Abstract PO039: Combined histone deacetylase and proteasome inhibition in patient-derived endometrial cancer organoid models promotes massive cell death

Abstract Patient-derived organoids (PDOs) are a promising model for personalized cancer treatment. Accumulating evidence indicates that PDOs can predict clinical outcomes in patients. A handful studies in several cancer types have established that PDOs can recapitulate both histological and genomic features of the lesion from which they were derived. Additionally, PDOs can grow with high efficiency in a short time, enabling prediction of responsiveness to chemotherapy and development of more targeted therapies for patients. Our long-term goal is to create a PDO biorepository comprising all major histopathological subtypes of endometrial cancer, perform drug screening on these PDOs, and identify novel single agent and combinatorial regimens to advance into clinical trials. Herein we describe progress to date on generation of endometrial PDOs and drug screening to identify potential therapeutic options. First, we created PDO cultures from seven patients with different histological subtypes of endometrial cancer, including early stage/grade endometrioid adenocarcinoma and high-grade serous carcinoma. Next, we exposed each PDO to a panel of 23 chemotherapeutic agents and targeted drugs. Surprisingly, despite a divergent response to standard chemotherapy (platinum and taxane compounds), all PDOs showed high responsiveness to the combination of a histone deacetylase (HDAC) inhibitor and a proteasome inhibitor. Specifically, we achieved nearly complete cell killing within 72 hrs of exposure of organoid cultures to HDAC and proteasome inhibitors, with concentrations in the low nanomolar range. Similar results were achieved with different proteasome inhibitors (bortezomib and ixazomib) and HDAC inhibitors (romidepsin and belinostat). At present, these classes of agents have primarily been studied in multiple myeloma, though multiple clinical trials of combined proteasome and HDAC inhibitor therapy are active in advanced solid tumors and lymphomas. HDAC inhibitors maintain the acetylation of histones and thereby increase the expression of genes associated with apoptosis and cell cycle arrest. Proteasome inhibitors prevent proteasomal degradation, leading to upregulation of proapoptotic protein expression, cell cycle arrest, and ER stress, downregulation of angiogenesis and the pro-inflammatory protein NF-κB, and ROS generation. Mechanistically, HDAC inhibitors and proteasome inhibitors promote dual proteasome and aggresome blockage and induce apoptosis due to the accumulation of misfolded proteins. Our findings of profound tumor cell death in multiple different PDOs serve as the foundation for a future clinical trial using the HDAC inhibitor ixazomib and proteasome inhibitor romidepsin in advanced and recurrent endometrial cancers as well as high-grade serous ovarian cancer, which shares histologic and molecular features. Concomitantly, we are investigating the in vitro and in vivo effects of the combination on the induction of apoptosis and endometrial tumor regression. Citation Format: Jianling Bi, Kristina W. Thiel, Eric J. Devor, Andreea M. Newtson, Yuping Zhang, Kimberly K. Leslie. Combined histone deacetylase and proteasome inhibition in patient-derived endometrial cancer organoid models promotes massive cell death [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO039.