Multiple drug resistance mediated by P-glycoprotein is not a major factor in a slow response to therapy in childhood ALL

Role of Drug Transporters in Elucidating Inter-Individual Variability in Pediatric Chemotherapy-Related Toxicities and Response

Pediatric cancer treatment has evolved significantly in recent decades. The implementation of risk stratification strategies and the selection of evidence-based chemotherapy combinations have improved survival outcomes. However, there is large interindividual variability in terms of chemotherapy-related toxicities and, sometimes, the response among this population. This variability is partly attributed to the functional variability of drug-metabolizing enzymes (DME) and drug transporters (DTS) involved in the process of absorption, distribution, metabolism and excretion (ADME). The DTS, being ubiquitous, affects drug disposition across membranes and has relevance in determining chemotherapy response in pediatric cancer patients. Among the factors affecting DTS function, ontogeny or maturation is important in the pediatric population. In this narrative review, we describe the role of drug uptake/efflux transporters in defining pediatric chemotherapy-treatment-related toxicities and responses. Developmental differences in DTS and the consequent implications are also briefly discussed for the most commonly used chemotherapeutic drugs in the pediatric population.

P-glycoprotein Activity Correlates With Treatment Response in 2 Leukemia Child Patients

Acute lymphoblastic leukemia is the most important childhood cancer. Multidrug resistance is an important factor of poor prognosis. We present the P-glycoprotein (P-gp) activity in 2 patients with different outcomes. Both patients had B-cell acute lymphoblastic leukemia; they were responding properly to the treatment, but one of them had an increment in the P-gp activity that correlates with an increment in the disease manifestation, the patient had to be hospitalized and developed sepsis and subsequently died. P-gp levels were correlated with disease progression. P-gp activity needs to be evaluated during treatment to assess and prevent disease relapse or the patient´s death.

Expression of P-glycoprotein, Cyclin D1 and Ki-67 in Acute Lymphoblastic Leukemia: Relation with Induction Chemotherapy and Overall Survival

Previous studies showed that non-cycling cells have a higher multidrug resistance (MDR) expression, which may be down-regulated by proliferation induction. Triggering these cells into proliferation down-regulates high MDR expression. The aim of this study was to determine the expression of P-glycoprotein (PGP) and cell cycle parameters (cyclin D1 and Ki-67) in acute lymphoblastic leukemia (ALL) at diagnosis, and to evaluate the correlation between the expressions of each marker, and the clinical significance of such expression with response to induction chemotherapy and overall survival. A total of 78 newly diagnosed ALL patients were enrolled in our study. PGP, cyclin D1 and Ki-67 were determined by flow cytometry. PGP expression was encountered in 10/78 (12.8%) of ALL cases. Cyclin D1 and Ki-67 were expressed in 16/77 (20.6%) and 27/76 (34.6%) of ALL cases, respectively. None of the parameters were associated with response to induction chemotherapy and overall survival. Based on the current analysis, we conclude that a joint immunophenotypic evaluation of PGP and cell cycle parameters like that adopted in this study is unlikely to reveal mechanisms of multidrug resistance associated with the clinical outcome.

High-throughput screening for daunorubicin-mediated drug resistance identifies mometasone furoate as a novel ABCB1-reversal agent

The overexpression of P-glycoprotein, encoded by the ATP Binding Cassette B1 (ABCB1) gene, contributes to multidrug resistance (MDR) and is considered one of the major obstacles to successful cancer chemotherapy. The authors previously developed a T-lineage acute lymphoblastic leukemia (T-ALL) cell line that overexpresses ABCB1 and exhibits MDR to daunorubicin (DNR), prednisolone, and vincristine. Using this cell line and the fluorescent probe JC-1, they developed a flow cytometry-based, high-throughput screening (HTS) assay that quantifies ABCB1 efflux. They screened a library of 880 off-patent drugs for their ability to inhibit ABCB1 efflux and then measured the ability of 11 lead compounds to reverse in vitro DNR-mediated drug resistance and the toxic doses for each agent. Seven of the 11 drugs were able to reverse drug resistance at a concentration significantly below its toxic dose. Of the remaining 7, only 1 compound, mometasone furoate, has not been previously described as an ABCB1 antagonist to DNR-mediated drug resistance. On the basis of its high ABC modulator activity and relatively large in vitro therapeutic window, this drug warrants further investigation. In addition, the approach used in this study is useful for identifying off-patent drugs that may be repurposed for novel clinical indications.

Genetic alterations determine chemotherapy resistance in childhood T-ALL: modelling in stage-specific cell lines and correlation with diagnostic patient samples

Acquired drug resistance eventually leads to treatment failure in T-cell acute lymphoblastic leukaemia (T-ALL). Immunophenotypic and cytogenetic heterogeneities within T-ALL influence susceptibility to cytotoxic therapy, and little is known about the mechanisms of drug resistance at specific stages of T-cell ontogeny. We developed tolerance to therapeutic concentrations of daunorubicin (DNR) and L-asparaginase (L-asp) in Jurkat (CD1a(-), sCD3(+)) and Sup T1 (CD1a(+), sCD3(-)) cell lines, having respective 'mature' and 'cortical' stages of developmental arrest. DNR resistant cells acquired multidrug resistance: 310-fold increased resistance to vincristine (VCR) and a 120-fold increased resistance to prednisolone (PRED). Microarray analysis identified upregulation of asparagine synthetase (ASNS) and argininosuccinate synthase 1 (ASS1) to cell lines with acquired resistance to L-asp, and in the case of DNR, upregulation of ATP-binding cassette B1 (ABCB1). Suppression of ABCB1, ASNS and ASS1 by RNA interference revealed their functional relevance to acquired drug resistance. Expression profiling of these genes in 80 T-ALL patients showed correlation with treatment response. This study expands the pool of available drug resistant cell lines having cortical and mature stages of developmental arrest, introduces three new drug resistant T-ALL cell lines, and identifies gene interactions leading to L-asp and DNR resistance.

Expression profiling of ATP-binding cassette transporters in childhood T-cell acute lymphoblastic leukemia

A major issue in the treatment of T-cell acute lymphoblastic leukemia (T-ALL) is resistance to chemotherapeutic drugs. Multidrug resistance can be caused by ATP-binding cassette (ABC) transporters. The majority of these proteins have not yet been examined in T-ALL. Using a newly developed microarray for the simultaneous quantification of 38 ABC transporter genes, we observed a consistent overexpression of ABCA2/ABCA3 in clinical samples of ALL. Therefore, we analyzed the association of these two genes with drug resistance. Treatment of CCRF-CEM and Jurkat cells with methotrexate, vinblastine, or doxorubicin led to an induction of ABCA3 expression, whereas a significant increase of ABCA2 expression was only observed in Jurkat cells. To study the causal relationship of ABCA2/A3 overexpression with drug resistance, we applied RNA interference (RNAi) technology. RNAi specific for ABCA2 or ABCA3 led to a partial decrease of expression in these two ABC transporters. Upon cotreatment of RNAi for ABCA2 with methotrexate and vinblastine, a partial decrease of ABCA2 expression as well as a simultaneous increase of ABCA3 expression was observed. Vice versa, ABCA3 RNAi plus drugs decreased ABCA3 and increased ABCA2 expression. This indicates that down-regulation of one ABC transporter was compensated by the up-regulation of the other. Application of RNAi for both ABCA2 and ABCA3 resulted in a more efficient reduction of the expression of both transporters. As a consequence, a significant sensitization of cells to cytostatic drugs was achieved. In conclusion, ABCA2 and ABCA3 are expressed in many T-ALL and contribute to drug resistance.

Differences in absorption, distribution, metabolism and excretion of xenobiotics between the paediatric and adult populations

In children, the therapeutic benefits and potential risks associated with drug treatment may be different from those in adults and will depend on the exposure, receptor sensitivity and relationship between effect and exposure. In this paper, key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the paediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, secretion and activity of bile and pancreatic fluid, bacterial colonisation and transporters, such as P-glycoprotein (P-gp), are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the paediatric population and adults are organ size, membrane permeability, plasma protein concentration and characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and transporters such as P-gp, which is present not only in the gut, but also in liver, kidney, brain and other tissues. As far as drug metabolism is concerned, important differences have been found in the paediatric population compared with adults both for phase I enzymes (oxidative [e.g., cytochrome P450 (CYP)1A2, and CYP3A7 versus -3A4], reductive and hydrolytic enzymes) and phase II enzymes (e.g., N-methyltransferases and glucuronosyltransferases). Generally, the major enzyme differences observed in comparison with the adult age are in newborn infants, although for some enzymes (e.g., glucuronosyltransferases and other phase II enzymes) important differences still exist between infants and toddlers and adults. Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the paediatric population compared with adults are glomerular filtration and tubular secretion. The ranking of the key factors varies according to the chemical structure and physicochemical properties of the drug examined, as well as to the characteristics of its formulation. It would be important to generate additional information on the developmental aspects of renal P-gp and of other renal transporters, as has been done and is still being done with the different -isozymes involved in drug metabolism.

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.

Multiple drug resistance protein (MDR-1), multidrug resistance-related protein (MRP) and lung resistance protein (LRP) gene expression in childhood acute lymphoblastic leukemia

CONTEXT

Despite the advances in the cure rate for acute lymphoblastic leukemia, approximately 25% of affected children suffer relapses. Expression of genes for the multiple drug resistance protein (MDR-1), multidrug resistance-related protein (MRP), and lung resistance protein (LRP) may confer the phenotype of resistance to the treatment of neoplasias.

OBJECTIVE

To analyze the expression of the MDR-1, MRP and LRP genes in children with a diagnosis of acute lymphoblastic leukemia via the semiquantitative reverse transcription polymerase chain reaction (RT-PCR), and to determine the correlation between expression and event-free survival and clinical and laboratory variables.

DESIGN

A retrospective clinical study.

SETTING

Laboratory of Pediatric Oncology, Department of Pediatrics, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Brazil.

METHODS

Bone marrow aspirates from 30 children with a diagnosis of acute lymphoblastic leukemia were assessed for the expression of messenger RNA for the MDR-1, MRP and LRP genes by semi-quantitative RT-PCR.

RESULTS

In the three groups studied, only the increased expression of LRP was related to worsened event-free survival (p = 0.005). The presence of the common acute lymphoblastic leukemia antigen (CALLA) was correlated with increased LRP expression (p = 0.009) and increased risk of relapse or death (p = 0.05). The relative risk of relapse or death was six times higher among children with high LRP expression upon diagnosis (p = 0.05), as confirmed by multivariate analysis of the three genes studied (p = 0.035).

DISCUSSION

Cell resistance to drugs is a determinant of the response to chemotherapy and its detection via RT-PCR may be of clinical importance.

CONCLUSIONS

Evaluation of the expression of genes for resistance to antineoplastic drugs in childhood acute lymphoblastic leukemia upon diagnosis, and particularly the expression of the LRP gene, may be of clinical relevance, and should be the object of prospective studies.

Favorable outcome in 20-year follow-up of children with very-low-risk ALL and minimal standard therapy, with special reference to TEL-AML1 fusion

BACKGROUND

As the treatment results of childhood ALL have improved, avoidance of late effects has become increasingly important. Identification of favorable prognostic factors helps to achieve this goal.

PROCEDURE

We studied the prognostic value of TEL-AML1 fusion and a risk factor composed of age, white blood cell count (WBC), lymphomatous features, and hemoglobin level (Hb). We also compared outcome between two cohorts; cohort 1 (n=100) diagnosed 1975-1981, and cohort 2 (n=102) 1989-1991. Both cohorts were retrospectively divided in two groups: very-low-risk (WBC <10 x 10(9)/L, age 2 to <10 years, no lymphomatous features, Hb <90 g/L), and non-low-risk (=the remainder). We performed fluorescent in situ hybridization (FISH) of TEL-AML1 fusion of the marrow samples obtained at diagnosis.

RESULTS

The median follow-up is 20 years in cohort 1, and 8 years in cohort 2. In both cohorts, the very-low-risk category comprised one-fourth of the children. TEL-AML1 fusion was more frequent in the very-low-risk (35%) than in the non-low-risk group (17%) (P=0.03). The 8-year event-free survival (EFS) of children with the fusion was better than of those without, 74 vs. 54% (P=0.040). The 8-year EFS in the very-low-risk group was 76% in cohort 1, and 79% in cohort 2 (n.s.). In the non-low-risk groups, EFS was 39 vs. 64% (P=0.02), respectively.

CONCLUSIONS

Our data support the reported association of TEL-AML1 fusion with a favorable outcome although the risk group had a greater impact. These very-long-term follow-up data also indicate that children with very-low-risk ALL (slow disease) had a favorable outcome already in the late 1970s, and may be over treated with the contemporary ALL protocols.

Drug metabolism and disposition in children

Key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the pediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, bacterial colonization and probably P-glycoprotein are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein concentration and plasma protein characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and probably P-glycoprotein, mainly that present in the gut, liver and brain. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I enzymes [oxidative (e.g. cytochrome CYP3A7 vs. CYP3A4 and CYP1A2), reductive and hydrolytic enzymes] and phase II enzymes (e.g. N-methyltransferases and glucuronosyltransferases). Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the pediatric population compared with adults are glomerular filtration and tubular secretion. It would be important to generate information on the developmental aspects of renal P-glycoprotein and of other renal transporters as done and still being done with the different isozymes involved in drug metabolism.

Loss at 12p detected by comparative genomic hybridization (CGH): association with TEL-AML1 fusion and favorable prognostic features in childhood acute lymphoblastic leukemia (ALL). A multi-institutional study

BACKGROUND

Genetic aberrations provide prognostic information in childhood ALL. The proportion of patients with detectable aberrations can be increased by combining G-banding with comparative genomic hybridization (CGH).

PROCEDURE

We studied 79 children with ALL by CGH and G-banding, and explored the relationship of these findings to clinical features and outcome.

RESULTS

CGH revealed DNA copy number changes in 57 patients (72%), 9 of whom had normal karyotype by G-banding. Gains were more frequent than losses, and changes of whole chromosomes more frequent than partial aberrations. Two frequent partial losses were found; at 9p and 12p. The 9 patients with loss at 12p were studied for the deletion of TEL (ETV6) gene and the fusion of TEL and AML1 genes by fluorescent in situ hybridization (FISH). Eight out of the 9 children with loss at 12p harbored the TEL-AML1 translocation and all 9 had the deletion of a nontranslocated TEL allele. All 9 had precursor-B phenotype and L1 morphology, and 8/9 had WBC below 50 x 10(9)/liter. All children were treated according to Nordic ALL protocols, had a good response to treatment based on day 15 bone marrow morphology, and 7 out of the 9 survived in continuous complete remission (median follow-up 74 months).

CONCLUSIONS

CGH is a valuable tool in screening for genetic aberrations in childhood ALL. DNA copy number losses detected at 12p associate with TEL-AML1 fusion as well as with favorable prognostic features.

Initial P-glycoprotein expression in childhood acute lymphoblastic leukemia: no evidence of prognostic impact in follow-up

Treatment results in childhood acute lymphoblastic leukemia (ALL) have improved remarkably during the past 20 years, but still 25% of children cannot be permanently cured. Drug resistance is a major cause of poor outcome. One of the most investigated resistance mechanisms is the P-glycoprotein (P-gp)-mediated multiple-drug resistance (MDR). The authors prospectively analyzed P-gp using flow cytometry with monoclonal antibody JSB1 in a population-based series of 103 children with ALL treated according to intensive Nordic ALL protocols. Increased P-gp expression was detected in 55 patients (53%). With a cutoff value of 1% P-gp-positive blasts in bone marrow, no difference was found in event-free survival (EFS) or overall survival between children with low vs. increased P-gp expression. The 4-year EFS in the whole series was 77%. Patients with T-ALL had higher P-gp levels than the others, 3.6% vs. 1.0% (p = .002). P-gp expression did not correlate with the white blood cell count, age, sex, or cytogenetics. The authors conclude that the level of P-gp expression cannot be used as a tool for treatment stratification in childhood ALL.

Novel mechanisms of drug resistance in leukemia

A key issue in the treatment of acute leukemia is the development of resistance to chemotherapeutic drugs. Several mechanisms may account for this phenomenon, including failure of the cell to undergo apoptosis in response to chemotherapy, or failure of the drug to reach and/or affect its intracellular target. This review focuses on the latter mechanism, and on intracellular drug transport resistance mechanisms in particular. Expression of the ATP-binding cassette (ABC) transporter P-glycoprotein (Pgp) has generally been reported to correlate with prognosis in acute myeloid leukemia (AML). Additionally, but more controversial, expression of the ABC transporter multidrug resistance protein (MRP) and the vault-transporter lung resistance protein (LRP) have been correlated with outcome in AML. Despite these findings, functional efflux assays indicate the presence of non-Pgp, non-MRP transporters in AML. Recently, a novel ABC transporter, breast cancer resistance protein (BCRP) was cloned and sequenced in our laboratory. Transfection and overexpression of BCRP in drug-sensitive cells confers drug-resistance to the cells. BCRP is a half-transporter, and may homodimerize or form heterodimers (with a yet unknown half-transporter) to produce an active transport complex. Relatively high expression of BCRP mRNA is observed in approximately 30% of AML cases, suggesting a potential role for this new transporter in drug resistance in leukemia.

Further elucidation of mechanism of resistance to vincristine in myeloid cells: role of hypochlorous acid in degradation of vincristine by myeloperoxidase

Inherent resistance of myeloblasts to vincristine (VCR) has been related to the activity of myeloperoxidase (MPO) which can degrade VCR in the presence of hydrogen peroxide (H2O2). We investigated the relationship between VCR degradation and hypochlorous acid (HOCl) generation from the reaction of H2O2 with chlorine (Cl) as catalyzed by MPO. A cell-free system, three human leukemia cell lines (CEM/CCRF, HL-60, U937) and 15 bone marrow samples from children with acute myeloid leukemia (AML) were studied. VCR cytotoxicity was evaluated by MTT assay and by quantitative measurement of apoptosis. In vitro levels of VCR in cell-free systems were measured by high performance liquid chromatography (HPLC), and intracellular HOCl levels by oxidation of 5-thio-2-nitrobenzoic acid with the accompanying decrease in the absorbency at 412 nm. VCR was degraded by increasing concentrations of HOCl in cell-free systems and this activity was inhibited by taurine, which is known to block HOCl activity. This finding was confirmed by the VCR cytotoxicity studies on cell lines. The HOCl-producing myeloblasts from patients were resistant to VCR. In five samples out of eight HOCl was also detected extracellularly. These results suggest that oxidation by HOCl may be the final step in VCR degradation catalyzed by MPO through its action on intracellular H2O2 and Cl. Leukemia (2000) 14, 47-51.

The effects of anticancer drugs in combination with nimodipine and verapamil on cultured cells of glioblastoma multiforme

The presence of the cellular multidrug resistance (MDR1) gene and its product, P-glycoprotein (Pgp), is thought to be a mechanism for the failure of chemotherapy in cancer patients. Calcium channel blockers have been shown to sensitise cancer cells to anticancer drugs by reversing Pgp expression in cell lines. The interactions between anticancer drugs such as carmustine (BCNU), vincristine (VCR) and procarbazine (PCB) and calcium channel blockers such as nimodipine and verapamil on cultured cells of glioblastoma from eight patients were therefore tested. Pgp expression was examined immunohistochemically using C219 monoclonal antibody in cytospin preparation. The cytotoxicity of the drugs was screened using microculture tetrazolium assay. The cells from five patients showed positive immunoreaction for Pgp. Nimodipine showed growth-inhibitory activity against glioblastoma cells at a rate of 16.55-26.88% (P < 0.05), but a similar effect was not observed with verapamil. While antiproliferative effects of BCNU were around 20.91-45.09% (P < 0.05) on the cells from seven patients, VCR was the most effective agent in inhibition of cell growth at a rate of 26.43-48.47% (P < 0.05). The response of the cells from five patients to PCB was from 11.98 to 16.32% (P < 0.05). When used together, nimodipine further enriched cytotoxicity of the anticancer drugs up to 11.14-40.85% (P < 0.05) without relation to Pgp expression. In conclusion, the enhancement of cytotoxicity of anticancer drugs by nimodipine suggests that there might be a synergy between anticancer drugs and nimodipine in the inhibition of glioma cell growth.

Reemphasis on lymphoblast L2 morphology as a poor prognostic factor in childhood acute lymphoblastic leukemia

BACKGROUND

In childhood acute lymphoblastic leukemia (ALL), the relationship between lymphoblast L1/L2 morphology and prognosis is controversial. According to some studies L2 morphology is associated with poor prognosis, whereas in others the association disappears after adjustment for other known risk factors.

PROCEDURE

We investigated the prognostic importance of lymphoblast L1/L2 morphology in childhood ALL treated with current Nordic ALL protocols in Finland. From the routine bone marrow (BM) aspirate and biopsy slides of 251 children with ALL diagnosed in 1990-1995, the blast cell morphology and early treatment responses were assessed blindly in a central review, using French-American-British (FAB) criteria with the Children's Cancer Group (CCG) modification.

RESULTS

L1 morphology (>90% L1) was found in 197 (80%) children and L2 (>/=10% L2) in 49 (20%). Early treatment response was poorer in L2 than in L1: >5% blasts in the marrow on day 15 were seen in 27% of L2 as opposed to 12% of L1 (P = 0.048). The 6-year event-free survival (EFS) in the study population was 75%, 76% in L1 and 70% in L2 (P = 0.34). In the group with white blood cell count (WBC) below 50 x 10(9)/liter at diagnosis, the L2 morphology was associated with inferior survival: 6-year EFS 74% in L2 and 84% in L1 (P = 0.07), with 6-year overall survival (OS) 81% vs. 91% (P = 0.035), respectively. L2 morphology was not associated with any other adverse prognostic factor analyzed.

CONCLUSIONS

With the intensive Nordic ALL protocols, lymphoblast L2 morphology is an independent poor prognostic factor, influencing both the early response to treatment and, in the low-WBC group, the ultimate outcome, and should be reemphasized in risk categorization of childhood ALL.

Bcl-2 plays a key role instead of mdr1 in the resistance to hexadecylphosphocholine in human epidermoid tumor cell line KB

We induced tolerance to hexadecylphosphocholine (HePC) in the human epidermoid tumor cell line, KB. After 70 weeks of adaptation, the IC50 of HePC in the resistant cells KBr was 32-fold higher than in parental KB cells, and they were 30-fold more resistant to another ether lipid analogue, ET-18-OCH3. The KBr cells also showed cross-resistance to vincristine and colchicine while remaining sensitive to other chemotherapy agents. RT-PCR assays showed that expression of the multidrug resistance gene (MDR1) was positive in KBr cells, whereas the expression of GST-pi (glutathione S-transferase pi) and MRP (multidrug resistance protein) was undetectable in KBr cells. Both an immunocytochemistry test and Western blot analysis indicated that the expression of bcl-2 in KBr cells was strongly positive, while it was only mildly expressed in KB cells. Verapamil could not reverse the resistance of KBr to HePC although it is a well-known reversing agent against MDR1. Our results suggest that bcl-2 instead of MDR1 plays a major role in the resistance of KBr cells.

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.