P-glycoproteins in pathology: the multidrug resistance gene family in humans

Inhibition of copper chaperones sensitizes human and canine osteosarcoma cells to carboplatin chemotherapy

Osteosarcoma (OSA) is the most common primary bone cancer in children, adolescents and dogs. Current combination surgical and chemotherapeutic treatments have increased survival. However, in recurrent or metastatic disease settings, the prognosis significantly decreases, representing an urgent need for better second-line and novel chemotherapeutics. The current gold standard for combination chemotherapy in OSA often includes a platinum agent, for example, cisplatin or carboplatin. These platinum agents are shuttled within the cell via copper transporters. Recent interest in targeting copper transport has been directed towards antioxidant protein 1 (Atox1) and copper chaperone for superoxide dismutase 1 (CCS), with Atox1 demonstrating the ability to aggregate platinum agents, preventing them from forming DNA adducts. DC_AC50 is a small molecule inhibitor of both Atox1 and CCS. To assess the impact of targeting these pathways on chemotherapy response, two human and two canine OSA cell lines were utilized. After treatment with single agent or combination drugs, cell viability was evaluated and pharmacological synergism calculated using the combination index method. Apoptosis, cell cycle distribution, clonogenic survival and migration were also evaluated. DC_AC50 synergised with carboplatin in combination treatment of human and canine OSA cells to reduce cancer cell viability. DC_AC50-treated cells were significantly less mitotically active, as demonstrated by decreased expression of phospho-histone H3 and cell cycle analysis. DC_AC50 also potentiated carboplatin-induced apoptosis in OSA cells and decreased clonogenic survival. Finally, DC_AC50 reduced the migratory ability of OSA cells. These results justify further investigation into inhibiting intracellular copper chaperones as a means of reducing/preventing acquired chemotherapy resistance.

Recent Aspects in the Diagnosis and Prognosis of Bladder Cancer

Epidemiologic studies have stated the progressive increase of bladder tumors during the last decades. The aim of our review is to refer to factors implicated in bladder carcinogenesis (such as activated oncogenes, growth factors and chromosomal aberrations) and to resistance to drug uptake (i.e., multidrug resistance gene and P-glycoprotein). The review also provides information of diagnostic and prognostic significance, based on DNA analysis of transitional cancer cells. In addition to cytometric data, alternative counterings for estimation of the S-phase fraction, useful in indicating the biologic behavior of bladder cancer, are presented. Knowledge of such mechanisms results in a better approach to the diagnosis, prognosis and prevention of bladder carcinomas, especially those that do not respond to systemic intravesical chemotherapy. We have tried to mention all significant factors related to the development of bladder cancer. We conclude that the progress made in understanding the pathogenesis of bladder cancer has been significant. However, more studies are needed in order to introduce and adopt reliable criteria to accurately predict the clinical behavior.

Antiproliferative Effects of Mitoxantrone in Adr-Sensitive and Adr-Resistant P388 Leukemia Cells Enhanced by Vitamin K3

Vitamin K3 was employed as a resistance-modifying agent to Investigate its activity in enhancing mitoxantrone (MITO)-induced cytotoxicity in parental (P388/S) and multidrug resistant (P388/ADR) P388 leukemia cells. Vitamin K3 potentiated the antitumor effects of MITO in P388/S and P388/ ADR tumor cells as monitored by inhibition of tumor cell survival (MTT assay). MITO and vitamin K3 in combination effected an enhanced inhibition of [3H]thymidine (DNA synthesis) and [3H]uridine (RNA synthesis) and also Increased the life span of the sensitive and resistant tumor-bearing animals. The effect of vitamin K3 on the induction of DNA strand breaks by MITO was also examined. Increased fragmentation of DNA was illustrated in the sensitive and resistant P388 leukemia cells exposed to the combination. Observations indicate the restoration of sensitivity in P388/ADR cells to MITO by vitamin K3 that may be due to its ability to increase the MITO-induced DNA strand breaks.

The Impact of Melatonin on Colon Cancer Cells' Resistance to Doxorubicin in an in Vitro Study

Multi-drug resistance (MDR) is the main cause of low effectiveness of cancer chemotherapy. P-glycoprotein (P-gp) is one of the main factors determining MDR. Some studies indicate the potential role of melatonin (MLT) in MDR. In this study, we examined the effect of MLT on colon cancer cell’s resistance to doxorubicin (DOX). Using the sulforhodamine B (SRB), method the effect of tested substances on the survival of LoVo (colon cancer cells sensitive to DOX) and LoVo_DX (colon cancer cells resistant to DOX) was rated. Using immunocytochemistry (ICC), the expression of P-gp in the LoVo and LoVo_DX was determined. With the real-time PCR (RT-PCR) technique, the ABCB1 expression in LoVo_DX was evaluated. Based on the results, it was found that MLT in some concentrations intensified the cytotoxicity effect of DOX in the LoVo_DX cells. In the ICC studies, it was demonstrated that certain concentrations of MLT and DOX cause an increase in the percentage of cells expressing P-gp, which correlates positively with ABCB1 expression (RT-PCR). The mechanism of overcoming resistance by MLT is probably not only associated with the expression of P-gp. It seems appropriate to carry out further research on the use of MLT as the substance supporting cancer chemotherapy.

Molecular mechanisms of chemoresistance in osteosarcoma (Review)

Due to the emergence of adjuvant and neoadjuvant chemotherapy, the survival rate has been greatly improved in osteosarcoma (OS) patients with localized disease. However, this survival rate has remained unchanged over the past 30 years, and the long-term survival rate for OS patients with metastatic or recurrent disease remains poor. To a certain extent, the reason behind this may be ascribed to the chemoresistance to anti-OS therapy. Chemoresistance in OS appears to be mediated by numerous mechanisms, which include decreased intracellular drug accumulation, drug inactivation, enhanced DNA repair, perturbations in signal transduction pathways, apoptosis- and autophagy-related chemoresistance, microRNA (miRNA) dysregulation and cancer stem cell (CSC)-mediated drug resistance. In addition, methods employed to circumvent these resistance mechanism have been shown to be effective in the treatment of OS. However, almost all the current studies on the mechanisms of chemoresistance in OS are in their infancy. Further studies are required to focus on the following aspects: i) Improving the delivery of efficacy through novel delivery patterns; ii) improving the understanding of the signal transduction pathways that regulate the proliferation and growth of OS cells; iii) elucidating the signaling pathways of autophagy and its association with apoptosis in OS cells; iv) utilizing high-throughput miRNA expression analysis to identify miRNAs associated with chemoresistance in OS; and v) identifying the role that CSCs play in tumor metastasis and in-depth study of the mechanism of chemoresistance in the CSCs of OS.

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.

Ultrasound microbubble-mediated delivery of the siRNAs targeting MDR1 reduces drug resistance of yolk sac carcinoma L2 cells

Background

MDR1 gene encoding P-glycoprotein is an ATP-dependent drug efflux transporter and related to drug resistance of yolk sac carcinoma. Ultrasound microbubble-mediated delivery has been used as a novel and effective gene delivery method. We hypothesize that small interfering RNA (siRNA) targeting MDR1 gene (siMDR1) delivery with microbubble and ultrasound can down-regulate MDR1 expression and improve responsiveness to chemotherapeutic drugs for yolk sac carcinoma in vitro.

Methods

Retroviral knockdown vector pSEB-siMDR1s containing specific siRNA sites targeting rat MDR1 coding region were constructed and sequence verified. The resultant pSEB-siMDR1 plasmids DNA were encapsulated with lipid microbubble and the DNA release were triggered by ultrasound when added to culture cells. GFP positive cells were counted by flow cytometry to determine transfection efficiency. Quantitative real-time PCR and western blot were performed to determine the mRNA and protein expression of MDR1. P-glycoprotein function and drug sensitivity were analyzed by Daunorubicin accumulation and MTT assays.

Results

Transfection efficiency of pSEB-siMDR1 DNA was significantly increased by ultrasound microbubble-mediated delivery in rat yolk sac carcinoma L2 (L2-RYC) cells. Ultrasound microbubble-mediated siMDR1s delivery effectively inhibited MDR1 expression at both mRNA and protein levels and decreased P-glycoprotein function. Silencing MDR1 led to decreased cell viability and IC₅₀ of Vincristine and Dactinomycin.

Conclusions

Our results demonstrated that ultrasound microbubble-mediated delivery of MDR1 siRNA was safe and effective in L2-RYC cells. MDR1 silencing led to decreased P-glycoprotein activity and drug resistance of L2-RYC cells, which may be explored as a novel approach of combined gene and chemotherapy for yolk sac carcinoma.

Association between ABCB1 (MDR1) gene 3435 C>T polymorphism and colchicine unresponsiveness of FMF patients

The multidrug resistance gene-1 (MDR1, adenosine triphosphate-binding cassette transporter: ABCB1, P-glycoprotein) encodes membrane proteins that play a crucial role in protecting cells from xenobiotics, chemicals, and drugs. The TT genotype of 3435 codon in exon 26 of MDR1 gene causes overexpression of gene activity and effluxes many chemically diverse compounds across the plasma membrane. We studied the association between C3435T polymorphisms (single nucleotide polymorphism) of MDR1 gene and colchicine-resistant familial Mediterranean fever (FMF) patients. Total genomic DNA samples from 52 FMF patients of colchicine unresponsiveness were used for FMF (MEFV) and MDR1 genes profile analyses. Target genes were genotyped by multiplex PCR-based reverse-hybridization Strip Assay method. The preliminary current results showed increased T allele frequency (0.596) in colchicine unresponsiveness of FMF patients. The distributions of the CC, CT, and TT genotypes in colchicine nonresponder FMF patients were 17%, 46%, and 37%, respectively. Our results indicate that C3435T polymorphism in exon 26 of MDR1 gene is associated with colchicine resistance in nonresponder FMF patients during the common therapy protocol.

Association of low tumor RNA integrity with response to chemotherapy in breast cancer patients

The CAN-NCIC-MA22 phase I/II clinical trial evaluated women with locally advanced or inflammatory breast cancer treated with epirubicin and docetaxel at 2 or 3 weekly intervals in sequential cohorts. The relationship between various biomarkers and treatment response was assessed. Breast biopsy cores were obtained from 50 patients pre-, mid-, and post-treatment. Immunohistochemical staining was performed to determine baseline levels of estrogen receptor (ER), progesterone receptor (PR), Her2/Neu protein (HER2), and topoisomerase II (Topo 2),expressed as percent positive stain. Tumor RNA integrity(RIN) and tumor cellularity were measured pre-, mid- and post-treatment by capillary electrophoresis and light microscopy after hematoxylin/eosin staining, respectively.Associations between 1) maximum RIN and 2) tumor cellularity at the three time points with baseline levels of ER,PR, Her2, and topo II were assessed using Spearman and Pearson correlation coefficients. Associations between RIN and tumor cellularity with chemotherapy dose level orpathologic response were assessed using one-way ANOVA.In this study, we observed that low mid-treatment maximum RIN (but not tumor cellularity) was associated with high chemotherapy drug dose level (P = 0.05) and eventual pathologic complete response (pCR) (P = 0.01). Posttreatment,low maximum RIN was found to be associated with low tumor cellularity (P = 0.004), and low tumor cellularity with pCR (P = 0.01). Post-treatment tumor cellularity was lowest in patients with tumors having high baseline PR levels (P = 0.05). The association of midtreatment RIN with drug dose level and with pCR suggests that tumor RIN may represent an important new biomarker for measuring response to chemotherapy in breast cancer patients.

Mechanisms of multidrug resistance in cancer treatment

Advanced breast cancer responds to a range of cytotoxic agents, but resistance always develops. Understanding the mechanisms of resistance may provide new therapeutic options. There are several major groups of resistance mechanisms. 1) The multidrug resistant phenotype. This is due to a membrane pump that can extrude a wide range of anticancer drugs--the P-glycoprotein. It is inhibited by a range of clinically used calcium channel blockers such as nifedipine and verapamil. Several other membrane proteins of 180 KD, 170 KD, 300 KD and 85 KD have been reported and are associated with MDR. 2) Glutathione transferences and detoxification mechanisms. These are a multigene family of enzymes that conjugate glutathione to chemically reactive groups. There are 3 major groups of enzymes--acidic, basic and neutral. They have been implicated in resistance to doxorubicin, melphalan cisplatinum chlorambucil and other alkylating agents. Other protecting systems include metallothionein and selenium dependent glutathione peroxidase. HSP27 confers doxorubicin resistance. 3) Topoisomerase II. DNA topoisomerases are involved in several aspects of DNA metabolism in particular genetic recombination, DNA transcription, chromosome segregation. They are a target for doxorubicin, mitoxantrone, VP16. Low levels of expression are associated with resistance. However, it is oestrogen inducible and this may be of therapeutic value. A novel topo IIb which is more drug resistant has been reported. 4) DNA repair. A score or more of genes are involved in the repair of DNA damage by drugs and radiation. Defective DNA repair may predispose to cancer of the breast and be responsible for adverse radiation reactions. Enhanced repair has been shown to be a mechanism of cisplatinum resistance. Several genes are inducible by DNA damage and may confer resistance e.g. A45. 5) Drug activation. Mitomycin C as well as cyclophosphamide and VP16 require activation for their effects. Low levels of cytochrome p450 reductase are associated with MMC resistance.

Therapeutic Targeting of ATP7B in Ovarian Carcinoma

PURPOSE

Resistance to platinum chemotherapy remains a significant problem in ovarian carcinoma. Here, we examined the biological mechanisms and therapeutic potential of targeting a critical platinum resistance gene, ATP7B, using both in vitro and in vivo models.

EXPERIMENTAL DESIGN

Expression of ATP7A and ATP7B was examined in ovarian cancer cell lines by real-time reverse transcription-PCR and Western blot analysis. ATP7A and ATP7B gene silencing was achieved with targeted small interfering RNA (siRNA) and its effects on cell viability and DNA adduct formation were examined. For in vivo therapy experiments, siRNA was incorporated into the neutral nanoliposome 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC).

RESULTS

ATP7A and ATP7B genes were expressed at higher levels in platinum-resistant cells compared with sensitive cells; however, only differences in ATP7B reached statistical significance. ATP7A gene silencing had no significant effect on the sensitivity of resistant cells to cisplatin, but ATP7B silencing resulted in 2.5-fold reduction of cisplatin IC(50) levels and increased DNA adduct formation in cisplatin-resistant cells (A2780-CP20 and RMG2). Cisplatin was found to bind to the NH(2)-terminal copper-binding domain of ATP7B, which might be a contributing factor to cisplatin resistance. For in vivo therapy experiments, ATP7B siRNA was incorporated into DOPC and was highly effective in reducing tumor growth in combination with cisplatin (70-88% reduction in both models compared with controls). This reduction in tumor growth was accompanied by reduced proliferation, increased tumor cell apoptosis, and reduced angiogenesis.

CONCLUSION

These data provide a new understanding of cisplatin resistance in cancer cells and may have implications for therapeutic reversal of drug resistance.

Lymphokine-activated killer cell susceptibility and adhesion molecule expression of multidrug resistant breast carcinoma

Reports showing susceptibility of multidrug resistant (MDR) cancer cells to immune effectors, together with P-glycoprotein (P-gp) expression in immune effector subsets, including immature natural killer (NK) cells, and some activated T cells, suggest P-gp or some changes associated with it, have implications in immune-mediated mechanisms. A series of experiments were done to determine the nature of alterations associated with susceptibility to immune effector cells of MDR tumor cells. A cell line isolated from the malignant pleural effusion of a breast cancer patient was transfected with human and murine MDR1 genes, and four variants with different levels of MDR were obtained. Lymphokine-activated killer (LAK) activity was measured by a ⁵¹Chromium release, and conjugate formation assays. MDR1 transfectant P-gp⁺ breast carcinoma lines had increased LAK susceptibility compared to their parent line. Some part of the increased LAK susceptibility of drug-resistant cell lines was at the binding/recognition level as shown by conjugate formation assays. This suggests that differences may exist between paired cell lines with respect to the expression of cell adhesion molecules (CAMs). Monoclonal antibodies (mAbs) to CAMs and flow cytometry were used to quantitate these antigens. The CAMs studied were those previously found to be upregulated by stimulating NK cells with (interleukin-2) IL-2; ICAM-1 (CD54), LFA-3 (CD58), N-CAM (CD56), and the β chain of LFA-1 (CD18). Although no differences in these CAMs were found between the breast carcinoma line and its MDR1-transfected variants, the target susceptibility results given above suggest that IL-2 treatment could be effective in combination with current protocols using chemotherapeutics, monoclonal antibodies (mAbs) and stem cell transplantation.

Immunohistochemical Detection of P-Glycoprotein (Clone C494) in Canine Mammary Gland Tumours

Elevated levels of P-glycoprotein have been reported in multidrug-resistant tumours in both humans and dogs. In the present study, we investigated the expression of P-glycoprotein in 57 canine mammary gland tumours, 10 mammary gland hyperplasia and seven normal mammary glands by immunohistochemistry. Tissue sections were incubated with an anti-Pgp monoclonal antibody and visualized with En Vision-DAB polymer. Normal and hyperplastic mammary tissues were negative or showed slight cytoplasmic immunoreactivity. Neoplastic cells in benign mammary tumours showed diffuse cytoplasmic staining, in contrast to malignant tumours that showed mainly a membranous staining pattern for Pgp (C494). We observed statistically significant differences among all the different groups of tissues analysed except for benign tumours versus hyperplasia (P = 0.221). Receiver-operating characteristic analysis showed that the best cut-off point to differentiate the threshold to differentiate negative from positive tissue samples was 18.40% of immunostained cells. These results provide a first indication that routine evaluation of Pgp expression in canine mammary gland tumours, taking into consideration a cut-off point for positivity, may be useful for selecting cases for chemotherapy.

MDR- and CYP3A4-mediated drug–herbal interactions

According to recent epidemiological reports, almost 40% of American population use complimentary and alternative medicine (CAM) during their lifetime. Patients detected with HIV or cancer often consume herbal products especially St. John's wort (SJW) for antidepressants in combination with prescription medicines. Such self-administered herbal products along with prescribed medicines raise concerns of therapeutic activity due to possible drug-herbal interactions. P-glycoprotein (P-gp) and cytochrome P450 3A4 (CYP3A4) together constitute a highly efficient barrier for many orally absorbed drugs. Available literature, clinical reports and in vitro studies from our laboratory indicate that many drugs and herbal active constituents are substrates for both P-gp and CYP3A4. Results from clinical studies and case reports indicate that self-administered SJW reduce steady state plasma concentrations of amitriptyline, cyclosporine, digoxin, fexofenadine, amprenavir, indonavir, lopinavir, ritonavir, saquinavir, benzodiazepines, theophyline, irinotecan, midazolan and warfarin. This herbal agent has been also reported to cause bleeding and unwanted pregnancies when concomitantly administered with oral contraceptives. Most of these medicinal agents and SJW are substrates for P-gp and/or CYP3A4. In vitro studies from our laboratory suggest that short-term exposure with pure herbal agents such as hypericin, kaempferol and quercetin or extract of SJW resulted in higher uptake or influx of ritonavir and erythromycin. Hypericin, kaempferol and quercetin also caused a remarkable inhibition of cortisol metabolism with the percent intact cortisol values of 64.58%, 89.6% and 90.1%, respectively, during short-term in vitro experiments. Conversely, long-term exposure of herbal agents (hyperforin, kaempferol and quercetin) showed enhanced expression of CYP3A4 mRNA in Caco-2 cells. In another study, we observed that long-term exposure of hypericin, kaempferol, quercetin and silibinin resulted in higher MDR-1 mRNA expression in Caco-2 cells. Therefore, herbs can pharmacokinetically act as inhibitors or inducers. Medicinal agents that are substrates P-gp-mediated efflux and/or CYP-mediated metabolism are likely to be potential candidates for drug-herbal interactions. The duration of exposure of cells/healthy volunteers/animals to herbals appears to be critical for drug-herbal interaction. An increase in plasma drug concentration is possible during concomitant administration of SJW and prescribed drugs. In contrast, prolonged intake of herbal supplement followed by drug administration may result in subtherapeutic concentrations. Therefore, clinical implications of such drug herbal interactions depend on a variety of factors such as dose, frequency and timing of herbal intake, dosing regimen, route of drug administration and therapeutic range. In vitro screening techniques will play a major role in identifying possible herb-drug interactions and thus create a platform for clinical studies to emerge. Mechanisms of drug-herbal interaction have been discussed in this review article.

Identification of polymorphisms on the MDR1 gene among Turkish population and their effects on multidrug resistance in acute leukemia patients

Multidrug-resistance (MDR) phenotype is a serious limitation to the effective chemotherapeutic treatment of many cancer types, including leukemia. One of the most important proteins, the over-expression of which is responsible for the multidrug-resistance phenotype in many cancer types, is P-glycoprotein. This protein is the product of the MDR1 gene. In previous studies, single-nucleotide polymorphisms (SNPs) C3435T, G2677T, and T-129C in the MDR1 gene were shown to be correlated with lower P-glycoprotein expression in normal tissues. It was suggested that this might have an advantage in cancer chemotherapy by resulting in a low drug-resistance phenotype. The frequencies of these SNPs were studied in 45 acute leukemia patients (25 of which were primary refractory and 20 of which were drug-sensitive) and 17 healthy individuals, forming a Turkish population of 62 individuals. In the first part of the study, these polymorphisms were compared with other populations. Marked differences were apparent between African and Turkish populations for the C3435T polymorphism. On the other hand, similarities were found between other Caucasian/Asian and Turkish populations (P < 0.001). However, for the G2677T polymorphism, the Turkish population is different than Japanese and German populations (P < 0.001). For the T-129C polymorphism, all individuals in the studied population were homozygous for the T/T genotype. In the second part of this study, drug-resistant and drug-sensitive acute leukemia patients were compared for these SNPs. These polymorphisms did not seem to have a significant effect on P-glycoprotein-mediated drug resistance in the patients studied.

Modulation of multidrug-resistance-associated P-glycoprotein in human U-87 MG and HUV-ECC cells with antisense oligodeoxynucleotides to MDR1 mRNA

OBJECTIVE

Glioblastoma is the highest dedifferentiated form of astrocytic brain tumors, and it is refractory to chemotherapy in most cases. To improve the clinical outcome of such tumors, new therapeutic strategies are needed. While malignancy is mainly associated with a nonfunctional apoptotic pathway, the lack of chemotherapeutic success correlates with overexpression of the multidrug resistance 1 (MDR1) gene product P-glycoprotein (P-gp). Previous investigations have shown that not only glioblastoma cells but also endothelial cells are important in the response to chemotherapy. The aim of the present investigations was to reduce the expression of P-gp in the human glioblastoma cell line U-87 MG and in the human endothelial cell line HUV-ECC.

METHODS

Therefore, these cells were treated with antisense oligodeoxynucleotides (asn-ODN) directed against the P-gp mRNA in order to increase the intracellular retention of doxorubicin (DOX) which had been given previously.

RESULTS

Flow cytometry revealed about 4-fold increased intracellular retention of DOX in both asn-ODN-treated cell lines as compared to asn-ODN non-treated cell lines.

CONCLUSION

These results suggest that asn-ODN-mediated inhibition of P-gp expression is an efficient way to increase intracellular retention of DOX.

A Mathematical Simulation to Explain the Coordinated Functions of Efflux and Metabolism Limiting the Transport of Anti-HIV Agents Across Caco-2 Cells

OBJECTIVES

The purpose of this study was to simulate a mathematical model that explains the coordinated function of P-glycoprotein (P-gp) and/or CYP3A4 in human intestinal enterocytes. In addition, this study aimed to determine the efflux interactions of anti-HIV protease inhibitors.

METHODS

Human colon carcinoma-derived Caco-2 cells were selected as a model system to evaluate the effects of P-gp-mediated efflux of HIV protease inhibitors. Anti-HIV agents ritonavir and saquinavir were selected as model drugs to determine efflux interactions. An absorption-metabolism classification system is hence proposed based on substrate specificities of drugs toward P-gp and/or CYP3A4 and their probable interactions with other compounds.

RESULTS

Enhanced apical to basal (A-B) ritonavir transport was observed on coadministration of saquinavir. Saturable, concentration-dependent inhibition of ritonavir efflux from Caco-2 monolayers was also observed with saquinavir. The IC(50) values of ritonavir (as a self-inhibitor) and saquinavir from dose-response curves, estimated by fitting the data to nonlinear equations, were found to be 7.15 and 33.2 micromol/L, respectively. The respective K(i) values determined were 8.5 and 28.91 micromol/L. The experimentally obtained K(i) values decreased in the close approximation with the IC(50) values.

CONCLUSION

Proposed mathematical simulations may prove to be a useful tool in predicting drug interactions by inhibition of P-gp mediated efflux and CYP3A4-mediated metabolism.

Multidrug resistance-1 (MDR-1) in autoimmune disorders III: increased P-glycoprotein activity in lymphocytes from immune thrombocytopenic purpura patients

OBJECTIVE

P-glycoprotein (P-gp) expression has been widely observed in normal and neoplastic cells. The physiologic role of P-gp involves hormone and metabolite secretion, bacterial product detoxification, and transport of several drugs to the extracellular space. Multidrug resistance-1 is characterized by drug extrusion through P-gp, reducing the intracellular levels of drugs and diminishing their pharmacological effects. Treatment of immune thrombocytopenic purpura (ITP) includes agents that are substrates of P-gp; hence, the objective of this study was to analyze the functional activity of P-gp in lymphocytes from patients with ITP.

PATIENTS AND METHODS

30 ITP patients (9 refractory, 5 dependent, 14 responders to treatment, and 2 with stable disease) and 25 healthy controls were studied. Peripheral blood mononuclear cells were isolated by gradient centrifugation and incubated with daunorubicin (a fluorescent drug extruded by P-gp). Functional activity of P-gp was analyzed by flow cytometry. Results were expressed as the percentage of lymphocytes able to extrude daunorubicin.

RESULTS

ITP patients showed an increased number of lymphocytes with P-gp activity (mean=12.3%+/-16%) when compared to controls (mean=0.87%+/-0.72%) (p<0.05). P-gp function was higher in the refractory group (median=9.4%) than in the treatment-dependent (median=5.4%), responder (median=6.4%), and stable disease (median=5.2%) groups, although no statistical differences were found among them.

CONCLUSION

Enhanced P-gp activity in ITP may be related to an unfavorable clinical outcome and poor response to treatment. Furthermore, P-gp function might affect therapeutic requirements for disease control.

Chemosensitization of carmustine with maitake beta-glucan on androgen-independent prostatic cancer cells: involvement of glyoxalase I

OBJECTIVE

To improve the poor efficacy (< 10%) of chemotherapy for patients with hormone-refractory prostate cancer, we investigated a possible cytotoxic effect of carmustine/beta-glucan combination on prostatic cancer PC-3 cells, focusing on a glutathione-dependent detoxifying enzyme, glyoxalase I (Gly-I).

METHODS

Carmustine (BCNU) is an anticancer agent and a putative inhibitor of Gly-I, while beta-glucan is a unique, nontoxic polysaccharide extracted from maitake mushrooms. The cytotoxic effects of BCNU or other anticancer agents with beta-glucan on PC-3 cells were assessed by cell-viability testing and Gly-I activity was measured using the spectrophotometric method.

RESULTS

BCNU, 5-fluorouracil (5-FU), and methotrexate (MTX) were capable of inducing approximately a 50% reduction in cell viability at 72 hours, while etoposide, cisplatin, and mitomycin C were all ineffective. Only the combination of BCNU (50 micro ;mol) and beta-glucan (60 micro g/mL) exhibited an enhanced cytotoxicity with an approximate 90% cell viability reduction, but little improvement was seen with any combinations of 5-FU, MTX, or beta-glucon. Gly-I assays revealed that such a profound (approximately 90%) cell death was accompanied by an approximate 80% reduction in Gly-I activity by 6 hours.

CONCLUSION

This study demonstrates a sensitized cytotoxic effect of BCNU with beta-glucan in PC-3 cells, which was associated with a drastic (approximately 80%) inactivation of Gly-I. Therefore, the BCNU/beta-glucan combination may help to improve current treatment efficacy by targeting Gly-I, which appears to be critically involved in prostate cancer viability.

Critical determinants of metastasis

The major cause of death from cancer is due to metastases that are resistant to conventional therapies. Several reasons account for the failure to treat metastases. First, neoplasms are biologically heterogeneous and contain subpopulations of cells with different angiogenic, invasive, and metastatic properties. Second, the process of metastasis selects for a small subpopulation of cells that preexist within a parental neoplasm. Third, and perhaps the greatest obstacle for therapy, is that the outcome of metastasis depends on multiple interactions ('cross-talk') of metastatic cells with homeostatic mechanisms which the tumor cells usurp. Most recent data demonstrate that the organ microenvironment can influence the growth, invasion, and response of metastases to chemotherapy. Therapy of metastasis should therefore be targeted against both the metastatic tumor cells and the homeostatic factors that promote metastasis.

P-glycoprotein, lung resistance-related protein and multidrug resistance-associated protein in de novo adult acute lymphoblastic leukaemia

P-glycoprotein (P-gp), lung resistance-related protein (LRP) and multidrug resistance-associated protein (MRP) expression, and blast cell intracellular daunorubicin accumulation (IDA) were evaluated in 95 previously untreated cases of adult acute lymphoblastic leukaemia (ALL) using flow cytometry. Forty-five out of 95 (47%) patients were P-gp positive (+), 12/66 (18%) were LRP+ and 11/66 (17%) were MRP+. Eighteen out of 66 (28%) patients showed a simultaneous multidrug resistance (MDR)-related protein expression higher than controls for more than one protein, while 24/66 (36%) cases did not overexpress any protein. Twenty-one out of 24 (87%) cases overexpressing at least one MDR-related protein had a defect in accumulating daunorubicin into their blast cells, while only 4/24 (16%) cases who did not overexpress any protein had similar features. The complete remission rates were similar in MDR-positive and -negative (-) patients but relapses within 6 months were more frequent in P-gp+ cases, and therefore the disease-free survival duration was shorter in P-gp+ than in P-gp- patients (P = 0.01). The number of MRP+ and/or LRP+ cases was too small to be able to draw any conclusion on their role in affecting or predicting therapy outcome. In conclusion, P-gp overexpression associated with a defect in daunorubicin accumulation is a frequent feature in adult ALL at onset and seems to be related to poorer therapy outcome and, consequently, a shorter disease-free survival. LRP and MRP overexpression seems to be a rare event and no conclusion can be drawn on its prognostic role.

Multidrug resistance transporters and modulation

Multidrug resistance (MDR), whereby tumor cells simultaneously possess intrinsic or acquired cross-resistance to diverse chemotherapeutic agents, hampers the effective treatment of cancer. Molecular investigations in MDR resulted in the isolation and characterization of genes coding for several proteins associated with MDR, including P-glycoprotein (P-gp), the multidrug resistance associated protein (MRP1), the lung resistance protein (LRP), and, more recently, the breast cancer resistance protein (BCRP). These transmembrane proteins cause MDR either by decreasing the total intracellular retention of drugs or redistributing intracellular accumulation of drugs away from target organelles. These proteins are expressed at varying degrees in different neoplasms, including the AIDS-associated non-Hodgkin lymphoma and Kaposi sarcoma and are generally associated with poor prognosis. Several MDR-reversing agents are in various stages of clinical development. First-generation modulators such as verapamil, quinidine, and cyclosporin required high doses of drugs to reverse MDR and were associated with unacceptable toxicities. Second- and third-generation MDR inhibitors include PSC 833, GF120918, VX-710, and LY335979, among others. Limitations to the use of these modulators include multiple and redundant cellular mechanisms of resistance, alterations in pharmacokinetics of cytotoxic agents, and clinical toxicities. Studies to validate the role of MDR reversal in the treatment of various malignancies are underway. A potential use of these agents may be to enhance intestinal drug absorption and increase drug penetration to biologically important protective barriers, such as the blood-brain, blood-cerebrospinal fluid, and the maternal-fetal barriers. The use of MDR modulators with drugs such as the antiviral protease inhibitors and cytotoxics may enhance drug accumulation in sanctuary sites that are traditionally impenetrable to these agents.

P-glycoprotein levels predict poor outcome in patients with osteosarcoma

To evaluate the relationship between the expression of P-glycoprotein by osteosarcomas and the rate of metastasis and death, a retrospective review of 172 patients who were diagnosed with osteosarcoma between 1987 and 1992 was performed. Forty patients had P-glycoprotein levels available. The majority of the osteosarcomas were Stage II-B (33 patients), with the remaining seven being Stage III. Tumor sites included 25 femurs, seven humeri, five tibias, and one each of pelvis, radius, and fibula. The patients with Stage III disease at presentation were treated differently from the time of diagnosis and therefore, these seven patients with Stage III osteosarcoma were excluded from additional analyses. The expression of P-glycoprotein by cultured tumor cells from biopsy specimens was determined using immunofluorescent microscopy. In the 33 patients with Stage IIB osteosarcoma with detectable P-glycoprotein, 67% (10 of 15) had metastases develop as compared with 28% (five of 18) of patients with undetectable P-glycoprotein. Similarly, 53% (eight of 15) of patients with tumors expressing P-glycoprotein died of disease compared with 11% (two of 18) with no detectable P-glycoprotein. Expression of P-glycoprotein by tumor cells seems to be associated with an estimated ninefold increase in the odds of death and a fivefold increase in the odds of metastases in patients with Stage IIB osteosarcoma. Kaplan-Meier survivorship analysis revealed that patients with detectable P-glycoprotein fared worse in terms of survival time and metastasis-free survival. Adjusting for covariates in the Cox proportional hazards model, expression of P-glycoprotein and its level were significantly predictive of time to death in patients with Stage IIB osteosarcoma.

P-glycoprotein (PGP), lung resistance-related protein (LRP) and multidrug resistance-associated protein (MRP) expression in acute promyelocytic leukaemia

We analysed the expression of three drug transporter proteins [p-glycoprotein (PGP), lung resistance-related protein (LRP) and multidrug resistance-associated protein (MRP1)] involved in anthracycline resistance that are frequently overexpressed in poor-risk adult acute non-lymphocytic leukaemia (ANLL), in 23 acute promyelocytic leukaemia (APL) patients at onset managed at a single institution. Cellular daunorubicin accumulation was also evaluated. At onset, no case had PGP or MRP1 expression that exceeded that of non-multidrug-resistant (MDR) cell lines. Only one case showed LRP overexpression. No peculiar MDR features distinguished the seven patients who relapsed from those who maintained complete remission. In the onset vs. first relapse, only one patient showed an increased (threefold) PGP expression at relapse. At second relapse, three out of four patients showed a PGP expression two- to threefold higher than baseline values. These results are consistent with the view that low PGP, LRP and MRP1 expression and the absence of defects in intracellular drug accumulation may account for the peculiarly high sensitivity of APLs to anthracycline. It does not support the screening of MDR markers in APL patients at onset as predicting factors of early relapse. The results suggest that no significant changes in PGP, LRP or MRP1 expression are likely to occur at first relapse. In contrast, PGP expression is likely to increase later in the patient history as a result of additional chemotherapy courses.

Liposome-encapsulated daunorubicin for PGP-related multidrug resistance

The possibility that Daunoxome (DNX), a combination of daunorubicin (DNR) with a liposomal targeting system, escapes PGP was tested. Two pairs of leukaemic cell lines, each consisting of the parental non-multidrug resistance (MDR) line and of a MDR variant, were studied for cytotoxicity (MTT test) and for cellular DNR kinetic and accumulation (flow cytometry). DNX and free DNR were equally toxic against non-MDR cells, whereas the liposomal anthracycline was more toxic than the free drug against the MDR variant. Non-MDR cells accumulated DNR more rapidly when they were exposed to free DNR than to DNX, but MDR cells accumulated more DNR when they were exposed to DNX. The kinetics of DNX and free DNR were also studied in the blast cells of 41 cases of acute leukaemia and they were found to be related to blast cell PGP expression. In 15 cases with a low PGP expression intracellular DNR accumulation was faster and higher with free DNR than with DNX. In 26 cases with a high PGP expression the area under the curve was similar with DNX and free DNR, but the kinetics of intracellular DNR accumulation showed an early low plateau with free DNR and a slow and continuous increase with DNX. In MDR cell lines the ratio was more favourable to DNX than to free DNR. We conclude that liposome encapsulated DNR is partially protected from PGP and that it is worth testing for the treatment of PGP-positive acute leukaemia.

Cyclosporin A reverses chemoresistance in patients with gynecologic malignancies

Multidrug resistance is a major obstacle in successful systemic therapy of gynecologic malignancies. The objectives of this study are to evaluate the activity of cyclosporin A used to overcome drug resistance in a variety of gynecologic malignancies. Forty women (29 with ovarian cancer, 7 with uterine cancer, 3 with cervical cancer, and 1 with choriocarcinoma) were treated with cyclosporin A, 4 mg/kg intravenously, 6 hours before and 18 hours after the specific chemotherapeutic agent, to which the tumor had developed drug resistance. All patients had shown resistance to the chemotherapy agent used in combination with cyclosporin A. All patients had been heavily pretreated (mean, 2.8 previous chemotherapy regimens). Overall, among 38 available patients with gynecologic malignancies, a 29% objective response rate was observed. Twenty-six (65%) of all patients received three or more cycles of cyclosporin A. There was a 25% response rate for patients with ovarian cancer patients and 50% for those with uterine cancer. There were no responses among the three patients with cervical cancer, and the patient with choriocarcinoma had a complete response. All patients were evaluable for toxicity. Leukopenia and nausea were the most common toxic reactions, but in most cases they were transient, and only three patients required a treatment delay. The most common grade 3 or 4 toxicity was thrombocytopenia, which was observed in 22% of the patients. Cyclosporin A is well tolerated and has significant potential for reversal of chemoresistance in heavily pretreated patients with ovarian and uterine malignancies.

P-glycoprotein, lung resistance-related protein and multidrug resistance associated protein in de novo acute non-lymphocytic leukaemias: biological and clinical implications

P-glycoprotein (PGP), lung resistance-related protein (LRP) and multidrug resistance associated protein (MRP) expression and the blast cells' intracellular daunorubicin accumulation (IDA) were evaluated in 96 previously untreated cases of de novo acute non-lymphocytic leukaemia (ANLL). 47/96 patients (49%) were classified as PGP+ 44/ 96 (46%) as LRP+, and 8/96 (8%) as MRP+. The more frequent MDR clusters were PGP-/LRP-/MRP- (32/96 cases, 33%) and the PGP+/LRP+/MRP- (27/96 cases, 28%) followed by PGP+/LRP-/MRP- (15/96 cases, 16%) and PGP-/LRP+/MRP- (14/96 cases, 14%). A favourable karyotype was observed more frequently in PGP- and LRP-cases. A highly significant correlation was found between either PGP or LRP overexpression and leukaemic blast cell IDA. All the patients received standard induction and consolidation treatments containing MDR-related (idarubicin, mitoxantrone, etoposide) and other (arabinosyl cytosine) drugs. Multivariate analysis showed that PGP overexpression was significantly associated with a poor response to treatment, both in terms of primary resistance or shorter survival. Other independent prognostic factors were age and cytogenetics. LRP overexpression did not reach statistical significance, although for LRP+ cases the trend was unfavourable. Due to small numbers, no conclusion could be made regarding MRP overexpression, but 5/8 cases showed unfavourable karyotypic abnormalities, 8/8 had a defective IDA and 6/8 failed to achieve remission. This study showed that both PGP and LRP overexpression are common features in de novo ANLL at onset whereas MRP overexpression is more rare. It suggested that overexpression of one of the MDR related proteins was associated with a defective IDA, and confirmed that, in addition to age and cytogenetics, PGP retains an independent prognostic value. It also suggested that LRP did not affect clinical outcome when patients were treated with idarubicin or mitoxantrone and arabinosyl cytosine.

Differential activity of P-glycoprotein in normal blood lymphocyte subsets

To better understand the phenomenon of P-glycoprotein (P-170) expression we investigated lymphocyte subpopulations for P-170 function in healthy volunteers. Studies were based on three-colour flow cytometry including the fluorescent probe rhodamine 123 (Rh123), which is transported by P-170. Marked Rh123 efflux was detected in CD8+ T lymphocytes with CD8+/CD45RA+ T cells (naive cells) showing significantly higher P-170 activity as compared with CD8+/CD45RA- cells (P<0.04). Vice versa, CD8+/CD45RO+ T cells (memory cells) demonstrated less P-170 activity than CD8+/CD45RO- cells (P<0.04). P-170 function was less prominent in CD4+ T cells, however, Rh123 efflux was higher in the CD4+/CD45RA+ and CD4+/CD45RO- subpopulations (P<0.025) corresponding to the CD8+ results. Dye efflux differed significantly between activated and non-activated CD8+ and CD4+ as well as CD8+/CD11b+ and CD8+/CD11b- T lymphocytes. Since CD16+ natural killer cells (NK) expressed the highest level of P-170, the NK cytotoxicity against 51Cr-labelled K562 target cells was assayed in the presence or absence of P-170 inhibitors. NK related cytotoxicity was significantly reduced in the presence of R-verapamil and dexnigaldipine-HCP in a dose-dependent manner. The differential expression of P-170 activity in naive and memory T cells together with the reduced NK related cytotoxicity in the presence of MDR-modulators suggest a physiological role of P-170 in immunological functions of these lymphocyte subsets. Consequently, the addition of MDR modulators to conventional chemotherapy as a strategy to overcome drug resistance should consider possible adverse immunosuppressive effects.

Comparative evaluation by semiquantitative reverse transcriptase polymerase chain reaction of MDR1, MRP and GSTp gene expression in breast carcinomas

Identification and quantitative evaluation of drug resistance markers are essential to assess the impact of multidrug resistance (MDR) in clinical oncology. The MDR1 gene confers pleiotropic drug resistance in tumour cells, but other molecular mechanisms are also involved in drug resistance. In particular, the clinical pattern of expression of the other MDR-related genes is unclear and their interrelationships are still unknown. Here, we report standardization of the procedures used to determine a reliable method of semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) using a standard series of drug-sensitive and increasingly resistant cell lines to evaluate the expression of three MDR-related genes, i.e. MDR1 (multidrug resistance gene 1), MRP (multidrug resistance related protein) and GSTp (glutathione-S-transferase p), reported to be endogenous standard genes for normalization of mRNAs. A total of 74 breast cancer surgical biopsies, obtained before any treatment, were evaluated by this method. When compared with classical clinical and laboratory findings, GSTp mRNA level was higher in diploid tumours. However, the main finding of our study suggests a clear relationship between two of these MDR-related gene expressions, namely GSTp and MRP. This finding provides new insight into human breast tumours, which may possibly be linked to the glutathione conjugate carrier function of MRP. Well defined semiquantitative RT-PCR procedures can therefore constitute a powerful tool to investigate MDR phenotype at mRNA levels of different related genes in small and precious tumour biopsy specimens.

Value of glutathione S-transferase pi and the oncogene products c-Jun, c-Fos, c-H-Ras, and c-Myc as a prognostic indicator in endometrial carcinomas

OBJECTIVE

To examine the relationship between the expressions of glutathione S-transferase pi (GST-pi) and four oncogene products, c-Jun, c-Fos, c-H-Ras, and c-Myc, and clinicopathological prognostic factors and patients' prognosis in endometrial carcinomas, and to assess their prognostic value in endometrial carcinomas.

METHODS

Specimens of endometrial carcinoma obtained from 63 patients were investigated immunohistochemically using respective specific antibodies.

RESULTS

The overall positive rates in 63 carcinoma specimens were 34.9% for GST-pi, 44.4% for c-Jun, 34.9% for c-Fos, 47.6% for c-H-Ras, and 54.0% for c-Myc. Multivariate analysis revealed that GST-pi expression correlated independently with paraaortic lymph node (PAN) metastasis, and c-Jun expression was independently related to pelvic lymph node (PLN) and PAN metastasis. The prognosis of patients with a GST-pi-positive tumor was significantly poorer than that of those with a GST-pi-negative tumor (P < 0.05). The patients with c-Jun-positive tumor also had a significantly worse prognosis than those with c-Jun-negative tumor (P < 0.05). No significant relationship between the expressions of the remaining three oncogene products, c-Fos, c-H-Ras, and c-Myc, and the examined prognostic factors and clinical outcome was apparent.

CONCLUSION

These results suggest that the expressions of GST-pi and c-Jun may reflect the metastatic potential of endometrial carcinomas and that their expressions of endometrial carcinoma may be useful as a prognostic indicator for predictive testing.

Clinical study of multi-drug resistance gene (MDR1) expression in primary ovarian cancer

This study was designed to measure the multi-drug resistance gene (MDR1) mRNA content and analyze clinical relationship between MDR1 expression and drug resistance in primary ovarian cancer. Reverse transcription PCR (RT-PCR) was used to measure MDR1 mRNA content in biopsy sample of 31 primary ovarian cancers (experimental group) and 30 gynecological tumors (control group). The level of 95.2% (20/21) MDR1 expression was relatively low, and the detected rate of MDR1 expression was 67.7% (21/31) in experimental group, which was higher than that in control group (40.0%, P < 0.05). The differences of MDR1 expression between the effective group and no effect group after combined chemotherapy was significant (P < 0.05). No significant relationship was found between MDR1 expression and clinical stage or histological classification or grade of differentiation in experimental group. We are led to concluded that primary ovarian cancers have drug-resistance clones which might express MDR1 spontaneously and expression of MDR1 may be used as a prognostic and predictive indicator for clinical response of ovarian cancers to combined chemotherapy.

Polymorphic expression of multidrug resistance mRNA in lung parenchyma of nonpregnant and pregnant rats: a comparison to cystic fibrosis mRNA expression

Multidrug resistance (MDR1b) and cystic fibrosis transmembrane conductance regulator (CFTR) proteins are members of the "ATP-binding cassette" superfamily of transporters. They are associated with chloride channel activities and ATP secretion and have complementary patterns of expression in several organs. In the rat uterus, CFTR expression is replaced by MDR1b expression during pregnancy. We have studied whether expression of MDR1b and CFTR also vary in the lung during pregnancy. No variations in MDR1b or CFTR mRNA levels during pregnancy were detected. However, there was an unusual degree of variation in MDR1b mRNA expression in lung parenchyma between animals in both the control group and the pregnant group. If present among humans, polymorphic expression of MDR1 in lung parenchyma may explain part of the differences in lung symptomatology observed in the CF patients carrying the same mutation.

Immunocytochemical detection of P-glycoprotein in the management of malignant effusions

P-glycoprotein (P-gp), a cell membrane protein, has been found in multidrug-resistant cancer cells. A total of 104 smears from patients with breast-cancer-associated pleural effusions and ovarian-cancer-related peritoneal effusions were studied for P-gp with the antibody C-219 and the avidin-biotin-immunoperoxidase method. Samples were taken before and 3 and 7 days after intracavitary bleomycin therapy and reaccumulation of effusion was assessed at 30 days. Smears that were P-gp-negative by the 7th day were associated with a good 30-day response to bleomycin in the majority of cases, while P-gp-positive smears were associated with a significant reaccumulation of fluid at 30 days. P-gp status is a valuable prognostic indicator of response to intracavitary bleomycin treatment in effusions from breast or ovarian cancer.

P-glycoprotein is positively correlated with p53 protein accumulation in human colorectal cancers

To explore the relationship between mutant p53 and Pgp expression, we have examined the levels of both proteins in human colorectal adenocarcinomas. Serial frozen sections of 40 surgical samples were stained with an anti-Pgp (MRK16) and two different anti-p53 protein antibodies (Abs), PAb421 and PAb1801. Nineteen (47.5%) of 40 samples examined were positive for Pgp, and 18 (45%) of 40 were positive for p53. The samples that stained positively with PAb421 also stained positively with PAb1801. Pgp expression was detected in 13 (76.5%) of 17 samples that were positive for p53 using PAb421 and in 15 (83.3%) of 18 samples that were positive for p53 using PAb1801. Thus, we found that p53 and Pgp were co-expressed in a significant number of samples (P < 0.002). There was no relationship between Pgp or p53 protein accumulation and histologic grade or stage. The present results demonstrate that Pgp expression is closely associated with p53 protein accumulation in human colorectal cancers. These data provide evidence to support the idea that mutant p53 activates the MDR1 gene in vivo.

P-glycoprotein expression in cartilaginous tumors

BACKGROUND AND OBJECTIVES

Malignant cartilage tumors demonstrate chemotherapeutic resistance through undetermined mechanisms. P-glycoprotein is the protein product of the multiple drug resistance gene 1 (MDR-1) and confers multidrug chemotherapeutic resistance in a variety of malignancies.

METHODS

MDR-1 expression was examined in 55 benign and malignant cartilage tumor specimens by immunohistochemistry using C219, C494, and JSB-1 antibodies, and by in situ hybridization with an MDR-1 specific oligonucleotide cDNA probe.

RESULTS

Constitutive expression of P-glycoprotein was observed in all benign and malignant cartilage tumor specimens with a similar pattern of immunohistochemical staining present with all three antibodies. In benign tumors and low grade chondrosarcomas, the staining pattern was weak to intermediate and localized to clusters of cells. However, higher grade-tumors (Grade II and III) expressed P-glycoprotein in a higher percentage of cells and with more intense staining. P-glycoprotein expression was absent in normal human articular cartilage, but was focally present in costal and growth plate cartilage. The immunohistochemistry results were confirmed by in situ hybridization in 10 cases.

CONCLUSIONS

P-glycoprotein is expressed constitutively in cartilaginous tumors, with greatest expression in high grade malignancies. The findings may account for the resistance of cartilage tumors to chemotherapeutic agents.

Classical multidrug resistance in acute myeloid leukaemia

Approximately 15-30% of acute myeloid leukaemia (AML) patients are primarily resistant to chemotherapy, and 60-80% of patients who achieve complete remission will inevitably relapse and succumb to their disease. The multidrug resistant (MDR) phenotype has been suspected as a major mechanism of therapy failure in AML; it is one of the best understood mechanisms of resistance to anticancer drugs. The classical MDR phenotype is characterized by the reduced ability of cells to accumulate drugs as compared to normal cells. The increased drug efflux is due to the activity of a 170 kDa glycoprotein, the P-glycoprotein (Pgp), a unidirectional drug-efflux pump which is encoded by the MDR1 gene. While studies of myeloid leukaemia and myeloma have provided the best evidence for the potential association between Pgp expression and clinical outcome, the lack of standardized methods for MDR detection and perhaps even more importantly, inconsistencies in the interpretation of MDR expression data account for divergent results in the literature. The clinicians' strong interest in MDR stems from the availability of agents capable of interfering with MDR, at least in vitro. If these laboratory results were reproducible in vivo, reversal of MDR would offer a rare opportunity to incorporate laboratory experience into the clinical management of patients.

Synovial sarcoma: immunohistochemical expression of P-glycoprotein and glutathione S transferase-pi and clinical drug resistance

Our purpose was to study the role of the expression of P-glycoprotein (Pgp) and glutathione S transferase-pi (GST-pi) in predicting the response to chemotherapy, relapse-free interval, and survival of patients with synovial sarcoma (SS). Thirty-seven cases of primary SS, without regional lymph node or distant metastases, were studied. There were 17 females and 20 males, ranging in age from 7 to 81 years (median, 31 years) with tumors located in the lower extremity (n = 24) upper extremity (n = 5) and trunchus (n = 8). The cases were retrospectively studied without knowledge of clinical course to compare the immunohistochemical expression of Pgp and GST-pi, flow cytometry parameters (ploidy and % of cells in S+G2 phases), and PCNA and Ki-67 labeling of primary tumors before any therapy, with that observed in local recurrences and metastases after chemotherapy. The relationship of the aforementioned parameters with clinicopathological features (gender, age, and histo-blood group of the patients, size, location, histological subtype. TNM stage, and clinical response to chemotherapy of the tumors) was also evaluated. Results revealed that Pgp and GST-pi were expressed in 29.7% and 40.5% of the cases, respectively. In 48.6% of the tumors there was expression of a least one of the drug resistance markers. The markers were coexpressed in 25.0% of the tumors. The prevalence of Pgp expression was lower, but not significantly, in stage I-II (17.6%) than in stage III (40.0%) tumors, and also in cases without clinical progression (16.7%), than in cases with (36.0%). No such differences were observed for GST-pi expression. Pgp and GST-pi expressions were significantly associated with biphasic SS and were particularly noticeable in solid/glandular areas of biphasic SS. The expression of the drug resistance markers was not significantly associated with gender, age, and histo-blood group of the patients, dimension, location, and proliferative activity of the tumors; it was also not significantly related to relapse-free interval and survival of the patients. The expression of Pgp and GST-pi was not significantly associated either to response to chemotherapy or influenced by chemotherapy. We conclude that Pgp and GST-pi expressions are not good predictors response to of the chemotherapy in patients with localized SS. Other drug resistance mechanisms may be active in SS.

The multidrug resistance-associated protein gene confers drug resistance in human gastric and colon cancers

To determine the expression of multidrug resistance-associated protein (MRP) gene and its role in gastric and colon cancers, we analyzed 10 gastric and 10 colon non-drug-selected cell lines and a similar number of tissue samples of these cancers. We compared the expression of MRP and mdrl mRNA in cell lines and tissues using reverse-transcriptase polymerase chain reaction. In mdrl-negative cells, the relationship between the level of MRP gene expression and sensitivity to anticancer drugs was examined. The effect of verapamil, an MRP-modulating agent, was also examined in these cells. The expression of MRP gene in gastric cancer cell lines varied from a low to a high level, but mdrl was not detected in any of these cell lines. Colon cancer cell lines expressed low to intermediate levels of MRP gene, and half of the cells co-expressed low to high levels of mdrl. In tissue samples, the expression pattern of the two multidrug resistance (MDR) genes was broadly similar to that described for the cell lines, except that most of the gastric cancer tissue samples did express low levels of mdrl. No significant correlation was observed between the level of MRP gene expression and sensitivity to anticancer drugs in gastric and colon cell lines. However, verapamil significantly increased the sensitivity to etoposide, doxorubicin and vincristine in cells highly expressing MRP gene. Our results indicate that MRP gene may be important in conferring MDR in gastric and colon cancer cells.

Multidrug resistance in ocular melanoma

AIMS/BACKGROUND

Metastatic disease in patients with ocular melanoma is resistant to chemotherapy. One of the main mechanisms of modulating multidrug resistance is the expression of the multidrug resistance gene 1 (MDR1) product (p-glycoprotein) by tumour cells. The purpose of this study was to evaluate the frequency of expression of the MDR1 gene in ocular melanoma whose primary treatment was surgical excision or enucleation.

METHODS

Twelve recent ocular melanomas were received fresh, snap frozen and cryostat sections of tumour were analysed for expression of MDR1 by immunohistochemistry using a well characterised monoclonal antibody to MDR1. Tumour explants were established in short term tissue culture from four tumours and cell blocks were examined by immunohistochemistry.

RESULTS

MDR1 expression was present in five of 12 ocular melanomas. Upregulation of protein expression was found in four cell lines established in short term culture from tumour explants. A recurrent tumour, initially treated by local excision and radioactive plaque, showed overexpression of MDR1 mRNA.

CONCLUSIONS

These results suggest that significant level of MDR1 may be intrinsically present in ocular melanomas before exposure to drugs involved in multidrug resistance, and indicate the possible importance of MDR1 in modulating chemoresistance in ocular melanoma. Chemosensitisation may be of potential value in planning adjuvant chemotherapy for patients with metastatic disease.

Screening for multidrug resistance in leukemia: cell reactivity to MRK-16 correlates with anthracycline retention and sensitivity of leukemic cells

The biologic and clinical importance of the multidrug resistance (MDR) that is related with the overexpression of the P170 glycoprotein (Pgp) is widely recognized. However, a major issue that has not yet been solved is the definition of the degree of Pgp expression which is associated with a significant decrease of the sensitivity of the cells to chemotherapy. For this reason we studied the leukemic cells from 83 cases of acute leukemia. Leukemic cells were fixed in PLP and treated with saponine. Pgp expression was assayed by flow cytometry, using the anti Pgp monoclonal antibody MRK-16. Results were expressed both as the number of positive cells and by the intensity of the reaction as defined by the mean fluorescence index (MFI), i.e. the ratio between the mean fluorescence intensity of the MRK-16 incubated cells and of the IgG2a incubated cells. Thus, Pgp expression was compared with the results of two in vitro tests of cell sensitivity to anthracyclines, daunorubicin (DNR) cell retention and DNR cytotoxicity. We found that it was not the number of MRK-16 positive cells, but the degree of the reaction with MRK-16 (MFI) that significantly related to the anthracycline toxicity tests. Therefore, we propose that for clinical purposes a quick and cheap determination of Pgp-related MDR in leukemic cells may be obtained by measuring the MFI with MRK-16 in a standard flow cytometry assay and that the assay may indeed be sufficient to estimate Pgp expression as well as the influence of Pgp on cell sensitivity to anthracyclines.

Detection of the multidrug resistance marker P-glycoprotein by immunohistochemistry in malignant lung tumours

BACKGROUND

The multidrug resistance marker P-glycoprotein (P-gp) was studied immunohistochemically in 78 primary malignant lung tumours. P-gp is a 170 kD transmembrane ATP dependent drug efflux pump which has been shown to be important in the resistance of some tumours to chemotherapy. Certain normal tissues express P-gp and tumours derived from these tissues are often insensitive to cytotoxic agents, showing raised P-gp levels innately or following chemotherapy or radiotherapy.

METHODS

Samples from 78 patients undergoing surgery for primary malignant lung tumours were snap frozen and stained immunohistochemically using the monoclonal antibody C219 which reacts with a P-gp epitope. None of the study group had received chemotherapy or radiotherapy before surgery was performed.

RESULTS

Twenty seven of the 78 lung tumours (34.6%) showed immunohistochemically detectable levels of P-gp which varied with tumour type; 17 of 54 squamous cell carcinomas (31.5%), seven of 15 adenocarcinomas (46.7%), and neither of two small cell carcinomas showing positive staining. In six of seven cases normal respiratory epithelium present showed the presence of P-gp.

CONCLUSIONS

P-gp is immunohistochemically detectable in frozen tissue from a proportion of malignant lung tumours before exposure to radiotherapy or drugs associated with multidrug resistance. It may have a role in tumour resistance to cytotoxic drugs, but further clinical studies will be required to evaluate any correlation between P-gp levels and response to treatment.