Abstract 440: The role of PELP1 inhibitor SMIP34 in the treatment of endometrial cancer

Background: Endometrial cancer (ECa) is the fourth most prevalent type of cancer in women. Although ECa mostly affects older women, both the mortality and incidence rates are rapidly rising in women under the age of 40. Response rates and progression free survival are still low for recurrent ECa treatments such as hormone therapy, chemotherapy, and targeted therapies like Bevacizumab and Everolimus. There is an unmet need for the development of novel targeted therapeutics to support current ECa-directed treatments. The progression of many cancers, including ECa, is linked to proto-oncogenic PELP1 (proline-, glutamic acid-, and leucine-rich protein 1). In this investigation, we evaluated the efficacy of the PELP1 inhibitor, SMIP34, both alone and in combination with mTOR inhibitors in ECa. Methods: Using 13 distinct ECa cells, the effect of SMIP34 alone and in conjunction with mTOR inhibitors was assessed using the cell viability and colony formation assays. Using flow cytometry and Annexin-V/PI labeling, the ability of SMIP34 to promote apoptosis was evaluated. The effect of SMIP34 on cell cycle progression was evaluated using FACS analyses. RT-qPCR, Western blotting, and global RNA-seq were used for mechanistic studies. ECa patient-derived organoids (PDO), explants (PDEX) and xenograft model were used to assess the impact of SMIP34. TNM and Dependency Map (DepMap) databases were used to profile the status of PELP1 in ECa. The status of PELP1 in ECa tissues was analyzed using IHC analyses of ECa tumor tissue Microarrays. Results: Analysis of TNM plots showed that PELP1 expression was higher in ECa than in normal endometrium. Data from DepMap confirmed that PELP1 is required for the survival and expansion of ECa cells. SMIP34 treatment of established and primary patient-derived ECa cells significantly reduced cell viability and colony formation with an IC50 of 2-10µM. PELP1 knockdown significantly reduced the effect of SMIP34. Further, SMIP34 treatment induced apoptosis and promoted S-phase arrest in ECa cells. RNA-seq analyses showed that SMIP34 regulated genes positively correlated with p53 and apoptosis pathways, while negatively correlated with ribosome and eukaryotic translation elongation pathways. Western blot analyses confirmed that SMIP34 treatment reduced the levels of PELP1 and its complex of proteins including TEX10, LAS1L, SENP3. Mechanistic studies demonstrated that SMIP34 treatment attenuated the activation of mTOR signaling in ECa cells. Accordingly, SMIP34 enhanced the effect of mTOR inhibitors on ECa cells. SMIP34 is effective in reducing cell viability in PDO and limited the cells proliferation of PDEX. Importantly, SMIP34 treatment significantly reduced of the growth of ECa cell line-derived xenografts. Conclusions: Collectively, our results suggest that SMIP34 inhibits ECa growth in vitro, in vivo, and ex vivo and combination of SMIP34 with mTOR inhibitor represents a novel therapeutic strategy for ECa. Citation Format: Xue Yang, Zexuan Liu, Weiwei Tang, Uday P. Pratap, Alexia B. Collier, Kristin A. Alwegg, Nicole Spencer, Xiaonan Li, Philip T. Valente, Edward R. Kost, Suryavathi Viswanadhapalli, Ratna K. Vadlamudi. The role of PELP1 inhibitor SMIP34 in the treatment of endometrial cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 440.