Significance of lung resistance-related protein in the clinical outcome of acute leukaemic patients with reference to P-glycoprotein

Mechanisms of drug resistance in acute myeloid leukemia

Acute myeloid leukemia (AML) is a kind of malignant hematopoietic system disease characterized by abnormal proliferation, poor cell differentiation, and infiltration of bone marrow, peripheral blood, or other tissues. To date, the first-line treatment of AML is still based on daunorubicin and cytosine arabinoside or idarubicin and cytosine arabinoside regimen. However, the complete remission rate of AML is still not optimistic, especially in elderly patients, and the recurrence rate after complete remission is still high. The resistance of leukemia cells to chemotherapy drugs becomes the main obstacle in the treatment of AML. At present, the research on the mechanisms of drug resistance in AML is very active. This article will elaborate on the main mechanisms of drug resistance currently being studied, including drug resistance-related proteins and enzymes, gene alterations, micro RNAs, and signal pathways.

Management of Acute Myelogenous Leukemia in the Elderly

BACKGROUND

Acute myelogenous leukemia (AML) is a hematopoietic neoplasm that primarily affects older adults. Despite scientific advances into the epidemiologic, genetic, and biological features of AML, this disease remains fatal to the majority of patients, particularly older individuals.

METHODS

We review the biologic and clinical characteristics of AML in the elderly and the treatment options that have emerged for them during the past several years.

RESULTS

Several biologic features of AML differ between older and younger individuals. Older patients often have disease that expresses multidrug resistance phenotype and cytogenetic abnormalities, which may be responsible in large part for the poor outcomes observed in older-aged subgroups. Traditional cytotoxic chemotherapy is associated with a low complete response rate and a high treatment-related mortality in older patients, which explains in part the poorer outcomes in cohorts over 60 years of age. Research into the pathophysiology of AML has revealed an abundance of intracellular signaling events that govern proliferation and survival of the malignant cell. Such discoveries have promoted recognition of new molecular and antigenic targets (eg, Flt-3 kinase, Ras, CD33 antigen) to which therapeutic development may be aimed.

CONCLUSIONS

New therapies directed against these unique targets may add to the current arsenal of antileukemic regimens and improve response rates and survival in older patients.

Overexpression of lung resistance-related protein and P-glycoprotein and response to induction chemotherapy in acute myelogenous leukemia

Lung resistance-related protein (LRP) and P-glycoprotein (P-gp) are associated with multidrug resistance. P-gp overexpression reduces intracellular anticancer drug concentrations and is correlated with low remission rates. However, whether the presence of LRP influences the response to induction chemotherapy remains controversial. Therefore, we investigated the relationship of LRP and P-gp overexpression with the response to induction chemotherapy. Univariate analysis revealed that there was a significant difference between complete remission rates for acute myelogenous leukemia patients depending on their blast cell expressions, between LRP positive versus negative, P-gp positive versus negative, and LRP/P-gp double positive versus other groups. Crude odds ratios (ORs) for complete remission were 0.390, 0.360, and 0.307 for LRP positive, for P-gp positive, and LRP/P-gp double positive patients, respectively. After controlling the confounding variables by stepwise multivariate logistical regression analysis, the presence of LRP/P-gp double positivity and P-gp positivity were found to be independent prognostic factors; adjusted ORs were 0.233 and 0.393, respectively. Furthermore, the monoclonal antibody against LRP significantly increased daunorubicin acumulation (P=0.004) in the nuclei of leukemic blast cells with LRP positivity in more than 10% of the cells. An LRP reversing agent, PAK-104P, was found to increase the daunorubicin content with marginal significance (P=0.060). The present results suggest that not only the presence of P-gp, but also LRP in leukemic blast cells is a risk factor for resistance to induction chemotherapy. Inhibiting LRP function, similar to the inhibition of P-gp function, will be necessary to improve the effectiveness of induction chemotherapy.

Multidrug resistance protein expression of adult T-cell leukemia/lymphoma

In adult T-cell leukemia/lymphoma (ATL), it is difficult to achieve remission and the reason for the resistance to chemotherapeutic agents may be linked to the presence of multidrug resistance (MDR) proteins. Lung resistance-related protein (LRP), multidrug resistance-associated protein and P-glycoprotein are three MDR proteins which we examined in ATL cells using multiparametric flow cytometry and real-time RT-PCR. LRP was highly expressed and suppressing LRP function increased doxorubicin accumulation in nuclei. This indicates LRP may be contributing to drug resistance in ATL patients, and the suppression of LRP function could be a new strategy for ATL treatment.

Antibody binding capacity for evaluation of MDR-related proteins in acute promyelocytic leukemia: Onset versus relapse expression

BACKGROUND

Multidrug resistance (MDR) remains a major obstacle for successful treatment in cancer, in particular in acute leukemia. In acute promyelocytic leukemia (APL), the high sensitivity to anthracyclines appears to be attributable to the low frequency of MDR proteins overexpression at onset even if 30% of patients still relapse and become resistant to therapy. In attempt to explain different blast cell sensitivity, we studied the expression of PGP, MRP1, MRP2, and LRP in 45 cases of APL, comparing onset of disease with relapse.

METHODS

PGP, LRP, and MRP on bone marrow or peripheral blood blast cells were evaluated by flow cytometry using the MRK-16, LRP-56, MRP-m6, and MRP2 antibodies and results expressed by the mean fluorescence index (MFI). The antibody binding capacity (ABC) for each MDR protein was also calculated.

RESULTS

At diagnosis, only 2 of 45 patients overexpressed PGP and 1 overexpressed LRP. PGP and LRP overexpressing cases significantly grew up during disease progression and at second relapse mean PGP MFI and mean LRP MFI were significantly higher than at onset (P = 0.001 and P = 0.008, respectively). By analyzing ABC, the same trend was more evident because a significant increment of PGP and LRP was observed at second (P = 0.002 and P = 0.002, respectively), but even at first relapse (P = 0.018 and P = 0.002, respectively). No changes were demonstrated in MRP1 and MRP2 expression in any phase of disease considered.

CONCLUSIONS

Our data confirm the low expression at diagnosis of proteins related to development of drug resistance in APL. The evidence of a relative easy induction of PGP and LRP, but not of MRP, can be useful in choosing drugs to employ for consolidation or rescue therapy.

Adult acute myeloid leukaemia

The curability of acute myeloid leukaemia (AML) in a fraction of adult patients was demonstrated a long time ago. Currently, the probability of cure is consistently above fifty per cent in patients with de novo disease expressing favourable-risk associated cytogenetic features. Even better, the cure rate exceeds 75% in the acute promyelocytic subtype since the introduction of retinoic acid-containing regimens. In the meantime, continuing progress in supportive care systems and stem cell transplant procedures is making myeloablative therapies, when needed, somewhat less toxic-and thereby more effective-than in the recent past. Therefore, evidence is accumulating to indicate an improved therapeutic trend over the years, with the notable exception of older (>55 years) patients with adverse-risk chromosomal aberrations and/or leukemia secondary to myelodysplasia or prior cancer-related chemotherapy and/or radiotherapy. This review conveys the many facets of this progress, focusing on diagnostic subsets, risk classes, newer biological issues and conventional as well as innovative therapeutic interventions with or without autologous/allogeneic stem cell transplantation.

Major vault protein/lung resistance-related protein (MVP/LRP) expression in nervous system tumors

Lung resistance-related protein (LRP) was identified as the major vault protein (MVP), the main component of multimeric vault particles. It functions as a transport-associated protein that can be associated with multidrug resistance. In previous studies, expression of MVP/LRP has been documented in tumors of various types. In general, good correlations have been reported for expression of MVP/LRP and decreased sensitivity to chemotherapy and poor prognosis. MVP/LRP expression has been documented in glioblastomas, but its expression in nervous system tumors in general has not been well characterized. Immunohistochemistry using anti-human MVP/LRP antibody (LRP-56) was performed on formalin-fixed, paraffin-embedded archival tissue from 69 primary central nervous system tumors. Expression of MVP/LRP was observed in 81.2% (56/69) of primary nervous system tumors, including astrocytomas (11/13), oligodendrogliomas (1/2), oligoastrocytomas (5/5), ependymoma (1/1), meningiomas (35/45), schwannomas (2/2), and neurofibroma (1/1). Various degrees and distributions of immunoreactivity to MVP/ LRP were observed. Neither the presence nor the degree of immunoreactivity to MVP/LRP showed any correlation with either tumor grade or the presence of brain invasion.

Different effects of metabolic inhibitors and cyclosporin A on daunorubicin transport in leukemia cells from patients with AML

The objective of this study was to determine the role of transport proteins in daunorubicin (Dnr) accumulation and efflux in leukemia cells from 36 patients with acute myeloid leukemia (AML). Mononuclear cells were isolated and incubated with 1 microM Dnr with/without addition of 3 microM cyclosporin A (CyA) or metabolic inhibitors (MI). Cellular Dnr concentration in leukemia blast cells was measured with flow cytometry. After washing and reincubation of the cells in drug-free medium, Dnr efflux was followed with/without addition of CyA or MI. Levels of mRNA expression for mdr1, multidrug resistance associated protein (mrp) and lung resistance protein (lrp) were determined with reverse transcriptase-polymerase chain reaction (RT-PCR). MI enhanced cellular Dnr accumulation to a higher extent than CyA whereas CyA reduced Dnr efflux more efficiently than MI (P<0.001). There was a significant difference in Dnr accumulation between samples with low and high mdr1 mRNA levels but only in the presence of MI or CyA. Our results imply that other factors than P-glycoprotein (Pgp) are of major importance for in vitro Dnr accumulation in AML blasts and that the role of Pgp as a drug efflux pump is not conclusive.

Messenger RNA analysis of the multidrug resistance related protein (MRP1) and the lung resistance protein (LRP) in de novo and relapsed childhood acute lymphoblastic leukemia

In this study, 86 children (58 initial ALL and 28 children with relapsed disease) were investigated for lung resistance protein (LRP) and multidrug resistance related protein (MRPI)-mRNA expression by semiquantitative RT-PCR. The majority of investigated cases demonstrated variable LRP and MRP1 mRNA expression, when normalized for beta-microglobulin expression. LRP and MRPI mRNA expression may be coordinately regulated, as expression of both transcripts was found to be significantly correlated (p = 0.0001). No differences of LRP and MRP expression were observed between initial and relapsed stage patients (LRP: p = 0.89 and for MRP: p = 0.09). The prognostic value of both resistance mechanisms was subjected to Kaplan-Meier analysis for event-free survival. For this analysis the patients were divided into groups with high or low LRP or MRPI mRNA expression by utilizing the median value as the cut-off point. Overexpression of both resistance mechanisms had no prognostic significance in our retrospective study (log-rank test for LRP: p = 0.12 and for MRPI: p = 0.95), however, patients who showed high LRP expression exhibited a lower tendency of remaining in continuous first remission.

In vitro drug resistance profiles of adult acute lymphoblastic leukemia: possible explanation for difference in outcome to similar therapeutic regimens

Age has important prognostic impact in acute lymphoblastic leukemia (ALL). Adults with ALL have a worse prognosis compared to children. This may be due to different, unfavorable biology, poor treatment tolerance, drug resistance, higher expression of drug resistance related proteins. The lymphoblasts from adult ALL show an increased in vitro resistance to cytotoxic drugs, including prednisolone, dexamethasone, cytosine arabinoside, daunorubicin, L-asparaginase and methotrexate. Glucocorticoid resistance may be a fundamental difference between children, adolescents and adults with ALL, which may underlie different biological aspects and also explain the difference in prognosis. It seems that in vitro resistance to prednisolone with respect to the age might be a continuous variable in ALL patients, except infants. The greater the age, the higher the in vitro resistance to prednisolone. This may be due to induction of various defense mechanisms, such as an activation of P-glycoprotein, which develops throughout the life and protect the human against xenobiotics. Among a number of various drug resistance mechanisms, only several weak differences between adults and children with ALL have been reported including higher P-glycoprotein expression, lower methotrexate polyglutamate accumulation and possibly more often p53 gene mutations in adults. Intrinsic resistance, induction of drug resistance proteins expression during chemotherapy and co-existence of various mechanisms are common phenomena in adult ALL. It seems that age itself, more than drug resistance profile, reflects factors which have direct effect on chemotherapy response in adult ALL.

Drug resistance in hematologic malignancies

Drug resistance eventually occurs in most hematologic malignancies treated with chemotherapy. The mechanisms responsible for drug resistance include expression of transporters of xenobiotics of the adenosine triphosphate-binding cassette protein superfamily (P-glycoprotein, multidrug resistance associated proteins, breast cancer resistance protein), modifications of enzymes like deoxycytidine kinase, and defects in chemotherapy-induced apoptosis. The efforts to overcome this drug resistance have been focused, thus far, on modulation of P-glycoprotein. Several compounds were manufactured for this purpose, and phase III trials of PSC833, one of the most potent P-glycoprotein inhibitors, are completed. The emergence of modulators with several adenosine triphosphate-binding cassette protein targets, like GG120918 (inhibiting P-glycoprotein and breast cancer resistance protein) and VX710 (inhibiting P-glycoprotein and multidrug resistance associated protein 1), are of clinical interest in malignancies often expressing several efflux pumps simultaneously. Another approach is the use of "furtive" drugs like liposomal or nanoparticular anthracyclines.