<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "Developing targeted therapies for\r\npediatric PFA ependymoma"^^ . "PFA ependymomas are highly aggressive brain tumors typically arising in young children (median age 3 years) and characterized by a poor outcome (10-year OS < 60%). Standard of care therapy for PFA ependymoma consists of surgery and radiotherapy, while chemotherapy has been largely ineffective and proposed targeted therapies have not yet translated to the clinics. This is also routed in the fact that for a long time, no genetic driver mutations could be identified for PFA ependymoma. Recently, aberrant EZHIP overexpression has been identified as likely driver of PFA ependymoma. By inhibiting EZH2, the catalytic subunit of the polycomb repressive complex 2 (PRC2), EZHIP prevents the distribution of the epigenetic repressor mark H3K27me3, resulting in de-repression of PRC2 target genes and corresponding expression changes. However, without any known enzymatic function, EZHIP cannot serve as the drug target, which is so urgently needed. Therefore, in my thesis I focused on the identification, mechanistic characterization and validation of potential alternative treatments for PFA ependymoma.\r\nFirstly, published IP-MS data from non-PFA ependymoma cells was analyzed to identify druggable interaction partners of EZHIP. After the identification of the deubiquitinase USP7, the interaction of USP7 and EZHIP in the nucleus was confirmed in PFA ependymoma cells by co-IP and immunofluorescence, and was found to be independent of EZH2, a separate interaction partner of both proteins. Functionally, USP7 interacts with EZHIP via the USP7 TRAF-like domain, resulting in deubiquitination of EZHIP, which prevents it from being degraded. This stabilization of EZHIP is mediated by the six lysine residues of EZHIP. Previously described somatic EZHIP mutations in patients were not found to interfere with the EZHIP-USP7 interaction. Genetic and pharmacological interventions were used to illustrate the vulnerability of PFA ependymoma cells to a loss of USP7 in vitro. PFA ependymoma cells were sensitive to USP7 inhibitors, while normal healthy human astrocytes were not affected, thereby presenting a potential therapeutic window. However, in vivo validation treatments in the PFA ependymoma PDOX model BT232 using a maximally tolerated dosing of the USP7 inhibitors P22077 and P005091 did not result in tumor growth inhibition or improved survival of the animals. The reason for this is unclear but could be due to limited brain penetrance or too low exposure of the USP7 inhibitors. Therefore, mid-throughput drug library screening of PFA ependymoma cells was applied to identify drugs that improve their performance in combination with USP7 inhibitors. Based on the appearance of multiple BET inhibitors as top hits of the screen, the drug class of BET inhibitors was identified and their synergy with USP7 inhibitors in PFA ependymoma was validated in vitro. Treatments of subcutaneous PFA ependymoma PDX models with the BET inhibitor OTX015, alone and in combination with P005091, are ongoing.\r\nSecondly, epigenetic drug library screening was performed in the PFA ependymoma cell line EPD210FH and two ST-ZFTA ependymoma cell lines (EP1NS, BT165) to identify drugs that would target ependymoma. Overall, BET and HDAC inhibitors showed high potencies. The 10 drugs showing sensitivity in the PFA ependymoma cells included four BET inhibitors, and three drugs were selective for the PFA subtype of ependymoma: Curcumin, the histone methyltransferase inhibitor Chaetocin and the EZH2 inhibitor UNC199.\r\nAbstract\r\nII\r\nThirdly, three publication-informed targets were tested in in vitro drug treatments of different PFA ependymoma cell lines. EZH2 inhibitors were evaluated for their ability to further unbalance the PRC2 complex. While UNC199 affected EPD210FH viability at micromolar potency, DZNep significantly reduced PFA ependymoma viability at nanomolar levels in vitro. In contrast, although PPARγ was found to be specifically overexpressed in PFA ependymoma in a cohort of pediatric brain tumors and in PFA ependymoma cell lines, PPARγ agonists failed to reduce PFA ependymoma survival in vitro. Moreover, As EZHIP might play a role in DNA damage repair, EZHIP-expressing cells were tested for their acclaimed sensitivity to PARP inhibition. Of the four tested PARP inhibitors, Talazoparib affected PFA ependymoma cells at nanomolar potencies, but also affected human astrocytes or ST-ZFTA cells. Furthermore, USP7 and PARP inhibitors were tested in combination for potential synergism, but this did not appear to be the case for PFA ependymoma.\r\nTaken together, my work presents USP7 as a potential target for PFA ependymoma. I identified the stabilization of the oncogenic driver EZHIP through deubiquitination by USP7. Targeting USP7 genetically or pharmacologically reduced EZHIP levels and affected PFA ependymoma survival, rendering USP7 inhibitors a mechanistically sound option to further validate for PFA ependymoma therapy. Additionally, further experiments should be performed to explore EZH2 and PARP inhibitors as therapeutic options for PFA ependymoma."^^ . "2024" . . . . . . . "Anne Lena"^^ . "Jenseit"^^ . "Anne Lena Jenseit"^^ . . . . . . "Developing targeted therapies for\r\npediatric PFA ependymoma (PDF)"^^ . . . "Thesis_JenseitA.pdf"^^ . . . "Developing targeted therapies for\r\npediatric PFA ependymoma (Other)"^^ . . . . . . "indexcodes.txt"^^ . . . "Developing targeted therapies for\r\npediatric PFA ependymoma (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "Developing targeted therapies for\r\npediatric PFA ependymoma (Other)"^^ . . . . . . "preview.jpg"^^ . . . "Developing targeted therapies for\r\npediatric PFA ependymoma (Other)"^^ . . . . . . "medium.jpg"^^ . . . "Developing targeted therapies for\r\npediatric PFA ependymoma (Other)"^^ . . . . . . "small.jpg"^^ . . "HTML Summary of #35281 \n\nDeveloping targeted therapies for \npediatric PFA ependymoma\n\n" . "text/html" . . . "500 Naturwissenschaften und Mathematik"@de . "500 Natural sciences and mathematics"@en . .