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© 2000 American Society for Clinical Oncology Mitoxantrone, Etoposide, and Cyclosporine Therapy in Pediatric Patients With Recurrent or Refractory Acute Myeloid LeukemiaFrom the Divisions of Pediatric Oncology, Medical Oncology, and Clinical Pharmacology, Stanford University School of Medicine, Palo Alto, and Children’s Cancer Group, Arcadia, CA, and Pediatric Oncology Group, Chicago, IL. Address reprint requests to Gary V. Dahl, MD, Department of Pediatrics, Division of Hematology, Oncology, 300 Pasteur Dr, Room G313, Stanford, CA 94305-5208; email Gary.Dahl{at}leland.stanford.edu
PURPOSE: To determine the remission rate and toxicity of mitoxantrone, etoposide, and cyclosporine (MEC) therapy, multidrug resistance-1 (MDR1) status, and steady-state cyclosporine (CSA) levels in children with relapsed and/or refractory acute myeloid leukemia. PATIENTS AND METHODS: MEC therapy consisted of mitoxantrone 6 mg/m2/d for 5 days, etoposide 60 mg/m2/d for 5 days, and CSA 10 mg/kg for 2 hours followed by 30 mg/kg/d as a continuous infusion for 98 hours. Because of pharmacokinetic interactions, drug doses were decreased to 60% of those found to be effective without coadministration of CSA. MDR1 expression was evaluated by reverse transcriptase polymerase chain reaction, flow cytometry, and the ability of CSA at 2.5 µmol/L to increase intracellular accumulation of 3H-daunomycin in blasts from bone marrow specimens. RESULTS: The remission rate was 35% (n = 23 of 66). Overall, 35% of patients (n = 23) achieved complete remission (CR), 12% of patients (n = 8) achieved partial remission, and 9% of patients (n = 6) died of infection. Exposure to CSA levels of greater than 2,400 ng/mL was achieved in 95% of patients (n = 56 of 59). Toxicities included infection, cardiotoxicity, myelosuppression, stomatitis, and reversible increases in serum creatinine and bilirubin. In most who had relapsed while receiving therapy or whose induction therapy had failed, response was not significantly different for MDR1-positive and MDR1-negative patients. CONCLUSION: Serum levels of CSA capable of reversing multidrug resistance are achievable in children with acceptable toxicity. The CR rate of 35% achieved in this study is comparable to previously reported results using standard doses of mitoxantrone and etoposide. The use of CSA may have improved the response rate for the MDR1-positive patients so that it was not different from that for the MDR1-negative patients.
WITH CURRENT chemotherapy regimens, approximately 75% to 85% of newly diagnosed children with acute myeloid leukemia (AML) will achieve complete remission (CR).1 Further consolidation/maintenance chemotherapy results in 5-year event-free survival (EFS) of 35% to 60%.2-6 The major reason for treatment failure is leukemic relapse, which is most likely to occur within the first 2 years after diagnosis. Only 30% to 50% of patients who relapse will achieve a second remission with chemotherapy, and these remissions are not durable. The likelihood of achieving a second remission is directly proportional to the length of the first remission.7 The lack of response to chemotherapy suggests the development of acquired drug resistance. Drug resistance may be present at the time of diagnosis or it may arise by somatic mutations during tumor growth. Numerous reports implicate the increased expression of the multidrug resistance-1 (MDR1)–encoded P-glycoprotein (P-gp) multidrug transporter as one cause of both intrinsic and acquired drug resistance.8-10 P-gp is a transmembrane ATP-dependent efflux pump that has broad substrate specificity. Increased amounts of P-gp confer multidrug resistance (MDR) in cells by reducing intracellular accumulation of a variety of cytotoxic drugs. Several key drugs used in the therapy of AML are transported by P-gp. These include anthracyclines and anthracenediones (daunorubicin and mitoxantrone, respectively), the vinca alkaloids (vincristine and vinblastine), and the epipodophyllotoxins (etoposide and teniposide). Several noncytotoxic drugs, such as verapamil and phenothiazines, have been shown to modulate MDR, at least in part by competitive inhibition of P-gp–mediated drug efflux.11 Verapamil and phenothiazines modulate MDR and P-gp at drug concentrations that produce unacceptable clinical toxicities (heart block and depression of the CNS). Cyclosporine (CSA) has also been shown to be a potent inhibitor of P-gp drug efflux in vitro. CSA concentrations of 1,000 to 2,000 ng/mL, which reverse P-gp in vitro, are readily achievable with short-term intravenous administration in adults patients with acceptable toxicities.12 Several studies in patients with AML have shown that P-gp overexpression is relatively frequent, especially in refractory and relapsed leukemia.8-10 In several adult AML studies, CR rates were significantly lower in AML patients with overexpression of MDR1/P-gp, but the overall prognostic significance of P-gp expression on outcome remains controversial. Interpretation of the clinical data has been hampered by lack of well-defined criteria for detecting a level of P-gp expression considered positive and inadequate standardization of drug efflux assays.13 Two recent reports of phase II trials using cyclosporines as MDR modulators in adult AML patients have shown improved remission rates in high-risk patients.14,15 We present the results of the largest pediatric study of an MDR reversal agent, and the first in childhood AML. The goals of this phase II study were (a) to determine the remission rate and toxicity of mitoxantrone, etoposide, and CSA (MEC) in children with refractory or relapsed AML, (b) to document steady-state CSA levels of greater than 2,400 ng/mL, (c) to determine MDR1 mRNA and P-gp expression in leukemic blasts, and (d) to perform functional P-gp assays with and without CSA. A phase III AML study—Pediatric Oncology Group (POG) 9421—with etoposide and mitoxantrone with/without CSA during the consolidation phase has just been completed.
Between April 1992 and June 1994, a total of 68 pediatric patients with AML were entered onto the MEC protocol, a POG phase II multicenter trial (POG 9222). These children had received unsucessful induction therapy with initial therapy or had relapsed during therapy or after one or more CRs. Forty-nine of the 66 assessable patients were initially treated on or as per POG 8821.16 In this study, patients received induction therapy with daunorubicin, cytarabine (Ara-C), and thioguanine, followed by a second induction with high-dose Ara-C (total anthracyclines, 135 mg/m2). Patients who entered remission were eligible for randomization. After randomization, an additional course of etoposide and azacytidine with intrathecal Ara-C was given, followed by either intensive chemotherapy (cumulative anthracyclines, 360 mg/m2), autologous transplantation, or allogeneic transplantation. Eight patients were treated according to POG pilot study 9194 (three cycles with daunorubicin, high-dose Ara-C, and thioguanine; etoposide and high-dose Ara-C; and high-dose Ara-C and daunorubicin [cumulative anthracyclines, 225 mg/m2]). The remaining patients were treated on various anthracycline-containing induction regimens. Relapse or induction failure was documented by bone marrow aspirate and biopsy in all patients. The characteristics of this patient population are listed in Table 1. In 68% of the assessable patients, either induction therapy failed or the patient relapsed while on therapy; the remainder had first remission duration of less than 1 year.
The diagnosis of AML was made on bone marrow smears routinely stained and evaluated according to the revised French-American-British (FAB) criteria.17 All patients had normal cardiac, renal, liver, and pulmonary function, and all but two had received less than 500 mg/m2 of prior daunorubicin therapy. The median prior daunorubicin dose was 265 mg/m2 (range, 72 to 500 mg/m2), and four patients had received additional cardiotoxic therapy (amsacrine in three and idarubicin in one). This study was approved by the institutional review boards of each participating POG institution, and the patient and/or parent or guardian was required to sign an approved consent form.
Criteria for Response
Cardiac Monitoring
Induction Therapy A bone marrow aspirate and biopsy samples were obtained 10 to 14 days from the start of the 5-day MEC course. If the aspirate had more than 25% blasts, patients were removed from study regardless of the cellularity. If patients had fewer than 25% blasts and cellularity of less than 25%, they were immediately given a second 5-day MEC course. If fewer than 5% blasts were noted and the biopsy was hypocellular (5% to 20%), a second course was delayed until the counts recovered. Patients who recovered with greater than 25% blasts before the second course were removed from the study. If there was residual leukemia after two courses, the patient was taken off the study. Patients who achieved a CR with one or two courses could receive two or one subsequent course(s), respectively, for consolidation. No more than three courses of MEC were given to any patient.
MDR1 Expression Fresh bone marrow samples were layered over Ficoll-Hypaque cushions and centrifuged at 600 x g for 15 minutes to separate mononuclear cells, which were then washed in cold phosphate-buffered saline containing 2% fetal bovine serum. These cells were then used for staining with 4E3, other hematopoietic markers (including CD34, CD13, CD15, CD33, CD14, CD2, CD19, and CD10), or isotype controls. 4E3 or MRK16 was detected using secondary phycoerythrin-conjugated goat-antimouse immunoglobulin (Fab)2 fragment (Tago, Burlingame, CA) at a 1/30 dilution. All other MoAbs were directly conjugated to fluorescein (Becton Dickinson or AMAC, Inc, Miami, FL). 4E3 staining of gated leukemic blasts was compared with isotype control as well as control cells expressing different levels of MDR1 P-gp (CEM, CEM/VBL-100, and CEM/VBL-300).18
Quantitation was accomplished initially by comparing mean fluorescence intensities or using the Kolmogorov-Smirnov statistic, referred to as D, which measures the difference between the means of two distributions.13,20-22 The ratio of the mean fluorescence intensity for 4E3 expression compared with the value using an isotype control antibody was then calculated. This ratio never exceeded 1.2 for the drug-sensitive (P-gp–negative) cell line, CEM. AML blasts were therefore considered positive if they had a shift of RT-PCR analysis of MDR1 expression. The level of MDR1 RNA was determined in bone marrow samples by RT-PCR using MDR1 and beta-2-microglobulin specific oligonucleotide primers as described by Noonan et al.24 Total RNA (100 ng) was used to make cDNA followed by amplification in a 4800 Thermocyler (Perkin Elmer, Norwalk, CT) set for a 30-second denaturation at 94°C, 1 minute of primer annealing at 55°C, and 2 minutes of extension/synthesis at 72°C. Primers used for amplification of MDR1 RNA were from nucleotides 2596 to 2615 for the sense direction and nucleotides 2733 to 2752 for the antisense direction, yielding a 167-nucleotide product. Primers used for amplification of ß2-microglobulin were from nucleotides 1544 to 1563 for the sense and from nucleotides 2253 to 2263 for the antisense direction. This combination yielded a 120-nucleotide product. PCR products were electrophoretically separated in a 3% agarose gel and the specific PCR amplicons were excised after ethidium bromide staining. The amount of radioactivity incorporated into each amplicon was then determined by liquid scintillation counting. Analyses were done after 25 and 35 cycles of amplification. A sample was considered positive for MDR expression if a band was visibly present after ethidium bromide staining and/or the MDR1 to ß2-microglobulin ratio of incorporated radioactive counts was greater than 0.7 (based on comparison with the drug-sensitive [P-gp–negative] CEM cell line, which had a ratio of less than 0.7 under the RT-PCR conditions used). The range of values varied from 0.8 to 1.8, with an average of 1.2 and a median of 1.1.
Cytotoxic Drug Accumulation Studies The intracellular accumulation of cytotoxic agents was determined in the absence and presence of P-gp inhibitors verapamil and CSA, as previously described.18,27-30 3H-Daunomycin (specific activity, ~1 to 5 Ci/mmol; Dupont, Wilmington, DE) and 3H-vinblastine (specific activity, ~5 to 25 Ci/mmol; Amersham International, Les Uris, France) were used in these studies. Isolated bone marrow mononuclear cells were resuspended at 1 x 106 cells/mL of RPMI medium containing 10% fetal bovine serum. Aliquots of 0.25 mL were then dispensed into 75-mm round-bottom plastic tubes and MDR reversal agents were added to a final concentration of 2.5 µmol/L. After a 30-minute incubation with gentle agitation at 37°C, tritiated cytotoxic drug was added to a final concentration of 8 nmol/L in the presence of the same but unlabeled drug at a final concentration of 10 µmol/L. After a 2-hour incubation, the entire contents of each tube were overlaid on a 200-µL cushion of Dow 550 silicone oil (Dow Corning, Midland, MI) and mineral oil (4:1) in a 1.5-mL Eppendorf tube and centrifuged at 10,000 x g at 4°C for 1 minute to separate the cells from drug-containing medium. The medium and oil mixture was removed by aspiration, and the cellular pellets were solubilized in 1 mL of 1 M NaOH at 60°C overnight before the amount of radioactivity accumulated in the cells was determined by liquid scintillation counting. The "fold increase" of radiolabeled drug accumulation was calculated as follows: The ratio of the drug accumulation as described earlier without a reversal agent compared to with a reversal agent was calculated. Along with each patient sample, drug accumulation for the drug-sensitive cell line, CEM, and the drug-resistant derivative, CEM/VBL 300, was simultaneously determined. The values for each patient’s drug accumulation ratio and for CEM cells were normalized by dividing by the ratio for CEM/VBL 300 cells. Last, a fold increase for the patient sample compared with CEM cells was determined. Values reported are the average of at least three determinations. A fold increase value of greater than 1.2 was considered positive, as this was the upper level observed using the drug-sensitive cell line, CEM.18,30 The range of values for patient samples greater than 1.2 varied from 1.23 to 6.59, with a median of 1.56.
Statistical Analysis Kendall’s tau-b32 was used to evaluate the correlation between the various measurements associated with the MDR1 status. The estimator of Kendall’s tau-b is based on the fraction of concordant versus discordant pairs of observations on two variables. A value of the estimator close to -1, +1, or 0 indicates strongly negative, strongly positive, or no correlation, respectively, between the variables.
Patient Characteristics Sixty-eight patients (age range, 1.4 months to 20 years) were entered onto the study and 66 were assessable for response and toxicity (Table 1). No patient was considered ineligible for entry onto the study, but two patients were administered nonprotocol cytotoxic therapy and therefore were considered nonassessable. The distribution of FAB subtypes was consistent with previously published experience.33 There were two cases of treatment-related secondary AML (tAML). The "other" category includes one patient with refractory anemia with excess blasts developing after a 3-month remission of AML and seven AML cases not given a FAB designation.
Response Marrow samples were received for determination of MDR1 status in 59 (90%) of 66 patients. Table 2 lists the disease status and response of patients with AML according to their MDR1 status as defined in the Materials and Methods. Fifty-five patients were tested by flow cytometry for the presence of 4E3 staining; 14 (25%) were positive and 41 (75%) were negative. Of these patients, CR was achieved by four (29%) of the 4E3-positive and by 14 (34%) of 4E3-negative patients. Fifty patients were tested for MDR1 status by RT-PCR. Ten (20%) were positive and 40 (80%) were negative. Of these patients, CR was achieved in four (40%) of the PCR-positive patients and 13 (33%) of the PCR-negative patients. Fifty-two patients were tested for MDR1 reversal by CSA in vitro. Twenty (38%) exhibited reversal and 32 (62%) did not. Of these patients, CR was achieved in nine (45%) with positive reversal by CSA and in nine (28%) with negative reversal by CSA in blast cells. In samples from 48 patients, results of all three MDR1/P-gp detection methods outlined earlier were available. When MDR1/P-gp positivity was defined as either 4E3+, PCR+, +CSA reversal, or any combination thereof, there were 27 (56%) positive and 21 (44%) negative samples. Of these patients, CR was achieved in 10 (37%) of MDR1/P-gp–positive patients and in seven (33%) of MDR1/P-gp–negative patients.
Only five patients were positive for MDR1 expression by all three methods, and 21 were negative for MDR1 by all three methods. The response (CR + PR) rates were 60% (three of five patients) and 38% (eight of 21 patients) for these two groups of patients. The difference was insignificant (two-sided P = .62 by Fisher’s exact test). The Mantel-Haenszel test shows that after adjustment for prior relapse status the CR rate in MDR1/P-gp–negative patients was not higher than that in MDR1/P-gp–positive patients when MDR1/P-gp positivity is defined as +4E3, +RT-PCR, +CSA reversal, or the presence of at least one of the above (one-sided P values were .30, .55, .86, and .39, respectively). In addition, the variables of age, sex, and FAB group were not significantly correlated with CR in univariate analysis. The two-sample binomial test shows that the remission rate (13 of 21 patients, 62%) in patients with off-therapy relapse was higher than the CR rate (10 of 45 patients, 22%) in patients with on-therapy relapse or induction failure (one-sided P = .0006).
Correlation Among 4E3 Staining, RT-PCR, and Cytotoxic Drug Accumulation With or Without CSA
CSA Blood Levels
Toxicity
Cardiotoxicity, manifested by decreased ejection fraction or shortening fraction, was noted in 15 (23%) of the patients after induction therapy. In 12 (80%) of these patients, cardiotoxic events were transient, were due to multifactorial clinical problems, and resolved without specific therapy. Three children developed congestive heart failure that required therapy with digitalis. For the 55 patients with available data, the median total bilirubin level during CSA infusion was 2.2 mg/100 mL (range, 0.6 to 9.7 mg/100 mL). The mostly direct hyperbilirubinemia was rapidly reversible once the CSA infusion was discontinued and was not accompanied by any other evidence of additional hepatic dysfunction. There was no relationship between the level of bilirubin, response rate, CSA level achieved, or MDR1/P-gp status.
The major objective of this protocol was to determine whether the MDR1/P-gp reversal agent CSA could be safely tolerated and produce significant response rates in pediatric patients when given in high doses with an active reinduction regimen of mitoxantrone and etoposide. In this study, high-dose CSA was administered continuously in a group-wide setting and found to be generally safe with acceptable toxicity. Grades 3 to 4 cardiac toxicity, likely related to chemotherapy, occurred in three patients (4.5%), who developed congestive heart failure and required treatment with digitalis. Although hyperbilirubinemia was common and directly related to CSA administration, it quickly normalized when the infusion was discontinued. In addition, the combination of CSA, mitoxantrone, and etoposide was determined to be an active induction regimen for children with relapsed and refractory AML, even though the doses of mitoxantrone and etoposide given during induction were decreased to 60% of those found to be effective without coadministration of CSA. Dose modifications were necessary because high-dose CSA produces significant increases in etoposide and mitoxantrone systemic exposure and resultant leukopenia and mucositis. Our group has performed pharmacokinetic analysis of patients receiving etoposide and mitoxantrone with and without CSA in an ongoing phase III trial.34 CSA produced significant increases in the area under the curve for etoposide and mitoxantrone, thus confirming the need for the dose adjustments used in this study and in our ongoing phase III trial. The CR rate of 35% achieved in this study is comparable to other results reported with mitoxantrone/etoposide.35 As in other studies, the likelihood of achieving a CR was higher in patients who relapsed off therapy, compared with those who relapsed on therapy or did not go into remission (62% v 15% and 33%, respectively). Approximately 50% of patients achieved a CR or PR with this MEC regimen, which allowed most to go on to bone marrow transplant. A second aim of this study was to determine the P-gp status of blasts in refractory childhood AML by several methods, including MDR1 mRNA, P-gp expression, and drug efflux studies. The methodology used to assess P-gp expression has evolved over the last several years. Early studies reported the level of MDR1 transcripts by RT-PCR or RNAse protection assays. Later, protein detection by immunoblotting and immunohistochemistry was introduced. More recently, functional assays have been developed. Despite these advances, it is difficult to assess the role that P-gp plays in clinical drug resistance due to tumor cell heterogeneity, sensitivity, and specificity of methods of detection. The best approach, as recommended by the international workshop on MDR1 detection methods, is to use tissue-specific controls, antibody controls, standardized MDR1 cell lines to calibrate detection methods, and two or more vendor-standardized anti–P-gp antibodies, and to report immunostaining data as staining intensity and the percentage of positive cells.11 Although this study was completed before these consensus recommendations, many of these guidelines were followed. The RT-PCR data were complemented with immunostaining and drug accumulation studies with and without modulators. Standardized cell lines with low expression of MDR1/P-gp were used as a reference for clinical samples. Flow cytometric assessment of P-gp had an adequate correlation with both RT-PCR and CSA enhancement of drug accumulation. Although adequate, the level of correlation highlights the need for protein and functional assays as necessary tools in evaluating the MDR1 status in clinical samples and in validating the analysis of MDR1 modulation trials. Limited data are available on the expression of MDR1/P-gp in marrow or blood samples from pediatric patients with AML. This series includes the largest sample of relapsed or refractory pediatric AML samples analyzed for MDR1/P-gp expression and function. There is one published report of MDR1/P-gp expression in pediatric patients with de novo AML.36 In this study, samples from 130 patients were evaluated, and 30% of infants and 8% of children older than 1 year expressed MDR1/P-gp at diagnosis. This study was limited to the use of the MRK-16 antibody with a fluorescein isothiocyanate–conjugated second-step reagent. MDR1/P-gp positivity did not have an effect on induction failure, incidence of relapse, EFS, or overall survival in this group of patients. The method of analysis was substandard because it relied on a single technique to study MDR1/P-gp status. If the data from this Children’s Cancer Group study are corroborated, then our group of relapsed and/or refractory pediatric AML patients shows an increased expression of MDR1/P-gp, similar to what is seen when comparing de novo and relapsed AML in adult patients. Although the response rate for MDR1/P-gp-negative patients is not significantly higher than that for MDR1/P-gp–positive patients, it is interesting to note that the patients relapsing off therapy before entry onto this regimen were more likely to achieve remission and more likely to be MDR1/P-gp positive. MDR1/P-gp status as a predictor of response to induction may be important for patients for whom induction therapy fails or for patients who relapse on therapy, but it may have little prognostic importance in those with late relapses. It is interesting to note that the prognostic importance of MDR1/P-gp expression and function was not seen in this relatively large group of patients treated with an MDR1/P-gp modulator during induction. It may be that the modulator improved the response rate for the MDR1/P-gp–positive patients so that it was not different from that of the MDR1/P-gp–negative patients. However, the contribution of dose-intensity to this outcome needs to be considered. It is impossible to determine the prognostic importance of MDR1/P-gp status and response to this therapy because of variations in treatment history and drug exposure before admission to this protocol. The induction failure and on- and off-therapy relapse groups were not balanced for MDR1/P-gp expression. The second largest subgroup of patients consisted of those who relapsed off therapy. These patients were more likely to be MDR1/P-gp–positive and historically have a higher chance of achieving remission. To determine the prognostic importance of MDR1/P-gp status and reinduction rate, a randomized trial, in which the target plasma concentration of the chemotherapeutic agents is matched in the group given the reversal agent and the control, is needed. In summary, the results of this study indicate that levels of CSA capable of reversing MDR1/P-gp in vitro are achievable in children with acceptable toxicity. Mucositis and hyperbilirubinemia were found to be major treatment-related toxicities in this population. Remissions were seen in heavily pretreated patients and in children who had failed to achieve an initial remission. The remission rate in MDR1/P-gp–negative patients was not significantly greater than that in MDR1/P-gp–positive patients. The correlation among 4E3 staining, RT-PCR, and CSA inhibition of drug efflux was adequate. Our methods of analysis using several diagnostic tools to determine the MDR1 status illustrate the pitfall of relying on a single method to diagnose the MDR1/P-gp status. Future studies will require the use of new flow cytometric analysis reagents and strict guidelines regarding clinical sample collection, preservation, and amount of sample to perform state-of-the-art analyses. In the laboratory setting it has been shown that the use of MDR1/P-gp modulators during cytotoxic therapy can abolish the selection of MDR1-mediated drug resistance in cancer cell lines.37 Thus a possible benefit of introducing MDR1/P-gp modulators in the therapy of patients with de novo AML may be a decrease in acquired drug resistance based on MDR1/P-gp overexpression. To follow up this study and to study further the incidence of P-gp positivity and the effect of P-gp reversal with CSA on outcome in de novo childhood AML, a randomized phase III study (POG 9421) was recently completed at POG institutions. When they become available, results from this study may help to determine the prognostic significance of MDR1/P-gp expression and the effect of modulation by CSA in children with AML.
Supported by the Career Development Award from the American Society of Clinical Oncology, Alexandria, VA, and by grants no. R01 CA 52168 and M01 RR 00070 from the National Institutes of Health, Bethesda, MD (to General Clinical Research Center, Stanford University School of Medicine).
1. Ebb DH, Weinstein HJ: Diagnosis and treatment of childhood acute myelogenous leukemia. Pediatr Clin North Am 44:847-862, 1997[Medline]
2.
Creutzig U, Ritter J, Schellong G: Identification of two risk groups in childhood acute myelogenous leukemia after therapy intensification in study AML-BFM-83 as compared with study AML-BFM-78. Blood 75:1932-1940, 1990 3. Ravindranath Y, Steuber CP, Krischer J, et al: High-dose cytarabine for intensification of early therapy of childhood acute myeloid leukemia: A Pediatric Oncology Group study. J Clin Oncol 9:572-580, 1991[Abstract]
4.
Wells RJ, Woods W, Lamphin B, et al: Impact of high-dose cytarabine and asparaginase intensification on childhood acute myeloid leukemia: A report from the Children’s Cancer Group. J Clin Oncol 11:538-545, 1993
5.
Hann IM, Stevens RF, Goldstone AH, et al: Randomized comparison of DAT versus ADE as induction chemotherapy in children and younger adults with acute myeloid leukemia: Results of the Medical Research Council’s 10th AML trial (MRC AML10). Adult and Childhood Leukaemia Working Parties of the Medical Research Council. Blood 89:2311-2318, 1997
6.
Woods WG, Kobrinsky N, Buckley JD, et al: Timed-sequential induction therapy improves postremission outcome in acute myeloid leukemia: A report from the Children’s Cancer Group. Blood 87:4979-4989, 1996 7. Stahnke K, Boos J, Bender-Gotze C, et al: Duration of first remission predicts remission rates and long-term survival in children with relapsed acute myelogenous leukemia. Leukemia 12:1534-1538, 1998[Medline]
8.
Marie JP, Zittoun R, Sikic BI: Multidrug resistance (MDR1) gene expression in adult acute leukemia: Correlation with treatment outcome and in vitro drug sensitivity. Blood 78:586-592, 1991
9.
Pirker R, Wallner J, Geissler K, et al: MDR 1 gene expression and treatment outcome in acute myeloid leukemia. Cancer Inst 83:708-712, 1991 10. Willman CL: Immunophenotyping and cytogenetics in older adults with acute myeloid leukemia: Significance of expression of the multidrug resistance gene-1 (MDR 1). Leukemia 1:S33-S35, 1996 (suppl) 11. Litman T, Zeuthern T, Skovsgaard T, et al: Competitive, non-competitive and cooperative interactions between substrates of P-glycoprotein as measured by its ATPase activity. Biochim Biophys Acta 1361:169-176, 1997[Medline] 12. Fisher GA, Sikic BI: Clinical studies with modulators of multidrug resistance. Oncol Clin North Am 9:363-382, 1995
13.
Beck WT, Grogan TM, Willman CL, et al: Methods to detect P-glycoprotein-associated multidrug resistance in patients’ tumors: Consensus recommendations. Cancer Res 56:3010-3020, 1996 14. List AF, Kopecky KJ, Willman CL, et al: Benefit of cyclosporine (CsA) modulation of anthracycline resistance in high-risk AML: A Southwest Oncology Group (SWOG) study. Blood 92:1998 (suppl 1, abstr 1281)
15.
Advani R, Saba HI, Tallman MS, et al: Treatment of refractory and relapsed acute myelogenous leukemia with combination chemotherapy plus the multidrug resistance modulator PSC 833 (Valspodar). Blood 93:787-795, 1999
16.
Ravindranath Y, Yeager AM, Chang MN, et al: Autologous bone marrow transplantation versus intensive consolidation chemotherapy for acute myeloid leukemia in childhood: Pediatric Oncology Group. N Engl J Med 334:1428-1434, 1996 17. Cheson BD, Cassileth PA, Head DR, et al: Report of the National Cancer Institute-sponsored workshop on definitions of diagnosis and response in acute myeloid leukemia. J Clin Oncol 8:813-819, 1990[Abstract]
18.
Arceci RJ, Stieglitz K, Bras J, et al: Monoclonal antibody to an external epitope of the human MDR 1 P-glycoprotein. Cancer Res 53:1-8, 1993
19.
Leith CP, Chen IM, Kopecky KJ, et al: Correlation of multidrug resistance (MDR 1) protein expression with functional dye/drug efflux in acute myeloid leukemia by multiparameter flow cytometry: Identification of discordant MDR-/efflux+ and MDR+/efflux- cases. Blood 86:2329-2342, 1995
20.
Leith CP, Kopecky KJ, Godwin J, et al: Acute myeloid leukemia in the elderly: Assessment of multidrug resistance (MDR 1) and cytogenetics distinguishes biologic subgroups with remarkably distinct responses to standard chemotherapy: A Southwest Oncology Group study. Blood 89:3323-3329, 1997
21.
Ivy SP, Olshefski RS, Taylor BJ, et al: Correlation of P-glycoprotein expression and function in childhood acute leukemia: A Children’s Cancer Group study. Blood 88:309-318, 1996 22. Pearson L, Leith CP, Duncan MH, et al: Multidrug resistance-1 (MDR 1) expression and functional dye/drug efflux is highly correlated with the t(8;21) chromosomal translocation in pediatric acute myeloid leukemia. Leukemia 10:1274-1282, 1996[Medline] 23. Ino T, Miyazaki H, Isogai M, et al: Expression of P-glycoprotein in de novo acute myelogenous leukemia at initial diagnosis: Results of molecular and functional assays, and correlation with treatment outcome. Leukemia 8:1492-1497, 1994[Medline] 24. Noonan KE, Beck C, Holzmayer TA, et al: Quantitative analysis of MDR1 (multidrug resistance) gene in human tumors by polymerase chain reaction. S A 87:7160-7164, 1990
25.
Mechetner EB, Roninson IB: Efficient inhibition of P-glycoprotein mediated multidrug resistance with a monoclonal antibody. Proc Natl Acad Sci U S A 89:5824-5828, 1992
26.
Broxterman HJ, Sonneveld P, Feller N, et al: Quality control of multidrug resistance assays in adult acute leukemia: Correlation between assays for P-glycoprotein expression and activity. Blood 87:4809-4816, 1996 27. Broxterman HJ, Lankelma J, Pinedo HM, et al: Theoretical and practical considerations for the measurement of P-glycoprotein function in acute myeloid leukemia. Leukemia 11:1110-1118, 1997[Medline]
28.
Cornwell MM, Pastan I, Gottesman MM: Certain calcium channel blockers bind specifically to multidrug-resistant human KB carcinoma membrane vesicles and inhibit drug binding to P-glycoprotein. J Biol Chem 262:2166-2170, 1987
29.
Hammond JR, Johnstone RM, Gros P: Enhanced efflux of [3H]vinblastine from Chinese hamster ovary cells transfected with a full-length complementary DNA clone for the MDR1 gene. Cancer Res 49:3867-3871, 1989
30.
Arceci RJ, Stieglitz K, Bierer BE: Immunosuppressants FK506 and rapamycin function as reversal agents of the multidrug resistance phenotype. Blood 80:1528-1536, 1992 31. Mantel N, Haenszel S: Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 22:719-748, 1959 32. Lehmann EL: Statistical methods based on ranks, in Nonparametrics. San Francisco, CA, Holden-Day, 1975, p 316 33. Barnard DR, Kalousek DK, Wiersma SR, et al: Morphologic, immunologic, and cytogenetic classification of acute myeloid leukemia and myelodysplastic syndrome in childhood: A report from the Children’s Cancer Group. Leukemia 10:5-12, 1996[Medline] 34. Lacayo NL, Lum B, Johnson S, et al: Pharmacokinetics of etoposide and mitoxantrone in a controlled trial of cyclosporine (CSA) as an MDR modulator in acute myeloid leukemia (AML) from the Pediatric Oncology Group (POG). Proc Am Soc Clin Oncol 16:514, 1997 (abstr 1850) 35. Ho AD, Lipp T, Ehninger G, et al: Combination of mitoxantrone and etoposide in refractory acute myelogenous leukemia—an active and well-tolerated regimen. J Clin Oncol 6:213-217, 1988[Abstract] 36. Sievers EL, Smith FO, Woods WG, et al: Cell surface expression of the multidrug resistance P-glycoprotein (P-170) as detected by monoclonal antibody MRK-16 in pediatric acute myeloid leukemia fails to define a poor prognostic group: A report from the Children’s Cancer Group. Leukemia 9:2042-2048, 1995[Medline]
37.
Beketic-Oreskovic L, Duran GE, Chen G, et al: Decreased mutation rate for doxorubicin resistance and suppression of MDR1 gene activation by PSC 833. J Natl Cancer Inst 87:1593-1602, 1995 Submitted August 4, 1999; accepted January 5, 2000. This article has been cited by other articles:
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Copyright © 2000 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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ABSTRACT
INTRODUCTION
1.3 times a mean fluorescent intensity for P-gp compared with the isotype control. In addition, 
2 statistic and, when appropriate for small sample size, Fisher’s exact test. The Mantel-Haenszel test
