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H J Broxterman

Publications and source records attributed to H J Broxterman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Modulation by (iso)flavonoids of the ATPase activity of the multidrug resistance protein.

The multidrug resistance protein (MRP) is an ATP-dependent transport protein for organic anions, as well as neutral or positively charged anticancer agents. In this study we report that dinitrophenyl-S-glutathione increases ATPase activity in plasma membrane vesicles prepared from the MRP-overexpressing cell line GLC4/ADR. This ATPase stimulation parallels the uptake of DNP-SG in these vesicles. We also show that the (iso)flavonoids genistein, kaempferol and flavopiridol stimulate the ATPase activity of GLC4/ADR membranes, whereas genistin has no effect. The present data are consistent with the hypothesis that certain (iso)flavonoids affect MRP-mediated transport of anticancer drugs by a direct interaction with MRP.

ATP-Binding Cassette Transporters↗
PubMed1997

Highly sensitive and specific detection of P-glycoprotein function for haematological and solid tumour cells using a novel nucleic acid stain.

Progress in our understanding of the contribution of P-glycoprotein (P-gp)-mediated resistance to chemotherapy failure in haematological as well as solid tumours has been hampered by the lack of highly sensitive, reliable methods for the detection of P-gp function in fresh human tumour cells. The present study identifies the novel nucleic acid stain SYTO16 as a highly sensitive and specific dye to assess P-gp function. The effect of P-gp is expressed here as the ratio of dye fluorescence (RF) from cells incubated with dye with or without 2 microM of the P-gp inhibitor PSC 833. Using flow cytometric analysis, an RF of 0.9 was found for SYTO16 in the KB3-1 (P-gp-) and 1.6 in KB8 (P-gp+) cells. Three types of patients' cells were studied: (1) in haematopoietic CD34+ cells, which are known to express P-gp, the RF was 6.0 for SYTO16 compared with 2.5 for rhodamine 123 and 1.3 for daunorubicin (mean of five individuals); (2) in acute myeloid leukaemia cells, the RF for SYTO16 was 1.0 in P-gp- and 4.5 in P-gp+ samples; (3) for the first time, we have quantitated P-gp function in fresh human solid tumour (sarcoma) cells. We found, in a P-gp+ leiomyosarcoma, an RF of 16 for SYTO16 and 2.7 for daunorubicin. This means that complete inhibition of P-gp function in these sarcoma cells would lead to an increase of daunorubicin accumulation with 170% compared with 30% in the CD34+ cells. Next, we showed that SYTO16 could be fixed in nuclei by 3.6% formaldehyde treatment, allowing quantification of the nuclear fluorescence on cytospins by laser scanning microscopy. In conclusion, SYTO16 proved to have a combination of favourable properties: it can be excited at 488 nm and has large fluorescence enhancement upon binding to nucleic acids, allowing the use of low, nontoxic (< 10 nM) concentrations. Because the RF for SYTO16 is much higher than for daunorubicin, it can be applied for the determination of P-gp function in relatively small numbers of low-P-gp-expressing tumour cells by laser scanning microscopy. Individual sarcomas were found to have high P-gp function compared with CD34+ cells. This assay may be used to select patients for P-gp modulation protocols.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Theoretical and practical considerations for the measurement of P-glycoprotein function in acute myeloid leukemia.

This paper summarizes experimental data and theoretical considerations, that are important for the measurement of P-glycoprotein (Pgp) function in acute myeloid leukemia (AML). The data are presented in subdivisions based on the techniques used, which will facilitate finding specific information. Based on our extensive experience with Pgp analysis, which includes radioactive assays, flow cytometry and fluorescence microscopy, we recommend a flow cytometry-based assay, that measures the effect of 2 microM PSC 833 on rhodamine 123 (R123) accumulation as the most practical and sensitive functional Pgp test. In combination with the flow cytometric measurement of Pgp using an antibody against an extracellular epitope (eg MRK16), this offers a sensitive and reproducible method for Pgp detection in AML, which is also rapid and practical. Furthermore, an R123 accumulation assay is specific for Pgp, because R123 is transported much less efficiently by the multidrug resistance protein (MRP) than by Pgp. Another probe of similar sensitivity and specificity is 3,3'-diethyloxacarbocyanine iodide. Alternatively, especially for the analysis of small numbers of cells (for example sorted subpopulations of leukemic cells), convenient and sensitive procedures are being developed by using DNA-binding Pgp substrates which remain fixed in the nuclei of the cells upon formaldehyde exposure for quantitative fluorescence laser scanning microscopy with image analysis. Less experimental data have been published to establish the optimal conditions for dual parameter flow cytometry (Pgp function, in eg Pgp+ or CD34+ cells). However, laboratories with flow cytometry experience will be able to implement this useful option to analyze subpopulations of cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Transport proteins in drug resistance: detection and prognostic significance in acute myeloid leukemia.

Resistance to natural product-derived anti-cancer drugs, such as the anthracyclines and etoposide, contributes to the failure of chemotherapeutic treatment of leukaemia. One biological resistance mechanism of potential importance is the overexpression of the plasma membrane drug transporter proteins P-glycoprotein (Pgp) and multidrug resistance protein (MRP). Many studies have reported evidence for a correlation of Pgp/MDR1 expression with unfavourable prognostic features in acute myeloid leukaemia (AML). Failure to achieve complete remission (CR) is correlated with Pgp and the CD34+ phenotype. For MRP fewer data are available, which suggest a basal expression level in most AMLs. Another protein reported to correlate with treatment failure in AML is the lung resistance protein or major vault protein (LRP), a protein with a still unknown function. Co-expression of Pgp and LRP especially seems to define an adverse prognostic population. Further progress towards the understanding of the clinical importance of these proteins is hampered by the lack of validation of methods to determine their expression. A reliable way to measure Pgp seems to be the assessment of the active transport of fluorescent Pgp substrates, such as rhodamine 123 out of AML cells. Such functional Pgp assays can be used to validate mRNA or protein measurements and to quantify the effect of Pgp or the magnitude of the effect of a blocker of the Pgp-mediated drug efflux on the intracellular drug concentration. The prognostic value of such methods has still to be shown.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Platelet: transporter of vascular endothelial growth factor.

In animal models, growth of tumors and their metastases is dependent on factors that stimulate vessel formation (angiogenesis). Most clinical studies confirm the importance of angiogenesis for cancer growth in patients. Recent studies on circulating angiogenic factors in patients have focused on serum vascular endothelial growth factor (VEGF) levels in a variety of cancer types. We measured serum VEGF concentrations and blood counts in 27 breast cancer patients during each of 6 cycles of chemotherapy with doxorubicin and cyclophosphamide supported by granulocyte macrophage colony-stimulating factor. Serum VEGF concentrations highly correlated with platelet counts during chemotherapy (r = 0.8; P < 0.01). In particular, during the first treatment cycle, after an initial episode of thrombocytopenia, a strong platelet rebound coincided closely with a serum VEGF peak (r = 0.9; P < 0.01). In addition, plasma VEGF concentrations from 15 other cancer patients and 30 healthy volunteers were 5- to 8-fold lower than their corresponding serum VEGF concentrations (P < 0.001). Activation of platelets increased the VEGF content 8-10 times. These findings demonstrate that VEGF is released by platelets during serum preparation. In this study, we found evidence for VEGF transport by platelets, indicating that serum VEGF concentrations reflect mainly platelet counts rather than tumor burden in cancer patients, as reported earlier. Platelets, known to be important for wound healing, have also been reported to contribute to metastasis formation and tumor growth in animal models. Indeed, tumors can be regarded as never-healing wounds. Our data suggest that platelets may have a stimulating role on angiogenesis-dependent tumor growth through their function as transporters of VEGF.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1996

Methods to detect P-glycoprotein-associated multidrug resistance in patients' tumors: consensus recommendations.

Multidrug resistance (MDR), especially that associated with overexpression of MDR1 and its product, P-glycoprotein (Pgp), is thought to play a role in the outcome of therapy for some human tumors; however, a consensus conclusion has been difficult to reach, owing to the variable results published by different laboratories. Many factors appear to influence the detection of Pgp in clinical specimens, including its low and heterogeneous expression; conflicting definitions of detection end points; differences in methods of sample preparation, fixation, and analysis; use of immunological reagents with variable Pgp specificity and avidity and with different recognition epitopes; use of secondary reagents and chromogens; and differences in clinical end points. Also, mechanisms other than Pgp overexpression may contribute to clinical MDR. The combined effect of these factors is clearly important, especially among tumors with low expression of Pgp. Thus, a workshop was organized in Memphis, Tennessee, to promote the standardization of approaches to MDR1 and Pgp detection in clinical specimens. The 15 North American and European institutions that agreed to participate conducted three preworkshop trials with well-characterized MDR myeloma and carcinoma cell lines that expressed increasing amounts of Pgp. The intent was to establish standard materials and methods for a fourth trial, assays of Pgp and MDR1 in clinical specimens. The general conclusions emerging from these efforts led to a number of recommendations for future studies: (a) although detection of Pgp and MDR1 is at present likely to be more reliable in leukemias and lymphomas than in solid tumors, accurate measurement of low levels of Pgp expression under most conditions remains an elusive goal; (b) tissue-specific controls, antibody controls, and standardized MDR cell lines are essential for calibrating any detection method and for subsequent analyses of clinical samples; (c) use of two or more vendor-standardized anti-Pgp antibody reagents that recognize different epitopes improves the reliability of immunological detection of Pgp; (d) sample fixation and antigen preservation must be carefully controlled; (e) multiparameter analysis is useful in clinical assays of MDR1/Pgp expression; (f) immunostaining data are best reported as staining intensity and the percentage of positive cells; and (g) arbitrary minimal cutoff points for analysis compromise the reliability of conclusions. The recommendations made by workshop participants should enhance the quality of research on the role of Pgp in clinical MDR development and provide a paradigm for investigations of other drug resistance-associated proteins.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

MRP is frequently expressed in human lung-cancer cell lines, in non-small-cell lung cancer and in normal lungs.

The multidrug resistance-associated protein (MRP), a new membrane transporter related to non-Pgp multidrug resistance, is overexpressed in some drug-selected cancer-cell lines. The role of MRP in unselected cell lines and in human cancer is unknown. MRP gene expression, determined by RNase protection assay and chemosensitivity to doxorubicin, etoposide and cisplatin, determined by MTT assay, were assessed in 18 non-drug-selected lung-cancer cell lines (10 small-cell lung cancer, 6 non-small-cell lung cancer, and 1 carcinoid). MRP gene expression was also investigated in normal lung tissue and primary non-small-cell lung cancer. All cell lines except one and all normal lung tissues and primary non-small-cell lung cancers expressed detectable levels of MRP. Expression was significantly lower in cell lines than in normal and neoplastic lung. MRP protein expression was also assessed by immunohistochemistry using the monoclonal antibody MRPr1; comparable levels of expression were observed between mRNA and protein in cell lines; however, in tumor samples intense staining was observed in tumor cells as well as in infiltrating normal cells in tumors, making the results less comparable to those obtained by RNase expression. MRP expression did not directly correlate with function in a calcein accumulation assay in 2 unselected cell lines. No gene amplification was observed by Southern-blot analysis, in the unselected cell lines or in tumor samples. In general, in cell lines, MRP gene expression was correlated with lower chemosensitivity to doxorubicin and etoposide, but not to cisplatin. However, MRP expression did not directly correlate with MRP function as assessed by a calcein accumulation assay in one of 2 unselected cell lines examined. Our results suggest that MRP may be implicated in drug resistance in unselected lung-cancer cell lines and its role in normal lung and primary lung cancer warrants further investigation in patients undergoing chemotherapy.

ATP-Binding Cassette Transporters↗
PubMed1996

Quality control of multidrug resistance assays in adult acute leukemia: correlation between assays for P-glycoprotein expression and activity.

We have compared multiple assays for the P-glycoprotein (Pgp/MDR1) phenotype in fresh and thawed adult acute leukemia to validate and quantitate measures for the expression and function of Pgp. The results are related to the Pgp-expressing KB8 and KB8-5 call lines. The most sensitive assay was the measurement of modulation of the rhodamine 123 (R123) fluorescence by 2 micromol/L PSC833, followed by the modulation of the probe calcein-AM. We also found a good intralaboratory and interlaboratory correlation between the values of the R123/PSC833 assay for fresh as well as thawed samples. In addition, the affects of PSC833 on 3H-daunorubicin (DNR) accumulation, DNR fluorescence, and 3H-vincristine accumulation were very similar. The correlation between the DNR/PSC833 and R123/PSC833 test was r = .86 (N = 51). The modulation of drug accumulation by 8 micromol/L verapamil was the some as the PSC833 effect for DNR (117%, N = 21), but was higher for vincristine in every single case (161% v 121%, N = 22; P< .001), indicating additional verapamil effects, not related to Pgp. The correlation of the staining of viable cells for Pgp with the monoclonal antibody MRK16 was r = .77 (N = 52) for the R123/PSC833 functional test and r = .84 (N = 50) for the DNR/PSC833 test. From these results it could be calculated that a maximal increase of the mean DNR accumulation of about 50% can be achieved by blocking Pgp pump activity with PSC833 in leukemic blast samples with the highest mean Pgp expression. Subpopulations of blast calls with higher Pgp activity are likely to be present. Their relevance has to be studied further. The methods outlined here allow the reliable, quantitative monitoring of the Pgp/MDR1 phenotype in leukemias in multicentered, clinical Pgp modulation studies.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Overexpression of the major vault transporter protein lung-resistance protein predicts treatment outcome in acute myeloid leukemia.

The monoclonal antibody LRP56 recognizes a 110-kD major vault protein (lung-resistance protein [LRP]) overexpressed in several P-glycoprotein-negative (Pgp-), multidrug resistant tumor cell lines. To determine the frequency of LRP overexpression, its prognostic significance, and its relation to Pgp, we analyzed bone marrow specimens from 87 consecutive patients with acute leukemia. Diagnoses included de novo acute myeloid leukemia (AML; 21 patients), leukemia arising from an antecedent hematologic disorder or prior cytotoxic therapy (secondary AML; 27 patients), AML in relapse (29 patients), and blast phase of chronic myeloid leukemia (CML-BP; 10 patients). A granular cytoplasmic staining pattern was detected by immunocytochemistry in 32 (37%) cases, including 7 (33%) de novo AML, 13 (48%) secondary AML, 11 (38%) relapsed AML, and 1 of 10 CML-BP. Among 66 evaluable patients with AML, LRP overexpression was associated with an inferior response to induction chemotherapy (P = .0017). Remissions were achieved in 35% of LRP+ patients as compared with 68% of LRP- patients. Although Pgp adversely affected response in univariate analysis (P = .0414), only LRP had independent prognostic significance when compared in a logistic regression model (P = .0046). Differences in remission duration (P = .075) and overall survival (P = .058) approached significance only for LRP. Sequential specimens from remitting patients receiving treatment with the Pgp modulator cyclosporin-A showed emergence of the LRP phenotype despite a decrease or loss of Pgp at the time of treatment failure (P =.0304). Significant associations were observed between LRP and age greater than 55 years (P = .017), Pgp (P = .040), and prior treatment with mitoxantrone (P = .020) but not with CD34. These findings indicate that overexpression of the novel transporter protein LRP is an important predictor of treatment outcome in AML.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Broad distribution of the multidrug resistance-related vault lung resistance protein in normal human tissues and tumors.

Multidrug resistance (MDR) to anticancer drugs is a major cause of treatment failure in cancer. The lung resistance protein LRP is a newly described protein related to MDR in several in vitro models. LRP has been shown to be a strong predictor of poor response to chemotherapy and prognosis in acute myeloid leukemia and in ovarian carcinoma patients. Recently, based on a 57% and 88% amino acid identity with major vault proteins from Dictyostelium discoideum and Rattus norvegicus, respectively, we identified LRP as the human major vault protein, the main component of highly conserved cellular organelles named vaults. We have studied the immunohistochemical expression of LRP in freshly frozen normal human tissues and 174 cancer specimens of 28 tumor types. LRP was broadly distributed in normal and malignant cells, but distinct patterns of expression were noticed. High LRP expression was seen in bronchus, digestive tract, renal proximal tubules, keratinocytes, macrophages, and adrenal cortex whereas varying ing levels were observed in other organs. LRP was detected in all tumor types examined, but its frequency varied, fairly reflecting the chemosensitivity of different cancers. For example, low rates of LRP positivity were seen in testicular cancer, neuroblastoma, and acute myeloid leukemia; intermediate in ovarian cancer; and high in colon, renal, and pancreatic carcinomas. The wide occurrence of LRP in normal and transformed cells in humans, its similar distribution to that of vaults in other species, as well as the high level of conservation among eukaryotic cells of both the amino acid sequence of the major vault protein and the composition and structure of vaults, suggest that vault function is important to eukaryotic cells.

Adult↗
PubMed1995

The LRP gene encoding a major vault protein associated with drug resistance maps proximal to MRP on chromosome 16: evidence that chromosome breakage plays a key role in MRP or LRP gene amplification.

A cDNA encoding the novel drug resistance gene, LRP (originally termed lung resistance-related protein), was isolated from HT1080/DR4, a 220-fold doxorubicin-resistant human fibrosarcoma cell line which displays a multidrug resistance phenotype and overexpresses the multidrug resistance protein (MRP) but does not overexpress P-glycoprotein encoded by the MDR1 gene. Using the full-length 2.8-kb cDNA probe, the gene for LRP was regionally localized to the 16p13.1-16p11.2 chromosomal segment in human metaphases. Dual color fluorescence in situ hybridization studies refined the localization of LRP to 16p11.2, a location approximately 27 cM proximal to MRP (16p13.1). Two color hybridization studies indicated that HT1080/DR4 fibrosarcoma cells contain amplification of both the MRP and LRP genes in a striking striped pattern in the homogeneously staining region, hsr(7)(p12p15). In contrast, only amplified MRP gene sequences were contained within the homogeneously staining region, hsr(18q). Amplification of LRP was not identified in any of seven other drug-resistant tumor cell lines characterized by 20-300-fold levels of doxorubicin resistance, including two cell lines known to overexpress LRP (SW1573/2R120 and GLC4/ADR). Amplified MRP gene sequences were identified in H69AR, GLC4/ADR, and HL-60/AR whereas only MDR1 gene amplification was observed in the S1B120 colon carcinoma cell line. These data indicate that although both the MRP and LRP genes map to the short arm of chromosome 16, they are rarely coamplified and are not normally located within the same amplicon. A key role for chromosome breakage in gene amplification is supported by the presence of non-random karyotypic anomalies near the MRP and LRP normal cellular loci.

Chromosome Mapping↗
PubMed1995

ATP-dependent efflux of calcein by the multidrug resistance protein (MRP): no inhibition by intracellular glutathione depletion.

In this study we report that the multidrug resistance protein (MRP) transports calcein from the cytoplasmic compartment of tumor cells, in contrast to P-glycoprotein which transports calcein acetoxymethyl ester from the plasmamembrane. The transport of calcein by MRP is ATP-dependent and is inhibited by probenecid and vincristine. Intracellular glutathione (GSH) depletion which occurred when cells were exposed to buthionine sulfoximine had no effect on the efflux of calcein, whereas it reversed the daunorubicin accumulation deficit in MRP overexpressing tumor cells. In conclusion, ATP-dependent transport of calcein and possibly other organic anions by MRP is not inhibited by a large decrease of the intracellular GSH concentration, that inhibits daunorubicin efflux by MRP.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Correlation between functional and molecular analysis of mdr1 P-glycoprotein in human solid-tumor xenografts.

The contribution of P-glycoprotein (Pgp) to multidrug resistance in human solid tumors is generally estimated from bulk mRNA measurements or immunohistochemistry, while direct measurement of the effect of Pgp on intracellular drug concentrations has not been pursued. We investigated the feasibility and sensitivity of a method for probing Pgp-mediated drug transport in cells isolated from solid tumors, using xenograft models. Human tumor xenografts (XG) were grown by s.c. injection of Pgp-expressing cell lines 2780AD, BRO/mdr1 and KB8-5. Tumor uptake of doxorubicin (DOX) after administration of DOX to the mice was determined. XG from untreated mice were enzymatically dissociated. The effect of the Pgp modulator bepridil on steady-state cellular daunorubicin (DNR) and vincristine (VCR) accumulation and chemosensitivity of these XG cells was compared with its effects in the cell lines (CL). mdr1 mRNA and Pgp (by flow cytometry) were measured. Also, the dependence on intracellular ATP concentration, [ATP]i, of the modulator effect was determined in intact KB8-5 cells. The results showed that i.v. administration of DOX to the mice led to lower DOX levels in the Pgp-expressing XG than in the "sensitive" XG, suggesting the presence of an in vivo functional Pgp in these XG tumor models. Dissociated, viable XG cells appeared to have ATP levels sufficient to sustain Pgp-ATPase-coupled drug transport. This was inferred from experiments using KB8-5 CL, which showed half-maximal inhibition of DNR transport at an [ATP]i of 1 to 2 mM. The effect of bepridil on DNR and VCR accumulation and chemosensitivity in the XG cells was in accordance with the XG expression of mdr1/Pgp. In KB8-5 XG cells, Pgp function was hardly detectable, in accordance with decreased mdr1/Pgp expression in vivo. In conclusion, Pgp activity can be determined in freshly dissociated XG human tumor cells. The results obtained with the more necrotic KB8-5 XG may represent some of the interpretation problems arising when low levels of Pgp expression occur within a heterogeneous cell population, such as may be expected in clinical human tumors. Also our results indicate that Pgp activity may be impaired in vivo at [ATP]i below 2 mM, which are realistic values for human solid tumors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Resistance-associated factors in human small-cell lung-carcinoma GLC4 sub-lines with increasing adriamycin resistance.

Previous studies have shown that the in vitro-selected adriamycin-resistant human small-cell lung-carcinoma cell line GLC4-ADR150 displays multidrug resistance as the result of 3-fold decreased DNA-topoisomerase II (topo II) activity and a 6-fold reduction in adriamycin accumulation. Not the MDR1 gene, but the MRP gene, was over-expressed in this cell line. The aim of our study was to establish which of these drug-resistance-associated factors are already involved in drug resistance occurring at early steps of selection with adriamycin. To address this question, changes in expression of topo II alpha/topo II beta, MRP and drug accumulation were measured along with adriamycin resistance (from 2- to 10- to 150-fold) and in a partial revertant cell line (10-fold resistant). Topo II alpha and II beta mRNA and protein levels were decreased in the resistant sub-lines, except in the 10-fold-resistant cell line. Cellular daunorubicin accumulation was decreased 1.2- to 5-fold with increasing resistance. MRP mRNA was over-expressed in all resistant sub-lines, with a marked increase in the 10-fold-resistant cells (level of expression as high as in the GLC4-ADR150 cells). Expression of an ATP-binding 190-kDa membrane protein and Western-blot analysis with anti-MRP anti-serum ASPKE, was in accordance with the expression of MRP mRNA in all cell lines. Expression of MRP mRNA and protein, however, was not proportional with the decrease in drug accumulation in all resistant sub-lines. This study also shows that drug accumulation, topo II and MRP expression were all changed at the earliest stage of resistance development of GLC4 cells upon adriamycin selection.

ATP-Binding Cassette Transporters↗