Abstract 394: Preclinical evaluation of ERX-208, a potent inducer of ER stress for the treatment of ovarian cancer

Abstract Background: Ovarian cancer (OCa) is the deadliest kind of gynecologic cancer in the United States. The long-term survival rate for OCa is less than 20% after five years. Intra-tumoral and inter-tumoral heterogeneity is implicated in tumor resistance to conventional therapies and the unsatisfactory clinical outcomes. Addressing these issues necessitates innovative therapies that target intrinsic common vulnerabilities within OCa. Recent studies have highlighted that high basal level of endoplasmic reticulum stress (ERS) in OCa as a critical vulnerability. We have identified a promising compound, ERX-208 that potently induces ERS in cancer cells. The objective of this study is to characterize the mechanisms and activity of ERX-208 using preclinical models. Methods: The biological activity of ERX-208 was examined across 17 distinct OCa cells, representing 5 diverse OCa subtypes. Mechanistic studies utilized Western blotting, immunohistochemistry (IHC), RNA-Seq analysis, and CRISPR/Cas9 knockouts (KO). Pharmacokinetics (PK) and toxicity studies were performed on C57BL/6 mice. Comprehensive preclinical assessments were carried out through cell line-derived xenografts (CDXs), patient-derived xenografts (PDXs), organoids (PDOs) and explants (PDEs). Results: ERX-208 demonstrated an IC50 of approximately 50-100 nM inducing ERS and reducing cell viability in OCa cells. Conversely, normal ovarian surface epithelial cells exhibited minimal effects from ERX-208. In vitro experiments revealed strong ERX-208-induced apoptosis in OCa cell lines. Mechanistic studies employing RNA sequencing, Western blotting, and RT-qPCR, confirmed activation of ERS pathways observed as early as 5 hours post-ERX-208 treatment. Our studies identified LIPA as a potential target, and KO of LIPA significantly diminished ERX-208 activity. Moreover, LIPA KO substantially impeded in vivo OCa tumor growth. ERX-208 up to a dose of 25 mg/kg showed no observable organ toxicity and had no effect on the mice's body weight. Dose range studies identified 10 mg/kg intraperitoneal as the minimal effective dose, achieving more than 50% tumor reduction. In preclinical models, ERX-208 inhibited the growth of OCa CDXs, PDXs, and ex vivo PDEs and PDO’s. IHC analyses indicated reduced proliferation (Ki-67) and increased activation of ERS markers, such as GRP78 and p-PERK. Conclusions: Collectively, our findings underscore the preclinical promise of ERX-208 as a potential therapeutic agent for treating OCa. Conflict: The patents surrounding ERX-208 are licensed to EtiraRx. Citation Format: Suryavathi Viswanadhapalli, Tae-Kyung Lee, Scott Elmore, Gaurav Sharma, Rahul Gopalam, Karla Parra, Tanner Reese, Michael Hsieh, Uday P. Pratap, Xue Yang, Behnam Ebrahimi, Henry Neal, Chia-Yuan Chen, Kara Kassees, Christian Cervantes, Zhenming Xu, Edward Kost, Gangadhara Reddy Sareddy, Rajeshwar R. Tekmal, Jung-Mo Ahn, Ganesh V. Raj, Ratna K. Vadlamudi. Preclinical evaluation of ERX-208, a potent inducer of ER stress for the treatment of ovarian cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 394.