Aim: To determine the effect of tea polyphenols and methotrexate on viability and reactive oxygen species (ROS) in a naturally resistant breast cancer cell line MDA-MB-231. Methodology: MDA-MB-231 cells were selected as a model for methotrexate resistant breast cancer. Drug tests were performed over 72 hours at concentrations 0-100 µM. Pre-treatments were with quercetin (QE) or epigallocatechin gallate (EGCG) for 5 hours followed by methotrexate. Cytotoxicity was measured using the MTT assay or resazurin fluorescence assay. ROS was determined using the 2', 7'-dichlorofluorescein diacetate assay. Intracellular GSH was measured using the monochlorobimane assay. Results: Methotrexate was cytotoxic to MDA-MB-231 cells with IC 50 of 35±4 µM. The IC 50 value was 68±9.4 µM with QE and 83±16 µM for EGCG. The pre-treatment with QE and EGCG lowered the IC 50 for methotrexate by 28% (P =0.009) and 16% (P=0.2027). Intracellular ROS concentrations increased after treatment with methotrexate, QE or EGCG singly and ROS Short Communication
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