930 Fibroblast activation protein alpha expression in tumor stroma and its association with immuno-regulatory circuits across epithelial tumors

BackgroundCarcinoma associated fibroblasts (CAFs) play important roles in modulating tumor development and prognosis through biochemical and biomechanical signals, but also through their immuno-modulatory characteristics. Fibroblast activation protein alpha (FAP), a serine protease with selectively high expression on CAFs, may be an ideal target for therapeutic intervention, including cancer immunotherapy. Therefore, a thorough understanding of FAP expression, but also immune cell composition and especially their interaction is key to optimally inform drug development and patient enrichment strategies.MethodsFormalin-fixed paraffin embedded tissue specimens comprising 253 primary tumors and 277 metastatic lesions were included in this study. Tumor sections were analyzed by digital immunohistochemistry (IHC) to assess tumor-stroma composition, FAP content and immune cell infiltration, complemented by transcriptomic analyses.ResultsAcross different types of epithelial tumors, FAP was detected by digital IHC in the tumor-associated stroma at a low to moderate proportion and with heterogeneous distribution patterns. Primary tumors in breast and lung cancer demonstrated a higher median FAP content (6.5% and 6.6% area coverage, respectively) compared to renal cell carcinoma (0.2% area coverage), which was confirmed on mRNA expression level. Median FAP levels were similar between primary and metastatic lesions in most tumor types except for renal cancer, for which FAP levels were significantly increased in metastasis lesions (3.3% area coverage). FAP content positively correlated with the density of FoxP3 positive regulatory T cells, but indication and tissue type specific differences were observed. Transcriptomic analysis revealed that both stroma-richness as well as higher FAP content were positively correlated with macrophage and dendritic cell gene signatures. However, while a higher stromal content was associated with signatures related to endothelial cells and preadipocytes, higher FAP content showed a stronger correlation with regulatory T cells. These findings are suggestive of a distinct biological role of FAP positive stroma in human tumors.ConclusionsFAP-targeted therapy is a promising strategy to optimize accumulation and action of anti-cancer drugs in the tumor microenvironment, potentially leading to more specific and effective therapies. Our study further elucidates the role of FAP by providing a comprehensive and granular landscape of FAP content in primary and metastatic tumor lesions derived from the same patient population and its association with immune cell composition. Future studies aim to elucidate the complex and dynamic interplay between malignant, stromal and immune cell populations in both temporal and spatial contexts and how that contributes to outcome in cancer immunotherapy.

Role of Fibroblast Activation Protein Alpha in Fibroblast-like Synoviocytes of Rheumatoid Arthritis

Fibroblast-like synoviocytes (FLSs) have been introduced in recent years as a key player in the pathogenesis of rheumatoid arthritis (RA), but the exact mechanisms of their transformation and intracellular pathways have not yet been determined. This study aimed to investigate the role of fibroblast activation protein-alpha (FAP-α) in the regulation of genes involved in the transformation and pathogenic activity of RA FLSs. Synovial FLSs were isolated from RA patients and non-arthritic individuals (n=10 in both groups) and characterized; using immunocytochemistry and flow cytometry analysis. FLSs were divided into un-treated and Talabostat-treated groups to evaluate the FAP-α effect on the selected genes involved in cell cycle regulation (p21, p53, CCND1), apoptosis (Bcl-2, PUMA), and inflammatory and destructive behavior of FLSs (IL-6, TGF-β1, MMP-2, MMP-9, P2RX7). Gene expression analysis was performed by quantitative real-time polymerase chain reaction (qRTPCR), and immunoblotting was carried out to evaluate FAP-α protein levels. The basal level of FAP-α protein in RA patients was significantly higher than non-arthritic control individuals. However, no differences were observed between RA and non-arthritic FLSs, at the baseline mRNA levels of all the genes. Talabostat treatment significantly reduced FAPα protein levels in both RA and non-arthritic FLSs, however, had no effect on mRNA expressions except an upregulated TGF-β1 expression in non-arthritic FLSs. A significantly higher protein level of FAP-α in FLSs of RA patients compared with that of healthy individuals may point to the pathogenic role of this protein in RA FLSs. However, more investigations are necessary to address the mechanisms mediating the FAP-α pathogenic role in RA FLSs.

Colorectal cancer cell intrinsic fibroblast activation protein alpha binds to Enolase1 and activates NF-κB pathway to promote metastasis

Fibroblast activation protein alpha (FAP) is a marker of cancer-associated fibroblast, which is also expressed in cancer epithelial cells. However, the role of FAP in colorectal cancer (CRC) cells remains to be elucidated. Here we investigate the expression pattern of FAP in CRC tissues and cells to prove that FAP is upregulated in CRC cells. Loss- of and gain-of-function assays identified FAP promotes migration and invasion instead of an effect on cell proliferation. Microarray assays are adopted to identify the different expressed genes after FAP knockdown and gene set enrichment analysis (GSEA) is used to exploit the involved signaling pathway. Our works reveal FAP exerts a function dependent on NF-κB signaling pathway and FAP expression is associated with NF-κB signaling pathway in clinical samples. Our work shows FAP is secreted by CRC cells and soluble FAP could promote metastasis. To investigate the mechanism of FAP influencing the NF-κB signaling pathway, LC/MS is performed to identify the proteins interacting with FAP. We find that FAP binds to ENO1 and activates NF-κB signaling pathway dependent on ENO1. Blocking ENO1 could partially reverse the pro-metastatic effect mediated by FAP. We also provide evidences that both FAP and ENO1 are associated with CRC stages, and high levels of FAP and ENO1 predict a poor survival in CRC patients. In summary, our work could provide a novel mechanism of FAP in CRC cells and a potential strategy for treatment of metastatic CRC.

Genetic ablation of fibroblast activation protein alpha attenuates left ventricular dilation after myocardial infarction

Introduction Regulating excessive activation of fibroblasts may be a promising target to optimize extracellular matrix deposition and myocardial stiffness. Fibroblast activation protein alpha (FAP) is upregulated in activated fibroblasts after myocardial infarction (MI), and alters fibroblast migration in vitro. We hypothesized that FAP depletion may have a protective effect on left ventricular (LV) remodeling after MI. Materials and methods We used the model of chronic MI in homozygous FAP deficient mice (FAP-KO, n = 51) and wild type mice (WT, n = 55) to analyze wound healing by monocyte and myofibroblast infiltration. Heart function and remodeling was studied by echocardiography, morphometric analyses including capillary density and myocyte size, collagen content and in vivo cell-proliferation. In non-operated healthy mice up to 6 months of age, morphometric analyses and collagen content was assessed (WT n = 10, FAP-KO n = 19). Results Healthy FAP-deficient mice did not show changes in LV structure or differences in collagen content or cardiac morphology. Infarct size, survival and cardiac function were not different between FAP-KO and wildtype mice. FAP-KO animals showed less LV-dilation and a thicker scar, accompanied by a trend towards lower collagen content. Wound healing, assessed by infiltration with inflammatory cells and myofibroblasts were not different between groups. Conclusion We show that genetic ablation of FAP does not impair cardiac wound healing, and attenuates LV dilation after MI in mice. FAP seems dispensable for normal cardiac function and homeostasis.

Imaging of Fibroblast Activation Protein Alpha Expression in a Preclinical Mouse Model of Glioma Using Positron Emission Tomography

Glioblastoma multiforme (GBM) is the most aggressive glioma of the primary central nervous system. Due to the lack of effective treatment options, the prognosis for patients remains bleak. Fibroblast activation protein alpha (FAP), a 170 kDa type II transmembrane serine protease was observed to be expressed on glioma cells and within the glioma tumor microenvironment. To understand the utility of targeting FAP in this tumor type, the immuno-PET radiopharmaceutical [89Zr]Zr-Df-Bz-F19 mAb was prepared and Lindmo analysis was used for its in vitro evaluation using the U87MG cell line, which expresses FAP endogenously. Lindmo analysis revealed an association constant (Ka) of 10−8 M−1 and an immunoreactivity of 52%. Biodistribution studies in U87MG tumor-bearing mice revealed increasing radiotracer retention in tumors over time, leading to average tumor-to-muscle ratios of 3.1, 7.3, 7.2, and 8.3 at 2, 24, 48 and 72 h, respectively. Small animal PET corroborated the biodistribution studies; tumor-to-muscle ratios at 2, 24, 48, and 72 h were 2.0, 5.0, 6.1 and 7.8, respectively. Autoradiography demonstrated accumulated activity throughout the interior of FAP+ tumors, while sequential tumor sections stained positively for FAP expression. Conversely, FAP− tissues retained minimal radioactivity and were negative for FAP expression by immunohistochemistry. These results demonstrate FAP as a promising biomarker that may be exploited to diagnose and potentially treat GBM and other neuroepithelial cancers.