Activity of three cytotoxic isoflavonoids from Erythrina excelsa and Erythrina senegalensis (neobavaisoflavone, sigmoidin H and isoneorautenol) toward multi-factorial drug resistant cancer cells.

INTRODUCTION

Resistance of cancer cells to chemotherapy has become a worldwide concern. Naturally occuring isoflavonoids possess a variety of biological activities including anti-cancer effects. The present study was aimed at investigating the cytotoxicity and the modes of action of three naturally occuring isoflavonoids, neobavaisoflavone (1), sigmoidin H (2) and a pterocarpan that is a special type of isoflavonoid, isoneorautenol (3) against a panel of nine cancer cell lines, including various sensitive and drug-resistant phenotypes.

METHODS

The cytotoxicity of the compounds was determined using a resazurin reduction assay, whereas the caspase-Glo assay was used to detect the activation of caspases 3/7, caspase 8 and caspase 9 in cells treated with compounds 3. Flow cytometry was used for cell cycle analysis and detection of apoptotic cells, analysis of mitochondrial membrane potential (MMP) as well as measurement of reactive oxygen species (ROS).

RESULTS

Compounds 3 showed significant cytotoxicity toward sensitive and drug-resistant cancer cell lines. Compounds 1 and 2 were selectively active, and IC50 values below 115 μM were obtained on 6/9 and 4/9 cell lines respectively with values ranging from 42.93 μM (toward CCRF-CEM cells) to 114.64 μM [against HCT116 (p53(+/+)) cells] for 1 and 25.59 μM (toward U87MG) to 110.51 μM [against HCT116 (p53(+/+)) cells] for 2. IC50 values ranging from 2.67 μM (against MDA-MB 237BCRP cells) to 21.84 (toward U87MG) were measured for compound 3 and between 0.20 μM (toward CCRF-CEM cells) and 195.12 μM (toward CEM/ADR5000 cells) for doxorubicin as control drug. BCRP-transfected MDA-MB-231 cells, HCT116 (p53(+/+)) and U87MG.ΔEGFR cells were hypersensitive (collateral sensitive) to compound 3 as compared to their counterpart cell lines. Compound 3 induced apoptosis in CCRF-CEM cells via activation of caspases 3/7, 8 and 9 as well as the loss of MMP and increased ROS production.

CONCLUSIONS

The cytotoxicity of the studied isoflavonoids and especially the pterocarpan 3 deserve more detailed exploration in the future to develop novel anticancer drugs against sensitive and otherwise drug-resistant phenotypes.