A Potential Daidzein Derivative Enhances Cytotoxicity of Epirubicin on Human Colon Adenocarcinoma Caco-2 Cells

Yu-Li Lo

doi:10.3390/ijms14010158

Abstract

In this study, we evaluated the effects of 8-hydroxydaidzein (8HD), an isoflavone isolated from fermented soy germ koji, and epirubicin (Epi), an antineoplastic agent, on the production of reactive oxygen species (ROS). We subsequently correlated the ROS levels to the anticancer mechanisms of Epi and 8HD in human colon adenocarcinoma Caco-2 cells. 8HD enhanced cytotoxicity of Epi and generated a synergistic effect. Epi and/or 8HD treatments increased the hydrogen peroxide and superoxide levels. Combined treatment markedly decreased mRNA expression levels of multidrug resistance protein 1 (MDR1), MDR-associated protein (MRP) 1, and MRP2. 8HD significantly intensified Epi intracellular accumulation in Caco-2 cells. 8HD and/or Epi-induced apoptosis, as indicated by the reduced mitochondrial membrane potential and increased sub-G1 phase in cell cycle. Moreover, 8HD and Epi significantly enhanced the mRNA expressions of Bax, p53, caspases-3, -8, and -9. To our best knowledge, this study verifies for the first time that 8HD effectively circumvents MDR in Caco-2 cells through the ROS-dependent inhibition of efflux transporters and p53-mediated activation of both death receptor and mitochondrial pathways of apoptosis. Our findings of 8HD shed light on the future search for potential biotransformed isoflavones to intensify the cytotoxicity of anticancer drugs through simultaneous reversal of pump and nonpump resistance.

Highlights

Combining different chemotherapeutics offer the benefit of having a second compound that enhances the anticancer efficacy of the primary agent, but decreases overall toxicity
We suggest for the first time that 8HD enhances Epi’s cytotoxicity through the reactive oxygen species (ROS)-dependent inhibition of multidrug resistance (MDR) transporters (e.g., P-gp, MRP1, and MRP2) and p53-mediated activation of both death receptor and mitochondrial pathways of apoptosis (e.g., Bax and caspases) in human colon adenocarcinoma Caco-2 cells
Epi potency in cell-growth inhibition was expressed as IC50 value, defined as the drug concentration necessary to inhibit cell growth by 50%

Summary

Introduction

Combining different chemotherapeutics offer the benefit of having a second compound that enhances the anticancer efficacy of the primary agent, but decreases overall toxicity. Validation of natural compounds, such as isoflavones, as adjuvant agents to the current antineoplastic agents has become a potent chemotherapy strategy [1]. Frequent development of multidrug resistance (MDR) hampers the efficacy of available anticancer drugs for colorectal cancer treatment [3]. MDR is the intrinsic and acquired resistance of cancer cells to chemotherapy. Multiple mechanisms contribute to chemoresistance, eventually leading to failure of cancer chemotherapy. The overexpression of P-glycoprotein (P-gp, product of MDR1) and MDR-associated proteins (MRPs), such as MRP1 and MRP2, which actively efflux anticancer drugs is one of the primary mechanisms of MDR [4]. Inhibitors of drug efflux pumps in conventional

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