Allogeneic transplantation for CML in the TKI era: striking the right balance

Stem cell allografting for chronic Myeloid leukemia in the tyrosine kinase era - forgotten but not gone

Due to the remarkable success of tyrosine kinase inhibitors (TKI) in chronic myeloid leukemia (CML), allogeneic stem cell transplantation (alloSCT) is not first-line treatment for delivering durable, long-term survival. Consequently, alloSCT is reserved for patients with TKI-resistant or TKI-intolerant chronic phase CML (CP-CML) and advanced phase CML (AP-CML). Advances in transplant technology, such as high-resolution HLA typing, introduction of reduced intensity conditioning and increased alternative donor availability, coupled with improved supportive care, have significantly reduced transplant-related mortality and expanded the pool of transplant-eligible patients. Refinement of conditioning regimens, innovative use of post-transplant cellular and pharmacological therapies, and judicious post-transplant monitoring are important strategies for reducing risk of relapse. Given its potential to cure, alloSCT will invariably remain a key part of the treatment algorithm. This article reviews the data underpinning the role and outcomes of alloSCT and provides an update on current recommendations.

The Contemporary Role of Hematopoietic Stem Cell Transplantation in the Management of Chronic Myeloid Leukemia: Is It the Same in All Settings?

Hematopoietic stem cell transplantation (HSCT) for chronic myeloid leukemia (CML) patients has transitioned from the standard of care to a treatment option limited to those with unsatisfactory tyrosine kinase inhibitor (TKI) responses and advanced disease stages. In recent years, the threshold for undergoing HSCT has increased. Most CML patients now have life expectancies comparable to the general population, and therefore, the goal of therapy is shifting toward achieving treatment-free remission (TFR). While TKI discontinuation trials in CML show potential for achieving TFR, relapse risk is high, affirming allogeneic HSCT as the sole curative treatment. HSCT should be incorporated into treatment algorithms from the time of diagnosis and, in some patients, evaluated as soon as possible. In this review, we will look at some of the recent advances in HSCT, as well as its indication in the era of aiming for TFR in the presence of TKIs in CML.

The Progress of Small Molecule Targeting BCR-ABL in the Treatment of Chronic Myeloid Leukemia

Chronic myelogenous leukemia (CML) is a malignant myeloproliferative disease. According to the American Cancer Society's 2021 cancer data report, new cases of CML account for about 15% of all leukemias. CML is generally divided into three stages: chronic phase, accelerated phase, and blast phase. Nearly 90% of patients are diagnosed as a chronic phase. Allogeneic stem cell transplantation and chemotherapeutic drugs, such as interferon IFN-α were used as the earliest treatments for CML. However, they could generate obvious side effects, and scientists had to seek new treatments for CML. A new era of targeted therapy for CML began with the introduction of imatinib, the first-generation BCR-ABL kinase inhibitor. However, the ensuing drug resistance and mutant strains led by T315I limited the further use of imatinib. With the continuous advancement of research, tyrosine kinase inhibitors (TKI) and BCR-ABL protein degraders with novel structures and therapeutic mechanisms have been discovered. From biological macromolecules to classical target protein inhibitors, a growing number of compounds are being developed to treat chronic myelogenous leukemia. In this review, we focus on summarizing the current situation of a series of candidate small-molecule drugs in CML therapy, including TKIs and BCR-ABL protein degrader. The examples provided herein describe the pharmacology activity of small-molecule drugs. These drugs will provide new enlightenment for future treatment directions.

A review on characterization of BCR - ABL transcript variants for molecular monitoring of chronic myeloid leukemia phenotypes

Chronic myeloid leukemia (CML) is a clonal myeloproliferative growth of human pluripotent stem cells which is estimated to occur at a rate of 1/100000 populations every year worldwide. A characteristic feature of this disease is the presence of the Philadelphia chromosome genotype, which results from the reciprocal translocation between human chromosomes 9 and 22. Two types of major genotypes are involved, which consequently result in two major types of expressed fusion mRNA transcripts: b3a2 and b2a2, i.e. major breakpoint segments (happening after exon 13 & after exon 14) of the BCR gene on chromosome 22 fuze with the ABL1 gene breakpoint (happening after exon 2) on chromosome 9, forming two genotypes coding for two transcripts: b3a2 (e14a2) and b2a2 (e13a2). The protein 'p210 BCR-ABL1', a protein which characteristically exhibits a high tyrosine kinase activity which is followed by the activation of various cellular processes that lead to increased cellular proliferation and cancer, is coded by both major BCR - ABL1 mRNA transcripts. Recent developments in the treatment of CML through molecular monitoring of the disease have managed to reduce patient morbidity and mortality. Advanced molecular techniques are aimed at detecting BCR-ABL1 transcript levels to monitor treatment response. Transcript typing is necessary to detect minimal residual disease and to achieve molecular response by helping to provide selective therapy based on the type of transcript identified, as transcript type is correlated with the disease course.The purpose of this review is to discuss: the role of the BCR-ABL1 fusion gene in the pathogenesis of CML; the role of BCR-ABL1 transcript characterization in the molecular monitoring of CML therapy; the association of BCR - ABL1 transcript types with different CML phenotypes, molecular responses, and treatment responses; and the laboratory techniques employed to detect and characterize BCR - ABL1 transcripts.

Targeting FLT3-TAZ signaling to suppress drug resistance in blast phase chronic myeloid leukemia

BACKGROUND

Although the development of BCR::ABL1 tyrosine kinase inhibitors (TKIs) rendered chronic myeloid leukemia (CML) a manageable condition, acquisition of drug resistance during blast phase (BP) progression remains a critical challenge. Here, we reposition FLT3, one of the most frequently mutated drivers of acute myeloid leukemia (AML), as a prognostic marker and therapeutic target of BP-CML.

METHODS

We generated FLT3 expressing BCR::ABL1 TKI-resistant CML cells and enrolled phase-specific CML patient cohort to obtain unpaired and paired serial specimens and verify the role of FLT3 signaling in BP-CML patients. We performed multi-omics approaches in animal and patient studies to demonstrate the clinical feasibility of FLT3 as a viable target of BP-CML by establishing the (1) molecular mechanisms of FLT3-driven drug resistance, (2) diagnostic methods of FLT3 protein expression and localization, (3) association between FLT3 signaling and CML prognosis, and (4) therapeutic strategies to tackle FLT3+ CML patients.

RESULTS

We reposition the significance of FLT3 in the acquisition of drug resistance in BP-CML, thereby, newly classify a FLT3+ BP-CML subgroup. Mechanistically, FLT3 expression in CML cells activated the FLT3-JAK-STAT3-TAZ-TEAD-CD36 signaling pathway, which conferred resistance to a wide range of BCR::ABL1 TKIs that was independent of recurrent BCR::ABL1 mutations. Notably, FLT3+ BP-CML patients had significantly less favorable prognosis than FLT3- patients. Remarkably, we demonstrate that repurposing FLT3 inhibitors combined with BCR::ABL1 targeted therapies or the single treatment with ponatinib alone can overcome drug resistance and promote BP-CML cell death in patient-derived FLT3+ BCR::ABL1 cells and mouse xenograft models.

CONCLUSION

Here, we reposition FLT3 as a critical determinant of CML progression via FLT3-JAK-STAT3-TAZ-TEAD-CD36 signaling pathway that promotes TKI resistance and predicts worse prognosis in BP-CML patients. Our findings open novel therapeutic opportunities that exploit the undescribed link between distinct types of malignancies.

Treatment after failure of frontline therapy of chronic myeloid leukemia in chronic phase including allogeneic hematopoietic stem cell transplantation

The treatment outcomes of chronic myeloid leukemia in chronic phase (CML-CP) have dramatically improved with comparable life-expectancy to average of general population in tyrosine kinase inhibitor (TKI) era. However, less than a half of patients who started with TKI can remain on frontline TKI. The reasons of switching TKI can be either intolerance or the lack of efficacy. Although a kinase domain (KD) mutation can guide to select salvage TKI from the point of view on the efficacy of TKIs, many factors need to be considered before choosing next-line TKI such as the high-risk features of CML, the adverse events with prior TKI, and the comorbidities of patients. The therapeutic options for CML-CP after failing frontline TKI due to treatment failure or suboptimal responses will be reviewed including allogeneic hematopoietic stem cell transplantation.

ACY-1215 suppresses the proliferation and induces apoptosis of chronic myeloid leukemia cells via the ROS/PTEN/Akt pathway

Chronic myeloid leukemia (CML) is a hematological tumor marked by the bcr-abl fusion gene formed by t (9;22) (q34; q11), which translated into the BCR-ABL protein. Tyrosine kinase inhibitors (TKIs) have been widely used to cure CML patients. Nevertheless, the emergence of TKI resistance has become the problem to the outcome of CML patients. Histone deacetylase 6 (HDAC6), a kind of Hsp90α deacetylase, was detected to be overexpressed in chronic myeloid leukemia stem cells. Besides, the loss of HDAC6 enzymatic activity can result in the degradation of Hsp90α's client proteins, such as BCR-ABL, the oncoprotein of CML. Here, we explored the expression of HDAC6 and discovered that it was upregulated compared with control in CML. Then we explored the effect of Rocilinostat (ACY-1215), a specific HDAC6 inhibitor, on CML cells. Our results proved that ACY-1215 could induce apoptosis and cell cycle arrest in a ROS-dependent manner. Moreover, we detected a downregulation of the BCR-ABL signaling pathway in the ACY-1215 treatment group. Mechanistically, we noted that the upregulation of PTEN was induced after being treated by ACY-1215 and its downstream protein p-Akt was decreased. The Akt activator SC79 can partially reverse the influence of ACY-1215 on CML cells. Besides, our results also proved that ACY-1215 can synergize with imatinib to suppress chronic myeloid leukemia in vitro and in vivo. On the whole, our study revealed that HDAC6 is a possible therapeutic target in CML, and the combination therapy of TKI and HDAC6 inhibitor may improve the outcome of CML patients.

Questions concerning tyrosine kinase-inhibitor therapy and transplants in chronic phase chronic myeloid leukaemia

In this provocative commentary, we consider several questions posed by the late chronic myeloid leukaemia (CML) expert Prof. Michele Baccarani, which he challenged us to address after his death. He noted only a small proportion of people with chronic phase CML receiving tyrosine kinase-inhibitor (TKI)-therapy are likely to achieve sustained therapy-free remission (TFR) and even fewer are likely to be cured. Persons most likely to fail TKItherapy can be identified at diagnosis or soon after starting TKI-therapy. These persons are likely to need lifetime TKI-therapy with attendant risks of adverse events, cost and psychological consequences. Allogeneic transplants achieve much higher rates of leukaemia-free survival compared with TKI-therapy but are associated with transplant-related adverse events including an almost 20 percent risk of transplant-related deaths within 1 year post-transplant and a compromised quality-of-life because of complications such as chronic graft-versus-host disease. Subject-, disease- and transplant-related co-variates associated with transplant outcomes are known with reasonable accuracy. Not everyone likely to fail TKI-therapy is a transplant candidate. However, in those who candidates are physicians and patients need to weigh benefits and risks of TKI-therapy versus a transplant. We suggest transplants should be more often considered in the metric when counseling people with chronic phase CML unlikely to achieve TFR with TKI-therapy. We question whether we are discounting a possible important therapy intervention; we think so.

MiR-125a-3p and MiR-320b Differentially Expressed in Patients with Chronic Myeloid Leukemia Treated with Allogeneic Hematopoietic Stem Cell Transplantation and Imatinib Mesylate

Chronic myeloid leukemia (CML), a hematopoietic neoplasm arising from the fusion of BCR (breakpoint cluster region) gene on chromosome 22 to the ABL (Abelson leukemia virus) gene on chromosome 9 (BCR-ABL1 oncogene), originates from a small population of leukemic stem cells with extensive capacity for self-renewal and an inflammatory microenvironment. Currently, CML treatment is based on tyrosine kinase inhibitors (TKIs). However, allogeneic hematopoietic stem cell transplantation (HSCT-allo) is currently the only effective treatment of CML. The difficulty of finding a compatible donor and high rates of morbidity and mortality limit transplantation treatment. Despite the safety and efficacy of TKIs, patients can develop resistance. Thus, microRNAs (miRNAs) play a prominent role as biomarkers and post-transcriptional regulators of gene expression. The aim of this study was to analyze the miRNA profile in CML patients who achieved cytogenetic remission after treatment with both HSCT-allo and TKI. Expression analyses of the 758 miRNAs were performed using reverse transcription quantitative polymerase chain reaction (RT-qPCR). Bioinformatics tools were used for data analysis. We detected miRNA profiles using their possible target genes and target pathways. MiR-125a-3p stood out among the downregulated miRNAs, showing an interaction network with 52 target genes. MiR-320b was the only upregulated miRNA, with an interaction network of 26 genes. The results are expected to aid future studies of miRNAs, residual leukemic cells, and prognosis in CML.

A Case of Tyrosine Kinase Inhibitor-Induced Bone Marrow Aplasia That Was Successfully Treated with Allogeneic Hematopoietic Stem Cell Transplantation

Here, we present a rare case of tyrosine kinase inhibitor (TKI)-induced bone marrow aplasia. A 58-year-old man presented with leukocytosis and was diagnosed with chronic myeloid leukemia. He was initially treated with imatinib for 6 years and abruptly discontinued treatment by himself. He was administered dasatinib 5 years after treatment interruption, and presented with pancytopenia 6 months after dasatinib initiation. Bone marrow biopsy revealed severe hypocellularity without blasts. Dasatinib was discontinued, and he recovered from pancytopenia 3 months later; however, BCR-ABL1 was positive for almost all white blood cells in the peripheral blood. We retreated with ponatinib, but pancytopenia developed again. The clinical course indicated TKI-induced bone marrow aplasia. Therefore, ponatinib was discontinued and the patient received an allogeneic hematopoietic stem cell transplantation from a haploidentical daughter using post-transplant cyclophosphamide. He had a major molecular response and had normal complete blood counts and bone marrow 1 year after transplantation.

Stopping tyrosine kinase inhibitors started after allogeneic HCT in patients with Philadelphia chromosome-positive leukemia

For patients with Philadelphia chromosome (Ph)-positive leukemia, there is no consensus regarding how long tyrosine kinase inhibitors (TKI) should be given or whether TKI could be stopped if TKI is administrated after allogeneic hematopoietic cell transplantation (allo-HCT). We analyzed relapse-free survival (RFS) in 92 allo-HCT patients who received TKI for >3 months after allo-HCT, and aimed to develop a novel indicator, called as current TKI- & relapse-free (cTRFree) achievement. TKI after allo-HCT was started as planned in 39 patients, based on measurable residual disease (MRD) in 53 at a median of 152 days after allo-HCT. There was no difference in post-TKI RFS between the planned and MRD-based starting groups (P = 0.69). Second-generation TKIs were associated with superior RFS in Ph-positive acute leukemia (HR 2.71, P = 0.031). TKI was stopped before relapse in 48 patients. Stopping TKI as a time-dependent covariate was not associated with subsequent hematological relapse (HR 1.18, P = 0.72). In the TKI-stop group, TKI administration for >6 months tended to be associated with superior RFS (HR = 0.30, P = 0.08). As an indicator of transplant success, cTRFree was 35% 5 years after starting TKI. TKI could be stopped for recipients with sustained undetectable MRD. However, further prospective studies will be required to establish clinical recommendations.

Prospects for achieving treatment-free remission in chronic myeloid leukaemia

In addition to the best possible overall survival, discontinuation of the tyrosine kinase-inhibitor (TKI) treatment [treatment free remission (TFR)] without observing a recurrence of the disease has become a major goal of the therapy of chronic myelogenous leukemia (CML). Many clinical studies have demonstrated that TFR is possible, although for the moment limited to a fraction of the CML patients able to achieve a stable deep molecular response (DMR). The factors associated to the possibility of remaining in TFR or of losing it, have been investigated by a number of controlled and observation clinical trials and although total TKI treatment duration, DMR duration and stability and, more recently, also the depth of the molecular response obtained at the time of discontinuation have been shown to be significant elements, most of the factors associated with a higher possibility of a successful discontinuation still remain elusive and are here reviewed.

Flow cytometry and targeted immune transcriptomics identify distinct profiles in patients with chronic myeloid leukemia receiving tyrosine kinase inhibitors with or without interferon-α

Background

Tumor cells have evolved complex strategies to escape immune surveillance, a process which involves NK cells and T lymphocytes, and various immunological factors. Indeed, tumor cells recruit immunosuppressive cells [including regulatory T-cells (Treg), myeloid-derived suppressor cells (MDSC)] and express factors such as PD-L1. Molecularly targeted therapies, such as imatinib, have off-target effects that may influence immune function. Imatinib has been shown to modulate multiple cell types involved in anti-cancer immune surveillance, with potentially detrimental or favorable outcomes. Imatinib and other tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) have dramatically changed disease course. Our study aimed to characterize the different populations of the immune system in patients with CML affected by their treatment.

Methods

Forty-one patients with CML [33 treated with TKIs and 8 with TKIs plus interferon (IFN)-α] and 20 controls were enrolled in the present study. Peripheral blood populations of the immune system [referred to as the overview of immune system (OVIS) panel, Treg cells and MDSCs] and PD-1 expression were evaluated by flow cytometry. The immunological profile was assessed using the mRNA Pan-Cancer Immune Profiling Panel and a NanoString nCounter FLEX platform.

Results

Patients receiving combination therapy (TKIs + IFN-α) had lower numbers of lymphocytes, particularly T cells [838/µL (95% CI 594–1182)] compared with healthy controls [1500/µL (95% CI 1207 – 1865), p = 0.017]. These patients also had a higher percentage of Treg (9.1%) and CD4⁺PD-1⁺ cells (1.65%) compared with controls [Treg (6.1%) and CD4⁺/PD-1⁺(0.8%); p ≤ 0.05]. Moreover, patients treated with TKIs had more Mo-MDSCs (12.7%) whereas those treated with TKIs + IFN-α had more Gr-MDSC (21.3%) compared to controls [Mo-MDSC (11.4%) and Gr-MDSC (8.48%); p ≤ 0.05]. CD56^bright NK cells, a cell subset endowed with immune-regulatory properties, were increased in patients receiving TKIs plus IFN-α compared with those treated with TKIs alone. Interestingly, serum IL-21 was significantly lower in the TKIs plus IFN-α cohort. Within the group of patients treated with TKI monotherapy, we observed that individuals receiving 2nd generation TKIs had lower percentages of CD4⁺ Treg (3.63%) and Gr-MDSC (4.2%) compared to patients under imatinib treatment (CD4⁺ Treg 6.18% and Gr-MDSC 8.2%), but higher levels of PD-1-co-expressing CD4⁺ cells (1.92%).

Conclusions

Our results suggest that TKIs in combination with IFN-α may promote an enhanced immune suppressive state.

CDK4/CDK6 inhibition as a novel strategy to suppress the growth and survival of BCR-ABL1T315I+ clones in TKI-resistant CML

Purpose

Ponatinib is the only approved tyrosine kinase inhibitor (TKI) suppressing BCR-ABL1^T315I-mutated cells in chronic myeloid leukemia (CML). However, due to side effects and resistance, BCR-ABL1^T315I-mutated CML remains a clinical challenge. Hydroxyurea (HU) has been used for cytoreduction in CML for decades. We found that HU suppresses or even eliminates BCR-ABL1^T315I+ sub-clones in heavily pretreated CML patients. Based on this observation, we investigated the effects of HU on TKI-resistant CML cells in vitro.

Methods

Viability, apoptosis and proliferation of drug-exposed primary CML cells and BCR-ABL1+ cell lines were examined by flow cytometry and ³H-thymidine-uptake. Expression of drug targets was analyzed by qPCR and Western blotting.

Findings

HU was more effective in inhibiting the proliferation of leukemic cells harboring BCR-ABL1^T315I or T315I-including compound-mutations compared to cells expressing wildtype BCR-ABL1. Moreover, HU synergized with ponatinib and ABL001 in inducing growth inhibition in CML cells. Furthermore, HU blocked cell cycle progression in leukemic cells, which was accompanied by decreased expression of CDK4 and CDK6. Palbociclib, a more specific CDK4/CDK6-inhibitor, was also found to suppress proliferation in primary CML cells and to synergize with ponatinib in producing growth inhibition in BCR-ABL1^T315I+ cells, suggesting that suppression of CDK4/CDK6 may be a promising concept to overcome BCR-ABL1^T315I-associated TKI resistance.

Interpretation

HU and the CDK4/CDK6-blocker palbociclib inhibit growth of CML clones expressing BCR-ABL1^T315I or complex T315I-including compound-mutations. Clinical studies are required to confirm single drug effects and the efficacy of `ponatinib+HU´ and ´ponatinib+palbociclib´ combinations in advanced CML.

Funding

This project was supported by the Austrian Science Funds (FWF) projects F4701-B20, F4704-B20 and P30625.

Complexity of chronic-phase CML management after failing a second-generation TKI

The treatment landscape of chronic myeloid leukemia (CML) was radically changed with the introduction of imatinib in 2001. With the emergence of treatment failure with imatinib, more specific and potent second- and third-generation tyrosine kinase inhibitors (TKIs) were developed. Currently, 6 TKIs and one protein synthesis inhibitor are available on the market for CML treatment. Despite the availability of these agents, it is not uncommon for some patients to experience treatment failure across several lines of therapy. Sequencing the available treatment options is a challenging task that becomes more complex after patients fail the more potent second- and third-generation TKIs. The ability to successfully salvage such patients is limited. In this paper, we will briefly review the mechanisms of treatment failure in chronic-phase CML (CP-CML) and focus on the complexity of managing patients who fail a second-generation TKI.

Somatic variants in epigenetic modifiers can predict failure of response to imatinib but not to second-generation tyrosine kinase inhibitors

There are no validated molecular biomarkers to identify newly-diagnosed individuals with chronic-phase chronic myeloid leukemia likely to respond poorly to imatinib and who might benefit from first-line treatment with a more potent second-generation tyrosine kinase inhibitor. Our inability to predict these ‘high-risk’ individuals reflects the poorly understood heterogeneity of the disease. To investigate the potential of genetic variants in epigenetic modifiers as biomarkers at diagnosis, we used Ion Torrent next-generation sequencing of 71 candidate genes for predicting response to tyrosine kinase inhibitors and probability of disease progression. A total of 124 subjects with newly-diagnosed chronic-phase chronic myeloid leukemia began with imatinib (n=62) or second-generation tyrosine kinase inhibitors (n=62) and were classified as responders or non-responders based on the BCRABL1 transcript levels within the first year and the European LeukemiaNet criteria for failure. Somatic variants affecting 21 genes (e.g. ASXL1, IKZF1, DNMT3A, CREBBP) were detected in 30% of subjects, most of whom were non-responders (41% non-responders, 18% responders to imatinib, 38% non-responders, 25% responders to second-generation tyrosine kinase inhibitors). The presence of variants predicted the rate of achieving a major molecular response, event-free survival, progression-free survival and chronic myeloid leukemia-related survival in the imatinib but not the second-generation tyrosine kinase inhibitors cohort. Rare germline variants had no prognostic significance irrespective of treatment while some pre-leukemia variants suggest a multi-step development of chronic myeloid leukemia. Our data suggest that identification of somatic variants at diagnosis facilitates stratification into imatinib responders/non-responders, thereby allowing earlier use of second-generation tyrosine kinase inhibitors, which, in turn, may overcome the negative impact of such variants on disease progression.

A kinase profile-adapted drug combination elicits synergistic cooperative effects on leukemic cells carrying BCR-ABL1T315I in Ph+ CML

In chronic myeloid leukemia (CML), resistance against second-generation tyrosine kinase inhibitors (TKI) remains a serious clinical challenge, especially in the context of multi-resistant BCR-ABL1 mutants, such as T315I. Treatment with ponatinib may suppress most of these mutants, including T315I, but is also associated with a high risk of clinically relevant side effects. We screened for alternative treatment options employing available tyrosine kinase inhibitors (TKI) in combination. Dasatinib and bosutinib are two second-generation TKI that bind to different, albeit partially overlapping, spectra of kinase targets in CML cells. This observation prompted us to explore anti-leukemic effects of the combination dasatinib + bosutinib in highly resistant primary CML cells, various CML cell lines (K562, K562R, KU812, KCL22) and Ba/F3 cells harboring various BCR-ABL1 mutant-forms. We found that bosutinib synergizes with dasatinib in inducing growth inhibition and apoptosis in all CML cell lines and in Ba/F3 cells exhibiting BCR-ABL1^T315I. Clear synergistic effects were also observed in primary CML cells in all patients tested (n = 20), including drug-resistant cells carrying BCR-ABL1^T315I. Moreover, the drug combination produced cooperative or even synergistic apoptosis-inducing effects on CD34⁺/CD38^- CML stem cells. Finally, we found that the drug combination is a potent approach to block the activity of major additional CML targets, including LYN, KIT and PDGFRα. Together, bosutinib and dasatinib synergize in producing anti-leukemic effects in drug-resistant CML cells. Whether such cooperative TKI effects also occur in vivo in patients with drug-resistant CML, remains to be determined in forthcoming studies.

We do still transplant CML, don't we?

The remarkable clinical activity of tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) has transformed patient outcome. Consequently, allogeneic stem cell transplantation (allo-SCT) is no longer the only treatment modality with the ability to deliver long-term survival. In contrast to the central position it held in the treatment algorithm 20 years ago, allografting is now largely reserved for patients with either chronic-phase disease resistant to TKI therapy or advanced-phase disease. Over the same period, progress in transplant technology, principally the introduction of reduced intensity conditioning regimens coupled with increased donor availability, has extended transplant options in patients with CML whose outcome can be predicted to be poor if they are treated with TKIs alone. Consequently, transplantation is still a vitally important, potentially curative therapeutic modality in selected patients with either chronic- or advanced-phase CML. The major causes of transplant failure in patients allografted for CML are transplant toxicity and disease relapse. A greater understanding of the distinct contributions made by various factors such as patient fitness, patient-donor HLA disparity, conditioning regimen intensity, and transplant toxicity increasingly permits personalized transplant decision making. At the same time, advances in the design of conditioning regimens coupled with the use of adjunctive posttransplant cellular and pharmacologic therapies provide opportunities for reducing the risk of disease relapse. The role of SCT in the management of CML will grow in the future because of an increase in disease prevalence and because of continued improvements in transplant outcome.

Front-line imatinib treatment in children and adolescents with chronic myeloid leukemia: results from a phase III trial

A total of 156 patients (age range 1.3-18.0 years, median 13.2 years; 91 (58.3%) male) with newly diagnosed CML (N = 146 chronic phase (CML-CP), N = 3 accelerated phase (CML-AP), N = 7 blastic phase (CML-BP)) received imatinib up-front (300, 400, 500 mg/m², respectively) within a prospective phase III trial. Therapy response, progression-free survival, causes of treatment failure, and side effects were analyzed in 148 children and adolescents with complete data. Event-free survival rate by 18 months for patients in CML-CP (median follow-up time 25 months, range: 1-120) was 97% (95% CI, 94.2-99.9%). According to the 2006 ELN-criteria complete hematologic response by month 3, complete cytogenetic response (CCyR) by month 12, and major molecular response (MMR) by month 18 were achieved in 98, 63, and 59% of the patients, respectively. By month 36, 86% of the patients achieved CCyR and 74% achieved MMR. Thirty-eight patients (27%) experienced imatinib failure because of unsatisfactory response or intolerance (N = 9). In all, 28/148 patients (19%) underwent stem cell transplantation (SCT). In the SCT sub-cohort 2/23 patients diagnosed in CML-CP, 0/1 in CML-AP, and 2/4 in CML-BP, respectively, died of relapse (N = 3) or SCT-related complications (N = 2). This large pediatric trial extends and confirms data from smaller series that first-line imatinib in children is highly effective.

Emerging alternatives to tyrosine kinase inhibitors for treating chronic myeloid leukemia

INTRODUCTION

BCR-ABL-directed tyrosine kinase inhibitors (TKIs) have revolutionised therapy for chronic myeloid leukemia. However, despite the availability and efficacy of this class of agents, lifelong treatment is still required in a significant proportion of patients Areas covered: We give an overview of the currently available BCR-ABL-directed TKIs and other conventional therapies for CML. We proceed to review the current market and some of the scientific rationale for new drug development before outlining a number of novel therapies, considered broadly as immunotherapies and targeted agents. Published English-language literature was reviewed regarding currently available TKIs; clinical trials repositories were reviewed to identify novel agents recently investigated or under active study. Expert opinion: We recommend discussion with patients and enrolment on an appropriate clinical trial where feasible. In situations where no trials are available, or if patients decline enrolment, we recommend use of an appropriate BCR-ABL directed TKI, selected on the basis of an evaluation of patient risk factors and side effect profile. Allogeneic stem cell transplant continues to have a role though this is generally limited to cases with advanced phases of disease or in cases with resistance-conferring mutations.

Altered Metabolism of Leukemic Cells: New Therapeutic Opportunity

The cancer metabolic program alters bioenergetic processes to meet the higher demands of tumor cells for biomass production, nucleotide synthesis, and NADPH-balancing redox homeostasis. It is widely accepted that cancer cells mostly utilize glycolysis, as opposed to normal cells, in which oxidative phosphorylation is the most employed bioenergetic process. Still, studies examining cancer metabolism had been overlooked for many decades, and it was only recently discovered that metabolic alterations affect both the oncogenic potential and therapeutic response. Since most of the published works concern solid tumors, in this comprehensive review, we aim to summarize knowledge about the metabolism of leukemia cells. Leukemia is a malignant disease that ranks first and fifth in cancer-related deaths in children and adults, respectively. Current treatment has reached its limits due to toxicity, and there has been a need for new therapeutic approaches. One of the possible scenarios is improved use of established drugs and another is to introduce new druggable targets. Herein, we aim to describe the complexity of leukemia metabolism and highlight cellular processes that could be targeted therapeutically and enhance the effectiveness of current treatments.

CXorf48 is a potential therapeutic target for achieving treatment-free remission in CML patients

Although the introduction of tyrosine kinase inhibitors (TKIs) has improved overall survival of patients with chronic myeloid leukemia (CML), about half of the patients eventually relapse after cessation of TKIs. In contrast, the remainder of the patients maintain molecular remission without TKIs, indicating that the patients' immune system could control proliferation of TKI-resistant leukemic stem cells (LSCs). However, the precise mechanism of immunity against CML-LSCs is not fully understood. We have identified a novel immune target, CXorf48, expressed in LSCs of CML patients. Cytotoxic T cells (CTLs) induced by the epitope peptide derived from CXorf48 recognized CD34⁺CD38^- cells obtained from the bone marrow of CML patients. We detected CXorf48-specific CTLs in the peripheral blood mononuclear cells from CML patients who have discontinued imatinib after maintaining complete molecular remission for more than 2 years. Significantly, the relapse rate of CXorf48-specific CTL-negative patients was 63.6%, compared to 0% in CXorf48-specific CTL-positive patients. These results indicate that CXorf48 could be a promising therapeutic target of LSCs for immunotherapy to obtain durable treatment-free remission in CML patients.

Hematopoietic Stem Cell Transplantation: A Bioethical Lens

Hematopoietic stem cell transplantation (HSCT) is one of a range of therapeutic options available to patients suffering from various diseases. HSCT procedure involves important ethical and legal aspects that can occur at every phase of the procedure: the clinical choice of whether to perform the procedure, pretransplantation preparation regimens, donor selection, stem cell harvest procedure, transplantation phase, and short-term and long-term follow-up care. In this discussion paper, we outline the ethical issue-facing physicians involved in HSCT. Currently, HSCT is a widely accepted treatment for many life-threatening diseases. It thus represents a real therapeutic hope for many patients. It does, however, carry a burden of possible morbidity and mortality. Consequently, there are substantial information and communication issues involved in the consent process for HSCT. In the final decision, the judgements of different parties, such as patients, family members, and healthcare professionals, intersect and overlap and this is particularly true when the patient is a minor. Finally, HSCT is a very expensive procedure. The social and economic concerns of HSCT are discussed within the actual contextual framework of the dramatic increase in healthcare costs and inequalities in healthcare in relation to socioeconomic status, educational status, and ethnicity.

Tyrosine kinase inhibitors in chronic myeloid leukaemia: which, when, for whom?

The therapeutic armamentarium for chronic myeloid leukaemia (CML) comprises mainly tyrosine kinase inhibitors (TKIs), with several agents available for frontline treatment, or for the treatment of disease resistance or intolerance to the first-choice or second-choice drug. The availability of different drugs is a major achievement, but means that choices must be made - which can be difficult and questionable at times. The most important end point considered in decision-making regarding treatment for any cancer is overall survival, but additional factors (such as age, prognostic category, safety, or the possibility of achieving treatment-free remission) should be considered when selecting an agent for frontline treatment. Regardless of the TKI selected for first-line treatment, guidelines that define the importance of reaching specific response indicators and procedures for vigilant follow-up monitoring are established to ensure timely implementation of second-line TKIs. Herein, we discuss the benefits and risks of the different TKIs available for the treatment of patients with CML, and how to decide when to employ these agents at different treatment settings.

Chronic myeloid leukemia: reminiscences and dreams

With the deaths of Janet Rowley and John Goldman in December 2013, the world lost two pioneers in the field of chronic myeloid leukemia. In 1973, Janet Rowley, unraveled the cytogenetic anatomy of the Philadelphia chromosome, which subsequently led to the identification of the BCR-ABL1 fusion gene and its principal pathogenetic role in the development of chronic myeloid leukemia. This work was also of major importance to support the idea that cytogenetic changes were drivers of leukemogenesis. John Goldman originally made seminal contributions to the use of autologous and allogeneic stem cell transplantation from the late 1970s onwards. Then, in collaboration with Brian Druker, he led efforts to develop ABL1 tyrosine kinase inhibitors for the treatment of patients with chronic myeloid leukemia in the late 1990s. He also led the global efforts to develop and harmonize methodology for molecular monitoring, and was an indefatigable organizer of international conferences. These conferences brought together clinicians and scientists, and accelerated the adoption of new therapies. The abundance of praise, tributes and testimonies expressed by many serve to illustrate the indelible impressions these two passionate and affable scholars made on so many people's lives. This tribute provides an outline of the remarkable story of chronic myeloid leukemia, and in writing it, it is clear that the historical triumph of biomedical science over this leukemia cannot be considered without appreciating the work of both Janet Rowley and John Goldman.