An over-the-counter natural remedy derived from honeybee hives arrests the growth of prostate cancer cells and tumors in mice, according to a new paper from researchers at the University of Chicago Medicine.

Caffeic acid phenethyl ester, or CAPE, is a compound isolated from honeybee hive propolis, the resin used by bees to patch up holes in hives. Propolis has been used for centuries as a natural remedy for conditions ranging from sore throats and allergies to burns and cancer. But the compound has not gained acceptance in the clinic due to scientific questions about its effect on cells.

In a paper published in Cancer Prevention Research, researchers combined traditional cancer research methods with cutting-edge proteomics to find that CAPE arrests early-stage prostate cancer by shutting down the tumor cells' system for detecting sources of nutrition.

"If you feed CAPE to mice daily, their tumors will stop growing. After several weeks, if you stop the treatment, the tumors will begin to grow again at their original pace," said Richard B. Jones, PhD, assistant professor in the Ben May Department for Cancer Research and Institute for Genomics and Systems Biology and senior author of the study. "So it doesn't kill the cancer, but it basically will indefinitely stop prostate cancer proliferation."

Natural remedies isolated from plant and animal products are often marketed as cure-alls for a variety of maladies, usually based on vague antioxidant and anti-inflammatory claims. While substances such as ginseng or green tea have been occasionally tested in laboratories for their medicinal properties, scientific evidence is commonly lacking on the full biological effects of these over-the-counter compounds.

"It's only recently that people have examined the mechanism by which some of these herbal remedies work," Jones said. "Our knowledge about what these things are actually doing is a bit of a disconnected hodge-podge of tests and labs and conditions. In the end, you're left with a broad, disconnected story about what exactly these things are doing and whether or not they would be useful for treating disease."

To study the purported anti-cancer properties of CAPE, first author Chih-Pin Chuu (now at the National Health Research Institutes in Taiwan) tested the compound on a series of cancer cell lines. Even at the low concentrations expected after oral administration, CAPE successfully slowed the proliferation of cultured cells isolated from human prostate tumors.

CAPE was also effective at slowing the growth of human prostate tumors grafted into mice. Six weeks of treatment with the compound decreased tumor volume growth rate by half, but when CAPE treatment was stopped, tumor growth resumed its prior rate. The results suggested that CAPE stopped cell division rather than killing cancerous cells.

To determine the cellular changes that mediated this effect, the researchers then used an innovative proteomics technique invented by Jones and colleagues called the "micro-western array." Western blots are a common laboratory tool used to measure the changes in protein levels and activity under different conditions. But whereas only one or a few proteins at a time can be monitored with Western blots, micro-western arrays allow researchers to survey hundreds of proteins at once from many samples.