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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↗
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

Expression of the human major vault protein LRP in acute myeloid leukemia.

Overexpression of a 110-kD protein (lung resistance-related protein [LRP]) may predict a poor response to chemotherapy in patients with acute myeloid leukemia (AML) and ovarian carcinoma. The LRP gene has recently been mapped to chromosome 16, close to the multidrug resistance-associated protein (MRP) gene. Seventy-seven samples from 67 patients with AML were examined for expression of LRP, MRP, and multidrug resistance (MDR1) mRNA using a semiquantitative reverse transcription polymerase chain reaction (RT-PCR) assay. Results were compared with 29 normal samples (11 normal peripheral blood and 18 normal bone marrow). Thirty-three patients with untreated AML were evaluable for response to chemotherapy. Levels of LRP, but not of MRP or MDR1 mRNA, were significantly higher in eight patients who failed to achieve complete remission (CR) compared with 25 patients who achieved CR (p = 0.033). A positive correlation was demonstrated between LRP and MRP (R = 0.368, p = 0.001) and between MRP and MDR1 mRNA levels (R = 0.301, p = 0.01) in the 77 clinical samples analyzed. In AML samples, a significant difference in MDR1 mRNA levels was found between presentation (47 samples) and relapse (30 samples) (p = 0.031). No significant difference was seen in LRP mRNA levels between these two groups or in eight patients studied sequentially at both presentation and relapse. Thirteen samples (10 at presentation, 3 at relapse) were analyzed for LRP protein expression by flow cytometry. Eight (5 at presentation, 3 at relapse) displayed greater than 10% positive cells (range 15-86%). These data suggest that LRP gene overexpression may constitute a novel mechanism of multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Multidrug resistance-related proteins in primary choroidal melanomas and in vitro cell lines.

PURPOSE: Metastatic uveal melanoma is strongly resistant to chemotherapy, and multidrug resistance (MDR) may be involved. To investigate the role of MDR, the presence of the MDR-associated proteins P-glycoprotein (Pgp), MRP, and lung resistance protein (LRP) was determined on primary choroidal melanomas and cell lines. METHODS: A panel of primary choroidal melanomas was examined for the presence of MDR-associated proteins by immunohistochemical analysis. In cell lines established from four primary choroidal melanomas and one metastatic choroidal melanoma, the expression of MDR-associated proteins was determined with monoclonal antibodies in cytospin preparations and flow cytometry. In addition, the functional capacities of transporter proteins Pgp and MRP as adenosine triphosphate-driven efflux pumps were determined by measuring the cellular accumulation and efflux of the fluorescent dyes rhodamine 123 and calcein-AM, with and without the presence of specific pump inhibitors PSC833 and probenecid. RESULTS: Low levels of Pgp and MRP were detected in most primary tumors and in some cell lines. Measurable transporter function of Pgp could be determined in cell line OCM-1. Lung-resistance protein was present in all primary tumors and cell lines and showed high expression levels. CONCLUSIONS: This study revealed the involvement of LRP and at least a minor role of Pgp and MRP in chemoresistance of choroidal melanoma. Compared with cutaneous melanomas, uveal melanomas appear to express slightly higher levels of Pgp. These findings provide insights into the drug-resistant phenotype of this disease and can aid in the design of therapeutic protocols.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Non-P-glycoprotein drug export mechanisms of multidrug resistance.

A variety of cellular mechanisms of multidrug resistance (MDR) have been identified in human drug-resistant cell lines, and may play an important role in the clinical response of hematologic malignancies to chemotherapy. P-glycoprotein (P-gp)-mediated drug efflux is the most well-characterized cellular mechanism of MDR; however, several other non-P-gp membrane transporter proteins have also been implicated in the development of an MDR phenotype in hematologic malignancies. These include the MDR-related protein (MRP), the lung-resistance protein (LRP), and the transporter of antigenic peptides (TAP). The transporter proteins MRP and TAP are both members of the adenosine triphosphate (ATP)-binding cassette (ABC) family of transmembrane transporters, but each has distinct differences in substrate specificity. Despite effective modulation of P-gp, one or more of these alternate mechanisms of drug resistance may contribute to an MDR phenotype in tumor cell lines. Development of multifunctional MDR modulators or novel therapeutics may be necessary to effectively circumvent MDR in hematologic malignancies.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

The prognostic significance of the expression and function of multidrug resistance transporter proteins in acute myeloid leukemia: studies of the Southwest Oncology Group Leukemia Research Program.

Resistance to chemotherapy is a major obstacle in the treatment of patients with acute myeloid leukemia (AML). The majority of AML patients are intrinsically resistant to chemotherapy at initial diagnosis before chemotherapeutic exposure; such intrinsic resistance frequently results from expression of the multidrug resistance gene (MDR-1), which encodes a membrane transporter protein, P-glycoprotein (P-gp), that mediates drug efflux in leukemic cells. Expression of novel transporter proteins that confer alternative forms of multidrug resistance (MDR), such as the lung-resistance protein (LRP) and the MDR-associated protein (MRP), occurs more frequently in leukemic patients at relapse. Preliminary studies indicate that these proteins may also confer therapeutic resistance in leukemia. In patients older than 55 years of age, AML is characterized by a high frequency of unfavorable cytogenetics, P-gp expression, and functional drug efflux, which contribute to poor clinical outcome. In a multivariate analysis, secondary AML, unfavorable cytogenetics, and P-gp expression/function were each significantly and independently associated with a lower complete remission (CR) rate. Resistant disease was associated with P-gp expression and unfavorable cytogenetics. Strikingly, elderly patients with P-gp- de novo AML and favorable or intermediate cytogenetics had a CR rate of 81%. Patients with P-gp+ secondary AML with unfavorable cytogenetics had a CR rate of only 12%. Therefore, characterization of elderly AML patients at diagnosis using biologic parameters may help identify those patients who are likely to achieve a CR with conventional regimens, as well as those patients who require alternate treatment designed to overcome MDR. In contrast, expression of P-gp and functional drug efflux is detected in only 25% to 30% of AML patients less than 50 years of age. While P-gp expression is less strongly associated with a poor outcome in younger versus older AML patients, it remains strongly associated with resistant disease. Studies are ongoing to determine the prognostic significance of LRP and MRP in various forms of leukemia.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Drug resistance in multiple myeloma.

The development of multidrug resistance (MDR) is a major obstacle to improving treatment outcomes in multiple myeloma. Recent studies have indicated that several specific mechanisms of MDR may be involved in clinically refractory multiple myeloma patients, such as expression of P-glycoprotein (P-gp), expression of the lung-resistance protein (LRP) and suppression of apoptosis via expression of Bcl-2. The emergence of these mechanisms of MDR in multiple myeloma is enhanced by exposure to chemotherapeutic agents. Recently, clinical reversal of MDR by noncytotoxic P-gp modulators such as verapamil, cyclosporin A (CsA), and PSC 833 was explored in acute leukemia and multiple myeloma. Preliminary results from clinical phase I/II trials indicate that reversal of MDR via modulation of P-gp is possible and that coadministration of these MDR modulators with chemotherapeutic agents alters the plasma pharmacokinetics of chemotherapeutic agents. Phase II and III clinical trials investigating the efficacy of these and other agents in the reversal of MDR in hematologic malignancies are ongoing.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

c-Ha-ras transfection and expression of MDR-related genes in MCF-10A human breast cell line.

BACKGROUND: We studied the relationship between ras transfection and the drug resistance phenotype in the MCF-10A cell line (a non-transformed immortalized human breast epithelial cell line). MATERIALS AND METHODS: Parental (MCF-10A) and c-Ha-ras transfected (MCF-10A H) cell lines were tested for resistance to Doxorubicin, Maphosphamide and Cisplatinum, by evaluating the inhibition of [3H]-thymidine incorporation. Cells were also examined for the expression of different resistance mechanisms by immunocytochemical and RT-PCR methods. RESULTS: ras-transfected cells were much more resistant to Cis-platinum than parental ones. GST-pi the GST isoenzyme frequently involved in human cancers) increased only in transfected cells. No expression of any other resistance mechanisms (MDR, MRP, LRP) was found by immunocytochemistry either in parental or in transfected cells; nevertheless, the more sensitive RT-PCR tests detected mrp products in parental and in transfected cells: gene expression levels were low and equivalent in both cell lines. CONCLUSIONS: ras transfection can induce resistance to Cis-platinum by increasing GST-pi expression.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Drug retention, efflux, and resistance in tumor cells.

Multiple drug resistance (MDR) in tumor cells has been related to the expression of transport proteins which alter cellular drug transport and distribution. Three different genes (mdr, MRP, and LRP) and their products have been implicated in MDR. Several fluorescent dyes have been used to monitor the effect of these transport proteins on drug retention, as well as for screening of drugs which block drug efflux and thus enhance cellular drug retention and cytotoxicity. The present review summarizes current knowledge about MDR phenotypic markers and techniques available for study of MDR by flow cytometry.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Lung-resistance-related protein expression is a negative predictive factor for response to conventional low but not to intensified dose alkylating chemotherapy in multiple myeloma.

This study was undertaken to assess the significance of lung-resistance related protein (LRP) expression in plasma cells from untreated multiple myeloma (MM) patients and to determine whether LRP was associated with a poor response and survival in patients treated with different dose regimens of melphalan. Seventy untreated patients received conventional oral dose melphalan (0.25 mg/kg, day 1 to 4) combined with prednisone (MP) or intravenous intermediate-IDM; 70 mg/m2) or high- (140 mg/m2) dose Melphalan (HDM). LRP expression was assessed with immunocytochemistry using the LRP-56 monoclonal antibody. LRP expression was found in 47% of patients. In the MP treated patients, LRP expression was a significant prognostic factor regarding response induction (P < .05), event free survival (P < .003), and overall survival (P < .001). In the intensified dose melphalan treated patients LRP did not have a prognostic value. The response rates of LRP-positive patients to MP and IDM/HDM were 18% versus 81%, respectively (P < .0001). We conclude that LRP is frequently expressed in untreated MM patients and is an independent predictor for response and survival in patients treated with MP. Pretreatment assessment of LRP identifies a subpopulation of patients with a poor probability of response to conventional dose melphalan. Dose intensification of melphalan is likely to overcome LRP-mediated resistance.

Adult↗
PubMed1998

Immunohistochemical detection of the human major vault protein LRP with two monoclonal antibodies in formalin-fixed, paraffin-embedded tissues.

Multidrug resistant cancer cells frequently overexpress the 110-kd lung resistance-related protein (LRP) as detected with the monoclonal antibody (MAb) LRP-56. Recently, we identified LRP as the major vault protein (MVP), which is the major constituent of vaults, multisubunit cellular organelles. Clinically, LRP/MVP expression in cancer at time of diagnosis provided a strong and independent prognostic factor for response to chemotherapy and outcome in different tumor types, notably acute myeloid leukemia and ovarian cancer. To facilitate additional immunohistopathological studies, we have optimized LRP/MVP detection in paraffin-embedded tissues using two monoclonal antibodies, LRP-56 and LMR-5. Blocking experiments showed that LRP-56 and LMR-5 MAbs detect different epitopes of LRP/MVP. Immunohistochemical studies with both MAbs in a panel of human multidrug resistant tumor cell lines, normal tissues, and colorectal tumors showed that LRP/MVP expression can be reliably detected after formalin-fixation and paraffm-embedding using overnight incubation at 4 degrees C with the primary MAbs at 5- to 10-fold higher concentrations (ie, 1 to 10 microg/ml) as currently used with frozen sections. Both streptavidin-biotin complex and alkaline phosphatase-anti-alkaline phosphatase techniques could be successfully used for signal-amplification. Staining quality did not benefit from antigen-retrieval pretreatments. The optimized staining methodology facilitates studies in archival material on the putative role of LRP/MVP in clinical drug resistance.

Antibodies, Monoclonal↗
PubMed1998

Expression of the lung resistance protein predicts poor outcome in de novo acute myeloid leukemia.

The 110-kD lung resistance protein (LRP) is overexpressed in P-glycoprotein-negative multidrug-resistant cell lines and most likely involved in the multidrug resistance (MDR) of these cell lines. To determine the clinical significance of LRP, we have studied LRP expression of leukemic blasts and its association with clinical outcome in patients with de novo acute myeloid leukemia (AML). LRP expression of leukemic blasts obtained from peripheral blood or bone marrow of previously untreated patients (n = 86) was determined by immunocytochemistry by means of monoclonal antibody LRP-56. LRP expression at diagnosis was detected in 31 (36%) patients. LRP expression was independent of age and sex of the patients, French-American-British subtype, cytogenetic abnormalities, and lactate dehydrogenase levels, but correlated with white blood cell count (P = .01). Eighty-two patients received standard induction chemotherapy that included cytarabine and MDR drugs (daunorubicin in most patients, additional etoposide in the majority of patients). The complete remission rate of induction chemotherapy was 72% (95% confidence interval [CI] = 61% to 82%) for the total study population. The complete remission rate was 81% (95% CI = 67% to 91%) for patients without LRP expression but only 55% (95% CI = 36% to 74%) for patients with LRP expression (P = .01). Overall survival and disease-free survival were estimated according to Kaplan-Meier in 82 and 59 patients, respectively. Overall survival was significantly longer in patients without LRP expression than in patients with LRP expression. At a median follow-up of 16 months, median overall survival was 17 months (95% CI = 12 to 38 months) for LRP-negative patients but only 8 months (95% CI = 4 to 12 months) for -positive patients (P = .006). Disease-free survival was 9 months (95% CI = 7 to 11 months) for LRP-negative patients and 6 months (95% CI = 5 to 8 months) for -positive patients (P = .078). Outcome was best in patients lacking both LRP and P-glycoprotein expression. In conclusion, LRP predicts for poor outcome and thus the LRP gene appears to be another clinically relevant drug resistance gene in AML.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Relationship between major vault protein/lung resistance protein, multidrug resistance-associated protein, P-glycoprotein expression, and drug resistance in childhood leukemia.

Cellular drug resistance is related to a poor prognosis in childhood leukemia, but little is known about the underlying mechanisms. We studied the expression of P-glycoprotein (P-gp), multidrug resistance (MDR)-associated protein (MRP), and major vault protein/lung resistance protein (LRP) in 141 children with acute lymphoblastic leukemia (ALL) and 27 with acute myeloid leukemia (AML) by flow cytometry. The expression was compared between different types of leukemia and was studied in relation with clinical risk indicators and in vitro cytotoxicity of the MDR-related drugs daunorubicin (DNR), vincristine (VCR), and etoposide (VP16) and the non-MDR-related drugs prednisolone (PRD) and L-asparaginase (ASP). In ALL, P-gp, MRP, and LRP expression did not differ between 112 initial and 29 unrelated relapse samples nor between paired initial and relapse samples from 9 patients. In multiple relapse samples, LRP expression was 1.6-fold higher compared with both initial (P = .026) and first relapse samples (P = .050), which was not observed for P-gp and MRP. LRP expression was weakly but significantly related to in vitro resistance to DNR (Spearman's rank correlation coefficient 0.25, P = .016) but not to VCR, VP16, PRD, and ASP. No significant correlations were found between P-gp or MRP expression and in vitro drug resistance. Samples with a marked expression of two or three resistance proteins did not show increased resistance to the tested drugs compared with the remaining samples. The expression of P-gp, MRP, and LRP was not higher in initial ALL patients with prognostically unfavorable immunophenotype, white blood cell count, or age. The expression of P-gp and MRP in 20 initial AML samples did not differ or was even lower compared with 112 initial ALL samples. However, LRP expression was twofold higher in the AML samples (P < .001), which are more resistant to a variety of drugs compared with ALL samples. In conclusion, P-gp and MRP are unlikely to be involved in drug resistance in childhood leukemia. LRP might contribute to drug resistance but only in specific subsets of children with leukemia.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

P-glycoprotein (PGP), and not lung resistance-related protein (LRP), is a negative prognostic factor in secondary leukemias.

BACKGROUND AND OBJECTIVE: In cell lines, there is an ongoing debate about the role of the lung resistance-related protein (LRP) whereas the role played by P-glycoprotein (PGP) in determining a multidrug resistance is well known. The aim of this study was to evaluate the frequency and the role of a PGP and an LRP overexpression in affecting the intracellular daunorubicin accumulation (IDA) and in predicting the therapy outcome on a subset of overt secondary acute non lymphocytic leukemias (ANLL). An adjunctive point was to evaluate the efficacy of the reversal agent SDZ PSC 833 (PSC) in counteracting impaired IDA. DESIGN AND METHODS: By flow cytometry, PGP and LRP expression and the IDA were evaluated on 54 overt secondary ANLL PGP and LRP overexpressions were respectively defined by an MRK-16 mean fluorescence index (MFI) > or = 6 (PGP+) and by an LRP-56 MFI > or = 5 i.e. by MRK-16 and LRP-56 MFIs higher than the one observed in normal leukocytes. The blasts' IDA was studied after a two-hour incubation in 1000 ng/mL daunorubicin in the presence or in the absence of the MDR reversal agent SDZ PSC 833 (PSC) 1.6 mumol. RESULTS: A PGP overexpression was detected in 40/54 (74%) cases while an LRP overexpression was observed on 33/54 (61%) cases. No differences were found in terms of PGP and LRP expressions between ANLL developing after chemo/radiotherapy (therapy-related ANLL) or evolving from a myelodysplastic syndrome (MDS-related ANLL). Compared to the PGP-, the PGP+ cases showed a significantly lower mean IDA (DNR NMFI 196 +/- 46 vs. 267 +/- 53, p < 0.001). The co-incubation of DNR with the PSC significantly increased only the mean IDA of the PGP+ cases, that grew from a DNR NMFI of 196 +/- 46 to a DNR NMFI of 284 +/- 67 (p < 0.0001). With respect to normal leukocytes, even the PGP- cases had an impaired IDA suggesting that other mechanisms, including an LRP overexpression, could affect the IDA. A strongly negative correlation was observed between PGP overexpression and therapy outcome, in fact, 8/10 (80%) PGP- but only 2/27 (7%) PGP+ patients obtained complete remission (p = 0.0002). Moreover, 7/33 (21%) cases showing an impaired IDA (NMFI < 280) but 4/4 (100%) with NMFI > 280 had complete remission (p = 0.006). No correlation was found between therapy response and LRP or CD34 expression. INTERPRETATION AND CONCLUSIONS: This data suggests that an important role in determining therapy outcome is played by PGP in secondary leukemias. Even if the LRP is frequently overexpressed in secondary leukemias and is likely to contribute to the reduction of the intracellular drug accumulation, the role played by LRP in determining the therapy-outcome has still to be cleared.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

Biochemical and clinical aspects of efflux pump related resistance to anti-cancer drugs.

This review paper will focus on the molecular biological, biochemical and biophysical aspects of the following three efflux pumps: P-glycoprotein (Pgp), Multidrug Resistance Protein (MRP) and Lung cancer Resistance-related Protein. Since suppression of the function of these pumps has clinical implications, novel approaches developed in our laboratory for blocking the function of Pgp and MRP are also discussed. The second part of this review will summarize the clinical significance and the results of clinical trials designed to suppress the effects of these efflux pumps.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

Coexpression of multidrug resistance involve proteins: a flow cytometric analysis.

Cross resistance to multiple natural cytotoxic products represents a major obstacle in myeloblastic acute leukaemia (AML). Multidrug resistance (MDR) often involves overexpression of plasma membrane drug transporter P-glycoprotein (PGP) or the resistance associated protein (MRP). Recently, a protein overexpressed in a non-PGP MDR lung cancer cell line and termed lung resistance related protein (LRP) was identified. These proteins are known to be associated with a bad prognosis in AML. We have developed a triple indirect labelling analysed by flow cytometry to detect the coexpression of these proteins. Since no cell line expressing all three antigens is known, we mixed K562 cells (resistant to Adriblastine, PGP+, MRP-, LRP-) with GLC4 cells (resistant to Adriblastine, PGP-, MRP+, LRP+) to create a model system to test the method. The antibodies used were UIC2 for PGP, MRPm6 for MRP and LRP56 for LRP. They were revealed by Fab'2 coupled with Fluoresceine-isothiocyanate, Phycoerythrin or Tricolor with isotype specificity. Cells were fixed and permeabilized after PGP labelling because MRPm6 and LRP56 recognize intracellular epitopes. PGP and LRP were easily detected. MRP is expressed at relatively low levels and was more difficult to detect because in the triple labelling the non specific staining was higher than in a single labelling. Despite the increased background in the triple labelling we were able to detect coexpression of PGP, MRP, LRP by flow cytometry. This method appears to be very useful to detect coexpression of markers in AML. Such coexpression could modify the therapeutic approach with revertants.

ATP Binding Cassette Transporter, Subfamily B, Mem↗