Abstract 229: Molecular-genomic characterization of metastatic gastric cancer organoids and establishment of organoid-immune cell co-culture model

Abstract Advanced gastric cancer (AGC) showed marked molecular heterogeneity with aggressive behavior and treatment resistance, especially AGC with ascites from peritoneal metastasis. Tumor organoids are valuable in vitro model for mimicking organ characteristics and are used for developing therapeutic strategies. Therefore, we aimed to understand the characteristics of organoids established from AGC patient-derived fluids. Also, we are in progress of setting up an organoid-immune cell co-culture model for drug screening of immune checkpoint inhibitors (ICI) for AGC. All established organoids from peritoneal and pleural fluid of AGC patients were authenticated through short tandem repeat (STR) profiling, comparing with their matched PBMCs. We compared the morphological characteristics using Operetta High Content Imaging (Perkin Elmer). Also, the in house targeted sequencing and RNA sequencing data were obtained from the genome database of the Song-Dang Institute for Cancer Research and it was verified using molecular methods. Then, we co-cultured organoids with healthy donor PBMCs that were pre-activated using anti-human CD3/CD28 Dynabeads (Gibco). 3D spheroids, rather than single cells, and the PBMCs were co-cultured in matrigel (Corning Inc.) for more than 3 days. The overall success rate of the organoid establishment was 53.8% (78/145), with different sources of peritoneal (54%, 61/113) and pleural fluids (53.1%, 17/32). The organoid success rate was various as in EBV positive (66.7%, 2/3) and dMMR (0%, 0/4). Based on the analysis of 91 patients eligible for histopathology, the success rate of HER2-negative (57.5%, 46/80) is higher than that of HER2-positive (36.4%, 4/11). The organoids were observed in a variety of morphologies categorized in 3 groups such as grape-like, compact and glandular structure. Based on genomic data of 31 organoids, we could subgrouping for TCGA subtypes and EMT subtype. RTKs were amplified in 10 organoids, including the amplification of ERBB2 (n=2), MET (n=4) and FGFR (n=4). And KRAS alterations including amplification (n=2) and G12A/D (n=2) mutation were also detected. Then, we established the condition for organoid-immune co-culture model with PBMCs with Dynabead activation for 3-10 days. We confirmed that higher dose of PBMCs killed the tumor cells with reduction of organoid size and partial disintegration. We established the proper PBMC dose and characterization to maintain the organoids co-culture for further drug (ICI) sensitivity testing. In conclusion, we evaluated phenotypic and molecular characteristics of gastric cancer organoids established from malignant peritoneal and pleural effusion. The established organoid-immune cell co-culture models can be utilized to evaluate a variety of drug screenings, including ICI and various combinations, helping in the selection of drugs for individual patient. Citation Format: Han Byeol Mun, juin Park, Jinsoo Jang, Jingmin Che, Tae Soo Kim, Woo Sun Kwon, Hyun Cheol Chung, Sun Young Rha. Molecular-genomic characterization of metastatic gastric cancer organoids and establishment of organoid-immune cell co-culture model [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(6_Suppl):Abstract nr 229.