OR05-06 Histone Deacetylase Inhibitor, Panobinostat, In Combination With A Smac-mimetic For The Treatment Of Ovarian Granulosa Cell Tumours
Authors: Chu Simon , Carolan Ashleigh , Giatrakis Chrissie , Nguyen Trang , Alexiadis Maria , Yu Tianzhi , Silke John , Fuller Peter J 
Published: October 2023

Abstract
Disclosure: S. Chu: None. A. Carolan: None. C. Giatrakis: None. T. Nguyen: None. M. Alexiadis: None. T. Yu: None. J. Silke: None. P.J. Fuller: None.
Background: Granulosa cell tumours (GCT) are uncommon ovarian cancers characterised by an indolent clinical course and significant late recurrence rates. Aside from invasive surgery, there are limited therapeutic options, highlighting the need for targeted therapies. Our laboratory has previously shown that targeting X-linked Inhibitor of Apoptosis Protein (XIAP) using small molecule inhibitors known as Smac-mimetics (SM) in combination with other compounds, is a compelling therapeutic strategy in GCT. XIAP inhibition sensitises cancer cells to anti-cancer therapies through the regulation of key pro-survival pathways, namely NFκB. Methods: High-throughput screening (HTS) using established drug libraries was performed in a GCT-derived cell line (KGN) and a transformed non-luteinized granulosa cell line (hGrC1), following pre-treatment with the SM, Compound A (CmpdA; 500nM). Drug combination hits were defined as a greater than&gt; 80% reduction in viability compared to CmpdA monotherapy alone. Subsequent validation studies were conducted to measure the effects on cell proliferation, apoptosis, and NFκB transactivation. The impact of the combination therapy was assessed by RNA-seq analysis to identify differentially expressed genes, significant pathways, and functional enrichment. Results: Here we report the use of a histone deacetylase inhibitor (HDACi), panobinostat, in combination with CmpdA, as a potential treatment for GCT. Using cell proliferation and viability assays, we demonstrated that 100nM panobinostat acts synergistically with 500nM CmpdA to significantly decrease cell proliferation and increase apoptosis, as demonstrated by increased caspase 3/7 activity. Apoptotic pathways were further assessed using flow cytometry. A potential mechanism of action for the compounds was tested using real-time PCR and luciferase reporter assays. In KGN cells, panobinostat demonstrated increased NFκB activity and TNFα expression, which decreased when combined with CmpdA, suggesting that there is enhanced activation of the extrinsic pathway of apoptosis. Transcriptomic analysis showed the top significantly enriched pathways related to mechanisms of cancer pathogenesis. In particular, we observed significant downregulation of SIRT1, a non-classical Class III HDAC that is potentially important in GCT tumorigenesis through its interactions with the FOXL2 transcription factor, affecting cancer pathways such as cell senescence, proliferation, and apoptosis. Conclusion: We present a promising combination therapeutic strategy for GCT that reduced cell proliferation, increased apoptosis, and reduced inflammatory gene expression. Further studies are now needed to confirm and translate these findings, and to identify the links between SIRT1, and the pathognomonic FOXL2C134W mutation of GCT.
Presentation: Thursday, June 15, 2023