Abstract P6-14-07: Epigenetic Pharmacomodulation of Therapeutic Targets in Breast Cancer with a Naturopathic Formulation of Propolis, a Honeybee Product
Authors: Omene CO , Wu J , Kalac M , O'Connor OA , Frenkel K. 
Published: April 2011

Background: Over 30% of cancer patients routinely use alternative formulations, commonly in combination with allopathic treatment, which may be linked with fewer adverse events. This is especially true for refractory breast cancer (BC), which remains a major clinical challenge for women in whom conventional therapy has lost therapeutic benefit. Propolis (PL), and its active component Caffeic Acid Phenethyl Ester (CAPE), is a widely available honeybee product with an extended safety history credited with anti-inflammatory, antioxidant, and antitumor properties. We have previously shown that CAPE is innocuous to normal human mammary epithelial cells, but inhibits growth of MCF-7 (ER+/PR+) and MDA-231 (TNBC) cells by cell cycle arrest and apoptosis; inhibits mdr-1 gene expression, NF-kB, and VEGF. In addition, CAPE inhibits the growth and tumorigenic potential of BC stem cells derived from MDA-231 cells. These findings are reminiscent of the pleiotropic effects of histone deacetylases inhibitors (HDACi) like vorinostat, aliphatic acids and depsipeptide in models of both epithelial and hematopoietic origin. We hypothesized that CAPE, which is structurally similar to the hydroxamic acid class of HDAC inhibitors, may mediates its effects on BC through epigenetic modifications and thus, may modulate determinants such as ER, PR, Her2 neu, and EGFR.

Materials & Methods: 3x10 5 cells/well of MDA-231, MCF-7, and SKBR3 (Her2+) cells were grown in 10% DMEM in 6 well tissue culture plates using 3ml of media for 12h and then incubated with different concentrations of CAPE (0-40μM) or PL (0-.05%) for 24h. Protein analysis of lysates was done by western blotting using various antibodies. Results: CAPE exposure leads to the acetylation of histone proteins in all the BC cell lines with subsequent decrease of EGFR over-expression and induction of ER in MDA-231 cells; decrease in ER and PR expression in MCF-7 cells; and decrease in p-Her 2 in SKBR3 cells. When normalized for the concentration of CAPE in PL, the HDAC inhibitory effects ofthe natural product, PL, are superior to single agent CAPE, establishing that the epigenetic effects of CAPE can be recapitulated in the natural product. CAPE's aliphatic structure is within the expected structural class of chemicals known to possess this unusual activity. Further, PL yielded similar results for ER, PR, EGFR and p-Her2 expression seen with CAPE.

Discussion: The mechanism of CAPE's effects appears to lie in its ability to inhibit HDACs, making CAPE and PL a naturally occurring epigenetic therapy. PL represents an unusual formulation of a natural product that possesses the properties of an epigenetic agent, which has the broader appeal of being viewed as a ‘natural product’ possessing unique therapeutic properties seen in many of the most promising novel therapeutics being developed by the pharmaceutical industry. Further, the enhanced effects of HDAC inhibition with PL compared to CAPE alone, make it a suitable candidate for a clinical trial, especially in heavily pretreated metastatic BC patients who may likely benefit from therapy with minimal added toxicity.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-14-07.