Abstract 160: FGFR1+ cancer associated fibroblasts (CAFs) produce an extracellular matrix (ECM) that curbs infiltration of phagocytic tumor-associated macrophages (TAMs)

Abstract About 40% of diffuse large B-cell lymphoma (DLBCL) pts do not respond to immunochemotherapy. In human and murine models, we and others have shown that the lymphoma microenvironment (LME) changes with disease progression and treatment resistance. This lymphoma cell-LME co-evolutionary process results in expansion of treatment-resistant lymphoma cells as well as reduced infiltration of T cells and reprogramming of CAFs and TAMs into immune suppressive entities. Our analysis of relapse or refractory (RR) -DLBCLs showed not only an immune depleted LME but also an enrichment of CAFs harboring activation of fibroblast growth factor receptor (FGFR1+). Since FGFR1 inhibitors (FGFR1i) are clinically available, we sought to determine its anti-neoplastic effect on DLBCL. We first confirmed that lymphoma cells, including murine and human, and primary and RR-DLBCLs, did not express FGFR1. Accordingly, no anti-tumoral effect was detected when the selective FGFR1i SSR128129E was administered in vitro to a lymphoma cell panel. However, oral administration of FGFR1i to pre-clinical lymphoma models including two RR-DLBCL patient-derived xenografts (PDX) and four syngeneic murine models representing distinct DLBCL genetic subtypes produced a significant anti-lymphoma effect in all cases. In addition to decreased lymphoma cells, we observed increase in the ECM and TAM infiltration, even in the murine models, suggesting that FGFR1i reprogrammed the CAFs. We thus conducted matrisome analysis (i. e. , ECM proteomics) in a murine model (p53 mutant) and found a significant up-regulation of proteoglycans and the immune active glycoproteins decorin, lumican and byglican (q-value 0. 05 vs. vehicle). To determine whether these ECM changes affect lymphoma cells, we performed 3D co-cultures of lymphoma cells embedded into de-celularized ECM obtained from FGFR1i vs. vehicle mice. We found that FGFR1i-ECM (vs. vehicle-ECM) modifies the secretome of lymphoma cells by upregulating several cytokines including IL6, IL16 and TNF-alpha. To further characterize the functional state of CAFs and TAMs, we conducted single cell RNA-seq in the two RR-DLBCL PDXs treated as before. We found that FGFR1-CAFs in the LME of FGFR1i tumors (vs. vehicle) were reprogrammed into inflammatory-like CAFs characterized by the expression of several monocyte/macrophage chemotactic factors including CCL2, CCL7, CXCL3, and CXCL12. Consequent with these findings we not only observed an increase infiltration of TAMs in the LME of FGFR1i tumors but also that they were reprogrammed in phagocytic phenotypes. In sum, our results suggest that CAF-FGFR1+ produce an immune “silent” ECM that characterizes RR-DLBCL while FGFR1i reverses this ECM phenotype ultimately resulting in the infiltration of antitumoral TAMs, delineating a novel ECM-directed therapeutic approach for this disease. Citation Format: Nicolás Di Siervi, Maria Victoria Revuelta, Nahuel Zamponi, Giorgio Inghirami, Leandro Cerchietti. FGFR1+ cancer associated fibroblasts (CAFs) produce an extracellular matrix (ECM) that curbs infiltration of phagocytic tumor-associated macrophages (TAMs) 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 (6Suppl): Abstract nr 160.