Expression of mdr1, mrp, topoisomerase II alpha/beta, and cyclin A in primary or relapsed states of acute lymphoblastic leukaemias

FLT3-ITD and MLL-PTD influence the expression of MDR-1, MRP-1, and BCRP mRNA but not LRP mRNA assessed with RQ-PCR method in adult acute myeloid leukemia

Fms-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) and mixed-lineage leukemia gene-partial tandem duplication (MLL-PTD) are aberrations associated with leukemia which indicate unsatisfactory prognosis. Downstream regulatory targets of FLT3-ITD and MLL-PTD are not well defined. We have analyzed the expression of MDR-1, multidrug resistant protein-1 (MRP-1), breast cancer resistance protein (BCRP), and lung resistance protein (LRP) messenger RNA (mRNA) in relation to the mutational status of FLT3-ITD and MLL-PTD in 185 acute myeloid leukemia (AML) adult patients. The real-time quantitative polymerase chain reaction method was performed to assess the expression of the MDR-1, MRP-1, BCRP, and LRP mRNA, and the results were presented as coefficients calculated using an intermediate method according to Pfaffl's rule. Significantly higher expressions of MDR-1 mRNA were found in patients who did not harbor FLT3-ITD (0.20 vs. 0.05; p = 0.0001) and MRP-1 mRNA in patients with this mutation (0.96 vs. 0.70; p = 0.002) and of BCRP mRNA in patients with MLL-PTD (0.61 vs. 0.38; p = 0.03). In univariate analysis, the high expression of MDR-1 mRNA (≥0.1317) negatively influenced the outcome of induction therapy (p = 0.05), whereas the high expression of BCRP mRNA (≥1.1487) was associated with a high relapse rate (RR) (p = 0.013). We found that the high expression of MDR-1 (≥0.1317), MRP-1 (≥0.8409), and BCRP mRNA (≥1.1487) significantly influenced disease-free survival (DFS; p = 0.059, 0.032, and 0.009, respectively) and overall survival (0.048, 0.014, and 0.059, respectively). Moreover, a high expression of BCRP mRNA (≥1.1487) proved to be an independent prognostic factor for RR (p = 0.01) and DFS (p = 0.002) in multivariate analysis. The significant correlation between the expression of MDR-1, MRP-1, and BCRP mRNA and FLT3-ITD or MLL-PTD in AML patients requires further investigation.

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.

Reversal effect of BM-cyclin 1 on multidrug resistance in C-A120 cells

In this study, multidrug-resistant human epidermoid C-A120 cells and the sensitive parental KB cells were used as experimental models. BM-cyclin 1, a traditional antimycoplasma drug, was tested to explore the reversal effect of multidrug resistance and its mechanisms in these cell lines. The MTT analysis showed that BM-cyclin 1 could reverse multidrug resistance effectively in C-A120 cells; the sensitivity of C-A120 cells to adriamycin, etoposide and cisplatin was enhanced by 6.0, 8.2 and 1.7 times, respectively. Immunoblotting analysis and reverse transcription-polymerase chain reaction were used to study the BM-cyclin 1-induced changes in topoisomerase IIalpha. The results showed that the expression of topoisomerase IIalpha in treated C-A120 cells increased significantly. Topoisomerase II catalytic activity increased by 30% compared with the untreated cells, as measured by decatenation of kinetopolast DNA. Immunoblotting analysis also indicated the transcription factor levels of specificity: those of protein 1 (Sp1) and nuclear factor-YA increased after treatment with BM-cyclin 1, whereas the mRNA and protein expression of multidrug resistance protein 2 was significantly downregulated. These results demonstrated that BM-cyclin 1 could effectively reverse the multidrug resistance of C-A120 cells by increasing the expression of topoisomerase IIalpha and by suppressing the expression of multidrug resistance protein 2, strongly suggesting that BM-cyclin 1 is a potential multidrug resistance reversal agent.

Increased expression of multidrug resistance gene (MDR1) at relapse in a child with acute lymphoblastic leukemia

Modern treatment protocols lead to complete remission in a high proportion of patients with childhood acute lymphoblastic leukemia (ALL). However, a large number of them show a relapse of the disease. Treatment failure in these patients is mainly attributable to de novo or acquired resistance to a wide variety of cytotoxic drugs, which is called multi drug resistance (MDR). Expression of multi drug resistance 1 gene (MDR1) is implicated in the drug-resistance mechanism. In order to contribute further information we present a rare case of a 15-month old girl with newly diagnosed CALLA positive pre-B acute lymphoblastic leukemia with favourable prognostic factors at diagnosis who experienced a relapse of the disease. Using reverse transcriptase polymerase chain reaction method, m-RNA expression of the MDR1 gene upon relapse, was five-fold compared with that at diagnosis. This is the first report on increased mRNA expression at relapse in a paired sample of a child with ALL in our region.

Prognostic significance of multidrug resistance-related proteins in childhood acute lymphoblastic leukaemia

An important problem in the treatment of children with acute lymphoblastic leukaemia (ALL) is pre-existent or acquired resistance to structurally and functionally unrelated chemotherapeutic compounds. Various cellular mechanisms can give rise to multidrug resistance (MDR). Best studied is the transmembrane protein-mediated efflux of cytotoxic compounds that leads to decreased cellular drug accumulation and toxicity. Several MDR-related efflux pumps have been characterised, including P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1), breast cancer resistance protein (BCRP) and lung resistance protein (LRP). P-gp expression and/or activity has been associated with unfavourable outcome in paediatric ALL patients, whereas MRP1 and BCRP do not seem to play a major role. LRP might contribute to drug resistance in B-lineage ALL, but larger studies are needed to confirm these results. The present review summarises the current knowledge concerning multidrug resistance-related proteins and focuses on the clinical relevance and prognostic value of these efflux pumps in childhood ALL.

Effects of P-glycoprotein modulation on the chemotherapy of xenotransplanted human hepatoblastoma

Multidrug resistance (MDR) contributes to limited treatment results in human hepatoblastoma (HB). The MDR1 gene and its product P-glycoprotein (P-gP) has been identified as important factor in this development. In other tumors, P-gP modulation leads to a restored chemosensitivity of the cells. The aim of this study was to analyze the P-gP-modulating effects of PSC 833, a cyclosporine derivate, and verapamil on the chemotherapy of HB in vivo. HB from 2 patients were transplanted subcutaneously into nude mice NMRI (nu/nu). Animals were divided into 7 groups: Group 1 (Control); Group 2 (CDDP); Group 3 (DOXO); Group 4 (DOXO + verapamil); Group 5 (DOXO + PSC 833); Group 6 (CDDP + verapamil); and Group 7 (CDDP + PSC 833). If DOXO was administered (regardless of the combination), the dose was two times 60 mg/m2. If CDDP was administered, the dose was two times 27 mg/m2. When the chemosensitizers were administered, the doses for PSC 833 and for verapamil were four times 5 mg/kg body-weight. In the combined treatment groups the chemosensitizers were given ten minutes prior to CDDP and DOXO. Tumor volume developments and a-fetoprotein (AFP) alterations were assessed. Relative expression levels of the MDR1 gene after treatment were determined using a semiquantitative rT-PCR approach. In a mixed HB, both chemosensitizers combined with DOXO or CDDP produced a significant reduction of tumor growth (p = .0001-.00063) and AFP levels (p = .0006-.0128) compared to tumors treated with DOXO or CDDP only. Treatment results were identical to those in a less differentiated pure embryonal HB, but only in one case (DOXO + PSC 833, p = .031) significant. The chemosensitizers had no influence on the MDR1 gene expression. MDR1 modulators improve the efficiency of DOXO and CDDP treatment in xenotransplanted HB. They do not induce a further increase of drug resistance in the tumors. The data provide evidence that chemosensitizers might improve treatment results in patients with advanced or relapsed HB.

MDR1 and MRP1 gene expression are independent predictors for treatment outcome in adult acute myeloid leukaemia

Multi drug resistance (MDR) is a major obstacle for cancer therapy. The three major candidates accounting for the development of MDR in acute myeloid leukaemia (AML) are multi drug resistance gene (MDR1), multi drug resistance-related protein gene (MRP1) and lung resistance protein gene (LRP). So far, the differential impact of resistance gene expression on treatment outcome in AML is not clear. Therefore, we examined MDR1, MRP1 and LRP gene expression at diagnosis in 331 adult AML patients in the context of other known prognostic factors, such as age, disease status, cytogenetics and FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication mutational status. Median observation time was longer than 5 years [64.1 months (40.0-87.6)]. MDR1 expression proved to be an independent prognostic factor for outcome of induction therapy (P <0.001) and overall survival (P=0.02), whereas MRP1 expression was an independent predictor for disease-free survival (P=0.01) in the multivariate analysis. This prognostic impact of both resistance genes was also found in patients with intermediate risk cytogenetics. LRP expression, however, had no impact on treatment outcome in AML. Our study shows that resistance gene expression should be considered together with age, cytogenetics and FLT3 mutational status for risk-adapted treatment strategies in AML in the future.

Adult acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in adults is a relatively rare neoplasm with a curability rate around 30% at 5 years. This consideration makes it imperative to dissect further the biological mechanisms of disease, in order to selectively implement an hitherto unsatisfactory success rate. The recognition of discrete ALL subtypes (some of which deserve specific therapeutic approaches, like T-lineage ALL (T-ALL) and mature B-lineage ALL (B-ALL)) is possible through an accurate combination of cytomorphology, immunophenotytpe and cytogenetic assays and has been a major result of clinical research studies conducted over the past 20 years. Two-three major prognostic groups are now easily identifiable, with a survival probability ranging from <10 to 20% (Philadelphia-positive ALL) to about 50-60% (low-risk T-ALL and selected patients with B-lineage ALL). These issues are extensively reviewed and form the basis of current knowledge. The second major point relates to the emerging importance of studies that reveal a dysregulated gene activity and its clinical counterpart. It is now clear that prognostication is a complex matter ranging from patient-related issues to cytogenetics to molecular biology, including the evaluation of minimal residual disease (MRD) and possibly gene array tests. On these bases, the role of a correct, highly personalised therapeutic choice will soon become fundamental. Therapeutic progress may be obtainable through a careful integration of chemotherapy, stem cell transplantation, and the new targeted treatments with highly specific metabolic inhibitors and humanised monoclonal antibodies.

Decrease of P-Glycoprotein Activity in K562/ADR Cells by M?CD and Filipin and Lack of Effect Induced by Cholesterol Oxidase Indicate That This Transporter Is Not Located in Rafts

The effect of low-density membrane domains on function of the plasma membrane transporter P-glycoprotéine (P-gp), involved in multidrug resistance (MDR) phenotype, has been investigated in K562/ADR cells. To this end we reversibly altered the cholesterol content of K562/ADR cells by using methyl-beta-cyclodextrin as a cholesterol chelator and conversely we repleted them through incubation with cholesterol in culture medium. We also used the cholesterol-binding fluorochrome filipin and cholesterol oxidase. Our data show that either cholesterol depletion or complex formation with filipin resulted in a strong decrease of P-gp activity. However, when cells were incubated with cholesterol oxidase that are known to disrupt rafts, no modification of the P-gp activity was observed. In addition, using a free-detergent methodology to separate by ultracentrifugation, "light," "heavy," and "extra heavy" fractions we show that no P-gp is found in the "light" fraction where rafts are usually detected. Altogether, our data strongly suggest that, in this cell line, P-gp is not localized in rafts.

Down-regulation of human topoisomerase IIalpha correlates with altered expression of transcriptional regulators NF-YA and Sp1

Topoisomerase IIalpha (Topo IIalpha) is an essential nuclear enzyme with a role in the maintenance of DNA topology. Topo IIalpha is a target for several anticancer drugs and the levels of activity of this enzyme have been implicated in the development of drug resistance. Our objective was to identify regulatory transcription factors involved in drug-induced down-regulation of Topo IIalpha. A breast cancer cell line was subjected to a pulsed exposure of doxorubicin and resistant clones propagated. Whole-cell extracts were studied by immunoblotting and RT-PCR for drug-induced changes in the amounts Topo IIalpha, Sp1, Sp3, NF-Y and MDR1. Topo IIalpha levels were reduced in six out of eight cell lines. Of these, three showed concomitant changes in the expression of Sp1 and NF-YA. Thus, we provide the first evidence for roles of Sp1 and NF-Y in bringing about the drug-induced down-regulation of Topo IIalpha gene expression.

Impact of Topoisomerase II alpha and spermine on the clinical outcome of children with acute lymphoblastic leukemia

It has been reported in the literature that a leukemic cell may be (or become) resistant to anti-cancer treatment because many mechanisms, such as efflux membrane pump (multi-drug resistance, MDR-P170), intracellular transport (LRP, MRP), or different detoxification systems (glutathione transferases, methallothioneines) may be implicated. Topoisomerase II alpha (TopoII) are also reported as responsible for resistance since their main action is to repair DNA breakage. Polyamines are described as having a protective DNA action by stabilizing the double stranded DNA helix. For these reasons we investigated 65 children with acute lymphoblastic leukemia using an immunocytochemical method to elucidate the potential role of Topoisomerase and polyamines in drug resistance. Most children (60/65) were treated with the French (acute lymphoblastic leukemia, ALL) protocol (FRALLE-93) in which B and C arms include (at least) VP16. Children with cytoplasmic TopoII positivity (18 cases) were more resistant since their overall survival was 34 months compared to more than 110 months for negative cases ( P = 0.0003). Polyamines may be associated with drug resistance since the overall survivals were 51 months and 92 months for positive and negative patients, respectively, but the P-value is only 0.13. We conclude that Topoisomerase and polyamines must be tested at diagnosis as new possible markers for chemo-resistance. Larger series are needed to confirm these preliminary results and to verify if the use of anti epipodophillotoxin agents (as it is the case for FRALLE B or C) should be excluded for positive cases.

Elevated levels of cyclin A1 and A (A2) mRNA in acute myeloid leukaemia are associated with increased survival

Cyclin A (A2) and cyclin A1 are members of the G2 cyclins, which are involved in the control of G2/M and G1/S transitions as well as mitosis. Human cyclin A1 was cloned as an A-type cyclin that is highly expressed in acute myeloid leukaemia (AML). The clinical significance of these cyclins in myeloid leukaemia remains to be clarified. We investigated the relative levels of these transcripts in 80 patients with de novo AML. Correlations with clinical parameters showed that the initial white blood cell count and serum lactate dehydrogenase levels were inversely associated with cyclin A (A2) mRNA levels (r = -0.276, P = 0.019) and cyclin A1 mRNA levels (r = -0.241, P = 0.042) respectively. They were independently associated with increased overall survival [P = 0.035 for cyclin A (A2) and P = 0.016 for cyclin A1]. Multivariate analysis using Cox's proportional hazard model showed that elevated cyclin A1 mRNA levels contributed significantly to the better prognosis of patients with AML. Furthermore, the analysis of survival probability showed that the group with high levels of both cyclin A (A2) and A1 survived significantly longer than the group with low expression of both these cyclins (P = 0.002). These data indicate that high expression levels of both cyclin A (A2) and A1 are associated with good prognosis in AML patients.

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.

Hydrolytically activated etoposide prodrugs inhibit MDR-1 function and eradicate established MDR-1 multidrug-resistant T-cell leukemia

Effective therapy of high-risk leukemia with established cytotoxic drugs may be limited by poor antitumor efficacy, systemic toxicity, and the induction of drug resistance. Here, we provide the first evidence that hydrolytically activated prodrugs may overcome these problems. For this purpose, VP16 was functionally blocked by hydrolytically cleavable carbonate linkers with unique characteristics to generate 2 novel prodrugs of VP16. First, we established a more than 3-log higher efficacy of the 2 prodrugs compared with VP16 on a panel of naturally drug-resistant tumor cell lines. Second, the prodrugs did overcome VP16-induced multidrug resistance-1 gene (MDR-1)-mediated multidrug resistance in vitro in a newly established VP16-resistant T-cell leukemia cell line MOVP-3 by functionally blocking MDR-1-mediated efflux. Third, in vivo studies showed a maximum tolerated dose of ProVP16-II (> 45mg/kg), which was at least 3-fold higher than that of VP16 (15 mg/kg). Finally, tests of ProVP16-II in a multidrug-resistant xenograft model of T-cell leukemia expressing MDR-1 indicated that only the mice treated with this prodrug revealed a complete and long-lasting regression of established, drug-resistant leukemia. In summary, the hydrolytically activated etoposide prodrugs proved effective against multidrug-resistant T-cell leukemia in vitro and in vivo and provide proof of concept for a highly promising new strategy for the treatment of MDR-1 drug-resistant malignancies.

Modification of topoisomerase genes copy number in newly diagnosed childhood acute lymphoblastic leukemia

Topoisomerase genes were analyzed at both DNA and RNA levels in 25 cases of newly diagnosed childhood acute lymphoblastic leukemia (ALL). The results of molecular analysis were compared to risk group classification of children in order to identify molecular characteristics associated with response to therapy. At diagnosis, allelic imbalance at topo-isomerase IIalpha (TOP2A) gene locus was found in 75% of informative cases whereas topoisomerase I and IIbeta gene loci are altered in none or only one case, respectively. By semi-quantitative Polymerase chain reaction, we found a 2.5 to 8-fold TOP2A gene amplification in 72% of the children, which was correlated to gene overexpression in every case. These results show that TOP2A gene amplification is a frequent event in ALL at diagnosis. Interestingly, we also identified a small population of children that do not present TOP2A gene amplification or gene overexpression and who are significantly associated with very high risk classified patients showing glucocorticoid resistance. In conclusion, characterization of TOP2A gene status in childhood ALL at diagnosis provides useful complementary information for risk assessment.

Correlation between cyclin A gene expression in adult patients with acute leukemia and drug resistance

In order to investigate the relationship between the expression of cyclin A and drug resistance in adult patients with acute leukemia (AL), the mRNA expression of cyclin A, mdr1, Top II alpha, bcl-2 was detected in 64 adult patients with AL and 20 normal controls by semi-reverse transcription polymerase chain reaction (semi-RT-PCR). It was found that the cyclin A and Top II alpha mRNA expression levels in drug resistant group were significantly lower than in sensitive group (P < 0.01). Under the same experimental condition no cyclin A mRNA expression was detectable in all normal controls. The mdr1 and bcl-2 mRNA expression levels in resistant group were significantly higher than in sensitive group (P < 0.01), cyclin A and Top II alpha gene expression levels were closely correlated (rs = +0.794, P = 0.000, n = 64) in all AL patients, but cyclin A was not correlated with mdr1 and bcl-2 gene expression levels. In drug resistant group there was a negative correlation between the gene expression levels of cyclin A and mdr1 (rs = -0.337, P = 0.029). The 10 AL patients with positive lower expression of both cyclin A and Top II alpha were all resistant to drugs. Logistic regression of Binary analysis showed the correlation between the lower expression of cyclin A and drug resistance. It was concluded that lower expression of cyclin A gene might be an unfavorable prognostic factor for patients with AL, and detection of both cyclin A and Top II alpha gene expression would predict drug resistance in AL patients.

MDR1 modulators improve the chemotherapy response of human hepatoblastoma to doxorubicin in vitro

PURPOSE

P-glycoprotein, a membrane efflux pump encoded by the MDR1 gene, plays an important role in the development of multidrug resistance in human hepatoblastoma (HB). Chemosensitizers antagonize the efflux action of P-glycoprotein. This study investigates the effects of 3 chemosensitizers (the cyclosporin analogue SDZ PSC 833 (PSC 833), the acridone carboxamide derivative GG 918, and verapamil) on the chemotherapy of HB in vitro.

METHODS

The doxorubicin (DOXO) concentration that produces 50% growth inhibition (IC50) in a HB cell line was determined and additional effects of PSC 833, GG 918, and verapamil were investigated in a cytotoxicity assay. The MDR1 gene expression after treatment was determined in a semiquantitative reverse transcription polymerase chain reaction approach.

RESULTS

The IC50 of DOXO is 2.5 microg/mL, 0.61 microg/mL for DOXO + PSC 833, 1.17 microg/mL for DOXO + verapamil, and 1.47 microg/mL for DOXO + GG 918. In combination with DOXO, cell growth was inhibited 4.1-fold by PSC 833, 2.1-fold by verapamil, and 1.9-fold by GG 918. The MDR1 gene expression was enhanced significantly in all treated cells, with and without modulator.

CONCLUSIONS

MDR1 modulators significantly improve the response of HB to DOXO in vitro. The combination of anticancer agents and MDR1 modulators might be a possible contribution to overcome multidrug resistance in HB.

The role of the MDR1 gene in the development of multidrug resistance in human hepatoblastoma: clinical course and in vivo model

BACKGROUND

The P-glyprotein (P-gp), which is a membrane channel encoded by the MDR1 gene, represents a possible explanation for multidrug resistance in human hepatoblastoma (HB). P-gp shows up-regulation in tumor cells after chemotherapy; however, to date, its exact role in HB has not been described. The authors investigated the role of the MDR1 gene in the clinical course of patients with HB and in an in vivo model of HB. They also studied the effects of the MDR1 antagonizer PSC 833 on chemotherapy in mice xenotransplanted with HB.

METHODS

Resected tumor specimens, including both primary tumors and recurrent tumors, from a child suffering from HB were investigated histologically. Cell suspensions from the originally removed tumor were incorporated subcutaneously into nude mice. Animals were treated with cisplatin (CDDP) plus PSC 833. MDR1 gene expression levels in the different resected tumors from the patient and in the xenotransplants after treatment were determined with polymerase chain reaction analysis.

RESULTS

MDR1 gene expression was increased in the patient's tumors after every course of chemotherapy from 30% to > 190%. In the xenotransplants, MDR1 gene expression was enhanced significantly after chemotherapy (P(CDDP) = 0.008; P(CDDP+PSC) = 0.002). Tumor volumes (P < 0.001) and serum alpha-fetoprotein levels (P = 0.0002) were significantly lower in the animals that were treated with CDDP + PSC compared with the animals that were treated with CDDP alone.

CONCLUSIONS

The current results suggest that MDR1 gene expression and P-gp are a potential mechanism of drug resistance in HB. The chemosensitizer PSC 833 significantly improved the effects of chemotherapy in animals xenotransplanted with HB. These data encourage further studies concerning the role of chemosensitizers in overcoming multidrug resistance in patients with HB.

Pharmacokinetic interactions of cyclosporine with etoposide and mitoxantrone in children with acute myeloid leukemia

The purpose of this study was to assess the effect of the multidrug resistance modulator cyclosporine (CsA) on the pharmacokinetics of etoposide and mitoxantrone in children with de novo acute myeloid leukemia (AML). Serial blood samples for pharmacokinetic studies were obtained in 38 children over a 24-h period following cytotoxin treatment with or without CsA on days 1 and 4. Drug concentrations were quantitated using validated HPLC methods, and pharmacokinetic parameters were determined using compartmental modeling with an iterative two-stage approach, implemented on ADAPT II software. Etoposide displayed a greater degree of interindividual variability in clearance and systemic exposure than mitoxantrone. With CsA treatment, etoposide and mitoxantrone mean clearance declined by 71% and 42%, respectively. These effects on clearance, in combination with the empiric 40% dose reduction for either cytotoxin, resulted in a 47% and 12% increases in the mean AUC for etoposide and mitoxantrone, respectively. There were no differences in the rates of stomatitis or infection between the two groups. CsA treatment resulted in an increased incidence of hyperbilrubinemia, which rapidly reversed upon conclusion of drug therapy. The variability observed in clearance, combined with the empiric 40% dose reduction of the cytotoxins, resulted in statistically similar systemic exposure and similar toxicity.

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.

Preferential efflux by P-glycoprotein, but not MRP1, of compounds containing a free electron donor amine

Multidrug resistance (MDR) in model systems is known to be conferred by two different integral proteins, the 170-kDa P-glycoprotein (P-gp) and the 190-kDa multidrug resistance-associated protein (MRP1), both of which pump drugs out of MDR cells. The presence of a nitrogen atom, charged at physiological pH, has frequently been considered to be a hallmark of P-gp substrates and inhibitors. The present study was aimed at investigating the role of nitrogen in the ability of the pump to recognise substrate. We measured the kinetics of active efflux of seven new anthracycline derivatives in P-gp-expressing K562/ADR cells and in MRP1-expressing GLC4/ADR cells. Six of these compounds represent analogues of daunorubicin in which the amino sugar nitrogen is bound to an amino- or a nitro-substituted benzyl moiety, the seventh is a doxorubicin derivative in which benzyl group is bound with 4'-oxygen. We found that the compounds with a nitro group on the benzyl ring were poor substrates for P-gp despite the presence of a secondary amine that can be protonated. In contrast, compounds that have a free amino group were very good substrates even though this amine is not protonated in the pH range studied (pK approximately 3). These results show that the nitrogen atom does not interact with P-gp in a charged form but rather as an electron donating group.

P-glycoprotein, lung resistance-related protein and multidrug resistance-associated protein in de novo adult acute lymphoblastic leukaemia

P-glycoprotein (P-gp), lung resistance-related protein (LRP) and multidrug resistance-associated protein (MRP) expression, and blast cell intracellular daunorubicin accumulation (IDA) were evaluated in 95 previously untreated cases of adult acute lymphoblastic leukaemia (ALL) using flow cytometry. Forty-five out of 95 (47%) patients were P-gp positive (+), 12/66 (18%) were LRP+ and 11/66 (17%) were MRP+. Eighteen out of 66 (28%) patients showed a simultaneous multidrug resistance (MDR)-related protein expression higher than controls for more than one protein, while 24/66 (36%) cases did not overexpress any protein. Twenty-one out of 24 (87%) cases overexpressing at least one MDR-related protein had a defect in accumulating daunorubicin into their blast cells, while only 4/24 (16%) cases who did not overexpress any protein had similar features. The complete remission rates were similar in MDR-positive and -negative (-) patients but relapses within 6 months were more frequent in P-gp+ cases, and therefore the disease-free survival duration was shorter in P-gp+ than in P-gp- patients (P = 0.01). The number of MRP+ and/or LRP+ cases was too small to be able to draw any conclusion on their role in affecting or predicting therapy outcome. In conclusion, P-gp overexpression associated with a defect in daunorubicin accumulation is a frequent feature in adult ALL at onset and seems to be related to poorer therapy outcome and, consequently, a shorter disease-free survival. LRP and MRP overexpression seems to be a rare event and no conclusion can be drawn on its prognostic role.

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

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

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

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

Anticancer drug-mediated induction of multidrug resistance-associated genes and protein kinase C isozymes in the T-lymphoblastoid cell line CCRF-CEM and in blasts from patients with acute lymphoblastic leukemias

The major determinants mediating drug resistance in acute lymphoblastic leukemias (ALL) unresponsive to chemotherapy, are still unclear. For example, it is still unknown whether selection or induction processes are responsible for drug resistance here or whether protein kinase C (PKC) isozymes contribute to the resistant phenotype. Therefore, inducibility of resistance factors or PKC isozymes genes was examined in CCRF-CEM cells treated with diverse anticancer drugs--adriamycin, camptothecin, etoposide or vincristine--at sublethal concentrations for 24 h. MDR1, MRP1, LRP and PKC isozyme alpha, beta(1), beta(2), epsilon, iota, eta, theta, zeta gene expression was determined by cDNA-PCR. We found significant dose-dependent, mostly combined, induction of the MDR1, MRP1 and LRP genes. Significantly enhanced gene expression of the majority of PKC isozyme genes was found after treatment with camptothecin. PKCzeta was upregulated throughout by each anticancer drug applied in this setting. A series of selected CCRF-CEM-derived multidrug resistance (MDR) sublines also showed enhanced expression of the PKC isozymes compared to the parental cell line. MDR1 and PKCeta gene expression levels were correlated highly significantly. Blasts from two patients with ALL during the first week of monotherapy with steroids revealed combined induction of the MDR1, multidrug resistance-associated protein 1 (MRP1), lung cancer resistance-related protein (LRP) and most PKC isozymes, predominantly PKCzeta. Another patient with T-ALL, who failed to respond to four months of intensive chemotherapy, showed an enhanced MRP1 gene expression combined with markedly overexpression of PKCeta and PKCtheta. Furthermore, the camptothecin and etoposide-mediated induction of resistance factors in the CCRF-CEM cell line could be suppressed by staurosporine, a rather unspecific inhibitor of protein kinases. However, selective inhibitors of PKC isozymes (bisindolylmaleimide GO 6850, indolocarbazole GO 6976) produced no significant effects here. Therefore, the PKC isozymes eta, theta and zeta are of interest as potential targets to overcome drug resistance in ALL.

Significance of MDR1, MRP1, GSTpi and GSTmu mRNA expression in acute lymphoblastic leukemia in Indian patients

Using, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) in 167 patients of acute lymphoblastic leukemia (ALL) from India at different stages of the disease (presentation 125, remission 33, first relapse nine), MRP1 and GSTpi expression were significantly higher at relapse than presentation (P=0.03 and P=0.01, respectively) and remission (P=0.007 and P=0.003, respectively). MRP1, GSTpi and GSTmu were expressed simultaneously in several samples with significant association of expression levels (P=0.0001). Association with clinicopathological features included higher MDR1 expression with age >15 years (P=0.04) and higher MRP1, GSTpi, GSTmu expression with WBC counts >100x10(9)/l. In 71 patients (age <25 years), inability to achieve CR was associated with a significantly higher MDR1 mRNA expression (P=0.03) indicating a prognostic significance. However, relapse or shorter Event Free Survival was independent of mRNA expression levels of the four genes. In view of the increased mRNA expression of MRP1/GST at the time of relapse and an association with risk factors such as a high WBC count, further studies directed towards investigating the functional aspects of GSH/GST/MRP1 mediated drug transport are warranted.

Mutations in ras proto-oncogenes are associated with lower mdr1 gene expression in adult acute myeloid leukaemia

Mutations in ras genes have been found to be the most frequent genetic aberrations in adult myeloid leukaemia (AML). Some reports have shown an improved outcome of ras-mutated AML. In order to understand the biology of ras mutation in AML, we studied a cohort of patients treated in a prospective multicentre trial for ras mutational status and resistance gene expression. Blast samples from 162 adult patients with de novo or secondary AML were examined for resistance gene expression (mdr1, mrp1 and lrp) and ras mutations using reverse transcription-polymerase chain reaction and protein nucleic acid-competitive polymerase chain reaction strategies respectively. Ras mutations were confirmed using DNA sequencing. Ras mutations leading to an exchange of amino acids were found in 40 (25%) patients. Thirty AML patients had N-ras mutations and nine patients had K-ras mutations. One patient showed both N-ras and K-ras mutations. Resistance gene expression was positive for mdr1 in 30%, for mrp1 in 43% and for lrp in 62% of patients. There was a strong inverse correlation between the presence of ras mutation and mdr1 expression (P = 0.005). However, no significant difference was seen between patients with or without ras mutations and mrp1 or lrp expression. Whereas mdr1 expression was associated with a lower complete remission rate (P < 0.04), ras mutations had no significant influence on remission status. Neither ras mutation nor mdr1 expression had a significant impact on overall or disease-free survival to date. For the first time, there is evidence that activated ras genes are associated with lower mdr1 expression in AML.

Topoisomerase II alpha and II beta expression in childhood acute lymphoblastic leukaemia: relation to prognostic factors and clinical outcome

BACKGROUND/AIMS

Many regimens used in the treatment of childhood acute lymphoblastic leukaemia (ALL) include Daunorubicin or Etoposide, which act as topoisomerase poisons. It has been suggested that there may be a relation between topoisomerase expression and response to topoisomerase poisons, based mainly on results from in vitro studies. Therefore, the aim of this study was to investigate this relation in a clinical setting and determine whether topoisomerase II alpha and II beta might be of predictive value in ALL.

METHODS

Cellular expression of topoisomerases II alpha and II beta was assessed in 177 cases of ALL by immunohistochemistry using monoclonal antibodies to the two enzymes. The percentages of cell nuclei showing positive staining for topoisomerase II alpha and II beta expression were assessed.

RESULTS

Taking the series as a whole, a clear separation of survival curves was seen with the established prognostic markers white blood cell (WBC) count, CD10 status, and sex. However, topoisomerase II alpha and II beta expression showed no relation to survival. No association was found between the topoisomerases and the prognostic markers CD10 and WBC count; however, topoisomerase II alpha expression was found to be related to sex, with expression being lower in girls (p = 0.002).

CONCLUSIONS

These results suggest that the response to topoisomerase poisons cannot be predicted by the assessment of topoisomerase II alpha and II beta expression as defined by immunohistochemistry.

Neuroblastoma cells expressing the noradrenaline transporter are destroyed more selectively by 6-fluorodopamine than by 6-hydroxydopamine

6-Hydroxydopamine (6-OHDA) has been used for lesioning catecholaminergic neurons and attempted purging of neuroblastoma cells from hematopoietic stem cells in autologous bone marrow transplantation (ABMT). Neurotoxicity is mediated primarily by reactive oxygen species. In ABMT, 6-OHDA, as a purging agent, has been unsuccessful. At physiological pH it autooxidizes before targeted uptake, resulting in nonspecific cytotoxicity of nontarget cells. A catecholamine analogue, similar to 6-OHDA but with a lower rate of autooxidation enabling uptake by target cells, is thus required. Electron paramagnetic resonance spectra in this study show that 6-fluorodopamine (6-FDA) hydrolyzes slowly to 6-OHDA at physiological pH. Oxygen consumption, H(2)O(2), and quinone production are found to be intermediate between those of 6-OHDA and dopamine (DA). Relative neurotoxicity of these compounds was assessed by cell viability and DNA damage in the human neuroblastoma lines SH-SY5Y and SK-N-LO, which express and lack the noradrenaline transporter, respectively. Specific uptake of DA and 6-FDA by SH-SY5Y cells was demonstrated by competitive m-[(131)I]iodobenzylguanidine uptake inhibition. The competition by 6-OHDA was low owing to rapid autooxidation during incubation with equal toxicity toward both cell types. 6-FDA toxicity was preferential for SH-SY5Y cells and reduced in the presence of desipramine, a catecholamine uptake inhibitor. We demonstrate that 6-FDA cytotoxicity is more specific for cells expressing catecholamine reuptake systems than is 6-OHDA cytotoxicity.

Increased expression of lung resistance-related protein and multidrug resistance-associated protein messenger RNA in childhood acute lymphoblastic leukemia

Immunophenotype might be an important indicator for multidrug resistance (MDR) profiles in childhood acute lymphoblastic leukemia (ALL). The authors analyzed the messenger RNA (mRNA) levels of MDR1, multidrug resistance-associated protein (MRP), and lung resistance-related protein (LRP) by reverse transcriptase-polymerase chain reaction (RT-PCR) in childhood pre-B ALL, T-cell ALL, and acute nonlymphoblastic leukemia (ANLL). Results showed that MRP and LRP, but not MDR1, mRNAs are overexpressed, particularly in children with pre-B ALL compared with T-cell ALL and ANLL tested. In addition, the MRP and LRP mRNA expression levels in initial diagnosis and first relapse samples of one patient with pre-B ALL were similar. Consequently, these preliminary results suggest that the expression of these MDR-related genes in childhood ALL might be regulated differently in a lineage dependent manner.

MDR1/P-GP expression as a prognostic factor in acute leukemias

P-glycoprotein (P-gp) is often expressed (40-50%) on leukemic cells at diagnosis in acute myelogenous leukemia (AML), and is even more frequently present after treatment failure. Several large cohorts of newly diagnosed AML patients treated with a classical anthracycline + standard doses of cytosine arabinoside were tested for the prognosis value of MDR1 phenotype, and demonstrated an high correlation between a significant increase of MDR1 gene expression and treatment failure (or, better, drug resistance). This P-gp(+) drug resistance could be due either to a particular phenotype of bad prognosis AML, as it is suggested by the association of myelodysplasia, complex karyotype and advanced age with MDR1 phenotype, or due primarily to the active efflux of anthracyclines and VP16 in P-gp(+) leukemic cells. Several observations tend to confirm the functional role of the P-gp in clinical drug resistance; (i) using multivariate analysis, MDR1 phenotype appears to be an independent variable, as potent (or higher) as karyotype and age for predicting in vivo drug resistance; (ii) the prognostic value is limited to the CD34(+)/P-gp(+) phenotype, wich is linked to a functional P-gp; (iii) the in vitro sensitivity to anthracyclines and VP16 is highly correlated with P-gp expression. All these data argue for an early use of P-gp modifier agents in the treatment of AML. The role of the MDR1 gene in ALL resistance is controversial and marginal compared to the sensitivity of ALL blasts to glucocorticoids, and the frequency of MDR1 phenotype is low at diagnosis, and is increasing only after repetitive chemotherapies.

A critical risk-benefit assessment argues against the use of anthracyclines in induction regimens for newly diagnosed childhood acute lymphoblastic leukemia

Although anthracyclines are associated with significant cardiac toxicity and their benefit remains unclear, they are included in nearly all current protocols for the treatment of childhood acute lymphoblastic leukemia (ALL). Currently open trials from most major groups use anthracyclines in the induction phase for all high-risk patients and in the delayed intensification phase for all patients regardless of risk classification. Our review of published randomized studies reveals no benefit for the addition of anthracyclines to induction phase of childhood ALL regimens consisting of vincristine, prednisone, and L-asparaginase (VPL), with or without a delayed intensification phase. No randomized studies have evaluated the use of anthracyclines in the delayed intensification phase of therapy. Furthermore, studies of relapsed patients indicated no benefit for the addition anthracyclines to maintenance regimens. Recent evidence from preclinical studies suggests that a combination of VPL with an anti-CD19 immunotoxin is more effective than VPL plus anthracyclines combination. Accumulated evidence exists that anthracyclines are associated with late-onset cardiac morbidity in about 25% of childhood ALL and other cancer survivors, and about 5% develop overt heart failure, with some requiring cardiac transplantation. Anthracycline-induced cardiotoxicity in children has no safe dose threshold and all doses are likely to cause significant myocardial damage. New data suggests that a unique cardiac mitochondrial exogenous NADH dehydrogenase is responsible for the anthracycline-induced oxygen radicals damage to the heart, and that chelators currently evaluated may not prevent late-onset cardiotoxicity in children. In view of these findings we urge extreme caution in using anthracyclines as part of multimodality ALL treatment programs, and strongly recommend reevaluation of what should be considered the best induction regimen for high-risk childhood ALL.

Microsatellite instability and clonal heterogeneity of MDR1 messenger RNA expression in trimetrexate-resistant human leukemia MOLT-3 cells developed in thymidine

Various gene alterations are involved in the drug resistance of leukemia cells. To understand the mechanism that underlies the emergence of cells with such gene alterations in human leukemia, we performed clonal analysis of the gene expression of mutant dihydrofolate reductase (DHFR) and mdr1 in trimetrexate-resistant human leukemia MOLT-3 cells. Trimetrexate-resistant (70- and 60-fold) sublines were developed in the presence or absence of an exogenous supply of thymidine (MOLT-3/TMQ70/Th+, MOLT-3/TMQ60/Th-, respectively). Ten clonal lines were isolated by methyl cellulose cloning from each of the 2 trimetrexate-resistant MOLT-3 sublines. All the clonal lines from the 2 sublines expressed mutated DHFR mRNA, with a base change (T --> C) at the second position of codon 31, as well as the wild-type mRNA, in accordance with cross-resistance to methotrexate. On the other hand, mdr1 mRNA expression was demonstrated by reverse-transcription polymerase chain reaction only in clonal lines from MOLT-3/TMQ70/Th+ cells. mdr1 mRNA expression in clonal lines from MOLT-3/TMQ70/Th+ cells and subclonal lines subsequently obtained from the 3 clonal lines with different mdr1 mRNA expression levels was heterogeneous, and its high expression levels were correlated with acquisition of the multidrug resistance (MDR) phenotype. Polymerase chain reaction-based assay for separate microsatellites, mfd27 and mfd41, demonstrated genomic instability among clonal and subclonal lines of MOLT-3. The clonal analysis of polymorphic microsatellites also suggested that emergence of MDR in trimetrexate-resistant MOLT-3 cells in thymidine was not only heterogeneous but also progressively expanding among clones. Genomic instability may play a role in the establishment and clonal evolution of drug resistance in leukemia cells.

A new PCR MIMIC strategy to quantify low mdr1 mRNA levels in drug resistant cell lines and AML blast samples

Determination of the MDR-phenotype in patients suffering from AML is an important hallmark of treatment outcome but is often complicated by technical problems in P-gp assessment. A PCR-MIMIC strategy was employed to construct PCR-fragments for a competitive and quantitative mdr1 reverse transcription-PCR-assay. Using K562 cells, which had been selected for drug resistance to the epipodophyllotoxin VP16, a stepwise increase of mdr1 levels depending on the concentration of VP16 was shown with the MIMIC technique. Comparison of mdr1 levels in drug selected K562 cells with the corresponding levels for P-gp and functional data indicated a mRNA threshold that has to be exceeded for the full expression of the MDR-phenotype. Subsequently mdr1 levels of 34 samples of de novo acute myeloid leukemia were determined with the PCR-MIMIC strategy. Ten patient samples could be identified with elevated mdr1 levels which were substantially lower than the levels observed in the MDR-cell line K 562 0.7 microM VP16. Outcome analysis revealed that eight of the ten patients had an unfavourable prognosis and did not achieve CR after induction chemotherapy. Coexpression of mdr1 and CD 34 was not associated with CR in all examined cases. Moreover all these patients had unfavourable cytogenetic aberrations. These data indicate a sensitive technique with applicability in patient material.

Myeloid antigen co-expression in childhood acute lymphoblastic leukaemia: relationship with in vitro drug resistance

Contradictory data have been reported about the prognostic value of myeloid antigen co-expression (My+) in childhood acute lymphoblastic leukaemia (ALL). In the present study the methyl thiazol tetrazoliumbromide (MTT) assay was used to compare the in vitro cytotoxicity of 14 drugs between 60 My+ (CD13+ and/or CD33+) and 107 My- ALL children at initial diagnosis. P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), major vault protein/lung resistance protein (LRP) and the intracellular daunorubicin concentration were studied by flow cytometry. My+ ALL samples were significantly more resistant, i.e. between 1.1- and 2.9-fold, to daunorubicin, doxorubicin, idarubicin, mitoxantrone, vincristine, 6-thioguanine, 6-mercaptopurine, teniposide, etoposide and ifosfamide compared with My- ALL samples. My- and My+ ALL did not significantly differ in sensitivity to prednisolone, dexamethasone, L-asparaginase and cytarabine. Comparable results were found when only common and preB ALL cases were analysed. Drug resistance in My+ ALL was not related to increased expression of P-gp, MRP or LRP compared with My- ALL (ratio My+/My-:P-gp 0.8, MRP 1.0, LRP 1.1). Accumulation and retention of daunorubicin did not significantly differ between My- and My+ ALL cells (ratio My+/My-: accumulation 1.2, retention 1.3). Therefore the nature of drug resistance in My+ ALL remains unknown. The lack of prognostic value for My+ in childhood ALL may be explained by the responsiveness of My+ ALL to glucocorticoids, L-asparaginase and cytarabine. In addition, the currently intensive treatment regimens may apply drug doses which are simply high enough to overcome the mild resistance to anthracyclines, mitoxantrone, vincristine, thiopurines, epipodophyllotoxins and ifosfamide in childhood My+ ALL.

BIRICODAR (VX-710; Incel): an effective chemosensitizer in neuroblastoma

Clinical studies have suggested that both MDR1 and MRP may play a significant role in the chemosensitivity and outcome of neuroblastoma. To clarify the nature of multidrug resistance (MDR) in this tumour a series of six neuroblastoma cell lines have been characterized with regard to P-glycoprotein, MRP and LRP expression using immunocytochemistry and expression of MDR1, MRP, LRP and topoisomerase II genes using reverse transcription polymerase chain reaction (RT-PCR). By RT-PCR, all lines expressed MRP, five expressed LRP and four expressed MDR1, but protein levels of each of these were variable. Chemosensitization to a range of MDR-associated drugs (vincristine, doxorubicin, etoposide, taxotere, topotecan) and non-MDR-associated drugs (cisplatin, melphalan) by three modulating agents, cyclosporin A, PSC 833 and the novel Biricodar (VX-710; Incel), was evaluated using a colourimetric cytotoxicity assay (MTS). Alteration of daunorubicin efflux by these agents was evaluated using FACS analysis. Clonogenic assay was used to study the influence of these chemosensitizers on vincristine cytotoxicity. Marked sensitization to vincristine was observed in MDR1-positive lines, and a similar but less consistent effect was seen with taxotere, doxorubicin and etoposide. With MRP-positive, MDR-negative lines, only VX-710 caused consistent sensitization. These data confirm MDR1 and MRP expression as contributory factors in chemoresistance in neuroblastoma and indicate that VX-710 may be a useful modulator of both mechanisms and worthy of clinical evaluation in this tumour.

Functional analysis of P-glycoprotein and multidrug resistance associated protein related multidrug resistance in AML-blasts

Despite the high effectiveness of various P-glycoprotein (P-gp) modulating substances in vitro their clinical value e.g. for combination treatment of acute myelogenous leukemias (AML) remains still unclear. This might be explainable by recent findings that other factors than P-gp (e.g. the multidrug resistance associated protein (MRP)) may also be involved in clinical occurring drug resistance. To study P-gp and MRP mediated MDR in AML blasts from patients with relapses at the functional level we measured rhodamine 123 (RHO) efflux in combination with a P-gp specific (SDZ PSC 833) or a MRP specific (MK571) modulator, respectively. Furthermore, direct antineoplastic drug action was monitored by determination of damaged cell fraction of a blast population using flow cytometry. We generally found strongly modulated RHO efflux by SDZ PSC 833 but slight RHO-efflux modulation by MK571 in blasts from relapsed states of AML expressing MDR1 or MRP mRNA at various levels. We could not demonstrate, though, significant PSC 833 or MK571 mediated modulation of the cytotoxic effects of etoposide. The results point to the possibility that combination of etoposide and a modulator might not improve responses to chemotherapy by targeting P-gp or MRP exclusively.

Selectively induced high MRP gene expression in multidrug-resistant human HL60 leukemia cells

A subclone HL60/DOX was selected from a human leukemic HL60 cell line for resistance to doxorubicin (DOX) by exposure to stepwise increasing concentrations of the drug and coexposure to a potential P-glycoprotein (P-gp) inhibitor, cepharanthine (a biscoclaurine alkaloid). Compared with the parent HL60 cells, the HL60/DOX cells were 13.0-fold more resistant to DOX and showed multidrug-resistant (MDR) phenotype characterized by 4.6-fold, 2.3-fold, and 5.7-fold cross-resistance to vincristine, pirarubicin, and etoposide, respectively, but no cross-resistance to alkylating agent, cisplatin. Immunocytochemical analyses using the specific monoclonal antibody, MRPr1, and quantitative analyses using a competitive reverse transcription-polymerase chain reaction (CRT-PCR) confirmed overexpression of MRP gene products (about 8-fold determined by CRT-PCR) in this resistant clone. The P-gp expression was not detectable by the monoclonal antibody, C219, in the HL60/DOX cells, and that was consistent with extremely low levels of mdr1 mRNA expression determined by CRT-PCR in this clone. Drug accumulation and efflux studies demonstrated the significantly increased efflux rate of DOX compared to the parent HL60 cells. This enhancement of DOX efflux was reversed by the addition of 10 microM verapamil. To investigate the additional underlying mechanisms contributing to MDR phenotype in the HL60/DOX cells, the levels of DNA topoisomerases (Topo) including Topo I, Topo IIalpha, and Topo IIbeta, and gamma-glutamylcystein synthetase (y-GCS) expression were determined using CRT-PCR techniques. Normal expression of each enzyme at the transcriptional level was demonstrated in this resistant clone. Southern blot analysis of the gene organization in the HL60/DOX cells revealed the amplification of MRP gene. These results indicate that alteration of the drug accumulation from enhanced efflux appears to be a major mechanism(s) of MDR phenotype and attributable to high levels of MRP expression in the HL60/DOX cells. Overexpression of MRP in this clone is regulated by the genomic amplification of DNA and increased levels of the MRP mRNA, independently with the normal expression of Topo I, Topo IIalpha, Topo IIbeta, or gamma-GCS.

Using the national cancer institute anticancer drug screen to assess the effect of MRP expression on drug sensitivity profiles

The MRP gene contributes to one form of multidrug resistance. To identify drugs interacting with MRP, we measured MRP mRNA expression by quantitative PCR in 60 cell lines of the National Cancer Institute Anticancer Drug Screen. Expression was detected in all cell lines (highest in lung carcinomas and central nervous system tumors) with a range of 14-fold. A mean graph of MRP mRNA levels was constructed to determine Pearson correlation coefficients (PCCs) with mean graphs of >40,000 compounds using the COMPARE analysis. Only 20 compounds had PCCs of >/=0.500. The PCCs for VP-16, doxorubicin, and vincristine were 0.008, 0.13, and 0.257, respectively. Initially, 36 compounds with PCCs of >/=0.428 were analyzed using two MRP-overexpressing cell lines; low levels of cross-resistance was demonstrated for 23 compounds (1.3-9.4-fold). Twenty-four compounds also were available for further studies. Using a fluorescence activated cell sorter assay to measure competition of calcein efflux from MRP-overexpressing cells, 10 compounds were found to increase calcein retention by >/=2-fold. Ten compounds also were able to reduce ATP-dependent [3H]LTC4 transport into vesicles from MRP-overexpressing cells. These results contrast with previous studies with MDR-1 in which high correlations were found and confirmed for a large number of compounds. Although other assays may be more revealing, in these unselected cell lines, MRP mRNA expression was a poor predictor of drug sensitivity. This raises the possibility that other factors, including conjugating enzymes, glutathione levels, or other transporters, confound the MRP effect.

In vitro and in vivo reversal of cancer cell multidrug resistance by the semi-synthetic antibiotic tiamulin

A large number of multidrug resistance (MDR) modulators, termed chemosensitizers, have been identified from a variety of chemicals, but most have been proven to be clinically toxic. Low concentrations of the pleuromutilin-derived semi-synthetic antibiotic tiamulin (0.1 to 10 microM) sensitized the three highly resistant P-glycoprotein (Pgp)-overexpressing tumor cell lines P388 (murine lymphoid leukemia), AS30-D (rat hepatoma), CEM (human lymphoblastic leukemia), and the barely resistant AS30-D/S cell lines to several MDR-related anticancer drugs. Flow cytometric analysis showed that tiamulin significantly increased the intracellular accumulation of daunomycin. When compared to reference modulating agents such as verapamil and cyclosporin A, tiamulin proved to be 1.1 to 8.3 times more efficient in sensitizing the resistant cell lines. Moreover, when given i.p. (1.6 microg/mg body weight), tiamulin increased the survival rate of adriamycin-treated mice bearing the P388/ADR25 tumor line by 29%. In the presence of an anticancer drug, tiamulin inhibited both ATPase and drug transport activities of Pgp in plasma membranes from tumor cells. Tiamulin is thus a potent chemosensitizer that antagonizes the Pgp-mediated chemoresistance in many tumor cell lines expressing the MDR phenotype at different levels and displays no toxic effects on contractile tissues at active doses, therefore providing the promise for potential clinical applications.

Physiological regulation of eukaryotic topoisomerase II

Topoisomerase II is an essential enzyme in all organisms with several independent roles in DNA metabolism. In this article we review our knowledge on the regulation of the expression and catalytic activity of topoisomerase II in both lower and higher eukaryotes. Current data indicate that the regulation of topoisomerase II gene expression is complex, with positive and negative controls in evidence at the level of both promoter activity and mRNA stability. Similarly, the activity of the mature enzyme can be regulated by the action of several different protein kinases. Of particular interest is the cell cycle-dependent phosphorylation of topoisomerase II, including multiple, mitosis-specific modifications, which are proposed to regulate the essential chromosome decatenation activity of the enzyme.

Rhodamine 123 efflux modulation in the presence of low or high serum from CD56+ hematopoietic cells or CD34+ leukemic blasts by B9309-068, a newly designed pyridine derivative

The newly designed pyridine derivative B9309-068 and a series of structurally different compounds were tested for their ability to modulate rhodamine 123 (RHO) efflux from CD56+ hematopoietic cells in the presence of either 10% fetal calf serum or undiluted human AB serum. Furthermore, efflux modulation was investigated on CD34+ blast populations obtained from four patients with relapsed state AML. Target cells were specified throughout by labeling with peridinine chlorophyll protein (PerCP)-conjugated monoclonal antibodies, allowing clear differentiation from RHO emission spectrum by flow cytometry. In the presence of low serum each compound efficiently modulated RHO efflux without significant differences in the range of final concentrations (1.0-3.0 microM). At 0.1 microM, however, RHO efflux was differentially modulated following the series GF120918 approximately B9309-068 > PSC 833 > DNIG approximately DVER. With CD56+ cells in the presence of undiluted human AB serum at a final modulator concentration of 0.1 microM, all chemosensitizers tested were found to be inefficient. At final concentrations of 0.3 microM or higher, distinct RHO efflux modulation was found with the following efficacies: B9309-068 approximately GF120918 > PSC 833 >> DVER approximately DNIG. The efficacies seen in undiluted human AB serum at 3.0 microM were comparable to those seen on CD56+ cells at final modulator concentrations of 0.1 microM in low serum. Our results identify the pyridine derivative B9309-068 as a promising compound for modulating P-glycoprotein-mediated drug resistance under conditions resembling the clinical setting. Nonetheless, modulation potencies of a series of structurally very different chemosensitizers was revealed to be substantially diminished at high serum concentrations in vitro.

Topoisomerase II and the response to antileukemic therapy

A number of recent studies have investigated the expression of topoisomerase II in clinical leukemia specimens. Here we outline the rationale for these studies, identify potential pitfalls, summarize recent results, and discuss unanswered questions in this area.