Abstract 1158: Modulation of splicing by inhibiting the kinase SRPK1 as a novel therapeutic strategy in myeloid leukemia
Authors: Tzelepis Konstantinos , Braekeleer Etienne De , Seiler Michael , Barbieri Isaia , Robson Sam , Yang Yu Hsuen , Gozdecka Malgorzata , Dudek Monika , Collord Grace , Dovey Oliver M. , Metzakopian Emmanouil , Garyfallos Dimitrios , Cooper Jonathan L. , Buonamici Silvia , Ponstingl Hannes , Stratton Michael R. , Bradley Allan , Huntly Brian J. , Pina Cristina , Kouzarides Tony , Yusa Kosuke , Vassiliou George S. 
Published: July 2017

Abstract
Acute myeloid leukemia (AML) is an aggressive cancer with a poor prognosis, for which the therapeutic landscape has changed little for decades. Aberrant mRNA splicing plays a key role in cancer development and genes coding for several of the major components of the spliceosome are targeted by somatic mutations in numerous cancers including myelodysplastic syndromes and AML. Recently, myeloid neoplasms bearing spliceosome gene mutations were shown to be preferentially susceptible to pharmacological disruption of the spliceosome. Here we report that targeting the spliceosome can also be an effective therapeutic strategy in other types of AML.
Recently, we generated a comprehensive catalogue of genetic vulnerabilities in AML using CRISPR-Cas9 genome-wide recessive screens and reported several novel intuitive and non-intuitive therapeutic candidates. Amongst these we identify SRPK1, the gene coding for a serine-threonine kinase that phosphorylates the major spliceosome protein SRSF1. Here, we demonstrate that targeted genetic disruption of SRPK1 in AML driven by MLL-fusion genes, led to differentiation and apoptosis. Additionally, mice transplanted with human AML cell lines carrying the MLL-AF9 fusion gene, namely MOLM-13 and THP-1, presented a significant prolongation of survival when SRPK1 was genetically disrupted by CRISPR-Cas9 editing. Similar effects were seen with pharmacological inhibition of SRPK1 in vitro and in vivo. At the molecular level we show that genetic or pharmacological inhibition of SRPK1 was associated with profound changes in the splicing of multiple genes involved in the MLL leukemogenic program in association with significant changes in enzymatic modifications of core histone tails.
We proceeded to perform a genome-wide CRISPR drop-out screen for sensitizers of MOLM13 cells to pharmacological inhibition of SRPK1 and identified, amongst other genes, BRD4 as a sensitizer. We go on to show that the BRD inhibitor iBET-151 synergizes with SRPK1 inhibition to kill MOLM-13 both in vitro and in vivo. Preliminary data indicates that SRPK1 inhibition has overlapping molecular effects to BRD inhibition. We are currently investigating the molecular bases of this observation.
Our work identifies SRPK1 as a novel therapeutic target in AML that can be used alone or in conjunctions with drugs targeting epigenetic modifications to improve their anti-leukemic effects.
Citation Format: Konstantinos Tzelepis, Etienne De Braekeleer, Michael Seiler, Isaia Barbieri, Sam Robson, Yu Hsuen Yang, Malgorzata Gozdecka, Monika Dudek, Grace Collord, Oliver M. Dovey, Emmanouil Metzakopian, Dimitrios Garyfallos, Jonathan L. Cooper, Silvia Buonamici, Hannes Ponstingl, Michael R. Stratton, Allan Bradley, Brian J. Huntly, Cristina Pina, Tony Kouzarides, Kosuke Yusa, George S. Vassiliou. Modulation of splicing by inhibiting the kinase SRPK1 as a novel therapeutic strategy in myeloid leukemia [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 1158. doi:10.1158/1538-7445.AM2017-1158