Identifying Combinatorial Growth Inhibitory Effects of Various Plant Extracts on Leukemia Cells through Systematic Experimental Design

Abstract

Plant extracts are widely studied for their anti-cancer and cancer preventive effects. In this study, we compared the leukemia growth inhibition effects of seven different plant extracts, theaflavin, epigallocatechin gallate (EGCG), epicathechin (EC), apigenin, quercetin, chrysin and tannic acid, in vitro using the K562 erythroleukemia cell line and application of the design of experiments (DoE) methodology. Our systematic approach enabled us to isolate the main factor contribution, two-factor interactions and produced interaction relationships and/or models to describe growth inhibitory effects of different plant extracts when they are used in combination. The results identified tannic acid as the most significant inhibitor in this group and had synergistic effects with EGCG at specific concentrations. The fitted model of their combined effects showed that the most potent combination is at low concentrations of tannic acid (10 -20 µM) and high concentrations of EGCG (80 -100 µM). We further showed that tannic acid induced both growth inhibition and apoptosis in K562 cells in ranges between 10 -100 µM. The polyphenol caused cell cycle arrest at G2-phase under the higher concentrations. In summary, use of DoE techniques effectively identified the most prominent inducer in this group of plant bioactive compounds and produced combinatorial bioactivity of various polyphenols and flavonoids over the entire range of concentrations under study. This study exemplifies the usefulness of DoE and serves as a guide in its utility for in vitro assessment of bioactivity in plant constituents.