267. IDENTIFYING CANCER-ASSOCIATED FIBROBLAST POPULATIONS DRIVING THERAPY RESISTANCE IN GASTROESOPHAGEAL ADENOCARCINOMAKulsum Tai, Michael Strasser, Sanjima Pal, Julie Bérubé, Wotan Zeng, Iris Kong, Adam Hoffman, James Tankel, Nicholas Bertos, Veena Sangwan, Sui Huang, Lorenzo Ferri
- General Medicine
Peri-operative docetaxel-based triplet chemotherapy is the standard-of-care treatment for advanced gastroesophageal adenocarcinoma (GEA). However, most patients recur due to innate or acquired resistance. Although distinct populations of cancer-associated fibroblasts (CAFs) within the tumor microenvironment play important roles in conferring chemoresistance in other cancer types, this paradigm has not been extensively studied in GEA. We aim to characterize CAF heterogeneity in a well-annotated cohort of GEA patients, identifying potential biomarkers and targets to overcome chemoresistance.
Immunofluorescence and flow cytometry assays were performed to validate previously reported CAF markers from the literature in primary patient fibroblasts. To identify specific CAF markers for GEA, an atlas was developed using single-cell RNA sequencing (scRNA-seq) data obtained from 46 GEA patient samples, including 28 patients with longitudinal samples over the docetaxel-based triplet chemotherapy treatment trajectory. Differential and gene ontology analyses were performed to characterize distinct CAF subpopulations and identify dynamic CAF markers across treatment timepoints, while correlating with in-patient treatment response to chemotherapy. In parallel, tumor organoid-CAF co-cultures were established for subsequent in vitro drug testing with standard-of-care chemotherapy.
CAF markers (VIM, FAP, PDPN, and S100A4) were found to be differentially expressed in fibroblasts isolated from good and poor pathological-response tumours. Analysis of scRNA-seq data reveals two main subpopulations of CAFs: myofibroblast CAFs (myCAFs) and inflammatory CAFs (iCAFs). Two markers, CCL20 and CHRDL1, were identified as differentially expressed between good and poor pathological responders in iCAFs, while nine markers, including ISG20 and C20orf27, were differentially expressed between clinical partial responders and poor responders. Dynamic CAF markers, including STAG2 and HAT1, were differentially expressed across treatment timepoints and were associated with pathological or clinical response.
GEA CAFs demonstrate extensive heterogeneity and comprise two major subpopulations. Several CAF markers were found to be associated with patient chemotherapy pathological or clinical response to chemotherapy, either in the chemonaïve setting or in the context of changes over the course of therapy. These putative biomarkers will be further validated and investigated, both in additional samples and in co-culture settings, to gain a better understanding of their clinical relevance and targeting potential.