Integrated analysis of patient samples identifies biomarkers for venetoclax efficacy and combination strategies in acute myeloid leukemia.

Deregulation of the BCL2 gene family plays an important role in the pathogenesis of acute myeloid leukemia (AML). The BCL2 inhibitor, venetoclax, has received FDA approval for the treatment of AML. However, upfront and acquired drug resistance ensues due, in part, to the clinical and genetic heterogeneity of AML, highlighting the importance of identifying biomarkers to stratify patients onto the most effective therapies. By integrating clinical characteristics, exome and RNA sequencing, and inhibitor data from primary AML patient samples, we determined that myelomonocytic leukemia, upregulation of BCL2A1 and CLEC7A, as well as mutations of PTPN11 and KRAS conferred resistance to venetoclax and multiple venetoclax combinations. Venetoclax in combination with an MCL1 inhibitor AZD5991 induced synthetic lethality and circumvented venetoclax resistance.

No Matter How You Splice It, RBM39 Inhibition Targets Spliceosome Mutant AML.

A report in this issue of Cancer Cell identifies the RNA-binding protein RBM39 as a potential target in spliceosome mutant AML that can be targeted by existing sulfonamide drugs. These results support a proposed clinical trial in patients with myeloid malignancies bearing spliceosome mutations relapsed or refractory to standard therapy.

Author Correction: Somatic chromosomal engineering identifies BCAN-NTRK1 as a potent glioma driver and therapeutic target.

This corrects the article DOI: 10.1038/ncomms15987.

Whole chromosome loss and associated breakage-fusion-bridge cycles transform mouse tetraploid cells.

Whole chromosome gains or losses (aneuploidy) are a hallmark of ~70% of human tumors. Modeling the consequences of aneuploidy has relied on perturbing spindle assembly checkpoint (SAC) components, but interpretations of these experiments are clouded by the multiple functions of these proteins. Here, we used a Cre recombinase-mediated chromosome loss strategy to individually delete mouse chromosomes 9, 10, 12, or 14 in tetraploid immortalized murine embryonic fibroblasts. This methodology also involves the generation of a dicentric chromosome intermediate, which subsequently undergoes a series of breakage-fusion-bridge (BFB) cycles. While the aneuploid cells generally display a growth disadvantage in vitro, they grow significantly better in low adherence sphere-forming conditions and three of the four lines are transformed in vivo, forming large and invasive tumors in immunocompromised mice. The aneuploid cells display increased chromosomal instability and DNA damage, a mutator phenotype associated with tumorigenesis in vivo Thus, these studies demonstrate a causative role for whole chromosome loss and the associated BFB-mediated instability in tumorigenesis and may shed light on the early consequences of aneuploidy in mammalian cells.

Somatic chromosomal engineering identifies BCAN-NTRK1 as a potent glioma driver and therapeutic target.

The widespread application of high-throughput sequencing methods is resulting in the identification of a rapidly growing number of novel gene fusions caused by tumour-specific chromosomal rearrangements, whose oncogenic potential remains unknown. Here we describe a strategy that builds upon recent advances in genome editing and combines ex vivo and in vivo chromosomal engineering to rapidly and effectively interrogate the oncogenic potential of genomic rearrangements identified in human brain cancers. We show that one such rearrangement, an microdeletion resulting in a fusion between Brevican (BCAN) and Neurotrophic Receptor Tyrosine Kinase 1 (NTRK1), is a potent oncogenic driver of high-grade gliomas and confers sensitivity to the experimental TRK inhibitor entrectinib. This work demonstrates that BCAN-NTRK1 is a bona fide human glioma driver and describes a general strategy to define the oncogenic potential of novel glioma-associated genomic rearrangements and to generate accurate preclinical models of this lethal human cancer.

Mad2 Overexpression Uncovers a Critical Role for TRIP13 in Mitotic Exit.

The mitotic checkpoint ensures proper segregation of chromosomes by delaying anaphase until all kinetochores are bound to microtubules. This inhibitory signal is composed of a complex containing Mad2, which inhibits anaphase progression. The complex can be disassembled by p31comet and TRIP13; however, TRIP13 knockdown has been shown to cause only a mild mitotic delay. Overexpression of checkpoint genes, as well as TRIP13, is correlated with chromosomal instability (CIN) in cancer, but the initial effects of Mad2 overexpression are prolonged mitosis and decreased proliferation. Here, we show that TRIP13 overexpression significantly reduced, and TRIP13 reduction significantly exacerbated, the mitotic delay associated with Mad2 overexpression, but not that induced by microtubule depolymerization. The combination of Mad2 overexpression and TRIP13 loss reduced the ability of checkpoint complexes to disassemble and significantly inhibited the proliferation of cells in culture and tumor xenografts. These results identify an unexpected dependency on TRIP13 in cells overexpressing Mad2.

Cox-2-derived PGE2 induces Id1-dependent radiation resistance and self-renewal in experimental glioblastoma.

BACKGROUND: In glioblastoma (GBM), Id1 serves as a functional marker for self-renewing cancer stem-like cells. We investigated the mechanism by which cyclooxygenase-2 (Cox-2)-derived prostaglandin E2 (PGE2) induces Id1 and increases GBM self-renewal and radiation resistance. METHODS: Mouse and human GBM cells were stimulated with dimethyl-PGE2 (dmPGE2), a stabilized form of PGE2, to test for Id1 induction. To elucidate the signal transduction pathway governing the increase in Id1, a combination of short interfering RNA knockdown and small molecule inhibitors and activators of PGE2 signaling were used. Western blotting, quantitative real-time (qRT)-PCR, and chromatin immunoprecipitation assays were employed. Sphere formation and radiation resistance were measured in cultured primary cells. Immunohistochemical analyses were carried out to evaluate the Cox-2-Id1 axis in experimental GBM. RESULTS: In GBM cells, dmPGE2 stimulates the EP4 receptor leading to activation of ERK1/2 MAPK. This leads, in turn, to upregulation of the early growth response1 (Egr1) transcription factor and enhanced Id1 expression. Activation of this pathway increases self-renewal capacity and resistance to radiation-induced DNA damage, which are dependent on Id1. CONCLUSIONS: In GBM, Cox-2-derived PGE2 induces Id1 via EP4-dependent activation of MAPK signaling and the Egr1 transcription factor. PGE2-mediated induction of Id1 is required for optimal tumor cell self-renewal and radiation resistance. Collectively, these findings identify Id1 as a key mediator of PGE2-dependent modulation of radiation response and lend insight into the mechanisms underlying radiation resistance in GBM patients.