The endopeptidase Separase, encoded by the ESPL1 gene, plays a key role in faithful segregation of sister chromatids by cleaving the cohesin complex at the metaphase to anaphase transition. Its overexpression associates with aneuploidy and bad prognosis in solid tumors. Little is known in Acute Myeloid Leukemia (AML). We profiled the genomic landscape of 405 and 78 AML cases by SNP array (SNP 6.0 and Cytoscan HD, Affymetrix) and whole exome sequencing (100 bp, paired-end, Illumina), respectively. Bone marrow blasts from 61 patients were analyzed by gene expression profiling (HTA 2.0, Affymetrix). Separase expression was determined by Immunohistochemistry (1:600 antibody dilution Abnova, clone 6H6) in 44 AML and 4 control bone marrow specimens. One patient exhibited a nonsynonimous mutation in ESPL1 (1.3%), which was predicted to alter the protein function. Moreover, ESPL1 copy number gain was observed in 5/405 cases (1.2%): 2 hyperdiploid AML, one trisomy 12 and 2 cases with a short gain at 12q. Notably, protein level detection in one of the 12q-gain cases confirmed Separase overexpression. To determine the incidence of Separase overexpression, we performed Immunohistochemistry on additional 43 AML. Separase was overexpressed in 29/44 AML (66%, Separase-high), being comparable to control marrow biopsies in the remaining 15 samples (Separase-low). Sixty-two percent of Separase-high AML were aneuploid. However, no significative association was observed, as previously reported for mutations in the cohesin genes in AML. Separase overexpression correlated with increased patients’ age (median age 64 vs. 57 years, p=.01), 17-fold upregulation of CD34 (p=.004) and a trend towards reduced overall survival (6-years follow-up). Separase overexpression was not mutually esclusive with cohesin gene mutations, it co-occurred with NPM1 and FLT3 lesions and frequent mutations in genes involved in protein post-translational modification and ubiquitination (p=.04). Separase-low cases were enriched for mutations in RAS signaling pathway (NRAS, KRAS, NF1, RIT1, GRAP2, RALGDS; p=4.5x10-5) and in cell migration-related genes (LIMS2, S1PR1, PPIA, PLXNB1, FAT1). Separase-high cases also showed a defined transcriptomic profile, characterized by reduced expression of HOXA/B family genes, the DNA damage repair gene ATM, the p53 regulator MDM2 and forced expression of the cell cycle markers CDC20, AURKB, NUSAP1 and of MYC, independently of chromosome 8 gain. Taken together, our data suggest that genomic lesions targeting ESPL1 are a rare event in AML. However, Separase overexpression is a common feature and defines a new subset of AML cases with a distinct gene expression profile, which may benefit of innovative targeted therapies including CDC20 and bromodomain inhibitors. Supported by: ELN, AIL, AIRC, progetto Regione-Università 2010-12 (L. Bolondi), FP7 NGS-PTL project.

Citation Format: Giorgia Simonetti, Antonella Padella, Simona Righi, Maria Chiara Fontana, Marco Manfrini, Cristina Papayannidis, Giovanni Marconi, Carmen Baldazzi, Marianna Garonzi, Alberto Ferrarini, Massimo Delledonne, Nicoletta Testoni, Elena Sabattini, Giovanni Martinelli. Separase overexpression defines a new subset of acute myeloma leukemia patients characterized by high CD34 and MYC levels [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3472. doi:10.1158/1538-7445.AM2017-3472