Mechanisms of drug resistance in cancer chemotherapy

Activity of ixabepilone in patients with metastatic breast cancer with primary resistance to taxanes

Primary drug resistance, defined as disease progression as best response to treatment, presents an important problem in everyday clinical practice. Primary taxane resistance, reported in up to 55% of patients with breast cancer, plays a critical role in minimizing the efficacy of taxane-based chemotherapy for metastatic breast cancer (MBC). The epothilones are a novel class of antineoplastic agents, developed to overcome tumor-resistance mechanisms. Ixabepilone, the first drug in this class, stabilizes microtubule polymerization, and induces cell-cycle arrest and apoptosis. Ixabepilone demonstrates low susceptibility to different and multiple mechanisms of drug resistance that play a crucial role in primary taxane resistance, such as tumor overexpression of neuronal-specific beta-tubulin isotype III and drug-efflux transporters. In phase II trials, ixabepilone demonstrated proven activity in patients with MBC whose tumors had primary or secondary resistance to taxanes and other agents. Ixabepilone also demonstrated activity in patients with tumor types such as renal-cell cancer and pancreatic cancer that are usually intrinsically insensitive to chemotherapy, including taxanes. To determine the activity of ixabepilone in patients with primary taxane resistance, a retrospective analysis of patient subsets from 2 clinical trials was conducted. Ixabepilone demonstrated clinical activity as monotherapy, and in combination with capecitabine, in patients with MBC who had disease progression as best response to previous taxane therapy. Response rates in patients with primary taxane resistance were comparable to responses observed in total patient populations. The clinical results support the hypothesis that ixabepilone can overcome or circumvent primary mechanisms of resistance to taxanes and other chemotherapeutic agents.

Paclitaxel and docetaxel resistance: molecular mechanisms and development of new generation taxanes

Taxanes represent one of the most promising classes of anticancer agents. Unfortunately, their clinical success has been limited by the insurgence of cellular resistance, mainly mediated by the expression of the MDR phenotype or by microtubule alterations. However, the remarkable relevance of paclitaxel and docetaxel in clinical oncology stimulated intensive efforts in the last decade to identify new derivatives endowed with improved activities towards resistant tumor cells, resulting in a huge number of novel natural and synthetic taxanes. Among them, several structurally different derivatives were found to exhibit a promising behavior against the MDR phenotype in terms of either MDR inhibiting properties, or enhanced cytotoxicity compared to parental drugs, or both. On the other hand, only in more recent years have the first taxanes retaining activity against resistant cancer cells bearing alterations of the tubulin/microtubule system emerged. This review describes the main molecular mechanisms of resistance to paclitaxel and docetaxel identified so far, focusing on the advances achieved in the development of new taxanes potentially useful for the treatment of resistant tumors.

Discovery and development of the epothilones : a novel class of antineoplastic drugs

The epothilones are a novel class of antineoplastic agents possessing antitubulin activity. The compounds were originally identified as secondary metabolites produced by the soil-dwelling myxobacterium Sorangium cellulosum. Two major compounds, epothilone A and epothilone B, were purified from the S. cellulosum strain So ce90 and their structures were identified as 16-member macrolides. Initial screening with these compounds revealed a very narrow and selective antifungal activity against the zygomycete, Mucor hiemalis. In addition, strong cytotoxic activity against eukaryotic cells, mouse L929 fibroblasts and human T-24 bladder carcinoma cells was observed. Subsequent studies revealed that epothilones induce tubulin polymerization and enhance microtubule stability. Epothilone-induced stabilisation of microtubules was shown to cause arrest at the G2/M transition of the cell cycle and apoptosis. The compounds are active against cancer cells that have developed resistance to taxanes as a result of acquisition of beta-tubulin overexpression or mutations and against multidrug-resistant cells that overexpress P-glycoprotein or multidrug resistance-associated protein. Thus, epothilones represent a new class of antimicrotubule agents with low susceptibility to key tumour resistance mechanisms. More recently, a range of synthetic and semisynthetic epothilone analogues have been produced to further improve the adverse effect profile (or therapeutic window) and to maximize pharmacokinetic and antitumour properties. Various epothilone analogues have demonstrated activity against many tumour types in preclinical studies and several compounds have been and still are being evaluated in clinical trials. This article reviews the identification and early molecular characterization of the epothilones, which has provided insight into the mode of action of these novel antitumour agents in vivo.

Role of Ss-A/Ro ribonucleoprotein 60 ku subunit variant 1 in multi-drug resistance of gastric cancer

AIM: To investigate the possible role of Ro 60 variant 1 in multi-drug resistance (MDR) of gastric cancer.

METHODS: Ro 60 variant 1 encoding gene was cloned using RT-PCR method. Ro 60 variant 1 sense eukaryotic expression vector was constructed using DNA recombination technique and transfected into SGC7901 cells with LipofectamineTM 2000. Drug sensitivity was detected by MTT assay. IC50 values of gastric cancer cells for chemotherapy drugs were calculated. Intracellular accumulation of adriamycin in gastric cancer cells was measured by sorting fluorescence- activated cells.

RESULTS: The expression level of Ro 60 variant 1 in SGC7901 cells was increased after transfection with sense genes. In vitro drug sensitivity assay showed that the sensitivity of SGC7901 cells transfected with Ro 60 variant 1 genes was significantly decreased compared with SGC7901 and SGC7901-pcDNA3.1 cells on vincristine (IC₅₀: 2.87 ± 0.10 mg/L vs 0.47 ± 0.07 mg/L, 0.63 ± 0.08 mg/L, P < 0.01), 5-FU(IC₅₀: 3.89 ± 0.12 mg/L vs 0.59 ± 0.17 mg/L, 0.92 ± 0.12 mg/L, P<0.01), mitomycin (IC₅₀: 1.02 ± 0.06 mg/L vs 0.50 ± 0.04 mg/L, 0.73 ± 0.09 mg/L, P < 0.05), cisplatin (IC₅₀: 1.15 ± 0.06 mg/L vs 0.46 ± 0.04 mg/L, 0.52 ± 0.05 mg/L, P < 0.01) and adriamycin (IC₅₀: 0.45 ± 0.03 mg/L vs 0.15 ± 0.03 mg/L, 0.16 ± 0.02 mg/L, P < 0.01). Flow cytometry revealed that accumulation of adriamycin in SGC7901 cells transfected with Ro 60 variant 1 gene was decreased (50.39 ± 2.09 mg/L vs 94.99 ± 4.07 mg/L, 88.06 ± 2.67 mg/L, P < 0.01), when compared with SGC7901 and SGC7901-pcDNA3.1 cells.

CONCLUSION: SGC7901 cells transfected with Ro 60 variant 1 sense genes exhibit MDR. Ro 60 variant 1 might play a certain role in MDR of gastric cancer.

Clusterin knockdown using the antisense oligonucleotide OGX-011 re-sensitizes docetaxel-refractory prostate cancer PC-3 cells to chemotherapy

OBJECTIVES

To characterize changes in secretory clusterin (sCLU) expression in prostate cancer cells after treatment with docetaxel and to determine whether sCLU knockdown can re-introduce chemosensitivity in a docetaxel-resistant, androgen-independent human prostate cancer model.

PATIENTS AND METHODS

A tissue microarray was constructed for 84 radical prostatectomy (RP) specimens from a multicentre Phase II trial of neoadjuvant combined androgen ablation and docetaxel (CUOG-P01a) and assessed for changes in the expression of the cytoprotective chaperone sCLU. The human prostate cancer cell line PC-3 was repeatedly exposed to docetaxel chemotherapy in vitro, and a docetaxel-resistant cell subline (PC-3dR) was developed and analysed.

RESULTS

sCLU levels were significantly higher in RP specimens treated with neoadjuvant combined androgen ablation and docetaxel than in untreated specimens. Similarly, sCLU expression increased 2.5-fold in the newly developed docetaxel-refractory PC-3dR cell line compared with parental PC-3 cells. There was a dose-dependent and sequence-specific decrease in sCLU levels in PC-3dR cells using OGX-011, an antisense oligonucleotide against human sCLU. OGX-011 and small-interference RNA both chemosensitized PC-3dR cells to docetaxel and mitoxantrone in vitro and apoptotic rates in PC-3dR cells were significantly increased when OGX-011 was combined with docetaxel. In vivo, growth of PC-3dR xenografts in nude mice was synergistically inhibited by OGX-011 combined with paclitaxel or mitoxantrone (by 76% and 44% compared with their mismatch controls, respectively).

CONCLUSION

The present findings indicate that targeted knockdown of sCLU enhances the effects of cytotoxic chemotherapy in docetaxel-refractory cells, and provide preclinical proof of principle for clinical trials testing OGX-011 in second-line chemotherapy regimens for patients with docetaxel-refractory prostate cancer.

Role of xenobiotic efflux transporters in resistance to vincristine

This study characterized interactions between efflux transporters (P-glycoprotein (MDR1) and multidrug resistance associated proteins (MRPs1-3)) and vincristine (VCR), using cell lines with differential transporter expression, and studied effects of P-glycoprotein inhibition on VCR transport and toxicity. Caco2 (express MDR1, MRPs 1-3), LS174T (express MDR1, MRPs 1, 3), and A549 (express MRPs 1-3) cells were used. To study VCR transport (effective permeability, P(eff)), VCR (1-500 nM) was added to the donor chambers of permeable supports containing Caco2 monolayers, and receiving chamber concentrations were measured. Cytotoxicity experiments were conducted with escalating concentrations of VCR in all cell lines. To determine the contribution of MDR1, experiments were also conducted with LY335979, a specific MDR1 inhibitor. VCR P(eff) was 2 x 10(-6)cm/s in Caco2 cells. LY335979 increased P(eff) in a dose dependent manner (up to 7-fold with 1 microM LY335979) in Caco2 cells. Caco2 and LS174T cell viability decreased significantly when co-incubated with both VCR and LY335979 (1 microM) (P<0.05), however this was not observed in A549 cells. In summary, MDR1 plays an important role in VCR efflux; MDR1 inhibition increased VCR P(eff) in Caco2 cells, and increased VCR cytotoxicity in Caco2 and LS174T cells (both express MDR1), but not A549 cells (minimal MDR1 expression). Inhibition of MDR1 may be a viable strategy to overcome VCR resistance in tumors expressing MDR1, however the presence of other efflux transporters should also be considered, as this will influence the success of such strategies.

Apoptotic pathways in tumor progression and therapy

Apoptosis is a cell suicide program that plays a critical role in development and tissue homeostasis. The ability of cancer cells to evade this programmed cell death (PCD) is a major characteristic that enables their uncontrolled growth. The efficiency of chemotherapy in killing such cells depends on the successful induction of apoptosis, since defects in apoptosis signaling are a major cause of drug resistance. Over the past decades, much progress has been made in our understanding of apoptotic signaling pathways and their dysregulation in cancer progression and therapy. These advances have provided new molecular targets for proapoptotic cancer therapies that have recently been used in drug development. While most of those therapies are still at the preclinical stage, some of them have shown much promise in the clinic. Here, we review our current knowledge of apoptosis regulation in cancer progression and therapy, as well as the new molecular targeted molecules that are being developed to reinstate cancer cell death.

DNA damage in peripheral blood lymphocytes in patients during combined chemotherapy for breast cancer

Combined chemotherapy is used for the treatment of a number of malignancies such as breast cancer. The target of these antineoplastic agents is nuclear DNA, although it is not restricted to malignant cells. The aim of the present study was to assess DNA damage in peripheral blood lymphocytes (PBLs) of breast cancer patients subjected to combined adjuvant chemotherapy (5-fluorouracil, epirubicin and cyclophosphamide, FEC), using a modified comet assay to detect DNA single-strand breaks (SSB) and double-strand breaks (DSB). Forty-one female patients with advanced breast cancer before and after chemotherapy and 60 healthy females participated in the study. Alkaline and neutral comet assays were performed in PBLs according to a standard protocol, and DNA tail moment was measured by a computer-based image analysis system. Breast cancer patients before treatment had higher increased background levels of SSB and DSB as compared to healthy women. During treatment, a significant increase in DNA damage was observed after the 2nd cycle, which persisted until the end of treatment. Eighty days after the end of treatment the percentage of PBLs with SSB and DSB remained elevated, but the magnitude of DNA damage (tail moment) returned to baseline levels. There was no correlation between PBL DNA damage and response to chemotherapy. DNA-SSB and DSB in PBLs are present in cancer patients before treatment and increase significantly after combined chemotherapy. No correlation with response to adjuvant chemotherapy was found. Biomonitoring DNA damage in PBLs of cancer patients could help prevent secondary effects and the potential risks of developing secondary cancers.

Inhibition of ABC transporters abolishes antimony resistance in Leishmania Infection

The emergence of antimony (Sb) resistance has jeopardized the treatment of visceral leishmaniasis in various countries. Previous studies have considered the part played by leishmanial parasites in antimony resistance, but the involvement of host factors in the clinical scenario remained to be investigated. Here we show that unlike infection with Sb-sensitive (Sbs) Leishmania donovani, infection with Sb-resistant (Sb r) L. donovani induces the upregulation of multidrug resistance-associated protein 1 (MRP1) and permeability glycoprotein (P-gp) in host cells, resulting in a nonaccumulation of intracellular Sb following treatment with sodium antimony gluconate (SAG) favoring parasite replication. The inhibition of MRP1 and P-gp with resistance-modifying agents such as lovastatin allows Sb accumulation and parasite killing within macrophages and offers protection in an animal model in which infection with Sb r L. donovani is otherwise lethal. The occurrence of a similar scenario in clinical cases is supported by the findings that unlike monocytes from SAG-sensitive kala-azar (KA) patients, monocytes from SAG-unresponsive KA patients overexpress P-gp and MRP1 and fail to accumulate Sb following in vitro SAG treatment unless pretreated with inhibitors of ABC transporters. Thus, the expression status of MRP1 and P-gp in blood monocytes may be used as a diagnostic marker for Sb resistance and the treatment strategy can be designed accordingly. Our results also indicate that lovastatin, which can inhibit both P-gp and MRP1, might be beneficial for reverting Sb resistance in leishmaniasis as well as drug resistance in other clinical situations, including cancer.

Effects of propolis extract on sensitivity to chemotherapeutic agents in HeLa and resistant sublines

The effects of a propolis extract obtained by supercritical fluid extraction on sensitivity to chemotherapeutic agents were examined in HeLa cells and resistant sublines thereof. In addition, the actions of propolis and caffeic acid phenethyl ester (CAPE), a constituent of propolis, on the multidrug efflux transporter P-glycoprotein/MDR1, were evaluated in paclitaxel-resistant HeLa/TXL cells (MDR1-overexpressing cells). In HeLa cells, the sensitivity to paclitaxel and doxorubicin, substrates of MDR1, was unchanged in the presence of propolis. In HeLa/TXL cells, propolis increased sensitivity to these MDR1 substrates. The accumulation of Rhodamine123, also a substrate for MDR1, by HeLa/TXL cells increased in the presence of 50 microg/mL, but not 10 microg/mL, of the extract. However, the growth inhibition of HeLa/TXL cells by paclitaxel was not changed by CAPE, although the accumulation of Rhodamine123 increased significantly in the presence of 100 microm, but not 1 nM or 1 microm, CAPE. Collectively, the extract was suggested to inhibit the function of MDR1 and to increase the sensitivity to MDR1 substrates in HeLa/TXL cells, effects likely to be caused by constituents other than CAPE.

Effect of betulinic acid on anticancer drug-resistant colon cancer cells

Primary or acquired resistance of tumours to established chemotherapeutic regimens is a major concern in oncology. Attempts to improve the survival of cancer patients largely depend on strategies to prevent tumour cell resistance. 5-Fluorouracil (5-FU)-based chemotherapy with a combination of other drugs such as irinotecan (IRT) and oxaliplatin (OXT) has been reported to be effective, even though an optimal regimen has yet to be defined due to the relatively high toxicity of the procedure. The aim of this study was to examine the effect of betulinic acid (BetA) as a chemosensitizer for anticancer drug treatment in chemoresistant colon cancer cell lines. A chemoresistant cell line to 5-fluorouracil (SNU-C5/5FU-R), irinotecan (SNU-C5/IRT-R) and oxaliplatin (SNU-C5/OXT-R) treatment were derived from the wild-type colon adenocarcinoma cell line (SNU-C5/WT). The effect of BetA or a combination of anticancer drugs and BetA on the multidrug resistance-related genes, caspases, Bcl-2, Bad and cell death in the SNU-C5/WT and SNU-C5/R cell lines was analysed. BetA alone was an effective chemotherapeutic drug for the SNU-C5/WT, SNU-C5/5FU-R and SNU-C5/OXT-R cells. The combination of BetA with IRT or OXT was effective against SNU-C5/5FU-R cells, and the combination of BetA with 5-fluorouracil, IRT or OXT was effective against SNU-C5/OXT-R cells. BetA induced cancer cell death by apoptosis through the mitochondrial pathway. These findings indicate that the use of BetA as a chemosensitizer may be a new strategy to enhance the efficacy of chemotherapy. However, further studies will be needed for confirmation.

Estrogen receptor alpha mediates breast cancer cell resistance to paclitaxel through inhibition of apoptotic cell death

Estrogen receptors (ER) are expressed in approximately 65% of human breast cancer. Cumulative data from clinical trials and retrospective analyses suggest that some chemotherapeutic agents may be less effective in patients with ER-positive (ER+) tumors than those with ER-negative (ER-) tumors. Paclitaxel is an active agent used in breast cancer chemotherapy. To investigate the possible influence of ER on the therapeutic efficacy of paclitaxel and its underlying mechanism, we established several isogenic ER+ cell lines by stable transfection of ERalpha expression vectors into ER- breast cancer BCap37 cells. We showed that 17-beta estradiol significantly reduces the overall cytotoxicity of paclitaxel in BCap37-expressing ERalpha but has no influence on the ER- parental cells. Further analyses indicate that expression of ERalpha in BCap37 cells mainly interferes with paclitaxel-induced apoptotic cell death, without affecting paclitaxel-induced microtubule bundling and mitotic arrest. Moreover, we found that the addition of ICI 182,780 (Fulvestrant), a selective ER down-regulator, could completely reverse the resistance of ER+ BCap37 cells to paclitaxel. These findings showed that ERalpha-mediated breast tumor cell resistance to paclitaxel was through selective inhibition of paclitaxel-induced tumor cell apoptosis. Additionally, the combination of ICI 182,780 also sensitizes MCF-7 and T47D cell lines to the treatment of paclitaxel, which further confirmed the correlation between ERalpha and drug resistance in ER+ tumor cells. The results obtained from this study provide useful information for understanding ER-mediated resistance to paclitaxel and possibly other antineoplastic agents.

Reversal of tumor resistance to apoptotic stimuli by alteration of membrane fluidity: therapeutic implications

In recent years, significant development and improvement have been observed in the treatment of cancer; however, relapses and recurrences occur frequently and there have not been any current therapies to treat such cancers. Cancers resistant to conventional therapies develop several mechanisms to escape death-inducing stimuli. A poorly understood mechanism is the involvement of the cancer cell plasma membrane composition and architecture and their involvement in regulating drug-inducing stimuli leading to cell death. Although the basic structure of the biological membrane was established 80 years ago, study of the physical properties of lipid bilayers still provides significant information regarding membrane organization and dynamics. Membrane fluidity is probably the most important physicochemical property of cell membranes. Alterations of membrane fluidity can seriously affect functional properties of the cell and induction of apoptotic pathways resulting in cell death. The role of membrane fluidity in the apoptotic process is clearly exemplified as it is seriously disrupted as a result of cell injury. The molecular signaling pathways leading to apoptosis are currently promising areas of research investigation and lead to unravel the underlying molecular mechanisms of tumor cells resistance to apoptotic stimuli and hence the development of new effective therapeutic agents. Recent findings indicate that most anticancer agents induce apoptosis, directly or indirectly, through alterations of tumor cell membrane fluidity. The present chapter summarizes the relationship between alterations of tumor cell membrane fluidity and tumor cell response to apoptotic-inducing stimuli. Several potential therapeutic applications directed at tumor cell membrane fluidity are proposed.

ABC transporter expression in hematopoietic stem cells and the role in AML drug resistance

ATP-binding cassette (ABC) transporters are known to play an important role in human physiology, toxicology, pharmacology, and numerous disorders including acute myeloid leukemia (AML). In AML only a few cells have properties allowing for ongoing proliferation and for expansion of this malignant disorder. These very primitive cells, referred to as leukemic stem cells, reside mostly in a quiescent cell cycle state. These cells have the capacity of self-renewal and are likely characterized by a high expression of a number of ABC transporters. In addition, over-expression of certain ABC transporters in leukemic cells has been associated with poor treatment outcome in AML patients. Therefore, to be able to improve diagnostics and therapies for AML patients, it may be important to better characterize this quiescent stem cell population. Particularly knowledge of the biology of highly expressed ABC transporters in these primitive leukemic cells might provide new insights to improve therapeutic options. This review provides an overview about ABC transporters and AML in general and particularly of the ABC transporters involved in multidrug resistance and cholesterol metabolism in primitive normal and leukemic cells.

Overcoming drug-resistant cancer by a newly developed copper chelate through host-protective cytokine-mediated apoptosis

PURPOSE

Previously, we have synthesized and characterized a novel Cu(II) complex, copper N-(2-hydroxy acetophenone) glycinate (CuNG). Herein, we have determined the efficacy of CuNG in overcoming multidrug-resistant cancer using drug-resistant murine and human cancer cell lines.

EXPERIMENTAL DESIGN

Action of CuNG following single i.m. administration (5 mg/kg body weight) was tested in vivo on doxorubicin-resistant Ehrlich ascites carcinoma (EAC/Dox)-bearing mice and doxorubicin-resistant sarcoma 180-bearing mice. Tumor size, ascitic load, and survival rates were monitored at regular intervals. Apoptosis of cancer cells was determined by cell cycle analysis, confocal microscopy, Annexin V binding, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay ex vivo. IFN-gamma and tumor necrosis factor-alpha were assayed in the culture supernatants of in vivo and in vitro CuNG-treated splenic mononuclear cells from EAC/Dox-bearing mice and their apoptogenic effect was determined. Source of IFN-gamma and changes in number of T regulatory marker-bearing cells in the tumor site following CuNG treatment were investigated by flow cytometry. Supernatants of in vitro CuNG-treated cultures of peripheral blood mononuclear cells from different drug-insensitive cancer patients were tested for presence of the apoptogenic cytokine IFN-gamma and its involvement in induction of apoptosis of doxorubicin-resistant CEM/ADR5000 cells.

RESULTS

CuNG treatment could resolve drug-resistant cancers through induction of apoptogenic cytokines, such as IFN-gamma and/or tumor necrosis factor-alpha, from splenic mononuclear cells or patient peripheral blood mononuclear cells and reduce the number of T regulatory marker-bearing cells while increase infiltration of IFN-gamma-producing T cells in the ascetic tumor site.

CONCLUSION

Our results show the potential usefulness of CuNG in immunotherapy of drug-resistant cancers irrespective of multidrug resistance phenotype.

Reversal of multidrug resistance in gastric cancer cell line by Ss-A/Ro ribonucleoprotein 60-ku subunit antisense nucleic acid

AIM: To investigate the possible function of Ro 60 antisense nucleic acid in multidrug resistant cell line of gastric cancer.

METHODS: Ro 60 antisense eukaryotic expression vector was constructed using DNA recombination technique, then transfected into SGC7901-VCR by Lipofectamine^TM2000. Drug sensitivity assay was performed using MTT assay, and IC₅₀ values of gastric cancer cells to chemotherapy drugs were calculated. The intracellular accumulation of adriamycin in gastric cancer cells was measured using fluorescence-activated cell sorting.

RESULTS: The expression level of Ro 60 in SGC7901-VCR cells was decreased after transfection with antisense genes. In vitro drug sensitivity assay show that SGC7901-VCR cells transfected with Ro 60 antisense genes showed significantly increased sensitivity to vincristine (IC₅₀: 7.66 ± 0.45 mg/L vs 19.56 ± 0.38, 17.48 ± 0.85 mg/L, P < 0.01), mitomycin (IC₅₀: 0.84 ± 0.03 mg/L vs 1.62 ± 0.06, 1.80 ± 0.03 mg/L, P < 0.01), cisplatin (IC₅₀: 0.51 ± 0.03 mg/L vs 0.87 ± 0.03, 0.88 ± 0.03 mg/L, P < 0.01) and adriamycin (IC₅₀: 0.22 ± 0.01 mg/L vs 0.52 ± 0.02, 0.43 ± 0.03 mg/L, P < 0.01), as compared with SGC7901-VCR and SGC7901-VCR-pcDNA3.1 cells. As showed by flow cytometry, the intracellular accumulation of adriamycin in the cells transfected with Ro 60 antisense gene was markedly increased in comparison with that in SGC7901-VCR or SGC7901-VCR-pcDNA3.1 cells (51.94 ± 1.26 mg/L vs 36.27 ± 0.98, 37.01 ± 0.91 mg/L, P < 0.01).

CONCLUSION: After transfected into multidrug resistant cell line of gastric cancer, Ro 60 antisense nucleic acid can inhibit the multidrug resistant phenotype of gastric cancer.

Flavanone metabolism in healthy and tumor-bearing rats

Flavanones, the main polyphenols of citrus fruits, are thought to contribute to the protective effects of these fruits against cardiovascular diseases and cancer. The metabolism of naringin (naringenin 7-O-neohesperidoside) is studied here in healthy (sham-operated, ShO) and tumor-bearing (TuB) rats. The tumor was induced by implanting Yoshida's sarcoma in hindlimb. Both groups received for 7 days a semi-synthetic diet containing 0.5% naringin in per feeding conditions. Flavanones were analyzed in plasma, liver, kidney and urine by tandem mass spectrometry. Naringenin conjugates (essentially glucuronides) accounted for up to 98% of the total flavanones in plasma. Low amounts of hesperetin (4'-O-methyl naringénine) and isosakuranetin (3'-hydroxy-4'-O-methylnaringenin) were also detected in all biological samples and accounted for 2% of the total flavanones in plasma. They were largely present as aglycones. The in vivo hydroxylation of flavanones is described here for the first time. Total concentrations of naringenin metabolites reached 17.3+/-2.7 microM in plasma 6 hours after the beginning of the meal in healthy rats and only 10.6+/-1.3 microM in TuB rats. The nature of metabolites was similar in both healthy and TuB rats and in plasma, tissues and urine. The lower concentration of flavanones in the TuB rats suggests that disease and more particularly cancer, may affect the bioavailability of flavonoids.

Preparation of HCT-8/5-fluorouracil multidrug resistant cell line and detection of P-glycoprotein

AIM: To develop HCT-8/5-fluorouracil multidrug resistant cell line and explore the mechanism its drug resistance.

METHODS: High concentration of 5-FU was used in the beginning to induce drug resistance of HCT-8 cell line, and thereafter, the concentration of 5-FU was increased in gradient. About 7 mo later, the cells could stably grow in 2.0 mg/L 5-FU, which was named HCT-8/5-FU multidrug resistant cell line. The resistant index of HCT-8/5-FU cells to 5-FU, adriamycin (ADM), and cisplatin (DDP) was examined with MTT assay, and growth curve was drawn. The morphological changes were observed by both light and electron microscopy. The function of P-glycoprotein (P-gp) was detected by flow cytometry using rhodamine staining.

RESULTS: The resistant index of HCT-8/5-FU cells to 5-FU is 16.6, and a cross-resistance to ADM and DDP was also noticed. In comparison with that of the parental cells, the growth rate of HCT-8/5-FU cells did not changed significantly, but the morphology of the cells was remarkably changed. Irregular nucleus, double nucleus and polymorphic nucleus appeared in HCT-8/5-FU cells, and the cells shaped as polygon-like and leptosomatic. The numbers of mitochondria, endoplasmic reticulum and lysosome were increased, and over-expression of P-gp was observed in HCT-8/5-FU cells.

CONCLUSION: HCT-8/5-FU multidrug resistant cell line is successfully developed. The drug-resistance mechanism of HCT-8/5-FU cell line may be related to the over-expression of P-gp.