by Rob Mitchum
A common feature of pharmacies and organic grocery stores is the aisle of natural remedies, featuring bottle upon bottle of herbs, extracts, and oils that promise a wide range of medical benefits. For legal reasons, the health claims made by these products are often fuzzy, boasting of vague antioxidant or anti-inflammatory activity. But online, the compounds are touted as a cure-all for everything from the common cold to depression to cancer, despite often scarce scientific evidence to support such claims. In many cases, scientists aren’t even sure what these compounds do on a biological level, limiting their usefulness in the clinic even if an anti-disease effect could be conclusively demonstrated.
The major obstacle to determining how a natural remedy works (or doesn’t) is the difficulty in assessing the totality of its effects upon a cell, rather than just the effect on one particular factor at a time. But a technique recently invented by University of Chicago researchers to monitor the activity of hundreds of proteins at once allowed scientists to assess the anti-cancer potential of one natural remedy aisle staple: beehive propolis.
“A typical problem in bringing some of these herbal remedies into the clinic is that nobody knows how they act, nobody knows the mechanism, and therefore researchers are typically very hesitant to add them to any pharmaceutical treatment strategy,” said Richard Jones, assistant professor in the Ben May Department for Cancer Research and Institute for Genomics and Systems Biology. “Now we’ll actually be able to systematically demonstrate the parts of cell physiology that are affected by these compounds.”
Beehive propolis is a sticky resin that honeybees use to patch up holes and fill cracks in their hives. Natural remedy suppliers sell this “bee glue” in the form of capsules or liquid extract, touting its abilities to boost immunity, fight off infections, and soften skin. According to anecdotal reports, the substance has been used for centuries to treat sore throats, allergies, and burns, or for less medicinal purposes such as car wax and instrument polish.
Chih-Pin Chuu, at the time a post-doctoral researcher in Jones’ laboratory, wanted to examine whether the active compound in beehive propolis — called caffeic acid phenethyl ester, or CAPE — was effective against cancer cells. Testing concentrations of CAPE that you would expect to find in the blood after a person swallowed a propolis capsule, Chuu found the compound successfully inhibited the growth of early-stage prostate cancer cell in culture dish experiments. Subsequent experiments on mice implanted with human prostate cancer cells confirmed CAPE’s anti-cancer effect, and hinted at a mechanism.
“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,” Jones said of the results, published in the journal Cancer Prevention Research. “So it doesn’t kill the cancer, but it basically will indefinitely stop prostate cancer proliferation.”
That activity suggests CAPE could be a promising co-treatment alongside a chemotherapy drug that targets the cells. But if CAPE were to truly make the crossover from holistic remedy to clinical option, the scientists would also have to demonstrate how the compound freezes cancer cells in a non-proliferative state. Enter the micro-western array, the innovative proteomics technique first described in 2010 by Jones and colleagues.
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. Chuu, Jones and their colleagues ran micro-western arrays to assess the impact of CAPE treatment on the proteins of cellular pathways involved in cell growth — experiments that would have been prohibitively expensive without the new technique.
“What this allowed us to do is screen about a hundred different proteins across a broad spectrum of signaling pathways that are associated with all sorts of different outcomes. You can pick up all the pathways that are affected and get a global landscape view, and that’s never been possible before,” Jones said. “It would have taken hundreds of Westerns, hundreds of technicians, and a very large amount of money for antibodies.”
With the micro-western array, researchers could quickly build a new model of CAPE’s cellular effects. Treatment with CAPE suppressed the activity of proteins in the p70S6 kinase and Akt pathways, both important sensors of sufficient nutrition that give the green light to cell proliferation when activated. To confirm that this suppression was the key mechanism for CAPE to stop cell proliferation, the team confirmed that over-expressing components of those pathways protected the cancer cells against the compound’s effects.
“It appears that CAPE basically stops the ability of prostate cancer cells to sense that there’s nutrition available,” Jones said. “They stop all of the molecular signatures that would suggest that nutrition exists, and the cells no longer have that proliferative response to nutrition.”
Despite the promising results in laboratory and mouse models, much more testing would need to be done before CAPE could legitimately be considered a clinical weapon against prostate cancer. One concern is that there is nobody with deep pockets to pay for the clinical trials needed to prove its effectiveness and safety in humans, since CAPE/propolis is a widely available, over-the-counter compound that can’t be patented by a drug company seeking profit. But Jones hopes that settling the issue of what CAPE (or other natural remedies the lab is currently testing) does to cellular pathways could make clinicians more comfortable in trying them alongside traditional drugs.
“It’s a rare event that a drug that’s not put forth by a pharmaceutical company goes through a clinical trial, so we’ll see how that works,” Jones said. “But if we were able to work out the mechanisms, you could say, A-ha, this compound would actually be beneficial in combination with other commonly-used therapies.”
Chuu, C., Lin, H., Ciaccio, M., Kokontis, J., Hause, R., Hiipakka, R., Liao, S., & Jones, R. (2012). Caffeic Acid Phenethyl Ester Suppresses the Proliferation of Human Prostate Cancer Cells through Inhibition of p70S6K and Akt Signaling Networks Cancer Prevention Research, 5 (5), 788-797 DOI: 10.1158/1940-6207.CAPR-12-0004-T