Suppression of P-gp induced multiple drug resistance in a drug resistant gastric cancer cell line by overexpression of Fas

Synthesis and evaluation of WK-X-34 derivatives as P-glycoprotein (P-gp/ABCB1) inhibitors for reversing multidrug resistance

The emergence of multidrug resistance (MDR) in malignant tumors is one of the leading threats encountered currently by many chemotherapeutic agents. A proposed strategy to overcome MDR is to disable the efflux function of P-glycoprotein (P-gp/ABCB1), a critical member of the ABC transporter family that significantly increases the efflux of various anticancer drugs from tumor cells. In this study, structural modification of a third-generation P-gp inhibitor WK-X-34 based on bioisosteric and fragment-growing strategies led to the discovery of the adamantane derivative PID-9, which exhibited the best MDR reversal activity (IC50 = 0.1338 μM, RF = 78.6) in this series, exceeding those of the reported P-gp inhibitors verapamil and WK-X-34. In addition, compared with WK-X-34, PID-9 showed decreased toxicity to cells. Furthermore, the mechanism studies revealed that the reversal activity of adamantane derivatives PID-5, PID-7, and PID-9 stemmed from the inhibition of P-gp efflux. These results indicated that compound PID-9 is the most effective P-gp inhibitor among them with low toxicity and high MDR reversal activity, which provided a fundamental structural reference for further discovery of novel, effective, and non-toxic P-gp inhibitors.

lncRNA ROR Promotes Gastric Cancer Drug Resistance

OBJECTIVE

Gastric cancer is one of the most common malignant tumors worldwide, and for resectable tumors, the most effective treatment is surgery with chemotherapy in neoadjuvant or adjuvant setting. However, the majority of patients fail to achieve the ideal initial response and/or develop resistance to chemotherapy. It was reported that long noncoding RNA regulator of reprogramming (ROR) is highly associated with the progression of gastric cancer. However, the role ROR in multidrug resistance (MDR) remains unclear.

METHODS

The messenger RNA levels of 63 specimens of patients with gastric cancer were determined by real-time polymerase chain reaction analysis and were correlated with drug resistance and survival of patients. To determine the cellular functions of ROR, we generated gastric cancer MDR cells. The effect of ROR depletion on multidrug resistance-associated protein 1 (MRP1) expression and cell apoptosis were examined by immunoblotting analyses, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and flow cytometry.

RESULTS

We found that ROR expression levels are positively associated with increased MDR and poor prognosis of patients with gastric cancer. Regulator of reprogramming expression is increased in gastric cancer cells resistant to adriamycin (ADR) and vincristine (VCR). Depletion of ROR reduced MRP1 expression and increased apoptosis of drug-resistant gastric cancer cells in response to ADR and VCR treatment.

CONCLUSIONS

We demonstrated that ROR expression promotes MRP1 expression and MDR of gastric cancer cells and is correlated with increased MDR and poor prognosis of patients with gastric cancer. Our finding highlighted the potential of targeting ROR to improve the efficacy of chemotherapy.

Role of ATP-binding cassette transporters, apoptosis, and long non-coding RNAs in gastric cancer multidrug resistance

Cancer multidrug resistance refers to the cross resistance of cancer cells to a variety of anticancer drugs, which can be primary or secondary. Several mechanisms attribute to cancer multidrug resistance. In this paper, the recent progress in the understanding of the mechanisms of multi-drug resistance of gastric cancer cells with regard to the role of adenosine triphosphate binding cassette transporters, apoptosis, and long non-coding RNAs is reviewed.

Methylation of miR-129-5p CpG island modulates multi-drug resistance in gastric cancer by targeting ABC transporters

Recent studies have reported that hyper-methylation in the promoter region of miRNAs could silence the expression of tumor suppressive miRNAs and might play significant roles in the process of tumor development. However, the potential mechanisms regarding how methylation of miRNA CpG Island could regulate cancer cell chemo-resistance have not yet been studied. Using microarray and BSP (Bisulfate Sequencing PCR) assays, we found that compared with the parent SGC7901/VCR cells, expression of miR-129-5p was restored in SGC7901/VCR gastric cancer multi-drug resistant cell line treated by de-methylation reagent (5-AZA-dC). Using gain or loss of function assays, we found the over-expressed miR-129-5p reduced the chemo-resistance of SGC7901/VCR and SGC7901/ADR cells, while down-regulation of miR-129-5p had an opposite effect. Furthermore, three members of multi-drug resistance (MDR) related ABC transporters (ABCB1, ABCC5 and ABCG1) were found to be direct targets of miR-129-5p using bioinformatics analysis and report gene assays. The present study indicated that hyper-methylation of miR-129-5p CpG island might play important roles in the development of gastric cancer chemo-resistance by targeting MDR related ABC transporters and might be used as a potential therapeutic target in preventing the chemo-resistance of gastric cancer.

Multi-drug resistance in cancer chemotherapeutics: mechanisms and lab approaches

Multi-drug resistance (MDR) has become the largest obstacle to the success of cancer chemotherapies. The mechanisms of MDR and the approaches to test MDR have been discovered, yet not fully understood. This review covers the in vivo and in vitro approaches for the detection of MDR in the laboratory and the mechanisms of MDR in cancers. This study also envisages the future developments toward the clinical and therapeutic applications of MDR in cancer treatment. Future therapeutics for cancer treatment will likely combine the existing therapies with drugs originated from MDR mechanisms such as anti-cancer stem cell drugs, anti-miRNA drugs or anti-epigenetic drugs. The challenges for the clinical detection of MDR will be to find new biomarkers and to determine new evaluation systems before the drug resistance emerges.

Suppressive effects of an ethanol extract of Gleditsia sinensis thorns on human SNU-5 gastric cancer cells

The thorns of Gleditsia sinensis are a traditional Oriental medicine used for the treatment of swelling, suppuration, carbuncle and skin diseases. In the present study, we identified a novel molecular mechanism by which an ethanol extract of Gleditsia sinensis thorns (EEGS) inhibits the growth of the SNU-5 human gastric cancer cell line. EEGS treatment inhibited cell growth and was associated with G1 phase cell cycle arrest at a concentration of 400 µg/ml (IC50) in SNU-5 cells. Treatment with EEGS also stimulated p21WAF1 expression, which significantly decreased the expression of cyclins and cyclin-dependent kinases (CDKs). Further study suggested that p38 MAP kinase pathways may be involved in the inhibition of cell proliferation through p21WAF1‑dependent G1 phase cell cycle arrest in EEGS-treated cells. In addition, NF-κB and AP-1 transcription factor binding sites were identified as the cis-elements for tumor necrosis factor-α (TNF-α)-induced matrix metalloproteinase-9 (MMP-9) expression in SNU-5 cells, as determined by gel-shift assay. Treatment of cells with EEGS suppressed MMP-9 expression induced by TNF-α via a decrease in the binding activity of both NF-κB and AP-1 motifs. These data demonstrate that EEGS-mediated inhibition of cell growth appears to involve the activation of p38 MAP kinase, subsequently leading to the induction of p21WAF1 and the downregulation of cyclin D1/CDK4 and cyclin E/CDK2 complexes. Moreover, EEGS strongly inhibited TNF-α-induced MMP-9 expression by impeding the DNA binding activity of NF-κB and AP-1. Overall, these results provide a potential mechanism for EEGS in the treatment of gastric cancer.

In vitro pharmacogenomic database and chemosensitivity predictive genes in gastric cancer

Gastric cancer is one of the most common cancers worldwide, and there are clinical caveats in predicting tumor response to chemotherapy. This study describes the construction of an in vitro pharmacogenomic database, and the selection of genes associated with chemosensitivity in gastric cancer cell lines. Gene expression and chemosensitivity databases were integrated using the Pearson correlation coefficient to give the GC-matrix. The 85 genes were selected that were commonly associated with chemosensitivity of the major anticancer drugs. We then focused on the genes that were highly correlated with each specific drug. Classification of cell lines based on the set of genes associated with each drug was consistent with the division into resistant or sensitive groups according to the chemosensitivity results. The GC-matrix of the gastric cancer cell line database was used to identify different sets of chemosensitivity-related genes for specific drugs or multiple drugs.

A new apoptosis inhibitor, CIAPIN1 (cytokine-induced apoptosis inhibitor 1), mediates multidrug resistance in leukemia cells by regulating MDR-1, Bcl-2, and Bax

We investigated the role of cytokine-induced apoptosis inhibitor 1 (CIAPIN1), a newly identified apoptosis inhibitor, in leukemia cell multidrug resistance (MDR) and its possible underlying mechanisms. CIAPIN1 was found to be overexpressed at the mRNA and protein levels in the vincristine-induced multidrug-resistant leukemia cell line HL-60/VCR, compared with HL-60, its parental cell line. In this study, we transfected HL-60 with a eukaryotic expression vector of CIAPIN1. In vitro drug sensitivity assays suggested that HL-60-CIAPIN1 cells conferred resistance to both P-glycoprotein (P-gp)-related and -unrelated drugs. Blocking CIAPIN1 expression in HL-60/VCR cells by CIAPIN1-specific small interfering RNA increased the cells' sensitivity to various chemotherapeutic drugs. Flow cytometry results suggested that CIAPIN1 expression could suppress adriamycin-induced apoptosis, accompanied by a decreased accumulation and increased release of adriamycin. Semiquantitative RT-PCR, Western blot analysis, and luciferase reporter assays suggested that CIAPIN1 could significantly upregulate the expression of MDR-1 and Bcl-2, the transcription of the MDR-1 gene, as well as downregulate the expression of Bax. Additionally, the inhibition of CIAPIN1 expression by RNA interference or P-gp inhibitor could partially reverse CIAPIN1-mediated MDR. Taken together, our findings suggest that downregulating CIAPIN1 could sensitize leukemia cells to chemotherapeutic drugs by downregulating MDR-1 and Bcl-2 and by upregulating Bax, yet not altering either glutathione-S-transferase activity or intracellular glutathione content in leukemia cells. Further study of CIAPIN1's function may reveal more of the mechanisms of leukemia MDR and result in the development of strategies to treat leukemia.

Mad2β, an alternative variant of Mad2 reducing mitotic arrest and apoptosis induced by adriamycin in gastric cancer cells

Mad2beta is an alternative splicing variant of spindle checkpoint gene mad2, which was previously found by us and was related to the drug resistance in gastric cancer cells. In this paper, we explored the molecular mechanisms that Mad2beta variant promoted the formation of multidrug resistance in gastric cancer cells. We found that Mad2beta variant was detected only in the two human drug resistant gastric cancer cell sublines SGC7901/VCR and SGC7901/ADR, and it did not appear in its parental cell line SGC7901 and other detected gastric cancer cell lines. Expressions of Mad2 mRNA and protein in SGC7901 cells transfected with Mad2beta, SGC7901/VCR and SGC7901/ADR were significantly lower than that in SGC7901 cells. Moreover, SGC7901 cells overexpressing Mad2beta variant became more resistant to adriamycin, vincristine and mitomycin by abrogating mitotic arrest and apoptosis. This suggests that expression of Mad2beta variant decreases the relative expression of efficient MAD2, which may help gastric cancer cells to develop the phenotype of multidrug resistance.

Bird's-eye view on gastric cancer research of the past 25 years

This paper provides a bird's-eye view of our 25-year research work on gastric cancer, including both exploration of pathogenesis and preclinical or clinical applications of diagnosis and treatment. Although there have been achievements and reasons for applause, there are, nonetheless, more failings and teachings. Some problems that we experienced 25 years ago are still problems we have to face today. We are absolutely not singing the same old tune. Looking back makes us wiser and our way smoother. Although it is a long and arduous way to further study gastric cancer, we are willing to devote ourselves to it.

Involvement of NF-kappa B activation in P-glycoprotein expression in vincristine-resistant human gastric cancer cells

AIM: To investigate the effect of vincristine on activation of nuclear factor-kappa B (NF-κB) and expression of p-glycoprotein (P-gp) in vincristine-resistant human gastric cancer SGC7901 cells (SGC7901/VCR) and the parent sensitive clone (SGC7901).

METHODS: NF-κB-DNA binding activity was determined by electrophoretic mobility shift assay (EMSA). Levels of inhibitory B (IB-) and P-gp were measured by cellular-ELISA. And immunocytochemistry was used to detect the translocation of P65.

RESULTS: IN comparison with the parent SGC7901 cells, the basal and vincristine-induced NF-κB-DNA binding activity at various concentrations were all higher in the SGC7901/VCR cells. Concurrent with the NF-κB activation, vincristine-induced IB- degradation and P-gp upregulation were also found to be highly enhanced in the SGC7901/VCR cells than that in the sensitive SGC7901 cells. In the SGC7901/VCR cells, the activation of NF-κB induced by vincristine showed a positive relation with the level of P-gp expression (r = 0.977, P < 0.01). And nuclear translocation of P65 occurred concomitantly with NF-κB activation. Furthermore, the inhibition of NF-κB by MG-132, a proteasome inhibitor, could reduce NF-κB activation, IB- degradation and P-gp upregulation.

CONCLUSION: The enhancement of NF-κB activation correlates with vincristine resistance and NF-κB may play an important role in the regulation of the P-gp expression.

Screening and identification of mimotope of gastric cancer associated antigen MGb1-Ag

AIM: Using a monoclonal antibody against gastric cancer antigen named MGb1 to screen a phage-displayed random peptide library fused with coat protein pIII in order to get some information on mimotopes.

METHODS: Through affinity enrichment and ELISA screening, positive clones of phages were amplified. 10 phage clones were selected after three rounds of biopanning and the ability of specific binding of the positive phage clones to MGb1-Ab were detected by ELISA assay (DNA sequencing was performed and the amino acid sequences were deduced) By blocking test, specificity of the mimic phage epitopes was identified.

RESULTS: There were approximately 200 times of enrichment about the titer of bound phages after three rounds of biopanning procedures. DNA of 10 phage clones after the third biopanning was assayed and the result showed that the positive clones had a specific binding activity to MGb1-Ab and a weak ability of binding to control mAb or to mouse IgG. DNA sequencing of 10 phage clones was performed and the amino acid sequences were deduced. According to the homology of the amino acid sequences of the displayed peptides, most of the phage clones had motifs of H(x)Q or L(x)S. And these 10 phage clones could also partly inhibit the binding of MGb1-Ab to gastric cancer cell KATO-III. The percentage of blocking was from (21.0 ± 1.6)% to (39.0 ± 2.7)%.

CONCLUSION: Motifs of H(x)Q and L(x)S selected and identified show a high homology in the mimic epitopes of gastric cancer associated antigen. There may be one or more clones which can act as candidates of tumor vaccines.

Effect of ZNRD1 gene antisense RNA on drug resistant gastric cancer cells

AIM: To investigate the expression level of ZNRD1 gene in gastric cancer cells SGC7901 and gastric cancer MDR (multidrug resistant) cells SGC7901/VCR, and to observe the drug sensitizing and proliferation effect of ZNRD1 antisense nucleic acid transduction on SGC7901/VCR cells.

METHODS: Amplification of sequences encoding ZNRD1 from SGC7901/VCR cDNA by PCR. The levels of ZNRD1 mRNA expression were demonstrated using semiquantitative reverse transcription polymerase chain reaction (RT-PCR). Eukaryotic expression vector pcDNA3.1-anti ZNRD1 was constructed and transfected into SGC7901/VCR cells by lipofectamine. Immunochemical method was used to detect the expression of protein in SGC7901/VCR cells and transfectants. The cell cycle alteration and the intracellular adriamycin (ADM) accumulation were observed by FACS. Growth curve and drug sensitization of cells for vincristine (VCR) were analyzed with MTT assay.

RESULTS: We cloned the open reading frame of full-length ZNRD1. The expression of ZNRD1 showed higher in SGC7901/VCR than in SGC7901 cells. The antisense ZNRD1 drug-resistant clones were selected after gene transfection. Immunochemical results showed that the expression level of ZNRD1 protein was lower in anti ZNRD1-SGC7901/VCR cells than that in non-transfectants. Comparing to SGC7901/VCR and pcDNA3.1-SGC7901/VCR, anti ZNRD1-SGC7901/VCR showed gradually accumulated in G₁ phase, with a concomitant decrease of cell population in S phase. FACS also suggested intracellular ADM accumulation increased 2fold in SGC7901/VCR cells after transfected with antisense ZNRD1. MTT assay showed that transfectants cells proliferation was lagged and more sensitive to VCR than non-transfectants.

CONCLUSION: ZNRD1 gene displayed highly expression in VCR resistant gastric cancer cells. Expression of ZNRD1 protein was effectively blocked in anti ZNRD1-SGC7901/VCR cells by gene transfection. ZNRD1 antisense nucleic acid transfection sensitized drug resistant gastric cancer cells to VCR, increased ADM accumulation and inhibited the cells proliferation. ZNRD1 antisense RNA transduction could reverse the MDR of human drug-resistant gastric cancer cell SGC7901/VCR to a degree.

Expressions of HSP and p53 protein in gastric mucosa of atrophic gastritis induced by high-salt hot water in rats

AIM: To study the relationship between hot high-salt diet and chronic atrophic gastritis (CAG) and gastric cancer, and detect the expression of HSP60, HSP 70 and HSP 90 a and p53 protein in the rat gastric mucosa of atrophic gastritis induced by high-salt hot water.

METHODS: Rat CAG models were firstly established by intragastrical feeding with 15% 55 ℃ salt water for 12 wk. Some rats were killed to detect HSP60, HSP 70, HSP 90 a and p53 protein every 4 wk by immunohistochemical method in the control group(intragastrically fed with 25 ℃ distilled water for 12 wk) and the experimental group.

RERULTS: The expression of HSP60, HSP70 and HSP90 a was low in gastric mucosal tissue cells of rats at 4 wk and 8 wk. There was no significant difference between the experimental and the control group (P > 0.05). The expression rates were significantly higher in the rats of experimental group at 12 weeks when CAG had formed than those in the control group (P < 0.01). The expression rates of HSP 70 were the highest (33%) among these proteins, the expression rates of HSP90 a were moderate (24%), and the expression rates of HSP60 were the lowest (6%). The p53 protein was not detected in normal group rats as well as in rats of the model group at 4 wk and 8 wk, but it was detected at 12 wk in the CAG rats of the model group with an expression rate of 15.5%, which was significantly associated with the expression of HSP70 and HSP90 a, especially, the former which had no association with the expression of HSP60.

CONCLUSION: Long time high-salt hot diet can induce CAG, and may even promote the development of gastric cancer. HSP70/HSP90 a and p53 proteins might have combined effect in the development from CAG to gastric cancer.

GZ. Screening of differentially expressed genes associated with atrophic gastritis by high density cDNA microarrays

AIM: To establish the rat model and to screen differentially expressed genes closely associated with atrophic gastritis.

METHODS: The rat atrophic gastritis model was induced by intragastrically giving hot high salt water, hot water and high salt water. Normal raising group and normal control group were used as control. Total RNAs of specimens were extracted, quantified, and reversely transcripted into cDNA. cDNAs from atrophic gastritis were labeled with Cy5, and cDNAs from the normal control group were labeled with Cy3, which were mixed with cDNAs from the control group with equal quantity, then hybridized with cDNA chips containing 8 248 genes. Chips were washed, scanned and analyzed.

RESULTS: There were atrophic lesions in rat gastric sinus confirmed by pathological examination in the hot high salt water group at the 12th week, but in the high salt water group and the hot water group, there were atrophic lesions at the 24th week. A total of 436 differentially expressed genes were identified by cDNA chip between the hot high salt water group and the normal control group, 145 genes were highly expressed in the hot high salt water group and 291 genes were highly expressed in the normal control group; 398 differentially expressed genes were identified in the hot water group and the normal control group, 98 genes were highly expressed in the hot water group, and 300 genes were highly expressed in the normal control group; and 36 differentially expressed genes were confirmed between the hot high salt water group and the high salt water group, 23 genes were highly expressed in the hot high salt water group and 13 genes were highly expressed in the high salt water group.

CONCLUSION: Rat atrophic gastritis models were established successfully, differentially expressed genes associated with atrophic gastritis induced respectively by hot high salt water, high salt water and hot water were identified by way of high density cDNA chip.

Intravenous chemotherapy for resected gastric cancer: meta-analysis of randomized controlled trials

AIM: To assess the safety and efficacy of different intravenous chemotherapeutic regimens in patients with gastric carcinomas who had undergone gastrectomy.

METHODS: A meta-analysis of all the relevant randomized controlled trials (RCTs) was performed. Language was restricted to Chinese and English. RCTs were identified from Medline and Embase (1980-2001/4), and Chinese Bio-medicine Database (1990-2001/1). Literature references were checked at the same time. We included randomized and quasi-randomized trials comparing the efficacy of intravenous chemotherapy after gastrectomy with that of surgery alone in patients with confirmed gastric carcinomas who had undergone gastrectomy. Selection criteria were: randomized or quasi-randomized trials with following-up results; Trials could be double-blind, single-blind or not blind; Chemotherapy groups were given intravenous chemotherapy after gastrectomy without neo-adjuvant chemotherapy, intraperitoneal hyperthermic perfusion, radiotherapy or chemoimmunotherapy; Controlled group included those receiving gastrectomy alone. The following data were extracted: the number of survival and death by the end of the follow-up; the different agents and doses of the intravenous chemotherapy; the baseline of the chemotherapy group and the controlled arm; the serious adverse events; the statistical consideration; cost-effectiveness analysis. The statistical analysis was performed by RevMan4.1 software which was provided by the Cochrane Collaboration. A P value of < 0.05 was considered statistically significant. Meta-analysis was done with random effects model. Heterogeneity was checked by chi-square test. Sensitivity analysis was performed by excluding the trials in which Jadad-scale was only 1 score. The result was expressed with odds ratio (OR) for the categorical variable.

RESULTS: Fourteen trials involving 4543 patients were included. Meta-analysis was done with random effects model Heterogeneity and sensitivity analysis were performed also. The effect of intravenous chemotherapy after gastrectomy was better than surgery alone (odds ratio 0.56, 95%CI 0.40-0.79). There was a significant difference between the two groups by u-test (P = 0.0008). Sensitivity analysis revealed the same difference (odds ratio 0.81, 95%CI 0.70-0.94). Of fourteen trials, only three studies were of high quality according to the Jadad-scale (with three score). There was one meta-analysis trial and the others, about ten trials, were of low quality. There was no trial which mentioned sample-size calculation, allocation concealment, intention-to-treat analysis. Most of the trials didn’t describe the blind-procedure. There were five trials which detailed the side-effects according to the toxicity grade by WHO standard. The side-effects halting treatment were haematologic and biochemical toxicity, debilitating nausea and vomiting. There were two patients died of chemotherapy toxicity.

CONCLUSION: Based on the review, intravenous chemotherapy after gastrectomy may have positive treatment effect on gastric cancer. However, the evidence is not strong because of the general low methodologic quality of the RCTs. Therefore, we can’t make the conclusion that intravenous chemotherapy after gastrectomy may have better treatment effect on gastric cancer than that of surgery alone. Rigorously designed, randomised, double-blind, placebo-controlled trials are required.

Subcellular daunorubicin distribution and its relation to multidrug resistance phenotype in drug-resistant cell line SMMC-7721/R

AIM: To investigate the correlation between subcellular daunorubicin distribution and the multidrug resistance phenotype in drug-resistant cell line SMMC-7721/R.

METHODS: The multidrug resistant cell line SMMC-7721/R, a human hepatocellular carcinoma cell line, was established. Antisense oligonucleotides (AS-ODN) were used to obtain different multidrug resistance phenotypes by inhibiting the expression of mdr1 gene and/or multidrug resistance-related protein gene (mrp) using Lipofectamine as delivery agent. Expression of mdr1 and mrp genes was evaluated by RT-PCR and Western blotting. Intracellular daunorubicin (DNR) concentration was measured by flow cytometry. Subcellular DNR distribution was analyzed by confocal laser scanning microscopy. Adriamycin (ADM) and DNR sensitivity was examined by MTT method.

RESULTS: Low level expression of mdr1 and mrp mRNAs and no expression of P-Glycoprotein (P-gp) and multidrug resistance-related protein (P₁₉₀) were detected in parental sensitive cells SMMC-7721/S, but over-expression of these two genes was observed in drug-resistant cell SMMC-7721/R. The expression of mdr1 and mrp genes in SMMC-7721/R cells was down-regulated to the level in the SMMC-7721/S cells by AS-ODN. Intracellular DNR concentration in SMMC-7721/S cells was 10 times higher than that in SMMC-7721/R cells. In SMMC7721/S cells intracellular DNR distributed evenly in the nucleus and cytoplasm, while in SMMC-7721/R cells DNR distributed in a punctate pattern in the cytoplasm and was reduced in the nucleus. DNR concentration in SMMC-7721/R cells co-transfected with AS-ODNs targeting to mdr1 and mrp mRNAs recovered to 25 percent of that in SMMC7721/S cells. Intracellular DNR distribution pattern in drug-resistant cells treated by AS-ODN was similar to drug-sensitive cell, and the cells resistance index (RI) to DNR and ADM decreased at most from 88.0 and 116.0 to 4.0 and 2.3, respectively. Co-Transfection of two AS-ODNs showed a stronger synergistic effect than separate transfection.

CONCLUSIONS: P-gp and P₁₉₀ are two members mediating MDR in cell line SMMC7721/R. Intracellular drug concentration increase and subcellular distribution change are two important factors in multidrug resistance (MDR) formation. The second factor, drugs transport by P-gp and P₁₉₀ from cell nucleus to organell in cytoplasm, may play a more important role.

Expression and function of classical protein kinase C isoenzymes in gastric cancer cell line and its drug-resistant sublines

AIM: To investigate the expression and function of classical protein kinase C (PKC) isoenzymes in inducing MDR phenotype in gastric cancer cells.

METHODS: Two cell lines were used in the study: gastric cancer cell SGC7901 and its drug-resistant cell SGC7901/VCR stepwise-selected by vincristine 0.3, 0.7 and 1.0 mg·L^-1, respectively. The expression of classical PKC (cPKC) isoenzymes in SGC7901 cells and SGC7901/VCR cells were detected using immunofluorescent cytochemistry, laser confocal scanning microscope and Western blot. The effects of anti-PKC isoenzymes antibody on adriamycin accumulation in SGC7901/VCR cells were determined using flow cytometric analysis.

RESULTS: (1) SGC7901 cells exhibited positive staining of PKC-α. SGC7901/VCR cells exhibited stronger staining of PKC-α than SGC7901 cells. The higher dosage vincristine selected, the much stronger staining of PKC-α was observed on SGC7901/VCR cells. (2) Both SGC7901 and SGC7901/VCR cells exhibited positive staining of PKC-β I and PKC-β II with no significant difference. (3) Compared with SGC7901, SGC7901/VCR cells had decreased adriamycin accumulation and retention. Accumulation of adriamycin in SGC7901 was 5.21 ± 2.56 mg·L^-1, in SGC7901/VCR 0.3 was 0.85 ± 0.29 mg·L^-1, in SGC7901/VCR 0.7 was 0.81 ± 0.32 mg·L^-1, and in SGC7901/VCR 1.0 was 0.80 ± 0.33 mg·L^-1; Retention of adriamycin in SGC7901 was 2.51 ± 1.23 mg·L^-1, in SGC7901/VCR 0.3 was 0.47 ± 0.14 mg·L^-1, in SGC7901/VCR 0.7 was 0.44 ± 0.15 mg·L^-1, and in SGC7901/VCR 1.0 was 0.41 ± 0.11 mg·L^-1. (4) Fluorescence intensity presented adriamycin accumulation in SGC7901/VCR cells was increased from 1.14 ± 0.36 to 2.71 ± 0.94 when cells were co-incubated with anti-PKC-α but not with anti-PKC-β I, PKC-α II and PKCγ antibodies.

CONCLUSION: PKC-α, but not PKC-β I, PKC-β II or PKCγ, may play a role in multidrug resistance of gastric cancer cells SGC7901/VCR.

Differential display of vincristine-resistance-related genes in gastric cancer SGC7901 cell

AIM: To isolate and clone the vincristine-resistine-related genes in gastric cancer SGC7901 cell line and to clarify the multidrug-resistant molecular mechanism of gastric cancer cells.

METHODS: The modified differential-display polymerase chain reaction (DD-PCR) was used to examine the differences in the mRNA composition of Vincristine-resistant gastric cancer SGC 7901 cells (SGC7901/VCR), induced by vincristine sulfate versus SGC7901 cells. The differentially expressed cDNA fragments were confirmed by reverseNorthern analysis, sequencing, BLAST analysis and Northern bolt analysis.

RESULTS: DD-PCR identified that 54 cDNA fragments were preferentially expressed in SGC 7901/VCR cells. When these cDNA fragments were analyzed by reverse Northern blot, 20 were reproducibly expressed at a high level in SGC7901/VCR. Sequencing and BLAST analysis revealed that seven of the genes were known genes: ADP-ribosylation factor 4, Cytochrome oxidase subunit II, Ss-A/Ro ribonucleoprtein autoantigen 60kd subunit, ribosomal protein S13, galaectin-8 gene, oligophrenin 1 mRNA, ribosomal protein L23 mRNA; thirteen of the genes were unknown genes. The length and abundance of the four unknown genes mRNA were further confirmed by Northern blot analysis.

CONCLUSION: The twenty differential known and unknown genes may be related to the vincristine-resistant mechanism in human gastric cancer SGC7901 cell line.

Fas counterattack in cholangiocarcinoma: A mechanism for immune evasion in human hilar cholangiocarcinomas

AIM: To investigate FasL expression in hilar cholangiocarcinoma tissues and cultured cholangiocarcinoma cells, and to assess its ability to induce apoptosis.

METHODS: We studied the expression of FasL by human hilar cholangiocaroinomas tissues by immunohistochemistry, and the QBC939 cholangiocarcinoma cell line by RT-PCR, immunohistochemistry, and Western Blot. TUNEL and flow cytometry were used to detect apoptotic cells.

RESULTS: Prevalent expression of FasL was detected in 39 resected hilar cholangiocarcinoma tissues. TUNEL staining disclosed a high level of cell death among lymphocytes infiltrating FasL positive areas of tumor. FasL mRNA and protein expressions in cholangiocarcinoma cells could induce Jurkat cells.

CONCLUSION: Hilar cholangiocarcinomas may elude immunological surveillance by inducing, via Fas/FasL system, the apoptosis of activated lymphocytes.

Molecular mechanism about lymphogenous metastasis of hepatocarcinoma cells in mice

AIM: To investigate the correlation between lymphogenous metastasis and matrix metalloproteinases (MMPs) activity and the expression of Fas ligand of tumor cells in lymph nodes.

METHODS: Fifty-six inbred 615-mice were equally divided into 2 groups and inoculated with Hca-F and Hca-P cells. Their lymph node metastatic rates were examined. Growth fraction of lymphocytes in host lymph nodes was detected by flow cytometry. The Hca-F and Hca-P cells were cultured with extract of lymph node, liver or spleen. The quantity of MMPs in these supernatants was examined by zymographic analysis. The expression of Fas ligand, PCNA, Bcl-2 protein of Hca-F and Hca-P cells in the mice were examined by immunohistochemistry. The apoptosis signals of macrophages in lymph nodes were observed with in situ DNA fragmentation.

RESULTS: On the 28^th day post-inoculation, the lymph node metastatic rate of Hca-F was 80% (16/20), whereas that of Hca-P was 25% (5/20). The growth fraction of lymphocytes was as follows: in the Hca-F cells, the proliferating peak of lymphocytes appeared on the 14^th day post-inoculation and then decreased rapidly, while in Hca-P cells, the peak appeared on the 7^th day post inoculation and then kept at a high level. With the extract of lymph node, the quantity of the MMP-9 activity increased (P < 0.01) and active MMP-9 and MMP-2 were produced by both Hca-F and Hca-P tumor cells, which did not produce MMPs without the extract of lymph node or with the extracts of the liver and spleen. The expression of Fas Ligand of Hca-F cells was stronger than that of Hca-P cells (P < 0.01). The expressions of PCNA and Bcl-2 protein of Hca-F cells in the tumors of inoculated area were the same as that of Hca-P cells. In situ DNA fragmentation showed that the positive signals of macrophages were around Hca-F cells.

CONCLUSION: Secretion of MMPs which was associated with metastatic ability of Hca-F and Hca-P tumor cells depends on the environment of lymph nodes. The increased expression of Fas ligand protein of Hca-F tumor cells with high lymphogenous metastatic potential in lymph nodes may help tumor cells escape from being killed by host lymphocytes.