Multiple centrosomes in tumor cells create the potential for multipolar divisions that can lead to aneuploidy and cell death. Nevertheless, many cancer cells successfully divide because of mechanisms that suppress multipolar mitoses. A genome-wide RNAi screen in Drosophila S2 cells and a secondary analysis in cancer cells defined mechanisms that suppress multipolar mitoses. In addition to proteins that organize microtubules at the spindle poles, we identified novel roles for the spindle assembly checkpoint, cortical actin cytoskeleton, and cell adhesion. Using live cell imaging and fibronectin micropatterns, we found that interphase cell shape and adhesion pattern can determine the success of the subsequent mitosis in cells with extra centrosomes. These findings may identify cancer-selective therapeutic targets: HSET, a normally nonessential kinesin motor, was essential for the viability of certain extra centrosome-containing cancer cells. Thus, morphological features of cancer cells can be linked to unique genetic requirements for survival.[Keywords: Centrosomes; mitosis; actin; adhesion; cancer; cell cycle] Supplemental material is available at http://www.genesdev.org.

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Patients treated with cytotoxic therapies, including autologous stem cell transplantation, are at risk for developing therapy-related myeloid neoplasms (tMN). Pre-leukemic clones (i.e., clonal hematopoiesis; CH) are detectable years before the development of these aggressive malignancies, though the genomic events leading to transformation and expansion are not well-defined. Here, leveraging distinctive chemotherapy-associated mutational signatures from whole-genome sequencing data and targeted sequencing of pre-chemotherapy samples, we reconstruct the evolutionary life-history of 39 therapy-related myeloid malignancies. A dichotomy is revealed, in which neoplasms with evidence of chemotherapy-induced mutagenesis from platinum and melphalan are hypermutated and enriched for complex structural variants (i.e., chromothripsis) while neoplasms with non-mutagenic chemotherapy exposures are genomically similar to de novo acute myeloid leukemia. Using chemotherapy-associated mutational signatures as temporal barcodes linked to a discrete clinical exposure in each patient's life, we estimate that several complex events and genomic drivers are acquired after chemotherapy is administered. For patients with prior multiple myeloma who were treated with high-dose melphalan and autologous stem cell transplantation, we demonstrate that tMN can develop from either a reinfused CH clone that escapes melphalan exposure and is selected following reinfusion, or from TP53-mutant CH that survives direct myeloablative conditioning and acquires melphalan-induced DNA-damage. Overall, we reveal a novel mode of tMN progression that is not reliant on direct mutagenesis or even exposure to chemotherapy. Conversely, for tMN that evolve under the influence of chemotherapy-induced mutagenesis, distinct chemotherapies not only select pre-existing CH, but also promote the acquisition of recurrent genomic drivers.

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Epigenetics has been defined as ‘a stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence’ and several epigenetic regulators are recurrently mutated in hematological malignancies. Epigenetic modifications include changes such as DNA methylation, histone modifications and RNA associated gene silencing. Transcriptional regulation, chromosome stability, DNA replication and DNA repair are all controlled by these modifications. Mutations in genes encoding epigenetic modifiers are a frequent occurrence in hematologic malignancies and important in both the initiation and progression of cancer. Epigenetic modifications are also frequently reversible, allowing excellent opportunities for therapeutic intervention. The goal of epigenetic therapies is to reverse epigenetic dysregulation, restore the epigenetic balance, and revert malignant cells to a more normal condition. The role of epigenetic therapies thus far is most established in hematologic malignancies, with several agents already approved by the US Food and Drug Administration. In this review, we discuss pharmacological agents targeting epigenetic regulators.

Background: Recurring mutations have been identified in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) which translate to therapeutic targets. Isocitrate dehydrogenase-1 and -2 (IDH1/2) mutations occur in ~20% of AML, and up to 12% of patients with MDS. Three conserved mutational hotspots in the IDH enzymes alter their function and lead to the production of (R)-2-hydroxyglutarate (2HG), an oncometabolite with numerous downstream effects, including impaired DNA damage repair. Specifically, homologous recombination (HR) is impaired by inhibiting the function of histone demethylases that are critical for HR and recruitment of the HR machinery to sites of DNA damage. In HR deficient tumors poly-ADP ribose polymerase (PARP) enzymes mediate a key salvage pathway. PARP inhibition in HR deficient tumors leads to synthetic lethality via simultaneous inhibition of HR and SSB mediated DNA repair. Our group previously demonstrated synthetic lethality with PARP inhibition in IDH mutant cells lines, and other IDH mutant models including primary patient-derived cell lines and genetically-matched tumor xenografts. Study Design and Methods: The PRIME trial (NCI10264) is a proof of concept, biomarker-driven, multi-institution, phase II open label clinical trial to assess the overall response of IDH1/2 mutant relapsed/refractory AML and MDS to PARP inhibitor monotherapy with olaparib. The clinical trial is executed by the Experimental Therapeutics Clinical Trials Network of the NCI. The Cancer Therapy Evaluation Program will provide olaparib. Eligibility criteria include documented IDH1 or IDH2 mutation in blood or bone marrow within 30 days of enrollment based on mutational testing by PCR or sequencing in a CLIA certified laboratory and willingness to undergo a bone marrow biopsy. Patients will be treated with olaparib 300 mg q12hrs each day of a 28-day cycle, using a tablet formulation, until disease progression, unacceptable toxicity, withdrawal of consent or death. Blood and bone marrow samples for 2-HG analysis will be collected prior to starting therapy and after 1 cycle (28 days), cycle 2, 3, 6, 9, 12 or when there is concern for disease progression (Figure 1). A Simon two-stage optimal design will be used to test the null (ORR=10%) versus the alternative hypothesis (ORR=40%) in each arm. In the first stage, 9 patients will be accrued in each arm. If one or fewer responses are observed in these 9 patients, that arm will be stopped early for futility. Otherwise, 11 additional patients will be accrued for a total of 18 in each arm. We reject the null hypothesis if at least 5 responses are observed in these 20 patients. In each arm, we have approximately 90% power to detect a 30% increase in ORR at a one-sided type I error rate of 0.05. Primary endpoint: Overall response rate (ORR) of 40%, i.e., a 30% ORR improvement (40% vs. historical control ORR = 10%) based on MDS International Working Group 2006 criteria and AML MDS International Working Group 2003 criteria after 6 cycles of treatment. Cumulative ORR will include complete remission, complete remission with incomplete blood count recovery, partial response, and bone marrow complete remission. Secondary endpoints: Progression-free survival (the interval between the time of initiation of olaparib to the time of documentation of olaparib failure or last follow-up) and overall survival (the interval between the time of initiation of olaparib to the time of death or last follow-up) for the trial. Exploratory studies: The PRIME trial will also test the utility of 2-HG and DNA damage markers such as γ-H2AX as potential biomarkers of response to olaparib. Using multiple viability assays on leukemia cell lines and bone marrow cultures we will assess synergistic therapeutic combinations to further improve outcomes in this patient population. To confirm efficacy in vivo without undue toxicity, promising combination therapies will be confirmed in cytokine-humanized immunodeficient "MISTRG" mice. We will also examine the impact of PARP inhibitors on the genomic, proteomic, metabolomic and immunologic landscape of IDH 1/2-mutant hematologic malignancies using DNA whole exome sequencing (WES), RNA-Seq, and liquid chromatography-mass spectrometry assessment of oncometabolites. Disclosures Bindra: Cybrexa: Consultancy, Equity Ownership. Prebet:pfizer: Honoraria; pfizer: Honoraria; pfizer: Honoraria; Boehringer Ingelheim: Research Funding; pfizer: Honoraria; Tetraphase: Consultancy; novartis: Honoraria; novartis: Honoraria; Genentech: Consultancy; Boehringer Ingelheim: Research Funding; novartis: Honoraria; Boehringer Ingelheim: Research Funding; Agios: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding; pfizer: Honoraria; novartis: Honoraria; Bristol-Myers Squibb: Honoraria, Research Funding; novartis: Honoraria. OffLabel Disclosure: We will be using PARP inhibitors as a novel therapy for patients with relapsed or refractory AML and high risk MDS based on preclinical data.