Epigallocatechin-3-Gallate (EGCG), a Polyphenol Extracted from Green Tea, Has Significant In Vitro Activity Against Myeloma Cells.

Abstract

Background: Epigallocatechin-3-gallate (EGCG) is a polyphenol extracted from green tea that has been studied for cancer prevention and treatment. Green tea and its extracts have been an integral part of traditional medicines from Asia and are thought to have considerable medicinal value. EGCG has been studied in many tumor types and in vitro studies have been encouraging. It is currently in Phase I/II clinical trial in the treatment of chronic lymphocytic leukemia. Here we examined the activity of EGCG in the setting of myeloma and its potential mechanisms of action.Methods: MM cell lines were cultured in RPMI 1640 containing 10% fetal bovine serum supplemented with L-Glutamine, penicillin, and streptomycin. The KAS-6/1 cell line was also supplemented with 1 ng/ml IL-6. Cytotoxicity of EGCG was measured using the MTT viability assay. Apoptosis was measured using flow cytometry upon cell staining with Annexin V-FITC and propidium iodide (PI). Fresh myeloma cells were obtained from bone marrow aspirates and subjected to ACK lysis to remove red cells. These cells were cultured in RPMI1640 with or with out EGCG and apoptotic rates were determined by Apo 2.7 expression on gated plasma cells. Flow cytometry was used for determining the phosphorylation state of various signaling proteins. Anti-angiogenic activity of EGCG was measured using a human in vitro angiogenesis kit (Angiokit).Results: EGCG treatment of myeloma cell lines resulted in dose- and time-dependent cytotoxicity to the cells. EGCG was cytotoxic to several myeloma cell lines, including IL-6 dependent cell lines KAS-6/1 and ANBL-6 as well as drug resistant cell lines MM1.R, Dox40 and LR5. The effect was maintained when the cells were grown in co-culture with marrow stromal cells, indicating the ability to overcome microenvironment mediated resistance. EGCG induced apoptosis of myeloma cell lines, apoptotic cells being measured as Annexin (+)/PI (−) cells by flow cytometry. It induced a dose-dependent apoptosis of freshly isolated myeloma cells with increased effect seen on the CD45+ myeloma cells compared to CD45- cells, reflecting increased activity on the proliferative fraction. Down regulation of Akt phosphorylation was seen following treatment of myeloma cells with EGCG. Using the Angiokit, we were able to demonstrate inhibition of tubule formation by EGCG at concentrations lower than those cytotoxic to myeloma cells. It was also able to overcome the angiogenic activity of VEGF.Conclusion: We demonstrate potent anti-myeloma activity of EGCG in vitro. In vivo studies in animal models of myeloma are ongoing. We demonstrate, as in other cell lines, inhibition of Akt pathways as a potential mechanism of action of EGCG. Ongoing studies are exploring other mechanisms. Most importantly, we demonstrate anti-angiogenic activity of this compound in the setting of myeloma, a finding in concordance with the inhibition of VEGF activity seen with other tumor systems.