Identification of common genes and pathways underlying imatinib and nilotinib treatment in CML: a Bioinformatics Study

Imatinib (IMA) and nilotinib are the first and second generations of BCR-ABL tyrosine kinase inhibitors, which widely applied in chronic myeloid leukemia (CML) treatment. Here we aimed to provide new targets for CML treatment by transcriptome analysis. Microarray data GSE19567 was downloaded and analyzed from Gene Expression Omnibus (GEO) to identify common genes, which are downregulated or upregulated in K562-imatinib and K562-nilotinib treated cells. The differentially expressed genes (DEGs) were assessed, and STRING and Cytoscape were used to create the protein-protein interaction (PPI) network. In imatinib and nilotinib treated groups' comparison, there were common 626 upregulated and 268 downregulated genes, which were differentially expressed. The GO analysis represented the enrichment of DEGs in iron ion binding, protein tyrosine kinase activity, transcription factor activity, ATP binding, sequence-specific DNA binding, cytokine activity, the mitochondrion, sequence-specific DNA binding, plasma membrane and cell-cell adherens junction. KEGG pathway analysis revealed that downregulated DEGs were associated with pathways including microRNAs in cancer and PI3K-Akt signaling pathway. Furthermore, upregulated DEGs were involved in hematopoietic cell lineage, lysosome and chemical carcinogenesis. Among the upregulated genes, MYH9, MYH14, MYL10, MYL7, MYL5, RXRA, CYP1A1, FECH, AKR1C3, ALAD, CAT, CITED2, CPT1A, CYP3A5, CYP3A7, FABP1, HBD, HMBS and PPOX genes were found as hub genes. Moreover, 20 downregulated genes, YARS, AARS, SARS, GARS, CARS, IARS, RRP79, CEBPB, RRP12, UTP14A, PNO1, CCND1, DDX10, MYC, WDR43, CEBPG, DDIT3, VEGFA, PIM1 and TRIB3 were identified as hub genes. These genes have the potential to become target genes for diagnosis and therapy of CML patients.

Assessment of quantitative polymerase chain reaction for BCR-ABL1 transcripts in chronic myeloid leukaemia: Are improved outcomes in patients with e14a2 transcripts an artefact of technology?

The clinical outcome of chronic myeloid leukaemia patients has vastly improved since the introduction of tyrosine kinase inhibitor treatment, with a significant proportion of patients able to achieve treatment-free remission. However, studies have shown that patients with the e13a2 transcript were less likely to achieve major molecular response compared to those with e14a2 transcripts. Most quantitative polymerase chain reaction (PCR) assays for detection of the BCR-ABL1 fusion gene do not differentiate between the two transcripts and we therefore hypothesised that technical bias linked to the qPCR assay could partially explain the discrepancy in outcomes. We designed an e14a2-specific assay and identified no difference in results compared to an e13a2 standard assay. We then demonstrated that the commercial e14a2 standards were causing a significant overestimation of the e13a2 transcripts. Finally, we reviewed patient management after the qPCR values were corrected, using our new evaluation. We concluded that despite statistically significant differences in qPCR results, there was no impact on patient management or outcome. We conclude that, at least in our institution, it would be inappropriate to perform separate assays for patients with e13a2 or e14a2.

Pulmonary complications of Bcr-Abl tyrosine kinase inhibitors

Tyrosine kinase inhibitors (TKIs) targeting the Bcr-Abl oncoprotein revolutionised the treatment of chronic myelogenous leukaemia. Following the success of imatinib, second- and third-generation molecules were developed. Different profiles of kinase inhibition and off-target effects vary between TKIs, which leads to a broad spectrum of potential toxicities.

Pulmonary complications are most frequently observed with dasatinib but all other Bcr-Abl TKIs have been implicated. Pleural effusions are the most frequent pulmonary complication of TKIs, usually associated with dasatinib and bosutinib. Pulmonary arterial hypertension is an uncommon but serious complication of dasatinib, which is often reversible upon discontinuation. Bosutinib and ponatinib have also been associated with pulmonary arterial hypertension, while imatinib has not. Rarely, interstitial lung disease has been associated with TKIs, predominantly with imatinib.

Mechanistically, dasatinib affects maintenance of normal pulmonary endothelial integrity by generating mitochondrial oxidative stress, inducing endothelial apoptosis and impairing vascular permeability in a dose-dependent manner. The mechanisms underlying other TKI-related complications are largely unknown. Awareness and early diagnosis of the pulmonary complications of Bcr-Abl TKIs is essential given their seriousness, potential reversibility, and impact on future treatment options for the underlying chronic myelogenous leukaemia.

Resistance in chronic myeloid leukemia: definitions and novel therapeutic agents

PURPOSE OF REVIEW

Chronic myeloid leukemia (CML) is hallmarked by the presence of fusion protein kinase derived from a reciprocal translocation between chromosome 9 and 22, breakpoint cluster region (BCR)-Abelson leukemia virus (ABL) 1, causing aberrant regulation of the downstream pathways leading to unchecked CML leukemia stem cells (LSCs) proliferation. Since the discovery of tyrosine kinase inhibitors (TKI), CML, once a fatal disease, has become a chronic illness if managed appropriately. Changing treatment landscape has unsurfaced the challenge of TKI resistance that is clinically difficult to overcome.

RECENT FINDINGS

In this review, we discuss the concept of TKI resistance and pathways leading to the resistance which allows for a survival advantage to CML LSCs. Aside from BCR-ABL-dependent mechanisms of resistance which involves aberrant expression in the regulatory pumps involving efflux and influx of the TKI affecting drug bioavailability, activation of alternate survival pathways may be accountable for primary or secondary resistance. Activation of these pathways, intrinsically and extrinsically to LSCs, may be mediated through various upstream and downstream signaling as well as conditions affecting the microenvironment. Several therapeutic approaches that combine TKI with an additional agent that inhibits the activation of an alternate pathway have been studied as part of clinical trials which we will discuss here.

SUMMARY

We categorize the resistance into BCR-ABL-dependent and BCR-ABL-independent subgroups to further describe the complex molecular pathways which can potentially serve as a therapeutic target. We further discuss novel combination strategies currently in early or advanced phase clinical trials aimed to overcome the TKI resistance. We further highlight the need for further research despite the tremendous strides already made in the management of CML.

Risk factors and mechanisms contributing to TKI-induced vascular events in patients with CML

Vascular adverse events (VAE) are an emerging problem in patients with chronic myeloid leukemia (CML) receiving second-generation BCR-ABL1 tyrosine kinase inhibitors (TKI). Relevant VAE comprise peripheral, cerebral, and coronary artery changes in patients receiving nilotinib, venous and arterial occlusive events during ponatinib therapy, and pulmonary hypertension in patients receiving dasatinib. Although each TKI binds to a unique profile of molecular targets in leukemic cells and vascular cells, the exact etiology of drug-induced vasculopathies remains uncertain. Recent data suggest that predisposing molecular factors, pre-existing cardiovascular risk factors as well as certain comorbidities contribute to the etiology of VAE in these patients. In addition, direct effects of these TKI on vascular endothelial cells have been demonstrated and are considered to contribute essentially to VAE evolution. In the current article, we discuss mechanisms underlying the occurrence of VAE in TKI-treated patients with CML, with special emphasis on vascular and perivascular target cells and involved molecular (vascular) targets of VAE-triggering TKI. In addition, we discuss optimal patient selection and drug selection through which the risk of occurrence of cardiovascular events can hopefully be minimized while maintaining optimal anti-leukemic effects in CML, thereby following the principles of personalized medicine.

Treatment patterns and healthcare costs among newly-diagnosed patients with chronic myeloid leukemia receiving dasatinib or nilotinib as first-line therapy in the United States

OBJECTIVE

To compare treatment patterns and economic outcomes of dasatinib and nilotinib as 1st-line therapies for chronic myeloid leukemia (CML).

METHODS

Adult CML patients initiated on first-line dasatinib or nilotinib in 2010-2014 were identified from two large US administrative claims databases. Treatment patterns, tyrosine kinase inhibitor (TKI) adherence and healthcare resource utilization (HRU) and costs were measured from the 1st-line TKI initiation (index date) to the end of follow-up.

RESULTS

A total of 604 and 418 patients were included in the dasatinib and nilotinib cohorts (mean ages = 50.9 and 52.5 years, 46.4% and 45.7% female), respectively. Among the dasatinib patients, 91% started with 100 mg/day, 3% with <100 mg/day, and 6% with >100 mg/day. Among the nilotinib patients, 76% started with 600 mg/day, 16% with >600 mg/day, and 8% <600 mg/day. The dasatinib cohort had a higher hazard of dose decrease (hazard ratio [HR] = 1.66; p = .002) and of switching to another TKI (HR =1.62; p = .019) compared to the nilotinib cohort. The hazard of dose increase (HR =0.76; p = .423) and treatment discontinuation (HR =1.10; p = .372) were not significantly different between cohorts. There was also no significant difference in TKI adherence levels (mean proportion of days covered [PDC] difference over first 6 months = -0.0003, p = .981; mean PDC difference over first 12 months = -0.0022, p = .880) and HRU (inpatient day incidence rate ratio [IRR] = 1.03, p = .930; emergency room IRR =1.26, p = .197; and days with outpatient services IRR = 1.01, p = .842). The dasatinib cohort incurred higher healthcare costs by $749 per patient per month (p = .044) compared to the nilotinib cohort.

LIMITATION

Information on CML phase and Sokal score was not available.

CONCLUSIONS

Dasatinib was associated with an increased hazard of dose decrease and switching to another TKI and higher healthcare costs, vs nilotinib.

Immunological Analyses of Leukemia Stem Cells

Traditionally, the intracellular localization and expression levels of specific proteins in CML Leukemia stem cells (LSCs) have been evaluated by fluorescence immunohistochemistry (FIHC). More recently, Duolink(®) in situ PLA technology has opened up a new and more quantitative way to evaluate signal transduction, posttranslational modification, and protein-protein interaction at the single-stem-cell level. This novel methodology, which employs two antibody-based probes, has already increased our understanding of the biology of the rare CML LSC population. In the future, the use of this approach may contribute to the development of novel therapeutics aimed at eradicating CML LSCs in CML patients.

New hope for chronic myelogenous leukemia patients: dasatinib offers better efficacy with shorter treatment

Although the discovery of tyrosine kinase inhibitors (TKIs) has dramatically improved the prognoses of chronic myelogenous leukemia (CML) patients, a cure has remained elusive. Unanswered questions include how long must a patient continue on TKI therapy, and how does a patient know when he/she can safely stop or finish this therapy? Imagawa et al. have carefully addressed these questions of safety and efficacy using a stop study of the second-generation TKI dasatinib. The results of a multicenter phase II trial termed the "dasatinib discontinuation" (DADI) trial indicated that 48% (30/63) of CML patients who had maintained a deep molecular response (DMR) to second-line or subsequent dasatinib therapy for at least for 1 year did not show any signs of disease relapse. Thus, even after it is stopped, dasatinib treatment may decrease the chance of disease relapse and provide a curative benefit to CML patients. This work by Imagawa et al. strongly supports the clinical utility of the second-generation TKI dasatinib for CML treatment.

Management of Chronic Myeloid Leukemia Patients Resistant to Tyrosine Kinase Inhibitors Treatment

Chronic myeloid leukemia (CML) is a myeloproliferative disorder associated with a characteristic chromosomal translocation called the Philadelphia chromosome. This oncogene is generated by the fusion of breakpoint cluster region (BCR) and Abelson leukemia virus (ABL) genes and encodes a novel fusion gene translating into a protein with constitutive tyrosine kinase activity. The discovery and introduction of tyrosine kinase inhibitors (TKIs) irreversibly changed the landscape of CML treatment, leading to dramatic improvement in long-term survival rates. The majority of patients with CML in the chronic phase have a life expectancy comparable with that of healthy age-matched individuals. Although an enormous therapeutic improvement has been accomplished, there are still some unresolved issues in the treatment of patients with CML. One of the most important problems is based on the fact that TKIs can efficiently target proliferating mature cells but do not eradicate leukemic stem cells, allowing persistence of the malignant clone. Owing to the resistance mechanisms arising during the course of the disease, treatment with most of the approved BCR-ABL1 TKIs may become ineffective in a proportion of patients. This article highlights the different molecular mechanisms of acquired resistance being developed during treatment with TKIs as well as the pharmacological strategies to overcome it. Moreover, it gives an overview of novel drugs and therapies that are aiming in overcoming drug resistance, loss of response, and kinase domain mutations.

Novel oral transforming growth factor-β signaling inhibitor EW-7197 eradicates CML-initiating cells

Recent strategies for treating CML patients have focused on investigating new combinations of tyrosine kinase inhibitors (TKIs) as well as identifying novel translational research agents that can eradicate CML leukemia‐initiating cells (CML‐LICs). However, little is known about the therapeutic benefits such CML‐LIC targeting therapies might bring to CML patients. In this study, we investigated the therapeutic potential of EW‐7197, an orally bioavailable transforming growth factor‐β signaling inhibitor which has recently been approved as an Investigational New Drug (NIH, USA), to suppress CML‐LICs in vivo. Compared to TKI treatment alone, administration of TKI plus EW‐7197 to CML‐affected mice significantly delayed disease relapse and prolonged survival. Notably, combined treatment with EW‐7197 plus TKI was effective in eliminating CML‐LICs even if they expressed the TKI‐resistant T315I mutant BCR‐ABL1 oncogene. Collectively, these results indicate that EW‐7197 may be a promising candidate for a new therapeutic that can greatly benefit CML patients by working in combination with TKIs to eradicate CML‐LICs.

A combination of sorafenib and nilotinib reduces the growth of castrate-resistant prostate cancer

Castrate-resistant prostate cancer (CRPC) remains incurable due to the lack of effective therapies. Several tyrosine kinases have been implicated in the development and growth of CRPC, as such targeting these kinases may offer an alternative therapeutic strategy. We established the combination of two tyrosine kinase inhibitors (TKIs), sorafenib and nilotinib, as the most cytotoxic. In addtion, to improve their bioavailability and reduce their metabolism, we encapsulated sorafenib and nilotinib into styrene-co-maleic acid micelles. The micelles' charge, size, and release rate were characterized. We assessed the effect of the combination on the cytotoxicity, cell cycle, apoptosis, protein expression, tumor spheroid integrity, migration, and invasion. The micelles exhibited a mean diameter of 100 nm, a neutral charge, and appeared highly stable. The micellar TKIs promoted greater cytotoxicity, decreased cell proliferation, and increased apoptosis relative to the free TKIs. In addition, the combination reduced the expression and activity of several tyrosine kinases and reduced tumor spheroid integrity and metastatic potential of CRPC cell lines more efficiently than the single treatments. The combination increased the therapeutic potential and demonstrated the relevance of a targeted combination therapy for the treatment of CRPC. In addition, the efficacy of the encapsulated drugs provides the basis for an in vivo preclinical testing.

Are nilotinib-associated vascular adverse events an under-estimated problem?

Vascular adverse events have been reported with nilotinib, a tyrosine kinase inhibitor prescribed for chronic myeloid leukaemia. However, few data specify their incidence, or whether they occur in predisposed patients. Hence, we prospectively studied 30 consecutive patients to assess the frequency of such adverse reactions and determine whether the patients presenting with these adverse events bear predisposing factors. From 3 to 73 months after nilotinib initiation, 10 of the 30 patients experienced vascular events. Three patients of these 10 were devoid of any patent cardiovascular risk factor, except for age. This study points out an occurrence more frequent than expected of vascular adverse events associated with nilotinib (> 30% vs. < 1% in summary of product characteristics), and particularly of vascular events of late onset in patients with no pre-existing risk factors.

Vascular safety issues in CML patients treated with BCR/ABL1 kinase inhibitors

Vascular safety is an emerging issue in patients with chronic myeloid leukemia (CML) treated with tyrosine kinase inhibitors (TKIs). Whereas imatinib exhibits a well-documented and favorable long-term safety profile without obvious accumulation of vascular events, several types of vascular adverse events (VAEs) have been described in patients receiving second- or third-generation BCR/ABL1 TKIs. Such VAEs include pulmonary hypertension in patients treated with dasatinib, peripheral arterial occlusive disease and other arterial disorders in patients receiving nilotinib, and venous and arterial vascular occlusive events during ponatinib. Although each TKI interacts with a unique profile of molecular targets and has been associated with a unique pattern of adverse events, the mechanisms of drug-induced vasculopathy are not well understood. Here, recent data and concepts around VAEs in TKI-treated patients with CML are discussed, with special reference to potential mechanisms, event management, and strategies aimed at avoiding occurrence of such events in long-term treated patients.

High imatinib dose overcomes insufficient response associated with ABCG2 haplotype in chronic myelogenous leukemia patients

Pharmacogenetic studies in chronic myelogenous leukemia (CML) typically use a candidate gene approach. In an alternative strategy, we analyzed the impact of single nucleotide polymorphisms (SNPs) in drug transporter genes on the molecular response to imatinib, using a DNA chip containing 857 SNPs covering 94 drug transporter genes. Two cohorts of CML patients treated with imatinib were evaluated: an exploratory cohort including 105 patients treated at 400 mg/d and a validation cohort including patients sampled from the 400 mg/d and 600 mg/d arms of the prospective SPIRIT trial (n=239). Twelve SNPs discriminating patients according to cumulative incidence of major molecular response (CI-MMR) were identified within the exploratory cohort. Three of them, all located within the ABCG2 gene, were validated in patients included in the 400 mg/d arm of the SPIRIT trial. We identified an ABCG2 haplotype (define as G-G, rs12505410 and rs2725252) as associated with significantly higher CI-MMR in patients treated at 400 mg/d. Interestingly, we found that patients carrying this ABCG2 "favorable" haplotype in the 400 mg arm reached similar CI-MMR rates that patients randomized in the imatinib 600 mg/d arm. Our results suggest that response to imatinib may be influenced by constitutive haplotypes in drug transporter genes. Lower response rates associated with "non- favorable" ABCG2 haplotypes may be overcome by increasing the imatinib daily dose up to 600 mg/d.

Targeting survival pathways in chronic myeloid leukaemia stem cells

Chronic myeloid leukaemia (CML) is a clonal myeloproliferative disorder characterized by the presence of a fusion oncogene BCR-ABL, which encodes a protein with constitutive TK activity. The implementation of tyrosine kinase inhibitors (TKIs) marked a major advance in CML therapy; however, there are problems with current treatment. For example, relapse occurs when these drugs are discontinued in the majority of patients who have achieved a complete molecular response on TKI and these agents are less effective in patients with mutations in the BCR-ABL kinase domain. Importantly, TKI can effectively target proliferating mature cells, but do not eradicate quiescent leukaemic stem cells (LSCs), therefore allowing disease persistence despite treatment. It is essential that alternative strategies are used to target the LSC population. BCR-ABL activation is responsible for the modulation of different signalling pathways, which allows the LSC fraction to evade cell death. Several pathways have been shown to be modulated by BCR-ABL, including PI3K/AKT/mTOR, JAK-STAT and autophagy signalling pathways. Targeting components of these survival pathways, alone or in combination with TKI, therefore represents an attractive potential therapeutic approach for targeting the LSC. However, many pathways are also active in normal stem cells. Therefore, potential targets must be validated to effectively eradicate CML stem cells while sparing normal counterparts. This review summarizes the main pathways modulated in CML stem cells, the recent developments and the use of novel drugs to target components in these pathways which may be used to target the LSC population.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Extracellular domain c-kit mutation with duplication of Ser501Ala502 found in gastrointestinal stromal tumors is more imatinib- and nilotinib-sensitive than that with duplication of Ala502Tyr503

The great majority of gastrointestinal stromal tumors (GISTs) have gain-of-function mutations of the c-kit gene, which encodes KIT receptor tyrosine kinase. Most of the mutations are located at exon 11, but some are at exon 9 or at other exons. Mutation types at exon 11 vary, while most mutations at exon 9 are a particular duplication of Ala502Tyr503 (KIT-Dup-Ala502Tyr503). Recently a duplication of Ser501Ala502 (KIT-Dup-Ser501Ala502) at exon 9 has been reported in two cases of pediatric mastocytosis and one case of adult mast cell leukemia. Although KIT-Dup-Ser501Ala502 had not been reported in GISTs, we found two GIST cases possessing the mutation in 45 GIST cases with exon 9 c-kit gene mutations, among a total of approximately 500 GIST cases examined. In this report, we briefly summarize clinicopathological findings of the two cases, and characterize the biology of the mutation. When autophosphorylation of KIT-Dup-Ser501Ala502 was examined by transient transfection of c-kit cDNA with Dup-Ser501Ala502 into CHO-K1 cells, KIT-Dup-Ser501Ala502 was ligand-independently activating. The inhibitory effect of selective tyrosine kinase inhibitors, imatinib and nilotinib, on KIT-Dup-Ser501Ala502 was examined and compared with that of KIT-Dup-Ala502Tyr503. Imatinib efficiently inhibited constitutive activation of KIT-Dup-Ser501Ala502 at a concentration of 0.1 μM, whereas it inhibited that of KIT-Dup-Ala502Tyr503 at a concentration of 10 μM. Constitutive activation of KIT-Dup-Ser502Ala503 was not inhibited by nilotinib even at a concentration of 10 μM but that of KIT-Dup-Ala501Tyr502 was almost completely inhibited at a concentration of 1 μM. The results suggest that imatinib and nilotinib could be more effective on GISTs with KIT-Dup-Ser501Ala502 than those with KIT-Dup-Ala502Tyr503. In fact, a patient with KIT-Dup-Ser501Ala502 showed long-term stable disease with administration of the usual dose of 400 mg imatinib. Although mutation sites of KIT-Dup-Ser501Ala502 and KIT-Dup-Ala502Tyr503 are closely located, imatinib- and nilotinib-sensitive KIT-Dup-Ser501Ala502 are distinguishable from KIT-Dup-Ala502Tyr503.

Imatinib, dasatinib and nilotinib: a review of adverse cutaneous reactions with emphasis on our clinical experience

In the last years, several tyrosine kinase inhibitors (TKIs) have been developed and approved for human cancer treatment. Imatinib mesylate was the first of this novel family of drugs that target cancer-specific molecules and signalling pathways. The appearance of imatinib resistances led to the introduction of second-generation TKIs with higher potency and selectivity, such as dasatinib and nilotinib. However, the range of activity of these agents is not simply directed at tumour cells. Patients and their clinicians are indeed frequently confronted with the cutaneous side-effects associated with the employ of these drugs, which represent the most common non-hematological adverse reactions. For this reason, a systematic dermatological survey of patients receiving these therapies is highly important, and an early and appropriate dermatological treatment is required. In this review, we analyse the clinical and pathological characteristics of the most commonly reported adverse skin events associated with first- and second-generation tyrosine kinase inhibitors, with a particular emphasis on our clinical experience.

Quality control methods for optimal BCR-ABL1 clinical testing in human whole blood samples

Reliable breakpoint cluster region (BCR)--Abelson (ABL) 1 measurement is essential for optimal management of chronic myelogenous leukemia. There is a need to optimize quality control, sensitivity, and reliability of methods used to measure a major molecular response and/or treatment failure. The effects of room temperature storage time, different primers, and RNA input in the reverse transcription (RT) reaction on BCR-ABL1 and β-glucuronidase (GUSB) cDNA yield were assessed in whole blood samples mixed with K562 cells. BCR-ABL1 was measured relative to GUSB to control for sample loading, and each gene was measured relative to known numbers of respective internal standard molecules to control for variation in quality and quantity of reagents, thermal cycler conditions, and presence of PCR inhibitors. Clinical sample and reference material measurements with this test were concordant with results reported by other laboratories. BCR-ABL1 per 10(3) GUSB values were significantly reduced (P = 0.004) after 48-hour storage. Gene-specific primers yielded more BCR-ABL1 cDNA than random hexamers at each RNA input. In addition, increasing RNA inhibited the RT reaction with random hexamers but not with gene-specific primers. Consequently, the yield of BCR-ABL1 was higher with gene-specific RT primers at all RNA inputs tested, increasing to as much as 158-fold. We conclude that optimal measurement of BCR-ABL1 per 10(3) GUSB in whole blood is obtained when gene-specific primers are used in RT and samples are analyzed within 24 hours after blood collection.

Nilotinib preclinical pharmacokinetics and practical application toward clinical projections of oral absorption and systemic availability

Nilotinib is a highly potent and selective bcr-abl tyrosine kinase inhibitor used for the treatment of patients who are in the chronic and accelerated phases of Philadelphia chromosome-positive (Ph+) chronic myeloid leukemia (CML). Nilotinib preclinical data and its use for practical predictions of systemic exposure profiles and oral absorption are described. The systemic clearance (CL) of nilotinib was relatively low in rodents with a value of less than 25% of hepatic blood flow (Q(H)), while it was moderate in monkeys and dogs (CL/Q(H)  = 32-35%). The steady state volume of distribution (V(ss) ) ranged from 0.55 to 3.9 l/kg across the species tested. The maximum concentration (C(max)) of nilotinib occurred at 0.5-4 h and the bioavailability was moderate (17-44%). The plasma protein binding was high (> 97.5%) in preclinical species and humans. The human CL (~ 0.1 l/h/kg) and V(ss) (~2.0 l/kg) were best predicted by the rat-dog-human proportionality method and allometric scaling method, respectively. The human intravenous pharmacokinetic profile was projected by the Wajima 'C(ss)-MRT' method. The predicted micro-constants from human intravenous profiles were incorporated into the advanced compartmental absorption and transit model within the GastroPlus program to simulate the oral concentration-time curves in humans. Overall, the simulated oral human pharmacokinetic profiles showed good agreement with observed clinical data, and the model predicted that the C(max) , AUC, t(½) , V(z) /F and CL/F values were within 1.3-fold of the observed values. The absolute oral bioavailability of nilotinib in healthy humans was predicted to be low (< 25%).

Development of an effective therapy for chronic myelogenous leukemia

Targeted small-molecule drugs have revolutionized treatment of chronic myeloid leukemia (CML) during the last decade. These agents interrupt a constitutively active BCR-ABL, the causative agent for CML, by interfering with adenosine 5' triphosphate-dependent ABL tyrosine kinase. Although the efficacy of tyrosine kinase inhibitors (TKIs) has resulted in overall survival of greater than 90%, TKIs are not curative. Moreover, no currently approved TKIs are effective against the T315I BCR-ABL variant. However, a new generation of TKIs with activity against T315I is on the horizon. We will highlight the clinical utility of historical CML therapeutics, those used today (first- and second-generation TKIs), and discuss treatment modalities that are under development. Recent advances have illuminated the complexity of CML, especially within the marrow microenvironment. We contend that the key to curing CML will involve strategies beyond targeting BCR-ABL because primitive human CML stem cells are not dependent on BCR-ABL. Ultimately, drug combinations or exploiting synthetic lethality may transform responses into definitive cures for CML.

Selection of therapy: rational decisions based on molecular events

This article reviews to what extent molecular data can be used to rationalize therapeutic choices in the treatment of chronic myeloid leukemia. Two categories of data are discussed: markers that globally measure risk but do not provide a molecular rationale for therapy selection; and biomarkers with a causal link to a clinical phenotype, such as certain mutations of the BCR-ABL kinase domain. As therapy selection is still mainly based on clinical criteria, molecular biomarkers are discussed in the context of available clinical prognostication tools, focusing on biomarkers that do not reflect disease burden as a surrogate of responsiveness to treatment.

Nilotinib as frontline and second-line therapy in chronic myeloid leukemia: open questions

Nilotinib is a second generation ABL tyrosine kinase inhibitor (TKI) that exerts major anti-leukemic effects in newly diagnosed patients with chronic myeloid leukemia (CML) as well as in most patients with imatinib-resistant CML. In freshly diagnosed patients, the anti-leukemic activity of nilotinib exceeds the efficacy of imatinib, and although long-term data for nilotinib are not available yet, the drug has recently been approved for firstline treatment of chronic phase CML in various countries. Still however, several questions concerning the optimal dose, follow-up parameters, long-term safety, and patient selection remain open. Likewise, it remains uncertain whether both Sokal low-risk and high-risk patients should receive nilotinib as frontline therapy in the future. Another question is whether nilotinib can completely eradicate CML in a subset of patients. Furthermore, it remains unclear whether and what comorbidity must be regarded as relative or absolute contra-indication for this TKI. To discuss these issues, the Austrian CML Working Group organized a series of meetings in 2010. In the current article, the outcomes from these discussions are summarized and presented together with recommendations for frontline use of TKIs in various groups of patients with CML. These recommendations should assist in daily practice as well as in the preparation and conduct of clinical trials.