Methotrexate Combination Effects with Genistein and Daidzein on MDA-MB-231 Breast Cancer Cell Viability

Aims: To investigate the effect of methotrexate and soy isoflavones genistein and daidzein on MDA-MB-231 breast cancer cell viability.

Study Design: In-vitro study using cultured cells

Place and Duration of Study: Nutrition Innovations Centre for Food & Health (NICHE), School of Biomedical Sciences, Ulster University, data collected September 2014-2015.

Methods: Human breast cancer MDA-MB-231 cells were cultured in DMEM (with 10% FBS, 1% Pen strep) and treated with methotrexate, genistein or daidzein for 72 hrs. Combinations treatments used non-fixed ratios of methotrexate (0-100 μM) and genistein or daidzein (30 μM) with cell viability monitored using the MTT assay.

Results: The 50% effect dose (EC50) was 44.7±6.4 μM for methotrexate, 55.8±3.9 μM for genistein or 67.4±12.2 μM for daidzein. Combination treatments with genistein or daidzein produced EC50 of 57.6±2.0 or 29.7±2.4 μM for methotrexate, respectively. The combination index (CI) was 1.9 for methotrexate-genistein whilst CI was 1.1 for methotrexate-daidzein near the median dose. Values for CI decreased from 5.0 towards 1.0 as the ratio of methotrexate: isoflavone increased. The results are discussed in terms of prevailing ideas concerning how phytochemicals affects drug adsorption, distribution, metabolism and excretion (ADME) and the expected consequences for cytotoxicity.

Conclusions: Treatment of MDA-MB-231 breast cancer cells with methotrexate and genistein or daidzein produces interactions consistent with antagonism (CI =1.1-5.0) but the effects are predicted to diminish with rising methotrexate to isoflavone ratio.