Abstract A54: Targeting new links in the proteostasis network as novel therapies in high-grade serous ovarian cancer

Abstract

Abstract High-grade serous ovarian cancer (HGSOC) is the most lethal subtype of ovarian cancer with high case-to-fatality ratio. However, not much advancement has been seen in the field in terms of novel adjuvant therapies. Somatic or germline mutations in HGSOC along with copy number variations results in intratumoral genetic heterogeneity, which leads to tumor growth and development of chemoresistant clones and treatment resistance. Moreover, molecular heterogeneity also leads to the accumulation of aberrant peptides and protein complexes with altered stoichiometry, causing extensive proteotoxic stress in cancer cells and adding to the known misfolded proteins stress in cancer cells due to enhanced protein synthesis, thus making these cancer cells more dependent on the protein clearance mechanisms. Not much is known about the molecular targets from the proteostasis network and their therapeutic potential in HGSOC. Here we explore the regulation and role of different components of ubiquitin proteasome system (UPS) in HGSOC and investigate the therapeutic effect of small-molecule inhibitors of UPS. We identified overexpression of deubiquitinating enzyme, ubiquitin carboxyl-terminal hydrolase 1 (UCHL1) in HGSOC, and high UCHL1 levels were correlated with the disease stage, tumor grade, and poor clinical outcome. UCHL1 overexpression in HGSOC was driven by mutant p53-mediated H3K4 trimethylation at the UCHL1 regulatory region. Mutant p53-UCHL1 axis transcriptionally promoted the expression of proteasomal subunit alpha 7 (PSMA7) and acylaminoacyl-peptide hydrolase (APEH), resulting in increased proteasome activity in HGSOC. Silencing UCHL1 or inhibiting proteasome activity in vitro and in vivo remarkably reduced HGSOC growth. Together, these results highlight the novel mechanisms of regulation of proteostasis in HGSOC and potential therapies targeting regulators of proteasome pathway. Citation Format: Kinzie Lighty, Yonghyun Shin, Fahmi Mesmer, Harikrishna Nakshatri, Marcin Iwanicki, Sumegha Mitra. Targeting new links in the proteostasis network as novel therapies in high-grade serous ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A54.