Development and characterization of multidrug resistant human hepatocarcinoma cell line in nude mice

Probing the Mechanism of Action of Cry41Aa on HepG2 through the Establishment of a Resistant Subline

Cry41Aa, also called parasporin-3, belongs to a group of toxins from the entomopathogenic bacterium Bacillus thuringiensis that show activity against human cancer cells. Cry41Aa exhibits preferential cytocidal activity towards HL-60 (human promyelocytic leukaemia cells) and HepG2 (human liver cancer cells) cell lines after being proteolytically activated. To better understand the mechanism of action of Cry41Aa, we evolved resistance in HepG2 cells through repeated exposure to increasing doses of the toxin. Concentrations of Cry41Aa that killed over 50% of the parental HepG2 cells had no significant effect on the viability of the resistant cells and did not induce either pore formation or p38 phosphorylation (both characteristic features of pore-forming toxins). Preliminary RNA sequencing data identified AQP9 as a potential mediator of resistance, but extensive investigations failed to show a causal link and did not support an enhanced cell repair process as the resistance mechanism.

Downregulation of δ opioid receptor by RNA interference enhances the sensitivity of BEL/FU drug‑resistant human hepatocellular carcinoma cells to 5‑FU

δ opioid receptor (DOR) was the first opioid receptor of the G protein‑coupled receptor family to be cloned. Our previous studies demonstrated that DOR is involved in regulating the development and progression of human hepatocellular carcinoma (HCC), and is involved in the regulation of the processes of invasion and metastasis of HCC cells. However, whether DOR is involved in the development and progression of drug resistance in HCC has not been reported and requires further elucidation. The aim of the present study was to investigate the expression levels of DOR in the drug‑resistant HCC BEL‑7402/5‑fluorouracil (BEL/FU) cell line, and its effects on drug resistance, in order to preliminarily elucidate the effects of DOR in HCC drug resistance. The results of the present study demonstrated that DOR was expressed at high levels in the BEL/FU cells, and the expression levels were higher, compared with those in normal liver cells. When the expression of DOR was silenced, the proliferation of the drug‑resistant HCC cells were unaffected. However, when the cells were co‑treated with a therapeutic dose of 5‑FU, the proliferation rate of the BEL/FU cells was significantly inhibited, a large number of cells underwent apoptosis, cell cycle progression was arrested and changes in the expression levels of drug‑resistant proteins were observed. Overall, the expression of DOR was upregulated in the drug‑resistant HCC cells, and its functional status was closely associated with drug resistance in HCC. Therefore, DOR may become a recognized target molecule with important roles in the clinical treatment of drug‑resistant HCC.

Silencing the EZH2 gene by RNA interference reverses the drug resistance of human hepatic multidrug-resistant cancer cells to 5-Fu

AIMS

The EZH2 gene, which is expressed in various solid tumours, including liver cancer, can regulate gene transcription and promote the generation and progression of tumours. Our aim was to investigate the relationship between EZH2 and multidrug-resistance of human hepatic cancer cells using RNA interference.

MAIN METHODS

We detected the expression of EZH2 in the human hepatic multidrug-resistant cancer cell line Bel/Fu by RT-PCR and western blot; then knocked EZH2 gene by RNA interference to investigate the proliferation, the cell cycle and cell apoptosis by MTT and flow cytometry; finally we checked the alteration of MDR1 methylation and MDR1 expression after EZH2 silencing by MS-PCR, RT-PCR and western blot.

KEY FINDINGS

EZH2 is highly expressed in Bel/Fu cells. After EZH2-depleted Bel/Fu cells were treated with 5-Fu, the cell proliferation was inhibited, the cell cycle arrested at G1, which may be associated with the alteration of G1/S checkpoint regulators, meanwhile the apoptotic rate of the cells increased. Furthermore, the expression of MDR1 decreased and the corresponding methylation levels of MDR1 were significantly increased in EZH2-depleted Bel/Fu cells.

SIGNIFICANCE

We demonstrate the relationship between EZH2 and multidrug-resistance in hepatic cancer for the first time. EZH2 may become a new target for gene therapy to reverse multidrug-resistance in hepatic cancer.

RNAi-mediated EZH2 depletion decreases MDR1 expression and sensitizes multidrug-resistant hepatocellular carcinoma cells to chemotherapy

The histone-lysine N-methyltransferase, enhancer of zeste homologue 2 (EZH2), functions as a transcriptional repressor and plays an important role in the development of various types of cancer. In this study, we observed the increased EZH2 expression in the Bel/FU multidrug-resistant hepatocellular carcinoma (HCC) cell line. The RNA interference (RNAi)-mediated depletion of EZH2 expression in the Bel/FU cells led to decreased multidrug resistance protein 1 (MDR1) expression, which resulted in increased apoptosis and sustained G1/S phase arrest. Moreover, siRNA targeting EZH2 sensitized Bel/FU cells to 5-fluorouracil treatment. These findings suggest that EZH2 plays a role in the development of multidrug resistance and may represent a novel therapeutic target for multidrug-resistant HCC.

Ultrasound reverses multidrug resistance in human cancer cells by altering gene expression of ABC transporter proteins and Bax protein

Multidrug resistance (MDR) is the major obstacle to successful chemotherapy of human malignancies and strategies for overcoming MDR phenomena are still unavailable to clinical use. Previous results showed that ultrasound (US) exposure could make MDR cancer cells become more sensitive to anticancer drugs, and the physical parameters of US exposure could adjust the uptake and retention of rhodamine 123 in MDR cells. In this study, we investigated the mechanisms of therapeutic ultrasound as a physical approach to overcoming MDR in a multidrug resistant human hepatocarcinoma cell line (HepG2/ADM). Our results demonstrated that the percentage of P-glycoprotein(+) (P-gp), multidrug resistance-associated protein(+) (MRP) and lung resistance-related protein(+) (LRP) cells was 96.97% ± 2.41%, 20.84% ± 3.12% and 1.16% ± 0.59% in HepG2/ADM cells, and 62.84% ± 3.42%, 10.26% ± 1.18% and 3.05% ± 0.37% in US-exposed HepG2/ADM cells, respectively. A significant decrease in the number of P-gp(+) and MRP(+) cells was observed between US-exposed HepG2/ADM and HepG2/ADM cells (p < 0.05). Using RT-PCR technique, we found that US could significantly downregulate the expression of P-glycoprotein (P-gp) and (MRP) at the mRNA level in HepG2/ADM cells. Compared with the control, the percentage of apoptotic cell death was significantly increased in HepG2/ADM after ultrasound exposure. Using immunocytochemistry, the percentage of Bcl-2(+) and Bax(+) cells was 21.7% and 4.1% in the control, and 18.46% and 8.1% in the US-exposed cells, respectively. The percentage of Bax(+) cells was significantly higher in US-exposed HepG2/ADM cells (p < 0.05), suggesting that US exposure could lead to cellular apoptosis in HepG2/ADM cells. It is concluded that US exposure could reverse MDR in HepG2/ADM cells via decreasing P-gp and MRP levels and their mRNA expressions and increasing expression of Bax protein. It may lead to the development of a novel strategy of using a targeted, noninvasive physical approach for the induction of MDR reversal in cancer cells.

Suppression of N-Ras by shRNA-expressing plasmid increases sensitivity of HepG2 cells to vincristine-induced growth inhibition

Oncogenic ras genes relate to the development of human cancers. In this study, we used a plasmid-mediated short-hairpin RNA (shRNA) targeting N-ras gene to combine with clinical drug vincristine (VCR) for the treatment of human hepatoma cells. Our results showed that anti-N-Ras shRNA expression vector (pCSH1-shNR) knocked down the target mRNA and protein. Higher efficacy on growth inhibition was observed when pCSH1-shNR was combined with VCR. This synergistic effect was associated with abrogation of VCR-induced overexpressions of P-glycoprotein and multidrug resistance-associated protein 1 by pCSH1-shNR through downregulations of N-Ras and total Ras. Western blot analysis showed that pCSH1-shNR-induced downregulations of N-Ras and total Ras were potentiated by VCR. Following Ras downregulation, phosphorylations of ERK1/2 and Akt were dramatically inhibited by combinatory treatment. The data showed that pCSH1-shNR-induced inhibition of nuclear factor-kappaB was enhanced by VCR. In addition, the combination of pCSH1-shNR and VCR synergistically inhibited the growth of human hepatoma HepG2 in vivo. Our findings suggested that combination of gene-specific therapeutics and appropriate chemotherapeutic agents might be a promising approach for the treatment of human hepatocellular carcinoma.

Optimization of ultrasound-mediated in vitro reversal of multidrug resistance in human hepatocarcinoma cell line HepG2

Previous studies have shown that ultrasound (US) could enhance cellular uptake and cytotoxicity of chemotherapeutic agents in drug-resistant cancer cells. The goal of this study was to investigate the optimization of physical parameters of US exposure for in vitro reversal of multidrug resistance (MDR) in human hepatocarcinoma cell line (HepG2). Using a constant total energy density (3.87 J/cm(2)) that could maintain cell viability at the 90% level, we exposed parent (HepG2) and MDR variant (HepG2/ADM) tumor cells to US in vitro to a variety of US frequency, exposure intensity and duty cycle. After US exposure, flow cytometry was performed to measure retention of rhodamine 123 (Rh123) in both HepG2 and HepG2/MDR cells. The results showed that US frequency and duty cycle (DC) could influence the intracellular retention of Rh123 in HepG2/ADM tumor cells; intensity and exposure duration appeared to be of little importance. At a constant total energy density of 3.87 J/cm(2), the optimal US parameters for in vitro reversal of MDR in HepG2/ADM tumor cells appear to be 0.8 MHz, 0.43 W/cm(2) and 60% DC, respectively. These findings support our hypothesis that varying the physical parameters would have an effect on efficiency of US-mediated reversal of MDR in cancer cells.

Cytotoxic effects and in vitro reversal of multidrug resistance by therapeutic ultrasound in human hepatocarcinoma cell line (HepG2)

Multidrug resistance (MDR) is one of the major obstacles to successful chemotherapy of human malignancies. Although many strategies have been explored to overcome MDR, none of them have been proven to be clinically useful until now. The aim of this study was to investigate whether a novel therapeutic ultrasound (US) approach would have useful effects on the reversal of MDR in cancer cells. Wild-type and MDR phenotype (HepG2/ADM) cells of the human hepatocarcinoma cell line HepG2 were exposed to 0.8 MHz US at an intensity of 0.43 W/cm(2) for a 9s exposure (total energy density: 3.87 J/cm(2)). After US exposure, cell number and viability were counted immediately, and flow cytometry was performed to measure retention of rhodamine 123 and adriamycin in HepG2 and HepG2/MDR cells. Both cell lines were then incubated in suspension with adriamycin, vincristine, etoposide, cisplatin and 5-fluorouracil, respectively, and the MTT assay was used to determine cytotoxicity. The results showed that US exposure could significantly increase the uptake of Rh123 and ADM by HepG2/ADM tumor cells. The resistant index for the chemotherapeutic drugs was significantly lower in the US-exposed HepG2/ADM cells than in those not exposed to US. It was therefore concluded that US exposure could enhance the sensitivity of HepG2/ADM tumor cells to these chemotherapeutic agents, and the functional and structural changes induced by previous US exposure in MDR tumor cells may be responsible for it. However, further study is needed to investigate the mechanism behind US-mediated reversal of MDR.

Knock-down of Sorcin Induces Up-regulation of MDR1 in HeLa Cells

In our previous study, the MDR1/Pglycoprotein-overexpressing multidrug resistant subline, Hvr100-6, was established from the human cervical carcinoma cell line HeLa-Ohio (HeLa) by stepwise exposure to an anti-microtubule agent, vinblastine sulfate, a typical substrate of MDR1. Their gene and protein expression profiles were analyzed herein, and 148 genes were identified to be differentially expressed by cDNA microarray analysis. The up-regulation of sorcin, a soluble resistance-related calcium-binding protein of 22 kDa, was confirmed in Hvr100-6 cells by the proteome analysis. To clarify the relationship between MDR1 and sorcin, HeLa cells were treated with small interfering RNAs (siRNAs) targeted for theirs mRNAs. The siRNA for MDR1 mRNA resulted in its decrease by 86% and 61% on the days 1 and 2 after the treatment, whereas the expression level of sorcin mRNA was not changed. On the other hand, the siRNA for sorcin mRNA suppressed its expression by 80-90% on days 1-3 after the treatment. Interestingly; suppression of sorcin induced a more than 3-fold increase in the expression level for MDR1 mRNA. An efflux function of MDR1 evaluated with using rhodamine 123 as a probe showed a tendency to be increased in HeLa cells treated with siRNA for sorcin, compared with that in the cells treated with scramble siRNA. The activity and the expression of caspase-3 in the sorcin knock-down HeLa cells were relatively higher than those in the cells treated with scramble siRNA. Thus, we demonstrated that sorcin might be a partial suppressor of MDR1 expression. Furthermore, the present study suggested that sorcin repressed apoptosis via dysfunction of caspase-3.