Prevalence and dynamics of bcr-abl kinase domain mutations during imatinib treatment differ in patients with newly diagnosed and recurrent bcr-abl positive acute lymphoblastic leukemia

Tyrosine kinase inhibitor resistance in de novo BCR::ABL1-positive BCP-ALL beyond kinase domain mutations

ABSTRACT

A better understanding of ABL1 kinase domain mutation-independent causes of tyrosine kinase inhibitor (TKI) resistance is needed for BCR::ABL1-positive B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Although TKIs have dramatically improved outcomes, a subset of patients still experiences relapsed or refractory disease. We aimed to identify potential biomarkers of intrinsic TKI resistance at diagnosis in samples from 32 pediatric and 19 adult patients with BCR::ABL1-positive BCP-ALL. Reduced ex vivo imatinib sensitivity was observed in cells derived from newly diagnosed patients who relapsed after combined TKI and chemotherapy treatment compared with cells derived from patients who remained in continuous complete remission. We observed that ex vivo imatinib resistance was inversely correlated with the amount of (phosphorylated) BCR::ABL1/ABL1 protein present in samples that were taken at diagnosis without prior TKI exposure. This suggests an intrinsic cause of TKI resistance that is independent of functional BCR::ABL1 signaling. Simultaneous deletions of IKZF1 and CDKN2A/B and/or PAX5 (IKZF1plus), as well as deletions of PAX5 alone, were related to ex vivo imatinib resistance. In addition, somatic lesions involving ZEB2, SETD2, SH2B3, and CRLF2 were associated with reduced ex vivo imatinib sensitivity. Our data suggest that the poor prognostic value of IKZF1(plus) deletions is linked to intrinsic mechanisms of TKI resistance other than ABL1 kinase domain mutations in newly diagnosed pediatric and adult BCR::ABL1-positive BCP-ALL.

Resistance of Lung Cancer to EGFR-Specific Kinase Inhibitors: Activation of Bypass Pathways and Endogenous Mutators

Epidermal growth factor receptor (EGFR)-specific tyrosine kinase inhibitors (TKIs) have changed the landscape of lung cancer therapy. For patients who are treated with the new TKIs, the current median survival exceeds 3 years, substantially better than the average 20 month survival rate only a decade ago. Unfortunately, despite initial efficacy, nearly all treated patients evolve drug resistance due to the emergence of either new mutations or rewired signaling pathways that engage other receptor tyrosine kinases (RTKs), such as MET, HER3 and AXL. Apparently, the emergence of mutations is preceded by a phase of epigenetic alterations that finely regulate the cell cycle, bias a mesenchymal phenotype and activate antioxidants. Concomitantly, cells that evade TKI-induced apoptosis (i.e., drug-tolerant persister cells) activate an intrinsic mutagenic program reminiscent of the SOS system deployed when bacteria are exposed to antibiotics. This mammalian system imbalances the purine-to-pyrimidine ratio, inhibits DNA repair and boosts expression of mutation-prone DNA polymerases. Thus, the net outcome of the SOS response is a greater probability to evolve new mutations. Deeper understanding of the persister-to-resister transformation, along with the development of next-generation TKIs, EGFR-specific proteolysis targeting chimeras (PROTACs), as well as bispecific antibodies, will permit delaying the onset of relapses and prolonging survival of patients with EGFR+ lung cancer.

Droplet digital polymerase chain reaction improves the detection of BCR-ABL1 kinase domain mutation in Philadelphia chromosome-positive acute lymphoblastic leukemia

INTRODUCTION

Sanger sequencing (SS) is the most frequently used method for detecting ABL1 kinase domain (KD) mutations in patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ ALL). However, it cannot detect low levels of mutation. Recently, droplet digital polymerase chain reaction (ddPCR) has been developed as a sensitive technique for detecting mutations in hematological neoplasms. The aim of our study was to explore the value of ddPCR in detecting ABL1 KD mutations.

METHODS

We compared the results of SS and ddPCR in detecting ABL1 KD mutations in a consecutive cohort of 65 adolescent and adult patients with Ph⁺ ALL treated with intensive multiagent chemotherapy plus TKIs.

RESULTS

At diagnosis, SS and ddPCR identified 1 (1.5%) and 26 (40%) out of 65 patients with positive ABL1 KD mutations, respectively. Patients with T315I mutations detected by ddPCR at diagnosis all developed SS-detectable T315I mutations during treatment with first- or second-generation TKIs, and non-T315I mutations detected by ddPCR at diagnosis displayed a limited prognostic impact.

CONCLUSION

Our study demonstrates that ddPCR is a highly sensitive and accurate mutation detection method and the presence of T315I mutations before treatment shows prognostic significance in the context of first- or second-generation TKIs.

JAK2 Alterations in Acute Lymphoblastic Leukemia: Molecular Insights for Superior Precision Medicine Strategies

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer, arising from immature lymphocytes that show uncontrolled proliferation and arrested differentiation. Genomic alterations affecting Janus kinase 2 (JAK2) correlate with some of the poorest outcomes within the Philadelphia-like subtype of ALL. Given the success of kinase inhibitors in the treatment of chronic myeloid leukemia, the discovery of activating JAK2 point mutations and JAK2 fusion genes in ALL, was a breakthrough for potential targeted therapies. However, the molecular mechanisms by which these alterations activate JAK2 and promote downstream signaling is poorly understood. Furthermore, as clinical data regarding the limitations of approved JAK inhibitors in myeloproliferative disorders matures, there is a growing awareness of the need for alternative precision medicine approaches for specific JAK2 lesions. This review focuses on the molecular mechanisms behind ALL-associated JAK2 mutations and JAK2 fusion genes, known and potential causes of JAK-inhibitor resistance, and how JAK2 alterations could be targeted using alternative and novel rationally designed therapies to guide precision medicine approaches for these high-risk subtypes of ALL.

Therapeutic approach and outcome of children with Philadelphia chromosome-positive acute lymphoblastic leukemia at first relapse in the era of tyrosine kinase inhibitors: An SFCE retrospective study

BACKGROUND

Since the introduction of tyrosine kinase inhibitors (TKIs), the profile of pediatric relapse of Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ ALL) has changed. However, the management of pediatric Ph⁺ ALL relapses is not currently standardized.

PROCEDURE

We retrospectively analyzed the therapeutic strategies and outcomes of pediatric Ph⁺ ALL patients in first relapse who were initially treated with a TKI-containing regimen in one of the French pediatric hematology centers from 2004 to 2019.

RESULTS

Twenty-seven children experienced a Ph⁺ ALL relapse: 24 (89%) had an overt relapse and three a molecular relapse. Eight involved the central nervous system. A second complete remission (CR2) was obtained for 26 patients (96%). Induction consisted of nonintensive chemotherapy for 13 patients (48%) and intensive chemotherapy for 14 (52%). Thirteen patients (48%) received consolidation. Allogenic hematopoietic stem cell transplantation (alloHSCT) was performed for 21 patients (78%). The TKI was changed for 23 patients (88%), mainly with dasatinib (n = 15). T315I was the most common mutation at relapse (4/7). The 4-year event-free survival and survival rates were 60.9% and 76.1%, respectively. Survival was positively associated with alloHSCT in CR2.

CONCLUSION

We show that pediatric first-relapse Ph⁺ ALL reinduces well with a second course of TKI exposure, despite the use of different therapeutic approaches. The main prognostic factor for survival was alloHSCT in CR2. Because of the small size of the cohort, we could not draw any conclusions about the respective impact of TKIs, but the predominance of the T315I mutation should encourage careful consideration of the TKI choice.

Emerging tyrosine kinase inhibitors for the treatment of adult acute lymphoblastic leukemia

Introduction: The broadening of targeted and immunotherapeutic strategies markedly impacted on the management of acute lymphoblastic leukemia (ALL). The advent of tyrosine kinase inhibitors (TKIs) changed the history of Philadelphia-chromosome positive (Ph+) ALL. Nowadays, almost all Ph+ ALL patients treated with TKIs achieve a complete hematologic response, and most become minimal residual disease negative. In Ph- ALL, genomic profiling studies have identified a subtype associated with a high relapse risk and a transcriptional profile similar to that of Ph+ ALL, the so-called Ph-like ALL. Given the high prevalence of kinase-activating lesions in this subset, there is compelling evidence from experimental models and clinical observations favoring TKI administration.Areas covered: We discuss the main findings exploring the efficacy of TKIs in ALL.Expert opinion: The use of more potent TKIs will further enhance the inhibitory activity on leukemia cells and increase the possibility of eradicating the disease at a molecular level. In the future, 'combined' approaches of different inhibitors may be considered to prevent/avoid resistance and/or mutations. A rapid identification of Ph-like ALL patients is needed to propose early TKI-based intervention. Several questions remain open, including the initial TKI choice in Ph+ ALL and whether Ph-like ALL patients might benefit from immunotherapy.

Next-generation sequencing improves BCR-ABL1 mutation detection in Philadelphia chromosome-positive acute lymphoblastic leukaemia

BCR-ABL1 kinase domain mutation testing in tyrosine kinase inhibitor (TKI)-resistant Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukaemia (ALL) patients is routinely performed by Sanger sequencing (SS). Recently, next-generation sequencing (NGS)-based approaches have been developed that afford greater sensitivity and straightforward discrimination between compound and polyclonal mutations. We performed a study to compare the results of SS and NGS in a consecutive cohort of 171 Ph+ ALL patients. At diagnosis, 0/44 and 3/44 patients were positive for mutations by SS and NGS respectively. Out of 47 patients with haematologic resistance, 45 had mutations according to both methods, but in 25 patients NGS revealed additional mutations undetectable by SS. Out of 80 patients in complete haematologic response but with BCR-ABL1 ≥0·1%, 28 (35%) and 52 (65%) were positive by SS and NGS respectively. Moreover, in 12 patients positive by SS, NGS detected additional mutations. NGS resolved clonal complexity in 34 patients with multiple mutations at the same or different codons and identified 35 compound mutations. Our study demonstrates that, in Ph+ ALL on TKI therapy, NGS enables more accurate assessment of mutation status both in patients who fail therapy and in patients with minimal residual disease above 0·1%.

New approaches to the treatment of older adults with acute lymphoblastic leukemia

Outcomes for older adults (defined here as ≥55-65 years old) with acute lymphoblastic leukemia (ALL) are poor, with long-term survival less than 20%. Pediatric chemotherapy regimens produce long-term cure rates of 80% to 90% in children and 60% to 70% in adolescents and young adults with Ph-negative ALL, however, tolerability of intensive chemotherapy becomes problematic with advanced age due to comorbidities and reduced tolerability of chemotherapy leading to high rates of treatment-related mortality. For older adults with Ph-positive ALL, BCR-ABL1-directed tyrosine kinase inhibitors in combination with corticosteroids or chemotherapy produce deep remissions with low treatment-related toxicity but optimal postremission therapy is not known. New therapeutic approaches for older adults with ALL involve integration of the novel targeted agents including monoclonal antibody-based therapy with blinatumomab and inotuzumab ozogamicin in the frontline. Ongoing studies will ideally define optimal combinations and sequencing of novel agents with or without chemotherapy, tyrosine kinase inhibitors, and/or corticosteroids to maximize efficacy while avoiding treatment-related death. Anti-CD19 chimeric antigen receptor modified T cells are a promising modality, with high rates of remission and minimal residual disease negativity achieved in early phase trials for adults with relapsed/refractory B-cell ALL but the tolerability of chimeric antigen receptor modified T cell therapies in older adults is yet to be well defined. Advances in minimal residual disease detection have helped to effectively stratify adults in complete response in terms of relapse risk and predicted relative benefit for allogeneic hematopoietic cell transplant. For older adults with ALL in complete response at high risk for relapse for whom myeloablative conditioning is predicted to result in excessive transplant-related mortality, reduced-intensity conditioning allogeneic hematopoietic cell transplant is a less toxic approach for providing a graft-versus-leukemia effect and long-term disease control.

Population-based utilization and costs associated with tyrosine kinase inhibitors for first-line treatment of chronic myelogenous leukemia among elderly patients

BACKGROUND: Following approval of imatinib, a breakthrough tyrosine kinase inhibitor (TKI), survival significantly improved by more than 20% since 2001 among treated chronic myelogenous leukemia (CML) patients. Subsequently, more expensive second-generation TKIs with varying selectivity profiles have been approved. Population-based studies are needed to evaluate the real-world utilization of TKI therapies, particularly given their escalating costs and recommendations for maintenance therapy. OBJECTIVE: To assess the utilization patterns of first-line TKIs, overall and by specific agent, among elderly CML patients in the United States, and the cost implications. METHODS: CML patients aged 65 years and older at diagnosis between 2007 and 2015 were identified from population-based cancer registries in the linked Surveillance, Epidemiology, and End Results (SEER)-Medicare database. The percentage of CML patients receiving imatinib, dasatinib, or nilotinib within the first year of diagnosis was calculated along with time to first-line treatment initiation. Bivariate comparisons and Cox proportional hazards models were used to identify factors associated with TKI initiation. Average monthly patient responsibility, including patient out-of-pocket (OOP) costs, stratified by Part D low-income subsidy (LIS) status were also calculated. RESULTS: Among the 1,589 CML patients included, receipt of any TKI within 1 year of diagnosis increased from 66.2% to 78.9%. In 2015, the distribution of first-line TKI therapies was 41.3% imatinib, 28.3% dasatinib, and 9.3% nilotinib. Almost 60% of patients initiated TKI treatment within 3 months of diagnosis. Multivariable analysis indicated that TKI use in the first year was lower among the very elderly (aged > 75 years vs. 65-69 years: HR = 0.72; 95% CI = 0.63-0.83), patients with more comorbidities (Hierarchical Condition Category risk score > 2 vs. HR = 0.74, 95% CI = 0.62-0.88), and patients ineligible for LIS (HR = 0.75; 95% CI = 0.65-0.87). Average monthly patient OOP cost was significantly lower for LIS-eligible versus LIS-ineligible patients: imatinib (2016: $12 vs. $487), dasatinib (2016: $34 vs. $557), and nilotinib (2016: $1 vs. $526). CONCLUSIONS: TKI use has increased significantly since 2007. While imatinib remained the most frequently prescribed first-line agent, by 2015 newer TKIs represented one third of the market share. Utilization patterns indicated persistent age, comorbidity, and financial barriers. TKI use is indicated for long-term therapy, and increased adoption of newer, more expensive agents raises concerns about the sustained affordability of CML treatment, particularly among unsubsidized patients. DISCLOSURES: No outside funding supported this study. There are no reported conflicts of interest.

A new pre-emptive TKIs strategy for preventing relapse based on BCR/ABL monitoring for Ph+ALL undergoing allo-HCT: a prospective clinical cohort study

Relapse is a major cause of treatment failure in Philadelphia-chromosome-positive acute lymphoblastic leukemia (Ph+ALL) undergoing allogeneic hematopoietic cell transplantation (allo-HCT). This study aimed to evaluate the effect of a new pre-emptive tyrosine kinase inhibitors (TKIs) strategy on relapse in Ph+ALL patients with complete remission undergoing allo-HCT. Pre-emptive TKIs initiation was based on BCR/ABL molecular monitoring. TKIs choice was based on BCR/ABL mutations. Donor lymphocyte infusion was recommended in those with poor response to TKIs. Prophylactic TKIs from historical data were as control. The primary endpoint was relapse. One hundred and sixty-seven Ph+ALL patients were enrolled in this study, including 103 in the pre-emptive group and 64 in the prophylactic group. The 3-year cumulative incidence of relapse was 11% and 31% in the pre-emptive and prophylactic groups (P = 0.001), respectively. The 3-year overall survival (OS) was 87% and 66% (P = 0.001), and leukemia-free survival (LFS) was 83% and 61% (P = 0.000), respectively, in the pre-emptive and prophylactic groups. Multivariate analysis showed that the pre-emptive strategy was the protective factor for relapse, OS, and LFS (P = 0.005, P = 0.005, and P = 0.003, respectively). Our data suggest that this new pre-emptive TKIs strategy based on BCR/ABL molecular monitoring might reduce relapse and improve survival for Ph+ALL patients undergoing allo-HCT. ClinicalTrials.Gov Identifier (NCT01883219).

A variant e13a3 BCR-ABL1 fusion transcript in refractory adult B-cell acute lymphoblastic leukemia achieving complete remission with CAR-Tcell therapy

Acute lymphoblastic leukemia (ALL) cases with e13a3 fusion transcripts are extremely rare. We report a 24-year-old male with Ph-positive (Ph+) ALL with an aberrant e13a3 fusion transcript treated with CD19-specific chimeric antigen receptor T-cell (CAR-T) therapy. He developed refractory disease post-chemotherapy induction, andreceived allogeneic hematopoietic stem cell transplantation (allo-HSCT) after salvage with imatinib in combination with chemotherapy regimen. Unfortunately, the patient relapsed after +90 days post-transplant. He was consented to CAR-T therapy trial and achieved complete remission, highlighting the efficacy of CAR-T treatment in relapsed-refractory B-ALL irrespective of the underlying genetic drivers in leukemia cells .

Ultra-accurate Duplex Sequencing for the assessment of pretreatment ABL1 kinase domain mutations in Ph+ ALL

Mutations of ABL1 are the dominant mechanism of relapse in Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph + ALL). We performed highly accurate Duplex Sequencing of exons 4–10 of ABL1 on bone marrow or peripheral blood samples from 63 adult patients with previously untreated Ph + ALL who received induction with intensive chemotherapy plus a BCR-ABL1 TKI. We identified ABL1 mutations prior to BCR-ABL1 TKI exposure in 78% of patients. However, these mutations were generally present at extremely low levels (median variant allelic frequency 0.008% [range, 0.004%–3.71%] and did not clonally expand and lead to relapse in any patient, even when the pretreatment mutation was known to confer resistance to the TKI received. In relapse samples harboring a TKI-resistant ABL1 mutation, the corresponding mutation could not be detected pretreatment, despite validated sequencing sensitivity of Duplex Sequencing down to 0.005%. In samples under the selective pressure of ongoing TKI therapy, we detected low-level, emerging resistance mutations up to 5 months prior to relapse. These findings suggest that pretreatment ABL1 mutation assessment should not guide upfront TKI selection in Ph + ALL, although serial testing while on TKI therapy may allow for early detection of clinically actionable resistant clones.

Next-generation sequencing for BCR-ABL1 kinase domain mutations in adult patients with Philadelphia chromosome-positive acute lymphoblastic leukemia: A position paper

Emergence of clones carrying point mutations in the BCR‐ABL1 kinase domain (KD) is a common mechanism of resistance to tyrosine kinase inhibitor (TKI)‐based therapies in Philadelphia chromosome‐positive (Ph+) acute lymphoblastic leukemia (ALL). Sanger sequencing (SS) is the most frequently used method for diagnostic BCR‐ABL1 KD mutation screening, but it has some limitations—it is poorly sensitive and cannot robustly identify compound mutations. Next‐generation sequencing (NGS) may overcome these problems. NSG is increasingly available and has the potential to become the method of choice for diagnostic BCR‐ABL1 KD mutation screening. A group discussion within an ad hoc constituted Panel of Experts has produced a series of consensus‐based statements on the potential value of NGS testing before and during first‐line TKI‐based treatment, in relapsed/refractory cases, before and after allo‐stem cell transplantation, and on how NGS results may impact on therapeutic decisions. A set of minimal technical and methodological requirements for the analysis and the reporting of results has also been defined. The proposals herein reported may be used to guide the practical use of NGS for BCR‐ABL1 KD mutation testing in Ph+ ALL.

A novel BCR-ABL1 mutation in a patient with Philadelphia chromosome-positive B-cell acute lymphoblastic leukemia

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) represents the most common genetic subtype of adult ALL (20%–30%) and accounts for approximately 50% of all cases in the elderly. It has been considered the subgroup of ALL with the worst outcome. The introduction of tyrosine kinase inhibitors (TKIs) allows complete hematologic remission virtually in all patients, with improved disease-free survival and overall survival. Nevertheless, the emergence of resistant mutations in BCR-ABL1 may require different TKI strategies to overcome the patient’s resistance and disease relapse. Here, we report a Ph+B-ALL case with persistent minimal residual disease (MRD) after treatment with dasatinib. The patient expressed the P190^BCR-ABL1 isoform and a novel BCR-ABL1 mutation, p.Y440C. The latter is in the C-terminal lobe of the kinase domain, which likely induces deviations in the protein structure and activity and destabilizes its inactive conformation. The treatment was substituted by bosutinib, which binds to the active conformation of the protein, prior to allogeneic bone marrow transplant to overcome the lack of a complete response to dasatinib. These findings strengthen the importance of BCR-ABL1 mutational screening in Ph+ patients, particularly for those who do not achieve complete molecular remission.

Direct and rapid identification of T315I-Mutated BCR-ABL expressing leukemic cells using infrared microspectroscopy

Despite the major success obtained by the use of tyrosine kinase inhibitors (TKI) in chronic myeloid leukemia (CML), resistances to therapies occur due to mutations in the ABL-kinase domain of the BCR-ABL oncogene. Amongst these mutations, the "gatekeeper" T315I is a major concern as it renders leukemic cells resistant to all licenced TKI except Ponatinib. We report here that Fourier transform infrared (FTIR) microspectroscopy is a powerful methodology allowing rapid and direct identification of a spectral signature in single cells expressing T315I-mutated BCR-ABL. The specificity of this spectral signature is confirmed using a Dox-inducible T315I-mutated BCR-ABL-expressing human UT-7 cells as well as in murine embryonic stem cells. Transcriptome analysis of UT-7 cells expressing BCR-ABL as compared to BCR-ABL T315I clearly identified a molecular signature which could be at the origin of the generation of metabolic changes giving rise to the spectral signature. Thus, these results suggest that this new methodology can be applied to the identification of leukemic cells harbouring the T315I mutation at the single cell level and could represent a novel early detection tool of mutant clones. It could also be applied to drug screening strategies to target T315I-mutated leukemic cells.

Current paradigms in the management of Philadelphia chromosome positive acute lymphoblastic leukemia in adults

Philadelphia chromosome-positive (Ph-positive) acute lymphoblastic leukemia (ALL) is a biologically, clinically, and genetically distinct subtype of precursor-B ALL. The Ph chromosome, results from a reciprocal translocation of the ABL1 kinase gene on chromosome 9 to the breakpoint cluster region (BCR) gene on chromosome 22. Depending on the translocation breakpoint, typically a p210 BCR-ABL1 or a p190 BCR-ABL onc protein are generated; both are constitutively active tyrosine kinases that play a central role to alter signaling pathways of cell proliferation, survival, and self-renewal, leading to leukemogenesis. In Ph-positive ALL, the p190-BCR-ABL (minor [m]-bcr) subtype is more frequent than the p210-BCR-ABL (major [M]-bcr) subtype, commonly found in chronic myeloid leukemia. The Philadelphia chromosome is the most frequent recurrent cytogenetic abnormality in elderly patients with ALL. Its incidence increases with age, reaching ∼50% in patients with ALL aged 60 years and over. Patients traditionally had a very poor outcome with chemotherapy, particularly if they do not undergo allogeneic hematopoietic cell transplantation (allo-HCT) in first complete remission (CR1). With the availability of multiple tyrosine kinase inhibitors (TKI), the therapeutic armamentarium is expanding quickly. However, there is no consensus on how to best treat Ph-positive ALL. With modern therapy, improved outcomes have led to the emergence of a number of controversies, including the need for intensive chemotherapy, the ideal TKI, and whether all eligible patients should receive an allo-HSCT, and if so, what type. Here, we discuss these controversies in light of the available literature.

Targeting of heme oxygenase-1 attenuates the negative impact of Ikaros isoform 6 in adult BCR-ABL1-positive B-ALL

The correlation between Heme oxygenase-1 (HO-1) and dominant-negative Ikaros isoform 6 (IK6) is unclear. Firstly, we detected that IK6 existed in 20 of 42 (47.6%) adult BCR-ABL1-positive B-lineage acute lymphoblastic leukemia (BCR-ABL1-positive B-ALL) by using reverse transcribed polymerase chain reaction (PCR) and nucleotide sequencing. IK6-positive patients had an unfavorable outcome compared with IK6-negative ones. Further study showed that the level of HO-1 expression was higher in IK6-positive patients' samples than that in IK6-negative ones. And there was a strong correlation between the expression of IK6 and HO-1. The growth of primary CD34+ leukemic cells derived from our IK6-positive patients' pool was prohibited by silencing HO-1, further promoting their apoptosis. Furthermore, primary CD34+ leukemic cells derived from IK6-positive patients shown poor responses to imatinib in comparison with wild-type (IK1) patients, suggesting that the expression of IK6 resisted to imatinib in adult BCR-ABL1-positive B-ALL. Importantly, inhibition of HO-1 also increased their sensitivity to tyrosine kinase inhibitors (TKIs). Finally, we found that IK6 activated downstream STAT5, and HO-1 was one of the downstream target genes of STAT5. In conclusion, HO-1 is an essential survival factor in BCR-ABL1-positive B-ALL with IK6, and targeting HO-1 can attenuate the negative impact of IK6.

Upfront treatment with the first and second-generation tyrosine kinase inhibitors in Ph-positive acute lymphoblastic leukemia

The treatment of Ph-positive acute lymphoblastic leukemia (Ph+ ALL) has entranced tyrosine kinase inhibitors (TKIs) era. Currently both imatinib and dasatinib are registered as the front-line treatment for Ph+ ALL, and the other 2^nd-generation TKIs are suggested as an alternative for those who failed the first-line treatment. However, it remains unclear who could benefit from the 2^nd-generation TKIs as the first-line treatment for Ph+ ALL. In this study we compared the efficacy and safety of the 1^st and 2^nd-generation TKIs in the front-line treatment of Ph+ ALL and found a trend toward better disease-free survival (DFS) in the 2^nd-generation TKIs group, though no significant difference in early response and long-term survival between the two groups. Furthermore, subgroup analysis showed that if allogeneic hematopoietic stem cell transplantation (allo-HSCT) was incorporated as consolidation, the 2^nd-generation TKIs benefited patients with better DFS and overall survival (OS). The two generation TKIs were well tolerated. Higher incidence of acquiring T315I mutation was observed in the patients relapsed on the 2^nd-generation TKIs. These findings suggested front-line treatment of Ph+ ALL with the 2^nd-generation TKIs might benefit patients with better survival when allo-HSCT was incorporated as consolidation therapy; meanwhile, the higher incidence of T315I mutation in patients relapsed on the 2^nd-generation TKIs deserved further attention.

Characteristics and mutation analysis of Ph-positive leukemia patients with T315I mutation receiving tyrosine kinase inhibitors

Background

TKIs are the first-line treatment for patients with Ph-positive (Ph+) leukemia. However, drug resistance is frequently observed, mainly due to mutations within the breakpoint cluster region-Abelson leukemia virus (BCR-ABL) kinase domain. The T315I substitution confers complete resistance to TKIs. The aim of this study was to analyze the clinical characteristics of 17 patients with T315I mutation after TKI treatment and provide a basis for prognosis.

Patients and methods

The clinical data of 17 TKI-resistant Ph+ leukemia patients who were found to have a ABL kinase domain mutation from September 2008 to January 2017 were collected. Karyotypes and BCR-ABL fusion gene were analyzed by R-banding and fluorescence in situ hybridization, respectively. Total RNA was extracted by TRIzol reagent, and the ABL kinase domain mutation was detected by direct sequencing.

Results

A total of 17 patients reached effective remission including major molecular response and complete cytogenetic response. However, all the patients subsequently developed a T315I mutation after treatment with TKIs. The rate of the BCR-ABL fusion gene in most of the patients who developed the T315I mutation was significantly higher than that before the mutation. At initial diagnosis, patients average platelet count was 149.7×10⁹/L, whereas the average platelet count was only 53.88×10⁹/L after the T315I mutation (P<0.01). The results also showed that the survival time of patients with a high proportion of blast cells or a high number of white blood cells was obviously shortened.

Conclusion

Patients platelet count decreased when detected with the T315I mutation compared with the initial diagnosis. Combined use of different TKIs and complex chromosomal karyotypes may promote the development of the T315I mutation. When the ratio of blast cells was >50% and the number of white blood cells was >20×10⁹/L, poor survival prognosis was observed.

Which tyrosine kinase inhibitor should we use to treat Philadelphia chromosome-positive acute lymphoblastic leukemia?

The incorporation of tyrosine kinase inhibitors (TKIs) into chemotherapy regimens has significantly improved the long-term survival of patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL). Successive generations of TKIs with increased potency against BCR-ABL and broader spectrum of activity against ABL kinase domain mutations have led to incremental improvements in the outcomes of patients with this disease. In particular, ponatinib, a potent pan-BCR-ABL TKI capable of overcoming the T315I mutation, holds significant promise in the treatment of Ph+ ALL, although the potential cardiovascular toxicity of this agent remains a concern. With the development of more potent TKIs that are capable of inducing deep and sustained remissions, future studies re-evaluating the need for intensive chemotherapy as well as the role for stem cell transplantation in first remission for patients with Ph+ ALL are warranted.

T-cell-rich HLA-haploidentical hematopoietic stem cell transplantation for relapsed/refractory pediatric Philadelphia chromosome-positive acute lymphoblastic leukemia without posttransplant tyrosine kinase inhibitor therapy

Intensive chemotherapy with tyrosine kinase inhibitor (TKI) improves the prognosis of patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph-ALL). However, the prognosis of cases of relapsed or refractory Ph-ALL remains poor. Here, we aimed to assess the efficacy of T-cell-rich HLA-haploidentical hematopoietic stem cell transplantation (TCR-haplo-HSCT) in eight patients with relapsed or refractory pediatric Ph-ALL. Transplant-related mortality was observed in two patients. All patients discontinued TKI after receiving TCR-haplo-HSCT. The 3-year probability of overall survival and event-free survival was 75.0 and 62.5%, respectively. These results indicate the efficacy of TCR-haplo-HSCT for relapsed/refractory pediatric Ph-ALL.

Growth of tyrosine kinase inhibitor-resistant Philadelphia-positive acute lymphoblastic leukemia: Role of bone marrow stromal cells

Human bone marrow stromal cells (hBMSCs) may contribute to the growth of tyrosine kinase inhibitor (TKI)-resistant chronic myelogenous leukemia (CML). However, there are certain differences in biology between CML and Philadelphia-positive acute lymphoblastic leukemia (Ph⁺ ALL). Little is known about the role and mechanism of hBMSCs on the growth of TKI-resistant Ph⁺ ALL. The current study co-cultured hBMSCs with the TKI-resistant SUP-B15. Next, the proliferation of SUP-B15 was detected using a Cell Counting Kit-8. Additionally, quantitative polymerase chain reaction and flow cytometry were used to detect the expression of the associated genes and proteins. The present study explores the role and mechanism of hBMSCs on the growth of TKI-resistant Ph⁺ ALL. The current study showed that hBMSCs promoted the proliferation of TKI-resistant Ph⁺ ALL. This was shown by the increase in cells in the S+G2-M phase of the cell cycle. It was also found that the expression of cyclins A, C, D1 and E was increased. Apoptosis was inhibited through upregulation of anti-apoptotic genes [B-cell lymphoma-2 (BCL-2) and BCL-extra large] and downregulation of apoptotic genes (BCL-XS, BCL-2-associated X protein, and caspases 3, 7 and 9). Expression of the breakpoint cluster region (BCR)-Abelson murine leukemia viral oncogene homolog 1 (ABL) gene, Wnt5a, and Wnt signaling pathway-associated genes (glycogen synthase kinase-3β, β-catenin, E-cadherin and phosphoinositide 3-kinase) and transcription factors (c-myc, ephrin type-B2, fibroblast growth factor 20 and matrix metalloproteinase 7) was also increased. Furthermore, the expression of drug resistance genes (low-density lipoprotein receptor, multidrug resistance-associated protein and multi-drug resistance gene) was increased and the expression of anti-oncogenes (death-associated protein kinase and interferon regulatory factor-1) was decreased. It was concluded that hBMSCs promote the growth of TKI-resistant Ph⁺ ALL by these aforementioned mechanisms. Therefore, targeting hBMSCs may be a promising approach for preventing the growth of TKI-resistant Ph⁺ ALL.

The development of targeted new agents to improve the outcome for children with leukemia

INTRODUCTION

Survival rates in pediatric leukemia have greatly improved in the last decades but still a substantial number of patients will relapse and die. New agents are necessary to overcome the limitations of conventional chemotherapy and hematopoietic stem cell transplantation and to reduce their undesirable long-term toxicities. The identification of driving molecular alterations of leukemogenesis in subsets of patients will allow the incorporation of new-targeted therapies. Areas covered: In this article the authors present a detailed review of the most recent advances in targeted therapies for pediatric leukemias. A comprehensive description of the biological background, adult data and early clinical trials in pediatrics is provided. Expert opinion: Clinical trials are the way to evaluate new agents in pediatric cancer. The development of new drugs in pediatric leukemia must be preceded by a solid biological rationale. Agents in development exploit all possible vulnerabilities of leukemic cells. Drugs targeting cell surface antigens, intracellular signaling pathways and cell cycle inhibitors or epigenetic regulators are most prominent. Major advances have occurred thanks to new developments in engineering leading to optimized molecules such as anti-CD19 bi-specific T-cell engagers (e.g. blinatumomab) and antibody-drug conjugates. The integration of new-targeted therapies in pediatric chemotherapy-based regimens will lead to improved outcomes.

Dasatinib and low-intensity chemotherapy in elderly patients with Philadelphia chromosome-positive ALL

Prognosis of Philadelphia-positive (Ph(+)) acute lymphoblastic leukemia (ALL) in the elderly has improved during the imatinib era. We investigated dasatinib, another potent tyrosine kinase inhibitor, in combination with low-intensity chemotherapy. Patients older than age 55 years were included in the European Working Group on Adult ALL (EWALL) study number 01 for Ph(+) ALL (EWALL-PH-01 international study) and were treated with dasatinib 140 mg/day (100 mg/day over 70 years) with intrathecal chemotherapy, vincristine, and dexamethasone during induction. Patients in complete remission continued consolidation with dasatinib, sequentially with cytarabine, asparaginase, and methotrexate for 6 months. Maintenance therapy was dasatinib and vincristine/dexamethasone reinductions for 18 months followed by dasatinib until relapse or death. Seventy-one patients with a median age of 69 years were enrolled; 77% had a high comorbidity score. Complete remission rate was 96% and 65% of patients achieved a 3-log reduction in BCR-ABL1 transcript levels during consolidation. Only 7 patients underwent allogeneic hematopoietic stem cell transplantation. At 5 years, overall survival was 36% and up to 45% taking into account deaths unrelated to disease or treatment as competitors. Thirty-six patients relapsed, 24 were tested for mutation by Sanger sequencing, and 75% were T315I-positive. BCR-ABL1(T315I) was tested by allele-specific oligonucleotide reverse transcription-quantitative polymerase chain reaction in 43 patients and detection was associated with short-term relapses. Ten patients (23%) were positive before any therapy and 8 relapsed, all with this mutation. In conclusion, dasatinib combined with low-intensity chemotherapy was well-tolerated and gave long-term survival in 36% of elderly patients with Ph(+) ALL. Monitoring of BCR-ABL1(T315I) from diagnosis identified patients with at high risk of early relapse and may help to personalize therapy.

[Characteristics and clinical outcome of T315I mutation in Philadelphia chromosome-positive acute lymphoblastic leukemia and chronic myeloid leukemia]

目的

分析伴T315I突变的Ph染色体阳性急性淋巴细胞白血病(Ph⁺ALL)和慢性髓性白血病(CML)的特征及疗效。

方法

收集2014年3月至2015年6月于郑州大学附属肿瘤医院行ABL激酶区突变检测并对酪氨酸激酶抑制剂(TKI)耐药的23例Ph⁺ ALL患者和95例CML患者的临床资料。采用R显带法进行染色体分析，实时定量PCR方法检测BCR-ABL融合基因，TRIzol法提取总RNA，直接测序法检测ABL激酶区突变。

结果

ABL激酶区突变发生率在TKI耐药Ph⁺ ALL和CML中分别为60.9%(14/23)、41.1%(39/95)，其中T315I突变发生率分别为34.8%(8/23)和5.3%(5/95)，差异具有统计学意义(χ²=13.586，P<0.01)。CML慢性期患者ABL激酶区突变发生率为38.8%(19/49)，加速期、急变期分别为47.1%(8/17)、41.4%(12/29)，差异无统计学意义(χ²=0.360，P=0.835)。Ph⁺ ALL、CML患者自开始TKI治疗至发生T315I突变的中位时间分别为10和19个月，T315I突变发生至死亡或随访终止的中位时间分别为2和3个月，中位血液学缓解持续时间分别为10和16个月，中位总生存时间分别为13和42个月。

结论

Ph⁺ ALL较CML更易出现T315I突变，但两者自开始TKI治疗至发生T315I突变的中位时间相近，在现有方案治疗下，两者血液学缓解持续时间、总生存时间相近。

BCR: a new target in resistance mediated by BCR/ABL-315I?

Targeting BCR/ABL with Tyrosine kinase inhibitors (TKIs) is a proven concept for the treatment of Philadelphia chromosome-positive (Ph+) leukemias but the “gatekeeper” mutation T315I confers resistance against all approved TKIs, with the only exception of ponatinib, a multi-targeted kinase inhibitor. Besides resistance to TKIs, T315I also confers additional features to the leukemogenic potential of BCR/ABL, involving endogenous BCR. Therefore we studied the role of BCR on BCR/ABL mutants lacking functional domains indispensable for the oncogenic activity of BCR/ABL. We used the factor independent growth of murine myeloid progenitor 32D cells and the transformation of Rat-1 fibroblasts both mediated by BCR/ABL. Here we report that T315I restores the capacity to mediate factor-independent growth and transformation potential of loss-of-function mutants of BCR/ABL. Targeting endogenous Bcr abrogated the capacity of oligomerization deficient mutant of BCR/ABL-T315I to mediate factor independent growth of 32D cells and strongly reduced their transformation potential in Rat-1 cells, as well as led to the up-regulation of mitogen activated protein kinase (MAPK) pathway.

Our data show that the T315I restores the capacity of loss-of-function mutants to transform cells which is dependent on the transphosphorylation of endogenous Bcr, which becomes a putative therapeutic target to overcome resistance by T315I.

Clinical impact of ABL1 kinase domain mutations and IKZF1 deletion in adults under age 60 with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL): molecular analysis of CALGB (Alliance) 10001 and 9665

Recent studies have identified oncogenic lesions in Philadelphia chromosome-positive (Ph+)  acute lymphoblastic leukemia (ALL) and ABL1 kinase mutations that confer resistance to tyrosine kinase inhibitors. We sought to determine the prevalence and clinical impact of these lesions in patients on CALGB 10001, a previously reported Phase II study of imatinib, chemotherapy, and hematopoietic cell transplant in adult Ph + ALL. Of the 58 enrolled, 22 relapsed. By direct sequencing, an ABL1 kinase mutation known to induce imatinib resistance was present at relapse in 13 of 20. Using quantitative PCR assays, the mutations were detectable at diagnosis or early during treatment in most (62%) relapsed patients. Aberrations in IKZF1, CDKN2A/B, and PAX5 were assessed in 28 samples using SNP arrays and genomic DNA sequencing. Of these, 22 (79%) had IKZF1 deletion. The combination of IKZF1 deletion and p210 BCR-ABL1 (p < 0.0001), high white blood cell count (p = 0.021), and minimal residual disease (p = 0.013) were associated with worse disease-free survival.

Naturally Occurring Mutations in the MPS1 Gene Predispose Cells to Kinase Inhibitor Drug Resistance

Acquired resistance to therapy is perhaps the greatest challenge to effective clinical management of cancer. With several inhibitors of the mitotic checkpoint kinase MPS1 in preclinical development, we sought to investigate how resistance against these inhibitors may arise so that mitigation or bypass strategies could be addressed as early as possible. Toward this end, we modeled acquired resistance to the MPS1 inhibitors AZ3146, NMS-P715, and CCT251455, identifying five point mutations in the kinase domain of MPS1 that confer resistance against multiple inhibitors. Structural studies showed how the MPS1 mutants conferred resistance by causing steric hindrance to inhibitor binding. Notably, we show that these mutations occur in nontreated cancer cell lines and primary tumor specimens, and that they also preexist in normal lymphoblast and breast tissues. In a parallel piece of work, we also show that the EGFR p.T790M mutation, the most common mutation conferring resistance to the EGFR inhibitor gefitinib, also preexists in cancer cells and normal tissue. Our results therefore suggest that mutations conferring resistance to targeted therapy occur naturally in normal and malignant cells and these mutations do not arise as a result of the increased mutagenic plasticity of cancer cells.

ALK kinase domain mutations in primary anaplastic large cell lymphoma: consequences on NPM-ALK activity and sensitivity to tyrosine kinase inhibitors

ALK inhibitor crizotinib has shown potent antitumor activity in children with refractory Anaplastic Large Cell Lymphoma (ALCL) and the opportunity to include ALK inhibitors in first-line therapies is oncoming. However, recent studies suggest that crizotinib-resistance mutations may emerge in ALCL patients. In the present study, we analyzed ALK kinase domain mutational status of 36 paediatric ALCL patients at diagnosis to identify point mutations and gene aberrations that could impact on NPM-ALK gene expression, activity and sensitivity to small-molecule inhibitors. Amplicon ultra-deep sequencing of ALK kinase domain detected 2 single point mutations, R335Q and R291Q, in 2 cases, 2 common deletions of exon 23 and 25 in all the patients, and 7 splicing-related INDELs in a variable number of them. The functional impact of missense mutations and INDELs was evaluated. Point mutations were shown to affect protein kinase activity, signalling output and drug sensitivity. INDELs, instead, generated kinase-dead variants with dominant negative effect on NPM-ALK kinase, in virtue of their capacity of forming non-functional heterocomplexes. Consistently, when co-expressed, INDELs increased crizotinib inhibitory activity on NPM-ALK signal processing, as demonstrated by the significant reduction of STAT3 phosphorylation. Functional changes in ALK kinase activity induced by both point mutations and structural rearrangements were resolved by molecular modelling and dynamic simulation analysis, providing novel insights into ALK kinase domain folding and regulation. Therefore, these data suggest that NPM-ALK pre-therapeutic mutations may be found at low frequency in ALCL patients. These mutations occur randomly within the ALK kinase domain and affect protein activity, while preserving responsiveness to crizotinib.

The role of ponatinib in Philadelphia chromosome-positive acute lymphoblastic leukemia

The introduction of tyrosine kinase inhibitors has improved outcomes in Philadelphia chromosome-positive acute lymphoblastic leukemia, yet relapse due to the development of resistance mutations remains a major obstacle. Ponatinib is a novel tyrosine kinase inhibitor designed to overcome single-resistance mutations in the ABL kinase. Three clinical trials confirmed the efficacy of ponatinib in the relapsed and front-line setting in Philadelphia positive acute lymphoblastic leukemia, even in the presence of the T315I mutation, which confers resistance to other tyrosine kinase inhibitors. The rate of relapse appears to be very low when used in combination with chemotherapy, suggesting a role for ponatinib in newly diagnosed patients. A major concern with the use of ponatinib is the associated high risk of life-threatening vascular thrombotic events. Potential strategies to reduce this risk include minimizing the use of ponatinib in patients with significant baseline cardiovascular risk, careful surveillance and treatment of cardiovascular risk-factors and dose reduction of ponatinib.

Tyrosine kinase inhibitors induce mesenchymal stem cell-mediated resistance in BCR-ABL+ acute lymphoblastic leukemia

Tyrosine kinase inhibitors (TKIs) are used as a frontline therapy for BCR-ABL(+) acute lymphoblastic leukemia (ALL). However, resistance to TKI therapy arises rapidly, and its underlying molecular mechanisms are poorly understood. In this study, we identified a novel cascade of events initiated by TKIs and traversing through mesenchymal stem cells (MSCs) to leukemic cells, leading to resistance. MSCs exposed to TKIs acquired a new functional status with the expression of genes encoding for chemo-attractants, adhesion molecules, and prosurvival growth factors, and this priming enabled leukemic cells to form clusters underneath the MSCs. This cluster formation was associated with the protection of ALL cells from therapy as leukemic cells switched from BCR-ABL signaling to IL-7R/Janus kinase signaling to survive in the MSC milieu. Our findings illustrate a novel perspective in the evolution of TKI resistance and provide insights for advancing the treatment of BCR-ABL(+) ALL.

Clinical significance of quantitative monitoring and mutational analysis of BCR-ABL1 transcript in Philadelphia chromosome positive B lymphoblastic leukemia

Quantitative detection of BCR-ABL1 transcript is essential in monitoring residual disease of Philadelphia chromosome positive B lymphoblastic leukemia (Ph+ B-LL). We studied the kinetics of BCR-ABL1 transcript in 41 Ph+ B-LL patients in correlation with their clinical outcome. A total of 23 patients achieved complete molecular remission at 6 months post-treatment. This was associated with a lower relapse risk and better overall survival. Likewise, sustainable complete molecular remission in 27 patients was associated with superior clinical outcome. Sporadic low level BCR-ABL1 was detected in 12 of 27 patients who had attained complete molecular remission. The relapse rate was significantly higher in non-transplant patients with persistent positive BCR-ABL1 than patients transplanted when BCR-ABL1 was detectable. All eight patients harboring ABL1 kinase domain mutations died of disease or were transferred to hospice care. We concluded that monitoring the level of BCR-ABL1 transcript after hematologic remission has predictive value to the long-term outcome.

Detection and management of minimal residual disease in acute lymphoblastic leukemia

The detection of minimal residual disease (MRD) has become part of the state-of-the-art diagnostics to guide treatment both in pediatric and adult acute lymphoblastic leukemia (ALL). This applies to the treatment of de novo and recurrent ALL. In high-risk ALL, MRD detection is considered an important tool to adjust therapy before and after hematopoietic stem cell transplantation. Precise quantification and quality control is instrumental to avoid false treatment assignment. A new methodological approach to analyzing MRD has become available and is based on next-generation sequencing. In principle, this technique will be able to detect a large number of leukemic subclones at a much higher speed than before. Carefully designed prospective studies need to demonstrate concordance or even superiority compared with those techniques in use right now: detection of aberrant expression of leukemia-specific antigens by flow cytometry of blood or bone marrow, or detection of specific rearrangements of the T-cell receptor or immunoglobulin genes by real-time quantitative polymerase chain reaction using DNA of leukemic cells. In some cases with known fusion genes, such as BCR/ABL, reverse transcriptase-polymerase chain reaction has been used as additional method to identify leukemic cells by analyzing RNA in patient samples. MRD detection may be used to modulate treatment intensity once it has been demonstrated at well-defined informative checkpoints that certain levels of MRD can reliably predict the risk of relapse. In addition, MRD is used as end point to determine the activity of a given agent or treatment protocol. If activity translates into antileukemic efficacy, MRD may be considered a surrogate clinical end point.

PF-114, a potent and selective inhibitor of native and mutated BCR/ABL is active against Philadelphia chromosome-positive (Ph+) leukemias harboring the T315I mutation

Targeting BCR/ABL with tyrosine kinase inhibitors (TKIs) is a proven concept for the treatment of Philadelphia chromosome-positive (Ph+) leukemias. Resistance attributable to either kinase mutations in BCR/ABL or nonmutational mechanisms remains the major clinical challenge. With the exception of ponatinib, all approved TKIs are unable to inhibit the 'gatekeeper' mutation T315I. However, a broad spectrum of kinase inhibition increases the off-target effects of TKIs and may be responsible for cardiovascular issues of ponatinib. Thus, there is a need for more selective options for the treatment of resistant Ph+ leukemias. PF-114 is a novel TKI developed with the specifications of (i) targeting T315I and other resistance mutations in BCR/ABL; (ii) achieving a high selectivity to improve safety; and (iii) overcoming nonmutational resistance in Ph+ leukemias. PF-114 inhibited BCR/ABL and clinically important mutants including T315I at nanomolar concentrations. It suppressed primary Ph+ acute lymphatic leukemia-derived long-term cultures that either displayed nonmutational resistance or harbor the T315I. In BCR/ABL- or BCR/ABL-T315I-driven murine leukemia as well as in xenograft models of primary Ph+ leukemia harboring the T315I, PF-114 significantly prolonged survival to a similar extent as ponatinib. Our work supports clinical evaluation of PF-114 for the treatment of resistant Ph+ leukemia.

Phase 1/2 study of nilotinib prophylaxis after allogeneic stem cell transplantation in patients with advanced chronic myeloid leukemia or Philadelphia chromosome-positive acute lymphoblastic leukemia

BACKGROUND

Allogeneic stem cell transplantation (SCT) remains the standard treatment for advanced chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL). Relapsed disease is the major cause of treatment failure, especially when SCT is given in the setting of advanced disease. Tyrosine kinase inhibitors can be given after transplantation prophylactically or after the detection of minimal residual disease (MRD) to reduce the relapse risk.

METHODS

Posttransplant nilotinib was started after the achievement of sustained engraftment and the resolution of transplant-related toxicities. Nilotinib was continued until progression or unacceptable toxicity.

RESULTS

Twenty-two patients with advanced CML (n = 15) or Ph(+) ALL (n = 7) underwent SCT with human leukocyte antigen-matched siblings (n = 11), unrelated donors (n = 7), or alternative donors (n = 4). Sixteen patients were given prophylactic nilotinib maintenance, which was started at a median of 38 days after transplantation. Six patients stopped the treatment because of toxicities (mostly gastrointestinal and hepatic). After nilotinib maintenance, 11 patients achieved (n = 9) or maintained (n = 2) a complete molecular response (CMR), and only 1 of them later relapsed. Four of the 5 patients not achieving CMR relapsed. At a median follow-up of 46 months, 9 patients were alive, and 13 had died. The 2-year overall and progression-free survival rates were 55% (95% confidence interval [CI], 34%-75%) and 45% (95% CI, 25%-66%), respectively. Among the 16 nilotinib recipients, the rates were 69% (95% CI, 46%-92%) and 56% (95% CI, 32%-81%), respectively. The 2-year nonrelapse mortality and relapse rates for all patients were 32% (95% CI, 17%-58%) and 23% (95% CI, 11%-49%), respectively.

CONCLUSIONS

Nilotinib is relatively safe and effective prophylactic therapy for the prevention of relapse after SCT. It may control MRD and convert patients to CMR, which is associated with prolonged survival. These observations merit further study in larger scale studies.

Outcome after HSCT in Philadelphia chromosome positive acute lymphoblastic leukemia in Sweden: a population-based study

Even in the tyrosine kinase inhibitor era, allogeneic hematopoietic stem cell transplantation (HSCT) is regarded as standard care for adult Philadelphia (Ph) positive acute lymphoblastic leukemia (ALL). In this retrospective national study, we have reviewed the outcome after HSCT in Sweden for adult Ph-positive ALL between 2000 and 2009. In total, 51 patients with median age 42 (range 20-66) years underwent HSCT. Mainly allogeneic HSCT was performed (24 related donor, 24 unrelated donor and one cord blood), and only two patients were treated with an autologous HSCT. The 5-year OS was 51 (37-64) %. The probabilities of morphological relapse and non-relapse mortality (NRM) at 5 years were 36 (23-49) and 18 (9-29) %, respectively. For the allogeneic transplanted, the 5-year OS was for patients <40 years 70 (50-90) % and for patients ≥40 years 34 (16-52) %, p = 0.002. The 5-year probability of NRM was for patients <40 years 10 (2-28) % compared to 25 (11-42) % for patients ≥40 years (p = 0.04). Patients with chronic graft-versus-host disease (GVHD) had a 5-year morphological relapse probability of 20 (6-40) % compared to 59 (35-77) % for patients without chronic GVHD (p = 0.03). Age ≥40 years and the absence of chronic GVHD were confirmed as independent negative prognostic factors for relapse and non-relapse mortality in a multivariate analysis although the impact of chronic GVHD was significant only in the older age cohort.

The pharmacological point of view of resistance to therapy in tumors

Resistance to therapy is a challenging clinical problem, whose solution is far from being reached. Gains in current knowledge have identified key elements at the basis of drug resistance and have suggested possible ways to overcome it. However, some points have always to be kept in mind whatever the type of tumor or drug (cytotoxic or targeted agent) when considering treatment resistance in tumors. In this review we discuss these points and their impact in resistance to cancer therapy: the importance of reaching active tumor drug concentration, reviewing the various micro- and macro-components of the host that can influence their concentrations and activity, the evolving complex heterogeneity of tumors, the intrinsic tumor cell susceptibility to the drug, and the emerging role of the tumor microenvironment. Both the data from the molecular and biological characterization of human tumors allow a better rational and timing use of the available arsenal of anticancer therapy and new strategies to improve the penetration of antitumor drugs in tumors are the new chances to delay and possibly eliminate the emergence of resistance in tumors.

Evidence-based guidelines for the use of tyrosine kinase inhibitors in adults with Philadelphia chromosome-positive or BCR-ABL-positive acute lymphoblastic leukemia: a Canadian consensus

Adult Philadelphia chromosome-positive (Ph+) or BCR-ABL-positive (BCR-ABL+) acute lymphoblastic leukemia (all) is an acute leukemia previously associated with a high relapse rate, short disease-free survival, and poor overall survival. In adults, allogeneic hematopoietic cell transplant in first remission remains the only proven curative strategy for transplant-eligible patients. The introduction of tyrosine kinase inhibitors (tkis) in the treatment of patients with Ph+ or BCR-ABL+ all has significantly improved the depth and duration of complete remission, allowing more patients to proceed to transplantation. Although tkis are now considered a standard of care in this setting, few randomized trials have examined the optimal use of tkis in patients with Ph+ all. Questions of major importance remain, including the best way to administer these medications, the choice of tki to administer, and the schedule and the duration to use. We present the results of a systematic review of the literature with consensus recommendations based on the available evidence.

Current concepts in pediatric Philadelphia chromosome-positive acute lymphoblastic leukemia

The t(9;22)(q34;q11) or Philadelphia chromosome creates a BCR-ABL1 fusion gene encoding for a chimeric BCR-ABL1 protein. It is present in 3-4% of pediatric acute lymphoblastic leukemia (Ph(+) ALL), and about 25% of adult ALL cases. Prior to the advent of tyrosine kinase inhibitors (TKI), Ph(+) ALL was associated with a very poor prognosis despite the use of intensive chemotherapy and frequently hematopoietic stem-cell transplantation (HSCT) in first remission. The development of TKIs revolutionized the therapy of Ph(+) ALL. Addition of the first generation ABL1 class TKI imatinib to intensive chemotherapy dramatically increased the survival for children with Ph(+) ALL and established that many patients can be cured without HSCT. In parallel, the mechanistic understanding of Ph(+) ALL expanded exponentially through careful mapping of pathways downstream of BCR-ABL1, the discovery of mutations in master regulators of B-cell development such as IKZF1 (Ikaros), PAX5, and early B-cell factor (EBF), the recognition of the complex clonal architecture of Ph(+) ALL, and the delineation of genomic, epigenetic, and signaling abnormalities contributing to relapse and resistance. Still, many important basic and clinical questions remain unanswered. Current clinical trials are testing second generation TKIs in patients with newly diagnosed Ph(+) ALL. Neither the optimal duration of therapy nor the optimal chemotherapy backbone are currently defined. The role of HSCT in first remission and post-transplant TKI therapy also require further study. In addition, it will be crucial to continue to dig deeper into understanding Ph(+) ALL at a mechanistic level, and translate findings into complementary targeted approaches. Expanding targeted therapies hold great promise to decrease toxicity and improve survival in this high-risk disease, which provides a paradigm for how targeted therapies can be incorporated into treatment of other high-risk leukemias.

Current and future management of Ph/BCR-ABL positive ALL

Following the introduction of targeted therapy with tyrosine kinase inhibitors (TKI) at the beginning of the past decade, the outcome of patients with Philadelphia-chromosome positive acute lymphoblastic leukemia (Ph+ ALL) has dramatically improved. Presently, the use of refined programs with first/second generation TKI's and chemotherapy together with allogeneic stem cell transplantation allow up to 50% of all patients to be cured. Further progress is expected with the new TKI ponatinib, overcoming resistance caused by T315I point mutation, other targeted therapies, autologous transplantation in molecularly negative patients, therapeutic monoclonal antibodies like inotuzumab ozogamicin and blinatumomab, and chimeric antigen receptor-modified T cells. Ph+ ALL could become curable in the near future even without allogeneic stem cell transplantation, minimizing the risk of therapy-related death and improving greatly the quality of patients' life.

Differential expression of miR-17~92 identifies BCL2 as a therapeutic target in BCR-ABL-positive B-lineage acute lymphoblastic leukemia

Despite advances in allogeneic stem cell transplantation, BCR-ABL-positive acute lymphoblastic leukaemia (ALL) remains a high-risk disease, necessitating the development of novel treatment strategies. As the known oncomir, miR-17~92, is regulated by BCR-ABL fusion in chronic myeloid leukaemia, we investigated its role in BCR-ABL translocated ALL. miR-17~92-encoded miRNAs were significantly less abundant in BCR-ABL-positive as compared to -negative ALL-cells and overexpression of miR-17~19b triggered apoptosis in a BCR-ABL-dependent manner. Stable isotope labelling of amino acids in culture (SILAC) followed by liquid chromatography and mass spectroscopy (LC-MS) identified several apoptosis-related proteins including Bcl2 as potential targets of miR-17~19b. We validated Bcl2 as a direct target of this miRNA cluster in mice and humans, and, similar to miR-17~19b overexpression, Bcl2-specific RNAi strongly induced apoptosis in BCR-ABL-positive cells. Furthermore, BCR-ABL-positive human ALL cell lines were more sensitive to pharmacological BCL2 inhibition than negative ones. Finally, in a xenograft model using patient-derived leukaemic blasts, real-time, in vivo imaging confirmed pharmacological inhibition of BCL2 as a new therapeutic strategy in BCR-ABL-positive ALL. These data demonstrate the role of miR-17~92 in regulation of apoptosis, and identify BCL2 as a therapeutic target of particular relevance in BCR-ABL-positive ALL.

Drug resistance and BCR-ABL kinase domain mutations in Philadelphia chromosome-positive acute lymphoblastic leukemia from the imatinib to the second-generation tyrosine kinase inhibitor era: The main changes are in the type of mutations, but not in the frequency of mutation involvement

BACKGROUND

Patients with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) frequently relapse on imatinib with acquisition of BCR-ABL kinase domain (KD) mutations. To analyze the changes that second-generation tyrosine kinase inhibitors (TKIs) have brought in mutation frequency and type, a database review was undertaken of the results of all the BCR-ABL KD mutation analyses performed in the authors' laboratory from January 2004 to January 2013.

METHODS

Interrogation of the database retrieved 450 mutation analyses in 272 patients with Ph+ ALL. Prescreening of samples was performed with denaturing high-performance liquid chromatography (D-HPLC), followed by direct sequencing of D-HPLC-positive cases.

RESULTS

BCR-ABL KD mutations were detected in 70% of imatinib-resistant patients, with T315I, E255K, and Y253H mutations accounting for 75% of cases. Seventy-eight percent of the patients reported to be resistant to second-generation TKIs after imatinib failure were positive for mutations, and 58% of them had multiple mutations. Analysis of patients relapsing on dasatinib revealed a newly acquired T315I mutation in almost two-thirds of the cases. Direct sequencing detected no mutations at diagnosis, even in patients who relapsed after a few months.

CONCLUSIONS

Second-generation TKIs ensure a more rapid debulking of the leukemic clone and have much fewer insensitive mutations, but long-term disease control remains a problem, and the T315I mutation is revealed to be an even more frequent enemy. BCR-ABL KD mutation screening of patients with Ph+ ALL who are receiving imatinib or second-generation TKIs would be a precious ally for timely treatment optimization. In contrast, the clinical usefulness of conventional direct sequencing at diagnosis seems to be very low. American Cancer Society.

Mechanisms of resistance to BCR-ABL and other kinase inhibitors

In this article, we are reviewing the molecular mechanisms that lead to kinase inhibitor resistance. As the oncogenic BCR-ABL kinase is the target of the first approved small-molecule kinase inhibitor imatinib, we will first focus on the structural and mechanistic basis for imatinib resistance. We will then show ways how next generations of BCR-ABL inhibitors and alternative targeting strategies have helped to offer effective treatment options for imatinib-resistant patients. Based on these insights, we discuss commonalities and further mechanisms that lead to resistance to other kinase inhibitors in solid tumors. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

Has MRD monitoring superseded other prognostic factors in adult ALL?

Significant improvements have been made in the treatment of acute lymphoblastic leukemia (ALL) during the past 2 decades, and measurement of submicroscopic (minimal) levels of residual disease (MRD) is increasingly used to monitor treatment efficacy. For a better comparability of MRD data, there are ongoing efforts to standardize MRD quantification using real-time quantitative PCR of clonal immunoglobulin and T-cell receptor gene rearrangements, real-time quantitative-based detection of fusion gene transcripts or breakpoints, and multiparameter flow cytometric immunophenotyping. Several studies have demonstrated that MRD assessment in childhood and adult ALL significantly correlates with clinical outcome. MRD detection is particularly useful for evaluation of treatment response, but also for early assessment of an impending relapse. Therefore, MRD has gained a prominent position in many ALL treatment studies as a tool for tailoring therapy with growing evidence that MRD supersedes most conventional stratification criteria at least for Ph-negative ALL. Most study protocols on adult ALL follow a 2-step approach with a first classic pretherapeutic and a second MRD-based risk stratification. Here we discuss whether and how MRD is ready to be used as main decisive marker and whether pretherapeutic factors and MRD are really competing or complementary tools to individualize treatment.