Expression of the multidrug resistance gene in myeloid leukemias

Biological characteristics of newly diagnosed poor prognosis acute myelogenous leukemia

A pilot study was conducted of the biological characteristics of the leukemia cells of newly diagnosed patients with poor prognosis acute myelogenous leukemia (AML). This study included measurements of the pretherapy proliferative rate of the leukemia cells in vivo, assessment of differentiation in vivo during remission induction therapy, and the level of expression of the fms, myc, and IL1 beta genes in pretherapy leukemia cells. Short cell cycle times were characteristic of the best prognostic category and were associated with a rapid reduction in marrow leukemia cells in cytosine arabinoside (araC)-sensitive patients. Expression of c-fms was associated with rapid reduction in marrow leukemia cells during araC therapy and with a successful treatment outcome. Expression of the IL1 beta gene was associated with short remissions. These studies suggest that when compared to newly diagnosed standard prognosis AML, the leukemia of poor prognosis patients is more likely to exhibit long cell cycle times, low levels of fms expression, and is less likely to be associated with myeloid differentiation during remission induction therapy.

Poor prognosis acute myelogenous leukemia

Poor prognosis AML consists of 3 clinically definable groups of patients whose response to therapy is substantially worse than that of standard prognosis patients. The response rate is lowest for those patients who have more than a single risk factor and for the patients who have low platelet and serum albumin levels at diagnosis. The treatment associated mortality of the latter patients is quite high. Even if one avoids the high mortality rate by carefully selecting patients the likelihood that drug resistant disease is present is very high. Since the basis for resistance is multifactorial, a variety of strategies will have to be explored as means to improve treatment outcome. At the present time, the greatest chance for long term survival is found in relatively young patients whose AML is induced into complete remission and who then receive a matched allogeneic bone marrow transplant.

Multidrug resistance (MDR) genes in haematological malignancies

The emergence of drug resistant cells is one of the main obstacles for successful chemotherapeutic treatment of haematological malignancies. Most patients initially respond to chemotherapy at the time of first clinical admission, but often relapse and become refractory to further treatment not only to the drugs used in the first treatment but also to a variety of other drugs. Laboratory investigations have now provided a cellular basis for this clinical observation of multidrug resistance (MDR). Expression of a glycoprotein (referred to as P-glycoprotein) in the membrane of cells made resistant in vitro to naturally occurring anticancer agents like anthracyclines, Vinca alkaloids and epipodophyllotoxins, has been shown to be responsible for the so-called classical MDR phenotype. P-glycoprotein functions as an ATP-dependent, unidirectional drug efflux pump with a broad substrate specificity, that effectively maintains the intracellular cytotoxic drug concentrations under a non-cytotoxic threshold value. Extensive clinical studies have shown that P-glycoprotein is expressed on virtually all types of haematological malignancies, including acute and chronic leukaemias, multiple myelomas and malignant lymphomas. Since in model systems for P-glycoprotein-mediated MDR, drug resistance may be circumvented by the addition of non-cytotoxic agents that can inhibit the outward drug pump, clinical trials have been initiated to determine if such an approach will be feasible in a clinical situation. Preliminary results suggest that some haematological malignancies, among which are acute myelocytic leukaemia, multiple myeloma and non-Hodgkin's lymphoma, might benefit from the simultaneous administration of cytotoxic drugs and P-glycoprotein inhibitors. However, randomised clinical trials are needed to evaluate the use of such resistance modifiers in the clinic.

Proliferative advantage rather than classical drug resistance as the cause of treatment failure in chronic myelogenous leukemia

This presentation discusses the role that proliferative advantage plays in making both the chronic and blastic phases of CML resistant to therapy. A case is made for the addition of "regrowth" inhibitors between courses of chemotherapy as a means of increasing the efficacy of therapy by suppressing or reducing the proliferative advantage that the target cells enjoy over those cells which one would like to repopulate the hematopoietic system.

Decreased resistance to N,N-dimethylated anthracyclines in multidrug-resistant Friend erythroleukemia cells

Doxorubicin-resistant Friend erythroleukemia cells, line F4-6 ADM2R, were selected by exposure of wild-type F4-6 cells to doxorubicin concentrations of up to 1 microgram/ml. In these cells, increased expression of multidrug resistance (MDR) genes was demonstrated by Northern blot analysis. The growth-inhibitory effect of doxorubicin, daunorubicin, N,N-dimethyldoxorubicin, N,N-dimethyldaunorubicin, morpholinodoxorubicin, and pyrromycin was comparatively investigated in resistant and wild-type cells. The doxorubicin-resistant F4-6 cells showed approx. 200-fold resistance to doxorubicin and about 100-fold resistance to daunorubicin with respect to the drug-sensitive counterpart. A dramatic decrease in resistance was observed for the N,N-dimethylated derivatives of doxorubicin and daunorubicin as well as for the N,N-dimethylated natural anthracycline pyrromycin and for morpholinodoxorubicin. Uptake studies using [14C]-daunorubicin and [14C]-N,N-dimethyldaunorubicin in resistant F4-6 cells showed a decreased accumulation of daunorubicin but no significant reduction in N,N-dimethyldaunorubicin accumulation as compared with the wild-type cells. Treatment with verapamil led to increased intracellular levels of daunorubicin in resistant cells, whereas an excess of N,N-dimethyldaunorubicin did not have this effect. Thus, the decreased resistance of the doxorubicin-resistant F4-6 cells to the N-alkylated anthracyclines may at least in part be due to a reduced affinity of these compounds for the efflux pump. The results indicate that the dimethylation of the amino group of the anthracycline sugar moiety and its incorporation within a morpholinyl ring may overcome MDR by similar mechanisms.

An overview of some studies of chronic myelogenous leukemia: biological-clinical observations and viewing the disease as a chaotic system

While much is known about CML at both the clinical and molecular biological levels, the precise relationship between the disease at these two levels is unclear. The appearance of the fusion gene bcr-abl and disorders in the regulation of the myc gene, and perhaps other oncogenes which code for nucleoproteins, appear to play integral roles in the genesis of the chronic and blastic phases of the disease. The resistance of this disease to cytotoxic therapy appears to reflect both "classical" drug resistance and the ability of those cells which survive cytotoxic therapy to rapidly replace the killed cells thereby offsetting the effects of chemotherapy ("regrowth resistance"). The clinical evolution of the disease is compatible with two fundamentally different processes: one compatible with a deterministic chaotic model and the other involves two basically independent linear phenomena which overlap and intersect as the blastic phase appears and replaces the chronic phase.

PCR-determined expression of the MDR1 gene in chronic lymphocytic leukemia

To determine the role the multiple drug-resistance (MDR 1) gene plays in chronic lymphocytic leukemia (CLL), we measured the expression of the MDR 1 gene in 30 patients with this disease. A rapid, highly sensitive, and nonradioactive technique based on the polymerase chain reaction (PCR) was used for that purpose. In this technique, called differential PCR, the target (MDR 1) and a reference gene (beta 2-microglobulin) are co-amplified by PCR from random hexamer-primed cDNA in the same reaction vessel. The level of target gene expression is reflected in the ratio between the intensities of the two resulting PCR product bands, as measured by high-performance liquid chromatography (HPLC). MDR 1 gene expression was detectable in 29/30 (97%) patients with CLL, with a median expression level of 0.36 U (human placenta = 1 U). There was no correlation between expression of the MDR 1 gene and clinical stage, time from diagnosis, absolute lymphocyte count, several lymphocyte surface markers, or prior treatment in the patients analyzed. Immunocytochemical studies of the same material using the monoclonal antibody C219 showed a very low or undetectable expression of the P-glycoprotein in the lymphocytes of all patients studied, whereas granulocytes were significantly more immunoreactive. We conclude that the level of expression of the MDR 1 gene in CLL is generally low, that the removal of granulocytes is important in studies of expression of MDR 1 mRNA in CLL, and that differential PCR provides a rapid and reliable method for quantifying the amount of a specific mRNA, even in very small samples of total RNA.

Flow cytometric analysis of P-glycoprotein in normal and leukemic cells

Classical multidrug resistance is characterized by overexpression of a membrane protein, P-glycoprotein, which acts like a drug-extruding pump, reducing accumulation of cytotoxic drugs inside malignant cells. We have developed a simple method for detecting an intracellular epitope of P-glycoprotein in normal and leukemic cells by the monoclonal antibody JSB-1 and fluorescence-activated flow cytometry. Permeabilization of blood and bone marrow cells in unprocessed samples is achieved by a commercially available red blood cell lysing solution which excellently preserves the light scatter properties of leukocytes. The method is suitable for analyzing samples in clinical routine. Lower than 1% reactivity was seen in the lymphoid gate of normal peripheral blood and bone marrow samples as compared with over 60% of reacting cells in some leukemic samples. Twelve patients with acute de novo leukemia were studied at presentation, 13 patients at a refractory stage, and 28 in remission. There was a positive correlation between the P-glycoprotein and the CD34 expression in acute myelogenous leukemia and an association between the P-glycoprotein expression and the blast count in both acute myelogenous and lymphatic leukemias.

In vitro analysis of drug resistance in tumor cells from patients with acute myelocytic leukemia

A 72 hours fluorometric microculture cytotoxicity assay (FMCA) was used for the study of chemotherapeutic drug resistance in tumor cell suspensions from patients with acute myelocytic leukemia (AML). A marked heterogeneity with respect to sensitivity was observed for a panel of cytotoxic drugs tested in 76 samples from 60 patients with treated or untreated AML. Primary resistance to vincristine (Vcr) and prednisolone in untreated AML was observed as well as 'acquired' resistance to several other antileukemic drugs. Cross resistance patterns for AML active drugs revealed significant positive relationships between anthracyclines, VP16 and amsacrine (Amsa), whereas mitoxantrone (Mitox) was more weakly correlated. Sensitivity to cytosine arabinoside was unrelated to the anthracyclines, VP16, Amsa and Mitox but showed a significant relationship to 6-thioguanine. Several resistance modifying agents, including the novel non-immunosuppressive cyclosporin A analogue PSC 833, were able to potentiate the effects of doxorubicin and Vcr at concentrations achievable in the clinic. However, the pattern of activity was heterogenous and the frequency of responsive samples was higher in relapse compared to de novo cases. Individual in vitro/in vivo correlations based on quartile distributions of all accumulated drug sensitivity data from AML patients indicated a high specificity with respect to the identification of drug resistance. The results suggest that the FMCA may provide clinically valuable information on chemotherapeutic drug resistance in AML.

Primer-dependent amplification of mdr1 mRNA by polymerase chain reaction

We have developed a sensitive reverse transcription (RT)-polymerase chain reaction (PCR) to evaluate multidrug resistance in various tissues, using seven mdr-specific primer sets. mdr1 mRNA expression was noted in 16/197 samples. However, the apparent degree of mdr1 mRNA expression depended on the sequence of the primers employed. These findings suggest that more than two sets of primers should be used for effective RT-PCR.

The multiple drug resistance gene, MDR1: expression at the protein and RNA levels

A comparison of three different approaches to detect MDR1 expression in myeloid leukemia cells was undertaken. With respect to the 4 different antibodies studied, a high proportion of false positive reactions were detected. Substantial discordance between MDR1 expression as indicated by Northern blot analysis, PCR, and immunohistochemistry was found. These findings complicate the clinical interpretation of data derived from these methods.

The treatment of acute myeloid leukaemia preceded by the myelodysplastic syndrome

Most cases of acute myeloid leukaemia in the elderly and about 15% of the cases in younger patients follow a myelodysplastic disease. This disease may differ biologically from de novo AML making cure more difficult. Understanding post-MDS AML is difficult because of its preponderance in the elderly and the many complicating factors of treating old people. However, it is likely that post-MDS AML is more resistant to chemotherapy than de novo AML, that periods of pancytopenia last longer following chemotherapy and remissions are shorter. In younger patients high complete remission rates are achievable with aggressive chemotherapy and good supportive care. Such patients are best served by subsequent allogeneic bone marrow transplantation if possible, and if not then bone marrow autograft or a maintained remission should be considered. For older patients cure is unlikely and the choice between low-dose cytarabine and aggressive chemotherapy must be made if treatment is to be contemplated at all. The former leads to less hospitalisation and fewer side effects, but the latter gives a greater chance of a complete remission. This will not be long lasting.

Multidrug resistance gene (MDR1) expression in human brain tumors

Multidrug resistance for many types of cancer outside the central nervous system (CNS) has been found to be due to the overexpression of the multidrug resistance gene MDR1, of which the gene-product P-glycoprotein acts as a membrane-bound efflux pump for many anticancer drugs. To examine whether brain tumors overexpress the MDR1 gene, 25 brain-tumor specimens were subjected to Northern blot analysis: 10 gliomas, eight meningiomas, three schwannomas, one malignant lymphoma, and three tumors metastatic to the brain. Ten fresh-frozen autopsy specimens of various parts of normal brain were also analyzed. Blots were hybridized with 32P-labeled Chinese hamster complementary deoxyribonucleic acid (cDNA) and 32P-labeled human MDR1 cDNA. The MDR1 gene messenger ribonucleic acid (mRNA) was detected in two tumors using the Chinese hamster probe (one sphenoid wing meningioma and one metastatic prostate tumor) and in one CNS lymphoma using the human probe. Intact mRNA could not be extracted from the fresh-frozen autopsy specimens of normal brain. Seventeen tumors were examined for P-glycoprotein by immunohistochemical staining using murine monoclonal antibody C219: eight gliomas, eight meningiomas, and one craniopharyngioma. The neoplastic cells from two gliomas and three meningiomas and the blood vessels within six gliomas and two meningiomas stained positively for P-glycoprotein. Seven of 10 normal brain specimens stained positively for P-glycoprotein in blood vessels but no specimen demonstrated staining of parenchymal cells. This study demonstrates that the MDR1 gene can be detected in normal brain, and in malignant, benign, and metastatic lesions. P-glycoprotein can be present in tumor blood vessels even when it is not seen in neoplastic cells. Although the role of P-glycoprotein in tumor blood vessels needs to be further examined and more clearly defined, drug resistance in malignant primary brain tumors may result from characteristics not solely of neoplastic cells but also tumor vasculature.

Sufficient levels of quinine in the serum circumvent the multidrug resistance of the human leukemic cell line K562/ADM

Reversal of multidrug drug resistance (MDR) has been achieved in vitro by a variety of agents including verapamil, quinidine, cyclosporine A, and amiodarone. The toxicity of these agents precludes the achievement of sufficient levels in the serum to circumvent efficiently the MDR in vivo. The authors previously demonstrated that quinine, the widely used antimalarial agent, is able to reverse primary resistance of rat colon cancer cells to anthracyclines. In this report, the efficiency of quinine formiate in reversing the doxorubicin (ADM) (Adriamycin, Adria Laboratories, Columbus, OH) resistance of the well-defined MDR human leukemic cell line K562/ADM was demonstrated. In culture medium, quinine is slightly less effective than verapamil in increasing the cytotoxicity and uptake of ADM when both drugs are used at the same concentration. A nontoxic dose of 5 micrograms/ml is necessary to reverse the MDR in K562/ADM cells. In patients receiving quinine formiate in a continuous intravenous infusion, a significant correlation (r = 0.84) was found between the serum levels of quinine and the ability of sera to increase ADM uptake in K562/ADM cells. When quinine is administered at a conventional dose (25 to 30 mg/kg/d), serum levels consistently reach more than 8 micrograms/ml without severe side effects; ear noises and vertigo are the dose-limiting side effects. At these concentrations, quinine induces a more than double increase in ADM uptake in K562/ADM cells. Pharmacokinetic data indicate that quinine should be administered 24 to 36 hours before anti-cancer drugs in clinical trials that test its efficiency as a modifier of MDR in human hematologic malignant neoplasms.

Transgenic mice that express the human multidrug-resistance gene in bone marrow enable a rapid identification of agents that reverse drug resistance

The development of preclinical models for the rapid testing of agents that circumvent multidrug resistance in cancer is a high priority of research on drug resistance. A common form of multidrug resistance in human cancer results from expression of the MDR1 gene, which encodes a Mr 170,000 glycoprotein that functions as a plasma membrane energy-dependent multidrug efflux pump. We have engineered transgenic mice that express this multidrug transporter in their bone marrow and demonstrated that these animals are resistant to leukopenia by a panel of anticancer drugs including anthracyclines, vinca alkaloids, etoposide, taxol, and actinomycin D. Differential leukocyte counts indicate that both neutrophils and lymphocytes are protected. Drugs such as cisplatin, methotrexate, and 5-fluorouracil, which are not handled by the multidrug transporter, produce bone marrow suppression in both normal and transgenic mice. The resistance conferred by the MDR1 gene can be circumvented in a dose-dependent manner by simultaneous administration of agents previously shown to be inhibitors of the multidrug transporter in vitro, including verapamil isomers, quinidine, and quinine. Verapamil and quinine, both at levels suitable for human trials that produced only partial sensitization of the MDR1-transgenic mice, were fully sensitizing when used in combination. We conclude that MDR1-transgenic mice provide a rapid and reliable system to determine the bioactivity of agents that reverse multidrug resistance in animals.

Multidrug resistance

Resistance of malignant cells to cytotoxic agents is often a limiting factor to successful chemotherapy. The classical multidrug resistance is characterised by overexpression of a membrane protein, P-glycoprotein, which acts like a drug extruding pump reducing accumulation of cytotoxic agents inside malignant cells, thereby preventing their function. Resistance is expressed simultaneously towards several structurally unrelated drugs. P-glycoprotein is also expressed in many normal human tissues, e.g., in the gastrointestinal tract, and this may be the reason for intrinsic resistance observed clinically in cancers derived from certain tissues. More often multidrug resistance is acquired during chemotherapy. The physiological function of P-glycoprotein is still unknown but it may have a role in cellular detoxification and secreting mechanisms. Interest in the phenomenon of multidrug resistance centres on the correlation of P-glycoprotein expression to clinical drug resistance. Another goal is to find mechanisms by which the function of P-glycoprotein as a multidrug transporter is prevented and drug resistance reversed.

Some reasons for the lack of progress in the treatment of acute myelogenous leukemia: a review of three consecutive trials of the treatment of poor prognosis patients

The failure of three consecutive treatment protocols to significantly increase the complete remission rate for poor prognosis newly diagnosed patients with acute myelocytic leukemia led to a detailed investigation of the causes of treatment failure. In the majority of cases treatment failure was attributable to "clinical resistance" to therapy. Upon close examination two types of "clinical resistance" were discernible: the failure of chemotherapy to produce adequate cytotoxic effects ("classical" drug resistance), and treatment failure attributed to the rapid regrowth of leukemia cells subsequent to the substantial killing of leukemia cells by cytotoxic therapy ("biological" resistance). Each form of resistance accounted for one-half of the treatment failures.

Mechanisms of multidrug resistance in human tumor cells. The roles of P-glycoprotein, DNA topoisomerase II, and other factors

Multidrug resistance (MDR) associated with overexpression of P-glycoprotein (Pgp) is a well-described experimental phenomenon that appears to have clinical correlates. However, recent descriptions of non-P-glycoprotein forms of MDR have complicated efforts to detect and circumvent MDR in the tumors of patients. One major form of natural product MDR appears to be due to alterations in the amount of activity of DNA topoisomerase II. Compared to Pgp-MDR cells, cells expressing this form of MDR (at-MDR) do not overexpress the mdr1 gene or its product, Pgp, are unaltered in drug accumulation and retention, are unaffected by such 'modulators' of Pgp-MDR as verapamil, and express this phenotype recessively. Recently, other MDR cell lines have been described with some characteristics of Pgp-MDR (decreased drug accumulation and retention, increased drug cytotoxicity by modulators of MDR), but not others (no expression of the mdr1 gene or Pgp). Whether any non-Pgp forms of MDR occur in patients' tumors remains to be determined.

Genetic basis of multidrug resistance of tumor cells

Multidrug resistance in animal cells is defined as the simultaneous resistance to a variety of compounds which appear to be structurally and mechanistically unrelated. One type of multidrug resistance is characterized by the decreased accumulation of hydrophobic natural product drugs, a phenotype which is mediated by an ATP-dependent integral membrane multidrug transporter termed P-glycoprotein or P170. The gene coding for P170 is called MDR. The nucleotide-binding domain of P-glycoprotein shares sequence homology with a family of bacterial permease ATP-binding components. In addition, P170 as a whole is structurally very similar to a number of prokaryotic and eukaryotic proteins believed to be involved in transport activities. This review summarizes our current knowledge of the molecular biology and clinical significance of MDR expression and P-glycoprotein transport activity, as well as some theories about the function of this protein in normal cells.