Curcumin Enhances the Effect of Chemotherapy against Colorectal Cancer Cells by Inhibition of NF-κB and Src Protein Kinase Signaling Pathways

Mehdi Shakibaei,Cora Lueders,Paviz Shayan,Ali Mobasheri,Ajay Goel,Franziska Busch,Bharat B Aggarwal

doi:10.1371/journal.pone.0057218

Abstract

ObjectiveDevelopment of treatment resistance and adverse toxicity associated with classical chemotherapeutic agents highlights the need for safer and effective therapeutic approaches. Herein, we examined the effectiveness of a combination treatment regimen of 5-fluorouracil (5-FU) and curcumin in colorectal cancer (CRC) cells.MethodsWild type HCT116 cells and HCT116+ch3 cells (complemented with chromosome 3) were treated with curcumin and 5-FU in a time- and dose-dependent manner and evaluated by cell proliferation assays, DAPI staining, transmission electron microscopy, cell cycle analysis and immunoblotting for key signaling proteins.ResultsThe individual IC50 of curcumin and 5-FU were approximately 20 µM and 5 µM in HCT116 cells and 5 µM and 1 µM in HCT116+ch3 cells, respectively (p<0.05). Pretreatment with curcumin significantly reduced survival in both cells; HCT116+ch3 cells were considerably more sensitive to treatment with curcumin and/or 5-FU than wild-type HCT116 cells. The IC50 values for combination treatment were approximately 5 µM and 1 µM in HCT116 and 5 µM and 0.1 µM in HCT116+ch3, respectively (p<0.05). Curcumin induced apoptosis in both cells by inducing mitochondrial degeneration and cytochrome c release. Cell cycle analysis revealed that the anti-proliferative effect of curcumin and/or 5-FU was preceded by accumulation of CRC cells in the S cell cycle phase and induction of apoptosis. Curcumin potentiated 5-FU-induced expression or cleavage of pro-apoptotic proteins (caspase-8, -9, -3, PARP and Bax), and down-regulated anti-apoptotic (Bcl-xL) and proliferative (cyclin D1) proteins. Although 5-FU activated NF-κB/PI-3K/Src pathway in CRC cells, this was down-regulated by curcumin treatment through inhibition of IκBα kinase activation and IκBα phosphorylation.ConclusionsCombining curcumin with conventional chemotherapeutic agents such as 5-FU could provide more effective treatment strategies against chemoresistant colon cancer cells. The mechanisms involved may be mediated via NF-κB/PI-3K/Src pathways and NF-κB regulated gene products.

Highlights

Colorectal cancer (CRC) is one of the leading causes of death in men and women, and ranks among the third most common cancers globally [1]
It has been reported that almost 50% of the patients with CRC, will develop recurrent disease, indicating that currently available treatment regimens are not able to control this deadly disease and there is an imperative need for improved therapies [2]. 5-Fluorouracil (5-FU) is one of the classical drugs used as chemotherapeutic agent against CRC. 5-FU treatment suppresses tumor cell growth and induces apoptosis by incorporation of its metabolites into DNA and RNA through thymidylate synthase
This study was designed to investigate how curcumin inhibits the proliferation of CRC cells and potentiates the effects of the chemotherapeutic agent 5-FU in an in vitro model of human CRC cells

Summary

Introduction

Colorectal cancer (CRC) is one of the leading causes of death in men and women, and ranks among the third most common cancers globally [1]. 5-FU treatment suppresses tumor cell growth and induces apoptosis by incorporation of its metabolites into DNA and RNA through thymidylate synthase. Gains made by the chemotherapeutic efficacy of 5-FU are somewhat limited in patients with colorectal cancer, primarily due to acquired progressive resistance of CRC cells to 5FU and toxicity to surrounding healthy cells [3,4]. Pro-inflammatory cytokines, chemotherapeutic agents and radiation therapy, that induce apoptosis activate NF-kB [7] and may mediate chemoresistance and radioresistance of tumor cells [8]. Inhibition of NF-kB in tumor cells blocks proliferation, causes cell cycle arrest, and leads to apoptosis, suggesting a central role for this transcription factor in cell proliferation and survival [9]. NF-kB plays an important role in cell proliferation and malignant transformation in different cells, binding to DNA target sites as homo- or heterodimer to influence downstream gene expression [10,11]

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Conclusion