Association partially supported one of the investigators.
The other researchers involved in this study were Debanjan Chakroborty, Chandrani Sarkar, Hongmei Yu, Jiang Wang and Zhongfa Liu of Ohio State University; and Partha Sarathi Dasgupta of Chittaranjan National Cancer Institute, Kolkata, India.
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