Multidrug resistance in haematological malignancies

Establishment and characterization of new cellular lymphoma model expressing transgenic human MDR1

Multidrug resistance (MDR) due to the expression of the MDR1 gene and its P-glycoprotein (Pgp) product is a major factor in the prognosis and clinical outcome of patients with refractory lymphomas and other malignancies. The aim of our study was to establish a lymphoma, cellular system where a de novo acquisition of multidrug resistance is specifically related to overexpression of a transgenic, human MDR1. A multidrug sensitive lymphoma cell line (LM1) was established from a sporadic T-cell lymphoma of BALB/c mouse and was transduced by a retroviral vector containing the human MDR1 cDNA. The resultant cell variant (LM1/MDR) was characterized in comparison to the parental LM1 cells. The LM1/MDR cell variant is cross-resistant to DOX, COL, ACT D and VBL. This cell variant expresses the human MDR1 and exhibits de novo functional Pgp activity that can be blocked by the Pgp-modulators VRP and KT-5720. The acquired MDR of LM1/MDR is not accompanied with gene amplification, alternative splicing or up-regulation of the murine endogenous mdr1a, mdr1b, mrp1, mrp2 and mrp3 transporter-genes. Therefore, the acquired MDR is, specifically, human MDR1-dependent as it has been found in malignant cells of most lymphoma patients. Moreover, this system can be used as a model to study MDR and the efficacy of drugs and modulators on malignant cells where human Pgp is a major factor of multidrug resistance.

Identification of genes associated with chemotherapy crossresistance and treatment response in childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) can be cured with combination chemotherapy in over 75% of children, but the cause of treatment failure in the remaining patients is unknown. We determined the sensitivity of ALL cells to individual antileukemic agents in 441 patients and used a genome-wide approach to identify 45 genes differentially expressed in ALL exhibiting crossresistance to prednisolone, vincristine, asparaginase, and daunorubicin. We also identified a distinct phenotype of discordant resistance to asparaginase and vincristine and 139 genes whose expression was associated with this novel phenotype. The expression of these genes discriminated treatment outcome in two independent patient populations, identifying a subset of patients with a markedly inferior outcome (37% +/- 13% 5 year DFS).

Expression of heat-shock proteins is associated with major adverse prognostic factors in acute myeloid leukemia

To identify prognostic factors alternative or additional to drug-resistance and apoptosis proteins, we studied the impact of the expression of heat-shock proteins (HSPs) in 98 newly diagnosed acute myeloid leukemia (AML). HSP27 was expressed by 39%, HSP60 by 26%, HSP70 by 58%, HSP90 by 41%, and HSP110 by 30% of cases. HSP expressions were correlated with that of differentiation antigens (CD34, CD14, CD15, CD33) and that of drug-resistance (MRP, MRK) and apoptosis (Bcl-2) proteins. HSP90 and HSP110 were correlated with FAB subtype and karyotypic grouping. Complete remission (CR) was obtained in 68 cases (69%). Median disease-free survival (DFS) of the 68 remitters was 18.1 months with a 3-year DFS rate of 41%. CR rates were higher in patients with lower expression of HSPs. Overall survival (OS) was significantly longer in patients with lower expression of HSPs. Cytogenetics, CD34 positive expression, MRK positive expression, and HSP110 positive expression remained as pejorative prognostic factors for OS in the multivariate analysis. When considering patients with intermediate risk cytogenetics, HSP110 and MRP positive expressions and CD33 negative expression were of poor outcome, while HSP27 and HSP60 positive expressions appeared of pejorative prognostic value in patients with unfavorable karyotypes.

CD34+ Cells from Acute Myeloid Leukemia, Myelodysplastic Syndromes, and Normal Bone Marrow Display Different Apoptosis and Drug Resistance–Associated Phenotypes

Myelodysplastic syndromes and acute myeloid leukemia (AML) are heterogeneous disorders in which conflicting results in apoptosis and multidrug resistance (MDR) have been reported. We have evaluated by multiparameter flow cytometry the expression of apoptosis- (APO2.7, bcl-2, and bax) and MDR-related proteins [P-glycoprotein (P-gp), multidrug resistance protein (MRP), and lung resistance protein (LRP)] specifically on bone marrow (BM) CD34+ cells, and their major CD32-/dim and CD32+ subsets, in de novo AML (n=90), high-risk myelodysplastic syndrome (n=9), and low-risk myelodysplastic syndrome (n=21) patients at diagnosis, and compared with normal BM CD34+ cells (n=6). CD34+ myeloid cells from AML and high-risk myelodysplastic syndrome patients displayed higher expression of bcl-2 (P <0.0001) and lower reactivity for APO2.7 (P=0.002) compared with low-risk myelodysplastic syndrome and normal controls. Similar results applied to the two predefined CD34+ myeloid cell subsets. No significant differences were found in the expression of P-gp, MRP, and LRP between low-risk myelodysplastic syndrome patients and normal BM, but decreased expression of MRP (P <0.03) in AML and high-risk myelodysplastic syndromes and P-gp (P=0.008) in high-risk myelodysplastic syndromes were detected. Hierarchical clustering analysis showed that low-risk myelodysplastic syndrome patients were clustered next to normal BM samples, whereas high-risk myelodysplastic syndromes were clustered together and mixed with the de novo AML patients. In summary, increased resistance to chemotherapy of CD34+ cells from both AML and high-risk myelodysplastic syndromes would be explained more appropriately in terms of an increased antiapoptotic phenotype rather than a MDR phenotype. In low-risk myelodysplastic syndromes abnormally high apoptotic rates would be restricted to the CD34- cell compartments.

The molecular basis of the action of disulfiram as a modulator of the multidrug resistance-linked ATP binding cassette transporters MDR1 (ABCB1) and MRP1 (ABCC1)

The overexpression of multidrug resistance protein 1 (MDR1) and multidrug resistance protein 1 (MRP1) gene products is a major cause of multidrug resistance in cancer cells. A recent study suggested that disulfiram, a drug used to treat alcoholism, might act as a modulator of P-glycoprotein. In this study, we investigated the molecular and chemical basis of disulfiram as a multidrug resistance modulator. We demonstrate that in intact cells, disulfiram reverses either MDR1- or MRP1-mediated efflux of fluorescent drug substrates. Disulfiram inhibits ATP hydrolysis and the binding of [alpha-32P]8-azidoATP to P-glycoprotein and MRP1, with inhibition curves comparable with those of N-ethylmaleimide, a cysteine-modifying agent. However, if the ATP sites are protected with excess ATP, disulfiram stimulates ATP hydrolysis by both transporters in a concentration-dependent manner. Thus, in addition to modifying cysteines at the ATP sites, disulfiram may interact with the drug-substrate binding site. We demonstrate that disulfiram, but not N-ethylmaleimide, inhibits in a concentration-dependent manner the photoaffinity labeling of the multidrug transporter with 125I-iodoarylazidoprazosin and [3H]azidopine. This suggests that the interaction of disulfiram with the drug-binding site is independent of its role as a cysteine-modifying agent. Finally, we have exploited MRP4 (ABCC4) to demonstrate that disulfiram can inhibit ATP binding by forming disulfide bonds between cysteines located in the vicinity of, although not in, the active site. Taken together, our results suggest that disulfiram has unique molecular interactions with both the ATP and/or drug-substrate binding sites of multiple ATP binding cassette transporters, which are associated with drug resistance, and it is potentially an attractive agent to combat multidrug resistance.

Effect of mitogen-activated protein kinase signal transduction pathway on multidrug resistance induced by vincristine in gastric cancer cell line MGC803

AIM: To investigate the correlation between mitogen-activated protein kinase (MAPK) signal transduction pathway and multidrug resistance (MDR) in MGC803 cells.

METHODS: Western blot was used to analyze the expression of MDR associated gene in transient vincristine (VCR) induced MGC803 cells, which were treated with or without the specific inhibitor of MAPK, PD098059. Morphologic analysis of the cells treated by VCR with or without PD098059 was determined by Wright-Giemsa staining. The cell cycle analysis was performed by using flow cytometric assay and the drug sensitivity of MGC803 cells which were exposed to VCR with or without PD098059 was tested by using MTT assay.

RESULTS: Transient exposure to VCR induced P-gp but not MRP1 or GST-π expression in MGC803 cells and the expression of P-gp was inhibited by PD098059. Apoptotic bodies were found in the cells treated with VCR or VCR+PD098059. FCM results indicated that more MGC803 cells showed apoptotic phenotype when treated by VCR and PD098059 (rate: 31.23%) than treated by VCR only (rate: 18.42%) (P < 0.05). The IC₅₀ (284 ± 13.2 μg/L) of MGC803 cells pretreated with VCR was 2.24-fold as that of negative control group (127 ± 17.6 μg/L) and 1.48-fold as that of the group treated with PD098059 (191 ± 27.9 μg/L).

CONCLUSION: This study shows that the expression of P-gp can be induced by transient exposure to VCR and this induction can be prevented by PD098059, which can block the activity of MAPK. MAPK signal transduction pathway may play some roles in modulating MDR1 expression in gastric cancer.

New agents in acute myeloid leukemia and other myeloid disorders

Over the past several decades, improvements in chemotherapeutic agents and supportive care have resulted in significant progress in treating patients with acute myeloid leukemia (AML). More recently, advances in understanding the biology of AML have resulted in the identification of new therapeutic targets. The success of all-trans-retinoic acid in acute promyelocytic leukemia and of imatinib mesylate in chronic myeloid leukemia have demonstrated that targeted therapy may be more effective and less toxic when well defined targets are available. At the same time, understanding mechanisms of drug resistance and means to overcome them has led to modification of some of the existing cytotoxic agents. Rational design and conduct of clinical trials is necessary to ensure that the full potential of these new agents is realized.

The peripheral benzodiazepine receptor ligand PK11195 overcomes different resistance mechanisms to sensitize AML cells to gemtuzumab ozogamicin

The antibody-targeted therapeutic, gemtuzumab ozogamicin (GO, Mylotarg), is approved for treatment of relapsed acute myeloid leukemia (AML). We previously showed that AML blasts from GO refractory patients frequently express the drug transporters P-glycoprotein (Pgp) and/or multidrug resistance protein (MRP). We also previously reported that inhibition of drug transport by the Pgp modulator, cyclosporine A (CSA), can increase GO sensitivity in Pgp(+) AML cells and that the peripheral benzodiazepine receptor ligand, PK11195, sensitizes AML cells to standard chemotherapeutics both by inhibiting Pgp-mediated efflux and by promoting mitochondrial apoptosis. We now show that PK11195 also can overcome multiple resistance mechanisms to increase GO sensitivity in AML cells, including resistance associated with expression of drug transporters and/or antiapoptotic proteins. PK11195 substantially increases GO cytotoxicity in AML cells from many different cell lines and primary patient samples, often more effectively than CSA. We also show that PK11195 is nontoxic in NOD/SCID mice and can sensitize xenografted human AML cells to GO. Since PK11195 is well tolerated in humans as a single agent, its further study as a multifunctional chemosensitizer for anti-AML therapies, including GO-based therapies, is warranted.

Increased myelotoxicity of idarubicin: is there a pharmacological basis? Results of a pharmacokinetic and an in vitro cytotoxicity study

BACKGROUND

Clinical trials evaluating idarubicin (IDA) in acute myeloid leukemia, multiple myeloma and non-Hodgkin's lymphoma (NHL) have provided some evidence for an increased myelotoxicity of IDA compared to other anthracyclines. IDA is known to be less sensitive towards multidrug resistance mediated by P-glycoprotein (P-gp). This phenotype is a major impediment to successful antineoplastic treatment, but P-gp is also expressed on hematopoietic stem cells (HSC).

METHODS

We investigated the pharmacokinetics of IDA and etoposide (ETO) in seven previously untreated patients with aggressive NHL. The patients received a CHOP-derived protocol (CIVEP) in which doxorubicin (DOX) was substituted by IDA 11-16 mg/m(2) and ETO 3 x 100 mg/m(2) was added. Furthermore, we evaluated in vitro the impact of P-gp expression on the cytotoxicity of DOX and IDA in cells from three parental chemosensitive leukemia and lymphoma cell lines (HL60, U937, CCRF) and their resistant sublines, as well as in CD34-positive HSC.

RESULTS

The peak plasma levels (C(max)), terminal elimination half-life (t(1/2)) and area under the concentration curve (AUC) both for IDA and for ETO did not differ from published data. In cell line models the numbers of viable cells in a P-gp-expressing resistant CCRF-VCR100 subline were significantly more reduced by IDA ( P<0.001), but there was no difference in the cytotoxicities of IDA and DOX in chemosensitive CCRF cells and in the (non-P-gp-expressing) resistant U937 and HL60 sublines. Cytotoxicity against HSC was more pronounced after incubation with IDA than after treatment with DOX ( P=0.014), even when a tenfold higher concentration of DOX than of IDA was used. The addition of cyclosporin A increased the cytotoxic effect of DOX but not that of IDA in HSC.

CONCLUSIONS

The pharmacokinetics of IDA and its main metabolite idarubicinol in CHOP-derived protocols were not different from data obtained with other combinations or monotherapy. The increased myelotoxicity of IDA may be a consequence of P-gp expression in CD34-positive HSC.

Spontaneous Reversal of P-Glycoprotein Expression in Multidrug Resistant Cell Lines*

Increased expression of P-glycoprotein encoded by the mdr-1 gene is a well-characterised mechanism for resistance to cancer chemotherapeutic drugs in cell lines. However, the P-glycoprotein expression after removal of the selection pressure has not fully been elucidated. The stability of P-glycoprotein expression in the presence (+) and absence (-) of vincristine (30 or 150 nM) was studied in multidrug resistant K562 cell lines (VCR30+, VCR150+, VCR30- and VCR150-) for 11 months. The P-glycoprotein protein and mdr-1 mRNA levels were determined at regular intervals using flow cytometry and real-time PCR, respectively. Chemosensitivity to a panel of antineoplastic drugs was measured using an MTT assay. The presence of vincristine (VCR30+ and VCR150+) resulted in high and stable levels of P-glycoprotein and mdr-1 mRNA during the whole period compared to wild type. As for the VCR30- and VCR150- subcultures, the expressions of P-glycoprotein and mdr-1 mRNA were stable for five months, and then the levels decreased rapidly. Concomitantly, the sensitivity to drugs known as P-glycoprotein substrates was restored. In conclusion, resistant cells growing in the presence of the inducing drug have a stable P-glycoprotein expression and resistance level, but removing the inducing drug may result in a sudden and rapid lowering of P-glycoprotein and mdr-1 mRNA levels as long as five months after drug withdrawal.

Expression of cell-surface antigens in acute promyelocytic leukaemia

Acute promyelocytic leukaemia (APL) with M3 (or M3v) morphology is the only AML subtype to date for which morphology and immunophenotype agree. In other words, FAB M3 is interchangeable with a unique marker profile. More precisely, we have finally recognized a surrogate marker profile for leukaemia derived from the (15;17) translocation and expressing PML/RARalpha transcripts. To present this as a new development may come as a surprise to many. After all, the antigen expression pattern of AML-M3 was well recognized for many years: absence or weak expression of HLA-DR, CD117, CD15, CD11b and CD34 in the context of a myeloid phenotype (CD33 and CD13 expression) and frequently associated with moderate to high side-scatter appearance upon flow cytometric evaluation, depending upon the degree of granularity of the leukaemic cells. While partially correct, this established APL phenotype is both flawed and limited in its ability to distinguish APL from other AML subtypes, such as natural-killer-cell AML. Given the availability of phenotype-specific therapy for APL, such as all-trans retinoic acid or arsenic trioxide, failing to diagnose APL or misdiagnosing a case of AML with an APL-like phenotype will result in serious clinical consequences. Faced with this dilemma, we have recently performed a comprehensive immunophenotypic analysis of APL patients entered on Eastern Cooperative Oncology Group trials. Our results give diagnostic power to only three antigens, HLA-DR, CD11a and CD18, all of which are characteristically expressed at low levels by APL cells. Despite some significant antigenic differences (e.g. in CD34 expression), this surrogate marker profile for t(15;17) APL applies to both the M3 and the M3v FAB phenotypes and to all three isoforms of the PML/RARalpha transcript.

Multidrug resistance protein attenuates gemtuzumab ozogamicin-induced cytotoxicity in acute myeloid leukemia cells

Gemtuzumab ozogamicin (GO) is a novel immunoconjugate therapy for acute myeloid leukemia (AML). P-glycoprotein (Pgp) confers resistance to GO and is associated with a worse clinical response. To address whether multidrug resistance protein (MRP) affects GO susceptibility, we characterized Pgp, MRP1, and MRP2 expression in CD33+ cell lines and CD33+ AML samples and analyzed the effect of the Pgp inhibitor cyclosporine (CSA) and the MRP inhibitor MK-571 on GO-induced cytotoxicity. MRP1, but not MRP2, expression correlated with MRP activity. MK-571 enhanced GO-induced cytotoxicity in Pgp-negative/MRP-positive NB4 and HL-60 cells. CSA, but not MK-571 alone, restored GO susceptibility in Pgp-positive/MRP-positive TF1 cells; however, MK-571 enhanced cytotoxicity in the presence of CSA. All patient samples exhibited MRP activity, and 17 of 23 exhibited Pgp activity. CSA increased GO-induced cytotoxicity in 12 Pgp-positive samples, whereas MK-571 alone was effective in only one sample with minimal Pgp activity. In 3 Pgp-positive/MRP-positive samples, MK-571 enhanced GO-induced cytotoxicity in the presence of CSA. Thus, MRP1 may attenuate susceptibility to GO. This effect was comparatively less than that for Pgp and required the inhibition of Pgp for detection in cells that coexpressed both transporters. Because MK-571 and CSA failed to affect cytotoxicity in a portion of Pgp-positive/MRP-positive AML samples, additional resistance mechanisms are likely important.

Differential response of human acute myeloid leukemia cells to gemtuzumab ozogamicin in vitro: role of Chk1 and Chk2 phosphorylation and caspase 3

Gemtuzumab ozogamicin (GO) is a humanized anti-CD33 antibody conjugated to the anticancer agent calicheamicin, approved for the treatment of CD33+-relapsed acute myeloid leukemia. We have investigated the effects of GO on 4 human myeloid leukemia lines of different French-American-British (FAB) types (KG-1, THP-1, HL-60, and NB-4), observing 3 different types of response. Exposure to GO (10-1000 ng/mL) induced G2 arrest (up to 80% of the cells) followed by apoptosis (45% of the cells) in HL-60 and NB-4 cells. By contrast, in THP-1 cells we observed a strong G2 arrest (up to 75% of the cells) with little apoptosis. Finally, the KG-1 line was completely resistant to the same concentrations of GO. These different responses did not correlate with the levels of expression of either CD33 or multiple-drug resistance proteins, although the higher cyclosporin A (CsA)-inhibitable efflux activity of KG-1 cells may play a role in the resistance of this line to the drug. We could show that Chk1 and Chk2 phosphorylation, but not p53 or p21 expression, correlated with G2 arrest, implicating the ataxia-telangiectasia mutated/ataxia-telangiectasia related (ATM/ATR)-Chk1/Chk2 pathway in the cell cycle response to GO. However, apoptosis was associated with caspase 3 activation. Freshly isolated acute myeloid leukemia (AML) cells showed patterns of response to GO in vitro similar to those observed with the cell lines, including phosphorylation of Chk2 and caspase 3 activation. Our results suggest that the different molecular pathways induced by the drug in vitro may reflect, at least in part, the variable response to GO obtained in vivo.

Validation and clinical implication of a quantitative real-time PCR determination of MDR1 gene expression: comparison with semi-quantitative PCR in 101 patients with acute myeloid leukemia

INTRODUCTION

The multidrug resistance protein 1 (MDR1) has the capacity to extrude chemotherapeutics and has been implicated in treatment failure in acute myeloid leukemia (AML). Previous methods for determination of MDR1 expression have included dye exclusion, demonstration of P-glycoprotein by flow cytometry and/or immunohistochemistry, and molecular polymerase chain reaction (PCR)-based assays for RNA expression. However, these assays have either proven difficult to standardize or tedious to perform. We have therefore designed a real-time quantitative (RQ)-PCR based assay measuring MDR1 gene expression and validated it in AML patients by direct comparison with a competitive reverse transcriptase polymerase chain reaction (RT-PCR) assay.

PATIENTS AND METHODS

Bone marrow or peripheral blood from 101 AML patients diagnosed (1987-96) at our department were assessed for quantitative expression of MDR1 employing TaqMan RQ-PCR. These data were compared with results obtained by a semi-quantitative competitive PCR assay employing an artificial internal RNA construct.

RESULTS

While the RQ-PCR method was able to determine MDR1 gene expression in a continuous fashion over five logs, the semi-quantitative PCR only yielded data in a discontinuous fashion and over four logs at best. Compared with the MDR1 positive and negative cell lines 8226 DOX40 and REH AML cells exhibited variation of 10 PCR cycles, equivalent to a 1000-fold difference. A significant correlation was observed between the two methods, Spearman's correlation coefficient = -0.502, P-value = 10-5.

CONCLUSION

We conclude that, RQ-PCR is a novel methodology, which enables sensitive and quantitative measurement of MDR1 gene expression. This assay is moreover suitable because of its high throughput for longitudinal follow-up and large number of patients.

Quantitative determination of MDR1 mRNA expression in peripheral blood lymphocytes: a possible role of genetic polymorphisms in the MDR1 gene

BACKGROUND

P-glycoprotein is a transmembrane efflux pump that extrudes a wide variety of drugs, thereby reducing their intracellular access. In humans, P-glycoprotein is encoded by the MDR1 gene. Recently, several single nucleotide polymorphisms in the MDR1 gene were identified. Moreover, it was postulated that, in addition to the full-length P-glycoprotein, a 'mini' P-glycoprotein was also present in lymphocytes.

MATERIALS AND METHODS

We investigated the effect of the genetic polymorphisms G2677T and C3435T in the MDR1 gene on MDR1 mRNA expression in FACS-sorted peripheral blood CD4+, CD8+, CD19+, and CD56+ cells. MDR1 mRNA expression was determined in 45 healthy individuals using a real-time quantitative RT-PCR.

RESULTS

We detected the highest expression of MDR1 mRNA in CD56+ cells, followed by CD8+ > CD4+ > CD19+ cells. However, genetic polymorphisms of the MDR1 gene failed to affect (P > 0.05) MDR1 mRNA levels in the peripheral blood lymphocytes. Furthermore, the transcript levels for the MDR1 N-terminal half were almost two-fold lower than that of the MDR1 C-terminal half in all cell populations investigated (P < 0.0001).

CONCLUSIONS

An almost two-fold difference in MDR1 C- and N-terminal half expressions supports the presence of mini-P-glycoprotein, an alternatively spliced form of the full-length molecule, in peripheral blood lymphocytes.

Stoichiometry and affinity of nucleotide binding to P-glycoprotein during the catalytic cycle

Drug transport mediated by P-glycoprotein (Pgp) is driven by hydrolysis of ATP at the two cytosolic nucleotide binding domains. However, little is currently known concerning the stoichiometry of nucleotide binding and how both stoichiometry and binding affinity change during the catalytic cycle of the transporter. To address this issue, we used fluorescence techniques to measure both the number of nucleotides bound to P-glycoprotein during various stages of the catalytic cycle and the affinity of nucleotide binding. Results showed that resting state P-glycoprotein bound two molecules of the fluorescent nucleotide derivative, 2'(3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate (TNP-ATP), whereas the vanadate-trapped transition state bound only one nucleotide molecule. Both resting and transition state P-glycoprotein showed similar affinity for TNP-ATP/TNP-ADP and unlabeled ATP/ADP. Following binding of various drugs, resting state P-glycoprotein displayed a higher affinity for nucleotides, up to 4-fold depending on the compound used. In contrast, the transition state showed substantially lower (up to 3-fold) nucleotide binding affinity when the drug binding site(s) is/are occupied. These results indicate that both nucleotide binding domains of P-glycoprotein are likely to be occupied with either ATP (or ADP) in the resting state and the transition state in the absence of transport substrates. Drugs alter the binding affinity to favor association of ATP with P-glycoprotein at the start of the catalytic cycle and release of ADP from the transition state following nucleotide hydrolysis.

Emerging cancer-targeted therapies

There is reason to believe that the unfolding revolution in molecular biology and translational research will allow selective targeting of tumor cells, and radically change the way general practitioners and pediatric oncologists treat and follow children with cancer. This article highlights some of the most promising approaches being tested in the field. By learning about the underlying biology, the remaining hurdles, the projected timeline, and the possible impact of new therapies on the practice of pediatric oncology, health care professionals and patients should be better prepared for the future of pediatric oncology.

Impact of the expression of P glycoprotein, the multidrug resistance-related protein, bcl-2, mutant p53, and heat shock protein 27 on response to induction therapy and long-term survival in patients with de novo acute myeloid leukemia

OBJECTIVE

Resistance to chemotherapy-induced apoptosis and a multidrug-resistance phenotype is the major problem in the treatment of acute myeloid leukemia (AML).

PATIENTS AND METHODS

We recently demonstrated that the coexpression of at least two proteins, including P glycoprotein, multidrug resistance-related protein, bcl-2 (flow cytometry), p53 (luminometric immunoassay), and heat shock protein 27 (Western blotting), was predictive for response to induction therapy in de novo AML comparing leukemic blasts of 20 responders with 20 nonresponders. After long-term follow-up, we now present our evaluation on the prognostic significance of these proteins in leukemic blasts of 124 untreated AML patients with regard to the probability of remission (PoR) and overall survival (OS).

RESULTS

Analyzing leukemic blasts obtained from bone marrow samples, we found that no single protein significantly correlated with PoR or OS. In contrast, the coexpression of at least two of these proteins was predictive for reduced OS in univariate as well as multivariate analysis. Although we could not identify any particular protein combination predictive for reduced OS, those patients with no or only one protein expressed in their leukemic blasts had a survival probability of 48% in contrast to 24% in those patients with the coexpression of two or more proteins. Among the clinical markers, only response to chemotherapy had a significant effect on OS and age was of prognostic relevance for PoR.

CONCLUSION

We conclude that overexpression of only one protein possibly involved in resistance, is not sufficient to influence the prognosis for long-term survival in AML, whereas the expression of more than one protein is predictive for reduced OS. Protein combination seems to be individually different, and targeting only one protein in further clinical trials may not help to overcome multifactorial resistance.

Thalidomide in the management of multiple myeloma

The discovery that multiple myeloma is associated with new vessel formation and is correlated with survival and proliferation led initially to the use of thalidomide for patients with relapsed or refractory disease. The outcome with conventional chemotherapy in this setting has historically been very poor. New insights into the biology of the disease suggests that thalidomide may work via a number of other mechanisms and the advent of the thalidomide analogues with their differential effects on survival and proliferation pathways has opened up a new era in the understanding and treatment of the disease. The encouraging results from phase I/II trials of these agents has meant that for the first time in 50 years there is the opportunity to improve outcome. Further work is in progress to define how best to use these drugs and their role in treatment at different stages of the disease.

Quantitative Analysis of a MDR1 Transcript for Prediction of Drug Resistance in Acute Leukemia

Background: Assessing the drug resistance of leukemic cells is important for treatment of leukemia. We developed a quantitative reverse transcription (RT)-PCR method for multidrug resistance 1 (MDR1) and multidrug resistance-related protein 1 (MRP1) transcripts to evaluate drug resistance, and applied it to clinical samples.

Methods: The cutoffs for copy numbers of MDR1 and MRP1 transcripts were defined based on copy numbers in healthy bone marrow mononuclear cells. To confirm that the cutoffs reflected biological resistance, we established vincristine (VCR)-resistant K562 sublines that showed various degrees of drug resistance and examined the correlation between the copy numbers of these transcripts and the biological resistance of these clones. In addition, we compared the sensitivity and specificity of quantitative RT-PCR to a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometric (FCM) analysis.

Results: The defined cutoff for copy numbers of MDR1 transcripts corresponded with the degree of biological resistance of VCR-resistant K562 sublines. Clinical study revealed that the concentrations of MDR1 mRNA in all relapsed patients with acute myelogenous leukemia (AML) were above the cutoff. Moreover, both AML and acute lymphoblastic leukemia patients with high MDR1 mRNA expression at diagnosis tended to show a low remission rate and short remission periods. No association was observed between the amounts of MRP1 transcripts and clinical outcomes. The specificity and sensitivity of quantitative RT-PCR for MDR1 were superior to the MTT assay and FCM analysis.

Conclusion: These results suggest the efficacy of this quantitative analysis of MDR1 transcripts for the prediction of clinical drug resistance in acute leukemia.

"Pros and cons" on how to measure multidrug resistance in leukemias

Drug resistance is one of the most significant challenges in the treatment of various types of malignancies, however most of the experimental and clinical data in multidrug resistance (MDR) has been obtained in leukemias. MDR is the term that describes innate or acquired resistance of tumor cells to a wide range of anticancer drugs. As its presence determines treatment outcome in several forms of leukemias, it is imperative that clinical laboratories provide the most useful data on its expression. Here, a brief review is provided on the pathomechanism and diagnostics of MDR. From the diagnostic point of view it is fortunate that MDR proteins display similar effluxing activity towards many dissimilar agents some of which can be used in fluorescent assays. These tests mimic the real clinical problem i.e. the extrusion activity of MDR proteins towards xenobiotics. Thus, we believe that functional assays when carried out in a standardized way and particularly combined with labeling for various surface markers can be recommended as a front-line test in MDR measurement.

Drug resistance in epilepsy: expression of drug resistance proteins in common causes of refractory epilepsy

Epilepsy is resistant to drug treatment in about one-third of cases, but the mechanisms underlying this drug resistance are not understood. In cancer, drug resistance has been studied extensively. Amongst the various resistance mechanisms, overexpression of drug resistance proteins, such as multi-drug resistance gene-1 P-glycoprotein (MDR1) and multidrug resistance-associated protein 1 (MRP1), has been shown to correlate with cellular resistance to anticancer drugs. Previous studies in human epilepsy have shown that MDR1 and MRP1 may also be overexpressed in brain tissue from patients with refractory epilepsy; expression has been shown in glia and neurones, which do not normally express these proteins. We examined expression of MDR1 and MRP1 in refractory epilepsy from three common causes, dysembryoplastic neuroepithelial tumours (DNTs; eight cases), focal cortical dysplasia (FCD; 14 cases) and hippocampal sclerosis (HS; eight cases). Expression was studied immunohistochemically in lesional tissue from therapeutic resections and compared with expression in histologically normal adjacent tissue. With the most sensitive antibodies, in all eight DNT cases, reactive astrocytes within tumour nodules expressed MDR1 and MRP1. In five of eight HS cases, reactive astrocytes within the gliotic hippocampus expressed MDR1 and MRP1. Of 14 cases of FCD, MDR1 and MRP1 expression was noted in reactive astrocytes in all cases. In five FCD cases, MRP1 expression was also noted in dysplastic neurones. In FCD and DNTs, accentuation of reactivity was noted around lesional vessels. Immunoreactivity was always more frequent and intense in lesional reactive astrocytes than in glial fibrillary acidic protein-positive reactive astrocytes in adjacent histologically normal tissue. MDR1 is able to transport some antiepileptic drugs (AEDs), and MRP1 may also do so. The overexpression of these drug resistance proteins in tissue from patients with refractory epilepsy suggests one possible mechanism for drug resistance in patients with these pathologies. We propose that overexpressed resistance proteins lower the interstitial concentration of AEDs in the vicinity of the epileptogenic pathology and thereby render the epilepsy caused by these pathologies resistant to treatment with AEDs.

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.

Chemosensitivity prediction by transcriptional profiling

In an effort to develop a genomics-based approach to the prediction of drug response, we have developed an algorithm for classification of cell line chemosensitivity based on gene expression profiles alone. Using oligonucleotide microarrays, the expression levels of 6,817 genes were measured in a panel of 60 human cancer cell lines (the NCI-60) for which the chemosensitivity profiles of thousands of chemical compounds have been determined. We sought to determine whether the gene expression signatures of untreated cells were sufficient for the prediction of chemosensitivity. Gene expression-based classifiers of sensitivity or resistance for 232 compounds were generated and then evaluated on independent sets of data. The classifiers were designed to be independent of the cells' tissue of origin. The accuracy of chemosensitivity prediction was considerably better than would be expected by chance. Eighty-eight of 232 expression-based classifiers performed accurately (with P < 0.05) on an independent test set, whereas only 12 of the 232 would be expected to do so by chance. These results suggest that at least for a subset of compounds genomic approaches to chemosensitivity prediction are feasible.

Effect of P-glycoprotein modulators on the human extraneuronal monoamine transporter

The aim of this work was to investigate the effect of P-glycoprotein modulators on human extraneuronal monoamine transporter (EMT)-mediated transport. The experiments were performed using a cell line from human embryonic kidney (HEK293 cells) stably transfected with pcDNA3hEMT (293(hEMT)), or with pcDNA3 alone (293(control)). Of the P-glycoprotein modulators tested, rhodamine123, verapamil and daunomycin concentration-dependently inhibited EMT-mediated uptake of [3H]1-methyl-4-phenylpyridinium ([3H]MPP(+)). The corresponding IC(50)'s were found to be 3.6, 37 and 130 microM, respectively. By contrast, vinblastine, digitoxin and cyclosporine A were devoid of effect. The endogenous organic cation tyramine, but not choline, inhibited EMT-mediated transport (IC(50) of 468 microM). Moreover, L-arginine and L-histidine (up to 1 mM) did not affect [3H]MPP(+) uptake. Finally, MPP(+) and tyramine trans-stimulated [3H]MPP(+) uptake, but rhodamine123 had no effect, and verapamil and daunomycin trans-inhibited [3H]MPP(+) uptake. In conclusion, this study shows that several cationic modulators of P-glycoprotein inhibit EMT-mediated transport. As a consequence, the interaction of P-glycoprotein modulators with EMT must be taken into account, and the consequences of this interaction must not be forgotten when using such drugs in vivo.

Drug resistance mechanisms in acute leukemia

Markers of anticancer drug resistance are predictive of treatment response and outcome in patients with acute myeloid leukemia. Immunologic detection of the drug efflux pumps, P-glycoprotein (Pgp) and multidrug resistance-associated protein 1 (MRP1), correlate with functional assays of drug resistance. These accumulation defects also appear operable in acute lymphoblastic leukemia. Many of the efflux pumps identified share significant structural homology with the large superfamily of ATP-binding cassette transporters. Other markers such as lung-resistance protein, bcl-2, and breast cancer-resistance protein, have been described in acute myeloid leukemia patients although their pathophysiology and clinical relevance are less clear and the methodology for their quantification are not well standardized. Preclinical studies have shown that small molecules capable of reversing efflux can restore drug sensitivity in resistant tumor models. Although initial clinical studies were limited by both potency and specificity of the reverser, later studies with more effective reversers have in many instances been limited by pharmacokinetic interactions exacerbating the clinical toxicities of chemotherapy. Although one large randomized study has demonstrated a proven survival advantage without increased toxicity using cyclosporine, the inconsistent results with other modulators raise doubt as to the utility and overall strategy of using drug efflux blockers in patients with established Pgp overexpression. Many of these patients have additional resistance mechanisms, and achieving meaningful clinical responses will likely require more complex clinical strategies. Preventing or delaying development of drug resistance in chemosensitive patients represents another therapeutic strategy to be tested.

Does P-glycoprotein play a role in anticancer drug pharmacokinetics?

The multidrug-resistance P-glycoprotein is a drug efflux transport protein abundantly present in various types of human cancer. The protein is encoded by the MDR1 gene and its function is sensitive to modulation by competitive inhibition. Clinical studies have indicated that inhibitors of P-glycoprotein function dramatically decrease the systemic clearance of anticancer agents, necessitating dose reduction. This dose reduction not only complicated the interpretation of toxicity and response data, but also presented a serious obstacle in the development and rational use of P-glycoprotein inhibitors. It is now evident that the pharmacokinetic interference between anticancer drugs and P-glycoprotein inhibitors is due primarily to competition for drug metabolizing enzymes. A wealth of recent experimental data shows that many of the previously tested P-glycoprotein inhibitors, including verapamil, cyclosporin A, and valspodar (SDZ PSC 833), are substrates and/or potent inhibitors of cytochrome P450 3A4 (CYP3A4). Future development and clinical use of potent P-glycoprotein modulators lacking high affinity for CYP3A4 should decrease the impact of these important drug interactions and will eventually result in improved therapeutic specificity and efficacy. Copyright 2000 Harcourt Publishers Ltd.