TMIC-22. IDENTIFICATION OF CANCER-ASSOCIATED FIBROBLASTS IN GLIOBLASTOMA and Defining Their Protumoral Effects

Abstract

While cancer-associated fibroblasts (CAFs) and their pro-tumoral effects have been demonstrated in systemic cancers, CAFs had been presumed absent in glioblastoma given the lack of normal fibroblasts in the healthy brain. Here, we show that 5–26% (mean=12%) of cells in human glioblastomas express CAF markers α-SMA or PDGFR-β, morphologically resemble fibroblasts, and transcriptomically resemble by RNA-seq CAFs from other cancers. Glioblastoma CAFs were chemotactically attracted to glioblastoma-initiating stem cells (P=0.02). While glioblastoma CAFs did not affect differentiated glioblastoma cell proliferation (P=0.4), CAFs increased glioblastoma stem cell proliferation (P=0.002) and expression of glioblastoma stem cell-associated genes (P< 0.001). To identify mediators of CAF/glioblastoma stem cell interactions, we created a resource of inferred crosstalk by mapping the expression of receptors to that of their cognate ligands/agonists, using our RNA-seq results from glioblastoma CAFs and stem cells, revealing PDGF-β/PDGFR and osteopontin/CD44 to mediate stem cell recruitment of CAFs and CAF enrichment of stem cells, as confirmed by blocking antibodies (P=0.02–0.03). CAFs also render the glioblastoma microenvironment more pro-tumoral by promoting M2 polarization of tumor-associated macrophages (P=0.01), an effect we found to arise from unique CAF production of the EDA splice variant of fibronectin binding toll-like receptor 4 (TLR4), a known EDA receptor expressed by macrophages (P=0.02). In patient glioblastomas, CAFs were enriched 3-fold in the subventricular zone (SVZ) (P=0.04) which houses the neural stem cells that generate glioblastoma stem cells. SVZs from epilepsy cases or autopsies of glioblastoma-containing brains without ventricular involvement lacked CAFs. Depleting CAFs in xenografts derived from neurosphere-containing glioblastoma stem cells slowed their growth in vivo (P< 0.001). These findings are among the first to identify and profile glioblastoma CAFs. CAF recruitment by glioblastoma stem cells and creation of a pro-tumoral microenvironment in the perivascular niche housing glioblastoma stem cells, particularly in the SVZ, makes them an intriguing therapeutic target.

The Role of Cancer-Associated Fibroblasts in Tumor Progression

“…Cancers where CAFs have definitively been characterized span solid tumors and carcinomas across almost every physiologic system, including head and neck [ 8 , 10 , 11 ], breast [ 12 , 13 , 14 ], lung [ 15 , 16 , 17 , 18 ], skin [ 19 , 20 , 21 ], gastrointestinal (GI) and biliary tract [ 22 , 23 , 24 ], and genitourinary (GU) cancers [ 25 , 26 ]. To date, there has not been any indication that CAFs are implicated in lymphoid and hematopoietic cancers, and there is sparse, but growing evidence alluding to the presence of CAFs in central nervous system (CNS) cancers such as glioblastoma multiforme (GBM) [ 27 , 28 , 29 ].…”

Identification of potential targets of the curcumin analog CCA-1.1 for glioblastoma treatment : integrated computational analysis and in vitro study

“…CASP3 expression was positively correlated with DCs. Despite the low frequency of fibroblasts in the healthy brain, CAFs are found in GBM 124 , 125 . Here, we found that CAFs are positively related to AKT1, TP53, and CASP3 expression.…”

Challenging Hurdles of Current Targeting in Glioblastoma: A Focus on Immunotherapeutic Strategies

“…Intriguingly, cancer associated fibroblasts (CAF) have been identified in GBM patients while they were presumably absent of CNS tumors. Now, some reports describe the presence of CAF with immunosuppressive effects, such as promoting glioma initiating cells growth and TAM polarization towards M2 [ 93 , 94 ]. Moreover, identification of CAF in GBM samples, but not from unaffected brain tissues in autopsy studies, further support their existence in vivo, rather than being only a genomic finding artefact.…”