Abstract B033: Determining the tumor supportive and inhibitory capabilities of cancer associated fibroblast subpopulations in central nervous system metastasis. [R
Authors: Simon Thomas , Buckley David N. , Gooden Gerald C. , Tew Ben Y. , Zada Gabriel , Salhia Bodour 
Published: January 2023

Abstract
Central nervous metastases (CM), like all tumors, are surrounded by a complex tumor microenvironment (TME) comprised of a meshwork of extracellular matrix (ECM) proteins and an assemblage of cell types including endothelial cells, pericytes, immune cells, and cancer-associated fibroblasts (CAFs). We have previously shown that CAFs can either support or inhibit tumor growth, suggesting that CM CAFs comprise a heterogenous subgroup of cells. Recently we reported, based on literature in other cancer types, that CAFs can be categorized into four main subpopulations: ‘desmoplastic’, ‘immune’, ‘contractile’ and ‘aggressive’. Accordingly, the purpose of our study is to identify CAF subpopulations in the TME of CM and determine their impact on CM growth. In order to identify CM CAF subpopulations and their respective markers, we performed single cell RNA sequencing (scRNA-seq) on 7 CM patient tissues and 4 patient-derived CM CAF cell lines established in our lab. We then used fluorescence-activated cell sorting (FACS) to enrich different CAF subpopulations in CAF cell lines for further molecular and functional in vitro and in vivo characterization. ScRNA-seq data in 7 CM tissues revealed the presence of CAFs. Upon further analysis, we identified the desmoplastic, immune, contractile, and aggressive CAF subpopulations. In the CAF cell lines, we identified the desmoplastic and aggressive CAF subpopulations. We propose that desmoplastic CAFs are tumor inhibitory and aggressive CAFs are tumor supporting. The desmoplastic subpopulation is characterized by high expression of Immunoglobulin Superfamily Containing Leucine Rich Repeat (ISLR) and low expression of a classic tumor supportive CAF marker Actin Alpha 2, Smooth Muscle (ACTA2, a-SMA). ISLR has recently been reported to be overexpressed in CAFs with tumor inhibitory capabilities in other cancer types. The aggressive subpopulation shows low ISLR expression and high a-SMA expression. FACS on one of the patient-derived CM CAF cell lines using ISLR antibody enriched ISLRhigh CAFs, with remaining CAFs confirmed to be ISLRlow. Further western blotting analysis revealed lower expression of a-SMA in ISLRhigh cells as compared to ISLRlow cells. This reciprocal expression of ISLR and a-SMA could represent the molecular basis driving the phenotype of desmoplastic and aggressive CAF subpopulations. Further in vitro and in vivo experiments are currently underway in our lab to determine the necessity and sufficiency of ISLR and a-SMA in determining tumor supportive capabilities of both desmoplastic and aggressive CAFs. The present study improves our understanding of the CM TME, which ultimately will help establish new strategies to harness the cancer restraining capabilities of tumor inhibitory CAFs in clinic to improve outcomes for patients with CM.
Citation Format: Thomas Simon, David N. Buckley, Gerald C. Gooden, Ben Y. Tew, Gabriel Zada, Bodour Salhia. Determining the tumor supportive and inhibitory capabilities of cancer associated fibroblast subpopulations in central nervous system metastasis. [R [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B033.