Quantitation of chemopreventive synergism between (-)-epigallocatechin- 3-gallate and curcumin in normal, premalignant and malignant human oral epithelial cells

Abstract

An in vitro model for oral cancer was used to examine the growth inhibitory effects of chemopreventive agents when used singly and in combination. The model consists of primary cultures of normal oral epithelial cells, newly established cell lines derived from dysplastic leukoplakia and squamous cell carcinoma. Two naturally occurring substances, (-)-epigallocatechin-3-gallate (EGCG) from green tea and curcumin from the spice turmeric were tested. Cells were treated singly and in combination and effects on growth determined in 5-day growth assays and by cell cycle analysis. Effective dose 50s and the combination index were calculated with the computerized Chou-Talalay method which is based on the median-effect principle. Agents were shown to differ in their inhibitory potency. EGCG was less effective with cell progression; the cancer cells were more resistant than normal or dysplastic cells. In contrast, curcumin was equally effective regardless of the cell type tested. Cell cycle analysis indicated that EGCG blocked cells in G1, whereas curcumin blocked cells in S/G2M. The combination of both agents showed synergistic interactions in growth inhibition and increased sigmoidicity (steepness) of the dose-effect curves, a response that was dose and cell type dependent. Combinations allowed for a dose reduction of 4.4-8.5-fold for EGCG and 2.2-2.8-fold for curcumin at ED50s as indicated by the dose reduction index (DRI). Even greater DRI values were observed above ED50 levels. Our results demonstrate that this model which includes normal, premalignant and malignant oral cells can be used to analyse the relative potential of various chemopreventive agents. Two such naturally-occurring agents, EGCG and curcumin, were noted to inhibit growth by different mechanisms, a factor which may account for their demonstrable interactive synergistic effect.

Green Tea Polyphenol and Curcumin Inversely Regulate Human Involucrin Promoter Activity via Opposing Effects on CCAAT/Enhancer-binding Protein Function

“…A key question is whether these agents have opposing actions with respect to other keratinocyte end points. As noted above, treatment of normal human oral epithelial cells with EGCG or curcumin results in a reduction in cell number (64). Our study indicates that both EGCG and curcumin reduce normal human keratinocyte cell number (not shown).…”

Curcumin inhibits cellular condensation and alters microfilament organization during chondrogenic differentiation of limb bud mesenchymal cells

“…It also suppresses the proliferation of a number of transformed cell types in vitro, including breast (Simon et al, 1998;Ramachandran and You, 1999), colon (Chen et al, 1999) and oral epithelial cells (Khafif et al, 1998). The anti-proliferative effects of curcumin include blocks at specific cell cycle stages, particularly a G2/M block (Hanif et al, 1997;Mehta et al, 1997;Ramachandran and You, 1999;Holy, 2002).…”

Flavonoids uptake and their effect on cell cycle of human colon adenocarcinoma cells (Caco2)

“…Agullo et al (1994) have demonstrated that quercetin has potent cytotoxicity against colon cancer cells in vitro, and that this is associated with antiproliferative activity. Literature data (Khafif et al, 1998) show a synergistic chemopreventive effect between EGCG and curcumin on the cell cycle of premalignant and malignant human oral epithelial cells. Flow cytometric studies have showed that EGCG and curcumin inhibited growth by different mechanisms; EGCG blocked all cells in the G 1 phase, whereas curcumin blocked cells in S/G 2 M phases.…”