Role of Rad51 Down-Regulation and Extracellular Signal-Regulated Kinases 1 and 2 Inactivation in Emodin and Mitomycin C-Induced Synergistic Cytotoxicity in Human Non–Small-Cell Lung Cancer Cells

Abstract

Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. It is a tyrosine kinase inhibitor and has anticancer effects on lung cancer. Rad51 plays a central role in homologous recombination, and high levels of Rad51 expression are observed in chemo-or radioresistant carcinomas. Our previous studies have shown that the mitogen-activated protein kinase kinase (MKK) 1/2-extracellular signal-regulated kinase (ERK) 1/2 signal pathway maintains the expression of Rad51. Therefore, in this study, we hypothesized that emodin could enhance the effects of the antitumor antibiotic mitomycin C (MMC)-mediated cytotoxicity by decreasing the expression of Rad51 and the phosphorylation of ERK1/2. Exposure of the human non-small-cell lung cancer H1703 or A549 cell lines to emodin decreased the MMC-elicited phosphorylated ERK1/2 and Rad51 levels. Moreover, emodin significantly decreased the MMC-elicited Rad51 mRNA and protein levels by increasing the instability of Rad51 mRNA and protein. In emodin-and MMC-cotreated cells, ERK1/2 phosphorylation was enhanced by constitutively active MKK1/2 (MKK1/2-CA), thus increasing Rad51 protein levels and protein stability. The synergistic cytotoxic effects induced by emodin combined with MMC were remarkably decreased by MKK1-CA-mediated enhancement of ERK1/2 activation. Depletion of endogenous Rad51 expression by small interfering Rad51 RNA transfection significantly enhanced MMC-induced cell death and cell growth inhibition. In contrast, overexpression of Rad51 protects lung cancer cells from the synergistic cytotoxic effects induced by emodin and MMC. We conclude that suppression of Rad51 expression or a combination of emodin with chemotherapeutic agents may be considered as potential therapeutic modalities for lung cancer.Lung cancer is the leading cause of cancer-related death in the world and can be broadly classified into small cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC) (Bhattacharjee et al., 2001). NSCLC accounts for approximately 85% of all lung cancers (Landis et al., 1999), and unlike SCLC, NSCLC is less sensitive to chemotherapeutic agents; the average 5-year survival rates are 10 to 15% . Mitomycin C (MMC) is an anticancer drug that forms monoadducts and intrastrand cross-links between the N-2 guanines of the d(CpG) sequence in the minor groove of DNA (Warren and Hamilton, 1996;Dronkert and Kanaar, 2001). MMC is typically used as a first-or second-line regimen to treat NSCLC and is often combined with other chemotherapeutic agents during advanced NSCLC treatment (Babiak et al., 2007). The therapeutic value of MMC depends on the ability of cells to remove DNA damage (McHugh et al., 2001).

Targeted abrogation of diverse signal transduction cascades by emodin for the treatment of inflammatory disorders and cancer

“…It has been seen that the expression of both these proteins are high in cancer, causing instability of the genome. Treatment of emodin increases the antitumor antibiotic, mitomycin C (MMC)-induced cytotoxicity via ERK1/2 inactivation and Rad51 down-regulation in lung cancer H1703 or A549 cells [53] and has an additive effect on cisplatin-induced cytotoxicity via downregulating ERCC1 expression in human NSCLC cells through regulation of the ERK1/2 signaling pathway [54]. In human nonsmall cell lung cancer (NSCLC), emodin with (or without) capecitabine induced cytotoxicity by down-regulating the expression of Rad51 and ERCC1 [47,55].…”

Knockdown of Rad51 expression induces radiation- and chemo-sensitivity in osteosarcoma cells

“…Recently, Lin, Y W et al have reported a variety of drugs that inhibit the expression of Rad51, such as DIDS [16], erlotinib [17], emodin [18], and gefitinib [19]. Therefore, these drugs can be investigated in future studies, particularly to test if their combination can enhance the therapeutic effect against osteosarcoma.…”

ALOE EMODIN ENHANCES TAMOXIFEN CYTOTOXICITY EFFECT ON ERa-POSITIVE BREAST CANCER CELLS, MCF-7, THROUGH DOWNREGULATION OF MEK1 AND MEK2

“…Aloe emodin also induced apoptosis in lung non-small carcinoma cells, H460, through inactivation of the ERK signalling pathway (27). Elevated levels of Rad51 expression seen in chemo or radioresistant lung carcinomas are decreased in nonsmall-cell lung cancer cells, H1703 and A549 by the synergistic effect of emodin (Rheum palmatum L root and rhizome extracts) with anti-tumor antibiotic mitomycin C through inactivation of ERK pathway (28). It enhanced the cytotoxicity effect of cisplatin in advanced non-small cell lung cancer cells, (NSCLC) through the downregulation of excision repair cross-complementation 1 (ERCC1), an enzyme crucial for the removal of adducts from genomic DNA, and inactivation of ERK survival pathway (29).…”