Abstract 4863: PMCA inhibition induces cytotoxic calcium stress and suppression of Wnt signaling in refractory molecular subtype of gastric cancer
Authors: Ban Saeli , Kim Jungmin , Bae Jonghwan , Park Ki Cheong , Lee Suji , Kim Moon Hwan , Cheong Jae-Ho 
Published: April 2023

Abstract
Background: Gastric cancer (GC) is the fourth leading cause of cancer-related deaths worldwide, but its genetic heterogeneity retards the development of novel therapeutics. Recently, tumor molecular classification identified clinically refractory SEM (i.e., Stem-like, EMT and Mesenchymal) subtype GC which exhibited over-expression of the plasma membrane Ca2+ ATPase (PMCA) whose role is circumventing calcium overload causing ER stress and apoptosis. Here, we showed that PMCA4 is associated with Wnt signaling activity by regulating Secreted Frizzled-Related Protein 2 (SFRP2) expression and demonstrated that PMCA4 inhibition might achieve dual mechanism-specific anti-cancer effect by inducing calcium-mediated apoptosis and restraining oncogenic Wnt activity in SEM subtype GC.
Materials and Methods: GC cell lines and patient-derived organoids (PDOs) were categorized either SEM-subtype (SNU484, SNU668, SK4, MKN1; GA077T, GA265T, GA333T, GA352T) or non-SEM subtype (MKN45, NCIN87, SNU16, SNU601; GA200T, GA247T, GA215T) based on transcriptome signatures or subtype-specific biomarker genes. PMCA4 expression was confirmed using western blot and its calcium clearance function was examined using Fluo-4 AM fluorescent Ca2+ dye. Biological and molecular characteristics of GC cell lines and PDOs upon PMCA4 inhibition were investigated using RT-qPCR, western blot, and TOPflash/FOPflash reporter assay. The target engagement of novel PMCA inhibitor PM058 (bis-indole maleimide derivative) was evaluated by cellular thermal shift assay (CETSA), and the efficacy was determined by CCK8 cell viability assay for cell lines and by Cell Titer-Glo for PDOs.Results: PMCA4 was highly expressed in SEM subtype GC cell lines and PDOs. The siRNA-mediated PMCA4 knockdown (KD) or pharmaceutical inhibition of PMCA4 suppressed the calcium clearance, the cell viability, and decreased cell invasion/migration. TCF/LEF-responsive reporter assay revealed that pharmaceutical inhibition of PMCA4 suppressed Wnt/beta-catenin signaling activity, proven by decrease in beta-catenin and Wnt target gene expression. PMCA inhibition was mechanistically associated with the increased expression of SFRP2, a Wnt antagonist. Importantly, PM058, a PMCA inhibitor, treatment resulted in highly efficacious anti-cancer effect in PDOs at nano molar range, which correlated with PMCA4 protein expression.Discussion and Conclusion: Our results provide the proof of concept that PMCA4 can be a promising therapeutic target for refractory subtype cancer. The proposed mechanism of PMCA4 inhibition is calcium overload - induced apoptosis and interfering with Wnt signaling activity via SFRP2 in GC. Importantly, we demonstrated a novel potent inhibitor PM058 that blocks PMCA function in clinically intractable SEM subtype GC cancer.
Citation Format: Saeli Ban, Jungmin Kim, Jonghwan Bae, Ki Cheong Park, Suji Lee, Moon Hwan Kim, Jae-Ho Cheong. PMCA inhibition induces cytotoxic calcium stress and suppression of Wnt signaling in refractory molecular subtype of gastric 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 4863.