Mitoxantrone, etoposide, and cytarabine with or without valspodar in patients with relapsed or refractory acute myeloid leukemia and high-risk myelodysplastic syndrome: a phase III trial (E2995)

Improving Efficacy of Intravesical Chemotherapy

OBJECTIVE

This paper reviews the most relevant findings published recently on intravesical chemotherapy for superficial bladder tumours and provides recommendations based on documented research.

METHODS

The evidence was categorised according to the North of England Evidence Based Guideline Development Project. Levels of evidence were based on the source of the information, meta-analyses, systematic reviews, well-designed randomised or nonrandomised controlled clinical trials, and uncontrolled studies or consensus. Three levels of recommendations were assigned to the evidence obtained.

RESULTS

Despite intravesical chemotherapy being used prophylactically after endoscopic resection of superficial bladder tumours, the recurrence rate is still 36-44%. Researchers have focused on improving the effectiveness of intravesical chemotherapy, each adopting a different strategy. Some have aimed to identify the optimum timing for instillations and others to improve the pharmacokinetics of agents by avoiding their dilution, increasing their stability, or improving the absorption of the drug by bladder mucosa. Some researchers are looking into new, single chemotherapeutic agents or combinations for intravesical use and others into avoiding chemoresistance with resistance-reverting agents (modulating agents) or by using in vitro chemosensitivity tests to identify the most sensitive drug.

CONCLUSION

Progress has been made in optimising intravesical chemotherapy for timing of instillations and pharmacokinetic interventions. Simple and inexpensive approaches may have a widespread, practical acceptance by urologists, but it is more difficult to extend new techniques requiring more complex and sometimes expensive instrumentation to the urologic community. Further research into finding more effective cytotoxic drugs, combinations, or modulating agents should be encouraged.

New agents for the treatment of acute myeloid leukemia

The heterogeneity of acute myeloid leukemia (AML) has been established by many new insights into the diagnosis, pathogenesis, clinical manifestations, treatment, and prognosis of patients with AML. Morphology remains the foundation for the diagnosis. However, additional diagnostic studies, including immunophenotyping, cytogenetic evaluation, and molecular genetic studies, are necessary to develop treatments because specific subtypes of AML can now be approached with targeted therapy. Acute promyelocytic leukemia (APL), defined by a single molecular abnormality, is now treated with specific targeted therapy, all-trans retinoic acid (ATRA), and this subtype of AML is now highly curable. Currently, a number of agents have been explored in AML, including anti-CD33 antibodies and immunoconjugate drugs, inhibitors of multidrug resistance proteins, farnesyl transferase inhibitors, tyrosine kinase inhibitors, anti-Bcl-2 transcription agents, and inhibitors of mammalian target of rapamycin (mTOR). New alkylating agents, and purine analogs such as Cloretazine and clofarabine, affect DNA and ribonucleoside reductases, respectively. These agents have shown promise in small studies. Large phase III studies will address whether these are effective in inducing complete responses. Combining targeted agents with chemotherapy may improve the response rates. The plan for the future is to find therapeutic strategies that are specific for patients based on the specific biology of the disease. Future studies will investigate combinations of targeted therapies with each other and with chemotherapies to maximize the inhibition of multiple pathways present in AML. Additionally, evaluation of the identified prognostic factors and gene mutations will enable further pathologic classification of patients with AML.

Selective expression of cholesterol metabolism genes in normal CD34+CD38- cells with a heterogeneous expression pattern in AML cells

OBJECTIVE

To identify adenosine triphosphate-binding-cassette (ABC) transporters that are selectively expressed in normal and/or leukemic CD34+CD38- stem cells.

METHODS

Microarray experiments on murine stem cells identified 13 ABC transporters with a high expression level. Corresponding human transporters were analyzed in normal CD34+CD38- and CD34+CD38+ bone marrow cells by quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Five ABC transporters, including ABCG1, were differentially expressed with a higher expression in CD34+CD38- cells. Besides ABCG1, known to be involved in cholesterol metabolism, expression of another major cholesterol transporter (ABCA1), some cholesterol metabolism genes (3-hydroxy-3-methyl-glutaryl-CoA reductase, low-density lipoprotein receptor), and the transcription factor controlling ABCA1 and ABCG1 expression, liver-X-receptor-alpha (LXR-alpha), were assessed. All these genes were predominantly expressed in the more primitive subpopulation, indicating a high rate of cholesterol metabolism and transport. Conversely in acute myeloid leukemia (AML), a heterogeneous expression pattern was found consisting of a considerably higher expression of particularly LXR-alpha in CD34+ cells and a reverse expression pattern in a subset of AML CD34+CD38+ cells.

CONCLUSION

These data suggest an active cholesterol metabolism and efflux in normal CD34+CD38- cells, although a subgroup of AMLs potentially demonstrate a hyperactive cholesterol metabolism.

Inhibition of efflux transporter ABCG2/BCRP does not restore mitoxantrone sensitivity in irinotecan-selected human leukemia CPT-K5 cells: evidence for multifactorial multidrug resistance

It has been shown that the human acute lymphoblastic leukemia (ALL) T cell line (RPMI 8402) selected with irinotecan (CPT-11) is transformed to a multidrug resistant (MDR) phenotype (CPT-K5) with cross-resistance to mitoxantrone (MX). Since MX is a well-documented substrate for the efflux transporter breast cancer resistant protein (BCRP/ABCG2), we assessed the contribution of drug efflux to MX resistance in CPT-K5 cells. Our results demonstrate that CPT-K5 cells had markedly higher expression levels of BCRP, negligible expression of MRP2 and P-gp, and lower intracellular retention of MX as compared to RPMI 8402 cells. Surprisingly, MX resistance in CPT-K5 cells was not reversed by the BCRP chemical inhibitor, novobiocin (NOV), or gene-specific siRNA, although intracellular MX concentrations were significantly increased when BCRP was functionally knocked down. These results suggest that up-regulation of BCRP plays a minimal role in conferring MX resistance to CPT-K5 cells, highlighting the existence of multiple, redundant mechanisms of drug resistance. The current results support the concept of "multifactorial multidrug resistance", a recently-described phenomenon that ascribes multidrug resistance to many possible cellular mechanisms, not only by efflux drug transporters.

ABCB1 Modulation Does Not Circumvent Drug Extrusion from Primitive Leukemic Progenitor Cells and May Preferentially Target Residual Normal Cells in Acute Myelogenous Leukemia

PURPOSE

Acute myelogenous leukemia (AML) is a disease originating from normal hematopoietic CD34+ CD38- progenitor cells. Modulation of the multidrug ATP-binding cassette transporter ABCB1 has not resulted in improved outcome in AML, raising the question whether leukemic CD34+ CD38- cells are targeted by this strategy.

EXPERIMENTAL DESIGN

ABCB1-mediated transport in leukemic CD34+ CD38- cells compared with their normal counterparts was assessed by quantitating the effect of specific ABCB1 modulators (verapamil and PSC-833) on mitoxantrone retention [defined as efflux index (EI), intracellular mitoxantrone fluorescence intensity in the presence/absence of inhibitor].

RESULTS

ABCB1 was the major drug transporter in CD34+ CD38- cells in normal bone marrow (n = 16), as shown by the abrogation of mitoxantrone extrusion by ABCB1 modulators (EI, 1.99 +/- 0.08). Surprisingly, ABCB1-mediated drug extrusion was invariably reduced in CD34+ CD38- cells in AML (n = 15; EI, 1.21 +/- 0.05; P < 0.001), which resulted in increased intracellular mitoxantrone retention in these cells (mitoxantrone fluorescence intensity, 4.54 +/- 0.46 versus 3.08 +/- 0.23; P = 0.004). Active drug extrusion from these cells occurred in the presence of ABCB1 modulators in the majority of samples, pointing in the direction of redundant drug extrusion mechanisms. Residual normal CD34+ CD38- cells could be identified by their conserved ABCB1-mediated extrusion capacity.

CONCLUSION

ABCB1-mediated drug extrusion is reduced in leukemic CD34+ CD38- progenitor cells compared with their residual normal counterparts. Redundant drug transport mechanisms confer mitoxantrone transport from leukemic progenitors. These data argue that ABCB1 modulation is not an effective strategy to circumvent drug extrusion from primitive leukemic progenitor cells and may preferentially target residual normal progenitors in AML.

Risikoadaptierte Therapie der akuten myeloischen Leukämie

Genetic and molecular techniques have provided increasing insights into the biology of acute myeloid leukemia (AML). These investigations showed that AML is not a homogeneous disease but a heterogeneous group of biologically different subentities. These subentities are currently primarily defined by cytogenetics and molecular markers. They differ substantially in response to therapy and long-term outcome and hence allow different risk groups of patients to be defined. These will guide therapeutic decisions in future therapeutic strategies and may ultimately lead to an individualized treatment concept.

A phase I clinical and pharmacokinetic study of the multi-drug resistance protein-1 (MRP-1) inhibitor sulindac, in combination with epirubicin in patients with advanced cancer

PURPOSE

Multi-drug resistance mediated by ATP-binding cassette trans-membrane protein pumps is an important cause of cancer treatment failure. Sulindac has been shown to be a competitive substrate for the clinically important resistance protein, multi-drug resistance protein-1 (MRP-1), and thus might enhance the anti-cancer activity of substrate chemotherapeutic agents, e.g. anthracyclines.

METHODS

We conducted a dose-escalating, single arm, prospective, open label, non-randomised phase I trial of epirubicin (75 mg/m(2)) in combination with escalating oral doses of sulindac (0-800 mg) in patients with advanced cancer to identify an appropriate dose of sulindac to use in future resistance studies. Anthracycline and sulindac pharmacokinetics were studied in cycles 1 and 3.

RESULTS

Seventeen patients (8 breast, 3 lung, 2 bowel, 1 melanoma, 1 renal, 1 ovarian and 1 of unknown primary origin, 16/17 having had prior chemotherapy) were enrolled. Eight patients received a full six cycles of treatment; 14 patients received three or more cycles. Dose-limiting toxicity was observed in two patients at 800 mg sulindac (1 renal impairment, 1 fatal haemoptysis in a patient with advanced lung cancer), and sulindac 600 mg was deemed to be the maximum tolerated dose. Sulindac had no effect on epirubicin pharmacokinetics. Among 15 patients with evaluable tumour, two partial responses were seen (malignant melanoma and breast cancer). Four others had prolonged stable disease.

CONCLUSION

Epirubicin 75 mg/m(2) and sulindac 600 mg are the recommended doses for phase II studies for these agents in combination.

Drug delivery across the blood–brain barrier: why is it difficult? how to measure and improve it?

The development of drugs that act in the CNS has been significantly impeded by the difficulty of delivering them across the blood-brain barrier (BBB). This article aims to provide the reader with a critical overview of important issues in the discovery and development of drugs that need to enter the brain to elicit pharmacological activity, focusing particularly on i) the role of drug transporters in brain permeation and how to manipulate them to enhance drug brain bioavailability; ii) the successful application, limitations and challenges of commonly used in vitro and in vivo methodologies for measuring drug transport across the BBB, and iii) a discussion of recently developed strategies (e.g., modulation of efflux transporters by chemical inhibitors and the employment of delivery vectors taking advantage of native transport systems at the BBB) for facilitating drug penetration into the brain.

Targeting multidrug resistance in cancer

Effective treatment of metastatic cancers usually requires the use of toxic chemotherapy. In most cases, multiple drugs are used, as resistance to single agents occurs almost universally. For this reason, elucidation of mechanisms that confer simultaneous resistance to different drugs with different targets and chemical structures - multidrug resistance - has been a major goal of cancer biologists during the past 35 years. Here, we review the most common of these mechanisms, one that relies on drug efflux from cancer cells mediated by ATP-binding cassette (ABC) transporters. We describe various approaches to combating multidrug-resistant cancer, including the development of drugs that engage, evade or exploit efflux by ABC transporters.

Expression dynamics of drug resistance genes, multidrug resistance 1 (MDR1) and lung resistance protein (LRP) during the evolution of overt leukemia in myelodysplastic syndromes

It is well-known that leukemic cells of overt leukemia (OL) that have transformed from myelodysplastic syndromes (MDS) are more resistant to chemotherapy as compared with de novo AML cells. Thus, to examine the expression levels of drug-resistant genes and their alterations with the development of OL in MDS, the expression of mRNA for MDR1 and LRP was determined in bone marrow samples from control, de novo AML, MDS, MDS at the time of OL transformation (MDS --> OL), and after transformation (OL) by quantitative real-time RT-PCR. The expression of MDR1 in MDS bone marrow at the time of initial diagnosis was as low as that for control subjects. However, the expression level was significantly elevated at the time of the development of OL (MDS --> OL) compared with the initial MDS subjects (P < 0.05), while expression was relatively reduced after OL development (OL). The expression of LRP was significantly higher in MDS and MDS --> OL samples than control subjects. However, the high expression of LRP in MDS --> OL was significantly reduced after OL development (OL). The expression levels of drug-resistant genes in MDS --> OL or OL were not significantly higher than those of de novo AML samples, although LRP expression in MDS or MDS --> OL was relatively higher than that of de novo AML. Detecting increases in the expression of MDR1 would be useful for predicting OL development in MDS patients.

Addition of cyclosporin-A to chemotherapy in secondary (post-MDS) AML in the elderly. A multicenter randomized trial of the Leukemia Working Group of the Hellenic Society of Hematology

In elderly patients with secondary leukemia, poor therapeutic response and low overall survival have been attributed mainly to age and to the primary resistance of leukemic cells to chemotherapy. Modulation of resistance has been attempted in different studies, but the results have been contradictory. We conducted an open, randomized multicenter clinical trial involving patients more than 60 years old with secondary leukemia preceded by a myelodysplastic syndrome. The induction chemotherapy regimen included idarubicin, cytarabine, and etoposide (group A); randomization involved simultaneous administration of cyclosporin-A per os (group B). Fifty-five patients were evaluated, 26 in group A and 29 in group B. Overall complete remission was achieved in 40% of the patients, 27% vs 52% in groups A and B, respectively (p=0.01). Leukemia-free survival was more favorable in patients who received cyclosporin-A, 12 vs 7 months for groups B and A, respectively (p=0.03). In a follow up period of 30 months, 7 out of 55 patients (13%) were alive, 4 of whom were in complete remission. Five out of the 7 alive patients were randomized in group B and had received cyclosporin-A. Treatment failure was higher in group A [19 of 26 patients (73%)] than in group B with CsA [14 of 29 patients (48%)] (p<0.0001). Treatment-related toxicity/mortality was 13%. Modulation of drug resistance by CsA in elderly people suffering from secondary acute leukemia may improve the outcome of chemotherapy without increasing drug toxicity and treatment-related mortality.

Phase III study of PSC-833 (valspodar) in combination with vincristine, doxorubicin, and dexamethasone (valspodar/VAD) versus VAD alone in patients with recurring or refractory multiple myeloma (E1A95)

BACKGROUND

Preliminary studies have shown valspodar (PSC-833: Novartis Pharmaceuticals, East Hanover, NJ) to be a potent inhibitor of multidrug resistance (MDR), one cause of resistance to chemotherapy. An international randomized control study (Phase III) evaluated the use of vincristine, doxorubicin, and dexamethasone (VAD) with (n = 46) and without (n = 48) valspodar in the treatment of patients with recurring or refractory multiple myeloma.

METHODS

Patients with documented recurrence or refractory myeloma were stratified based on prior treatment exposure and creatinine and randomized. Because of interaction of valspodar with vincristine and doxorubicin, the doses of these drugs were reduced compared with the VAD-alone arm, and the doxorubicin was further reduced in the last 15 patients when given with valspodar based on pharmacokinetic and toxicity studies.

RESULTS

There were no complete or near-complete responses. There were 29% partial responses (PRs) in the VAD-alone arm and 44% with valspodar (P = 0.2). Median progression-free survival was 7 months with VAD alone and 4.9 months with valspodar (P = 0.50). Subjective response was 19% with VAD alone and 17% with valspodar (P = 1.0). Median survival with VAD alone was 18.5 months and 15.3 with the addition of valspodar (P = 0.055). Toxicity of Grade 3 or greater was higher (P < 0.0001) in the valspodar arm (89%) compared with the VAD-alone arm (58%). The reduction of doxorubicin dose reduced toxicity but not significantly (P = 0.11).

CONCLUSION

The addition of the MDR-modulating agent valspodar to VAD did not improve treatment outcome. Toxicity was increased in the valspodar-treated group compared with VAD alone.

[Cell cycle and apoptosis mechanisms implicated in intravesical chemotherapy resistances in superficial bladder cancer]

It is well documented the effectiveness of intravesical chemotherapy following transurethral resection to prevent recurrences of superficial bladder cancer. But it is also known that efficacy may be limited by tumour cell resistance to one or several of the drugs available for instillation. In addition to the genetically determined unicellular mechanisms classically described in the literature such as glycoprotein P-170 expression (mdr-1), overexpression of Bcl-2 or glutation S-transferase activity, it has been recently shown that multicellular mechanisms may also be involved in drug resistance. Multicellular resistance can only be demonstrated in three-dimensional cultures and fails to be shown in monolayers or cell suspensions. This is explained by the fact that cell-to-cell and cell-to-stroma adhesion limits drug penetration and by the variable susceptibility to cytotoxicity determined by oxygen and tissue proliferation gradients. A better understanding of the molecular mechanisms involved in drug resistance is necessary to increase intravesical chemotherapy effectiveness. Current research includes improving drug penetration, searching resistance reversing agents and developing in vitro chemosensitivity tests to identify drug resistance.

New agents in the treatment of childhood leukemias and myelodysplastic syndromes

Relapsed or refractory leukemia remains the most common therapeutic problem in pediatric oncology. Particularly challenging is the patient who has recurrence following a stem cell transplant. Insights into the molecular pathogenesis of the leukemias have produced an array of new agents. These new agents will be more selective in hitting their targets, and so their use will be more narrowly defined than with classical cytotoxic drugs. These new agents include all-trans retinoic acid, gemtuzumab ozogamicin, imatinib mesylate, rituximab, and a bevy of signal transduction inhibitors and therapeutic monoclonal antibodies. Other new agents, such as liposomal daunorubicin, PEG-asparaginase, or clofarabine, represent chemical modifications of established antileukemic drugs. Increasingly, molecular profiling will be used to guide the development and application of new drugs.

Management of patients with higher risk myelodysplastic syndromes

Higher risk myelodysplastic syndromes (MDS) include patients in the Intermediate-2 and high-risk categories of the International Prognostic Scoring System, as well as patients with MDS secondary to radiation or chemical exposure. Ideally, the goal of therapy is to alter the natural history of disease in these patients to achieve cure or durable remission. High-intensity chemotherapy can achieve moderate rates of complete remission, however, durability of remission and overall survival tend to be short. Hematopoietic stem cell transplantation (HSCT) offers the possibility of cure, with long-term disease-free survival inversely related to age. Patients who are elderly or have poor functional status are candidates for reduced intensity HSCT, although this is still an experimental modality. Azacitidine is a hypomethylating agent that is a reasonable option for many patients ineligible for high-intensity therapies. Other therapies, such as immunomodulatory agents, arsenic trioxide, and farnesyl transferase inhibitors have thus far shown limited usefulness in higher risk MDS. This paper reviews the various therapeutic options for higher risk MDS, providing rationale for specific management approaches for these patients.

Towards a pathogenesis-oriented therapy of acute myeloid leukemia

Genetic and molecular techniques have provided increasing insights into the biology of acute myeloid leukemia (AML). These investigations showed that AML is not a homogeneous disease but a heterogeneous group of biologically different subentities. These subentities are currently primarily defined by cytogenetics by which three main subgroups can be discriminated: AML with balanced translocations, AML with unbalanced aberrations and AML without cytogenetically detectable aberrations. Within the latter group molecular alterations are identified in more than half of cases such as NPM mutations, FLT3 mutations, MLL duplications and mutations of CEBP-alpha. The clinical meaning of these findings is illustrated by substantial differences in response to therapy and long-term outcome. As demonstrated by the recent multicenter trial of the German AML Cooperative Group (AMLCG) and other studies intensification of induction therapy may improve the results in distinct subtypes but fails to do so in others. Therefore, new strategies need to be explored which incorporate the knowledge about the biology of AML to develop biology adapted treatment strategies. This process has just begun and is predominantly determined by the availability of new agents and their evaluation in clinical phase I and II studies. A variety of targets are currently explored and some trials have yielded promising results already. The step towards a biology adapted treatment of AML is long and requires the combined efforts of researchers, clinicians and the pharmaceutical industry. The first steps towards this goal have been taken and give rise to the hope for more effective and more specific therapies of AML.

Phase I combining a P-glycoprotein inhibitor, MS209, in combination with docetaxel in patients with advanced malignancies

PURPOSE

The purpose of this study was to investigate the safety and tolerability of MS209, a potent inhibitor of P-glycoprotein, when given in combination with docetaxel and to determine whether MS209 affects docetaxel pharmacokinetics.

EXPERIMENTAL DESIGN

Patients with advanced solid malignancies were eligible for this phase I trial. Docetaxel as 1-hour infusion was given alone during the first cycle. MS209 was introduced as of cycle 2 and given orally 30 minutes after docetaxel infusion. The dose escalation scheme followed a modified Fibonacci model with six steps (docetaxel, 60-100 mg/m2 and MS209, 300-1,200 mg per body).

RESULTS

A total of 30 patients were treated at five dose levels. Dose-limiting toxicities were febrile neutropenia, infection, stomatitis, dysphagia, and fatigue. The maximum tolerated dose was reached at level 5 (docetaxel, 80-MS: 1,200). Pharmacokinetic analysis failed to show a strong pharmacokinetic interaction between the two compounds, but at the highest dose levels, there is a trend to an increase of docetaxel AUC when this agent is given in combination with MS209.

CONCLUSION

MS209 can be given in combination with docetaxel, with limited effect on docetaxel toxicity or pharmacokinetics.

Sorcin, an important gene associated with multidrug-resistance in human leukemia cells

Sorcin, or soluble resistance-related calcium-binding protein, is a 22kD calcium-binding protein initially identified in many mutli-drug resistant (MDR) cell lines. We previously observed by gene profiling that sorcin is significantly up-regulated in a doxorubicin-induced MDR leukemia cell line, K562/A02, over its parent cells. We have also demonstrated that the level of sorcin expression in leukemia patients correlates not only directly with that of the mdr1 gene, but also inversely with patients' response to chemotherapies and overall prognosis. In this report, we have carried out experiments to dissect out the contribution of sorcin by itself to drug resistant phenotype in K562 cells. Overexpression of sorcin protein by gene transfection in K562 cells resulted in increased drug resistance, from 4.1- to 22.5-fold, to a variety of chemotherapeutic agents, including doxorubicin, etoposide, homoharringtonine and vincristine. On the other hand, inhibition of sorcin expression in both MDR K562/A02 and the sorcin-transfected K562 cells with sorcin-targeting small interfering RNA led to varying extent of reversal of drug resistance. These results confirm that sorcin is an important gene associated with the development of MDR in leukemia cells.

Advances in the molecular genetics of acute leukemia

Acute leukemias are characterized by the unrestrained clonal proliferation of hematopoietic precursor cells coupled with aberrant or arrested differentiation. The molecular basis of hematopoiesis and leukemogenesis is still being defined, yet it is increasingly evident that acute leukemias have recurrent molecular features that can be exploited for diagnostic, prognostic, and therapeutic purposes. Modern molecular technologies already influence treatment strategies for these diseases, and it is likely that as such technology matures it will have an increasing impact on all aspects of acute leukemia management. This article reviews recent developments in the molecular classification, prognostication, and treatment of the acute leukemias.

The prognostic significance of P-glycoprotein, multidrug resistance-related protein 1 and lung resistance protein in pediatric acute lymphoblastic leukemia: a retrospective study of 295 newly diagnosed patients by the Children's Oncology Group

Multidrug resistance (MDR) is a phenomenon by which cells become resistant to an array of structurally unrelated chemotherapeutic agents. The prognostic value that P-glycoprotein (Pgp), multidrug resistance-related protein 1 (MRP1), and lung resistance protein (LRP) have in the setting of pediatric acute lymphoblastic leukemia (ALL) is controversial. In a retrospective study, we analyzed samples obtained from 295 similarly treated pediatric ALL patients to assess whether the overexpression and/or function of these proteins at diagnosis affects outcome. Most patients (70%, 207/295) did not overexpress an MDR protein. A small number of patients expressed functional Pgp (1%, 3/295) and some overexpressed functional MRP1 (10%, 19/295), with a statistically significant number of the latter being of T-lineage as opposed to pre-B (P < 0.001). A small number of patients (2%, 6/295) also overexpressed both Pgp and MRP1. Additional patients expressed increased levels of LRP. Elevated levels of these proteins at diagnosis did not correlate with risk factors and did not predict an adverse prognosis. Life-table estimates and Kaplan-Meier plots did not show any significant differences between patients who overexpressed an MDR protein compared with those who did not, nor was any difference noted when the different MDR + groups were compared with one another. These data strongly support the conclusion that the overexpression of these functional drug efflux pumps at diagnosis does not contribute to treatment failure in pediatric ALL.

Drug therapy for acute myeloid leukemia

Although improvement in outcomes has occurred in younger adults with acute myeloid leukemia (AML) during the past 4 decades, progress in older adults has been much less conspicuous, if at all. Approximately 50% to 75% of adults with AML achieve complete remission (CR) with cytarabine and an anthracycline such as daunorubicin or idarubicin or the anthracenedione mitoxantrone. However, only approximately 20% to 30% of the patients enjoy long-term disease survival. Various postremission strategies have been explored to eliminate minimal residual disease. The optimal dose, schedule, and number of cycles of postremission chemotherapy for most patients are not known. A variety of prognostic factors can predict outcome and include the karyotype of the leukemic cells and the presence of transmembrane transporter proteins, which extrude certain chemotherapy agents from the cell and confer multidrug resistance and mutations in or over expressions of specific genes such as WT1, CEBPA, BAX and the ratio of BCL2 to BAX, BAALC, EVI1, KIT, and FLT3. Most recently, insights into the molecular pathogenesis of AML have led to the development of more specific targeted agents and have ushered in an exciting new era of antileukemia therapy. Such agents include the immunoconjugate gemtuzumab ozogamicin, multidrug resistance inhibitors, farnesyl transferase inhibitors, histone deacetylase and proteosome inhibitors, antiangiogenesis agents, Fms-like tyrosine kinase 3 (FLT3) inhibitors, and apoptosis inhibitors.

Cyclosporin A is a broad-spectrum multidrug resistance modulator

PURPOSE

Overexpression of the multidrug resistance proteins P-glycoprotein (Pgp), multidrug resistance protein (MRP-1), breast cancer resistance protein (BCRP), and lung resistance protein (LRP) is associated with treatment failure in acute myeloid leukemia (AML) and other malignancies. The Pgp modulator cyclosporin A has shown clinical efficacy in AML, whereas its analogue PSC-833 has not. Cyclosporin A is known to also modulate MRP-1, and we hypothesized that broad-spectrum multidrug resistance modulation might contribute to its clinical efficacy.

EXPERIMENTAL DESIGN

We studied the effects of cyclosporin A and PSC-833 on in vitro drug retention and cytotoxicity in resistant cell lines overexpressing Pgp, MRP-1, and BCRP and on nuclear-cytoplasmic drug distribution and cytotoxicity in cells overexpressing LRP. Cellular drug content was assessed by flow cytometry and nuclear-cytoplasmic drug distribution by confocal microscopy.

RESULTS

Cyclosporin A enhanced retention of the substrate drug mitoxantrone in cells overexpressing Pgp (HL60/VCR), MRP-1 (HL60/ADR), and BCRP (8226/MR20, HEK-293 482R) and increased cytotoxicity 6-, 4-, 4-, and 3-fold, respectively. Moreover, cyclosporin A enhanced nuclear distribution of doxorubicin in 8226/MR20 cells, which also express LRP, and increased doxorubicin cytotoxicity 12-fold without an effect on cellular doxorubicin content, consistent with expression of wild-type BCRP, which does not efflux doxorubicin. Cyclosporin A also enhanced nuclear doxorubicin distribution in a second cell line with LRP overexpression, HT1080/DR4. PSC-833 enhanced mitoxantrone retention and cytotoxicity in cells overexpressing Pgp, but had no effect in cells overexpressing MRP-1, BCRP, or LRP.

CONCLUSIONS

Cyclosporin A modulates Pgp, MRP-1, BCRP, and LRP, and this broad-spectrum activity may contribute to its clinical efficacy.

Tumour stem cells and drug resistance

The contribution of tumorigenic stem cells to haematopoietic cancers has been established for some time, and cells possessing stem-cell properties have been described in several solid tumours. Although chemotherapy kills most cells in a tumour, it is believed to leave tumour stem cells behind, which might be an important mechanism of resistance. For example, the ATP-binding cassette (ABC) drug transporters have been shown to protect cancer stem cells from chemotherapeutic agents. Gaining a better insight into the mechanisms of stem-cell resistance to chemotherapy might therefore lead to new therapeutic targets and better anticancer strategies.

Dose escalation studies of cytarabine, daunorubicin, and etoposide with and without multidrug resistance modulation with PSC-833 in untreated adults with acute myeloid leukemia younger than 60 years: final induction results of Cancer and Leukemia Group B Study 9621

PURPOSE

P-glycoprotein (Pgp) is strongly inhibited by PSC-833. A chemotherapy dose-escalation study was performed with PSC-833 in patients younger than 60 years with untreated acute myeloid leukemia. Clinical rather than pharmacokinetic end points were used to develop two induction therapies containing drugs susceptible to Pgp-mediated efflux and associated with comparable toxicities at the maximum-tolerated doses.

PATIENTS AND METHODS

A total of 410 patients were enrolled. Fifteen induction regimens containing variable doses of daunorubicin (DNR) and etoposide (ETOP) and fixed doses of cytarabine were evaluated with (ADEP) or without (ADE) a fixed dose of PSC-833.

RESULTS

Doses selected for phase III testing were DNR 90 mg/m(2) and ETOP 100 mg/m(2) in ADE, and DNR and ETOP each 40 mg/m(2) in ADEP. Intolerable mucosal toxicity occurred at higher doses of ADEP. Although the design of this study precludes direct comparisons, there was an apparent advantage for receiving ADEP with respect to disease-free and overall survival in patients < or = 45 years old, despite the significantly lower doses of DNR and ETOP given in ADEP compared with ADE.

CONCLUSION

A large clinical data set was used to develop induction regimens containing two drugs susceptible to Pgp-mediated efflux, with and without an inhibitor of Pgp function. The chosen doses have comparable antileukemia activity and toxicity, making them suitable for use in a phase III comparative study of induction chemotherapy for patients with acute myeloid leukemia younger than 60 years. That trial will also clarify whether patients < or = 45 years old are especially likely to benefit from Pgp inhibition during induction therapy.