Inhibitory Effect of Caffeic Acid Phenethyl Ester (CAPE) on Human Multiple Myeloma Cell Growth: Induction of Apoptosis and Stress/toxicity Pathways

Purpose: At appropriate doses and time after exposure, CAPE inhibits proliferation of multiple myeloma (MM) cells. To better understand mechanism of this effect, MM cell apoptosis and pathway-focused gene expression studies were conducted. Methods: 1) Cell growth inhibition: Cultured MM 8226 cells were treated with 1, 5, 10, and 20 µM CAPE for 6 hrs, 24 hrs, or 48 hrs, respectively. Cell viability was measured using the Presto Blue assay. 2) Apoptosis assay: Cultured MM 8226 cells were treated with 1, 5, 10, 25, and 50 µM CAPE for 24 hrs. A FITC Annexin V Apoptosis Detection Kit (BD Biosciences) was used to detect apoptosis of MM 8226 cells treated with CAPE. 3) Stress/toxicity pathway analysis: Cultured MM 8226 cells were treated with 20 µM CAPE or 0.1% DMSO (vehicle control) for 6 hrs and 24 hrs. Total RNA was prepared from treated cells (Qiagen), and gene expression was analyzed using specific PCR arrays (Stress & Toxicity PathwayFinderTM, RT2ProfilerTM PCR Array, SABiosciences, Qiagen). These arrays contain gene-specific primer sets for 84 relevant genes involved in different pathways (oxidative stress, hypoxia, cell death, inflammatory response, etc.) and 5 housekeeping genes, whose Ct values were used as a normalization factor. Fold changes were calculated using Ct method. A cutoff of 2 fold in terms of fold changes between CAPE treated and control groups was selected. A p value less than 0.05 were used to identify statistically significant up- and down-regulated genes. Results: CAPE inhibits growth of MM 8226 cells in both dose and time-dependent manner. Apoptosis of MM 8226 cells was detected after 24 h CAPE treatment and found to be dose dependent. A number of genes of MM 8226 cells were identified with expressions significantly altered by 20 µM CAPE at 6 and 24 hrs, respectively. Regulation of some genes changed over time. Those genes were found mostly involved in stress/toxicity pathways related to oxidative stress, hypoxia, inflammatory response, and DNA damage signaling. Conclusions: CAPE inhibits growth of multiple myeloma cells, and this may be due to an induction of MM cell apoptosis. Expression of genes involved in different stress/toxicity pathways, in particular oxidative stress, hypoxia, inflammatory response, and DNA damage signaling, were significantly altered. This may provide an insight into the mechanism of CAPE inhibitory effects on multiple myeloma cell proliferation