JOHNS HOPKINS (US) — A heart drug taken from the leaves of flowering foxglove may also be effective in treating prostate cancer.
Men taking digoxin to treat congestive heart failure and heart rhythm abnormalities show a 24 percent lower risk for prostate cancer, a finding which may pave new ways to treat the cancer.
“This is not a drug you’d give to healthy people,” says Elizabeth Platz, professor of epidemiology, oncology, and urology at Johns Hopkins University, stressing the drug should not be considered useful in preventing the disease.
Serious side effects include male breast enlargement and heart rhythm irregularities, The drug also commonly causes nausea, vomiting, and headache.
Derived from leaves of foxglove, a type of flowering plant, digoxin has been prescribed for decades to treat congestive heart failure and heart rhythm abnormalities.
A project to screen 3,000 existing drugs used against other diseases or conditions for their potential to also fight prostate cancer, brought to light the drug’s potential, a study published in the journal Cancer Discovery.
In the first stage of research, researchers identified 38 compounds already FDA-approved or with a history of medical use that reduced prostate cancer cell growth in the laboratory by at least 50 percent.
William Nelson, professor of oncology and Srinivasan Yegnasubrumanian, assistant professor of environmental health sciences then took the list of 38 drugs to Platz, a prostate cancer research collaborator.
“We realized that combining our laboratory and epidemiologic approaches could reduce the possibility that results on the candidate drugs might be due to chance,” Platz says. “Adding the epidemiology study to the drug screen step provided an assessment of the drug’s potential activity in people.”
Disulfiram, used to treat chronic alcoholism, was the top hit on the list of potential anti-prostate cancer drugs, but because it is rarely used among the general population, it could not be evaluated effectively in the epidemiologic study. The second strongest candidate was digoxin.
To see if they could identify a link between digoxin and prostate cancer in humans, they turned to a cohort of about 47,000 men aged 40-75 who participated in Harvard’s Health Professionals Follow-up Study from 1986 through 2006 and did not have a cancer diagnosis before 1986.
Participants had completed a questionnaire every two years, reporting on demographic information, medical history, medication use, and lifestyle factors. Researchers evaluated the medical records and pathology reports of men who reported a prostate cancer diagnosis during the study.
Among the study participants, 5,002 cases of prostate cancer were reported. Two percent of all study participants reported regular use of digoxin at the beginning of the study, and those men had a 24 percent lower relative risk of getting prostate cancer compared with men who did not use the drug. Those who used digoxin for more than 10 years had about half the risk of developing prostate cancer as those who did not.
Even after ruling out such potentially confounding factors as PSA screening, family history of prostate cancer, and use of other heart drugs, the lower risk of prostate cancer among digoxin users held up, the researchers say.
The next steps will be to determine the mechanism of digoxin’s effect on prostate cancer cells, which could support testing digoxin or other drugs that work in the same way in clinical trials as a potential prostate cancer therapy.
Digoxin alters enzymatic pathways for sodium and potassium in heart cells, and according to the researchers, may also have an effect on the same or different pathways in prostate cancer.
Funding for the research was provided in part by the National Cancer Institute, National Institutes of Health, and the National Heart, Lung, and Blood Institute.
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