Recent advances in the treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia

Efficacy of Ponatinib Versus Earlier Generation Tyrosine Kinase Inhibitors for Front-line Treatment of Newly Diagnosed Philadelphia-positive Acute Lymphoblastic Leukemia

INTRODUCTION

Complete molecular response (CMR) and 2- and 3-year overall survival (OS) were compared for patients with newly diagnosed Philadelphia-positive acute lymphoblastic leukemia (Ph⁺ ALL) who had undergone front-line combination chemotherapy plus ponatinib versus combination therapy plus earlier generation tyrosine kinase inhibitors (TKIs; imatinib, dasatinib, and nilotinib).

PATIENTS AND METHODS

We identified 26 Ph⁺ ALL studies: 25 of earlier generation TKIs and 1 of ponatinib. The outcomes from studies of combination chemotherapy plus earlier generation TKIs were summarized using pooled estimates with 95% confidence intervals (CIs) from a random-effects meta-analysis. A binomial distribution was assumed to calculate the 95% CIs for the results from the single-arm combination chemotherapy plus ponatinib trial. Adjusted logistic meta-regression analyses were used to compare the outcomes between the TKI groups.

RESULTS

The percentage of patients achieving a CMR was greater with combination chemotherapy plus ponatinib (79%) than the pooled percentage of patients achieving a CMR with combination chemotherapy plus earlier generation TKIs (34%). Greater OS was observed with ponatinib compared with the pooled OS for earlier generation TKIs (2-year, 83% vs. 58%; 3-year, 79% vs. 50%). Odds ratios for ponatinib versus earlier generation TKIs were 6.09 (95% CI, 1.16-31.90; P = .034) for CMR, 3.70 (95% CI, 0.93-14.73; P = .062) for 2-year OS, and 4.49 (95% CI, 1.00-20.13; P = .050) for 3-year OS.

CONCLUSION

Ponatinib plus chemotherapy might be associated with better outcomes than chemotherapy with earlier generation TKIs in patients with newly diagnosed Ph⁺ ALL.

The Philadelphia chromosome in leukemogenesis

The truncated chromosome 22 that results from the reciprocal translocation t(9;22)(q34;q11) is known as the Philadelphia chromosome (Ph) and is a hallmark of chronic myeloid leukemia (CML). In leukemia cells, Ph not only impairs the physiological signaling pathways but also disrupts genomic stability. This aberrant fusion gene encodes the breakpoint cluster region-proto-oncogene tyrosine-protein kinase (BCR-ABL1) oncogenic protein with persistently enhanced tyrosine kinase activity. The kinase activity is responsible for maintaining proliferation, inhibiting differentiation, and conferring resistance to cell death. During the progression of CML from the chronic phase to the accelerated phase and then to the blast phase, the expression patterns of different BCR-ABL1 transcripts vary. Each BCR-ABL1 transcript is present in a distinct leukemia phenotype, which predicts both response to therapy and clinical outcome. Besides CML, the Ph is found in acute lymphoblastic leukemia, acute myeloid leukemia, and mixed-phenotype acute leukemia. Here, we provide an overview of the clinical presentation and cellular biology of different phenotypes of Ph-positive leukemia and highlight key findings regarding leukemogenesis.

A DNA/HDAC dual-targeting drug CY190602 with significantly enhanced anticancer potency

Genotoxic drugs constitute a major treatment modality for human cancers; however, cancer cells' intrinsic DNA repair capability often increases the threshold of lethality and renders these drugs ineffective. The emerging roles of HDACs in DNA repair provide new opportunities for improving traditional genotoxic drugs. Here, we report the development and characterization of CY190602, a novel bendamustine-derived drug with significantly enhanced anticancer potency. We show that CY190602's enhanced potency can be attributed to its newly gained ability to inhibit HDACs. Using this novel DNA/HDAC dual-targeting drug as a tool, we further explored HDAC's role in DNA repair. We found that HDAC activities are essential for the expression of several genes involved in DNA synthesis and repair, including TYMS, Tip60, CBP, EP300, and MSL1. Importantly, CY190602, the first-in-class example of such DNA/HDAC dual-targeting drugs, exhibited significantly enhanced anticancer activity in vitro and in vivo. These findings provide rationales for incorporating HDAC inhibitory moieties into genotoxic drugs, so as to overcome the repair capacity of cancer cells. Systematic development of similar DNA/HDAC dual-targeting drugs may represent a novel opportunity for improving cancer therapy.

Time to tune the treatment of Ph+ ALL

In this issue of Blood, Chalandon et al report the results of a prospective randomized study comparing standard vs less-intensive chemotherapy, both combined with imatinib, for patients with newly diagnosed Philadelphia chromosome–positive (Ph+) acute lymphoblastic leukemia (ALL). They show that the less-intensive therapy reduces early mortality without impairing efficacy, resulting in a significantly higher hematologic complete remission (CR) rate and an equivalent major molecular response (MMolR) rate.

Philadelphia chromosome-positive acute lymphoblastic leukemia with extramedullary and meningeal relapse after allogeneic hematopoietic stem cell transplantation that was successfully treated with dasatinib

Central nervous system (CNS) relapse is a critical issue while treating Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph-positive ALL). A 58-year-old woman with Ph-positive ALL who relapsed after bone marrow transplantation for meningeal leukemia was treated with high-dose methotrexate, which resulted in remission. She underwent allogeneic cord blood transplantation followed by reduced intensity conditioning chemotherapy with imatinib; however, she experienced CNS relapse and developed an extramedullary mass on the right side of the temporal region. We treated 40 mg of dasatinib once daily, which had to be temporarily discontinued because she developed grade 2 pleural effusion and grade 2 hematemesis. After reinitiation of dasatinib, the extramedullary mass disappeared and meningeal leukemia ameliorated almost immediately. With 40 mg dasatinib administered once daily, its trough level and cerebrospinal fluid (CSF) concentration were 32 ng/mL and below the sensitivity threshold of 1 ng/mL, respectively. Treatment was continued, and the patient remained in complete remission until she died of pneumonia 7 years after the initial diagnosis of ALL. Dasatinib can be an effective treatment for Ph-positive ALL with CNS relapse. Although the concentration in the CSF seems low, it may be sufficient to exert anti-leukemic effects in the human CNS.

The effect of imatinib therapy on the outcome of allogeneic stem cell transplantation in adults with Philadelphia chromosome-positive acute lymphoblastic leukemia

OBJECTIVE

To evaluate the efficacy of imatinib administration before and/or after allogeneic hematopoietic stem cell transplantation (allo-HSCT) for patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL).

METHOD

Patients with imatinib therapy time exceeding 30 days pre-/post-transplant were screened in our data. Imatinib was used in induced or consolidated chemotherapy pre-transplant, or maintenance therapy after 60 days post-transplant (therapy time was less than 180 days) regardless of the molecular status of the disease.

RESULTS

Sixty-nine patients with Ph+ ALL were enrolled in the retrospective analysis. Forty-four patients received imatinib therapy, including 24 pre-transplant, 9 post-transplant, and 11 both pre- and post-transplant. With a median follow-up time of 395 days (range, 55-2762 days) post-transplant, 3-year estimated overall survival was 62.3 ± 16.6, 40.0 ± 21.9, 41.7 ± 22.2, and 25.9 ± 11.4%, respectively (P = 0.221), and disease-free survival (DFS) was 53.6 ± 17.9, 20.0 ± 17.9, 33.3 ± 25.5% and 23.6 ± 11.4%, respectively (P = 0.421), in patients with imatinib therapy pre-transplant, post-transplant, both pre- and post-transplant, neither pre- nor post-transplant. The incidence of relapse at 3 year for patients with imatinib therapy post-transplant (n = 20) was 63.6%, comparing with 24.2% (P = 0.018) in patients without imatinib therapy post-transplant (n = 49). The ratio of CD4+CD25+Foxp3+ cells in blood was significantly higher at 30 and 60 days after imatinib therapy than that at the time of pre-imatinib in 20 patients (P = 0.019 and 0.001, respectively).

CONCLUSIONS

Application of imatinib pre-transplant might have benefited for patients with Ph+ ALL. Whether administration of imatinib, regardless of the molecular status of the disease post-transplant increases relapse, is a worthy goal for further study.

Rapid detection of prognostically significant fusion transcripts in acute leukemia using simplified multiplex reverse transcription polymerase chain reaction

Multiplex reverse transcription polymerase chain reaction (mRT-PCR) has recently emerged as an alternative to cytogenetics. We designed and used simplified mRT-PCR system as a molecular screen for acute leukemia. Fifteen fusion transcripts were included: BCR-ABL1, PML-RARA, ZBTB16-RARA, RUNX1-RUNX1T1, CBFB-MYH11, DEK-NUP214, TCF3-PBX1, ETV6-RUNX1, MLL-AFF1, MLL-MLLT4, MLL-MLLT3, MLL-MLLT10, MLL-ELL, MLL-MLLT1, and MLL-MLLT6. A total of 121 diagnostic acute leukemia specimens were studied, comparing the mRT-PCR system with standard cytogenetics. Fifty-six cases (46.3%) had fusion transcripts revealed by our mRT-PCR assay. The concordance rate between mRT-PCR and cytogenetics was 91.7%. However, false negative results were found in three cases who have inv(16), t(4;11) or t(11;19)(q23;p13.1), respectively. Seven cryptic translocations including ETV6-RUNX1, MLL-MLLT3, MLL-MLLT4, and PML-RARA were detected. This mRT-PCR assay is a useful screening tool in acute leukemia because it provides rapid and reliable detection of clinically important chimeric transcripts. In addition, cryptic translocations provide additional genetic information that could be clinically useful.

Molecular diagnostics, targeted therapy, and the indication for allogeneic stem cell transplantation in acute lymphoblastic leukemia

In recent years, the panel of known molecular mutations in acute lymphoblastic leukemia (ALL) has been continuously increased. In Philadelphia-positive ALL, deletions of the IKZF1 gene were identified as prognostically adverse factors. These improved insights in the molecular background and the clinical heterogeneity of distinct cytogenetic subgroups may allow most differentiated therapeutic decisions, for example, with respect to the indication to allogeneic HSCT within genetically defined ALL subtypes. Quantitative real-time PCR allows highly sensitive monitoring of the minimal residual disease (MRD) load, either based on reciprocal gene fusions or immune gene rearrangements. Molecular diagnostics provided the basis for targeted therapy concepts, for example, combining the tyrosine kinase inhibitor imatinib with chemotherapy in patients with Philadelphia-positive ALL. Screening for BCR-ABL1 mutations in Philadelphia-positive ALL allows to identify patients who may benefit from second-generation tyrosine kinase inhibitors or from novel compounds targeting the T315I mutation. Considering the central role of the molecular techniques for the management of patients with ALL, efforts should be made to facilitate and harmonize immunophenotyping, cytogenetics, and molecular mutation screening. Furthermore, the potential of high-throughput sequencing should be evaluated for diagnosis and follow-up of patients with B-lineage ALL.

Molecular diagnostics, targeted therapy, and the indication for allogeneic stem cell transplantation in acute lymphoblastic leukemia

In recent years, the panel of known molecular mutations in acute lymphoblastic leukemia (ALL) has been continuously increased. In Philadelphia-positive ALL, deletions of the IKZF1 gene were identified as prognostically adverse factors. These improved insights in the molecular background and the clinical heterogeneity of distinct cytogenetic subgroups may allow most differentiated therapeutic decisions, for example, with respect to the indication to allogeneic HSCT within genetically defined ALL subtypes. Quantitative real-time PCR allows highly sensitive monitoring of the minimal residual disease (MRD) load, either based on reciprocal gene fusions or immune gene rearrangements. Molecular diagnostics provided the basis for targeted therapy concepts, for example, combining the tyrosine kinase inhibitor imatinib with chemotherapy in patients with Philadelphia-positive ALL. Screening for BCR-ABL1 mutations in Philadelphia-positive ALL allows to identify patients who may benefit from second-generation tyrosine kinase inhibitors or from novel compounds targeting the T315I mutation. Considering the central role of the molecular techniques for the management of patients with ALL, efforts should be made to facilitate and harmonize immunophenotyping, cytogenetics, and molecular mutation screening. Furthermore, the potential of high-throughput sequencing should be evaluated for diagnosis and follow-up of patients with B-lineage ALL.

ABL1 fusion genes in hematological malignancies: a review

Chromosomal rearrangements involving the ABL1 gene, leading to a BCR-ABL1 fusion gene, have been mainly associated with chronic myeloid leukemia and B-cell acute lymphoblastic leukemia (ALL). At present, six other genes have been shown to fuse to ABL1. The kinase domain of ABL1 is retained in all chimeric proteins that are also composed of the N-terminal part of the partner protein that often includes a coiled-coil or a helix-loop-helix domain. These latter domains allow oligomerization of the protein that is required for tyrosine kinase activation, cytoskeletal localization, and neoplastic transformation. Fusion genes that have a break in intron 1 or 2 (BCR-ABL1, ETV6-ABL1, ZMIZ1-ABL1, EML1-ABL1, and NUP214-ABL1) have transforming activity, although NUP214-ABL1 requires amplification to be efficient. The NUP214-ABL1 gene is the second most prevalent fusion gene involving ABL1 in malignant hemopathies, with a frequency of 5% in T-cell ALL. Both fusion genes (SFPQ-ABL1 and RCSD1-ABL1) characterized by a break in intron 4 of ABL1 are associated with B-cell ALL, as the chimeric proteins lacked the SH2 domain of ABL1. Screening for ABL1 chimeric genes could be performed in patients with ALL, more particularly in those with T-cell ALL because ABL1 modulates T-cell development and plays a role in cytoskeletal remodeling processes in T cells.

Changing paradigm of the treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia

In the pre-imatinib era, the treatment outcome of patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL) was dismal. Complete remission was generally achieved only in about 50% to 60% of patients, and allogeneic hematopoietic stem cell transplantation (allo-HSCT), when feasible in younger patients, was virtually the sole curative modality. Imatinib has changed the situation dramatically, however, in combination with conventional chemotherapy or with corticosteroid alone, producing about 95% complete remission and thus increasing the number of patients undergoing allo-HSCT. Currently, the overall survival of patients who have undergone allo-HSCT exceeds 50%, and a considerable proportion of patients for whom allo-HSCT is not feasible are predictably curable. The next question is how to prevent relapse, which is observed not only in more than half of patients for whom allo-HSCT is not feasible but also in a considerable number of patients after allo-HSCT. Thus, improvement of postremission therapy is crucial. Whether intensive chemotherapy with currently available cytotoxic drugs contributes to the prevention of relapse is questionable, because intensive chemotherapy alone in the pre-imatinib era nearly always failed to cure this disease. Promising partners to be combined with imatinib or with a second-generation tyrosine kinase inhibitor (TKI) will be corticosteroids and vincristine. New TKIs such as dasatinib should be incorporated into the early phase of postremission therapy. Recognizing the small number of patients with Ph(+) ALL, intergroup or international studies are necessary to develop the best postremission therapy. In the near future, it is hoped that Ph(+) ALL will become one of the leukemias for which allo-HSCT is offered only for relapsed or extremely high-risk patients.

ABL tyrosine kinases: evolution of function, regulation, and specificity

ABL-family proteins comprise one of the best conserved branches of the tyrosine kinases. Each ABL protein contains an SH3-SH2-TK (Src homology 3-Src homology 2-tyrosine kinase) domain cassette, which confers autoregulated kinase activity and is common among nonreceptor tyrosine kinases. This cassette is coupled to an actin-binding and -bundling domain, which makes ABL proteins capable of connecting phosphoregulation with actin-filament reorganization. Two vertebrate paralogs, ABL1 and ABL2, have evolved to perform specialized functions. ABL1 includes nuclear localization signals and a DNA binding domain through which it mediates DNA damage-repair functions, whereas ABL2 has additional binding capacity for actin and for microtubules to enhance its cytoskeletal remodeling functions. Several types of posttranslational modifications control ABL catalytic activity, subcellular localization, and stability, with consequences for both cytoplasmic and nuclear ABL functions. Binding partners provide additional regulation of ABL catalytic activity, substrate specificity, and downstream signaling. Information on ABL regulatory mechanisms is being mined to provide new therapeutic strategies against hematopoietic malignancies caused by BCR-ABL1 and related leukemogenic proteins.

Intensified consolidation therapy with dose-escalated doxorubicin did not improve the prognosis of adults with acute lymphoblastic leukemia: the JALSG-ALL97 study

We designed a treatment protocol for newly diagnosed adult acute lymphoblastic leukemia (ALL) in the pre-imatinib era, employing intensified consolidation therapy with a total of 330 mg/m² doxorubicin and adopting slightly modified induction and maintenance regimen of the CALGB 8811 study. Of 404 eligible patients (median age 38 years, range 15-64 years), 298 (74%) achieved complete remission (CR). The 5-year overall survival (OS) rate was 32%, and the 5-year disease-free survival (DFS) rate was 33%. Of 256 Philadelphia chromosome (Ph)-negative patients, 208 (81%) achieved CR and the 5-year OS rate was 39%, and 60 of them underwent allogeneic-hematopoietic stem cell transplantation (allo-HSCT) from related or unrelated donors during the first CR, resulting in 63% 5-year OS. Of 116 Ph-positive patients, 65 (56%) achieved CR and the 5-year OS rate was 15%, and 22 of them underwent allo-HSCT from related or unrelated donors during the first CR, resulting in 47% 5-year OS. In Ph-negative patients, multivariate analysis showed that older age, advanced performance status and unfavorable karyotypes were significant poor prognostic factors for OS and higher WBC counts for DFS. The present treatment regimen could not show a better outcome than that of our previous JALSG-ALL93 study for adult ALL.

Emerging therapy for the treatment of acute lymphoblastic leukemia

IMPORTANCE OF THE FIELD

Over the last few decades, advances in acute lymphoblastic leukemia (ALL) therapy have led to long-term survival rates of > 80% in children; however, comparable rates have yet to be achieved in adults, and a large majority of patients relapse from their disease.

AREAS COVERED IN THIS REVIEW

The review describes historical therapy and advancements in ALL treatment over the past few decades, while providing a concise review of the future direction of ALL therapy. Literature was collected through peer reviewed journals and the Pharmaprojects drug profile for ALL.

WHAT THE READER WILL GAIN

Current information regarding prognostic factors for relapse, salvage therapy options and emerging drugs are provided in the review.

TAKE HOME MESSAGE

Development of new drugs with novel mechanisms, unique formulations of existing medications, as well as manipulation of current combinations of drugs remain vital to the success in adult ALL.

LLL-3, a STAT3 inhibitor, represses BCR-ABL-positive cell proliferation, activates apoptosis and improves the effects of Imatinib mesylate

PURPOSE

The chimeric protein BCR-ABL, a constitutively active protein-tyrosine kinase, triggers downstream signalling proteins, such as STAT3, ultimately resulting in the survival of myeloid progenitors in BCR-ABL-positive leukemias. Here, we evaluated the effect of LLL-3, an inhibitor of STAT3 activity, on cell viability and its addictive effects with Imatinib mesylate (IM) treatment in BCR-ABL-positive cells.

METHODS

Viability of cell lines was determined using the WST-1 assay in response to drug treatment, either LLL-3 alone or in conjunction with IM. Annexin V-FITC/PI staining, sub-G1 DNA content and Caspase-3/7 activation assays were performed to evaluate apoptosis.

RESULTS

LLL-3 treatment decreased cell viability, triggered apoptosis and activated Caspases-3/7 in K562 cells. LLL-3 increases IM treatment to inhibited cell viability and activation of apoptosis in BCR-ABL-positive cell lines.

CONCLUSIONS

LLL-3 reduced cell viability and induced apoptosis in K562 cells. Moreover, the observed addictive effects of co-treatment with IM and LLL-3 suggest this combination has therapeutic potential.

Transplantation in adult ALL

The value of the allogeneic graft-versus-leukemia effect in adult acute lymphoblastic leukemia (ALL) has now been conclusively demonstrated and confirmed. While this is true for adults in all age groups, it may not be the best clinical option for young adults for whom increasingly intensive pediatric protocols are clearly of benefit. On the other hand, there is potentially wider applicability of allogeneic donor transplantation for adults 25 to 45 years old, for whom matched unrelated donors may be as safe and effective as sibling donors, and for the patient older than 45 years for whom reduced-intensity conditioning may be a promising way forward. Since the treatment-related mortality of allogeneic transplantation remains significant, careful selection of patients is mandatory. Patients with the Philadelphia chromosome, those with t(4;11) and those with a complex karyotype remain transplant candidates, and allogeneic transplantation remains the best option for salvage, where achievable, in a remission beyond first. As in childhood ALL minimal residual disease studies may be extremely useful in predicting outcome and, therefore, strategy, but at present there are less definite data in adults. Clinical indications to harness the allogeneic effect will mature as the true value of pediatric protocols in adult patients and the safety and efficacy of a sibling, unrelated and reduced intensity transplant emerge in this disease.