Anticancer properties of complexes derived from bidentate ligands

Cancer is the abnormal division and multiplication of cells in an organ or tissue. It is the second leading cause of death globally. There are various types of cancer such as prostate, breast, colon, lung, stomach, liver, skin, and many others depending on the tissue or organ where the abnormal growth originates. Despite the huge investment in the development of anticancer agents, the transition of research to medications that improve substantially the treatment of cancer is less than 10%. Cisplatin and its analogs are ubiquitous metal-based anticancer agents notable for the treatment of various cancerous cells and tumors but unfortunately accompanied by large toxicities due to low selectivity between cancerous and normal cells. The improved toxicity profile of cisplatin analogs bearing bidentate ligands has motivated the synthesis of vast metal complexes of bidentate ligands. Complexes derived from bidentate ligands such as β-diketones, diolefins, benzimidazoles and dithiocarbamates have been reported to possess 20 to 15,600-fold better anticancer activity, when tested on cell lines, than some known antitumor drugs currently on the market, e.g. cisplatin, oxaliplatin, carboplatin, doxorubicin, and 5-fluorouracil. This work discusses the anticancer properties of various metal complexes derived from bidentate ligands, for possible application in chemotherapy. The results discussed were evaluated by the IC50 values as obtained from cell line tests on various metal-bidentate complexes. The structure-activity relationship study of the complexes discussed, revealed that hydrophobicity is a key factor that influences anticancer properties of molecules.

Characterization of SN38-resistant T47D breast cancer cell sublines overexpressing BCRP, MRP1, MRP2, MRP3, and MRP4

Background

Although several novel resistant breast cancer cell lines have been established, only a few resistant breast cancer cell lines overexpress breast cancer resistance proteins (BCRP). The aim of this study was to establish new resistant breast cancer cell lines overexpressing BCRP using SN38 (7-ethyl-10-hydroxycamptothecin), an active metabolite of irinotecan and was to discover genes and mechanisms associated with multidrug resistance.

Methods

SN38-resistant T47D breast cancer cell sublines were selected from the wild-type T47D cells by gradually increasing SN38 concentration. The sensitivity of the cells to anti-cancer drugs was assessed by 3-(4,5-methylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Expression profiles of the resistance-related transporters were examined using RT-qPCR, and western blot analysis. Intracellular fluorescent dye accumulation in the resistant cells was determined using flow cytometry.

Results

The SN38-resistant T47D breast cancer cell sublines T47D/SN120 and T47D/SN150 were established after long-term exposure (more than 16 months) of wild-type T47D cells to 120 nM and 150 nM SN38, respectively. T47D/SN120 and T47D/SN150 cells were more resistant to SN38 (14.5 and 59.1 times, respectively), irinotecan (1.5 and 3.7 times, respectively), and topotecan (4.9 and 12 times, respectively), than the wild-type parental cells. Both T47D/SN120 and T47D/SN150 sublines were cross-resistant to various anti-cancer drugs. These resistant sublines overexpressed mRNAs of MRP1, MRP2, MRP3, MRP4, and BCRP. The DNA methylase inhibitor 5-aza-2′-deoxycytidine and the histone deacetylase inhibitor trichostatin A increased the expression levels of BCRP, MRP1, MRP2, MRP3, and MRP4 transcripts in T47D/WT cells. Fluorescent dye accumulation was found to be lower in T47D/SN120 and T47D/SN150 cells, compared to that in T47D/WT cells. However, treatment with known chemosensitizers increased the intracellular fluorescent dye accumulation and sensitivity of anti-tumor agents.

Conclusion

T47D/SN120 and T47D/SN150 cells overexpressed MRP1, MRP2, MRP3, MRP4, and BCRP, which might be due to the suppression of epigenetic gene silencing via DNA hypermethylation and histone deacetylation. Although these resistant cells present a higher resistance to various anti-cancer drugs than their parental wild-type cells, multidrug resistance was overcome by treatment with chemosensitizers. These SN38 resistant T47D breast cancer cell sublines expressing resistance proteins can be useful for the development of new chemosensitizers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09446-y.

CDK Inhibition Reverses Acquired 5-Fluorouracil Resistance in Hepatocellular Carcinoma Cells

Background. 5-Fluorouracil (5-FU) has been widely applied in treating cancers. However, its usage is largely limited in hepatocellular carcinoma (HCC), due to acquired resistance. Here, we aim to identify target proteins and investigate their roles in 5-FU sensitivity of HCC cells. Methods. Mass spectrometry (MS) proteomics was performed on 5-FU-resistant cell line (BEL7402/5-FU) and its parental cell line (BEL7402) with 5-FU treatment. In order to identify potential targets, we compared the proteomics between two cell line groups and used bioinformatics tools to select hub proteins from all differentially expressed proteins. Results. We finally focused on a group of cell cycle-related kinases (CDKs). By CCK8 assay, we confirmed that the CDK inhibitor significantly decreased the IC50 of 5-FU-resistant cells. Conclusions. Our study verified that CDK inhibition can reverse 5-FU resistance of HCC cells.

Upregulation of histone acetylation reverses organic anion transporter 2 repression and enhances 5-fluorouracil sensitivity in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in the world. The failure of chemotherapy in HCC patients is partly due to inadequate intracellular drug accumulation caused by abnormally expressed drug transporters. Human organic anion transporter 2 (hOAT2), a transporter mainly expressed in liver and kidney, is responsible for uptake of various antineoplastic drugs such as 5-fluorouracil (5-FU). Among 32 pairs of human HCC samples, we preliminarily found that OAT2 was suppressed in HCC tissues compared with matched tumor-adjacent tissues at both mRNA and protein levels, which resulted in 5-FU resistance in HCC. However, the epigenetic regulatory mechanisms of OAT2 downregulation have not been investigated. In this study, we first proved it was histone hypoacetylation rather than DNA hypermethylation that participated in transcriptional repression of OAT2 in two HCC cell lines (BEL-7402 and SMMC-7721). In general, there were two pathways confirmed using tissues and cells: 1) Increased histone deacetylase sirtuin 7 (SIRT7) mediated loss of histone 3 lysine 18 acetylation (H3K18ac) at the promoter of OAT2 and inhibited its transcription. 2) More histone deacetylase 7 (HDAC7) instead of lysine acetyltransferase 8 (KAT8) enrichment at the promoter of OAT2 led to low levels of histone 4 lysine 16 acetylation (H4K16ac). Further, we found that histone deacetylases inhibitor vorinostat (SAHA) could reverse histone hypoacetylation state to activate OAT2 transcription and enhance uptake of classic OAT2 substrate zidovudine. Therefore, we evaluated the effect of combining SAHA and 5-FU and the results demonstrated that SAHA could sensitize HCC cells to 5-FU. Collectively, we proposed such a combination treatment to overcome 5-FU resistance in HCC from the perspective of epigenetically restoring OAT2.

Upregulated UCA1 contributes to oxaliplatin resistance of hepatocellular carcinoma through inhibition of miR-138-5p and activation of AKT/mTOR signaling pathway

Hepatocellular carcinoma (HCC) inevitably developed oxaliplatin (OXA) resistance after long-term treatment, but the mechanism remains unclear. Here, we found that LncRNA UCA1 was upregulated in most of OXA-resistant HCC tissues and cells (HepG2/OXA and SMMC-7721/OXA). Follow-up analysis and online Kaplan-Meier Plotter revealed that HCC patients with high UCA1 level had a shorter survival compared with those with low expression. Overexpression of UCA1 increased OXA IC50 in HepG2 and SMMC-7721 cells, whereas knockdown of UCA1 decreased OXA IC50 in resistant counterparts. Moreover, dual luciferase reporter assay showed that co-transfection of UCA1-WT plasmid with miR-138-5p mimics enhanced fluorescence signals, whereas co-transfection of UCA1-Mut plasmid and miR-138-5p mimics did not induce any changes. Consistently, UCA1 levels in HepG2/OXA and SMMC-7721/OXA cells were downregulated after transfected with miR-138-5p mimics. UCA1 silencing or transfection of miR-138-5p mmics inhibited the activation of AKT and mTOR in HepG2/OXA and SMMC-7721/OXA cells, whereas UCA1 overexpression increased the phosphorylated AKT and mTOR levels in parental counterparts. Rapamycin or miR-138-5p mimics similarly suppressed the activation of AKT and mTOR, whereas UCA1 overexpression exert opposite roles. Interestingly, administration of rapamycin or miR-138-5p mimics apparently antagonized the effects of UCA1 on AKT and mTOR activation. Besides, depletion of UCA1 triggered more dramatic regression of HepG2 xenografts than that of HepG2/OXA xenografts with OXA treatment and impaired the p-AKT and p-mTOR levels in vivo. In conclusion, our findings provide the evidence that UCA1 may contribute to OXA resistance via miR-138-5p-mediated AK /mTOR activation, suggesting that UCA1 is a potential therapeutic target for HCC.

Effect of Foslip® mediated photodynamic therapy on 5-fluorouracil resistant human colorectal cancer cells

Colorectal cancer (CRC) is the commonest cancer in Hong Kong and is often treated with 5-fluorouracil (5-FU). However the clinical application of 5-FU was limited by drug resistance in CRC. Photodynamic therapy (PDT) is a novel treatment combating CRC via the combination of photosensitizer, molecular oxygen and light activation. In this study, 5-FU resistant HT29 (HT29FU) was established and its susceptibility to Foslip® PDT tested. Effect of 5-FU to HT29 cells was measured via qPCR. Efficacy of Foslip® PDT on HT29 and HT29FU cells were measured via photosensitizer uptake, cellular localization, cytotoxicity, cell cycle distribution and signal proteins expression. 5-FU significantly induced ABCB1 mRNA expression in HT29 cells; whereas with a 24 fold increase in HT29FU cells. Both cells responded similarly to Foslip® PDT, with the inhibitory concentration IC₂₀, IC₅₀ and IC₇₀ achieved at 1 ng/mL, 2 ng/mL and 5 ng/mL with 2 J/cm² light activation respectively. Foslip® PDT triggered apoptosis and reduced JNK protein expression at IC₇₀ on both cells. Effect of Foslip® PDT on HT29 cells was independent to 5-FU resistance properties. Therefore, Foslip® PDT could be a potential treatment for 5-FU resistant cancer patients. Further investigations on the Foslip® PDT mediated molecular changes in HT29FU cells deserve to be explored.

Cepharanthine combined with 5-fluorouracil inhibits the growth of p53-mutant human colorectal cancer cells

Mutant p53 is primarily responsible for ineffectiveness of many anticancer drugs. The present study showed that cepharanthine alone or combined with 5-fluorouracil effectively controlled the growth of HT-29 human colorectal cancer cells harboring mutant p53 both in vitro and in vivo. The combination of cepharanthine and 5-fluorouracil additively induced apoptotic and necrotic cell death. Their combination significantly upregulated the expression of BAK and cleaved PARP in tumor tissues. Moreover, cepharanthine could prevent 5-fluorouracil-induced BCRP and MRP1 expression. These findings suggest that cepharanthine is a promising agent for treating patients with colorectal cancer containing p53 mutation.

2',4'-Dihydroxy-6'-methoxy-3',5'-dimethylchalcone induced apoptosis and G1 cell cycle arrest through PI3K/AKT pathway in BEL-7402/5-FU cells

Hepatocellular carcinoma is the fifth most common and the third most lethal cancer worldwide. In recent years, natural flavonoids have drawn great attention as repository for the exploitation of novel antineoplastic agents. 2',4'-Dihydroxy-6'-methoxy-3',5'-dimethylchalcone (DMC), a functional chalcone isolated from the buds of Cleistocalyx operculatus, has been reported to exert potent cytotoxicity against multi-drug resistant BEL-7402/5-FU cells. In this study, the precise mechanisms of DMC-mediated growth inhibition in BEL-7402/5-FU cells were further investigated. DMC was found to trigger apoptosis predominantly via the mitochondria-dependent pathway and the enhancement of reactive oxygen species (ROS) generation. Meanwhile, DMC induced G1 cell cycle arrest through downregulation of cyclin D1 and CDK4. Furthermore, DMC increased p53 level and inhibited NF-κB nuclear-localization via suppression of PI3K/AKT signaling axis, which might be the underlying mechanism of DMC-induced apoptosis and cell cycle arrest in BEL-7402/5-FU cells. Collectively, the study elucidated the mechanisms by which DMC may inhibit the growth of BEL-7402/5-FU cells and suggested the possibility that DMC might be a promising candidate therapeutic agent for hepatoma treatment in the future.

Quantification and expert evaluation of evidence for chemopredictive biomarkers to personalize cancer treatment

Predictive biomarkers have the potential to facilitate cancer precision medicine by guiding the optimal choice of therapies for patients. However, clinicians are faced with an enormous volume of often-contradictory evidence regarding the therapeutic context of chemopredictive biomarkers.

We extensively surveyed public literature to systematically review the predictive effect of 7 biomarkers claimed to predict response to various chemotherapy drugs: ERCC1-platinums, RRM1-gemcitabine, TYMS-5-fluorouracil/Capecitabine, TUBB3-taxanes, MGMT-temozolomide, TOP1-irinotecan/topotecan, and TOP2A-anthracyclines. We focused on studies that investigated changes in gene or protein expression as predictors of drug sensitivity or resistance. We considered an evidence framework that ranked studies from high level I evidence for randomized controlled trials to low level IV evidence for pre-clinical studies and patient case studies.

We found that further in-depth analysis will be required to explore methodological issues, inconsistencies between studies, and tumor specific effects present even within high evidence level studies. Some of these nuances will lend themselves to automation, others will require manual curation. However, the comprehensive cataloging and analysis of dispersed public data utilizing an evidence framework provides a high level perspective on clinical actionability of these protein biomarkers. This framework and perspective will ultimately facilitate clinical trial design as well as therapeutic decision-making for individual patients.

Role of uL3 in Multidrug Resistance in p53-Mutated Lung Cancer Cells

Cancer is one of the most common causes of death among adults. Chemotherapy is crucial in determining patient survival and quality of life. However, the development of multidrug resistance (MDR) continues to pose a significant challenge in the management of cancer. In this study, we analyzed the role of human ribosomal protein uL3 (formerly rpL3) in multidrug resistance. Our studies revealed that uL3 is a key determinant of multidrug resistance in p53-mutated lung cancer cells by controlling the cell redox status. We established and characterized a multidrug resistant Calu-6 cell line. We found that uL3 down-regulation correlates positively with multidrug resistance. Restoration of the uL3 protein level re-sensitized the resistant cells to the drug by regulating the reactive oxygen species (ROS) levels, glutathione content, glutamate release, and cystine uptake. Chromatin immunoprecipitation experiments and luciferase assays demonstrated that uL3 coordinated the expression of stress-response genes acting as transcriptional repressors of solute carrier family 7 member 11 (xCT) and glutathione S-transferase α1 (GST-α1), independently of Nuclear factor erythroid 2-related factor 2 (Nrf2). Altogether our results describe a new function of uL3 as a regulator of oxidative stress response genes and advance our understanding of the molecular mechanisms underlying multidrug resistance in cancers.

Downregulation of NPM reverses multidrug resistance in human hepatoma cells via inhibition of P-glycoprotein expression

Multidrug resistance (MDR) is an important issue in current cancer treatments. In human cancer, drug resistance is primarily associated with the overexpression of multidrug resistance gene 1 (MDR1). Therefore, the human MDR1 gene promoter may be a target for anti‑MDR drug screening. Numerous methods to prevent MDR have been investigated. However, they have been proven to be clinically ineffective. Therefore, the aim of the present study was to investigate whether downregulation of nucleophosmin (NPM) demonstrates any effects on the reversal of MDR in hepatocellular carcinoma (HCC) cells. In the present study, two in vitro MDR HCC cell lines, HepG2/Adriamycin (ADM) and SMMC7721/ADM, were established and the level of MDR was measured. The results demonstrated that NPM downregulation markedly reversed the effects of MDR in the model used. In addition, NPM downregulation reduced P-glycoprotein expression, as well as MDR1 expression. These results suggested that downregulation of NPM may be a novel and effective method of reversing the effects of MDR, and may be a potential adjuvant for tumor chemotherapy.

Decellularized matrices as in vitro models of extracellular matrix in tumor tissues at different malignant levels: Mechanism of 5-fluorouracil resistance in colorectal tumor cells

Chemoresistance is a major barrier for tumor chemotherapy. It is well-known that chemoresistance increases with tumor progression. Chemoresistance is altered by both genetic mutations and the alteration of extracellular microenvironment. Particularly, the extracellular matrix (ECM) is remodeled during tumor progression. Therefore, ECM remodeling is expected to cause the acquisition of chemoresistance in highly malignant tumor tissue. Here, we prepared cultured cell-derived decellularized matrices that mimic native ECM in tumor tissues at different stages of malignancy, and 5-fluorouracil (5-FU) resistance was compared among these matrices. 5-FU resistance of colorectal tumor cells increased on the matrices derived from highly malignant tumor HT-29 cells, although the resistance did not increase on the matrices derived from low malignant tumor SW480 cells and normal CCD-841-CoN cells. The resistance on HT-29 cell-derived matrices increased through the activation of Akt and the upregulation of ABCB1 and ABCC1 without cell growth promotion, suggesting that ECM remodeling plays important roles in the acquisition of chemoresistance during tumor progression. It is expected that our decellularized matrices, or "staged tumorigenesis-mimicking matrices", will become preferred cell culture substrates for in vitro analysis of comprehensive ECM roles in chemoresistance and the screening and pharmacokinetic analysis of anti-cancer drugs.

Investigation of potential molecular biomarkers and small molecule drugs for hepatocellular carcinoma transformed from cirrhosis

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in China and the third leading cause of cancer-associated morality. The aim of the present study was to investigate and analyze differentially-expressed genes (DEGs) between cirrhosis and HCC, in order to screen the key genes involved in the transformation from cirrhosis to HCC and provide novel targets for the diagnosis and treatment of HCC in patients with cirrhosis. The gene expression profile, GSE17548, was obtained from Gene Expression Omnibus database and the DEGs were identified by LIMMA package in R language. Kyoto Encyclopedia of Genes and Genomes and gene ontology biology process analysis were performed for the DEGs. Differential co-expression network (DEN) analysis was conducted and the network was visualized using Cytoscape. Small molecule drugs were also screened from the Comparative Toxicogenomics Database for higher degree DEGs. A total of 95 DEGs were obtained, including 46 upregulated and 49 downregulated genes. The upregulated DEGs were primarily involved in biological processes and pathways associated with the cell cycle, while the downregulated DEGs were primarily involved in immune-associated biological processes. A total of 22 key DEGs were identified by DEN analysis, which distinguished HCC from cirrhosis samples. Furthermore, estradiol, benzo(a)pyrene, acetaminophen, copper sulfate and bisphenol A were identified as the five most associated chemicals to these 22 DEGs. In conclusion, the hub genes and chemicals identified by the present study may provide a theoretical basis for additional research on diagnosis and treatment of HCC transformed from cirrhosis.

Loss of Runt-related transcription factor 3 induces resistance to 5-fluorouracil and cisplatin in hepatocellular carcinoma

Runt-related transcription factor 3 (RUNX3) is known to function as a tumor suppressor in gastric cancer and other types of cancers, including hepatocellular carcinoma (HCC). However, its role has not been fully elucidated. In the present study, we aimed to evaluate the role of RUNX3 in HCC. We used the human HCC cell lines Hep3B, Huh7 and HLF; RUNX3 cDNA was introduced into Hep3B and Huh7 cells, which were negative for endogenous RUNX3 expression, and RUNX3 siRNA was transfected into HLF cells, which were positive for endogenous RUNX3. We analyzed the expression of RUNX3 and multidrug resistance-associated protein (MRP) by immunoblotting. MTT assays were used to determine the effects of RUNX3 expression on 5-fluorouracil (5-FU) and cisplatin (CDDP) sensitivity. Finally, 23 HCC specimens resected from patients with HCC at Okayama University Hospital were analyzed, and correlations among immunohistochemical expression of RUNX3 protein and MRP protein were evaluated in these specimens. Exogenous RUNX3 expression reduced the expression of MRP1, MRP2, MRP3 and MRP5 in the RUNX3-negative cells, whereas knockdown of RUNX3 in the HLF cells stimulated the expression of these MRPs. An inverse correlation between RUNX3 and MRP expression was observed in the HCC tissues. Importantly, loss of RUNX3 expression contributed to 5-FU and CDDP resistance by inducing MRP expression. These data have important implications in the study of chemotherapy resistance in HCC.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

Puerarin inhibits growth and induces apoptosis in SMMC-7721 hepatocellular carcinoma cells

Puerarin, a predominant isoflavonoid compound extracted from the Chinese medicinal herb Radix Puerariae, is considered to exhibit an antitumor effect. In the present study, the effects of puerarin on SMMC-7721 human hepatocellular carcinoma cells were investigated. Cell viability was assessed by MTT assay. Apoptosis was detected by flow cytometry with Annexin V-fluorescein isothiocyante staining and morphological observation of nuclear changes by Hoechst staining. The mitochondrial membrane potential (MMP) was monitored using rhodamine 123. The generation of reactive oxygen species (ROS) was quantified using dichloro‑dihydro‑fluorescein diacetate. Polymerase chain reaction and western blot analysis were used to detect the expression levels of apoptosis‑associated genes. The results revealed that high concentrations of puerarin (500, 1,000 and 1,500 µg/ml) significantly inhibited the proliferation of SMMC-7721 cells in a time- and dose-dependent manner. Simultaneously, apoptotic rates were increased and cell morphology was changed following puerarin treatment. Furthermore, puerarin‑induced apoptosis of SMMC-7721 cells was associated with loss of MMP and generation of ROS. Puerarin treatment increased caspase‑3,8,9 and apoptosis‑inducing factor (AIF) mRNA expression levels in SMMC‑7721 cells, while the phosphorylation levels of P38, extracellular signal‑regulated kinase (ERK1) and c-Jun N‑terminal kinase were also increased. Furthermore, caspase-9 and AIF protein expression was upregulated. In conclusion, puerarin inhibited proliferation and induced apoptosis in SMMC‑7721 cells via the mitochondria‑dependent pathway; however, the specific mechanisms require further investigation.

Establishment of paclitaxel-resistant breast cancer cell line and nude mice models, and underlying multidrug resistance mechanisms in vitro and in vivo

BACKGROUND

Breast cancer is a common malignant tumor which affects health of women and multidrug resistance (MDR) is one of the main factors leading to failure of chemotherapy. This study was conducted to establish paclitaxel-resistant breast cancer cell line and nude mice models to explore underlying mechanisms of MDR.

METHODS

The breast cancer drug-sensitive cell line MCF-7 (MCF-7/S) was exposed in stepwise escalating paclitaxel (TAX) to induce a resistant cell line MCF-7/TAX. Cell sensitivity to drugs and growth curves were measured by MTT assay. Changes of cell morphology and ultrastructure were examined by optical and electron microscopy. The cell cycle distribution was determined by flow cytometry. Furthermore, expression of proteins related to breast cancer occurrence and MDR was tested by immunocytochemistry. In Vivo, nude mice were injected with MCF-7/S and MCF-7/TAX cells and weights and tumor sizes were observed after paclitaxel treatment. In addition, proteins involved breast cancer and MDR were detected by immunohistochemistry.

RESULTS

Compared to MCF-7/S, MCF-7/TAX cells had a higher resistance to paclitaxel, cross-resistance and prolonged doubling time. Moreover, MCF-7/TAX showed obvious alterations of ultrastructure. Estrogen receptor (ER) expression was low in drug resistant cells and tumors while expression of human epidermal growth factor receptor 2 (HER2) and Ki-67 was up-regulated. P-glycoprotein (P-gp), lung resistance-related protein (LRP) and glutathione-S-transferase-π (GST-π) involved in the MDR phenotype of resistant cells and tumors were all overexpressed.

CONCLUSION

The underlying MDR mechanism of breast cancer may involve increased expression of P-gp, LRP and GST-π.

FUT family mediates the multidrug resistance of human hepatocellular carcinoma via the PI3K/Akt signaling pathway

The fucosyltransferase (FUT) family is the key enzymes in cell-surface antigen synthesis during various biological processes such as tumor multidrug resistance (MDR). The aim of this work was to analyze the alteration of FUTs involved in MDR in human hepatocellular carcinoma (HCC) cell lines. Using mass spectrometry (MS) analysis, the composition profiling of fucosylated N-glycans differed between drug-resistant BEL7402/5-FU (BEL/FU) cells and the sensitive line BEL7402. Further analysis of the expressional profiles of the FUT family in three pairs of parental and chemoresistant human HCC cell lines showed that FUT4, FUT6 and FUT8 were predominant expressed in MDR cell lines. The altered levels of FUT4, FUT6 and FUT8 were responsible for changed drug-resistant phenotypes of BEL7402 and BEL/FU cells both in vitro and in vivo. In addition, regulating FUT4, FUT6 or FUT8 expression markedly modulated the activity of the phosphoinositide 3 kinase (PI3K)/Akt signaling pathway and MDR-related protein 1 (MRP1) expression. Inhibition of the PI3K/Akt pathway by its specific inhibitor wortmannin, or by Akt small interfering RNA (siRNA), resulted in decreased MDR of BEL/FU cells, partly through the downregulation of MRP1. Taken together, our results suggest that FUT4-, FUT6- or FUT8-mediated MDR in human HCC is associated with the activation of the PI3K/Akt pathway and the expression of MRP1, but not of P-gp, indicating a possible novel mechanism by which the FUT family regulates MDR in human HCC.

Reversal effect of bufalin on multidrug resistance in human hepatocellular carcinoma BEL-7402/5-FU cells

Multidrug resistance (MDR) is a major obstacle to chemotherapy in patients with hepatocellular carcinoma (HCC). To overcome MDR and improve chemotherapeutic efficacy, novel reversal agents with higher efficacy and lower toxicity are urgently needed for HCC. The present study was designed to examine the potential reversal activity of bufalin, a toxic ligand isolated from the traditional Chinese medicine 'Chansu' and to elucidate the possible related mechanisms. A multidrug-resistant HCC cell line, BEL-7402/5-FU, was used as the cell model. The working concentration of bufalin as an effective reversal agent, and the cell viability in the reversal experiments were determined by MTT assay. The effects of bufalin at a non-cytotoxic dose on cell cycle distribution, apoptosis and drug efflux pump activity were measured by flow cytometry. Qualitative observation of apoptosis was also carried out by confocal microscopy. Furthermore, the effects of bufalin on the expression of potential genes involved in MDR of BEL-7402/5-FU cells, including thymidylate synthase (TS), P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), B-cell lymphoma-extra large (Bcl-xL) and Bcl-2-associated X protein (Bax), were determined using real-time PCR and western blot analysis. The results showed that bufalin at a concentration of 1 nM enhanced the chemosensitivity of BEL-7402/5-FU cells to 5-FU with a reversal fold of 3.8 which was similar to that of 1 µM verapamil. Bufalin significantly arrested the cell cycle at the G₀/G₁ phase, induced apoptosis through an increase in the Bax/Bcl-xL ratio, inhibited drug efflux pump activity via downregulation of MRP1, and reduced the expression of TS in BEL-7402/5-FU cells. The present study revealed that bufalin effectively reversed MDR in BEL-7402/5-FU cells through multiple pathways. The combination of bufalin with cytotoxic drugs may serve as a promising strategy for the chemotherapy of HCC.