Five putative drug resistance parameters (MDR1/P-glycoprotein, MDR-associated protein, glutathione-S-transferase, bcl-2 and topoisomerase IIα) in 57 newly diagnosed acute myeloid leukaemias

Role of Intracellular Drug Disposition in the Response of Acute Myeloid Leukemia to Cytarabine and Idarubicin Induction Chemotherapy

Despite its often low efficacy and high toxicity, the standard treatment for acute myeloid leukemia (AML) is induction chemotherapy with cytarabine and idarubicin. Here, we have investigated the role of transporters and drug-metabolizing enzymes in this poor outcome. The expression levels (RT-qPCR) of potentially responsible genes in blasts collected at diagnosis were related to the subsequent response to two-cycle induction chemotherapy. The high expression of uptake carriers (ENT2), export ATP-binding cassette (ABC) pumps (MDR1), and enzymes (DCK, 5-NT, and CDA) in the blasts was associated with a lower response. Moreover, the sensitivity to cytarabine in AML cell lines was associated with ENT2 expression, whereas the expression of ABC pumps and enzymes was reduced. No ability of any AML cell line to export idarubicin through the ABC pumps, MDR1 and MRP, was found. The exposure of AML cells to cytarabine or idarubicin upregulated the detoxifying enzymes (5-NT and DCK). In AML patients, 5-NT and DCK expression was associated with the lack of response to induction chemotherapy (high sensitivity and specificity). In conclusion, in the blasts of AML patients, the reduction of the intracellular concentration of the active metabolite of cytarabine, mainly due to the increased expression of inactivating enzymes, can determine the response to induction chemotherapy.

Ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017): a novel scaffold that resensitizes multidrug resistant leukemia cells to chemotherapy

Multidrug resistance (MDR) is a major hurdle in the treatment of cancer, and there is a pressing need for new therapies. We have recently developed ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017), derived from a dual inhibitor of Bcl-2 and SERCA proteins, sHA 14-1, with selective cytotoxicity toward MDR cancer cell lines in vitro. In this study, we present new evidence for its therapeutic potential in treatment of MDR cancers and offer mechanistic insights toward its preferential targeting of drug-resistant cancer. CXL017 selectively suppressed the growth of tumors derived from the MDR cancer cell line, HL60/MX2, in vivo. In addition, even after chronic exposure to CXL017, HL60/MX2 failed to develop stable resistance to CXL017, whereas it acquired >2000-fold resistance to cytarabine (Ara-C), the major first-line chemotherapy for the treatment of acute myeloid leukemia (AML). Remarkably, instead of acquiring further cross-resistance, HL60/MX2 cells exposed to CXL017 were resensitized to standard therapies (10- to 100-fold). Western blotting analyses revealed that CXL017 exposure significantly down-regulated Mcl-1 and Bax and up-regulated Noxa, Bim, Bcl-X(L), SERCA2, and SERCA3 proteins, along with a reduction in endoplasmic reticulum (ER) calcium content. Given the well-established functions of Bcl-2 family proteins and ER calcium in drug resistance, our results suggest that the down-regulation of Mcl-1 and the up-regulation of Noxa and Bim along with the decrease in ER calcium content are likely responsible for CXL017-induced resensitization of MDR cancer cells. These data also demonstrate the unique potential of CXL017 to overcome MDR in cancer treatment.

Prognostic significance of beta-catenin and topoisomerase IIalpha in de novo acute myeloid leukemia

The Wnt/beta-catenin signaling is important for controlling self-renewal of hematopoietic stem cells and its constitutive activation has recently been documented in a significant proportion of acute myeloid leukemia (AML) cases. Topoisomerase IIalpha (Topo IIalpha) is a marker of cell proliferation and a crucial target for anthracycline cytotoxicity, the mainstay of management employed in AML. We retrospectively investigated the prognostic roles of beta-catenin and topo IIalpha in a cohort of 59 patients with newly diagnosed AML by immunohistochemistry. Aberrant beta-catenin expression was demonstrated in 13 patients (22%), and it was more likely to occur in those with unfavorable karyotypes. Advanced age and poor performance status adversely influenced the achievement of complete remission, while neither aberrant beta-catenin expression nor enhanced topo IIalpha activity did. On multivariate survival analysis, four factors independently predicted a shortened overall survival: aberrant beta-catenin expression, high topo IIalpha activity, poor-risk cytogenetics, and presence of at least one comorbidity factor. Our results suggest that both beta-catenin and topo IIalpha independently predicted an adverse prognosis and might serve as new markers for risk stratification in AML patients.

Level of DNA topoisomerase IIalpha mRNA predicts the treatment response of relapsed acute leukemic patients

The DNA topoisomerase IIalpha (Topo IIalpha) is known as a target enzyme for many chemotherapeutic agents. We investigated the Topo IIalpha mRNA expression by real-time RT-PCR in 37 paired samples at diagnosis and at relapse of acute leukemic patients in relation to drug sensitivity and clinical outcome. The Topo IIalpha levels in leukemic blasts at relapse were significantly higher than that at diagnosis, especially in ALL. The increase in the Topo IIalpha level at relapse was significant in cases which could not achieve a second remission, but not significant in cases which achieved a second remission. These results suggest that the change of Topo IIalpha expression in leukemic blasts at relapse may predict therapeutic responsiveness.

The clinical relevance of the expression of several multidrug-resistant-related genes in patients with primary acute myeloid leukemia

Multidrug resistance (MDR) is a complex phenomenon that includes the expression of many different genes regulating drug transport or metabolism, cellular repair or detoxification mechanisms. The co-expression of several genes could be at the basis of the resistant phenotype in vivo. In order to test a possible prognostic role of the expression and co-expression of several MDR-related genes (MDR1, topoisomerase IIalpha, topoisomerase IIbeta, MRP, GSTpi, LRP), 35 patients affected by acute myeloid leukemia (AML) were tested by RT-PCR assays. In our series, topoisomerase IIbeta was significantly co-expressed with MRP (p = 0.05), GSTpi (p = 0.017) and LRP (p = 0.005). GSTpi was co-expressed with LRP (p = 0.03) and MRP (p = 0.007); on the other hand, 53.8% of patients were LRP and MRP-positive (p = 0.02). The PCR-positivity did not differ according to biological/clinical characteristics of patients, including age; this latter was the only parameter conditioning the response and overall survival. Neither the expression nor the co-expression of the tested genes was significantly correlated with the response to the induction treatment and long-term outcome.

Potential mechanisms of resistance to cytarabine in AML patients

To determine whether the human equilibrative nucleoside transporter 1 (hENT1), deoxycytidine kinase (dCK), cytoplasmic 5'-nucleotidase (5NT), cytidine deaminase (CDD), topoisomerase I (TOPO I) and topoisomerase II alpha (TOPO II) are involved in clinical resistance to cytarabine (ara-C), we analyzed the level of expression of these parameters by reverse transcriptase polymerase chain reaction (rt-PCR), at diagnosis in the blast cells of 77 acute myeloid leukemia (AML) patients treated with ara-C, including 31 for whom samples were collected at first relapse. By univariate and/or multivariate analyses, patients with expression of 5NT or hENT1 deficiency at diagnosis had significantly shorter disease-free survival (DFS) and overall survival (OS). These results suggest that expression of 5NT and reduced hENT1 in leukemic blasts at diagnosis are correlated with clinical outcome and may play a role in resistance mechanisms to ara-C in patients with AML.

In vivo mechanisms of resistance to cytarabine in acute myeloid leukaemia

Factors that reduce the intracellular concentration of triphosphorylated cytarabine (ara-CTP), the active form of cytarabine (ara-C), may induce chemoresistance in acute myeloid leukaemia (AML) patients. These factors include reduced influx of ara-C by the hENT1 transporter, reduced phosphorylation by deoxycytidine kinase (dCK), and increased degradation by high Km cytoplasmic 5'-nucleotidase (5NT) and/or cytidine deaminase (CDD). Increased levels of DNA polymerase alpha (DNA POL) and reduced levels of topoisomerase I (TOPO I) and topoisomerase II (TOPO II) have also been detected in ara-C-resistant cell lines. To determine whether these factors are implicated in clinical ara-C resistance, we analysed the expression of these parameters at diagnosis, using reverse transcription polymerase chain reaction, in the blast cells of 123 AML patients treated with ara-C. At diagnosis, hENT1, dCK, CDD, 5NT, TOPO I, TOPO II, DNA POL and MDR1 were expressed in 83%, 22%, 7%, 37%, 59%, 37%, 39% and 16% of patients respectively. In univariate analysis, patients with expression of 5NT or DNA POL at diagnosis had significantly shorter disease-free survival (DFS). In multivariate analysis, DNA POL positivity and hENT1 deficiency were related to a shorter DFS. In univariate analysis, patients with 5NT-positive blasts had significantly shorter overall survival (OS). In multivariate analysis, shorter OS was related to DNA POL positivity. These results suggest that expression of DNA POL, 5NT and hENT1 at diagnosis may be resistance mechanisms to ara-C in AML patients.

Increased expression of the breast cancer resistance protein (BCRP) in relapsed or refractory acute myeloid leukemia (AML)

Expression of the multidrug resistance proteins P-glycoprotein, encoded by the MDR1 gene, multidrug resistance-associated protein (MRP1) and the lung resistance-related protein or major vault protein (LRP/MVP) is associated with clinical resistance to chemotherapy in acute myeloid leukemia (AML). Recently, the breast cancer-resistant protein (BCRP), the equivalent of mitoxantrone-resistant protein (MXR) or placental ABC transporter (ABCP), was described in AML. We investigated MDR1, MRP1, LRP/MVP and BCRP mRNA expression simultaneously in 20 paired clinical AML samples from diagnosis and relapse or refractory disease, using quantitative Taqman analysis. In addition, standard assays for P-glycoprotein expression and function were performed. BCRP was the only resistance protein that was expressed at a significantly higher RNA level (median 1.7-fold, P = 0.04) at relapsed/refractory state as compared to diagnosis. In contrast, LRP/MVP mRNA expression decreased as disease evolved (P = 0.02), whereas MDR1 and MRP1 mRNA levels were not different at relapse as compared to diagnosis. Also, at the protein level no difference of MDR1 between diagnosis and relapse was found. A significant co-expression of BCRP and MDR1 was found at diagnosis (r = 0.47, P = 0.04). The present results suggest that BCRP, but not MDR1, MRP1 or LRP/MVP is associated with clinical resistant disease in AML.

Expression of topoisomerase IIalpha in the G0/G1 cell cycle phase of fresh leukemic cells

Topoisomerase IIalpha (topo IIalpha) is the target enzyme for several antineoplastic drugs. Correlation between low expression of topo IIalpha and drug resistance has been shown in vitro, but there is limited evidence of a correlation to initial response to treatment or to overall prognosis. Normal cells express topo IIalpha in S/G2/M phase of the cell cycle but not in G0/G1 phase. However, some data suggest that topo IIalpha could be expressed in G0/G1 phase in malignant cells. We have investigated the expression of topo IIalpha in leukemic cells from 25 patients with acute leukemia by flow cytometry, separating cells of different cell cycle phases. We demonstrated that 9/25 samples showed >50% positive cells in G0/G1, and another five samples showed >20%. This finding could possibly provide an explanation to previous difficulties in correlating topo IIalpha expression with clinical outcome. Six of eight patients, where >20% of the cells in G0/G1 were positive for topo IIalpha, entered CR, compared to one of five patients with <20% topo IIalpha positive cells in G0/G1. We suggest that topo IIalpha expression in G0/G1 in leukemic cells may be of predictive value for clinical response to cytostatic drugs.

Mitochondrial membrane sensitivity to depolarization in acute myeloblastic leukemia is associated with spontaneous in vitro apoptosis, wild-type TP53, and vicinal thiol/disulfide status

Nonresponse to remission-induction chemotherapy, which remains a major problem in acute myeloblastic leukemia (AML), has been linked to cellular resistance to apoptosis. Because the apoptosis induced by chemotherapeutic drugs is mediated by loss of mitochondrial transmembrane potential (MTP), it was postulated that sensitivity to mitochondrial membrane depolarization might be heterogeneous in AML. Using the uncoupling agent carbonyl cyanide m-chlorophenylhydrazone (mClCCP), the mitochondrial membrane sensitivity to depolarization (mClCCP concentrations that inhibit 50% of the transmembrane potential [IC(50)]) in AML blasts was measured and demonstrated marked interclonal heterogeneity, with the existence of comparatively sensitive (median mClCCP IC(50), 4 microM) and resistant (median mClCCP IC(50), 10 microM) clones. Furthermore, the mClCCP IC(50) was inversely associated with spontaneous in vitro apoptosis (P =.001). It was high in cases with mutant TP53 and correlated with the total cellular level of the multidrug resistance-associated protein (P =.019) but not of bcl-2, bax, or bcl-x. It was also found that the dithiol oxidant diamide, in contrast to the monovalent thiol oxidant diethyl maleate, increased the sensitivity of mitochondrial membranes to mClCCP. To confirm that TP53 directly affects MTP in leukemic cells and to establish the role of vicinal thiol oxidation in the TP53-dependent pathway, CEM 4G5 leukemia cells with forced, temperature-dependent expression of TP53 were studied. Monobromobimane, which inhibits mitochondrial membrane depolarization by preventing dithiol cross-linking, inhibited depolarization and apoptosis in 4G5 cells. It was concluded that in leukemia, TP53 and vicinal thiol/disulfide status are determinants of mitochondrial membrane sensitivity to depolarization, which is in turn associated with spontaneous apoptosis.

Chemotherapy resistance in acute myeloid leukaemia

The development of refractory disease in acute myeloid leukaemia (AML) is frequently associated with the expression of one or several multidrug resistance (MDR) genes. MDR1, MRP1 and LRP have been identified as important adverse prognostic factors in AML. Recently it has become possible to reverse clinical multidrug resistance by blocking P-glycoprotein-mediated drug efflux. The potential relevance of MDR and new approaches to treat refractory disease, are discussed.

MDR-1 expression and deletions of chromosomes 7 and 5(Q) separately indicate adverse prognosis in AML

In order to assess any correlation between MDR-1 expression and chromosomal aberrations, and to define their impact on clinical outcome in newly diagnosed AML pts, we investigated bone marrow and peripheral blood samples of 49 consecutive pts admitted to our hospital. Monosomy 7, trisomy 8 and 5q- were evaluated by means of interphase fluorescence in situ hybridization (FISH). Monosomy 7 was present in 6 pts, trisomy 8 in 5 pts, and 5q- in 6 pts. More than one aberration was seen in 7 pts. Chromosomal aberrations were mostly found in older pts (12/14 >60 years; p=0.03) and in pts with CD34 positive leukemic blasts (13/14 coexpressed CD34, p=0.0004). In 25 pts also standard G-banding analysis was performed leading to concordant results regarding chromosomes 7, 8 and 5. Flow cytometry identifyed MDR-1 positivity (MDR+) in 16 pts. MDR-1 expression appeared to be a characteristic feature in CD34+ AML (12/16 were CD34+ and MDR+ pts; p=0.013). No correlation, however, was found between chromosomal aberrations and MDR-1 expression. Pts with aberrations of either chromosomes 7, 8 or 5 detected by FISH (FISH+) were predominantly resistant to induction therapy (6/8 pts, p=0.004). A lower rate of complete remission (CR) was also seen in pts with MDR-1 expression (p=0.006). MDR+/FISH+ pts (n=3) were all refractory to remission induction, while all MDR-/FISH- pts (n=19) achieved CR (p=0.0006). MDR-1+ as well as pts with aberrations of chromosomes 7, and 5(q) showed a significantly decreased probability of overall survival. In conclusion, MDR-1 expression as well as abnormalities of chromosomes 7, and 5(q) predict poor clinical outcome in AML. The identification of these prognostic factors provides useful information for risk adapted treatment strategies.

Drug resistance factors in acute myeloid leukemia: a comparative analysis

To compare the clinical relevance of drug resistance factors in de novo acute myeloid leukemia (AML), we determined their relationship to both response to induction chemotherapy and survival of the patients in univariate as well as multivariate analyses. The drug resistance factors immunocytochemically studied in 111 patients at the time of diagnosis included the lung resistance protein (LRP), P-glycoprotein (P-gp), multidrug resistance protein (MRP1) and bcl-2. In the univariate analyses, age (P = 0.005), karyotype (P = 0.03), LRP (P = 0.003), P-gp (P = 0.02) and bcl-2 (P = 0.03) predicted for response to induction chemotherapy, whereas MRP1 had no predictive value. Age (P = 0.05), karyotype (P = 0.05) and LRP (P = 0.03) retained their predictive value in the multivariate logistic regression analyses. With regard to overall survival, age (P = 0. 008), karyotype (P = 0.006), LRP (P = 0.001) and P-gp (P = 0.01) were of prognostic value in the univariate Cox regression analyses but only age (P = 0.01), karyotype (P = 0.02) and LRP (P = 0.01) retained their prognostic significance in the multivariate analyses. A risk score based on the number of independent prognostic factors allowed division of patients into four groups with different outcome. In these groups, the complete remission rates were 93%, 75%, 47% and 33%, respectively, and median overall survival was 2.4, 1.2, 0.6 and 0.2 years, respectively. Thus, several drug resistance factors did predict outcome in the univariate analyses but LRP was the only drug resistance factor with independent predictive and prognostic significance. The proposed risk score might be useful for risk-adapted treatment in the future. Leukemia (2000) 14, 68-76.

Effect of all-trans retinoic acid on chemotherapy induced apoptosis and down-regulation of Bcl-2 in human myeloid leukaemia CD34 positive cells

Acute myeloid leukaemia (AML) is a heterogeneous malignant disease in which disease progression at the level of CD34 positive cells has a major impact in drug resistance and relapse. The multi-drug resistance (MDR1) gene product, P-glycoprotein is expressed mainly in CD34 positive AML cells and Bcl-2 is expressed simultaneously with several putative drug resistance parameters in these cells. Bcl-2 over-expression is associated with CD34 positivity, poor response to chemotherapy and reduced overall survival in AML patients. Recently, all-trans retinoic acid (RA) has been reported to enhance cytarabine-induced apoptosis and downregulate Bcl-2 in several human myeloid leukaemia CD34 negative cells. The two CD34 positive human myeloid leukaemia cell lines: KG1 and KGla have the unique feature of expressing significant functional P-glycoprotein. Thus, the efficacy of RA in enhancing cytrabine- and fludarabine-induced apoptosis and overcoming the resistance was examined in both KG1 (CD34+CD7-) and KGla (CD34+CD7+) human myeloid leukaemia cells in the present study. Both cytarabine and fludarabine induced a dose dependent increase in the number of apoptotic cells in both CD34 positive cell types. Interestingly, the cytarabine-induced apoptosis was significantly more than fludarabine-induced apoptosis in both cell types. All-trans RA alone failed to induce apoptosis or inhibit proliferation of either of the two human CD34 positive leukaemia cell types. However, RA enhanced cytarabine- or fludarabine-induced apoptosis and inhibition of proliferation in KG1 CD34+CD7- but not in KGla CD34+CD7+ myeloid leukaemia cells. As single agents, RA, cytarabine and fludarabine reduced Bcl-2 expression in a dose dependent manner in both cell types. Using a quantitative ELISA assay, the Bcl-2 protein concentration was reduced by 86 or 100%, after 72 h of treatment with 10 microM cytarabine or fludarabine, respectively, in both CD34 positive leukaemia cell types. The addition of RA to cytarabine enhanced its induced reduction of Bcl-2 in KG1 CD34+CD7- but not in KGla CD34+CD7+ human myeloid leukaemia cells. Meanwhile, RA failed to augment fludarabine-induced reduction of Bcl-2 in both cell types. In conclusion, the present results suggest a potential role for the combination of RA and cytarabine in the treatment of refractory and/or relapsed AML patients with CD34+CD7- but not CD34+CD7+ blast cells.

Escaping cell death: survival proteins in cancer

Defects in apoptosis signaling pathways are common in cancer cells. Such defects may play an important role in tumor initiation because apoptosis normally eliminates cells with damaged DNA or dysregulated cell cycle, i.e., cells with increased malignant potential. Moreover, impaired apoptosis may enhance tumor progression and promote metastasis by enabling tumor cells to survive the transit in the bloodstream and to grow in ectopic tissue sites lacking the otherwise required survival factors. Finally, raised apoptosis threshold may have deleterious consequences by rendering cancer cells resistant to various forms of therapy. The intensive apoptosis research during the past decade has resulted in the identification of several proteins which may promote tumorigenesis by inhibiting apoptosis. Of special relevance in human cancer are those commonly expressed in primary tumors and functioning at the common part of the signaling pathway leading to apoptosis. Proteins fulfilling these criteria include antiapoptotic members of the Bcl-2 protein family, heat shock proteins, Hsp70 and Hsp27, as well as survivin, the novel cancer-associated member of the inhibitor of apoptosis protein family. Understanding the molecular mechanisms of action of these proteins may offer novel modes of rationally and selectively manipulating the sensitivity of cancer cells to therapy.

Different expression of glutathione S-transferase alpha, mu and pi in childhood acute lymphoblastic and myeloid leukaemia

Expression of three major classes of glutathione S-transferases (GSTs), i.e. alpha, mu and pi class, P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) were studied in childhood acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML) and normal peripheral blood lymphocytes by flow cytometry. In vitro cytotoxicity of 4-hydroxy-ifosfamide (IFOS), daunorubicin (DNR) and prednisolone (PRED) was assessed by the MTT assay. Expression of alpha, mu and pi class GST did not significantly differ between leukaemic cells from 100 initial and 14 unrelated relapse ALL patients (GSTalpha P=026; GSTmu P=O009; GSTpi P=0.13). The expression of GSTalpha (1.4-fold, P=0.0004), GSTpi (13-fold, P = 0001) and to a lesser extent also GSTmu (1.1-fold, P=0.03) was higher in ALL compared with normal peripheral blood lymphocytes. Expression of GSTmu and GST7pi was significantly higher in 18 AML compared with 100 ALL patients at initial diagnosis (respectively 1.3-fold, P=0.0005 and 2-fold, P<0.0001). In contrast, GSTalpha was median 2-fold lower expressed in the AML samples (P< 0.0001). Expression levels of alpha, mu and pi class GSTs were not related to the degree of resistance to IFOS, DNR and PRED nor to immunophenotype, white blood cell count or age at presentation of childhood ALL. One exception was a remarkably low expression of GSTalpha in IFOS-sensitive samples compared with a heterogenous expression in IFOS-resistant samples (P= 0.02). Expression of GSTpi, but not of GSTalpha or GSTmu, weakly correlated with the expression of MRP (Rs 0.36, P = 0.002, n = 74) but not with P-gp. However, a high expression of both GSTpi and MRP was not associated with in vitro resistance to IFOS, DNR or PRED. The present data suggest that expression of GSTs is not linked to the degree of resistance to IFOS, DNR and PRED or clinical risk factors in childhood ALL. Whether the high expression of GSTmu and GSTpi in AML cells contributes to the relative resistance to IFOS, DNR and PRED compared with ALL samples (P < or = 0.0001) warrants further study.

Clinical resistance to topoisomerase-targeted drugs

This review describes topoisomerase (topo)-mediated drug resistance and topo expression in human tissues and cancers. In some in vitro studies a relation has been observed between topo I, IIalpha or IIbeta expression and sensitivity to topo inhibitors. Drug resistance to topo inhibitors may, however, be multifactorial. Several topo inhibitors are substrates for drug membrane transporters. As most topo inhibitors are cell cycle specific, disturbances in cell cycle regulation can also confer resistance, and downstream events following DNA damage induced by topo inhibitors may be involved in regulating cell death or survival. Several studies in patient specimens have shown a relation between topo IIalpha expression and the proliferative state of the tumor, higher topo IIalpha levels being seen in more highly proliferating tumor types. In contrast, topo IIbeta appears to be expressed in both proliferating and quiescent cells. Furthermore, higher topo I levels were observed in some tumors when compared to their normal counterparts. In some studies a reduced topo IIalpha level was seen in samples taken after chemotherapy treatment, as compared with specimens prior to treatment. No unequivocal relation was observed, however, between expression or activity of the topo genes and response to chemotherapy; nonetheless only a few studies have properly addressed this question. This review summarizes the results of the clinical studies performed so far, and analyzes the critical issues in performing studies on patient material.