Abstract 5842: Determining the tumor supportive and inhibitory capabilities of cancer associated fibroblast subpopulations in central nervous system metastasis
Authors: Simon Thomas , Buckley David N. , Gooden Gerald C. , Tew Ben Y. , Zada Gabriel , Salhia Bodour 
Published: April 2023

Abstract
Central nervous metastases (CM) are surrounded by a complex tumor microenvironment (TME) comprised of a meshwork of extracellular matrix (ECM) proteins and an assemblage of cell types including cancer-associated fibroblasts (CAFs). We have previously shown that patient-derived CM CAFs can either support or inhibit tumor growth in vivo, suggesting that CM CAFs comprise a heterogenous subgroup of cells. Accordingly, we recently reported, based on literature in other cancer types, that CAFs can be categorized into four main subpopulations: ‘desmoplastic’, ‘immune’, ‘contractile’ and ‘aggressive’. The purpose of our study is to identify different CAF subpopulations in the TME of CM and determine their impact on CM growth. To do this, we performed single cell RNA sequencing (scRNA-seq) on 10 CM patient tissues and 8 patient-derived CM CAF cell lines established in our lab. ScRNA-seq analysis of tumor tissues revealed that desmoplastic, immune, contractile, and aggressive CAF subpopulations are also present in the TME of CM. In addition, scRNA-seq showed that CM CAF cell lines were mainly comprised of the desmoplastic and aggressive CAF subpopulations. These two subpopulations showed differential expression of the newly described tumor inhibitory CAF marker Immunoglobulin Superfamily Containing Leucine Rich Repeat (ISLR) and classic tumor supportive CAF marker Actin Alpha 2, Smooth Muscle (ACTA2, α-SMA), with desmoplastic CAFs showing ISLRhigh/α-SMAlow expression while aggressive CAFs were associated with ISLRlow/α-SMAhigh expression. Next, we used fluorescence activated cell sorting (FACS) based on the expression of ISLR on the cell surface to enrich and expand the ISLRhigh/α-SMAlow desmoplastic CAF and the ISLRlow/α-SMAhigh aggressive CM CAF subpopulations. Reciprocal expression of α-SMA and ISLR was confirmed by western blot and immunofluorescence after FACS. Additionally, co-culture experiments showed that ISLRhigh/α-SMAlow CM CAFs inhibit CM cell proliferation. In summary, our data show that there are several molecularly defined subpopulations of CAFs in the TME of CM that can act to either inhibit or promote CM tumor growth in vitro and in vivo. Our results support that the desmoplastic CM CAFs characterized by ISLRhigh/α-SMAlow can inhibit tumor growth. Overall, 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 order 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. [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 5842.