Overexpression of the mdr1 gene in blast cells from patients with acute myelocytic leukemia is associated with decreased anthracycline accumulation that can be restored by cyclosporin-A

Typical multi-drug resistance (MDR) in human and animal cell lines is caused by overactivity of a unidirectional drug efflux pump. This pump is composed of a 170-kDa transmembrane glycoprotein (P-glycoprotein) that is encoded by the so-called mdr1 gene. The functionally relevant characteristic of MDR cells is a defect in drug accumulation that can be restored by agents which inhibit the P-glycoprotein pump. The purpose of our study was to find out whether P-glycoprotein inhibitors could increase the daunorubicin (DNR) accumulation in acute myelocytic leukemia (AML) cells, overexpressing the mdr1 gene. Using dot blot analysis with an mdr1-specific cDNA probe, we identified leukemic cell samples, obtained from chemotherapy-resistant AML patients, that had relatively high levels of mdr1 expression. These leukemic cells showed a reduced ability to accumulate DNR in vitro, as quantitated by flow cytometry. Addition of cyclosporin-A (Cy-A), a drug known to inhibit the P-glycoprotein pump, to the incubation medium resulted in an increase (up to 60%) in steady-state drug uptake by the leukemic cells. The degree of Cy-A-induced increase in drug accumulation in the leukemic cells correlated approximately with the level of overexpression of the mdr1 gene. Our data indicate that Cy-A is a good candidate for combination chemotherapy with cytotoxic drugs in clinical trials, aimed at the treatment of drug resistance in AML.     

Expression of the multidrug transporter, P-glycoprotein, in acute leukemia cells and correlation to clinical drug resistance

The overexpression of a cell-surface glycoprotein termed P-glycoprotein (P-gp) is frequently associated with multi-drug resistance (MDR) in cell lines in vitro. To evaluate the implications of P-gp expression in clinical drug resistance, the authors examined the expression of P-gp in leukemia cells from patients with acute myelogenous leukemia (AML) and those with acute lymphoblastic leukemia (ALL) at initial presentation and relapse, using immunoblotting with a monoclonal antibody against P-gp, C219. Nine of 17 patients with AML and four of 11 patients with ALL had P-gp-positive results at the initial presentation, and most P-gp-positive patients did not respond to chemotherapy. Four of seven patients at the relapsed stage and all three patients with preceding myelodysplastic syndrome had P-gp-positive results. The expression of P-gp and clinical refractoriness to chemotherapy were highly correlated. These data indicate that the expression of P-gp is closely related to clinical drug resistance in acute leukemia.     

Expression of the mdr3 gene in prolymphocytic leukemia: association with cyclosporin-A-induced increase in drug accumulation

Typical multidrug resistance in human and animal cell lines is caused by overactivity of an unidirectional transmembrane drug efflux pump, encoded by the MDR genes, called mdr genes in mice and humans and pgp genes in hamsters. In humans, two mdr genes, mdr1 and mdr3, with approximately 80% nucleotide homology, have been identified. There is increasing evidence that overexpression of the mdr1 gene plays a role in resistance to anticancer agents in specific tumor types. However, currently no data are available on a possible role for mdr3 in drug resistance. Here we report high levels of expression of mdr3 gene sequences in leukemic cells from 6 out of 6 patients with prolymphocytic leukemia (PLL). No mdr1 expression was detected in 5 out of 6 of these samples, whereas a low level of mdr1 expression was found in a sample from one PLL patient in the course of transformation to non-Hodgkin's lymphoma. Except for this patient, all other PLL cases studied had not received prior chemotherapy. In vitro drug uptake studies showed that daunorubicin accumulation in PLL cells was increased by cyclosporin A. Since cyclosporin A is an inhibitor of the mdr1-encoded P-glycoprotein drug pump, these data suggest that in PLL cells mdr3 also codes for a drug efflux pump. Our findings could partly explain the primary refractoriness of PLL to chemotherapy.     

Expression of the multidrug transporter P-glycoprotein is highly correlated with clinical outcome in childhood acute lymphoblastic leukemia: results of a long-term prospective study

The improved cure rate in childhood ALL may be attributed largely to the effective multidrug regimens currently applied in well-designed clinical trials. However, in a minority of patients with ALL, chemotherapy failure remains a leading cause of cancer related death, most probably due to cellular drug resistance. The better-known mechanism of such resistance is mediated by P-glycoprotein (P-gp). In a long term prospective study (mean time of follow-up: 65 months) the multidrug efflux pump P-gp was examined immunocytochemically in leukemic cells of 102 protocol-treated children with de novo acute lymphoblastic leukemia (ALL) and of 37 children with relapsed ALL. Fourteen percent expressed P-gp at initial diagnosis and 35% were P-gp positive at relapse. The patients being P-gp positive at initial diagnosis had a higher rate of leukemic relapse than the P-gp negative patients (P = 0.02). In the relapsing patients, those who were P-gp positive had a 2.18-fold greater risk for leukemic death than those who were P-gp negative. Paired analysis on diagnostic and relapsed samples from 20 patients did not support the hypothesis of P-gp mediated expression being a chemotherapy induced phenomenon. The cumulative event free survival for de novo ALL patients was significantly higher in the P-gp negative patient group. Multivariate analysis showed that P-gp expression is independent of other known risk factors. In conclusion we strongly advise that tests for P-gp in leukemic blasts should be conducted for every child with ALL, since this parameter selects a subgroup of patients with increased risk for leukemic relapse.     

Multidrug Resistance in Leukemias and its Reversal

Drug resistance often results in failure of anticancer chemotherapy in leukemias. Several mechanisms of drug resistance are known with multidrug resistance (MDR) being the best characterized one. MDR can be due to enhanced expression of certain genes (MDR1, MRP or LRP). alterations in glutathione-S-transferase activity or GSH levels and to reduction of the amount or the activity of topoisomerase II. Here we review the current status of the clinical significance of the various mechanisms of MDR in leukemias and also discuss possibilities for the reversal of MDR, MDR1 gene expression has been seen in many leukemias, notably in acute myeloid leukemia (AML) and blast crisis of chronic myeloid leukemia. Both MDR1 RNA and P-glycoprotein expression of the leukemic cells have been shown to correlate with poor clinical outcome in AML. However, preliminary results indicate that the MRP gene as well as the LRP gene can be expressed in AML. Thus, drug resistance in leukemias appears to be multifactorial. P-glycoprotein-mediated MDR can be reversed by several drugs. These resistance modifiers are currently evaluated with regard to their clinical efficacy. Despite some encouraging results, reversal of drug resistance and subsequent improvement in clinical outcome remains to be shown.     

STUDY ON AUTOINHIBITORY ACTIVITY OF LYMPHOID LEUKEMIA

Autoinhibitory activity has been discovered in murine T lymphocyte leukemia models derived from 615 mice in our lab. It was designated 615 mice leukemia associated inhibitor (LAI-615) . To further confirm whether LAI activity could be found in human leukemia, 6 ALL cases and 2 AML cases were examined. The results showed that 5/6 of ALL and 1/2 of AML cases had detectable LAI activity. The different sensitivities of LAI activity were also found between autologous bone marrow cells and human leukemic cell lines, which indicate that autoinhibitory activity might have individual specificity.     

淋巴细胞白血病的自身抑制活性研究

我们由615小鼠诱发的T淋巴细胞白血病发现了白血病相关自身抑制活性LAI—615。为探索人类白血病有无类似的自身抑制活性,对6例ALL和2例AML病人骨髓上清进行了Sephadex G-200凝胶过滤分析,结果5/6ALL和1/2AML的病例有自身抑制活性。这些抑制活性呈现个体特异性。     

NHL-30.5: a monoclonal antibody reactive with an acute myeloid leukemia (AML)-associated antigen

The reactivity of a murine IgG1 monoclonal antibody, NHL-30.5, that detects a surface antigen expressed on acute myeloid leukemia (AML) cells has been studied. Initially raised against the HL-60 cell line, NHL-30.5 has subsequently reacted with blood and/or bone marrow cells from 15 of 19 AML patients studied at presentation or in relapse, 1 patient with chronic myelomonocytic leukemia (CMML), 1 patient with myelofibrosis (MF) who subsequently developed AML, and 1 of 5 patients with acute lymphoblastic leukemia (ALL). It has shown no detectable binding to cells from AML patients in remission (0/3), patients with chronic myelogenous leukemia in chronic phase (CML) (0/7), normal bone marrow (0/9), normal peripheral blood mononuclear cells, granulocytes, platelets, erythrocytes, monocytes, or splenocytes by radioimmunoassay or fluorescence analysis using flow cytometry. HL-60 cells induced to differentiate following incubation in the presence of dimethylsulfoxide (DMSO) lost their ability to bind NHL-30.5. Immunoprecipitation of iodinated HL-60 cell surface components showed the antigen to have an apparent mol./wt of 180,000 under reducing conditions. These results suggest that the antigen is different from any other myeloid antigens reported to date, and may be useful in further studies of leukemic cell phenotypes.     

Expression of MDR1 by Normal Bone Marrow Cells and its Implication for Leukemic Hematopoiesis

Expression of MDR1 is a well-characterized mechanism leading to resistance of tumor cells to drugs like vinca-alkaloids, anthracyclines, and epipodophyllotoxins. In hematopoiesis, recent data indicate that not only leukemic cells, but also some populations of normal hematopoietic cells, particularly CD34+ progenitor cells as well as peripheral blood lymphocytes, express a functional multidrug-resistant phenotype. Among CD34+ cells, we found evidence that myeloid committed precursor cells (CD34+/CD33+) have lower levels of MDR1 expression than earlier CD34+ cell populations, but there was no difference in MDR 1 expression between CD34+/HLA-DR- and CD34+/HLA-DR+ sub-populations. During normal myeloid differentiation, MDR1 expression is down-regulated, which is similar to our observations in acute myelogenous leukemia (AML): MDR 1 expression was only rarely detected in acute promyelocytic leukemia, which was in contrast to other subtypes of AML; also, within leukemic subpopulations of the same patient, higher MDR 1 levels were correlated with a more immature immunophenotype. Regarding regulation of MDR 1 expression, we did not observe changes of MDR 1 expression in normal CD34+ cells in response to various cytokines. However, in 2 patients with AML treated with interleukin-3 and granulocyte-colony stimulating factor, respectively, a significant down-regulation of MDR1 expression was found after 24 hours. In conclusion, there is evidence that the pattern of MDR 1 expression observed in leukemias reflects the distribution of MDR1 in normal hematopoiesis. In contrast to normal CD34+ cells, leukemic cells from some AML patients can respond to cytokines with a down-regulation of MDR 1, which may contribute to response to cytokine/chemotherapy combinations.     

MDR1 RNA Expression as a Prognostic Factor in Acute Myeloid Leukemia: An Update

In order to confirm our initial report on the negative impact of MDR1 gene expression on the outcome of de novo acute myeloid leukemia (AML), we present an update of our prospective study with a larger number of patients and a longer duration of follow-up. At diagnosis, MDR1 RNA expression of the leukemic cells was negative in 37% and positive in 63% of the patients (N = 79). The complete remission rate of induction chemotherapy was 76% for MDR1 RNA negative and 54% for MDR1 RNA positive patients (p = 0.05). At a median observation duration of 33 months, the duration of overall survival was 19 months for the MDR1 RNA negative patients but only 8 months for the patients with MDR1 gene expression (p = 0.02). Thus the long-term data also indicate that MDR1 gene expression is an unfavourable prognostic factor in AML.     

Relevance of mdr1 gene expression in acute myeloid leukemia and comparison of different diagnostic methods.

In an attempt to determine the incidence and clinical relevance of mdr1 gene expression in acute myeloid leukemia (AML), we examined 126 specimens obtained from adult patients with de novo AML by slot blot and immunocytochemistry. We found a high incidence of mdr1 gene expression in newly diagnosed patients (27% by immunocytochemistry and 43% by slot blot). No difference was observed between newly diagnosed patients and relapsed patients. However, patients with resistant disease showed statistically higher incidence of mdr1 gene expression compared to the untreated and relapsing patients (60% versus 27% by immunocytochemistry, p 0.005; and 73% versus 45% by slot blot, p less than 0.05). The expression of mdr1 gene correlated significantly with clinical drug resistance: 62% of patients positive for mdr1-mRNA and 68% of patients positive for P-glycoprotein (P-gp) eventually developed resistance to chemotherapy, while this was the case for a lower percentage of patients who did not express mdr1 gene (only 23% by slot blot analysis, p = 0.0052, or 24% by immunocytochemistry, p = 0.0009). A combined parameter, mdr1-mRNA/P-gp, had a very high prognostic value in terms of specificity and sensitivity. All nine patients (100%) who were mdr1-mRNA+/P-gp+ progressed to clinical drug resistance afterward, whereas 11 of 13 (85%) patients who were mdr1-mRNA-1 P-gp- entered complete remission and only two patients later developed drug resistance (p = 0.0005). It could thus be used as a reliable parameter in clinical settings.     

Detection of multidrug resistance markers, P-glycoprotein and mdr1 mRNA, in human leukemia cells

We have examined the expression of P-glycoprotein in clinical leukemic cell samples by using a monoclonal antibody (MRK16) against P-glycoprotein. We found that leukemia cells isolated from 3 out of 6 patients with blast crisis of chronic myelogenous leukemia were reactive to MRK16. These 3 cell lines expressed high levels of mdr1 mRNA, which codes for P-glycoprotein. The present result indicates that the clinically refractory state of the tumor may be predicted in part by determining P-glycoprotein expression using the monoclonal antibody against P-glycoprotein, and the mdr1 probe.     

Multidrug resistance in acute leukemia: a conserved physiologic function.

Native resistance to conventional chemotherapy remains an important cause of treatment failure in the adult acute leukemias. Delineation of cellular mechanisms of drug resistance therefore represents a prerequisite to the development of more effective treatment strategies. The multidrug resistance (MDR) phenotype represents one such mechanism of resistance with direct clinical relevance. This phenotype occurs normally in certain mammalian tissues, and is detectable in tumor cell lines selected for resistance to naturally occurring antineoplastics. The mdr1 gene or its glycoprotein product, P-glycoprotein, is detected with high frequency in secondary acute myeloid leukemia (AML) and poor-risk subsets of acute lymphoblastic leukemia. In prospective studies in AML, MDR overexpression is an independent determinant of response to treatment and overall survival with conventional-dose induction regimens. Investigations of mdr1 regulation in normal hematopoietic elements has shown a pattern which corresponds to its regulation in acute leukemia, explaining the linkage of mdr1 to specific cellular phenotypes. Therapeutic trials are now in progress to test the ability of various MDR-reversal agents to restore chemotherapy sensitivity in high-risk acute leukemias.     

A study of multidrug resistance and cell kinetics in a child with near-haploid acute lymphoblastic leukemia

Marked hypodiploidy is found in a small group of patients with acute lymphoblastic leukemia (ALL) and is associated with very poor prognosis. Cells from a patient with near-haploid ALL (karyotype: 27 XY, DNA index = 0.5) were investigated by multiparameter flow cytometry at relapse and at multiple time-points during reinduction chemotherapy. The cell cycle of these near-haploid leukemic blasts and their chromatin structure was studied by acridine orange (AO) DNA/RNA flow cytometric assays. Most leukemic cells were in "G0", and no recruitment of the bone marrow cells into the G1 phase of the cell cycle was found during reinduction therapy with high dose cytosine arabinoside. After two cycles of chemotherapy, the patient achieved clinical remission, but persistent haploid cells were identified by flow cytometry and he relapsed after 8 weeks and died after 16.7 weeks. The leukemic blasts expressed very high levels of a 180 kd p-glycoprotein associated with multidrug resistance and daunomycin efflux could be blocked by verapamil. Expression of gp 180 and the verapamil effect on intracellular daunomycin concentration indicate multidrug resistance. We conclude that cell kinetic quiescence and multidrug resistance may both be factors responsible for the poor prognosis of this patient with near-haploid ALL. Further studies of this patient group should determine if these mechanisms are indeed responsible for the poor prognosis associated with near-haploid leukemia.     

Interaction of Acute Leukemia Cells with the Bone Marrow Microenvironment: Implications for Control of Minimal Residual Disease

There is increasing evidence for an interaction between acute leukemia cells and the microenvironment of the bone marrow. Blast cells from cases of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) bind to cellular and extracellular matrix components of the bone marrow stroma. In AML, adhesion to stroma is mediated by the combined action of β (principally VLA-4) and β2 integrins, while in precursor-B ALL VLA-4 and VLA-5 integrins play a major role. Adhesion molecules such as CD31, CD44, non-β1, β2 integrins, growth factor receptors such as c-kit, and other molecules are also likely to play a role. Binding of acute leukemia blasts to ligands on stroma has several pathophysiological consequences. Stromal contact is able to inhibit programmed cell death (apoptosis) in a proportion of cases of both AML and ALL. In ALL, diffusible molecules derived from stroma appear to contribute. Marrow stroma also plays a part in regulating leukemic cell proliferation. While this is partly due to stromal production of hemopoictic growth factors, in soluble or transmembrane form or bound to extracellular matrix, signalling mediated directly by binding of adhesion molecules on teukemic cells may also have a role. Contact of ALL blasts with marrow fibrobtasts is followed by migration of leukemic cells, utilizing VLA-4 and VLA-5 integrins, potentially allowing homing of blasts to favourable microenvironmental sites, or controlling egress into the circulation. AML cells compete for stromal binding sites with natural killer cells and cytotoxic lymphocytes, which are known to inhibit their clonogenic growth. We speculate that these complex interactions between leukemic blasts, cellular and matrix components of stroma, and cytotoxic lymphocytes, play a critical role in determining the fate of small numbers of leukemic cells surviving after cytotoxic chemotherapy.     

急性白血病细胞P-gp LRP的表达及其临床意义

目的：研究急性白血痛细胞P-糖蛋白（P—gp）、肺耐药蛋白（LRP）的表达情况，观察其表达率与临床症状及化疗缓解率的关系。方法：利用P—gp、LRP单克隆抗体，采用流式细胞技术分别测定15例正常对照和79例急性白血病（AL）患者P-gp、LRP的表达率，分析两种蛋白表达的临床意义。结果：初治急性淋巴细胞白血病（ALL）组P—gp、LRP的表达率均高于初治急性髓细胞白血病（AML）组（P〈0．01），复发／难治ALL组P—gp的表达率与复发／难治AML组相比无显著性差异（P〉0．05），而LRP的表达率较复发／难治AML组的表达率高（P〈0．01）。复发／难治组P—gp、LRP的表达率均高于相应的初治组（P〈0．05）。急性白血病患者P—gp、LRP的表达之间无相关性（L=0．0746，P〉0．05）。急性白血病细胞P—gp^＋／LRP^＋组缓解率低于P—gp^＋／LRP^-、P—gp^-／LRP^＋组（P〈0．05），并明显低于P—gp^-／LRP^-组（P〈0．01）。结论：复发／难治组P—gp、LRP的表达率高于初治组，而两者的表达率无相关性。P—gp、LRP表达阳性的患者缓解率低，且易出现髓外浸润。同时检测P—gp、LRP的表达较单独检测一种蛋白更具有临床意义。