Philadelphia chromosome-positive acute lymphoblastic leukemia: current treatment and future perspectives

The Philadelphia chromosome (Ph) is the most common cytogenetic abnormality associated with adult acute lymphoblastic leukemia (ALL). Before the advent of tyrosine kinase inhibitors (TKIs), Ph-positive ALL carried a dismal prognosis and was characterized by a poor response to most chemotherapy combinations, short remission durations, and poor survival rates. Outcomes for patients with Ph-positive ALL improved substantially with the introduction of TKIs, and the TKI imatinib induced complete remissions in >95% of patients with newly diagnosed Ph-positive ALL when it was combined with chemotherapy. However, imatinib resistance remains a problem in a substantial proportion of patients with Ph-positive ALL, and multiple molecular mechanisms that contribute to imatinib resistance have been identified. Second-generation TKIs (eg, dasatinib and nilotinib) have demonstrated promising efficacy in the treatment of imatinib-resistant, Ph-positive ALL. Future strategies for Ph-positive ALL include novel, molecularly targeted treatment modalities and further evaluations of TKIs in combination with established antileukemic agents. For this article, the authors reviewed past, current, and future treatment approaches for adult and elderly patients with Ph-positive ALL with a focus on TKIs and combined chemotherapeutic regimens.     

Outcome of Philadelphia chromosome-positive adult acute lymphoblastic leukemia

Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL) represents the most common cytogenetic abnormality in adult ALL. It is found in 15% to 30% of patients, and its incidence increases with age. As in children, prognosis in Ph-positive adult ALL is poor. No therapeutic approach has had substantial impact on its unfavorable course. We analyzed the characteristics and outcome of newly diagnosed adults with Ph-positive ALL treated at the M. D. Anderson Cancer Center between 1980 and 1997. The diagnosis of patients was based on typical morphological and immunophenotypic criteria of marrow aspirate and biopsy specimens. Cytogenetic and molecular studies were also performed. A total of 67 patients were included in this study. From 1980 until 1991, 38 patients with Ph-positive ALL were treated with vincristine, Adriamycin, and dexamethasone (VAD), or with acute myeloid leukemia (AML)-like induction protocols. Since 1992 a total of 29 patients received induction therapy with an intensified treatment protocol, called "hyper-CVAD". The outcome of patients treated with standard and intensified treatment regimens was compared and results of our institution contrasted with data obtained from other centers. Ph-positive ALL was present in 67 of 498 patients with newly diagnosed ALL (13%). Patients with Ph-positive ALL had a higher median age (44 versus 34, P=0.007), higher median white blood cell (WBC) counts at presentation (25 versus 8, P=0.0002), and higher peripheral median percentage of blast counts (63 versus 40, P=0.023). FAB subtype L2 (70% versus 49%, P=0.001) and CALLA-positive pre-B immunophenotype (75% versus 37%, P<0.001) predominated among Ph-positive ALL. Myeloid marker coexpression was more frequent in Ph-positive ALL when compared with Ph-negative ALL (52% vs. 27% for CD13, P<0.001, and 44% vs. 27% for CD33, P=0.005). Among patients treated with hyper-CVAD, the complete remission (CR) rate was 90% versus 55% (P=0.002) with pre-hyper-CVAD regimens (VAD and AML-like induction protocols), the median CR duration was 43 weeks versus 32 weeks (P>0.5), median disease-free survival (DFS) was 42 weeks versus 29 weeks (P=0.008), and median survival was 66 weeks versus 45 weeks (P>0.5). Patients with hyperdiploid Ph-positive ALL on hyper-CVAD therapy achieved significantly longer CR duration and DFS than hypo- and pseudodiploid cases (59 weeks versus 42 and 31 weeks, P=0.02 and 0.04, respectively). In contrast, patients treated with regimens prior to hyper-CVAD had significantly shorter CR duration (21 weeks versus 33 and 29 weeks, P=0.03) and DFS with hyperdiploid karyotypes when compared to pseudodiploid and hypodiploid cases (16 weeks versus 30 and 13 weeks, P=0.008). In conclusion, our results demonstrate improved response rate and DFS with current intensive regimens (hyper-CVAD) in patients with Ph-positive ALL, but no advantage in overall survival.     

ABL1 methylation in Ph-positive ALL is exclusively associated with the P210 form of BCR-ABL.

In human Ph-positive leukemia there is a clear association of different forms of the BCR-ABL oncogene with distinct types of leukemia. The P190 form of BCR-ABL is rarely observed in chronic myeloid leukemia (CML) but is present in 50% of Ph-positive acute lymphoblastic leukemia (ALL). In contrast, the P210 form is observed both in CML and 50% of Ph-positive ALL. Methylation of the proximal promoter of the ABL1 gene has been shown to be a nearly universal event associated with clinical progression of CML. This raises the question of whether methylation of the ABL1 promoter is an epigenetic modification also associated with Ph-positive ALL. To study this issue, we used methylation-specific PCR and bisulfite sequencing to determine the methylation status of the ABL1 promoter in 18 Ph-positive ALL samples. We report here that gene-specific ABL1 promoter methylation is associated mainly with the P210 form of BCR-ABL and not the P190 form. While six out of the seven P210-positive ALL samples had ABL1 promoter methylation, none of the 11 P190-positive ALL samples demonstrated ABL1 promoter methylation. In addition, we estimated the extent and relative abundance of ABL1 promoter methylation in several Ph-positive ALL samples and compared it to the methylation pattern in chronic, accelerated and blastic crisis phases of CML. We put forth a model that correlates the different types of leukemias with the different levels of ABL1 promoter methylation.     

Treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia with imatinib in combination with chemotherapy

The presence of the Philadelphia chromosome (Ph) is associated with a very poor prognosis in acute lymphoblastic leukemia (ALL). Although hematologic complete remission (CR) is achieved in 50% to 80% of adult patients by intensive chemotherapy in multicenter studies, long-term outcome is dismal, with overall survival of approximately 10%. Currently, allogeneic hematopoietic stem cell transplantation (allo-SCT) is thought to be the only curative therapeutic modality for this leukemia in adults, but the long-term survival rates are about 40% or less, far from satisfactory. Imatinib mesylate, a recently introduced specific tyrosine kinase inhibitor of BCR-ABL, in combination with chemotherapy, resulted in more than 90% hematologic CR in adult Ph-positive ALL, including molecular CR in more than 50% of patients. The higher CR rate and less frequent relapse gave more patients a chance to receive SCT. Patients who did not qualify for allo-SCT because of the lack of a suitable donor, advanced age, or underlying medical conditions apparently showed better survival than historical control patients treated with chemotherapy alone. Although longer follow-up is required to determine the effect on survival, imatinib in combination with chemotherapy clearly has a major potential to improve the treatment of Ph-positive ALL and may cure a substantial proportion of patients without SCT.     

The Medical Research Council trials in adult acute lymphocytic leukemia

Overall, the MRC Adult Leukaemia Trials have been successful, in that since the 1970s they have demonstrated a stepwise improvement in outcome. Examination of the survival curves shows the DFS rate at 5 years in UKALL Trial 1 of 5% rising to 38% in UKALL Trial XII (year 2000). Unfortunately, compared with children with ALL, these results in adults must be regarded as poor, because in the UKALL children's trials the EFS rate at 5 years for a child entered in the year 2000 is expected to be above 80%. With a low proportion of all adults entered into randomized trials, one cannot be certain that improvements result from treatment rather than patient selection. Only recently have randomized trials in adults become large enough to detect plausible treatment effects. The authors believe that the main contribution of these trials so far, confirmed by other groups, is in examining prognostic features in al patients and finding that age and the presence of the Ph chromosome, independent of WBC count, gender, and cell type, is the main feature for predicting outcome. The UKALL XII trial will provide valuable information on the relative merits of transplantation and molecular studies of MRD. An in-depth study of a large number of Ph chromosome-positive ALL leukemias will also provide information on which to base future studies. Preliminary data suggest that all Ph-positive patients should undergo some sort of allograft early after CR is achieved, because these patients are not rescued by BMT after relapse. At the time of the publication of this article, preliminary studies suggest that STIs may not be as effective in Ph-positive ALL as in chronic granulocytic leukemia. The challenge for the future is to understand the biologic role of age and its impact on outcome so as to overcome "ageism" in adult ALL.     

Treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia with imatinib in combination with chemotherapy

The presence of the Philadelphia chromosome (Ph) is associated with a very poor prognosis in acute lymphoblastic leukemia (ALL). Although hematologic complete remission (CR) is achieved in 50% to 80% of adult patients by intensive chemotherapy in multicenter studies, long-term outcome is dismal, with overall survival of approximately 10%. Currently, allogeneic hematopoietic stem cell transplantation (allo-SCT) is thought to be the only curative therapeutic modality for this leukemia in adults, but the long-term survival rates are about 40% or less, far from satisfactory. Imatinib mesylate, a recently introduced specific tyrosine kinase inhibitor of BCR-ABL, in combination with chemotherapy, resulted in more than 90% hematologic CR in adult Ph-positive ALL, including molecular CR in more than 50% of patients. The higher CR rate and less frequent relapse gave more patients a chance to receive SCT. Patients who did not qualify for allo-SCT because of the lack of a suitable donor, advanced age, or underlying medical conditions apparently showed better survival than historical control patients treated with chemotherapy alone. Although longer follow-up is required to determine the effect on survival, imatinib in combination with chemotherapy clearly has a major potential to improve the treatment of Ph-positive ALL and may cure a substantial proportion of patients without SCT.     

SOHO State of the Art Updates & Next Questions: Intensive and Non–Intensive Approaches for Adults With Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) was historically considered to be a very poor-risk subtype of ALL. However, with the introduction of highly potent BCR-ABL tyrosine kinase inhibitors (TKIs), Ph+ ALL can now be considered relatively favorable-risk acute leukemia. Considering the high rates of measurable residual disease negativity and excellent long-term survival that has been achieved with regimens incorporating later-generation TKIs and particularly with ponatinib, lower-intensity and even chemotherapy-free regimens are now being evaluated for patients of all ages with Ph+ ALL. The very encouraging early results observed with blinatumomab-based, chemotherapy-free regimens challenge previous notions that all patients with Ph+ ALL should undergo allogeneic stem cell transplantation in first remission, as these regimens are capable of achieving deep and durable remissions without need for transplant in the vast majority of patients, particularly when combined with ponatinib. In this review, we discuss the evolving approach to the treatment of adults with newly diagnosed Ph+ ALL and the major principles that should guide therapy in this disease. We also review the rationale and data supporting the use of novel, chemotherapy-free regimens in Ph+ ALL, and how these approaches may soon become new standards of care.     

Minimal residual disease-based effect and long-term outcome of first-line dasatinib combined with chemotherapy for adult Philadelphia chromosome-positive acute lymphoblastic leukemia

BackgroundThe use of imatinib combined with chemotherapy has demonstrated improved outcome in adults with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph-positive ALL). However, a substantial proportion of patients continue to die as a result of disease progression.Patients and methodsWe assessed the minimal residual disease (MRD)-based effect and long-term outcome of first-line incorporation of dasatinib (100 mg once daily) into chemotherapy alternatively for adults with Ph-positive ALL. The primary end point was the major molecular response (MMR) rate by the end of the second dasatinib cycle. Patients with a donor proceeded to allogeneic stem cell transplantation (SCT) as early as possible. MRD monitoring was centrally evaluated by real-time quantitative polymerase chain reaction (4.5-log sensitivity) using bone marrow samples.ResultsFifty-one patients (median age, 46 years) were enrolled and treated with this strategy. After the first dasatinib cycle, 50 patients (98.0%) achieved complete remission (CR). By the end of the second dasatinib cycle, 46 (93.9%) of 49 assessable patients had persistent CR, and 38 (77.6%) had MMR (32.7%) or undetectable MRD (44.9%). On the basis of the MRD kinetics by this time point, the numbers of early-stable, late, and poor molecular responders were 23 (46.9%), 15 (30.7%), and 11 (22.4%), respectively. Thirty-nine patients (76.5%) underwent allogeneic SCT in CR1. After a median follow-up of 54 months, the 4-year cumulative incidence of relapse and disease-free survival (DFS) rate for all patients were 30.0% and 52.0%, respectively, and the corresponding outcomes among those receiving allogeneic SCT in CR1 were 20.5% and 64.1%, respectively. Poor molecular responders had a higher risk of relapse and DFS than those of early-stable molecular responders.ConclusionThis dasatinib-based protocol was effective for achieving a good quality molecular response and durable DFS in adults with Ph-positive ALL.Trial registrationclinicaltrials.gov, NCT01004497.     

New therapeutic approaches and prognostic factors in chronic myeloid leukemia

Imatinib mesylate is now the first-choice treatment for all newly diagnosed CML patients, but despite the impressive percentage of responding patients, some CML cases show primary resistance or relapse after an initial response. Although some clinical and biological findings have been found to be associated with a lower probability of response to imatinib, at present no precise markers allowing to predict outcome for individual patients exist. The most common mechanisms of resistance to imatinib include BCR-ABL kinase domain mutations, BCR-ABL amplification and overexpression, and clonal evolution with activation of additional transformation pathways. These mechanisms are caused by the genomic instability, which characterises the Ph-positive clone. Several approaches to overcome resistance have been proposed, including novel tyrosine kinase inhibitors (TKIs) that have now reached the clinical or pre-clinical phase of evaluation. Clinical trials with these novel TKIs have shown good rates of hematologic and cytogenetic responses that appear also durable in time, but still cases of resistance are also observed, supporting the notion that genomic instability represents the major determinant affecting the final outcome of the CML patients when treated with TKIs. Understanding exactly the mechanisms leading to genomic instability of the Ph-positive cells represents therefore the real challenge for the near future.     

Philadelphia Chromosome–like Acute Lymphoblastic Leukemia

Philadelphia chromosome–like acute lymphoblastic leukemia (Ph-like ALL) is a recently described B-cell precursor ALL with a gene expression profile and a high frequency of IKZF1 gene alteration similar to that of Ph-positive ALL. Its prevalence is approximately 12% in children, 21% in adolescents (16-20 years of age), and 20% to 24% in adults older than 40 years, with a peak (27%) in young adults 21 to 39 years old. It occurs more often in male individuals and patients with Down syndrome. Ph-like ALL is overrepresented in those with Hispanic ethnicity and is associated with inherited genetic variants in GATA3 (rs3824662). It is a clinically and biologically heterogeneous subtype of B-ALL. Although most patients with Ph-like ALL have positive minimal residual disease after remission induction and poor event-free survival, approximately 40% of pediatric patients responded well to chemotherapy and can be cured with relatively low intensity of treatment. The treatment outcome correlated negatively with increasing age at presentation. Ph-like ALL is characterized by a wide range of genetic alterations that dysregulate several cytokine receptor and kinase signaling pathways, including CRLF2 rearrangement in half of the cases and translocation of nonreceptor tyrosine kinases (predominantly ABL-class and Janus kinases). Patients with ABL-class fusions respond clinically to ABL1 tyrosine kinase inhibitors, whereas mutations activating the JAK-STAT pathway are amendable to treatment with JAK inhibitors in vitro or in preclinical models. Prospective studies are needed to determine if incorporation of tyrosine kinase inhibitor targeting kinase alterations into intensive chemotherapy regimens will improve outcome of patients with Ph-like ALL.     

SOHO State of the Art Update and Next Questions: Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia

The widespread adoption of Bcr–Abl-directed tyrosine kinase inhibitors (TKIs) into first-line regimens for patients with Philadelphia chromosome (Ph)-positive (Ph⁺) acute lymphoblastic leukemia (ALL) has revolutionized the outcomes of patients with this disease. Whereas Ph⁺ ALL was historically associated with cure rates of <25% in the pre-TKI era, now long-term survival in more than 75% of patients has been reported. With the promising efficacy of later-generation TKIs (eg, ponatinib) and the emerging understanding of the prognostic significance of various cooperative genomic alterations and of minimal residual disease, the widespread use of allogeneic hematopoietic stem cell transplantation in first remission for patients with Ph⁺ ALL has been increasingly questioned. Furthermore, with the development of more potent Bcr-Abl TKIs, several studies are evaluating novel strategies that reduce or eliminate chemotherapy. Herein, we review the major genomic and molecular prognostic factors in Ph⁺ ALL and also discuss the current and future treatment paradigms for this disease.     

Derivative chromosome 9 deletions are a significant feature of childhood Philadelphia chromosome positive acute lymphoblastic leukaemia.

Deletions from the derivative chromosome 9, der(9), of the translocation, t(9;22)(q34;q11), at the site of the ABL/BCR fusion gene, have been demonstrated by fluorescence in situ hybridisation (FISH), in both Philadelphia chromosome (Ph)-positive chronic myeloid leukaemia (CML) and acute lymphoblastic leukaemia (ALL). In CML they occur in 10-15% of cases and appear to indicate a worse prognosis, whereas in ALL, the situation is unclear. This study presents the findings of dual fusion FISH used to detect such deletions in a series of 27 BCR/ ABL-positive childhood ALL patients. Metaphase FISH was essential for the accurate interpretation of interphase FISH signal patterns. Three cases (11%) had a single fusion signal, resulting from deletions of the der(9). Three other patients with variant translocations and one with an insertion, also had a single fusion, but with no evidence of deletions. Gain of a fusion in approximately one-third of patients indicated a second Ph, which appears to be a diagnostic marker of Ph-positive ALL. This study shows that the incidence of deletions from the der(9) in childhood ALL is at least as high as that reported for CML.     

Secondary myelodysplastic syndrome in a patient with Philadelphia-positive acute lymphoblastic leukemia after achieving a major molecular response with hyperCVAD plus imatinib mesylate

The addition of imatinib to high-intensity chemotherapy has improved the outcome of patients with Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL). However, the possible long-term side effects of this combination are not yet known. Development of new clonal abnormalities in complete cytogenetic remission after treatment with imatinib has been reported in patients with chronic myeloid leukemia but not in patients with Ph-positive ALL. Here, we present a patient with Ph-positive ALL who received hyperCVAD plus imatinib and achieved hematologic, cytogenetic, and major molecular responses. The patient then developed myelodysplastic syndrome and solitary central nervous system relapse of ALL.     

IFN-alpha treatment of p190 bcr abl transgenic mice

Interferon-alfa (IFN-alpha) is one of the most effective drugs in the treatment of chronic myeloid leukemia (CML). Recently, IFN-alpha has also been tried in the treatment of Ph-positive acute lymphoid leukemia (ALL), a disease in part sharing the same molecular genetic lesion as CML, namely a BCR/ABL fusion gene. In the present study we analyzed the effect of IFN-alpha (rHuIFN-alphaA/D) on a mouse model for Ph-positive ALL - mice transgenic for the P190 BCR/ABL fusion gene. IFN-alpha treatment was started in the early leukemic phase and continued throughout the course of the disease in eight transgenic animals. No prolonged survival or altered disease pattern with regard to the development of leukemia and/or lymphoma was observed. We conclude that IFN-alpha, at least in a transgenic setting, does not interfere with the leukemogenic process induced by the P190 BCR/ABL fusion gene.     

“Society of Hematologic Oncology (SOHO) State of the Art Updates and Next Questions”—Treatment of ALL

The outcome of adult acute lymphoblastic leukemia (ALL) has substantially improved by adopting pediatric-inspired regimens, and approximately half of the patients are nowadays cured. The evaluation of minimal residual disease currently represents the most important prognostic indicator, which drives treatment algorithms, which include allogeneic stem cell transplantation (allo-SCT) allocation. Indeed, for high-risk patients, allo-SCT should be pursued as soon as possible, whereas in standard-risk patients this procedure should be avoided also in light of related toxicity and because there are no significant benefits. Furthermore, better characterization of the molecular genetic events can drive therapeutic decisions: a historical example in this respect is represented by the use of tyrosine kinase inhibitors (TKIs) in Philadelphia chromosome-positive ALL; in the upcoming future, TKIs might be used also in other subgroups, such as breakpoint cluster region/Abelson 1-like cases and others with deregulated tyrosine kinases. Finally, the greatest progress is currently achieved with new immunotherapies targeting frequently expressed surface antigens in ALL. It is also a new chance for elderly ALL patients, so far spared from intensive chemotherapy and allo-SCT. These targeted therapies will substantially change this treatment algorithm and the great challenge is to find optimal sequence of the extended therapy options in an individual patient.     

Efficacy of EGFR tyrosine kinase inhibitors for non-adenocarcinoma NSCLC patients with EGFR mutation

Purpose

The epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs) gefitinib and erlotinib have shown dramatic response rate (RR) and significant prolongation of progression-free survival (PFS) in non-small-cell lung cancer (NSCLC) patients with EGFR mutation. Since only a few patients with non-adenocarcinoma histology have been enrolled in clinical trials, the efficacy of EGFR TKIs in non-adenocarcinoma NSCLC patients with EGFR mutation has not yet been fully determined.

Methods

We retrospectively analyzed clinical outcomes, including RR, PFS, and OS, in patients who were treated with the EGFR TKIs gefitinib or erlotinib and compared the results with those of adenocarcinoma patients with EGFR mutation and non-adenocarcinoma patients with wild-type EGFR.

Results

Among 250 patients with non-adenocarcinoma of the lung who underwent EGFR mutation genotyping, 21 were found to have an EGFR mutation (8.4?%). Twelve of the 21 patients were treated with the EGFR TKIs gefitinib (n?=?6) or erlotinib (n?=?6). The most common mutation was exon 19 deletion (n?=?7). The RR and disease control rate for 12 patients receiving EGFR TKIs were 50 and 75?%, respectively. The median PFS was 3.67?months (95?% CI: 1.34?C5.99), which was significantly lower than that of 269 adenocarcinoma patients with EGFR mutation (13.53?months) but better than that of 32 non-adenocarcinoma patients with wild-type EGFR (1.83?months) who were treated with EGFR TKIs.

Conclusions

The results of this study show that the EGFR mutation rate in Korean patients with non-adenocarcinoma of the lung is relatively high and that the clinical outcomes of EGFR TKIs are modest.     

AMN107, a novel aminopyrimidine inhibitor of p190 Bcr-Abl activation and of in vitro proliferation of Philadelphia-positive acute lymphoblastic leukemia cells

BACKGROUND: Previous studies have shown that patients with Bcr-Abl-positive acute lymphoblastic leukemia (ALL) either have primary disease that is refractory to imatinib mesylate or develop disease recurrence after an initial response. METHODS: The authors investigated the effects of a newly designed Bcr-Abl inhibitor, AMN107, by comparing its in vitro inhibitory potency on p190 Bcr-Abl ALL cell lines with that of imatinib. RESULTS: In two Philadelphia (Ph)-positive ALL cell lines, AMN107 was found to be 30-40 times more potent than imatinib in inhibiting cellular proliferation. AMN107 was also more effective than imatinib in inhibiting phosphorylation of p190 Bcr-Abl tyrosine kinase in cell lines and primary ALL cells. The inhibition of cellular proliferation was associated with the induction of apoptosis in only one of the cell lines. No activity was observed in cell lines lacking the BCR-ABL genotype. CONCLUSIONS: The results of the current study suggest the superior potency of AMN107 compared with imatinib in Ph-positive ALL and support clinical trials of AMN107 in patients with Ph-positive ALL.     

Oncogene-independent resistance in Philadelphia chromosome - positive (Ph+) acute lymphoblastic leukemia (ALL) is mediated by activation of AKT/mTOR pathway

Tyrosine kinase inhibitors (TKIs) such as imatinib, nilotinib, dasatinib, and ponatinib have significantly improved the life expectancy of Philadelphia chromosome-positive (Ph⁺) acute lymphocytic leukemia (ALL) patients; however, resistance to TKIs remains a major clinical challenge. Point mutations in the tyrosine kinase domain (TKD) of BCR-ABL1 have emerged as the predominant cause of acquired resistance. In approximately 30% of patients, the mechanism of resistance to TKIs remains elusive. This study aimed to investigate mechanisms of nonmutational resistance in Ph⁺ ALL. Here we report the development of a nonmutational resistance cell line SupB15-RT; conferring resistance to approved ABL kinase inhibitors (AKIs) and allosteric inhibitors GNF-2, ABL001, and crizotinib, except for dasatinib (IC90 50nM), a multitarget kinase inhibitor. We found that the AKT/mTOR pathway is activated in these cells and their proliferation inhibited by Torin-1 with an IC50 of 24.7 nM. These observations were confirmed using 3 different ALL patient-derived long term cultures (PDLTCs): (1) HP (BCR-ABL1 negative), (2) PH (BCR-ABL1 positive and responsive to TKIs) and (3) BV (BCR-ABL1 positive and nonmutational resistant to TKIs). Furthermore, Torin-1 and NVP-BEZ235 induced apoptosis in PH and BV cells but not in HP cells.Our experiments provide evidence of the involvement of AKT/mTOR pathway in the evolution of nonmutational resistance in Ph⁺ ALL which will assist in developing novel targeted therapy for Ph⁺ ALL patients with BCR-ABL1 independent nonmutational resistance.     

Kinase domain point mutations in Philadelphia chromosome-positive acute lymphoblastic leukemia emerge after therapy with BCR-ABL kinase inhibitors

BACKGROUND: BCR-ABL kinase domain (KD) mutations are detected in approximately 45% of patients with imatinib-resistant chronic myeloid leukemia. Patterns of KD mutations in Philadelphia chromosome (Ph)-positive acute lympho- blastic leukemia (ALL) are less well studied. METHODS: The authors assessed KD mutations in patients with recurrent Ph-positive ALL after treatments that included 1 or more kinase inhibitors (n = 24 patients) or no prior kinase inhibitor (KI) therapy (n = 12 patients). RESULTS: ABL KD mutations were detected by direct sequencing in 15 of 17 patients (88%) who had recurrent Ph-positive ALL and received prior imatinib (n = 16) or dasatinib (n = 1) treatment and in 6 of 7 patients (86%) who had resistant/recurrent tumors treated with >or=2 KIs compared with 0 of 12 patients with recurrent Ph-positive ALL who never received KIs. A restricted set of mutations was observed, mostly Y253H and T315I, and were detected on average 10 months after KI initiation, and mutations were not detected in the initial tumor samples before KI therapy in 12 patients who were assessed. Using a more sensitive pyrosequencing method, mutations were not detected at codons 315 and 253 in the diagnostic samples from those 12 patients or in 30 patients with Ph-positive ALL who never developed recurrent disease. CONCLUSIONS: ABL KD mutations, especially at codons 315 and 253, emerged at the time of disease recurrence in the vast majority of patients who had Ph-positive ALL and received maintenance KI therapy. Thus, the authors concluded that ongoing KI exposure may alter the patterns of recurrence and favor the outgrowth of clones with KI-resistant mutations.