Expression of multidrug resistance-associated protein (MRP), MDR1 and DNA topoisomerase II in human multidrug-resistant bladder cancer cell lines

The Reversal Effect and Its Mechanisms of Tetramethylpyrazine on Multidrug Resistance in Human Bladder Cancer

Chemotherapy is an important strategy for the treatment of bladder cancer. However, the main problem limiting the success of chemotherapy is the development of multidrug resistance (MDR). To improve the management of bladder cancer, it is an urgent matter to search for strategies to reverse MDR. We chose three kinds of herbal medicines including ginsenoside Rh2, (-)-Epigallocatechin gallate (EGCG) and Tetramethylpyrazine (TMP) to detect their effects on bladder cancer. Reversal effects of these three herbal medicines for drug resistance in adriamycin (ADM)-resistant Pumc-91 cells (Pumc-91/ADM) were assessed by Cell Counting Kit-8 (CCK-8) cell proliferation assay system. The mechanisms of reversal effect for TMP were explored in Pumc-91/ADM and T24/DDP cells. After Pumc-91/ADM and T24/DDP cells were treated with TMP, cell cycle distribution analysis was performed by flow cytometry. The expression of MRP1, GST, BCL-2, LRP and TOPO-II was evaluated using quantitative real-time polymerase chain reaction (qRT-PCR), immunefluorescence assay and western blot. It was observed that TMP was capable of enhancing the cytotoxicity of anticancer agents on Pumc-91/ADM cells in response to ADM, however Rh2 and EGCG were unable to. The reversal effect of TMP was also demonstrated in T24/DDP cells. Moreover, the treatment with TMP in Pumc-91/ADM and T24/DDP cells led to an increased of G1 phase accompanied with a concomitant decrease of cell numbers in S phase. Compared to the control group, an obvious decrease of MRP1, GST, BCL-2 and an increase of TOPO-II were shown in TMP groups with a dose-dependency in mRNA and protein levels. However, there was no difference on LRP expression between TMP groups and the control group. TMP could effectively reverse MDR of Pumc-91/ADM and T24/DDP cells and its mechanisms might be correlated with the alteration of MRP1, GST, BCL-2 and TOPO-II. TMP might be a potential candidate for reversing drug resistance in bladder cancer chemotherapy.

DAB2IP regulates the chemoresistance to pirarubicin and tumor recurrence of non-muscle invasive bladder cancer through STAT3/Twist1/P-glycoprotein signaling

There is a high frequency of tumor recurrence in non-muscle invasive bladder cancer (NMIBC) after transurethral resection and postoperative intravesical chemotherapy, however, the molecular mechanisms leading to the chemoresistance and tumor re-growth remain largely unknown. In this study, we observed a significant decrease of DAB2IP expression in high-grade and recurrent NMIBC specimens, which was negatively correlated with Twist1 expression and predicted a lower recurrence-free survival of patients. Mechanistically, DAB2IP could inhibit the phosphorylation and transactivation of STAT3, and then subsequently suppress the expression of Twist1 and its target gene P-glycoprotein, both of which were crucial for the pirarubicin chemoresistance and tumor re-growth of bladder cancer cells. Overall, this study reveals a new promising biomarker modulating the chemoresistance and tumor recurrence of NMIBC after bladder preservation surgery.

The interaction of celecoxib with MDR transporters enhances the activity of mitomycin C in a bladder cancer cell line

BACKGROUND

An in vitro model was developed to understand if celecoxib could synergize with Mitomycin C (MMC), commonly used for the prevention of non-muscle invasive bladder cancer recurrence, and eventually elucidate if the mechanism of interaction involves multi drug resistance (MDR) transporters.

METHODS

UMUC-3, a non COX-2 expressing bladder cancer cell line, and UMUC-3-CX, a COX-2 overexpressing transfectant, as well as 5637, a COX-2 overexpressing cell line, and 5637si-CX, a non COX-2 expressing silenced 5637 cell line, were used in the present study. The expression of COX-2 and MDR pumps (P-gp, MDR-1 and BCRP) was explored through western blot. The anti-proliferative effect of celecoxib and MMC was studied with MTT test. Three biological permeability assays (Drug Transport Experiment, Substrate Transporter Inhibition, and ATP cell depletion) were combined to study the interaction between MDR transporters and celecoxib. Finally, the ability of celecoxib to restore MMC cell accumulation was investigated.

RESULTS

The anti-proliferative effect of celecoxib and MMC were investigated alone and in co-administration, in UMUC-3, UMUC-3-CX, 5637 and 5637si-CX cells. When administered alone, the effect of MMC was 8-fold greater in UMUC-3. However, co-administration of 1 μM, 5 μM, and 10 μM celecoxib and MMC caused a 2,3-fold cytotoxicity increase in UMUC-3-CX cell only. MMC cytotoxicity was not affected by celecoxib co-administration either in 5637, or in 5637si-CX cells. As a result of all finding from the permeability experiments, celecoxib was classified as P-gp unambiguous substrate: celecoxib is transported by MDR pumps and interferes with the efflux of MMC. Importantly, among all transporters, BCRP was only overexpressed in UMUC-3-CX cells, but not in 5637 and 5637si-CX.

CONCLUSIONS

The UMUC-3-CX cell line resembles a more aggressive phenotype with a lower response to MMC compared to the wt counterpart. However, the administration of celecoxib in combination to MMC causes a significant and dose dependent gain of the anti-proliferative activity. This finding may be the result of a direct interaction between celecoxib and MDR transporters. Indeed, BCRP is overexpressed in UMUC-3-CX, but not in UMUC-3, 5637, and 5637si-CX, in which celecoxib is ineffective.

Identification of proteins differentially expressed in adriamycin-resistant (pumc-91/ADM) and parental (pumc-91) human bladder cancer cell lines by proteome analysis

PURPOSE

Resistance to chemotherapy drugs remains a difficult problem in bladder cancer treatment. Protein expression is an important factor underlying multidrug resistance (MDR) in bladder cancer. The aim of the study was to explore differentially expressed proteins responsible for MDR between an adriamycin-resistant human bladder cancer cell line (pumc-91/ADM) and its parental cell line (pumc-91).

METHODS

Two-dimensional gel electrophoresis (2-DE) combining image analysis was used to screen the differentially expressed protein spots between the pumc-91/ADM and pumc-91 cell lines. Then, the protein spots were identified using MALDI-TOF/TOF mass spectrometry. Among the identified proteins, annexin A2 (ANXA2) and nucleophosmin (NPM1) were then further verified using RT-PCR and Western blot analysis.

RESULTS

A total of 30 proteins, including 19 up-regulated and 11 down-regulated proteins, were successfully identified in pumc-91/ADM. According to their different functions, these 30 proteins were classified into 12 categories. Annexin A2 (ANXA2) and nucleophosmin (NPM1) were up-regulated in pumc-91/ADM compared with pumc-91.

CONCLUSION

The proteins identified may have an important clinical significance in MDR, and ANXA2 and NPM1 may take part in mechanism of MDR in bladder cancer.

Molecular analysis of the multidrug transporter, P-glycoprotein

Inherent or acquired resistance of tumor cells to cytotoxic drugs represents a major limitation to the successful chemotherapeutic treatment of cancer. During the past three decades dramatic progress has been made in the understanding of the molecular basis of this phenomenon. Analyses of drug-selected tumor cells which exhibit simultaneous resistance to structurally unrelated anti-cancer drugs have led to the discovery of the human MDR1 gene product, P-glycoprotein, as one of the mechanisms responsible for multidrug resistance. Overexpression of this 170 kDa N-glycosylated plasma membrane protein in mammalian cells has been associated with ATP-dependent reduced drug accumulation, suggesting that P-glycoprotein may act as an energy-dependent drug efflux pump. P-glycoprotein consists of two highly homologous halves each of which contains a transmembrane domain and an ATP binding fold. This overall architecture is characteristic for members of the ATP-binding cassette or ABC superfamily of transporters. Cell biological, molecular genetic and biochemical approaches have been used for structure-function studies of P-glycoprotein and analysis of its mechanism of action. This review summarizes the current status of knowledge on the domain organization, topology and higher order structure of P-glycoprotein, the location of drug- and ATP binding sites within P-glycoprotein, its ATPase and drug transport activities, its possible functions as an ion channel, ATP channel and lipid transporter, its potential role in cholesterol biosynthesis, and the effects of phosphorylation on P-glycoprotein activity.

Cytokine-mediated reversal of multidrug resistance

The occurrence of the multidrug resistance phenotype still represents a limiting factor for successful cancer chemotherapy. Numerous efforts have been made to develop strategies for reversal and/or modulation of this major therapy obstacle through targeting at different levels of intervention. The phenomenon of MDR is often associated with overexpression of resistance-associated genes. Since the classical type of MDR in human cancers is mainly mediated by the P-glycoprotein encoded by the multidrug resistance gene 1, mdr1, the majority of reversal approaches target the expression and/or function of the mdr1 gene/P-glycoprotein. Due to the fact that the multidrug phenotype always represents the net effect of a panel of resistance-associated genes/gene products, other resistance genes, e.g. those encoding the multidrug resistance-associated protein MRP or the lung resistance protein LRP, were included in the studies. Cytokines such as tumor necrosis factor alpha and interleukin-2 have been shown to modulate the MDR phenotype in different experimental settings in vitro and in vivo. Several studies have been performed to evaluate their potential as chemosensitizers of tumor cells in the context of a combined application of MDR-associated anticancer drugs like doxorubicin and vincristine with cytokines. Moreover, the capability of cytokines to modulate the expression of MDR-associated genes was demonstrated, either by external addition or by transduction of the respective cytokine gene. Knowledge of the combination effects of cytokines and cytostatics and its link to their MDR-modulating capacity may contribute to a more efficient and to a more individualized immuno-chemotherapy of human malignancies.

Twist confers chemoresistance to anthracyclines in bladder cancer through upregulating P-glycoprotein

BACKGROUND

The membrane transporter P-glycoprotein (P-gp) was found to mediate chemoresistance, which is one of the obstacles to effective chemotherapy in several types of human cancer. The transcription factor Twist, which has been reported to participate in cancer invasion and metastasis, also plays a vital role in the progression of chemoresistance. However, the effect of Twist on P-gp-related chemoresistance remains dubious.

METHODS AND RESULTS

We found that Twist can regulate the expression of P-gp and then confer resistance to anthracycline drugs in human bladder cancer cells. Firstly, Twist was found to be coexpressed with P-gp in human bladder cancer cells and tissues, which were associated with enhanced chemoresistance to anthracycline drugs. Secondly, knockdown of Twist by specific siRNA treatment significantly sensitized bladder cancer cells to anthracycline drugs via inhibiting P-gp expression. Bladder cancer cells that survived transient exposure to anthracycline drugs showed higher levels of P-gp expression and more nuclear localization of Twist than untreated cells.

CONCLUSION

We report a novel mechanism of anthracycline chemoresistance in bladder cancer in which activated Twist mediates P-gp expression in addition to its antiapoptotic roles. Therapeutic strategies targeting Twist may improve the management of recurrent bladder cancer after chemotherapy.

Expression analysis of TOP2A, MSH2 and MLH1 genes in MCF7 cells at different levels of etoposide resistance

PURPOSE

Development of resistance against anti-cancer drugs is one of the major obstacles of chemotherapy in the treatment of cancer. Etoposide is a topoisomerase II alpha (TOP2A) inhibitor, which is used in the treatment of breast cancer. Alterations in the expression of drug targets or DNA repair genes are among the important resistance mechanisms against TOP2A inhibitors. In this study, expression changes in TOP2A gene and two important mismatch repair (MMR) genes MSH2 and MLH1 were examined in order to understand the relationship between differential expression of these genes and drug resistance against etoposide.

METHODS

Resistant cell lines were developed from parental MCF7 cell line by stepwise selection in increasing doses of etoposide. Total RNA was isolated from parental and resistant cell lines by using TriReagent. Expression levels of TOP2A, MSH2 and MLH1 were analysed by reverse transcription quantitative polymerase chain reaction (RT-qPCR). Statistical analyses were performed by one way ANOVA.

RESULTS

Etoposide resistant sublines MCF7/1000E, MCF7/1250E and MCF7/2000E were approximately 2, 3 and 4 fold resistant relative to parental MCF7/S cells, respectively. TOP2A, MSH2 and MLH1 expressions decreased in etoposide resistant sublines relative to MCF7/S cells. Expression levels of TOP2A and MLH1 in resistant sublines differed between 10-95 and 18-58 percent of the expression levels in the parental cells, respectively. MSH2 expression levels were decreased 18-82 percent in resistant cells. A transient 15 percent increase in the expression of this gene was observed in subline MCF7/1250E.

CONCLUSIONS

Decrease in the expression levels of TOP2A, MSH2 and MLH1 may play significant roles in the development of chemotherapeutic resistance to etoposide in breast cancer. These genes may be considered for further development of new strategies to overcome resistance against topoisomerase II inhibitors.

Intravesical administration of pirarubicin against superficial bladder cancer: Relationship between tumor tissue concentration and exposure time in the bladder or therapeutic effect

The aim of this study was to investigate the relationship between tissue concentrations and exposure times or therapeutic effect of an anthracycline anticancer drug, pirarubicin, in bladder cancer tissue after single intravesical administration against superficial bladder cancer. The concentrations of pirarubicin in tumor tissues and serum were measured at designated collection times after a single intravesical administration of pirarubicin (30 mg) in 22 patients with superficial bladder cancer. A wide range of concentrations of pirarubicin in bladder cancer tissue was observed (2.3-125 μg/g of tissue), although serum pirarubicin concentrations were not detected in any of the patients. Recurrence of superficial bladder cancer after transurethral resection of the bladder tumor (TUR-BT) was observed in 2 patients (9%). The concentration of pirarubicin in the tumor tissue tended to be higher as the exposure time increased. There was a weak relationship between the pirarubicin tissue concentration and tumor size. However, no significant relationship between tissue pirarubicin concentrations and the prophylactic effect against intravesical recurrence of bladder cancer after TUR-BT was observed. All patients had no adverse events, such as bladder irritation and local toxicity, caused by the treatment with pirarubicin. These findings suggest that prior to single intravesical administration of pirarubicin to patients with superficial bladder cancer the exposure time and tumor size should be considered.

P300/CBP-associated factor regulates Y-box binding protein-1 expression and promotes cancer cell growth, cancer invasion and drug resistance

Twist1 has been proposed to have oncogenic properties. Although Twist1 was reported to interact with p300/CBP-associated factor (PCAF) and to inhibit the functions of PCAF, it remains unclear how PCAF affects the functions of Twist1, cell growth, invasive ability, and cellular sensitivity to anticancer agents. We found that PCAF, Twist1, and Y-box binding protein-1 (YB-1) expressions were elevated in cisplatin- and doxorubicin-resistant cancer cells. Luciferase reporter assays revealed that PCAF manipulation modulated YB-1 transcription in a Twist1-dependent manner. In addition, PCAF regulated the Twist1 intracellular localization and the Twist1 transcriptional activity through its acetylation function to the Twist1. Suppression of PCAF expression reduced YB-1 expression in human urothelial cancer KK47 cells. As a result, the cell growth and invasive ability of KK47 cells was retarded by PCAF knockdown, and PCAF knockdown rendered KK47 cells sensitive to cisplatin and doxorubicin, but not to 5-fluorouracil. The present data suggest that Twist1 and YB-1 as well as PCAF may be promising molecular therapeutic targets.

Foxo3a expression and acetylation regulate cancer cell growth and sensitivity to cisplatin

Many advanced cancers receive cisplatin-based chemotherapy. However, cisplatin resistance is a major obstacle for cancer chemotherapy. Foxo3a is a member of the Foxo transcription factor family, which modulates the expression of genes involved in DNA damage repair, apoptosis, and other cellular processes. In this study, we found that cisplatin-resistant cells were more sensitive to the anticancer agent mithramycin than their parental cells, and had a decreased level of Foxo3a expression. Foxo3a knockdown increased cell proliferation and resistance to cisplatin. On the other hand, mithramycin stimulated Foxo3a expression through reactive oxygen species production and sensitized cells to cisplatin, which was abolished by Foxo3a knockdown, while the acetylation status of Foxo3a was decreased in response to cisplatin treatment and was lower in cisplatin-resistant cells. Knockdown of Foxo3a-associated acetyltransferase p300 promoted cancer-cell growth and cisplatin resistance. In addition, non-acetylation-mimicking Foxo3a overexpression decreased cancer cell growth and sensitized cells to cisplatin less than wild-type Foxo3a overexpression. The current work may contribute to the evaluation of the therapeutic potential of inducing the Foxo3a pathway and acetylating the Foxo3a transcription factor, and lead to the reevaluation of cancer treatments based on mithramycin.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

Targeted therapies in the management of metastatic bladder cancer

The management of metastatic urothelial carcinoma (UC) of the bladder is a common and complex clinical challenge. Despite the fact that UC is one of the most frequent tumors in the population, long term survival for metastatic disease remains low, and chemotherapy is curative for only a small minority of patients. UC is genetically heterogeneous, and it is surrounded by a complex tissue microenvironment. The problems of clinical practice in the field of metastatic bladder cancer have begun to stimulate translational research. Advances in the understanding of the molecular biology of urothelial cancer continue to contribute to the identification of molecular pathways upon which new therapeutic approaches can be targeted. New agents and strategies have recently been developed which can direct the most appropriate choice of treatment for advanced disease. A review of literature published on the targeted therapy for metastatic bladder cancer is presented, focusing on the molecular pathways shut down by the new therapeutic agents.

Multidrug resistance protein 1 is not associated to detergent-resistant membranes

Multidrug resistance protein 1 (MRP1) is a member of the ATP-binding cassette superfamily. Using the energy provided by ATP hydrolysis, it transports a broad spectrum of substrates across the plasma membrane, including hormones, leukotriene C(4), bile salts, and anti-cancer drugs. Recent works have suggested that P-glycoprotein is associated to cholesterol and sphingolipid-rich membrane microdomains and that cholesterol upregulates its ATPase and drug transport activities. Confocal microscopy experiments and Triton X-100 extraction of detergent-resistant membranes provide evidence that MRP1 is not located in raft-like structures and that its activity is downregulated by cholesterol. The data are discussed in terms of cholesterol-protein interaction and topology.

Altered phosphorylation of topoisomerase I following overexpression in an ovarian cancer cell line

There is a growing interest regarding the use of camptothecins (CPTs) for the management of ovarian cancer. Since topoisomerase I has been established as a prime target of these drugs in other experimental models, it was important to determine whether sensitivity to CPTs in ovarian cancer cells is also correlated with the cellular level of this enzyme. Despite the 7-fold increase in topoisomerase expression achieved by adenovirus-mediated expression, the sensitivity to a CPT derivative (topotecan), was not improved compared with control cells harboring an endogenous level of the enzyme. This observation is in accordance with the similar level of topoisomerase I activity found in control and overexpressing cells and suggests that these cells may efficiently regulate the enzyme activity. Indeed, topoisomerase I overexpressing cells are characterized by a lack of alkaline phosphatase sensitivity and elimination of the hyperphosphorylated form of the protein. Taken together, these observations strongly suggest that an alteration in the phosphorylation state of topoisomerase I could limit its activity and prevent improvement of CPT response in ovarian cancer cells. In addition, a limited extent of topoisomerase I phosphorylating activity was found in nuclear extract of OVCAR-3 cells. Hence, providing enhancement in topoisomerase I expression may not result in improvement of CPT response in ovarian cancer cells because of an efficient control of the phosphorylation state of the enzyme.

[Cell cycle and apoptosis mechanisms implicated in intravesical chemotherapy resistances in superficial bladder cancer]

It is well documented the effectiveness of intravesical chemotherapy following transurethral resection to prevent recurrences of superficial bladder cancer. But it is also known that efficacy may be limited by tumour cell resistance to one or several of the drugs available for instillation. In addition to the genetically determined unicellular mechanisms classically described in the literature such as glycoprotein P-170 expression (mdr-1), overexpression of Bcl-2 or glutation S-transferase activity, it has been recently shown that multicellular mechanisms may also be involved in drug resistance. Multicellular resistance can only be demonstrated in three-dimensional cultures and fails to be shown in monolayers or cell suspensions. This is explained by the fact that cell-to-cell and cell-to-stroma adhesion limits drug penetration and by the variable susceptibility to cytotoxicity determined by oxygen and tissue proliferation gradients. A better understanding of the molecular mechanisms involved in drug resistance is necessary to increase intravesical chemotherapy effectiveness. Current research includes improving drug penetration, searching resistance reversing agents and developing in vitro chemosensitivity tests to identify drug resistance.

Decrease of P-Glycoprotein Activity in K562/ADR Cells by M?CD and Filipin and Lack of Effect Induced by Cholesterol Oxidase Indicate That This Transporter Is Not Located in Rafts

The effect of low-density membrane domains on function of the plasma membrane transporter P-glycoprotéine (P-gp), involved in multidrug resistance (MDR) phenotype, has been investigated in K562/ADR cells. To this end we reversibly altered the cholesterol content of K562/ADR cells by using methyl-beta-cyclodextrin as a cholesterol chelator and conversely we repleted them through incubation with cholesterol in culture medium. We also used the cholesterol-binding fluorochrome filipin and cholesterol oxidase. Our data show that either cholesterol depletion or complex formation with filipin resulted in a strong decrease of P-gp activity. However, when cells were incubated with cholesterol oxidase that are known to disrupt rafts, no modification of the P-gp activity was observed. In addition, using a free-detergent methodology to separate by ultracentrifugation, "light," "heavy," and "extra heavy" fractions we show that no P-gp is found in the "light" fraction where rafts are usually detected. Altogether, our data strongly suggest that, in this cell line, P-gp is not localized in rafts.

The activity profile of the hexacyclic camptothecin derivative DX-8951f in experimental human colon cancer and ovarian cancer

DX-8951f or exatecan mesylate ((1S,9S)-1-amino-9-ethyl-5-fluoro-2,3-dihydro-9-hydroxy-4-methyl-1H,12H-benzo[de]pyrano[3',4':6,7]indolizino[1,2-b]quinoline-10-13(9H,15H)-dione methanesulfonate dihydrate), is a new water-soluble derivative of camptothecin. We determined the activity of DX-8951f in experimental human colon cancer and ovarian cancer, being tumor types sensitive to camptothecins. With the use of the MTT assay, DX-8951f was more potent than SN-38 in four out of five human colon cancer cell lines and three out of four human ovarian cancer cell lines (P<0.05). DX-8951f was considerably more potent than topotecan in all cell lines tested (P<0.05). Prolonged exposure to DX-8951f resulted in a greater increase in inhibition of cell proliferation as compared to that obtained with SN-38 or topotecan (P<0.05). Overexpression of Pgp, MRP1, and LRP did not affect the in vitro activity of DX-8951f. DX-8951f administered daily x 5 or weekly x 2 resulted in growth inhibition <50% in two human colon cancer xenografts grown s.c. in nude mice. In three human ovarian cancer xenografts, however, >50% growth inhibition was observed at both schedules. In the OVCAR-3 human ovarian cancer model, DX-8951f showed considerably greater activity than topotecan (P<0.01). DX-8951f combined with cisplatin or paclitaxel did not indicate the presence of a pharmacological interaction. In OVCAR-3 xenografts the combination was clearly more effective than DX-8951f alone, as the number of complete remissions increased substantially. In conclusion, this study shows that DX-8951f is highly potent in vitro and highly effective in experimental human ovarian cancer in vivo. Prolonged exposure to DX-8951f in vitro greatly increased the antiproliferative effects, which may be a rationale for testing a continuous infusion schedule in the clinic. Addition of cisplatin or paclitaxel improved the in vivo antitumor effects of DX-8951f.

Real-time RT-PCR for the determination of topoisomerase II mRNA level in leukaemic cells

We developed a real-time RT-PCR assay for the quantification of topoisomerase II (topo II) mRNA level. It was applied on peripheral leukaemic cells from 23 patients with acute myelogenous leukaemia (AML) and 23 with chronic lymphocytic leukaemia (CLL). RNA template dilutions from 0.25 to 25ng per reaction were used as standard curves for topo IIalpha, beta and the internal control 18S rRNA. About 57% (26/46) and 26% (12/46) of the specimens had detectable topo IIbeta and alpha mRNA, respectively. The correlation between these two factors was rho=0.7 and P=0.0001. No relationship between topo IIalpha or beta mRNA level and response to chemotherapy was found in AML patients (n=19 assessable for response). Our method is rapid and convenient for quantification of topo IIalpha and beta mRNA levels, and could be suitable for investigation in a larger population.

Preferential efflux by P-glycoprotein, but not MRP1, of compounds containing a free electron donor amine

Multidrug resistance (MDR) in model systems is known to be conferred by two different integral proteins, the 170-kDa P-glycoprotein (P-gp) and the 190-kDa multidrug resistance-associated protein (MRP1), both of which pump drugs out of MDR cells. The presence of a nitrogen atom, charged at physiological pH, has frequently been considered to be a hallmark of P-gp substrates and inhibitors. The present study was aimed at investigating the role of nitrogen in the ability of the pump to recognise substrate. We measured the kinetics of active efflux of seven new anthracycline derivatives in P-gp-expressing K562/ADR cells and in MRP1-expressing GLC4/ADR cells. Six of these compounds represent analogues of daunorubicin in which the amino sugar nitrogen is bound to an amino- or a nitro-substituted benzyl moiety, the seventh is a doxorubicin derivative in which benzyl group is bound with 4'-oxygen. We found that the compounds with a nitro group on the benzyl ring were poor substrates for P-gp despite the presence of a secondary amine that can be protonated. In contrast, compounds that have a free amino group were very good substrates even though this amine is not protonated in the pH range studied (pK approximately 3). These results show that the nitrogen atom does not interact with P-gp in a charged form but rather as an electron donating group.

Increased expression of multidrug resistance-associated proteins in bladder cancer during clinical course and drug resistance to doxorubicin

Overexpression of the P-glycoprotein/multidrug resistance 1 (MDR1) and multidrug resistance protein 1 (MRP1) gene is closely associated with the clinical outcome of various malignancies, and it is involved in responses to some anticancer chemotherapeutic agents including doxorubicin. Six human MRP subfamily members (MRP2-7) with structural similarities to MRP1 have been identified. Recently, the relationships between MRP2 and MRP3 expression levels of some cancer cells and drug sensitivity to doxorubicin have been reported, but the relationship between the clinical samples and drug sensitivity remains unclear. We determined the expressions of the MDR1, MRP1, MRP2 and MRP3 gene in bladder cancer during the clinical course and sought to learn whether the expression was correlated with drug responses to doxorubicin. Doxorubicin, used in chemotherapeutic treatment including intravesical and systemic chemotherapy, is an important anticancer agent for the treatment of bladder cancer. We used quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for our study, and the sensitivity to doxorubicin in bladder cancer was determined using the in vitro succinate dehydrogenase inhibition test. Using 47 clinical samples of bladder cancer, we confirmed the significant correlation of MDR1, MRP1 and MRP3 mRNA levels with resistance to doxorubicin. We showed that the expression of MDR1, MRP1, MRP2 and MRP3 in recurrent tumors and residual tumors after chemotherapeutic treatment was higher than that in untreated primary tumors. In particular, the MDR1 expression in residual tumors was 5.7-fold higher than that in untreated primary tumors.

Developing therapies for advanced bladder cancer

Chemotherapy is an indispensable measure in the treatment of invasive or metastatic bladder cancer as even if metastases are not clinically apparent, the majority of cases of invasive bladder cancer are accompanied by micrometastases. At present, MVAC (methotrexate, vinblastine, adriamycin, cisplatin) is the gold standard for bladder cancer chemotherapy. There have consequently been many attempts at MVAC dose-intensification as well as many studies of the feasibility of neoadjuvant chemotherapy using MVAC. Unfortunately, the majority of results from these studies have been negative or contradictory. However, a recent large-scale randomised, controlled study yielded more promising results. Evidence has recently emerged which indicates that a useful chemotherapeutic strategy could possibly be devised by adjusting the dose and timing of MVAC. Increasing effort is also being put into the development of new gold standards for bladder cancer chemotherapy based on the use of newly developed antitumour drugs, and a number of candidates have emerged. It is hoped that the future we will see successful establishment of a number of useful regimens as a result of Phase III clinical studies using MVAC as their control regimen. For example, both gemcitabine and the taxanes, in combination with other drugs, are strong candidates for this purpose. The ultimate therapeutic strategy for bladder cancer will be a therapeutic approach which permits conservation of the bladder even when the malignancy is invasive and steady progress is already being made toward this goal, in limited cases, by means of multidisciplinary treatment.

Blockage of IGF-1R signaling sensitizes urinary bladder cancer cells to mitomycin-mediated cytotoxicity

A major problem which is poorly understood in the management of bladder cancer is low sensitivity to chemotherapy and high recurrence after transurethral resection. Insulin-like growth factor 1 receptor (IGF-1R) signaling plays a very important role in progression, invasion and metastasis of bladder cancer cells. In this study, we investigated whether IGF-1R was involved in the growth stimulating activity and drug resistance of bladder cancer cells. The results showed: The mRNAs of IGF-1, IGF-2 and IGF-1R were strongly expressed in serum-free cultured T24 cell line, whereas normal urothelial cells did not express these factors/receptors or only in trace levels; T24 cell responded far better to growth stimulation by IGF-1 than did normal urothelial cells; blockage of IGF1R by antisense oligodeoxynucleotide (ODN) significantly inhibited the growth of T24 cell and enhanced sensitivity and apoptosis of T24 cells to mitomycin (MMC). These results suggested that blockage of IGF-IR signaling might potentially contribute to the treatment of bladder cancer cells which are insensitive to chemotherapy.

Modulation of doxorubicin sensitivity by cyclosporine A in hepatocellular carcinoma cells and their doxorubicin-resistant sublines

BACKGROUND AND AIMS

Cyclosporine A (Cys) and verapamil (Ver) sensitize multidrug-resistant (MDR) cells to various anticancer drugs by interacting with membrane glycoproteins involved in the drug efflux. In the present study, we assessed the effect of Cys on the modulation of doxorubicin (DOR) sensitivity in hepatocellular carcinoma (HCC) cell lines, and their DOR-resistant sublines.

METHODS

The sensitivity to DOR and the chemosensitizing effects of Cys were assessed by using two human HCC cell lines, PLC/PRF/5 and Hep-3B, and their DOR-resistant sublines, PLC/DOR and 3B/DOR. The expression of multidrug resistance 1 (MDR1) and multidrug resistance-associated protein (MRP) mRNA in these cells were detected by using a RT-PCR. The HCC cell lines grown in individual wells of 24-well plates were incubated with DOR that were sequentially diluted in culture medium in combination with 5 micromol/L Cys for 24 h. The cell viability in each well was measured by using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

The mRNA of MDR1 and that of MRP were readily detectable in the HCC cell lines by RT-PCR. When 5 micromol/L Cys was added to the culture, the 50% inhibiting concentration (IC50) of DOR was reduced from 0.93 +/- 0.29 microg/mL to 0.32 +/- 0.10 microg/mL in PLC/PRF/5, and from 0.25 +/- 0.07 microg/mL to 0.09 +/- 0.04 microg/mL in Hep-3B. Furthermore, in the presence of 5 micromol/L Cys, the IC50 of DOR was reduced from 48.63 +/- 17.04 microg/mL to 0.49 +/- 0.14 microg/mL in PLC/DOR, and from 4.60 +/- 1.22 microg/mL to 0.15 +/- 0.06 microg/mL in 3B/DOR. The amounts of PCR products of MDR1 mRNA in PLC/DOR and 3B/DOR were greater than those in PLC/PRF/5 and Hep-3B, respectively.

CONCLUSIONS

In HCC, the amplification of MDR1 mRNA is probably the main mechanism underlying acquired DOR resistance. Cyclosporine is also indicated to be highly active in potentiating the anticancer activity of DOR in HCC cells and their DOR-resistant sublines.

Synthesis and structure--activity analysis of novel dihydropyridine derivatives to overcome multidrug resistance

The structure activity relationships were studied on newly synthesized 1,4-dihydropyridine derivatives possessing a 1-pentyl group at the 4-position, and 3-pyridylpropylester was found to be one of the effective fragments for overcoming P-glycoprotein mediated multidrug-resistance (MDR) in cultured human cancer cells, in vitro. 3-Pyridylpropylester was also found to be one of the effective fragments for increasing the life span of P-glycoprotein overexpressing MDR P388 leukemia-bearing mice, in vivo. All compounds had weak calcium antagonistic activities, but there appeared no relationship between MDR reversing effect and calcium antagonistic activity.

New highly lipophilic camptothecin BNP1350 is an effective drug in experimental human cancer

BNP1350, 7-[(2-trimethylsilyl)ethyl]-20(S)-camptothecin, is a novel semi-synthetic, highly lipophilic, silicon-containing camptothecin and an inhibitor of topoisomerase I. It has been supercomputer engineered for superior oral bioavailability, superior lactone stability, broad anti-tumor activity, increased potency and insensitivity to Pgp/MRP/LRP drug resistance. We determined the efficacy of BNP1350 in experimental human colon cancer and compared its anti-tumor effects with those of CPT-11/SN-38. We also determined a possible influence of Pgp, MRP and LRP on the efficacy of BNP1350. The in vitro anti-proliferative capacity of the compounds using various exposure times was assessed in five colon cancer cell lines and indicated that BNP1350 was similarly effective or slightly more potent than SN-38. Four cell lines of other origin with sublines expressing Pgp, MRP and/or LRP showed that BNP1350 was significantly more effective than SN-38 (p < 0.05) and that the activity of BNP1350 was not reduced in multidrug-resistant cells. For in vivo experiments, BNP1350 was given 1.0 mg/kg i.p. or 1.5 mg/kg p.o. daily x 5 and CPT-11 20 mg/kg i.p. daily x 5 being equitoxic schedules in nude mice bearing s.c. human tumor xenografts. The schedules were studied in colon cancer xenografts COLO320, COLO205 or WiDr as well as in two Pgp-positive xenografts 2780AD and BRO/mdr1.1 and the parental Pgp-negative A2780 ovarian cancer xenografts and BRO melanoma xenografts. Growth inhibition of >50% was obtained for BNP1350 given i.p. in six out of the seven xenografts studied. BNP1350 was similarly effective when given i.p. or p.o. CPT-11 was as effective as BNP1350, except in BRO and BRO/mdr1.1 xenografts. Pgp expression in xenografts in vivo confirmed that there was no negative influence on the efficacy of BNP1350. In conclusion, BNP1350 shows a broad spectrum of activity in experimental human tumors and is a suitable candidate for oral treatment of cancer.

Progress in the management of metastatic bladder cancer

BACKGROUND

Inadequate survival results from single agents in the management of advanced bladder cancer have prompted several trials involving multidrug combinations to increase response rates and survival.

METHODS

Since the development of the MVAC regimen (methotrexate, vinblastine, doxorubicin, and cisplatin) and the CMV regimen (cisplatin, methotrexate, and vinblastine), other regimens have been tested. We evaluate results from regimens that include cisplatin combined with gemcitabine, paclitaxel, or docetaxel, and paclitaxel combined with gemcitabine or carboplatin.

RESULTS

Objective results observed with various new combinations are promising. Objective response (OR) rates of 41%, 59%, and 71% are reported with a regimen of gemcitabine plus cisplatin. Paclitaxel plus cisplatin produced OR rates of 65% and 72%.

CONCLUSIONS

The use of combination cytotoxic chemotherapy regimens in treating patients with metastatic bladder cancer has nearly doubled median survival to 12 months, with a 3-year survival of approximately 20% to 25%. Caution must be exercised in using some of the newer regimens as survival may be inferior compared with the MVAC regimen.

Low-dose twice-daily fractionated X-irradiation of ovarian tumor cells in vitro generates drug-resistant cells overexpressing two multidrug resistance-associated proteins, P-glycoprotein and MRP1

Failure of chemotherapy is frequently observed in patients previously treated with radiotherapy. To establish a cellular model for examining this resistance phenotype a series of mammalian tumor cell lines were exposed in vitro to fractionated X-irradiation and were then shown to express resistance to multiple antitumor drugs, including vincristine, etoposide and cisplatin. In these experiments the radiation was delivered as 10 fractions of 5 Gy (dose resulting in 1 log cell kill) given intermittently over several months. We now report that a comparable multidrug-resistance profile is expressed by human SK-OV-3 human ovarian tumor cells exposed in vitro to low dose (2 Gy) twice-daily fractions of X-rays given for 5 days on two consecutive weeks, essentially mimicking clinical practice, involving an overexpression of two MDR-associated proteins, P-glycoprotein and the multidrug resistance protein 1 (MRP1), with the latter being readily detectable by immunocytochemistry.

Expression of drug resistance-related genes in head and neck squamous cell carcinomas and normal mucosa

We examined the expression levels of mRNA for multidrug resistance 1 (MDR1), multidrug resistance-associated protein (MRP), human canalicular multispecific organic anion transporter (cMOAT), lung resistance-related protein (LRP), topoisomerase IIalpha, beta (Topo IIalpha, beta) and topoisomerase I (Topo I) genes in human head and neck squamous cell carcinoma (HNSCC) specimens and mucosa (HNM) specimens, to elucidate their roles in relation to the biological characteristics and drug resistance in vivo. Fifty-eight samples (45 head and neck carcinomas and 13 head and neck mucosa) obtained during surgical resection or biopsy from 38 patients were analyzed using the quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. MDR1, MRP, LRP, Topo IIalpha, Topo IIbeta, and Topo I gene transcripts were detected in all the samples tested, but cMOAT mRNA was not detected in them. Comparisons of the expression levels in HNSCC with those in HNM showed that the Topo IIalpha gene expression level was higher in HNSCC than in HNM (P=0.0298). Moreover, the Topo IIalpha mRNA level was significantly higher in metastatic lymph node samples of HNSCC than in HNM samples (P=0.0205). There were no significant differences in the six genes' expression levels between samples exposed to platinum drugs and those not exposed to platinum drugs. These results suggest that it may be effective in anticancer therapy to use topoisomerase-targetting drugs against HNSCC, especially metastatic neck tumors, and that the expression of these genes in HNSCC is not associated with platinum drug exposure.

Structural, mechanistic and clinical aspects of MRP1

The cDNA encoding ATP-binding cassette (ABC) multidrug resistance protein MRP1 was originally cloned from a drug-selected lung cancer cell line resistant to multiple natural product chemotherapeutic agents. MRP1 is the founder of a branch of the ABC superfamily whose members (from species as diverse as plants and yeast to mammals) share several distinguishing structural features that may contribute to functional and mechanistic similarities among this subgroup of transport proteins. In addition to its role in resistance to natural product drugs, MRP1 (and related proteins) functions as a primary active transporter of structurally diverse organic anions, many of which are formed by the biotransformation of various endo- and xenobiotics by Phase II conjugating enzymes, such as the glutathione S-transferases. MRP1 is involved in a number of glutathione-related cellular processes. Glutathione also appears to play a key role in MRP1-mediated drug resistance. This article reviews the discovery of MRP1 and its relationships with other ABC superfamily members, and summarizes current knowledge of the structure, transport functions and relevance of this protein to in vitro and clinical multidrug resistance.

Mechanisms of drug resistance in chemotherapy for urogenital carcinoma

Cancer chemotherapy is the principal approach for urogenital cancers. However, the acquisition of resistance to anticancer agents is a critical factor that limits the successful treatment of malignancies. The multidrug resistant (MDR) phenotype has been widely recognized in cancer chemotherapy in urogenital tumors and the mechanisms underlying MDR have also been extensively studied. One of the principle mechanisms in MDR is caused by the overexpression of P-glycoprotein (P-gp), encoded by the multidrug resistance gene (MDR1). It functions as an ATP-dependent active efflux pump of chemotherapeutic agents in human cancer cells. Recently, other drug resistance proteins, including multidrug resistance-associated protein (MRP1) and cMOAT (or MRP2), were also identified from multidrug resistant cells. A functional analysis of MRP1 has shown that MRP1 may have the potential to act as a transporter of glutathione conjugates, which has been known as a central detoxification pathway in anticancer agents. Furthermore, several other resistance-related proteins (e.g. glutathione S-transferase, metallothionein, thioredoxin, topoisomerase I, II, O6-alkylguanine-DNA methyltransferase, etc.) have been found to be up- or down-regulated in resistant cells and these molecules are believed to contribute to the resistant phenotype as well. Based on the molecular characteristics identified in MDR, several experimental and clinical approaches have been studied to overcome MDR. One of these strategies is to reverse MDR by using such P-gp inhibitors as verapamil and cyclosporine A. In this review, we summarize the recent advances in MDR-related molecules and clinical trials to circumvent MDR in urogenital carcinomas.

Selectively induced high MRP gene expression in multidrug-resistant human HL60 leukemia cells

A subclone HL60/DOX was selected from a human leukemic HL60 cell line for resistance to doxorubicin (DOX) by exposure to stepwise increasing concentrations of the drug and coexposure to a potential P-glycoprotein (P-gp) inhibitor, cepharanthine (a biscoclaurine alkaloid). Compared with the parent HL60 cells, the HL60/DOX cells were 13.0-fold more resistant to DOX and showed multidrug-resistant (MDR) phenotype characterized by 4.6-fold, 2.3-fold, and 5.7-fold cross-resistance to vincristine, pirarubicin, and etoposide, respectively, but no cross-resistance to alkylating agent, cisplatin. Immunocytochemical analyses using the specific monoclonal antibody, MRPr1, and quantitative analyses using a competitive reverse transcription-polymerase chain reaction (CRT-PCR) confirmed overexpression of MRP gene products (about 8-fold determined by CRT-PCR) in this resistant clone. The P-gp expression was not detectable by the monoclonal antibody, C219, in the HL60/DOX cells, and that was consistent with extremely low levels of mdr1 mRNA expression determined by CRT-PCR in this clone. Drug accumulation and efflux studies demonstrated the significantly increased efflux rate of DOX compared to the parent HL60 cells. This enhancement of DOX efflux was reversed by the addition of 10 microM verapamil. To investigate the additional underlying mechanisms contributing to MDR phenotype in the HL60/DOX cells, the levels of DNA topoisomerases (Topo) including Topo I, Topo IIalpha, and Topo IIbeta, and gamma-glutamylcystein synthetase (y-GCS) expression were determined using CRT-PCR techniques. Normal expression of each enzyme at the transcriptional level was demonstrated in this resistant clone. Southern blot analysis of the gene organization in the HL60/DOX cells revealed the amplification of MRP gene. These results indicate that alteration of the drug accumulation from enhanced efflux appears to be a major mechanism(s) of MDR phenotype and attributable to high levels of MRP expression in the HL60/DOX cells. Overexpression of MRP in this clone is regulated by the genomic amplification of DNA and increased levels of the MRP mRNA, independently with the normal expression of Topo I, Topo IIalpha, Topo IIbeta, or gamma-GCS.

Using the national cancer institute anticancer drug screen to assess the effect of MRP expression on drug sensitivity profiles

The MRP gene contributes to one form of multidrug resistance. To identify drugs interacting with MRP, we measured MRP mRNA expression by quantitative PCR in 60 cell lines of the National Cancer Institute Anticancer Drug Screen. Expression was detected in all cell lines (highest in lung carcinomas and central nervous system tumors) with a range of 14-fold. A mean graph of MRP mRNA levels was constructed to determine Pearson correlation coefficients (PCCs) with mean graphs of >40,000 compounds using the COMPARE analysis. Only 20 compounds had PCCs of >/=0.500. The PCCs for VP-16, doxorubicin, and vincristine were 0.008, 0.13, and 0.257, respectively. Initially, 36 compounds with PCCs of >/=0.428 were analyzed using two MRP-overexpressing cell lines; low levels of cross-resistance was demonstrated for 23 compounds (1.3-9.4-fold). Twenty-four compounds also were available for further studies. Using a fluorescence activated cell sorter assay to measure competition of calcein efflux from MRP-overexpressing cells, 10 compounds were found to increase calcein retention by >/=2-fold. Ten compounds also were able to reduce ATP-dependent [3H]LTC4 transport into vesicles from MRP-overexpressing cells. These results contrast with previous studies with MDR-1 in which high correlations were found and confirmed for a large number of compounds. Although other assays may be more revealing, in these unselected cell lines, MRP mRNA expression was a poor predictor of drug sensitivity. This raises the possibility that other factors, including conjugating enzymes, glutathione levels, or other transporters, confound the MRP effect.

A mutant yeast topoisomerase II (top2G437S) with differential sensitivity to anticancer drugs in the presence and absence of ATP

To further characterize the mechanistic basis for cellular resistance/hypersensitivity to anticancer drugs, a yeast genetic system was used to select a mutant type II topoisomerase that conferred cellular resistance to CP-115,953, amsacrine, etoposide, and ellipticine. The mutant enzyme contained a single point mutation that converted Gly437 --> Ser (top2G437S). Purified top2G437S displayed wild-type enzymatic activity in the absence of drugs but exhibited two properties that were not predicted by the cellular resistance phenotype. First, in the absence of ATP, it was hypersensitive to all of the drugs examined and hypersensitivity correlated with increased drug affinity. Second, in the presence of ATP, top2G437S lost its hypersensitivity and displayed wild-type drug sensitivity. Since the resistance of yeast harboring top2G437S could not be explained by alterations in enzyme-drug interactions, physiological levels of topoisomerase II were determined. The Gly437 --> Ser mutation reduced the stability of topoisomerase II and decreased the cellular concentration of the enzyme. These findings suggest that the physiological drug resistance phenotype conferred by top2G437S results primarily from its decreased stability. This study highlights the need to analyze both the biochemistry and the physiology of topoisomerase II mutants with altered drug sensitivity in order to define the mechanistic bridge that links enzyme function to cellular phenotype.

Expression of multidrug resistance protein gene in patients with glioma after chemotherapy

Two different ATP-binding membrane glycoproteins, the 170 kDa P-glycoprotein (P-gp) and the 190 kDa multidrug resistance protein (MRP), are involved in the acquisition of multidrug resistance phenotypes in cancer cells. Overexpression of P-gp is often observed in various human tumors when treated with anticancer agents. In this study, we asked whether MRP was overexpressed in human gliomas after cancer chemotherapy. We investigated expression of MRP and P-gp before and after chemotherapy in tumor samples from patients with glioma. MRP expression was observed in 16 (70%) of 23 untreated patients, and the proportion of MRP-positive cells in the whole cell population ranged from 3 to 32% in the 16 MRP-positive patients. P-gp-positive tumors were observed in 4 (18%) of 23 patients, and the proportional rates of P-gp-positive cells in the whole cell population ranged from 4 to 23%. The proportional rate of MRP-positive or P-gp-positive glioma cells increased after chemotherapy when compared with that before chemotherapy in all patients examined. We could observe no statistically significant correlation between expression of MRP or P-gp and tumor grade. These results suggest that MRP as well as P-gp may be involved in acquired or intrinsic drug resistance in human glioma.

Prognostic markers in bladder cancer: a contemporary review of the literature

PURPOSE

We provide a contemporary review of bladder tumor markers and summarize their role as prognostic indicators.

MATERIALS AND METHODS

A comprehensive review of the literature on prognostic markers for transitional cell carcinoma of the bladder was performed.

RESULTS

Intense research efforts are being made to identify and characterize better various bladder cancers and their true biological potential. The need to predict which superficial tumors will recur or progress and which invasive tumors will metastasize has led to the identification of a variety of potential prognostic markers. Blood group antigens, tumor associated antigens, proliferating antigens, oncogenes, peptide growth factors and their receptors, cell adhesion molecules, tumor angiogenesis and angiogenesis inhibitors, and cell cycle regulatory proteins have recently been identified. The potential clinical applications of these tumor markers are under active investigation. Recent attention has focused on which tumor markers may predict the responsiveness of a particular bladder cancer to systemic chemotherapy.

CONCLUSIONS

At present conventional histopathological evaluation of bladder cancer (tumor grade and stage) cannot predict accurately the behavior of most bladder tumors. With a better understanding of the cell cycle, and cell to cell and cell to extracellular matrix interactions as well as improved diagnostic techniques (immunohistochemistry), progress is being made to identify and characterize other potential prognostic markers for transitional cell carcinoma of the bladder. The ultimate goal is to develop reliable prognostic markers that will accurately predict not only the course but also the response of a tumor to therapy. This information may then be used to dictate more aggressive treatment for tumors that are likely to progress and less aggressive treatment for those that are unlikely to progress. In the future these biological markers may also be used in gene therapy for the treatment of bladder cancer.

Differential expression of DNA topoisomerase II alpha and II beta genes between small cell and non-small cell lung cancer

DNA topoisomerase II (Topo II) inhibitors are widely used in lung cancer chemotherapy, but small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) show different sensitivity to them. In this study, we examined the gene expression levels of both isoforms of Topo II (II alpha and II beta) in lung cancer specimens to investigate the differential expression between SCLC and NSCLC. The expression levels of the Topo II alpha and Topo II beta genes were assessed in 80 autopsy samples (40 primary tumors and 40 corresponding normal lung tissues) by using the reverse transcription polymerase chain reaction. We found that the expression levels of the Topo II alpha gene in tumors were significantly higher than those in normal lung tissues, and that those in SCLC were significantly higher than those in NSCLC. There were no significant differences in Topo II beta gene expression between tumors and normal lung tissues and between SCLC and NSCLC. Further-more, correlation analysis revealed that Topo II alpha expression was correlated with Topo II beta expression in both tumor and normal lung tissues. These results indicate that a difference exists in the regulation of the Topo II gene between lung tumors and normal lung tissues. Our finding of differential expression of Topo II alpha between SCLC and NSCLC also suggests that the Topo II alpha expression level is associated with sensitivity to Topo II inhibitors.

Reduced cellular accumulation of topotecan: a novel mechanism of resistance in a human ovarian cancer cell line

In order to unravel possible mechanisms of clinical resistance to topoisomerase I inhibitors, we developed a topotecan-resistant human IGROV-1 ovarian cancer cell line, denoted IGROV(T100r), by stepwise increased exposure to topotecan (TPT). The IGROV(T100r) cell line was 29-fold resistant to TPT and strongly cross-resistant to SN-38 (51-fold). However, the IGROV(T100r) showed only threefold resistance to camptothecin (CPT). Remarkably, this cell line was 32-fold resistant to mitoxantrone, whereas no significant cross-resistance against other cytostatic drugs was observed. No differences in topoisomerase I protein levels and catalytic activity as well as topoisomerase I cleavable complex stabilization by CPT in the IGROV-1 and IGROV(T100r) cell lines were observed, indicating that resistance in the IGROV(T100r) cell line was not related to topoisomerase I-related changes. However, resistance in the resistant IGROV(T100r) cell line to TPT and SN-38 was accompanied by decreased accumulation of the drugs to approximately 15% and 36% of that obtained in IGROV-1 respectively. No reduced accumulation was observed for CPT. Notably, accumulation of TPT in the IGROV-1 cell line decreased under energy-deprived conditions, whereas the accumulation in the IGROV(T100r) cell line increased under these energy-deprived conditions. The efflux of TPT at 37 degrees C was very rapid in the IGROV-1 as well as the IGROV(T100r) cell line, resulting in 90% efflux within 20 min. Importantly, the efflux rates of TPT in the IGROV-1 and IGROV(T100r) cell lines were not significantly different and were shown to be independent on P-glycoprotein (P-gp) or multidrug resistance-associated protein (MRP). These results strongly suggest that the resistance of the IGROV(T100r) cell line to TPT and SN-38 is mainly caused by reduced accumulation. The reduced accumulation appears to be mediated by a novel mechanism, probably related to impaired energy-dependent uptake of these topoisomerase I drugs.

Circumvention of multidrug resistance in genitourinary tumors

Chemotherapy is the principal strategy to systemically challenge metastasized cancers of genitourinary origin. Unfortunately, the efficacy of chemotherapy is often hampered by multidrug resistance, the resistance to a variety of structurally and functionally distinct cytotoxic agents. Multidrug resistance can be either intrinsic or acquired, and can be caused by several mechanisms. The so-called classical multidrug resistance, mediated by the MDR1 gene product P-glycoprotein, has been held mainly responsible for inferring the multidrug resistance phenotype on urologic malignancies. However, several other multidrug resistance pathways have been identified. Multidrug resistance can be caused by the membrane-bound multidrug-resistance-associated protein, the detoxifying glutathione metabolism, the antiapoptotic protein BCL2, and changes in levels or activity of the topoisomerase enzymes. Strategies to overcome multidrug resistance of genitourinary tumors have arisen from the better understanding of the biologic and molecular mechanisms of multidrug resistance, and have been studied in experimental and clinical settings. However, attempts to modulate multidrug resistance in clinical renal cell, bladder, prostate, and testicular cancer have not been very rewarding so far, despite the optimism that had arisen from experimental data. Nevertheless, application of novel therapies to reverse multidrug resistance and to increase efficacy of chemotherapy for urologic cancers should be further pursued, within the setting of controlled clinical trials, to improve on current strategies.

CPT-11 sensitivity in relation to the expression of P170-glycoprotein and multidrug resistance-associated protein

The relevance of P170-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) for the sensitivity to CPT-11 was investigated in human malignant cell lines as well as in human tumour xenografts. In vitro, the P-gp-positive sublines BRO/mdr1.1 (transfected with MDR1) and 2780AD were slightly cross-resistant against carboxylesterase-activated CPT-11. Cross-resistance against SN-38 was present in 2780AD cells, but not in BRO/mdr1.1 cells. The P-gp modulators BIBW22BS, verapamil and dexniguldipine partly reversed the resistance against CPT-11 in the P-gp-positive sublines. BIBW22BS was the most effective modulator in the reversal of the resistance against carboxylesterase-activated CPT-11 as well as against SN-38 in the 2780AD subline. In contrast to doxorubicin and vincristine, the BRO/mdr1.1 xenografts were at least as sensitive to CPT-11 as the BRO xenografts. The 2780AD xenografts were slightly less sensitive than the parent tumours, but there was no difference in topoisomerase I DNA unwinding activity. Therefore, the high retention of the multidrug-resistant phenotype of 2780AD cells in vivo may be the cause of the low cross-resistance against CPT-11. The MRP-positive subline GLC4/ADR was cross-resistant against carboxylesterase-activated CPT-11 and SN-38. GLC4/ADR cells, however, demonstrated a twofold lower topoisomerase I activity than GLC4 cells. Cross-resistance against the camptothecin derivatives was not apparent in the MRP-transfected subline of SW1573/S1. In conclusion, P-gp-positive cells show a low cross-resistance against CPT-11/SN38, which is only apparent with high P-gp expression in vivo. MRP does not seem to play a role in the sensitivity to CPT-11.

Emergence of different mechanisms of resistance in the evolution of multidrug resistance in murine erythroleukemia cell lines

We examined the genetic and biochemical bases for drug resistance and the order of appearance of different mechanisms underlying the increasingly more resistant murine erythroleukemia cell lines established in Adriamycin (ADR). In the first-step low-level resistant cell line PC4-A5 (able to grow in 5 ng/mL ADR), there was a 2-fold reduction in topoisomerase IIalpha and topoisomerase IIbeta mRNA levels, as well as topoisomerase IIalpha protein and activity levels as compared with the parental cell line. The topoisomerase IIalpha activity levels remained reduced as the cells became increasingly more resistant. In contrast, the topoisomerase II mRNA and protein levels returned to approximately the parental levels in resistant cells growing in higher drug concentrations (40-160 ng/mL). Parental cells expressed the multidrug resistance protein (MRP), but beginning with PC4-A5 MRP expression decreased and remained reduced in increasingly resistant cell lines. At high levels of ADR resistance, the cells expressed the mdr3 gene concomitant with the appearance of vincristine resistance and energy-dependent daunomycin and vincristine efflux. Glutathione levels, internal pH, and expression of the major vault protein (MVP) remained unchanged in all cell lines. Fluorescence microscopy revealed no alterations in daunomycin distribution or vesicle numbers between the parental and resistant cell lines. Different resistance mechanisms emerge sequentially as cells become more resistant to ADR; the mechanisms are retained during the development of multidrug resistance (MDR). In intermediate-level MDR cell lines (PC4-A10 and PC4-A20), resistance involves an as yet undetermined mechanism(s).

Tumor necrosis factor-alpha and expression of the multidrug resistance-associated genes LRP and MRP

BACKGROUND AND PURPOSE

Cancer cells that express P-glycoprotein, multidrug resistance-associated protein (MRP), or lung resistance protein (LRP) have demonstrated resistance to a wide variety of chemotherapeutic drugs. Recently, we reported that human colon carcinoma cells that express all three proteins exhibit reduced P-glycoprotein gene expression and a loss of multidrug resistance after exposure to tumor necrosis factor-alpha, a hormone-like protein produced by cells of the immune system. In this study, we examined the effects of tumor necrosis factor-alpha on MRP and LRP gene expression in the same colon carcinoma cells.

METHODS

HCT15 and HCT116 colon carcinoma cells were incubated with tumor necrosis factor-alpha at 100 U/mL for 2, 12, 24, 48, or 72 hours; alternatively, cells transfected with an expression vector containing a human tumor necrosis factor-alpha complementary DNA were studied. The effects of tumor necrosis factor-alpha on MRP and LRP messenger RNA expression were evaluated by means of reverse transcription and the polymerase chain reaction; effects on MRP and LRP protein expression were examined by use of specific monoclonal antibodies and flow cytometry. The flow cytometry data were analyzed by use of the two-sided, nonparametric Mann-Whitney rank sum test.

RESULTS

Treatment with exogenous tumor necrosis factor-alpha reduced the level of LRP messenger RNA in both cell types in an apparently time-dependent fashion; in HCT15 cells, almost no LRP messenger RNA was detected after 48 hours of treatment. In contrast, the level of MRP messenger RNA was increased in HCT116 cells by such treatment, but the level in HCT15 cells was unchanged. Treatment with exogenous tumor necrosis factor-alpha induced changes in LRP and MRP protein expression in the two cell types that paralleled the changes found for messenger RNA. In transfected cells, the endogenous production of tumor necrosis factor-alpha reduced LRP gene expression (both messenger RNA and protein) and increased MRP gene expression (both messenger RNA and protein), regardless of cell type.

CONCLUSION

In human colon carcinoma cells, tumor necrosis factor-alpha influences MRP and LRP gene expression in opposite ways. The findings for LRP gene expression parallel our earlier findings for P-glycoprotein expression in these cells.

IMPLICATION

In developing strategies for overcoming multidrug resistance in tumor cells, the possibility that an agent can suppress one or more mechanisms of drug resistance and enhance others should be considered.