Apoptotic and immunomodulatory effects of green tea extracts (GTE) on chemoresistant human tumor cells

Abstract

e22101 Background: GTE and Epigallocatechin 3-gallate (EGCG), the most abundant polyphenol in GTE, have been shown to exert inhibitory effects on carcinogenesis; modulatory effects on tumor proliferation and differentiation; and immunomodulatory effects on tumor immunity in different pre-clinical models. These pluripotent effects suggest that GTE may have clinical activity that could be exploited for treatment of chemo-insensitive but immunologically responsive tumors. Thus, the present study investigated the effects of EGCG on the proliferation and immunologic sensitivity of human renal cell cancer (RCC) and malignant melanoma (MM) cell lines. Methods: Human RCC (769-P) and MM (A375) cell lines were tested following incubation in media ± 21.8μM EGCG, a pharmacologically-achievable concentration produced by 8, 200mg capsules GTE daily. Tumor proliferation was assessed by MTS assay; lytic sensitivity to IL2-activated human peripheral blood lymphocytes (IL2PBL) by 51Chromium release assay; and gene expression by quantitative RT-PCR assay. Results: EGCG produced significant inhibition of proliferation of both RCC and MM cells (61.5% and 67.3% of media control values respectively; p<0.01 by 2-tailed, paired t test). EGCG also caused significantly increased expression (≥ 2 times (×) media control values) of pro-apoptotic genes in both RCC: BCL2L1 (5.4×); BCL2L10 (7.9×); BIK (2.9×); Caspase 5 (6.3×); and Caspase 14 (6.3×) and MM cells: Caspase8 (2X) and Card6 (2.5X). Unfortunately, EGCG pre-treatment also decreased the sensitivity of RCC (43% of control) and MM (53% of control) to IL2PBL-mediated lysis (p<0.01 respectively). This occured in association with significant upregulation of Fas ligand mRNA in RCC (6.3×) and TRAF2 mRNA in MM (33 ×). Conclusions: The results of this pre-clinical study demonstrate that EGCG exerts significant antiproliferative effects against human RCC and MM cells in vitro in association with increased expression of different pro-apoptotic genes. Unfortunately, EGCG-treated cells also demonstrated reduced sensitivity to lysis by IL2-activated human lymphocytes. Taken together, the results suggest that GTE may have activity in vivo in patients against chemoresistant RCC or MM but should not be used in conjunction with IL2 therapy. No significant financial relationships to disclose.