Caffeic acid phenethyl ester (CAPE, a product of propolis) as an inhibitor of human breast cancer growth in a pre-clinical study and its effects on factors involved in cell cycle, angiogenesis, and drug resistance

5710 Our original goal has been to establish whether caffeic acid phenethyl ester (CAPE), a bioactive anti-inflammatory component of the propolis, a product of honeybees, can suppress breast cancer formation using a xenograft nude mouse model. We found that orally administered CAPE inhibits growth of human breast cancer cells in nude mice regardless of whether these cells are estrogen receptor (ER) positive (MCF-7) or negative [MDA-MB-231 (MDA-231)] cells. This finding is additionally important because there are fewer therapies available for ER negative tumors. The suppression of xenograft growth was most effective at very low doses of 50 nmol (14.2 μg) CAPE/mouse/day for MCF-7 and 10 nmol (2.84 μg) for MDA-231 xenografts when mice were provided CAPE-containing diets two days prior to cell inoculation for up to 45-60 days afterwards. Toxicity and Drug Resistance gene microarrays using MCF-7 and MDA-231 cells showed that CAPE causes strong down-regulation of anti-apoptotic and cell proliferation genes, as well as of NF-κB transcription factors. Notably, multi-drug resistance 1 ( mdr-1 ) gene was decreased in MDA-231 cells about 4-fold by CAPE, which strongly suggests that CAPE could be useful as an adjuvant to therapeutic drugs, such as paclitaxel (Taxol), which are expelled from tumor cells by mdr-1 protein products. Our preliminary results show that treatment of MDA-231 cells with low doses of CAPE (0.5-20 μM) followed 15 min later with Taxol (1-5 nM) show a dose-dependent decrease in cell viability, with optimal conditions being 1 nM Taxol and 1-5 μM CAPE. Since growth of tumors in vivo requires neovascularization, we also looked for the effects of CAPE on the formation of VEGF, an angiogenic factor, in cultured cells. CAPE had no effect on low VEGF (vascular endothelial growth factor) produced by MCF-7 cells, but dose-dependently inhibited VEGF formation by MDA-231 cells . We also found that a low CAPE dose inhibits formation of capillary-like tubes by endothelial cells. These results suggest that CAPE should inhibit angiogenesis also in mice growing human breast cancer xenografts. We also found that CAPE dose-dependently inhibits viability of both types of cells by enhancing formation of p21 and p27 cell cycle inhibitory proteins and increasing apoptosis. In conclusion, CAPE seems to be very promising as an anti-breast cancer agent because of its anti-proliferative and pro-apoptotic effects, as well as inhibiting angiogenesis. Notably, CAPE also decreases heat shock protein genes as well as mdr-1 and its protein products responsible for drug resistance, thus holding a promise for increasing effectiveness of chemotherapeutic drugs and decreasing their side effects. [This work was supported in part by grants from Susan G. Komen for Cure Foundation (BCTR0600476) and NIEHS (ES00260)]