Oncogenesis, Microenvironment Modulation and Clinical Potentiality of FAP in Glioblastoma: Lessons Learned from Other Solid Tumors

The axis of tumor-associated macrophages, extracellular matrix proteins, and cancer-associated fibroblasts in oncogenesis

The extracellular matrix (ECM) is a complex, dynamic network of multiple macromolecules that serve as a crucial structural and physical scaffold for neighboring cells. In the tumor microenvironment (TME), ECM proteins play a significant role in mediating cellular communication between cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). Revealing the ECM modification of the TME necessitates the intricate signaling cascades that transpire among diverse cell populations and ECM proteins. The advent of single-cell sequencing has enabled the identification and refinement of specific cellular subpopulations, which has substantially enhanced our comprehension of the intricate milieu and given us a high-resolution perspective on the diversity of ECM proteins. However, it is essential to integrate single-cell data and establish a coherent framework. In this regard, we present a comprehensive review of the relationships among ECM, TAMs, and CAFs. This encompasses insights into the ECM proteins released by TAMs and CAFs, signaling integration in the TAM-ECM-CAF axis, and the potential applications and limitations of targeted therapies for CAFs. This review serves as a reliable resource for focused therapeutic strategies while highlighting the crucial role of ECM proteins as intermediates in the TME.

[68Ga]Ga-FAPI PET/CT in brain tumors: comparison with [18F]F-FDG PET/CT

Purpose

To investigate the feasibility of [68Ga]Ga-FAPI PET/CT in brain tumor imaging and to compare it with [18F]F-FDG PET/CT.

Methods

25 patients with MRI-suspected brain tumors were included in the study. They underwent whole body [18F]F-FDG PET/CT and [68Ga]Ga-FAPI PET/CT and brain scans. The target-to-background ratio (TBR) of brain tumors was calculated with the background of surrounding normal brain tissues uptake. The SUVmax and TBR of [18F]F-FDG PET/CT and [68Ga]Ga-FAPI PET/CT were compared. Additionally, the correlation between the uptake of the tracer by lesions with the greatest diameter of the lesion, the breadth of the oedema band, and the enhancement scores of the MRI enhancement scans was analyzed.

Result

[68Ga]Ga-FAPI PET/CT was superior to [18F]F-FDG PET/CT for lesion detection, especially for brain metastases. Among gliomas, only high-grade gliomas uptake [68Ga]Ga-FAPI. Compared with [18F]F-FDG PET/CT, [68Ga]Ga-FAPI PET/CT had a lower SUVmax but a significantly better TBR. On [68Ga]Ga-FAPI PET/CT, the TBR may be associated with brain tumor blood-brain barrier disruption.

Conclusions

[68Ga]Ga-FAPI PET/CT is a promising imaging tool for the assessment of brain tumors. Lack of physiological uptake of [68Ga]Ga-FAPI in normal brain parenchyma results in high TBR values, leading to better visualization of lesions and contributing to subsequent targeted therapy studies.

Advances in knowledge

Clinical utility of [68Ga]Ga-FAPI PET/CT in brain tumors remains unclear, and there aren't many similar studies in the literature. We evaluated the role of [68Ga]Ga-FAPI PET/CT in diagnosing brain tumors.

Role of FGF21 in mediating the effect of phosphatidylcholine on GBM

Objective

The causal relationship and mechanisms between lipids and glioblastoma (GBM) remain unclear. This study aims to investigate the independent causal relationship between liposomal phosphatidylcholine 16:0_22:6 (PC16) and GBM, and to identify the potential mediating role of the inflammatory factor-fibroblast growth factor 21(FGF21).

Methods

Utilizing summary statistics from genome-wide association studies (GWAS) of lipids (179 types in 7174 Finnish individuals), GBM (243 cases and 287137 controls), and inflammatory factors (91 types in 14824 European individuals), a two-sample Mendelian Randomization (MR) approach was employed to establish the causal link between liposomal PC16 and GBM. Additionally, a two-step MR method was used to quantify the proportion of the causal effect of PC16 on GBM that is mediated by the inflammatory factor FGF21.

Results

MR analyses revealed a strong causal relationship between PC16 and GBM (OR=1.72, 95% CI: 1.11-2.68, P=0.016), but no reverse causality was observed from GBM to PC16 (OR=1.01, 95% CI: 0.99-1.02, P=0.38). Mediation analysis showed a strong causal relationship between PC16 and the FGF21 (OR = 0.94, 95% CI: 0.89-0.99, P=0.018) as well as between FGF21 and GBM (OR = 0.42, 95% CI: 0.25-0.71, P=0.001), with the mediation effect accounting for 9.78% of the total effect. This suggests that the causal relationship between PC16 and GBM is likely mediated by the intermediary factor FGF21. No evidence of pleiotropy was found in the sensitivity analysis of these positive results.

Conclusion

In summary, the findings of this study suggest that liposomal PC16 may increase the risk of GBM occurrence, and FGF21 may play a significant mediating role in this causal relationship.

The Role of Fibroblast Activation Protein in Glioblastoma and Gliosarcoma: A Comparison of Tissue, 68Ga-FAPI-46 PET Data, and Survival Data

Despite their unique histologic features, gliosarcomas belong to the group of glioblastomas and are treated according to the same standards. Fibroblast activation protein (FAP) is a component of a tumor-specific subpopulation of fibroblasts that plays a critical role in tumor growth and invasion. Some case studies suggest an elevated expression of FAP in glioblastoma and a particularly strong expression in gliosarcoma attributed to traits of predominant mesenchymal differentiation. However, the prognostic impact of FAP and its diagnostic and therapeutic potential remain unclear. Here, we investigate the clinical relevance of FAP expression in gliosarcoma and glioblastoma and how it correlates with 68Ga-FAP inhibitor (FAPI)-46 PET uptake. Methods: Patients diagnosed with gliosarcoma or glioblastoma without sarcomatous differentiation with an overall survival of less than 2.5 y were enrolled. Histologic examination included immunohistochemistry and semiquantitative scoring of FAP (0-3, with higher values indicating stronger expression). Additionally, 68Ga-FAPI-46 PET scans were performed in a subset of glioblastomas without sarcomatous differentiation patients. The clinical SUVs were correlated with FAP expression levels in surgically derived tumor tissue and relevant prognostic factors. Results: Of the 61 patients who were enrolled, 13 of them had gliosarcoma. Immunohistochemistry revealed significantly more FAP in gliosarcomas than in glioblastomas without sarcomatous differentiation of tumor tissue (P < 0.0001). In the latter, FAP expression was confined to the perivascular space, whereas neoplastic cells additionally expressed FAP in gliosarcoma. A significant correlation of immunohistochemical FAP with SUVmean and SUVpeak of 68Ga-FAPI-46 PET indicates that clinical tracer uptake represents FAP expression of the tumor. Although gliosarcomas express higher levels of FAP than do glioblastomas without sarcomatous differentiation, overall survival does not significantly differ between the groups. Conclusion: The analysis reveals a significant correlation between SUVmean and SUVpeak in 68Ga-FAPI-46 PET and immunohistochemical FAP expression. This study indicates that FAP expression is much more abundant in the gliosarcoma subgroup of glioblastomas. This could open not only a diagnostic but also a therapeutic gap, since FAP could be explored as a theranostic target to enhance survival in a distinct subgroup of high-risk brain tumor patients with poor survival prognosis.

The tumor-associated fibrotic reactions in microenvironment aggravate glioma chemoresistance

Malignant gliomas are one of the most common and lethal brain tumors with poor prognosis. Most patients with glioblastoma (GBM) die within 2 years of diagnosis, even after receiving standard treatments including surgery combined with concomitant radiotherapy and chemotherapy. Temozolomide (TMZ) is the first-line chemotherapeutic agent for gliomas, but the frequent acquisition of chemoresistance generally leads to its treatment failure. Thus, it's urgent to investigate the strategies for overcoming glioma chemoresistance. Currently, many studies have elucidated that cancer chemoresistance is not only associated with the high expression of drug-resistance genes in glioma cells but also can be induced by the alterations of the tumor microenvironment (TME). Numerous studies have explored the use of antifibrosis drugs to sensitize chemotherapy in solid tumors, and surprisingly, these preclinical and clinical attempts have exhibited promising efficacy in treating certain types of cancer. However, it remains unclear how tumor-associated fibrotic alterations in the glioma microenvironment (GME) mediate chemoresistance. Furthermore, the possible mechanisms behind this phenomenon are yet to be determined. In this review, we have summarized the molecular mechanisms by which tumor-associated fibrotic reactions drive glioma transformation from a chemosensitive to a chemoresistant state. Additionally, we have outlined antitumor drugs with antifibrosis functions, suggesting that antifibrosis strategies may be effective in overcoming glioma chemoresistance through TME normalization.

Tracking tumor alteration in glioma through serum fibroblast activation protein combined with image

PURPOSE

Detecting tumor progression of glioma continues to pose a formidable challenge. The role of fibroblast activation protein (FAP) in gliomas has been demonstrated to facilitate tumor progression. Glioma-circulating biomarkers have not yet been used in clinical practice. This study seeks to evaluate the feasibility of glioma detection through the utilization of a serum FAP marker.

METHODS

We adopted enzyme-linked immunosorbent assay (ELISA) technique to quantify the relative FAP level of serum autoantibodies in a cohort of 87 gliomas. The correlation between preoperative serum autoantibody relative FAP levels and postoperative pathology, including molecular pathology was investigated. A series of FAP tests were conducted on 33 cases of malignant gliomas in order to ascertain their efficacy in monitoring the progression of the disease in relation to imaging observations. To validate the presence of FAP expression in tumors, immunohistochemistry was conducted on four gliomas employing a FAP-specific antibody. Additionally, the investigation encompassed the correlation between postoperative tumor burden, as assessed through volumetric analysis, and the relative FAP level of serum autoantibodies.

RESULTS

A considerable proportion of gliomas exhibited a significantly increased level of serum autoantibody relative FAP level. This elevation was closely associated with both histopathology and molecular pathology, and demonstrated longitudinal fluctuations and variations corresponding to the progression of the disease The correlation between the rise in serum autoantibody relative FAP level and tumor progression and/or exacerbation of symptoms was observed.

CONCLUSIONS

The measurement of serum autoantibody relative FAP level can be used to detect the disease as a valuable biomarker. The combined utilization of its detection alongside MR imaging has the potential to facilitate a more accurate and prompt diagnosis.

Identifying the oncogenic roles of FAP in human cancers based on systematic analysis

BACKGROUND

Fibroblast activation protein-α (FAP) is a specific marker of cancer-associated fibroblasts (CAFs) and plays a crucial role in tumor development. However, the biological processes underlying FAP expression in tumor progression and tumor immunity have not been fully elucidated.

METHODS

We utilized RNA-seq data from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) to perform differential analysis of FAP expression in tumor tissues and matched-normal tissues. The relationship between FAP expression and clinical prognosis, DNA methylation, and tumor-infiltrating immune cells in pan-cancer was assessed using R Studio (version 4.2.1). Additionally, we employed gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA) to investigate the biological functions and pathways associated with FAP expression.

RESULTS

FAP exhibits high expression in most malignancies, albeit to a lesser extent in CESC, KICH, UCEC, SKCM, THCA, and UCS. Furthermore, FAP is either positively or negatively associated with the prognosis of several malignancies. In seven types of cancer, FAP expression is positively correlated with DNA methylation. CIBERSORT analysis revealed an inverse correlation between FAP expression and T cells, B cells, monocytes, and NK cells, while it exhibited a positive correlation with M0, M1, and M2 macrophages. Enrichment analysis further demonstrated that FAP modulates the cell cycle, epithelial-mesenchymal transition (EMT) process, angiogenesis, and immune-related functions and pathways.

CONCLUSION

Our findings indicate a close relationship between FAP expression and tumorigenesis as well as tumor immunity. FAP has the potential to serve as a diagnostic, prognostic, and immunotherapy marker.

The Prognostic and therapeutic value and clinical implications of fibroblast activation protein-α as a novel biomarker in colorectal cancer

The identification of contributing factors leading to the development of Colorectal Cancer (CRC), as the third fatal malignancy, is crucial. Today, the tumor microenvironment has been shown to play a key role in CRC progression. Fibroblast-Activation Protein-α (FAP) is a type II transmembrane cell surface proteinase expressed on the surface of cancer-associated fibroblasts in tumor stroma. As an enzyme, FAP has di- and endoprolylpeptidase, endoprotease, and gelatinase/collagenase activities in the Tumor Microenvironment (TME). According to recent reports, FAP overexpression in CRC contributes to adverse clinical outcomes such as increased lymph node metastasis, tumor recurrence, and angiogenesis, as well as decreased overall survival. In this review, studies about the expression level of FAP and its associations with CRC patients' prognosis are reviewed. High expression levels of FAP and its association with clinicopathological factors have made as a potential target. In many studies, FAP has been evaluated as a therapeutic target and diagnostic factor into which the current review tries to provide a comprehensive insight. Video Abstract.

A Simple 3D Cell Culture Method for Studying the Interactions between Human Mesenchymal Stromal/Stem Cells and Patients Derived Glioblastoma

We have developed a 3D biosphere model using patient-derived cells (PDCs) from glioblastoma (GBM), the major form of primary brain tumors in adult, plus cancer-activated fibroblasts (CAFs), obtained by culturing mesenchymal stem cells with GBM conditioned media. The effect of MSC/CAFs on the proliferation, cell-cell interactions, and response to treatment of PDCs was evaluated. Proliferation in the presence of CAFs was statistically lower but the spheroids formed within the 3D-biosphere were larger. A treatment for 5 days with Temozolomide (TMZ) and irradiation, the standard therapy for GBM, had a marked effect on cell number in monocultures compared to co-cultures and influenced cancer stem cells composition, similar to that observed in GBM patients. Mathematical analyses of spheroids growth and morphology confirm the similarity with GBM patients. We, thus, provide a simple and reproducible method to obtain 3D cultures from patient-derived biopsies and co-cultures with MSC with a near 100% success. This method provides the basis for relevant in vitro functional models for a better comprehension of the role of tumor microenvironment and, for precision and/or personalized medicine, potentially to predict the response to treatments for each GBM patient.

Fibroblast Activation Protein Activates Macrophages and Promotes Parenchymal Liver Inflammation and Fibrosis

BACKGROUND & AIMS

Fibroblast activation protein (FAP) is expressed on activated fibroblast. Its role in fibrosis and desmoplasia is controversial, and data on pharmacological FAP inhibition are lacking. We aimed to better define the role of FAP in liver fibrosis in vivo and in vitro.

METHODS

FAP expression was analyzed in mice and patients with fibrotic liver diseases of various etiologies. Fibrotic mice received a specific FAP inhibitor (FAPi) at 2 doses orally for 2 weeks during parenchymal fibrosis progression (6 weeks of carbon tetrachloride) and regression (2 weeks off carbon tetrachloride), and with biliary fibrosis (Mdr2-/-). Recombinant FAP was added to (co-)cultures of hepatic stellate cells (HSC), fibroblasts, and macrophages. Fibrosis- and inflammation-related parameters were determined biochemically, by quantitative immunohistochemistry, polymerase chain reaction, and transcriptomics.

RESULTS

FAP+ fibroblasts/HSCs were α-smooth muscle actin (α-SMA)-negative and located at interfaces of fibrotic septa next to macrophages in murine and human livers. In parenchymal fibrosis, FAPi reduced collagen area, liver collagen content, α-SMA+ myofibroblasts, M2-type macrophages, serum alanine transaminase and aspartate aminotransferase, key fibrogenesis-related transcripts, and increased hepatocyte proliferation 10-fold. During regression, FAP was suppressed, and FAPi was ineffective. FAPi less potently inhibited biliary fibrosis. In vitro, FAP small interfering RNA reduced HSC α-SMA expression and collagen production, and FAPi suppressed their activation and proliferation. Compared with untreated macrophages, FAPi regulated macrophage profibrogenic activation and transcriptome, and their conditioned medium attenuated HSC activation, which was increased with addition of recombinant FAP.

CONCLUSIONS

Pharmacological FAP inhibition attenuates inflammation-predominant liver fibrosis. FAP is expressed on subsets of activated fibroblasts/HSC and promotes both macrophage and HSC profibrogenic activity in liver fibrosis.

86Y-Labeled Albumin-Binding Fibroblast Activation Protein Inhibitor for Late-Time-Point Cancer Diagnosis

Fibroblast activation protein inhibitor (FAPI) is a novel quinoline-based radiopharmaceutical that has theranostic potential, yet the limited tumor retention hinders late-time diagnosis and radionuclide treatment. This study synthesized four albumin-binding FAPIs (TE-FAPI-01 to 04) and evaluated their in vitro stability, binding affinity, in vivo biodistribution, and tumor uptake with ⁶⁸Ga, ⁸⁶Y, and ¹⁷⁷Lu labeling, aiming to select the best molecule that has favorable pharmacokinetics to extend the blood circulation and tumor uptake in FAP-expressing tumors. All TE-FAPIs were stable in saline and plasma and displayed high FAP-binding affinity, with IC₅₀ values ranging from 3.96 to 34.9 nmol/L. The capabilities of TE-FAPIs to be retained in circulation were higher than that of FAPI-04, and TE-FAPI-04 displayed minimum physiological uptake in major organs compared with other molecules. TE-FAPI-03 and TE-FAPI-04 exhibited persistent tumor accumulation, with tumor radioactivity 24 h after administration of 2.84 ± 1.19%ID/g and 3.86 ± 1.15%ID/g for ¹⁷⁷Lu-TE-FAPI-03 and ¹⁷⁷Lu-TE-FAPI-04, respectively, both of which outperformed ¹⁷⁷Lu-FAPI-04 (0.34 ± 0.07%ID/g). TE-FAPI-04 was recognized as the albumin-binding FAPI with the most favorable pharmacokinetics and imaging performance. The enhanced circulation half-life and tumor uptake of TE-FAPI-04 aided the theranostics of malignant tumors and warrant further clinical investigations.

Glioblastoma Multiforme Selective Nanomedicines for Improved Anti-Cancer Treatments

Glioblastoma Multiforme (GBM) is a devastating disease with a low survival rate and few efficacious treatment options. The fast growth, late diagnostics, and off-target toxicity of currently used drugs represent major barriers that need to be overcome to provide a viable cure. Nanomedicines (NMeds) offer a way to overcome these pitfalls by protecting and loading drugs, increasing blood half-life, and being targetable with specific ligands on their surface. In this study, the FDA-approved polymer poly (lactic-co-glycolic) acid was used to optimise NMeds that were surface modified with a series of potential GBM-specific ligands. The NMeds were fully characterised for their physical and chemical properties, and then in vitro testing was performed to evaluate cell uptake and GBM cell specificity. While all targeted NMeds showed improved uptake, only those decorated with the-cell surface vimentin antibody M08 showed specificity for GBM over healthy cells. Finally, the most promising targeted NMed candidate was loaded with the well-known chemotherapeutic, paclitaxel, to confirm targeting and therapeutic effects in C6 GBM cells. These results demonstrate the importance of using well-optimised NMeds targeted with novel ligands to advance delivery and pharmaceutical effects against diseased cells while minimising the risk for nearby healthy cells.

In vitro and in vivo evaluation of 211At-labeled fibroblast activation protein inhibitor for glioma treatment

Glioma is the most common primary intracranial tumor without effective treatment. Positron emission tomography tracers labeled with 68Ga targeting fibroblast activation protein (FAP) have shown favorable characteristics in the diagnosis of glioma. However, to the best of our knowledge, FAP-targeted endoradiotherapy has never been explored in glioma. Hence, in this study, we investigated the therapeutic effect of 211At-labeled fibroblast activation protein inhibitor (FAPI) for glioma in vitro and in vivo. By astatodestannylation reaction, we prepared 211At-FAPI-04 with a radiochemical yield of 45 ± 6.7% and radiochemical purity of 98%. With good stability in vitro, 211At-FAPI-04 showed fast and specific binding to FAP-positive U87MG cells, and could significantly reduce the cell viability, arrested cell cycle at G2/M phase and suppressed cell proliferative efficacy. Biodistribution studies revealed that 6-fold higher accumulation in tumor sites was achieved by intratumoral injection in comparison with intravenous injection. In U87MG xenografts, 211At-FAPI-04 obviously suppressed the tumor growth and prolonged the median survival in a dose-dependent manner without obvious toxicity to normal organs. In addition, reduced proliferation and increased apoptosis were also observed after 211At-FAPI-04 treatment. All these results suggest that targeted alpha-particle therapy (TAT) mediated by 211At-FAPI-04 can provide an effective and promising strategy for the treatment of glioma.

The effect of iodine-131 beta-particles in combination with A-966492 and Topotecan on radio-sensitization of glioblastoma: An in-vitro study

Glioblastoma tumors are resistant to radiotherapy, and the need for drugs to induce radio-sensitization in tumor cells has always been a challenge. Besides, radiotherapy using targeted radionuclide would be effective even for resistant tumors. It has been shown topoisomerase I and poly (ADP-ribose) polymerase (PARP) enzymes have critical roles in the repair process of DNA injury in cells. Therefore, the inhibition of the activity of these enzymes can halt this process and result in the accumulation of damaged DNA in cells and the induction of cell death in tumors. In the present research, the impact of beta-particles of iodine-131 in combination with Topotecan (TPT), as the inhibitor of topoisomerase I, and A-966492, as the inhibitor of the PARP enzyme on the possible increase of radio-sensitivity of glioblastoma cells was assessed. For this purpose, a human glioblastoma cell line, U87MG, was cultured in flasks coated with Poly-Hema to achieve 300 μm-diameter spheroids. Then, nontoxic concentrations of A-966492 and TPT were applied in the cell culture media. The viability of the cells treated with iodine131 in combination with A-966492 and TPT was determined by the clonogenic assay. The expression rate of gamma-H2AX, as a biomarker of DNA double-strand breaks, was analyzed using immunofluorescence microscopy to unravel the effect of TPT, A-966492 (1 μM), and radiation on the cell death induction. The combination of each TPT or A-966492 with radiation resulted in the increased rate of cell death, and the ratios of sensitizer enhancement at 50% survival (SER50) were elevated by 1.45 and 1.25, respectively. Chemo- and radio-sensitization were promoted when iodine-131 was combined with A-966492 and TPT, with the SER50 of 1.68. Also, the expression of γ-H2AX was significantly increased in cells treated with A-966492 and TPT combined with radiation. The results demonstrated that iodine-131, in combination with A-966492 and TPT, had marked effects on radio-sensitizing and can be used as a targeted radionuclide for targeting radiotherapy in combination with topoisomerase I and PARP inhibitors to enhance radiotherapy in clinics.