Comparison of 'sequential' versus 'standard' chemotherapy as re-induction treatment, with or without cyclosporine, in refractory/relapsed acute myeloid leukaemia (AML): results of the UK Medical Research Council AML-R trial

[CLAG±DAC regimen in the treatment of refractory/relapsed acute myeloid leukemia]

Objective: To investigate the efficacy and prognosis of CLAG±DAC (Clofarabine, Cytarabine, G-CSF±Decitabine) chemotherapy in patients with relapsed/refractory acute myeloid leukemia (R/R AML) . Methods: Continuous cases of R/R AML treated with the CLAG+DAC protocol or CLAG alone at the First Affiliated Hospital of Soochow University from January 2017 to December 2021 were retrospectively analyzed. The baseline characteristics, individual treatment regimen, treatment effect, disease progression, and survival status of patients were recorded. The factors influencing the efficacy of the CLAG±DAC chemotherapy regimens were analyzed, and the overall survival (OS) time after reinduction was calculated using the Kaplan-Meier method. Results: This study included a total of 53 patients, with 33 male patients and an average age of 40.6 years. Thirty-three patients achieved complete remission (CR+CRi) of the disease after the CLAG±DAC chemotherapy regimen and six patients achieved partial remission (PR), while 14 did not. Thirty-two patients eventually underwent hematopoietic stem cell transplantation, and the median OS of the patients was 55.9 months until follow-up. Patients with disease remission after the application of the CLAG±DAC chemotherapy had a significantly longer survival time than those without remission (P<0.001). The results of the multifactorial analysis have revealed that combined DAC (OR=4.60, 95% CI 1.14-23.5, P=0.04) and DNMT3A mutation (OR=0.14, 95% CI 0.01-0.89, P=0.05) were the factors influencing the efficacy of the CLAG±DAC chemotherapy regimen. The remission rate was relatively higher in patients with R/R AML combined with FLT3-ITD mutation by applying the DAC+CLAG regimen (OR=10.84, 95%CI 1.48-288.50, P=0.04) . Conclusion: The CLAG±DAC regimen is considered effective in patients with R/R AML, whereas decitabine combined with the CLAG regimen is more suitable for patients with R/R AML combined with FLT3-ITD mutation.

A clinical trial of zosuquidar plus gemtuzumab ozogamicin (GO) in relapsed or refractory acute myeloid leukemia (RR AML): evidence of efficacy based on leukemic blast P-glycoprotein functional phenotype

PURPOSE

To evaluate safety, tolerability, potential efficacy, and pharmacodynamics (PD) of zosuquidar (Zos) in combination with gemtuzumab ozogamicin (GO) in elderly patients with relapsed or refractory (RR) acute myeloid leukemia (AML).

METHODS

Patients with RR AML (N = 41) were treated with Zos as a 48-h continuous intravenous infusion initiated 4 h prior to a 2-h infusion of GO on days 1 and 15. P-glycoprotein (P-gp) status of the patients' leukemic blasts and PD determinations were assessed with ex vivo bioassays. Patient outcomes were analyzed for the total cohort and as stratified into P-gp-positive (P-gp +) and P-gp-negative (P-gp‒) subgroups.

RESULTS

The eligible cohort exhibited a 34% overall remission rate (ORR), a composite of patients that exhibited complete remission (CR), CR with incomplete platelet recovery, or morphologic remission. Patients with 1st relapsed disease exhibited 40% ORR. P-gp phenotype did not significantly predict ORR. However, the P-gp + subgroup exhibited a greater median overall survival (OS) of 6.0 months vs. 1.8 months for patients in the P-gp‒ subgroup (p = 0.01). PD analyses revealed 90-95% inhibition of blast P-gp function during Zos infusion. Treatment related toxicities were observed and resolved with decrease or discontinued Zos or GO dosages.

CONCLUSIONS

Zos plus GO elicited appreciable ORR for an elderly patient population with RR AML. The greater OS of the P-gp + subgroup vs. the P-gp‒ subgroup suggests that patients with P-gp + leukemic blasts were being more effectively targeted by GO with Zos co-therapy. The poorer OS of the P-gp‒ subgroup suggests activity of Zos-insensitive multidrug resistant mechanisms.

CLINICAL TRIALS

GOV IDENTIFIER

NCT00233909; First posted October 06, 2005.

Infigratinib (BGJ 398), a Pan-FGFR Inhibitor, Targets P-Glycoprotein and Increases Chemotherapeutic-Induced Mortality of Multidrug-Resistant Tumor Cells

The microtubule-targeting agents (MTAs) are well-known chemotherapeutic agents commonly used for therapy of a broad spectrum of human malignancies, exhibiting epithelial origin, including breast, lung, and prostate cancer. Despite the impressive response rates shortly after initiation of MTA-based therapy, the vast majority of human malignancies develop resistance to MTAs due to the different mechanisms. Here, we report that infigratinib (BGJ 398), a potent FGFR1-4 inhibitor, restores sensitivity of a broad spectrum of ABCB1-overexpressing cancer cells to certain chemotherapeutic agents, including paclitaxel (PTX) and doxorubicin (Dox). This was evidenced for the triple-negative breast cancer (TNBC), and gastrointestinal stromal tumor (GIST) cell lines, as well. Indeed, when MDR-overexpressing cancer cells were treated with a combination of BGJ 398 and PTX (or Dox), we observed a significant increase of apoptosis which was evidenced by an increased expression of cleaved forms of PARP, caspase-3, and increased numbers of Annexin V-positive cells, as well. Moreover, BGJ 398 used in combination with PTX significantly decreased the viability and proliferation of the resistant cancer cells. As expected, no apoptosis was found in ABCB1-overexpressing cancer cells treated with PTX, Dox, or BGJ 398 alone. Inhibition of FGFR-signaling by BGJ 398 was evidenced by the decreased expression of phosphorylated (i.e., activated) forms of FGFR and FRS-2, a well-known adaptor protein of FGFR signaling, and downstream signaling molecules (e.g., STAT-1, -3, and S6). In contrast, expression of MDR-related ABC-transporters did not change after BGJ 398 treatment, thereby suggesting an impaired function of MDR-related ABC-transporters. By using the fluorescent-labeled chemotherapeutic agent PTX-Alexa488 (Flutax-2) and doxorubicin, exhibiting an intrinsic fluorescence, we found that BGJ 398 substantially impairs their efflux from MDR-overexpressing TNBC cells. Moreover, the efflux of Calcein AM, a well-known substrate for ABCB1, was also significantly impaired in BGJ 398-treated cancer cells, thereby suggesting the ABCB1 as a novel molecular target for BGJ 398. Of note, PD 173074, a potent FGFR1 and VEGFR2 inhibitor failed to retain chemotherapeutic agents inside ABCB1-overexpressing cells. This was consistent with the inability of PD 173074 to sensitize Tx-R cancer cells to PTX and Dox. Collectively, we show here for the first time that BGJ 398 reverses the sensitivity of MDR-overexpressing cancer cells to certain chemotherapeutic agents due to inhibition of their efflux from cancer cells via ABCB1-mediated mechanism.

Allogeneic Stem Cell Transplantation with Sequential Melphalan-Based Conditioning in AML: Residual Morphological Blast Count Determines the Risk of Relapse

Introduction

Allogeneic hematopoietic cell transplantation (HCT) during chemotherapy-induced aplasia may offer long-term survival in acute myeloid leukemia (AML) with otherwise poor prognosis including ELN adverse risk, relapsed or refractory disease. However, the value of residual morphologic disease prior HCT in this context has not been conclusively settled until yet. Therefore, we aimed to investigate variables predicting outcome in this unique setting of sequential conditioning therapy, with a focus on pretreatment morphologic blast count. In contrast to the most popular FLAMSA-RIC protocol, we used a melphalan-based conditioning regimen during aplasia.

Methods

We retrospectively analyzed data from 173 AML patients who underwent a sequential melphalan-based conditioning therapy between 2003 and 2015 at our centre. All patients participated either in the prospective Phase 2 BRIDGE trial (NCT01295307), the Phase 3 AML2003 study (NCT00180102) or were treated according to this protocol and underwent allogeneic HCT after melphalan-based conditioning in treatment-induced aplasia.

Results

Median bone marrow blast count prior to conditioning was 10% (range, 0–96%). Four year probabilities of EFS and OS were 34% (95% CI, 28–43%) and 43% (95% CI, 36–52%), respectively. In multivariate analysis, blast count >20% was associated with worse EFS (HR = 1.93; p = 0.009) and OS (HR = 1.80; p = 0.026). This effect was not significant anymore for HCT during 1st line therapy.

Conclusion

Allogeneic HCT in aplasia with a melphalan-based conditioning regimen has the potential to cure a subset of adverse risk AML patients, even with persistent morphological disease prior HCT. However, a high pre-transplant blast count still indicates patients with a dismal prognosis, especially in the relapsed patient group, for whom post-transplant strategies should be considered to further optimize post HCT outcome.

Drug resistance: from bacteria to cancer

The phenomenon of drug resistance has been a hindrance to therapeutic medicine since the late 1940s. There is a plethora of factors and mechanisms contributing to progression of drug resistance. From prokaryotes to complex cancers, drug resistance is a prevailing issue in clinical medicine. Although there are numerous factors causing and influencing the phenomenon of drug resistance, cellular transporters contribute to a noticeable majority. Efflux transporters form a huge family of proteins and are found in a vast number of species spanning from prokaryotes to complex organisms such as humans. During the last couple of decades, various approaches in analyses of biochemistry and pharmacology of transporters have led us to understand much more about drug resistance. In this review, we have discussed the structure, function, potential causes, and mechanisms of multidrug resistance in bacteria as well as cancers.

Genomic stability at the coding regions of the multidrug transporter gene ABCB1: insights into the development of alternative drug resistance mechanisms in human leukemia cells

AIM

Despite considerable efforts to reverse clinical multidrug resistance (MDR), targeting the predominant multidrug transporter ABCB1/P-glycoprotein (P-gp) using small molecule inhibitors has been unsuccessful, possibly due to the emergence of alternative drug resistance mechanisms. However, the non-specific P-gp inhibitor cyclosporine (CsA) showed significant clinical benefits in patients with acute myeloid leukemia (AML), which likely represents the only proof-of-principle clinical trial using several generations of MDR inhibitors. Nevertheless, the mutational mechanisms that may underlie unsuccessful MDR modulation by CsA are not elucidated because of the absence of CsA-relevant cellular models. In this study, our aims were to establish CsA-resistant leukemia models and to examine the presence or absence of ABCB1 exonic mutations in these models as well as in diverse types of human cancer samples including AMLs.

METHODS

Drug-resistant lines were established by stepwise drug co-selection and characterized by drug sensitivity assay, rhodamine-123 accumulation, [3H]-labeled drug export, ABCB1 cDNA sequencing, and RNase protection assay. The genomic stability of the ABCB1 coding regions was evaluated by exome sequencing analysis of variant allele frequencies in human populations. Moreover, the mutational spectrum of ABCB1 was further assessed in diverse types of cancer samples including AMLs in the Cancer Genome Atlas (TCGA) at the National Cancer Institute.

RESULTS

We report the development of two erythroleukemia variants, RVC and RDC, which were derived by stepwise co-selection of K562/R7 drug-resistant leukemia cells with the etoposide-CsA and doxorubicin-CsA drug combinations, respectively. Interestingly, both RVC and RDC cell lines, which retained P-gp expression, showed altered multidrug-resistant phenotypes that were resistant to CsA modulation. Strikingly, no mutations were found in the ABCB1 coding regions in these variant cells even under long-term stringent drug selection. Genomically, ABCB1 displayed relatively low variant allele frequencies in human populations when compared with several ABC superfamily members. Moreover, ABCB1 also exhibited a very low mutational frequency in AMLs compared with all types of human cancer. In addition, we found that CsA played a role in undermining the selection of highly drug-resistant cells via induction of low-level and unstable drug resistance.

CONCLUSION

Our data indicate that ABCB1 coding regions are genomically stable and relatively resistant to drug-induced mutations. Non-ABCB1 mutational mechanisms are responsible for the drug-resistant phenotypes in both RVC and RDC cell lines, which are also prevalent in clinical AML patients. Accordingly, we propose several relevant models that account for the development of alternative drug resistance mechanisms in the absence of ABCB1 mutations.

The Evolving AML Genomic Landscape: Therapeutic Implications

Improved understanding of the genomic and molecular landscape of acute myeloid leukemia (AML) has resulted in a significant evolution of our understanding of AML biology and allows refined prognostication for those receiving standard combination chemotherapy induction. This dramatic increase in knowledge preceded, and was somewhat responsible for, at least some of eight new FDA drug approvals for AML. This review discusses the impact of genomics on clinical care of AML patients and highlights newly approved FDA drugs. Despite these recent clinical advances, however, the outcome for most patients diagnosed with AML remains dire. Thus, we describe here some of the challenges identified with treating AML including off-target toxicity, drug transporters, clonal heterogeneity, and adaptive resistance, and some of the most promising opportunities for improved therapy.

Topoisomerase II inhibitors in AML: past, present, and future

Introduction: Topoisomerase II inhibitors have long been used in the frontline and as salvage therapy for AML, with daunorubicin and idarubicin being prototypical agents in this therapeutic class, classically in combination with nucleoside analogs, e.g. cytarabine. Most recently, several other compounds from this drug class have or are being investigated. Areas covered: The current paper reviews older and newer topoisomerase II inhibitors in clinical development for the treatment of AML. The authors discuss the clinical use of these agents, current trials involving them as well as their safety profile. Important side effects of these medications including therapy-related AML (t-AML) are also covered. Expert opinion: Topoisomerase II inhibitors have helped improve outcomes in AML. Recently, the FDA approved several agents including CPX-351 for the treatment of secondary and t-AML. CPX-351 may have applicability in other high-risk myeloid diseases. Future directions include a combination of these agents with other targeted therapies. Finally, the authors believe that small molecule inhibitors, such as venetoclax and possibly immunotherapy options could also be incorporated to our treatment paradigm in selected patients.

Daunorubicin and cytarabine for certain types of poor-prognosis acute myeloid leukemia: a systematic literature review

INTRODUCTION

Induction chemotherapy based on anthracyclines and cytarabine (Ara-C) combination remains the standard of care for acute myeloid leukemia (AML) patients who are considered candidate for intensive and curative approaches. However, the toxicity of this regimen is high, with disappointing clinical outcomes among the so-called poor-prognosis AML subsets, which generally refer to patients with adverse cytogenetic risk, secondary AML including therapy-related AML, poor-prognosis mutations, especially FLT3-ITD, and relapse/refractory AML. Areas covered: To the best of our knowledge, the role and efficacy of 7 + 3 schedules containing daunorubicin (DNR) and Ara-C for certain types of poor-prognosis AML has not been systematically assessed. A critical approach to the role of DNR and Ara-C induction could be relevant to establish which patients should be enrolled in clinical trials using novel therapies. Expert commentary: In this regard, a recent randomized clinical trial (RCT) showed improved results in older patients with sAML or high-risk cytogenetics who received CPX-351 compared with standard 7 + 3 combination. We perform a systematic literature review to analyze the clinical outcomes reported with DNR plus Ara-C regimens in adult patients with poor-prognosis AML, the use of liposomal formulations of DNR and Ara-C and the RCTs which compared standard 7 + 3 with the addition of a third drug.

Evidence of a role for functional heterogeneity in multidrug resistance transporters in clinical trials of P-glycoprotein modulation in acute myeloid leukemia

BACKGROUND

Multidrug resistance (MDR) transporter proteins such as P-glycoprotein (P-gp) efflux a variety of chemotherapeutic drugs from acute myeloid leukemia (AML) blasts leading to clinical drug resistance.

METHODS

This study examined heterogeneity of MDR functional efflux by AML blasts using two flow cytometry bioassays. Bone marrow specimens (N = 50) from elderly patients with newly diagnosed AML were analyzed for CD34+ blasts with MDR efflux function. Efflux was measured with a fluorescent dye (DiOC₂ ) as a surrogate for oncology drugs that are substrates for MDR efflux. P-gp-mediated efflux was differentiated from non-P-gp MDR activities using zosuquidar, a highly selective P-gp modulator. The bioassays included a zosuquidar-dependent DiOC₂ accumulation bioassay that measured only P-gp. The second method, termed the efflux bioassay, could detect P-gp and other non-P-gp efflux depending on bioassay culture conditions.

RESULTS

Sixty-two percent of the specimens were considered positive for blasts with P-gp function, and 26% of such P-gp-positive specimens also exhibited zosuquidar-resistant (i.e., non-P-gp) MDR efflux activity; 37% of P-gp-negative AML blast specimens displayed zosuquidar-resistant MDR function in the efflux bioassay.

CONCLUSIONS

These results confirm the heterogeneous nature of MDR efflux pumps in AML blasts, and provide support for the hypothesis that non-P-gp MDR contributed to negative results with zosuquidar in AML trials like ECOG-ACRIN E3999. © 2018 International Clinical Cytometry Society.

Vosaroxin plus cytarabine versus placebo plus cytarabine in patients with first relapsed or refractory acute myeloid leukaemia (VALOR): a randomised, controlled, double-blind, multinational, phase 3 study

BACKGROUND

Safe and effective treatments are urgently needed for patients with relapsed or refractory acute myeloid leukaemia. We investigated the efficacy and safety of vosaroxin, a first-in-class anticancer quinolone derivative, plus cytarabine in patients with relapsed or refractory acute myeloid leukaemia.

METHODS

This phase 3, double-blind, placebo-controlled trial was undertaken at 101 international sites. Eligible patients with acute myeloid leukaemia were aged 18 years of age or older and had refractory disease or were in first relapse after one or two cycles of previous induction chemotherapy, including at least one cycle of anthracycline (or anthracenedione) plus cytarabine. Patients were randomly assigned 1:1 to vosaroxin (90 mg/m(2) intravenously on days 1 and 4 in a first cycle; 70 mg/m(2) in subsequent cycles) plus cytarabine (1 g/m(2) intravenously on days 1-5) or placebo plus cytarabine through a central interactive voice system with a permuted block procedure stratified by disease status, age, and geographical location. All participants were masked to treatment assignment. The primary efficacy endpoint was overall survival and the primary safety endpoint was 30-day and 60-day all-cause mortality. Efficacy analyses were done by intention to treat; safety analyses included all treated patients. This study is registered with ClinicalTrials.gov, number NCT01191801.

FINDINGS

Between Dec 17, 2010, and Sept 25, 2013, 711 patients were randomly assigned to vosaroxin plus cytarabine (n=356) or placebo plus cytarabine (n=355). At the final analysis, median overall survival was 7·5 months (95% CI 6·4-8·5) in the vosaroxin plus cytarabine group and 6·1 months (5·2-7·1) in the placebo plus cytarabine group (hazard ratio 0·87, 95% CI 0·73-1·02; unstratified log-rank p=0·061; stratified p=0·024). A higher proportion of patients achieved complete remission in the vosaroxin plus cytarabine group than in the placebo plus cytarabine group (107 [30%] of 356 patients vs 58 [16%] of 355 patients, p<0·0001). Early mortality was similar between treatment groups (30-day: 28 [8%] of 355 patients in the vosaroxin plus cytarabine group vs 23 [7%] of 350 in the placebo plus cytarabine group; 60-day: 70 [20%] vs 68 [19%]). Treatment-related deaths occurred at any time in 20 (6%) of 355 patients given vosaroxin plus cytarabine and in eight (2%) of 350 patients given placebo plus cytarabine. Treatment-related serious adverse events occurred in 116 (33%) and 58 (17%) patients in each group, respectively. Grade 3 or worse adverse events that were more frequent in the vosaroxin plus cytarabine group than in the placebo plus cytarabine group included febrile neutropenia (167 [47%] vs 117 [33%]), neutropenia (66 [19%] vs 49 [14%]), stomatitis (54 [15%] vs 10 [3%]), hypokalaemia (52 [15%] vs 21 [6%]), bacteraemia (43 [12%] vs 16 [5%]), sepsis (42 [12%] vs 18 [5%]), and pneumonia (39 [11%] vs 26 [7%]).

INTERPRETATION

Although there was no significant difference in the primary endpoint between groups, the prespecified secondary analysis stratified by randomisation factors suggests that the addition of vosaroxin to cytarabine might be of clinical benefit to some patients with relapsed or refractory acute myeloid leukaemia.

FUNDING

Sunesis Pharmaceuticals.

High receptor tyrosine kinase (FLT3, KIT) transcript versus anti-apoptotic (BCL2) transcript ratio independently predicts inferior outcome in pediatric acute myeloid leukemia

OBJECTIVE

In acute myeloid leukemia (AML), simultaneous expression of proliferative (FLT3, KIT) and anti-apoptotic genes (BCL2) is unknown. The aim of the study was to prospectively evaluate proliferative and anti-apoptotic gene transcripts, their interrelationship and impact on the outcome in pediatric AML patients.

METHODS

We assessed proliferative and anti-apoptotic gene transcripts by Q-polymerase chain reaction (TaqMan probe) in 64 consecutive pediatric AML patients. Survival data was analyzed by Kaplan-Meier curves followed by log rank test to compare statistical significance between groups. Stepwise multivariable Cox regression method was used to evaluate independent prognostic factors.

RESULTS

In univariate analysis, transcript ratio of FLT3/BCL2 and FLT3+KIT/BCL2 significantly predicted event free survival (EFS) (<0.01 and <0.01 respectively) and overall survival (OS) (<0.01 and<0.01 respectively). In stepwise Cox-regression model, high white blood cell count and high FLT3+KIT/BCL2 ratio predicted EFS (HR: 2.2 and 2.3); high hemoglobin and high FLT3+KIT/BCL2 ratio predicted OS (HR: 0.45 and 3.85). Prognostic index (PI) was calculated using the hazard coefficient of independent prognostic factors; at 57.3 months, predicted OS of patients with the highest PI of 1.8 was 8% versus 73% for the lowest PI of -0.3. The mean PI of patients who died was 1.8±0.72 versus 0.54±0.70 for those who are alive, P=0.004.

CONCLUSIONS

This first study showed that individual expression of proliferative and anti-apoptotic transcripts is not as important in AML patients, rather their interrelationship and relative level probably determines the outcome.

The modulation of ABC transporter-mediated multidrug resistance in cancer: a review of the past decade

ATP-binding cassette (ABC) transporters represent one of the largest and oldest families of membrane proteins in all extant phyla from prokaryotes to humans, which couple the energy derived from ATP hydrolysis essentially to translocate, among various substrates, toxic compounds across the membrane. The fundamental functions of these multiple transporter proteins include: (1) conserved mechanisms related to nutrition and pathogenesis in bacteria, (2) spore formation in fungi, and (3) signal transduction, protein secretion and antigen presentation in eukaryotes. Moreover, one of the major causes of multidrug resistance (MDR) and chemotherapeutic failure in cancer therapy is believed to be the ABC transporter-mediated active efflux of a multitude of structurally and mechanistically distinct cytotoxic compounds across membranes. It has been postulated that ABC transporter inhibitors known as chemosensitizers may be used in combination with standard chemotherapeutic agents to enhance their therapeutic efficacy. The current paper reviews the advance in the past decade in this important domain of cancer chemoresistance and summarizes the development of new compounds and the re-evaluation of compounds originally designed for other targets as transport inhibitors of ATP-dependent drug efflux pumps.

Repositioning of Tyrosine Kinase Inhibitors as Antagonists of ATP-Binding Cassette Transporters in Anticancer Drug Resistance

The phenomenon of multidrug resistance (MDR) has attenuated the efficacy of anticancer drugs and the possibility of successful cancer chemotherapy. ATP-binding cassette (ABC) transporters play an essential role in mediating MDR in cancer cells by increasing efflux of drugs from cancer cells, hence reducing the intracellular accumulation of chemotherapeutic drugs. Interestingly, small-molecule tyrosine kinase inhibitors (TKIs), such as AST1306, lapatinib, linsitinib, masitinib, motesanib, nilotinib, telatinib and WHI-P154, have been found to have the capability to overcome anticancer drug resistance by inhibiting ABC transporters in recent years. This review will focus on some of the latest and clinical developments with ABC transporters, TKIs and anticancer drug resistance.

Relative receptor tyrosine kinases and anti-apoptotic transcripts hold potential for predicting inferior outcome in adult acute myeloid leukemia: a prospective pilot study

INTRODUCTION

Acute myeloid leukemia is characterized by accumulation of immature cells because of imbalance between proliferation and apoptosis. In AML, simultaneous expression of proliferative (FLT-3, c-KIT) and antiapoptotic genes (BCL-2), are unknown.

PATIENTS AND METHODS

We prospectively assessed proliferative and antiapoptotic gene transcripts using Taqman probe chemistry in 48 adult AML patients. A stepwise Cox regression model was applied for independent prognostic factors.

RESULTS

Thirty-two of 48 (75%) patients achieved complete remission. At follow-up ranging from 0.5 to 57.3 months, event-free survival (EFS) was 26.9 ± 6.3% (range, 15.5%-39.6%) and OS 34.5 ± 7.46% (range, 20.5%-48.9%). High white blood cell count correlated with an inferior complete remission rate (P = .021). Cytogenetics and FLT-3 internal tandem duplication did not predict EFS or OS. The transcripts of FLT-3, c-KIT, and BCL-2 showed a significant linear association with each other in Pearson correlation (FLT-3 vs. c-KIT: R = 0.8234; P < .001; c-KIT vs. BCL-2: R = 0.3377; P = .01; FLT-3 vs. BCL-2: R = 0.3815; P = .007). In a validation cohort (Microarray Data Set GSE1159) of adult AML patients, the global gene expression profile depicted a similar interrelationship. Patients with a greater platelet count were associated with increased transcript levels of BCL-2 (P = .034). In univariate analysis, a high transcript level of FLT-3 and high transcript ratio of FLT-3/BCL-2 and FLT-3 and c-KIT/BCL-2 significantly predicted OS (P = .043, .028, and .028, respectively). In a stepwise Cox regression model, high FLT-3 and c-KIT/BCL-2 ratio predicted OS (HR, 2.29).

CONCLUSION

To our knowledge, this is the first study that evaluated proliferative and antiapoptotic transcripts simultaneously, and results have shown that it is the relative levels of these transcripts that determine outcome in AML patients rather than their expression in isolation.

Quantitative assessment of BAX transcript and flow cytometric expression in acute myeloid leukemia: a prospective study

OBJECTIVE

Quantitative assessment of BAX transcripts and protein in acute myeloid leukemia (AML).

METHODS

We quantitatively evaluated BAX gene transcripts by real-time polymerase chain reaction (TaqMan probe chemistry) and protein expression by flow cytometry.

RESULTS

Consecutive 112 AML patients with a median age of 16 (1-59) years were recruited in the study. By flow cytometry, the percentage expression was in linear correlation with relative median fluorescent intensity (RMFI; R = 0.4425; P < 0.001). However, there was no linear relationship between the transcript copies of the BAX with its RMFI (R = -0.0559; P = 0.586). The expression of the BAX at both protein and transcript level was significantly higher in AML patients as compared with normal control. RMFI of the BAX were higher in the cohort with lower white blood cell count (P = 0.029). None of the other baseline characteristics correlated with either the BAX transcript or the RMFI. BAX expression did not correlate with complete remission rate, event free, disease free, and overall survival.

CONCLUSION

BAX gene expression in AML was evaluated first time with two different methods but did not correlate with the survival outcome.

BAX/BCL2 RMFI ratio predicts better induction response in pediatric patients with acute myeloid leukemia

BAX/BCL2 ratio in pediatric AML has not been evaluated. In this first prospective study, we evaluated BAX/BCL2 transcript and RMFI ratio in 64 patients using real-time PCR (TaqMan Probe chemistry) and flow-cytometry, respectively. There was no correlation of BAX/BCL2 transcript ratio with RMFI ratio (R = -0.05; P = 0.715). Patients with WBC count >50,000/mm(3) had lower BAX/BCL2 RMFI ratio (P = 0.043), whereas no difference in ratio was observed among patients of different cytogenetics subgroups (P = 0.786). Higher BAX/BCL2 RMFI ratio was associated positively with CR rate (P = 0.03), but this study was unable to show that it translated into improved EFS or OS.

Homoharringtonine in combination with cytarabine and aclarubicin in the treatment of refractory/relapsed acute myeloid leukemia: a single-center experience

To assess the efficacy and toxicity of HAA regimen (Homoharringtonine 4 mg/m(2)/day, days 1-3; cytarabine 150 mg/m(2)/day, days 1-7; aclarubicin 12 mg/m(2)/day, days 1-7) as a salvage therapy in the treatment of refractory and/or relapsed acute myeloid leukemia (AML), 46 patients with refractory and/or relapsed AML, median age 37 (16-65) years, participated in this clinical study. The median follow-up was 41 (10-86) months. Eighty percent of patients achieved complete remission (CR), and the first single course of re-induction HAA regimen resulted in CR rate of 76.1 %. The study protocol allowed two courses of induction. The CR rates of patients with favorable, intermediate and unfavorable cytogenetics were 90 %, 88.9 %, and 37.5 %, respectively. For all patients, the estimated 3-year overall survival (OS) rate was 42 %, and the estimated relapse free survival (RFS) at 3 years for the 36 CR cases was 49 %. The toxicities associated with HAA regimen were acceptable. HAA is a good choice in cases with refractory/relapsing AML for salvage chemotherapy, preferably with a high-efficacy and low-toxicity profile.

The clinically relevant pharmacogenomic changes in acute myelogenous leukemia

Acute myelogenous leukemia (AML) is an extremely heterogeneous neoplasm with several clinical, pathological, genetic and molecular subtypes. Combinations of various doses and schedules of cytarabine and different anthracyclines have been the mainstay of treatment for all forms of AMLs in adult patients. Although this combination, with the addition of an occasional third agent, remains effective for treatment of some young-adult patients with de novo AML, the prognosis of AML secondary to myelodysplastic syndromes or myeloproliferative neoplasms, treatment-related AML, relapsed or refractory AML, and AML that occurs in older populations remains grim. Taken into account the heterogeneity of AML, one size does not and should not be tried to fit all. In this article, the authors review currently understood, applicable and relevant findings related to cytarabine and anthracycline drug-metabolizing enzymes and drug transporters in adult patients with AML. To provide a prime-time example of clinical applicability of pharmacogenomics in distinguishing a subset of patients with AML who might be better responders to farnesyltransferase inhibitors, the authors also reviewed findings related to a two-gene transcript signature consisting of high RASGRP1 and low APTX, the ratio of which appears to positively predict clinical response in AML patients treated with farnesyltransferase inhibitors.

Importance of detecting multidrug resistance proteins in acute leukemia prognosis and therapy

Multidrug resistance (MDR) is a multifactorial phenomenon and the role of these proteins in generating the MDR phenotype is controversial. With this in mind, this review compiled the current data on the role of ABCB1, ABCC1, and LRP proteins in the prognosis of hematologic neoplasms and their influence on the choice of therapy. Literature showed that the detection of these proteins, mainly ABCB1, is important in the AL prognosis. However, there is controversy regarding the methodology used for their detection. In summary, the expression and activity profiles of ABCB1, ABCC1, and LRP, proteins capable of promoting the efflux of a variety of chemotherapeutic agents from the cell cytoplasm represent one of the greatest causes of failure in AL treatment.

Amonafide: a future in treatment of resistant and secondary acute myeloid leukemia?

Development of the novel topoisomerase II inhibitor, amonafide, began almost 40 years ago. The drug was selected for further investigation owing to evidence of marked antineoplastic efficacy in preclinical models of cancer. When its usefulness in the treatment of various solid malignancies proved limited, focus was shifted to establishing its use as an antileukemic agent, specifically against secondary and treatment-associated acute myeloid leukemia (AML). While Phase I and II studies gave rise to hopes that amonafide might hold the key to treating older patients, including those with multidrug resistant, cytogenetically unfavorable secondary and treatment-associated AML, when used in combination with cytarabine, it failed to demonstrate a survival advantage over standard-of-care therapy in randomized studies. This article will outline the development of amonafide from the laboratory to the bedside and discuss the potential place that this agent has in the current management of AML.

Drug resistance: still a daunting challenge to the successful treatment of AML

Resistance to chemotherapy remains a challenging issue for patients and their physicians. P-glycoprotein (Pgp, MDR1, ABCB1), as well as a family of structurally and functionally related proteins, are plasma membrane transporters able to efflux a variety of substrates from the cell cytoplasm, including chemotherapeutic agents. The discovery of ABCB1 made available a potential target for pharmacologic down-regulation of efflux-mediated chemotherapy resistance. In patients with acute myeloid leukemia (AML), a neoplasm characterized by proliferation of poorly differentiated myeloid progenitor cells, leukemic cells often express ABCB1 at high levels, which may lead to the development of resistance to chemotherapy. Thus, AML seemed to be a likely cancer for which the addition of drug efflux inhibitors to the chemotherapeutic regimen would improve outcomes in patients. Despite this rational hypothesis, the majority of clinical trials evaluating this strategy have failed to reach a positive endpoint, most recently the Eastern Cooperative Oncology Group E3999 trial. Here we review data suggesting the importance of ABCB1 in AML, address the failure of clinical trials to support a therapeutic strategy aimed at modulating ABCB1-mediated resistance, and consider the type of research that should be conducted in this field going forward.

Molecular pathways: regulation and therapeutic implications of multidrug resistance

Multidrug transporters constitute major mechanisms of MDR in human cancers. The ABCB1 (MDR1) gene encodes a well-characterized transmembrane transporter, termed P-glycoprotein (P-gp), which is expressed in many normal human tissues and cancers. P-gp plays a major role in the distribution and excretion of drugs and is involved in intrinsic and acquired drug resistance of cancers. The regulation of ABCB1 expression is complex and has not been well studied in a clinical setting. In this review, we elucidate molecular signaling and epigenetic interactions that govern ABCB1 expression and the development of MDR in cancer. We focus on acquired expression of ABCB1 that is associated with genomic instability of cancer cells, including mutational events that alter chromatin structures, gene rearrangements, and mutations in tumor suppressor proteins (e.g., mutant p53), which guard the integrity of genome. In addition, epigenetic modifications of the ABCB1 proximal and far upstream promoters by either demethylation of DNA or acetylation of histone H3 play a pivotal role in inducing ABCB1 expression. We describe a molecular network that coordinates genetic and epigenetic events leading to the activation of ABCB1. These mechanistic insights provide additional translational targets and potential strategies to deal with clinical MDR.

The controversial role of ABC transporters in clinical oncology

The phenomenon of multidrug resistance in cancer is often associated with the overexpression of the ABC (ATP-binding cassette) transporters Pgp (P-glycoprotein) (ABCB1), MRP1 (multidrug resistance-associated protein 1) (ABCC1) and ABCG2 [BCRP (breast cancer resistance protein)]. Since the discovery of Pgp over 35 years ago, studies have convincingly linked ABC transporter expression to poor outcome in several cancer types, leading to the development of transporter inhibitors. Three generations of inhibitors later, we are still no closer to validating the 'Pgp hypothesis', the idea that increased chemotherapy efficacy can be achieved by inhibition of transporter-mediated efflux. In this chapter, we highlight the difficulties and past failures encountered in the development of clinical inhibitors of ABC transporters. We discuss the challenges that remain in our effort to exploit decades of work on ABC transporters in oncology. In learning from past mistakes, it is hoped that ABC transporters can be developed as targets for clinical intervention.

AAML03P1, a pilot study of the safety of gemtuzumab ozogamicin in combination with chemotherapy for newly diagnosed childhood acute myeloid leukemia: a report from the Children's Oncology Group

BACKGROUND

The development of antigen-targeted therapies may provide additional options to improve outcomes in children with acute myeloid leukemia (AML). The Children's Oncology Group AAML03P1 trial sought to determine the safety of adding 2 doses of gemtuzumab ozogamicin, a humanized anti-CD33 antibody-targeted agent, to intensive chemotherapy during remission induction and postremission intensification for children with de novo AML.

METHODS

AAML03P1 enrolled 350 children with previously untreated AML. Patients with a matched family donor received 3 courses of chemotherapy followed by hematopoietic stem cell transplantation; those without a matched family donor received 5 courses of chemotherapy. Gemtuzumab ozogamicin 3 mg/m(2)/dose was administered on Day 6 of Course 1 and Day 7 of Course 4.

RESULTS

Toxicities observed in all courses of therapy were typical of AML chemotherapy regimens, with infection being most common. Patients achieved a complete remission rate of 83% after 1 course and 87% after 2 courses. The mortality rate was 1.5% after the first gemtuzumab ozogamicin-containing induction course and 2.6% after 2 induction courses. The 3-year event-free survival and overall survival rates were 53 ± 6% and 66 ± 5%, respectively.

CONCLUSIONS

This trial determined that it is safe and feasible to include gemtuzumab ozogamicin in combination with intensive chemotherapy. The survival rates compare favorably with the recently published results of clinical trials worldwide.

ATP Binding Cassette transporters associated with chemoresistance: transcriptional profiling in extreme cohorts and their prognostic impact in a cohort of 281 acute myeloid leukemia patients

BACKGROUND

A major issue in the treatment of acute myeloid leukemia is resistance to chemotherapeutic drugs. An increasing number of ATP-Binding-Cassette transporters have been demonstrated to cause resistance to cancer drugs. The aim of this study was to highlight the putative role of other ATP-Binding-Cassette transporters in primary chemoresistant acute myeloid leukemia.

DESIGN AND METHODS

In the first part of this study, using taqman custom arrays, we analyzed the relative expression levels of 49 ATP-Binding-Cassette genes in 51 patients divided into two extreme cohorts, one very sensitive and one very resistant to chemotherapy. In the second part of this study, we evaluated the prognostic impact, in a cohort of 281 patients, of ATP-Binding-Cassette genes selected in the first part of the study.

RESULTS

In the first part of the study, six genes (ATP-Binding-CassetteA2, ATP-Binding-CassetteB1, ATP-Binding-CassetteB6, ATP-Binding-CassettC13, ATP-Binding-CassetteG1, and ATP-Binding-CassetteG2) were significantly over-expressed in the resistant group compared with the sensitive group. In the second cohort, overexpression of 5 of these 6 ATP-Binding-Cassette genes was correlated with outcome in univariate analysis, and only the well-known ATP-Binding-CassetteB1 and G2, and the new ATP-Binding-CassetteG1 in multivariate analysis. Prognosis decreased remarkably with the number of these over-expressed ABC genes. Complete remission was achieved in 71%, 59%, 54%, and 0%, (P=0.0011) and resistance disease in 21%, 37%, 43%, and 100% (P<0.0001) of patients over-expressing 0, 1, 2, or 3, ABC genes, respectively. The number of ATP-Binding-Cassette genes expressed, among ATP-Binding-CassetteB1, G1, and G2, was the strongest prognostic factor correlated, in multivariate analysis, with achievement of complete remission (P=0.01), resistant disease (P=0.01), and overall survival (P=0.02).

CONCLUSIONS

Using expression profiling, we have emphasized the diversity of ATP-Binding-Cassette transporters that cooperate to promote chemoresistance rather than overexpression of single transporters and the putative role of new ATP-Binding-Cassette tranporters, such as ATP-Binding-CassetteG1. Modulation of these multiple transporters might be required to eradicate leukemic cells.

Zosuquidar, a novel modulator of P-glycoprotein, does not improve the outcome of older patients with newly diagnosed acute myeloid leukemia: a randomized, placebo-controlled trial of the Eastern Cooperative Oncology Group 3999

Zosuquidar, which modulates P-glycoprotein (P-gp) with minimal delay of anthracycline clearance, may reverse P-gp-mediated resistance in acute myeloid leukemia without increased toxicity. A total of 449 adults older than 60 years with acute myeloid leukemia or high-risk myelodysplastic syndrome enrolled in a randomized placebo-controlled double-blind trial (Eastern Cooperative Oncology Group 3999). Overall survival was compared between patients receiving conventional-dose cytarabine and daunorubicin and either zosuquidar (550 mg; 212 patients) or placebo (221 patients). Median and 2-year overall survival values were 7.2 months and 20% on zosuquidar and 9.4 months and 23% on placebo, respectively (P = .281). Remission rate was 51.9% on zosuquidar and 48.9% on placebo. All cause mortality to day 42 was not different (zosuquidar 22.2% vs placebo 16.3%; P = .158). In vitro modulation of P-gp activity by zosuquidar and expression of P-gp, multidrug resistance-related protein 1, lung resistance protein, and breast cancer resistance protein, were comparable in the 2 arms. Poor-risk cytogenetics were more common in P-gp(+) patients. P-gp expression and cytogenetics were correlated, though independent prognostic factors. We conclude that zosuquidar did not improve outcome in older acute myeloid leukemia, in part, because of the presence P-gp independent mechanisms of resistance. This trial is registered at www.clinicaltrials.gov as #NCT00046930.

Sequential phase II Southwest Oncology Group studies (S0112 and S0301) of daunorubicin and cytarabine by continuous infusion, without and with ciclosporin, in older patients with previously untreated acute myeloid leukaemia

Attempts to overcome multi-drug resistance in acute myeloid leukaemia (AML) have been limited by toxicities. To investigate the effect of reducing peak drug levels, we performed sequential phase II studies using continuous infusion daunorubicin and cytarabine without (AD) and then with ciclosporin (ADC) in older patients with AML. Untreated patients (age 56+ years) received daunorubicin (45 mg/m2 per day for 3 d) and cytarabine (200 mg/m2 per day for 7 d), both by continuous infusion, without (S0112, 60 patients) and then with (S0301, 50 patients) the addition of ciclosporin. Complete response (CR) rates were 38% on S0112 and 44% on S0301. Fatal induction toxicities occurred in 17% and 12% respectively, arising primarily from infection and haemorrhage. Median overall and relapse-free survival was 7 and 8 months for AD respectively, and 6 and 14 months for ADC. Patients with phenotypic or functional P-glycoprotein had somewhat higher CR rates with ADC than AD, although confidence intervals overlapped. In these sequential trials, continuous infusion AD produced CR rates comparable to those with bolus daunorubicin. The addition of ciclosporin did not cause undue toxicities, produced a similar CR rate, and possibly improved relapse-free survival. Further correlate analyses did not identify a subpopulation specifically benefitting from the addition of ciclosporin.

Pharmacogenomics in acute myeloid leukemia

Acute myeloid leukemia (AML) in adults is a heterogeneous malignant pathology with a globally unfavorable prognosis. The classification of AML allows identification of subgroups with favorable prognosis. However, besides these specific subgroups, most patients will have an intermediate or unfavorable prognosis often resulting in induction failure, probably due to drug resistance of the leukemic blasts, and more frequently resulting in early relapse after achieving complete remission. This unfavorable situation leads to a strong need to develop new diagnostic and therapeutic options. However, development of these therapies and their efficient use requires a better understanding of the biology and the molecular pathogenesis of AML. Pharmacogenomics focuses on the genetic variation of drug-metabolizing enzymes, targets and transporters, and how these genetic variations interact to produce specific drug-related phenotypes. Potential genetic markers may serve to functionally subclassify patients by their disease and therefore influence the nature and intensity of treatment. This review summarizes important aspects of and recent advances in the field of pharmacogenomics in AML.

The impact of dose escalation and resistance modulation in older patients with acute myeloid leukaemia and high risk myelodysplastic syndrome: the results of the LRF AML14 trial

The acute myeloid leukaemia (AML)14 trial addressed four therapeutic questions in patients predominantly aged over 60 years with AML and High Risk Myelodysplastic Syndrome: (i) Daunorubicin 50 mg/m(2) vs. 35 mg/m(2); (ii) Cytarabine 200 mg/m(2) vs. 400 mg/m(2) in two courses of DA induction; (iii) for part of the trial, patients allocated Daunorubicin 35 mg/m(2) were also randomized to receive, or not, the multidrug resistance modulator PSC-833 in a 1:1:1 randomization; and (iv) a total of three versus four courses of treatment. A total of 1273 patients were recruited. The response rate was 62% (complete remission 54%, complete remission without platelet/neutrophil recovery 8%); 5-year survival was 12%. No benefits were observed in either dose escalation randomization, or from a fourth course of treatment. There was a trend for inferior response in the PSC-833 arm due to deaths in induction. Multivariable analysis identified cytogenetics, presenting white blood count, age and secondary disease as the main predictors of outcome. Although patients with high Pgp expression and function had worse response and survival, this was not an independent prognostic factor, and was not modified by PSC-833. In conclusion, these four interventions have not improved outcomes in older patients. New agents need to be explored and novel trial designs are required to maximise prospects of achieving timely progress.

Novel postremission strategies in adults with acute myeloid leukemia

PURPOSE OF REVIEW

Given the high rates of relapse in acute myeloid leukemia (AML), there is tremendous opportunity for the development of new therapeutic strategies in the postremission state. Unfortunately, the currently available modalities for postremission therapy, namely chemotherapy, have proven largely ineffective in changing the natural history of AML. The challenges to overcome therapeutic failure in the minimal residual disease status may relate to an incomplete understanding of the mechanisms and cell populations that are directly related to disease relapse as well as suboptimal ability to identify patients at highest risk for relapse.

RECENT FINDINGS

Being a heterogeneous disease, relapsed AML is unlikely to emanate from one predominant mechanism; instead, there are likely multiple biologic factors at play that allow for clinical relapse to occur. These factors likely include multidrug resistance proteins, aberrant signal transduction pathways, survival of leukemia stem cells, microenvironmental interactions, and immune tolerance. Many novel strategies are in development that target these mechanisms, ranging from chemotherapeutic modalities, to signal transduction inhibitors, to upregulation of antileukemic immune responses.

SUMMARY

Understanding the underlying mechanisms of leukemic cell survival and resistance has spurred the development of novel therapeutic approaches to overcome these mechanisms in the hope of eradicating minimal residual disease and improving survival in AML.

Current and emerging therapies for acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a clonal disease characterized by the proliferation and accumulation of myeloid progenitor cells in the bone marrow, which ultimately leads to hematopoietic failure. The incidence of AML increases with age, and older patients typically have worse treatment outcomes than do younger patients.

OBJECTIVE

This review is focused on current and emerging treatment strategies for nonpromyelocytic AML in patients aged <60 years.

METHODS

A literature review was conducted of the PubMed database for articles published in English. Publications from 1990 through March 2009 were scrutinized, and the search was updated on August 26, 2009. The search terms used were: acute myeloid leukemia in conjunction with treatment, chemotherapy, stem cell transplantation, and immunotherapy. Clinical trials including adults with AML aged > or =19 years were selected for analysis. Conference proceedings from the previous 5 years of The American Society of Hematology, The European Hematology Association, and The American Society for Blood and Marrow Transplantation were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles.

RESULTS

Cytarabine (AraC) is the cornerstone of induction therapy and consolidation therapy for AML. A standard form of induction therapy consists of AraC (100-200 mg/m(2)), administered by a continuous infusion for 7 days, combined with an anthracycline, administered intravenously for 3 days. Consolidation therapy comprises treatment with additional courses of intensive chemotherapy after the patient has achieved a complete remission (CR), usually with higher doses of the same drugs as were used during the induction period. High-dose AraC (2-3 g/m(2)) is now a standard consolidation therapy for patients aged <60 years. Despite substantial progress in the treatment of newly diagnosed AML, 20% to 40% of patients do not achieve remission with the standard induction chemotherapy, and 50% to 70% of first CR patients are expected to relapse within 3 years. The optimum strategy at the time of relapse, or for patients with the resistant disease, remains uncertain. Allogeneic stem cell transplantation has been established as the most effective form of antileukemic therapy in patients with AML in first or subsequent remission. New drugs are being evaluated in clinical studies, including immunotoxins, monoclonal antibodies, nucleoside analogues, hypomethylating agents, farnesyltransferase inhibitors, alkylating agents, FMS-like tyrosine kinase 3 inhibitors, and multidrug-resistant modulators. However, determining the success of these treatment strategies ultimately requires well-designed clinical trials, based on stratification of the patient risk, knowledge of the individual disease, and the drug's performance status.

CONCLUSIONS

Combinations of AraC and anthracyclines are still the mainstay of induction therapy, and use of high-dose AraC is now a standard consolidation therapy in AML patients aged <60 years. Although several new agents have shown promise in treating AML, it is unlikely that these agents will be curative when administered as monotherapy; it is more likely that they will be used in combination with other new agents or with conventional therapy.

A phase I trial of continuous infusion of the multidrug resistance inhibitor zosuquidar with daunorubicin and cytarabine in acute myeloid leukemia

Zosuquidar is a potent and specific inhibitor of P-glycoprotein (P-gp). In preliminary experiments, blockade of P-gp for at least 12 h was required to reverse daunorubicin resistance. Because of the short half-life of zosuquidar, we performed a phase I trial of this drug as a 72-h infusion (CIV) in 16 patients during leukemic induction with daunorubicin and cytarabine. Study goals were to establish safety and determine the dose required for P-gp inhibition in NK cells and AML blasts. > 90% P-gp inhibition was achieved within 2h at a plasma threshold of 132 ng/ml zosuquidar. The recommended phase II dose of zosuquidar is 700 mg/day.

Cyclosporine diminishes multidrug resistance in K562/ADM cells and improves complete remission in patients with acute myeloid leukemia

This study was designed to investigate the effects of cyclosporine A (CsA) on a multidrug resistance cultured cell line, and its effect on complete remission in patients with acute myeloid leukemia (AML). A multidrug resistant K562/ADM cell line and drug-sensitive K562 cell line was used. The intracellular concentration of daunorubicin and the accumulation of Rhodamine 123 (Rh123) in the K562/ADM and K562 cells were evaluated. Clinical effects of CsA were also studied in 65 patients with AML. In the K562/ADM cells, the 50% of inhibition concentration (IC50) of daunorubicin only group was 23.0+/-5.2 micromol/L, which was greater than in other groups co-administered with CsA (1.2+/-4.8 micromol/L), verapamil (1.5+/-5.4 micromol/L) or CsA+verapamil (1.4+/-4.3 micromol/L) (all P<0.01). The relative fluorescence intensity of Rh123 in the K562/ADM cells treated with CsA and daunorubicin was increased from 48.9% to 69.8% (P<0.05). CsA also improved the complete remission rate in the AML patients (72.7% vs 21.9%, P<0.01). We conclude that CsA can significantly diminish the multidrug resistance in K562/ADM cells. It also enhances the complete remission rates in patients with AML. CsA may be used as an integral part of the chemotherapy for AML.

Addition of cyclosporin A to the combination of mitoxantrone and etoposide to overcome resistance to chemotherapy in refractory or relapsing acute myeloid leukaemia: a randomised phase II trial from HOVON, the Dutch-Belgian Haemato-Oncology Working Group for adults

Cyclosporin A (CsA) inhibits the P-gp pump that can be responsible for failure of cytostatic treatment in acute myeloid leukaemia (AML). Eighty patients with relapsing/refractory AML were randomly assigned to mitoxantrone (M) and etoposide (VP) (MVP) in unmitigated antileukaemic doses with or without CsA, to investigate if toxicity was manageable and if antileukaemic therapy could be improved. CsA did not delay haematological recovery, but fewer CsA patients received post-induction therapy because of haematological and non-haematological toxicity. CR rate was 43% for MVP and 53% for CsA; DFS was 9 and 8 months, and OS 8 and 9 months, respectively. Seventeen of 38 CR patients proceeded to stem cell transplantation (SCT). After a median follow-up of 66 months, six patients were still alive. Addition of CsA did not improve treatment outcome, possibly due to inadequate post-induction therapy as a result of increased toxicity.

Tariquidar (XR9576): a P-glycoprotein drug efflux pump inhibitor

P-glycoprotein actively transports structurally unrelated compounds out of cells, conferring the multidrug resistance phenotype in cancer. Tariquidar is a potent, specific, noncompetitive inhibitor of P-glycoprotein. Tariquidar inhibits the ATPase activity of P-glycoprotein, suggesting that the modulating effect is derived from the inhibition of substrate binding, inhibition of ATP hydrolysis or both. In clinical trials, tariquidar is tolerable and does not have significant pharmacokinetic interaction with chemotherapy. In patients, inhibition of P-glycoprotein has been demonstrated for 48 h after a single dose of tariquidar. Studies to assess a possible increase in toxicity of chemotherapy and the impact of P-glycoprotein inhibition on tumor response and patient outcome are ongoing. Tariquidar can be considered an ideal agent for testing the role of P-glycoprotein inhibition in cancer.

ABC transporter expression in hematopoietic stem cells and the role in AML drug resistance

ATP-binding cassette (ABC) transporters are known to play an important role in human physiology, toxicology, pharmacology, and numerous disorders including acute myeloid leukemia (AML). In AML only a few cells have properties allowing for ongoing proliferation and for expansion of this malignant disorder. These very primitive cells, referred to as leukemic stem cells, reside mostly in a quiescent cell cycle state. These cells have the capacity of self-renewal and are likely characterized by a high expression of a number of ABC transporters. In addition, over-expression of certain ABC transporters in leukemic cells has been associated with poor treatment outcome in AML patients. Therefore, to be able to improve diagnostics and therapies for AML patients, it may be important to better characterize this quiescent stem cell population. Particularly knowledge of the biology of highly expressed ABC transporters in these primitive leukemic cells might provide new insights to improve therapeutic options. This review provides an overview about ABC transporters and AML in general and particularly of the ABC transporters involved in multidrug resistance and cholesterol metabolism in primitive normal and leukemic cells.

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.

Fludarabine and cytosine are less effective than standard ADE chemotherapy in high-risk acute myeloid leukemia, and addition of G-CSF and ATRA are not beneficial: results of the MRC AML-HR randomized trial

The optimum chemotherapy schedule for reinduction of patients with high-risk acute myeloid leukemia (relapsed, resistant/refractory, or adverse genetic disease) is uncertain. The MRC AML (Medical Research Council Acute Myeloid Leukemia) Working Group designed a trial comparing fludarabine and high-dose cytosine (FLA) with standard chemotherapy comprising cytosine arabinoside, daunorubicin, and etoposide (ADE). Patients were also randomly assigned to receive filgrastim (G-CSF) from day 0 until neutrophil count was greater than 0.5 x 10(9)/L (or for a maximum of 28 days) and all-trans retinoic acid (ATRA) for 90 days. Between 1998 and 2003, 405 patients were entered: 250 were randomly assigned between FLA and ADE; 356 to G-CSF versus no G-CSF; 362 to ATRA versus no ATRA. The complete remission rate was 61% with 4-year disease-free survival of 29%. There were no significant differences in the CR rate, deaths in CR, relapse rate, or DFS between ADE and FLA, although survival at 4 years was worse with FLA (16% versus 27%, P = .05). Neither the addition of ATRA nor G-CSF demonstrated any differences in the CR rate, relapse rate, DFS, or overall survival between the groups. In conclusion these findings indicate that FLA may be inferior to standard chemotherapy in high-risk AML and that the outcome is not improved with the addition of either G-CSF or ATRA.