Cancer Biology and Translational Studies Phosphatidylinositol-3-kinase (PI3K)/Akt Signaling is Functionally Essential in Myxoid Liposarcoma Marcel Trautmann 1,2 , Magdalene Cyra 1,2 , Ilka Isfort 1,2 , Birte Jeiler 1,2 , Arne Kr € uger 1,2 , Inga Gr € unewald 1,2 , Konrad Steinestel 1,3 , Bianca Altvater 4 , Claudia Rossig 4,5 , Susanne Hafner 6 , Thomas Simmet 6 , Jessica Becker 7 , Pierre Åman 8 , Eva Wardelmann 1 , Sebastian Huss 1 , and Wolfgang Hartmann 1,2 Abstract Myxoid liposarcoma (MLS) is an aggressive soft-tissue tumor characterized by a specific reciprocal t(12;16) translocation resulting in expression of the chimeric FUS–DDIT3 fusion protein, an oncogenic transcription factor. Similar to other translocation-associated sarcomas, MLS is characterized by a low frequency of somatic mutations, albeit a subset of MLS has previously been shown to be associated with activating PIK3CA mutations. This study was performed to assess the prevalence of PI3K/Akt signaling alterations in MLS and the potential of PI3K- directed therapeutic concepts. In a large cohort of MLS, key components of the PI3K/Akt signaling cascade were evaluated by next generation seqeuncing (NGS), fluorescence in situ hybridization (FISH), and immunohistochemistry (IHC). In three MLS cell lines, PI3K activity was inhibited by RNAi and the small-molecule PI3K inhibitor BKM120 (buparlisib) in vitro. An MLS cell line–based avian chorioallantoic membrane model was applied for in vivo confirmation. In total, 26.8% of MLS cases displayed activating alterations in PI3K/Akt signaling components, with PIK3CA gain-of-function mutations repre- senting the most prevalent finding (14.2%). IHC suggested PI3K/Akt activation in a far larger subgroup of MLS, implying alternative mechanisms of pathway activation. PI3K-directed therapeutic interference showed that MLS cell proliferation and viability significantly depended on PI3K-mediated signals in vitro and in vivo. Our preclinical study underlines the elementary role of PI3K/Akt signals in MLS tumorigenesis and provides a molecularly based rationale for a PI3K-targeted therapeutic approach which may be particularly effective in the subgroup of tumors carrying activating genetic alterations in PI3K/Akt signaling components. Introduction Myxoid liposarcoma (MLS) accounts for approximately 5%–10% of all soft-tissue sarcomas, representing about 20% of all malignant adipocytic tumors (1). MLS constitutes the most frequent liposarcoma subtype in patients below the age of 20 years. A high rate of local recurrence and particular propensity to develop distant metastases has been reported in approximately 40% of MLS patients (2). MLS exhibit a morphologic spectrum ranging from myxoid tumors with low cellularity to hypercellular, round-cell sarcomas associated with an aggressive clinical course (3). Genet- ically, 95% of MLS are characterized by a chromosomal t(12;16) (q13;p11) translocation, juxtaposing the FUS and DDIT3 genes. The remaining 5% display an alternative chromosomal t(12;22) (q13;q12) rearrangement leading to an EWSR1-DDIT3 gene fusion (4). The resulting FUS-DDIT3 and EWSR1-DDIT3 fusion proteins have been shown to play an essential role in MLS tumorigenesis, acting as pathogenic transcriptional (dys-)regula- tors (5–8). Current therapeutic approaches in high-grade MLS complement radical surgery and adjuvant radiation and/or con- ventional chemotherapy based on anthracyclines and ifosfamide, recently supplemented by agents such as trabectedin or eribu- lin (9–11). Although MLS displays a higher chemosensitivity than other liposarcoma subtypes, the substantial frequency of recur- rence and metastasis in MLS underlines the urgent need for novel, biology-guided therapeutic strategies. In principle, counteracting the effects of the aberrant FUS–DDIT3 transcription factor repre- sents the most promising strategy to selectively target MLS tumor cells; however, the therapeutic interference with (chimeric) tran- scription factors in vivo represents a particular challenge. In line with the situation in other translocation-associated soft-tissue and bone sarcomas driven by specific gene fusions, 1 Gerhard-Domagk-Institute of Pathology, M€ unster University Hospital, M€ unster, Germany. 2 Division of Translational Pathology, Gerhard-Domagk-Institute of Pathology, M€ unster University Hospital, M€ unster, Germany. 3 Institute of Pathol- ogy and Molecular Pathology, Bundeswehrkrankenhaus Ulm, Ulm, Germany. 4 Department of Pediatric Hematology and Oncology, University Children's Hospital M€ unster, M€ unster, Germany. 5 Cells in Motion Cluster of Excellence (EXC 1003 – CiM), University of M€ unster, M€ unster, Germany. 6 Institute of Pharmacology of Natural Products & Clinical Pharmacology, Ulm University, Ulm, Germany. 7 Institute of Human Genetics, School of Medicine & University Hospital Bonn, University of Bonn, Bonn, Germany. 8 Sahlgrenska Cancer Center, University of Gothenburg, Gothenburg, Sweden. Note: Supplementary data for this article are available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/). M. Trautmann and M. Cyra contributed equally to this article. Corresponding Authors: Marcel Trautmann and Wolfgang Hartmann. Division of Translational Pathology, Gerhard-Domagk-Institute of Pathology, Münster Univer- sity Hospital, Domagkstr. 17, 48149, Germany. Phone: þ49 (0) 251-83-57623 and -58479, Fax: þ49 (0) 251-83-57559. E-mail: marcel.trautmann@ukmuenster.de and wolfgang.hartmann@ukmuenster.de doi: 10.1158/1535-7163.MCT-18-0763 Ó2019 American Association for Cancer Research. Molecular Cancer Therapeutics Mol Cancer Ther; 18(4) April 2019 834 Downloaded from http://aacrjournals.org/mct/article-pdf/18/4/834/1860624/834.pdf by guest on 11 June 2022