SFPQ-ABL1 and BCR-ABL1 use different signaling networks to drive B-cell acute lymphoblastic leukemia.

Philadelphia-like (Ph-like) acute lymphoblastic leukemia (ALL) is a high-risk subtype of B-cell ALL characterized by a gene expression profile resembling Philadelphia chromosome-positive ALL (Ph+ ALL) in the absence of BCR-ABL1. Tyrosine kinase-activating fusions, some involving ABL1, are recurrent drivers of Ph-like ALL and are targetable with tyrosine kinase inhibitors (TKIs). We identified a rare instance of SFPQ-ABL1 in a child with Ph-like ALL. SFPQ-ABL1 expressed in cytokine-dependent cell lines was sufficient to transform cells and these cells were sensitive to ABL1-targeting TKIs. In contrast to BCR-ABL1, SFPQ-ABL1 localized to the nuclear compartment and was a weaker driver of cellular proliferation. Phosphoproteomics analysis showed upregulation of cell cycle, DNA replication, and spliceosome pathways, and downregulation of signal transduction pathways, including ErbB, NF-κB, vascular endothelial growth factor (VEGF), and MAPK signaling in SFPQ-ABL1-expressing cells compared with BCR-ABL1-expressing cells. SFPQ-ABL1 expression did not activate phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling and was associated with phosphorylation of G2/M cell cycle proteins. SFPQ-ABL1 was sensitive to navitoclax and S-63845 and promotes cell survival by maintaining expression of Mcl-1 and Bcl-xL. SFPQ-ABL1 has functionally distinct mechanisms by which it drives ALL, including subcellular localization, proliferative capacity, and activation of cellular pathways. These findings highlight the role that fusion partners have in mediating the function of ABL1 fusions.

Cotargeting BCL-2 and MCL-1 in high-risk B-ALL.

Improving survival outcomes in adult B-cell acute lymphoblastic leukemia (B-ALL) remains a clinical challenge. Relapsed disease has a poor prognosis despite the use of tyrosine kinase inhibitors (TKIs) for Philadelphia chromosome positive (Ph+ ALL) cases and immunotherapeutic approaches, including blinatumomab and chimeric antigen receptor T cells. Targeting aberrant cell survival pathways with selective small molecule BH3-mimetic inhibitors of BCL-2 (venetoclax, S55746), BCL-XL (A1331852), or MCL1 (S63845) is an emerging therapeutic option. We report that combined targeting of BCL-2 and MCL1 is synergistic in B-ALL in vitro. The combination demonstrated greater efficacy than standard chemotherapeutics and TKIs in primary samples from adult B-ALL with Ph+ ALL, Ph-like ALL, and other B-ALL. Moreover, combined BCL-2 or MCL1 inhibition with dasatinib showed potent killing in primary Ph+ B-ALL cases, but the BH3-mimetic combination appeared superior in vitro in a variety of Ph-like ALL samples. In PDX models, combined BCL-2 and MCL1 targeting eradicated ALL from Ph- and Ph+ B-ALL cases, although fatal tumor lysis was observed in some instances of high tumor burden. We conclude that a dual BH3-mimetic approach is highly effective in diverse models of high-risk human B-ALL and warrants assessment in clinical trials that incorporate tumor lysis precautions.

Targeted therapy and disease monitoring in CNTRL-FGFR1-driven leukaemia.

We report two patients with leukaemia driven by the rare CNTRL-FGFR1 fusion oncogene. This fusion arises from a t(8;9)(p12;q33) translocation, and is a rare driver of biphenotypic leukaemia in children. We used RNA sequencing to report novel features of expressed CNTRL-FGFR1, including CNTRL-FGFR1 fusion alternative splicing. From this knowledge, we designed and tested a Droplet Digital PCR assay that detects CNTRL-FGFR1 expression to approximately one cell in 100 000 using fusion breakpoint-specific primers and probes. We also utilised cell-line models to show that effective tyrosine kinase inhibitors, which may be included in treatment regimens for this disease, are only those that block FGFR1 phosphorylation.

VDAC2 enables BAX to mediate apoptosis and limit tumor development.

Intrinsic apoptosis is critical to prevent tumor formation and is engaged by many anti-cancer agents to eliminate tumor cells. BAX and BAK, the two essential mediators of apoptosis, are thought to be regulated through similar mechanisms and act redundantly to drive apoptotic cell death. From an unbiased genome-wide CRISPR/Cas9 screen, we identified VDAC2 (voltage-dependent anion channel 2) as important for BAX, but not BAK, to function. Genetic deletion of VDAC2 abrogated the association of BAX and BAK with mitochondrial complexes containing VDAC1, VDAC2, and VDAC3, but only inhibited BAX apoptotic function. Deleting VDAC2 phenocopied the loss of BAX in impairing both the killing of tumor cells by anti-cancer agents and the ability to suppress tumor formation. Together, our studies show that efficient BAX-mediated apoptosis depends on VDAC2, and reveal a striking difference in how BAX and BAK are functionally impacted by their interactions with VDAC2.

Dysregulation of BCL-2 family proteins by leukemia fusion genes.

The genomic lesions that characterize acute lymphoblastic leukemia in childhood include recurrent translocations that result in the expression of fusion proteins that typically involve genes encoding tyrosine kinases, cytokine receptors, and transcription factors. These genetic rearrangements confer phenotypic hallmarks of malignant transformation, including unrestricted proliferation and a relative resistance to apoptosis. In this Minireview, we discuss the molecular mechanisms that link these fusions to the control of cell death. We examine how these fusion genes dysregulate the BCL-2 family of proteins, preventing activation of the apoptotic effectors, BAX and BAK, and promoting cell survival.

Bcl-2, Bcl-x(L), and Bcl-w are not equivalent targets of ABT-737 and navitoclax (ABT-263) in lymphoid and leukemic cells.

The BH3-mimetic ABT-737 and an orally bioavailable compound of the same class, navitoclax (ABT-263), have shown promising antitumor efficacy in preclinical and early clinical studies. Although both drugs avidly bind Bcl-2, Bcl-x(L), and Bcl-w in vitro, we find that Bcl-2 is the critical target in vivo, suggesting that patients with tumors overexpressing Bcl-2 will probably benefit. In human non-Hodgkin lymphomas, high expression of Bcl-2 but not Bcl-x(L) predicted sensitivity to ABT-263. Moreover, we show that increasing Bcl-2 sensitized normal and transformed lymphoid cells to ABT-737 by elevating proapoptotic Bim. In striking contrast, increasing Bcl-x(L) or Bcl-w conferred robust resistance to ABT-737, despite also increasing Bim. Cell-based protein redistribution assays unexpectedly revealed that ABT-737 disrupts Bcl-2/Bim complexes more readily than Bcl-x(L)/Bim or Bcl-w/Bim complexes. These results have profound implications for how BH3-mimetics induce apoptosis and how the use of these compounds can be optimized for treating lymphoid malignancies.

Temozolomide in pediatric low-grade glioma.

BACKGROUND: We describe a retrospective series of children with low-grade glioma who received temozolomide. PROCEDURE: Eligible patients had had a diagnosis of low-grade glioma with or without histological confirmation. Temozolomide was administered at a dose of 200 mg/m(2) daily for 5 days, in a 4-week cycle. Therapy was stopped on completion of the targeted 12 cycles of chemotherapy or on evidence of tumor progression. RESULTS: Thirteen eligible patients were identified, eight male and five female. Median age at diagnosis was 5.5 years (range 2.6-15.0 years) and at commencement of temozolomide treatment was 9.0 years (range 3.8-15.2 years). Nine patients had a histological diagnosis of pilocytic astrocytoma. Twelve patients had received carboplatin prior to temozolomide, including three in combination with vincristine. A total of 111 cycles of therapy have been administered. Hematological toxicity and nausea were the most common adverse effects. Median time to progression was 6.7 months (range 1.5-41.8 months). Event-free survival rate at 3 years was 57%. Twelve of 13 patients remain alive at the time of report. Eleven have stable disease (SD). CONCLUSION: Temozolomide appears to be active in pediatric low-grade glioma, with the advantage of oral administration and excellent tolerability.

Adverse hypersensitivity reactions to mesna as adjunctive therapy for cyclophosphamide.

Mesna is widely used for the prevention of cyclophosphamide-related hemorrhagic cystitis. It has been associated with hypersensitivity-like cutaneous and systemic reactions in adult patients. We report a series of children with malignant disease, who developed such reactions following mesna administration and discuss possible mechanisms and management issues.