Increased expression of seprase, a membrane-type serine protease, is associated with lymph node metastasis in human colorectal cancer

Fibroblast activation protein is a cellular marker of fibrotic activity in canine idiopathic pulmonary fibrosis

Canine idiopathic pulmonary fibrosis (CIPF) is a progressive fibrotic interstitial lung disease of unknown etiology, afflicting aging West Highland white terriers (WHWTs) and leading to progressive respiratory failure. Fibroblast activation protein (FAP), a protease overexpressed in many cancers, is upregulated in idiopathic pulmonary fibrosis in humans. The aim of this study was to investigate FAP as a marker of active fibrosis in lung biopsies from WHWTs affected with CIPF, as well as the potential of plasmatic FAP as a biomarker. After establishing a scoring system to evaluate the severity and activity of fibrosis on histopathological lung sections, anti-FAP immunohistochemistry was performed on healthy and CIPF samples. FAP expression was characterized using both visual and digital quantitative pathology software analyses and then correlated to fibrosis severity and activity. Levels of plasmatic FAP in WHWTs affected with CIPF were measured by enzyme-linked immunosorbent assay and compared with healthy dogs. Lung samples from 22 WHWTs affected with CIPF were collected. According to the fibrosis scoring system, they were classified as cases of mild (5), moderate (9) and severe (8) fibrosis and were attributed scores of fibrosis activity. Fifteen healthy lung samples were classified as non-fibrotic. Healthy lung samples were FAP-negative, whereas fibroblasts were FAP-positive in 20 CIPF samples. FAP immunohistochemical expression correlated mildly with fibrosis severity (p < 0.05; R 2 = 0.22) but highly with fibrosis activity scores (p < 0.001; R 2 = 0.68). Digital image analysis detected a higher percentage of FAP-positive cells in areas of active fibrosis (p < 0.001) and FAP-positive cells were distributed outside mature fibrosis lesions, clustered in active fibrosis areas or scattered within alveolar septa. On the other hand, plasmatic FAP was significantly lower in dogs affected with CIPF compared with healthy dogs (p < 0.01). In conclusion, this study provides a valuable histological scoring system to assess the severity and activity of fibrosis in CIPF. It demonstrates that FAP is a good cellular marker of fibrotic activity in CIPF, and thus constitutes a promising target to be exploited for diagnostic and therapeutic applications. Additionally, it suggests that plasmatic FAP, although non-specific, could be altered in CIPF.

IL-17a promotes hepatocellular carcinoma by increasing FAP expression in hepatic stellate cells via activation of the STAT3 signaling pathway

Studies have shown that hepatic stellate cells (HSCs) and interleukin-17a (IL-17a) play important roles in liver tumorigenesis. In addition, fibroblast activation protein-α (FAP) has been shown to be a key regulator of hepatic stellate cell activation. In this study, in vivo and in vitro experiments were performed to verify the promoting effects of IL-17a administration, IL-17a overexpression, and FAP upregulation in HSCs on liver fibrosis and liver tumorigenesis. The cleavage under targets & release using nuclease (CUT&RUN) technique was used to verify the binding status of STAT3 to the FAP promoter. The in vitro studies showed that IL-17a activated HSCs and promoted HCC development and progression. FAP and IL-17a overexpression also activated HSCs, promoted HCC cell proliferation and migration, and inhibited HCC cell apoptosis. The in vivo studies suggested that IL-17a and FAP overexpression in HSCs facilitated liver tumor development and progression. The CUT&RUN results indicated that FAP expression was regulated by STAT3, which could bind to the FAP promoter region and regulate its transcription status. We concluded that IL-17a promoted HCC by increasing FAP expression in HSCs via activation of the STAT3 signaling pathway.

Fibroblast activation protein drives tumor metastasis via a protease-independent role in invadopodia stabilization

During metastasis, tumor cells invade through the basement membrane and intravasate into blood vessels and then extravasate into distant organs to establish metastases. Here, we report a critical role of a transmembrane serine protease fibroblast activation protein (FAP) in tumor metastasis. Expression of FAP and TWIST1, a metastasis driver, is significantly correlated in several types of human carcinomas, and FAP is required for TWIST1-induced breast cancer metastasis to the lung. Mechanistically, FAP is localized at invadopodia and required for invadopodia-mediated extracellular matrix degradation independent of its proteolytic activity. Live cell imaging shows that association of invadopodia precursors with FAP at the cell membrane promotes the stabilization and growth of invadopodia precursors into mature invadopodia. Together, our study identified FAP as a functional target of TWIST1 in driving tumor metastasis via promoting invadopodia-mediated matrix degradation and uncovered a proteolytic activity-independent role of FAP in stabilizing invadopodia precursors for maturation.

Fibroblast activation protein as a potential theranostic target in brain metastases of diverse solid tumours

Brain metastases are a very common and serious complication of oncological diseases. Despite the vast progress in multimodality treatment, brain metastases significantly decrease the quality of life and prognosis of patients. Therefore, identifying new targets in the microenvironment of brain metastases is desirable. Fibroblast activation protein (FAP) is a transmembrane serine protease typically expressed in tumour-associated stromal cells. Due to its characteristic presence in the tumour microenvironment, FAP represents an attractive theranostic target in oncology. However, there is little information on FAP expression in brain metastases. In this study, we quantified FAP expression in samples of brain metastases of various primary origin and characterised FAP-expressing cells. We have shown that FAP expression is significantly higher in brain metastases in comparison to non-tumorous brain tissues, both at the protein and enzymatic activity levels. FAP immunopositivity was localised in regions rich in collagen and containing blood vessels. We have further shown that FAP is predominantly confined to stromal cells expressing markers typical of cancer-associated fibroblasts (CAFs). We have also observed FAP immunopositivity on tumour cells in a portion of brain metastases, mainly originating from melanoma, lung, breast, and renal cancer, and sarcoma. There were no significant differences in the quantity of FAP protein, enzymatic activity, and FAP+ stromal cells among brain metastasis samples of various origins, suggesting that there is no association of FAP expression and/or presence of FAP+ stromal cells with the histological type of brain metastases. In summary, we are the first to establish the expression of FAP and characterise FAP-expressing cells in the microenvironment of brain metastases. The frequent upregulation of FAP and its presence on both stromal and tumour cells support the use of FAP as a promising theranostic target in brain metastases.

FAP promotes metastasis and chemoresistance via regulating YAP1 and macrophages in mucinous colorectal adenocarcinoma

Mucinous colorectal adenocarcinoma (MC) is less likely to respond to chemotherapy and is associated with poorer prognosis compared with non-MC (NMC). Fibroblast activation protein (FAP) was found and validated to be upregulated in MC patients and was negatively correlated with prognosis and therapeutic outcomes in colorectal cancer (CRC) patients who were treated with adjuvant chemotherapy. Overexpression of FAP promoted CRC cell growth, invasion and metastasis, and enhanced chemoresistance. Myosin phosphatase Rho-interacting protein (MPRIP) was identified as a direct interacting protein of FAP. FAP may influence the efficiency of chemotherapy and prognosis by promoting the crucial functions of CRC and inducing tumor-associated macrophages (TAMs) recruitment and M2 polarization through regulating theRas Homolog Family Member/Hippo/Yes-associated protein (Rho/Hippo/YAP) signaling pathway. Knockdown of FAP could reverse tumorigenicity and chemoresistance in CRC cells. Thus, FAP may serve as a marker for prognosis and therapeutic outcome, as well as a potential therapeutic target to overcome chemoresistance in MC patients.

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.

The Superiority of Fibroblast Activation Protein Inhibitor (FAPI) PET/CT Versus FDG PET/CT in the Diagnosis of Various Malignancies

Cancer represents a major cause of death worldwide and is characterized by the uncontrolled proliferation of abnormal cells that escape immune regulation. It is now understood that cancer-associated fibroblasts (CAFs), which express specific fibroblast activation protein (FAP), are critical participants in tumor development and metastasis. Researchers have developed various FAP-targeted probes for imaging of different tumors from antibodies to boronic acid-based inhibitor molecules and determined that quinoline-based FAP inhibitors (FAPIs) are the most appropriate candidate as the radiopharmaceutical for FAPI PET/CT imaging. When applied clinically, FAPI PET/CT yielded satisfactory results. Over the past few years, the utility and effectiveness of tumor detection and staging of FAPI PET/CT have been compared with FDG PET/CT in various aspects, including standardized uptake values (SUVs), rate of absorbance and clearance. This review summarizes the development and clinical application of FAPI PET/CT, emphasizing the diagnosis and management of various tumor types and the future prospects of FAPI imaging.

Exposure of Immunogenic Tumor Antigens in Surrendered Immunity and the Significance of Autologous Tumor Cell-Based Vaccination in Precision Medicine

The mechanisms by which immune systems identify and destroy tumors, known as immunosurveillance, have been discussed for decades. However, several factors that lead to tumor persistence and escape from the attack of immune cells in a normal immune system have been found. In the process known as immunoediting, tumors decrease their immunogenicity and evade immunosurveillance. Furthermore, tumors exploit factors such as regulatory T cells, myeloid-derived suppressive cells, and inhibitory cytokines that avoid cytotoxic T cell (CTL) recognition. Current immunotherapies targeting tumors and their surroundings have been proposed. One such immunotherapy is autologous cancer vaccines (ACVs), which are characterized by enriched tumor antigens that can escalate specific CTL responses. Unfortunately, ACVs usually fail to activate desirable therapeutic effects, and the low immunogenicity of ACVs still needs to be elucidated. This difficulty highlights the significance of immunogenic antigens in antitumor therapies. Previous studies have shown that defective host immunity triggers tumor development by reprogramming tumor antigenic expressions. This phenomenon sheds new light on ACVs and provides a potential cue to improve the effectiveness of ACVs. Furthermore, synergistically with the ACV treatment, combinational therapy, which can reverse the suppressive tumor microenvironments, has also been widely proposed. Thus, in this review, we focus on tumor immunogenicity sculpted by the immune systems and discuss the significance and application of restructuring tumor antigens in precision medicine.

Ultrasensitive Fibroblast Activation Protein-α-Activated Fluorogenic Probe Enables Selective Imaging and Killing of Melanoma In Vivo

Melanoma is a malignant cancer with a high risk of metastasis and continued increase in death rates over the past decades, and its prognosis is highly related to the disease's stage, while early detection and treatment of melanoma are significant to the improvement of its therapy outcome. Different from the traditional methods for disease diagnosis, enzyme-activated fluorescent probes were developed rapidly due to their high sensitivity and temporal-spatial ratio and have been widely applied in tumor detection, surgical navigation, and cancer-related research. Fibroblast activation protein-α (FAPα), a serine-type cell surface protease that plays important roles in cell invasion and extracellular matrix degradation, is widely involved in tumor progression such as malignant melanoma, so developing a FAPα activity-based molecular tool would be of great potential for the early diagnosis and therapy of melanoma. However, few fluorescent probes targeting FAPα have been applied in melanoma-related studies, and thus, the construction of FAPα activity-based fluorescent probes for melanoma detection is in urgent need. By incorporating the selective recognition unit with a red-emission fluorophore, cresyl violet, we herein report an ultrasensitive (limit of detection = 5.3 ng/mL) fluorogenic probe for FAPα activity sensing, named CV-FAP; the acquired probe showed a significantly higher binding affinity (15.7-fold) and overall catalytic efficiency (2.6-fold) when compared with those of the best reported FAPα probes. The good performance of CV-FAP made it possible to discriminate malignant melanoma cells and tumor-bearing mice from normal cells and mice with high contrast. More importantly, CV-FAP showed significant antitumor activity toward melanoma in cultured cells and tumor-bearing nude mice (over 95% inhibited tumor growth) with good safety, which made it an ideal theranostic agent for melanoma.

Comparison of [68 Ga]Ga-DOTA-FAPI-04 PET/CT and [18F]FDG PET/CT in colorectal cancer

AIM

In this study, we aimed to evaluate the diagnostic sensitivity of [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT in the evaluation of primary or recurrent tumor, and nodal, peritoneal, and distant organ metastases in patients with newly diagnosed or relapsed colorectal cancer (CRC) in comparison with [¹⁸F]FDG PET/CT.

MATERIALS AND METHOD

Thirty-nine patients with histopathologically confirmed primary or relapsed CRC were included in our study. All patients underwent both [¹⁸F]FDG and [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT imaging in the same week. Primary lesions, lymph nodes, and metastatic lesions were recorded on both scans. SUVmax and background values were measured from the primary and metastatic lesions; tumor-to-background ratio (TBR) was calculated and compared. The results of the operation were compared with PET findings in patients who underwent surgical treatment without neoadjuvant chemotherapy (NAC).

RESULTS

The sensitivity and specificity of [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT in the evaluation of primary tumors were 100%, while the sensitivity of [¹⁸F]FDG PET/CT was 100% and its specificity was 85.3%. When evaluated with surgical results in the detection of lymph nodes, [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT had a sensitivity of 90% and a specificity of 100%, whereas [¹⁸F]FDG PET/CT had a sensitivity of 80% and a specificity of 81.8%. The sensitivity and specificity of [⁶⁸ Ga]Ga-DOTA-FAPI PET/CT for peritoneal implants were 100%, and the sensitivity of [¹⁸F]FDG PET/CT was 55%. The SUVmax of primary lesions was higher with [¹⁸F]FDG (p < 0.001), while TBR was higher in [⁶⁸ Ga]Ga-DOTA-FAPI PET/CT than [¹⁸F]FDG PET/CT (p: 0.008). SUVmax and TBR of the lymph nodes were significantly higher in [⁶⁸ Ga]Ga-DOTA-FAPI PET/CT than [¹⁸F]FDG PET/CT (p < 0.001 for both).

CONCLUSION

[⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT achieved much higher sensitivity and specificity in the detection of primary lesions, and especially the lymph nodes and peritoneal metastases, suggesting that it can be employed in the assessment of primary tumor and metastases in patients with CRC in routine clinical practice.

68Ga-FAPI as a Diagnostic Tool in Sarcoma: Data from the 68Ga-FAPI PET Prospective Observational Trial

Bone and soft-tissue sarcomas express fibroblast activation protein (FAP) on tumor cells and associated fibroblasts. Therefore, FAP is a promising therapeutic and diagnostic target. Novel radiolabeled FAP inhibitors (e.g., 68Ga-FAPI-46) have shown high tumor uptake on PET in sarcoma patients. Here, we report the endpoints of the 68Ga-FAPI PET prospective observational trial. Methods: Forty-seven patients with bone or soft-tissue sarcomas undergoing clinical 68Ga-FAPI PET were eligible for enrollment into the 68Ga-FAPI PET observational trial. Of these patients, 43 also underwent 18F-FDG PET. The primary study endpoint was the association between 68Ga-FAPI PET uptake intensity and histopathologic FAP expression analyzed with Spearman r correlation. Secondary endpoints were detection rate, positive predictive value (PPV), interreader reproducibility, and change in management. Datasets were interpreted by 2 masked readers. Results: The primary endpoint was met, and the association between 68Ga-FAPI PET uptake intensity and histopathologic FAP expression was significant (Spearman r = 0.43; P = 0.03). By histopathologic validation, PPV was 1.00 (95% CI, 0.87-1.00) on a per-patient and 0.97 (95% CI, 0.84-1.00) on a per-region basis. In cases with histopathologic validation, 27 of 28 (96%) confirmed patients and 32 of 34 (94%) confirmed regions were PET-positive, resulting in an SE of 0.96 (95% CI, 0.82-1.00) on a per-patient and 0.94 (95% CI, 0.80-0.99) on a per-region basis. The detection rate on a per-patient basis in 68Ga-FAPI and 18F-FDG PET was 76.6% and 81.4%, respectively. In 8 (18.6%) patients, 68Ga-FAPI PET resulted in an upstaging compared with 18F-FDG PET. 68Ga-FAPI PET readers showed substantial to almost perfect agreement for the defined regions (Fleiss κ: primary κ = 0.78, local nodal κ = 0.54, distant nodal κ = 0.91, lung κ = 0.86, bone κ = 0.69, and other κ = 0.65). Clinical management changed in 13 (30%) patients after 68Ga-FAPI PET. Conclusion: We confirm an association between tumoral 68Ga-FAPI PET uptake intensity and histopathologic FAP expression in sarcoma patients. Further, with masked readings and independent histopathologic validation, 68Ga-FAPI PET had a high PPV and sensitivity for sarcoma staging.

FAP and FAPI-PET/CT in Malignant and Non-Malignant Diseases: A Perfect Symbiosis?

A fibroblast activation protein (FAP) is an atypical type II transmembrane serine protease with both endopeptidase and post-proline dipeptidyl peptidase activity. FAP is overexpressed in cancer-associated fibroblasts (CAFs), which are found in most epithelial tumors. CAFs have been implicated in promoting tumor cell invasion, angiogenesis and growth and their presence correlates with a poor prognosis. However, FAP can generally be found during the remodeling of the extracellular matrix and therefore can be detected in wound healing and benign diseases. For instance, chronic inflammation, arthritis, fibrosis and ischemic heart tissue after a myocardial infarction are FAP-positive diseases. Therefore, quinoline-based FAP inhibitors (FAPIs) bind with a high affinity not only to tumors but also to a variety of benign pathologic processes. When these inhibitors are radiolabeled with positron emitting radioisotopes, they provide new diagnostic and prognostic tools as well as insights into the role of the microenvironment in a disease. In this respect, they deliver additional information beyond what is afforded by conventional FDG PET scans that typically report on glucose uptake. Thus, FAP ligands are considered to be highly promising novel tracers that offer a new diagnostic and theranostic potential in a variety of diseases.

Fibroblast Activation Protein-α as a Target in the Bench-to-Bedside Diagnosis and Treatment of Tumors: A Narrative Review

Fibroblast activation protein-α (FAP) is a type II integral serine protease that is specifically expressed by activated fibroblasts. Cancer-associated fibroblasts (CAFs) in the tumor stroma have an abundant and stable expression of FAP, which plays an important role in promoting tumor growth, invasion, metastasis, and immunosuppression. For example, in females with a high incidence of breast cancer, CAFs account for 50–70% of the cells in the tumor’s microenvironment. CAF overexpression of FAP promotes tumor development and metastasis by influencing extracellular matrix remodeling, intracellular signaling, angiogenesis, epithelial-to-mesenchymal transition, and immunosuppression. This review discusses the basic biological characteristics of FAP and its applications in the diagnosis and treatment of various cancers. We review the emerging basic and clinical research data regarding the use of nanomaterials that target FAP.

In Vitro and In Situ Activity-Based Labeling of Fibroblast Activation Protein with UAMC1110-Derived Probes

Fibroblast activation protein (FAP) is a proline-selective protease that belongs to the S9 family of serine proteases. It is typically highly expressed in the tumor microenvironment (TME) and especially in cancer-associated fibroblasts, the main cell components of the tumor stroma. The exact role of its enzymatic activity in the TME remains largely unknown. Hence, tools that enable selective, activity-based visualization of FAP within the TME can help to unravel FAP’s function. We describe the synthesis, biochemical characterization, and application of three different activity-based probes (biotin-, Cy3-, and Cy5-labeled) based on the FAP-inhibitor UAMC1110, an in-house developed molecule considered to be the most potent and selective FAP inhibitor available. We demonstrate that the three probes have subnanomolar FAP affinity and pronounced selectivity with respect to the related S9 family members. Furthermore, we report that the fluorescent Cy3- and Cy5-labeled probes are capable of selectively detecting FAP in a cellular context, making these chemical probes highly suitable for further biological studies. Moreover, proof of concept is provided for in situ FAP activity staining in patient-derived cryosections of urothelial tumors.

Multimodal Molecular Imaging of the Tumour Microenvironment

The tumour microenvironment (TME) surrounding tumour cells is a highly dynamic and heterogeneous composition of immune cells, fibroblasts, precursor cells, endothelial cells, signalling molecules and extracellular matrix (ECM) components. Due to the heterogeneity and the constant crosstalk between the TME and the tumour cells, the components of the TME are important prognostic parameters in cancer and determine the response to novel immunotherapies. To improve the characterization of the TME, novel non-invasive imaging paradigms targeting the complexity of the TME are urgently needed.The characterization of the TME by molecular imaging will (1) support early diagnosis and disease follow-up, (2) guide (stereotactic) biopsy sampling, (3) highlight the dynamic changes during disease pathogenesis in a non-invasive manner, (4) help monitor existing therapies, (5) support the development of novel TME-targeting therapies and (6) aid stratification of patients, according to the cellular composition of their tumours in correlation to their therapy response.This chapter will summarize the most recent developments and applications of molecular imaging paradigms beyond FDG for the characterization of the dynamic molecular and cellular changes in the TME.

In search of definitions: Cancer-associated fibroblasts and their markers

The tumor microenvironment has been identified as one of the driving factors of tumor progression and invasion. Inside this microenvironment, cancer-associated fibroblasts (CAFs), a type of perpetually activated fibroblasts, have been implicated to have a strong tumor-modulating effect and play a key role in areas such as drug resistance. Identification of CAFs has typically been carried based on the expression of various "CAF markers", such as fibroblast activation protein alpha (FAP) and alpha smooth muscle actin (αSMA), which separates them from the larger pool of fibroblasts present in the body. However, as outlined in this Review, the expression of various commonly used fibroblast markers is extremely heterogeneous and varies strongly between different CAF subpopulations. As such, novel selection methods based on cellular function, as well as further characterizing research, are vital for the standardization of CAF identification in order to improve the cross-applicability of different research studies in the field. The aim of this review is to give a thorough overview of the commonly used fibroblast markers in the field and their various strengths and, more importantly, their weaknesses, as well as to highlight potential future avenues for CAF identification and targeting.

Cancer-associated fibroblasts (CAFs) promote the lymph node metastasis of esophageal squamous cell carcinoma

Lymph node metastasis is a pathognomonic feature of spreading tumors, and overcoming metastasis is a challenge in attaining more favorable clinical outcomes. Esophageal cancer is an aggressive tumor for which lymph node metastasis is a strong poor prognostic factor, and the tumor microenvironment (TME), and cancer-associated fibroblasts (CAFs) in particular, has been implicated in esophageal cancer progression. CAFs play a central role in the TME and have been reported to provide suitable conditions for the progression of esophageal cancer, similar to their role in other malignancies. However, little is known concerning the relevance of CAFs to the lymph node metastasis of esophageal cancer. Here, we used clinical samples of esophageal cancer to reveal that CAFs promote lymph node metastasis and subsequently verified the intercellular relationships in vitro and in vivo using an orthotopic metastatic mouse model. In the analysis of clinical samples, FAP⁺ CAFs were strongly associated with lymph node metastasis rather than with other prognostic factors. Furthermore, CAFs affected the ability of esophageal cancer cells to acquire metastatic phenotypes in vitro; this finding was confirmed by data from an in vivo orthotopic metastatic mouse model showing that the number of lymph node metastases increased upon injection of cocultured cancer cells and CAFs. In summary, we verified in vitro and in vivo that the accumulation of CAFs enhances the lymph node metastasis of ESCC. Our data suggest that CAF targeted therapy can reduce lymph node metastasis and improve the prognosis of patients with esophageal cancer in the future.

Fibroblast activation protein-α in tumor cells promotes colorectal cancer angiogenesis via the Akt and ERK signaling pathways

Fibroblast activation protein-α (FAP-α) is a cell surface serine protease of the post-prolyl peptidase family, and stromal FAP-α expression may serve important functions in tumor occurrence and progression. In recent years, FAP-α expression in tumor cells has been detected in a number of types of tumor, and its roles in tumor growth and metastasis have been reported. However, the presence of FAP-α in colorectal cancer (CRC) cells lacks sufficient evidence and its role in angiogenesis remains unknown. The present study confirmed FAP-α expression in CRC cells at the tissue and cellular level, using immunohistochemistry and western blot analysis, respectively; it additionally identified that FAP-α in CRC cells was positively associated with vascular endothelial growth factor (VEGF)-A expression and microvessel density in stained tissue samples for the first time. In addition, western blotting identified that FAP-α overexpression in SW1116 cells significantly upregulated VEGF-A expression, and silencing of FAP-α in HT29 cells markedly inhibited VEGF-A expression. Survival analysis demonstrated that patients with high expression of FAP-α and VEGF-A had the shortest survival time. To detect the effects of FAP-α on human umbilical vein endothelial cells (HUVECs), conditioned medium (CM) from CRC cell lines was used and it was identified that CM from SW1116 cells with overexpressed FAP-α exhibited significantly increased VEGF-R2, phosphorylated extracellular signal-regulated kinase (p-ERK) and p-RAC-α serine/threonine-protein kinase (Akt) in HUVECs, in addition to the proliferation rate. Conversely, CM from HT29 cells with FAP-α silenced exhibited a significantly inhibited proliferation rate. Molecular mechanism analysis demonstrated that p-ERK and p-Akt in SW1116 and HT29 cells were affected by alterations in FAP-α expression, and treatment with a p-ERK inhibitor (U0126) and p-Akt inhibitor (LY294002) ameliorated VEGF-A upregulation induced by FAP-α overexpression. All the results confirmed the presence of FAP-α in CRC cells and suggested that FAP-α may effectively promote angiogenesis in CRC via the Akt and ERK signaling pathways.

Inhibitor-Decorated Polymer Conjugates Targeting Fibroblast Activation Protein

Proteases are directly involved in cancer pathogenesis. Expression of fibroblast activation protein (FAP) is upregulated in stromal fibroblasts in more than 90% of epithelial cancers and is associated with tumor progression. FAP expression is minimal or absent in most normal adult tissues, suggesting its promise as a target for the diagnosis or treatment of various cancers. Here, we report preparation of a polymer conjugate (an iBody) containing a FAP-specific inhibitor as the targeting ligand. The iBody inhibits both human and mouse FAP with low nanomolar inhibition constants but does not inhibit close FAP homologues dipeptidyl peptidase IV, dipeptidyl peptidase 9, and prolyl oligopeptidase. We demonstrate the applicability of this iBody for the isolation of FAP from cell lysates and blood serum as well as for its detection by ELISA, Western blot, flow cytometry, and confocal microscopy. Our results show the iBody is a useful tool for FAP targeting in vitro and potentially also for specific anticancer drug delivery.

Fibroblast activation protein-α-expressing fibroblasts promote the progression of pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an extensive desmoplastic stromal response. Fibroblast activation protein-α (FAP) is best known for its presence in stromal cancer-associated fibroblasts (CAFs). Our aim was to assess whether FAP expression was associated with the prognosis of patients with PDAC and to investigate how FAP expressing CAFs contribute to the progression of PDAC.

METHODS

FAP expression was immunohistochemically assessed in 48 PDAC specimens. We also generated a fibroblastic cell line stably expressing FAP, and examined the effect of FAP-expressing fibroblasts on invasiveness and the cell cycle in MiaPaCa-2 cells (a pancreatic cancer cell line).

RESULTS

Stromal FAP expression was detected in 98% (47/48) of the specimens of PDAC, with the intensity being weak in 16, moderate in 19, and strong in 12 specimens, but was not detected in the 3 control noncancerous pancreatic specimens. Patients with moderate or strong FAP expression had significantly lower cumulative survival rates than those with negative or weak FAP expression (mean survival time; 352 vs. 497 days, P = 0.006). Multivariate analysis identified moderate to strong expression of FAP as one of the factors associated with the prognosis in patients with PDAC. The intensity of stromal FAP expression was also positively correlated to the histological differentiation of PDAC (P < 0.05). FAP-expressing fibroblasts promoted the invasiveness of MiaPaCa-2 cells more intensively than fibroblasts not expressing FAP. Coculture with FAP-expressing fibroblasts significantly activated cell cycle shift in MiaPaCa-2 cells compared to coculture with fibroblasts not expressing FAP. Furthermore, coculture with FAP expressing fibroblasts inactivated retinoblastoma (Rb) protein, an inhibitor of cell cycle progression, in MiaPaCa-2 cells by promoting phosphorylation of Rb.

CONCLUSIONS

The present in vitro results and the association of FAP expression with clinical outcomes provide us with a better understanding of the effect of FAP-expressing CAFs on the progression of PDAC.

Whole Tumor Antigen Vaccines: Where Are We?

With its vast amount of uncharacterized and characterized T cell epitopes available for activating CD4⁺ T helper and CD8⁺ cytotoxic lymphocytes simultaneously, whole tumor antigen represents an attractive alternative source of antigens as compared to tumor-derived peptides and full-length recombinant tumor proteins for dendritic cell (DC)-based immunotherapy. Unlike defined tumor-derived peptides and proteins, whole tumor lysate therapy is applicable to all patients regardless of their HLA type. DCs are essentially the master regulators of immune response, and are the most potent antigen-presenting cell population for priming and activating naïve T cells to target tumors. Because of these unique properties, numerous DC-based immunotherapies have been initiated in the clinics. In this review, we describe the different types of whole tumor antigens that we could use to pulse DCs ex vivo and in vivo. We also discuss the different routes of delivering whole tumor antigens to DCs in vivo and activating them with toll-like receptor agonists.

Fibroblast activation protein overexpression and clinical implications in solid tumors: a meta-analysis

OBJECTIVE

Fibroblast activation protein (FAP) plays a vital role in tumor invasion and metastasis. Previous studies have reported its prognostic value in different tumors. However, the results of these reports remain controversial. In this study, a meta-analysis was performed to clarify this issue.

METHODS

A search of the PubMed, Embase and CNKI databases was conducted to analyze relevant articles. The outcomes included the relations between FAP expression and histological differentiation, tumor invasion, lymph node metastasis, distant metastasis and overall survival (OS). Sensitivity analysis by FAP expression in different cells and tumor types were further subjected to sensitivity analyses as subgroups. Pooled odds ratios (ORs) and hazard ratios (HRs) were evaluated using the random-effects model.

RESULTS

The global analysis included 15 studies concerning various solid tumors. For global analysis, FAP overexpression in tumor tissue displayed significant associations with poor OS and tumor progression (OS: HR = 2.18, P = 0.004; tumor invasion: OR = 4.48, P = 0.007; and lymph node metastasis: OR = 3.80, P = 0.004). The subgroup analyses yielded two notable results. First, the relation between FAP overexpression and poor OS and tumor lymph node metastasis was closer in the patients with FAP expression in tumor cells. Second, the pooled analyses of colorectal cancers or pancreatic cancers all indicated that FAP overexpression was associated with a detrimental OS (HR: 1.72, P = 0.009; HR: 3.18, P = 0.005, respectively). The magnitude of this effect was not statistically significant compared with that in patients with non-colorectal cancers or non-pancreatic cancers. These analyses did not display a statistically significant correlation between FAP expression and histological differentiation and distant metastasis in all of the groups.

CONCLUSIONS

FAP expression is associated with worse prognosis in solid tumors, and this association is particularly pronounced if FAP overexpression is found in the tumor cells rather than the stroma.

Expression and clinical implications of HAb18G/CD147 in hepatocellular carcinoma

AIM

HAb18G/CD147 is an important factor in invasion and metastasis of hepatocellular carcinoma (HCC). However, the clinical implications of HAb18G/CD147 expression in HCC are still unclear. In this study, we clarify the clinical significance of HAb18G/CD147. We characterize the association between HAb18G/CD147 expression and presentation of fibrosis or chronic hepatitis B, as well as its effect on HCC development.

METHODS

The expression of HAb18G/CD147 in human hepatocarcinoma cell lines was analyzed by reverse transcription polymerase chain reaction and western blotting. Tumor tissues were obtained from HCC patients who underwent surgical resection between 2002 and 2006. All patients who had received previous therapy were excluded. HCC tissues were analyzed by immunohistochemistry using anti-HAb18G/CD147.

RESULTS

HAb18G/CD147 was widely expressed in Hep-G2, SMCC-7721 and BEL7402 cell lines, but not expressed in L-02, a human normal hepatic cell line. HAb18G/CD147 was mainly localized to the membrane of tumor cells in 74.0% (37/50) HCC patients. We found that higher HAb18G/CD147 expression and poor tumor differentiation were correlated with patient survival (P = 0.026 and P = 0.014, respectively). Furthermore, the distribution of HAb18G/CD147 was similar to that of hepatitis B virus (HBV) infection, but negatively related to hepatic cirrhosis.

CONCLUSION

HAb18G/CD147 has shown its potentials in HCC development and patient survival. Moreover, it may also cooperate with chronic HBV infection and cirrhosis during HCC development. Its functions in the two factors may be different. Therefore, HAb18G/CD147 may be a marker for poor prognosis in HCC patients and could be a useful therapeutic target for interfering with or reversing HCC progression.

Transcriptional regulation of seprase in invasive melanoma cells by transforming growth factor-β signaling

The tumor invasive phenotype driven by seprase expression/activity has been widely examined in an array of malignant tumor cell types; however, very little is known about the transcriptional regulation of this critical protease. Seprase (also named fibroblast activation protein-α, antiplasmin-cleaving enzyme, and dipeptidyl prolyl peptidase 5) is expressed at high levels by stromal fibroblast, endothelial, and tumor cells in a variety of invasive tumors but is undetectable in the majority of normal adult tissues. To examine the transcriptional regulation of the gene, we cloned the human seprase promoter and demonstrated that endogenous seprase expression and exogenous seprase promoter activity are high in invasive melanoma cells but not in non-invasive melanoma cells/primary melanocytes. In addition, we identified a crucial TGF-β-responsive cis-regulatory element in the proximal seprase promoter region that enabled robust transcriptional activation of the gene. Treatment of metastatic but not normal/non-invasive cells with TGF-β1 caused a rapid and profound up-regulation of endogenous seprase mRNA, which coincided with an abolishment of the negative regulator c-Ski, and an increase in binding of Smad3/4 to the seprase promoter in vivo. Blocking TGF-β signaling in invasive melanoma cells through overexpression of c-Ski, chemically using SB-431542, or with a neutralizing antibody against TGF-β significantly reduced seprase mRNA levels. Strikingly, RNAi of seprase in invasive cells greatly diminished their invasive potential in vitro as did blocking TGF-β signaling using SB-431542. Altogether, we found that seprase is transcriptionally up-regulated in invasive melanoma cells via the canonical TGF-β signaling pathway, supporting the roles of both TGF-β and seprase in tumor invasion and metastasis.

Clinical impact of HAb18G/CD147 expression in esophageal squamous cell carcinoma

BACKGROUND

HAb18G/CD147 expression has been associated with many tumor invasion molecules, which play important roles in recurrence and poor differentiation of esophageal squamous cell carcinoma (ESCC). However, the clinical implications of HAb18G/CD147 in ESCC are still unclear.

AIMS

In this study, we clarified the clinical significance of HAb18G/CD147 and characterized the association between HAb18G/CD147 and tumor invasion in ESCC cases.

METHODS

Tumor tissues were obtained from 86 ESCC patients who underwent surgical resection between 2002 and 2005. All patients that had received previous therapy were excluded. ESCC tissues were analyzed by IHC using anti HAb18G/CD147 antibody. The expression of HAb18G/CD147 mRNA in esophageal cancer cell lines was analyzed by RT-PCR.

RESULTS

HAb18G/CD147 was uniformly expressed in EC109 and EC871214 cell lines, but negatively expressed in EPC2, esophageal normal squamous cell line. HAb18G/CD147 mainly localized to the membrane of tumor cells in 84.9% of ESCC patients (64 out of 86 cases). Furthermore, we also found that higher HAb18G/CD147 expression levels significantly correlated with lymph node metastasis, depth of tumor invasion and differentiation (P < 0.05). But the expression levels of HAb18G/CD147 in lymph node metastatic tissues were almost equal to that in the primary tumor tissues. Furthermore, lymph node metastasis and expression of HAB18G/CD147 were independent prognostic indicators in ESCC.

CONCLUSIONS

The expression of HAb18G/CD147 might be involved in the progression and survival of ESCC. Therefore, HAb18G/CD147 could be a clinical marker for the poor prognosis in ESCC patients and may also be a potentially therapeutic target to improve the progression of ESCC.

Genome-wide association and fine mapping of genetic loci predisposing to colon carcinogenesis in mice

To identify the genetic determinants of colon tumorigenesis, 268 male mice from 33 inbred strains derived from different genealogies were treated with azoxymethane (AOM; 10 mg/kg) once a week for six weeks to induce colon tumors. Tumors were localized exclusively within the distal colon in each of the strains examined. Inbred mouse strains exhibit a large variability in genetic susceptibility to AOM-induced colon tumorigenesis. The mean colon tumor multiplicity ranged from 0 to 38.6 (mean = 6.5 ± 8.6) and tumor volume ranged from 0 to 706.5 mm(3) (mean = 87.4 ± 181.9) at 24 weeks after the first dose of AOM. AOM-induced colon tumor phenotypes are highly heritable in inbred mice, and 68.8% and 71.3% of total phenotypic variation in colon tumor multiplicity and tumor volume, respectively, are attributable to strain-dependent genetic background. Using 97,854 single-nucleotide polymorphisms, we carried out a genome-wide association study (GWAS) of AOM-induced colon tumorigenesis and identified a novel susceptibility locus on chromosome 15 (rs32359607, P = 6.31 × 10(-6)). Subsequent fine mapping confirmed five (Scc3, Scc2, Scc12, Scc8, and Ccs1) of 16 linkage regions previously found to be associated with colon tumor susceptibility. These five loci were refined to less than 1 Mb genomic regions of interest. Major candidates in these loci are Sema5a, Fmn2, Grem2, Fap, Gsg1l, Xpo6, Rabep2, Eif3c, Unc5d, and Gpr65. In particular, the refined Scc3 locus shows high concordance with the human GWAS locus that underlies hereditary mixed polyposis syndrome. These findings increase our understanding of the complex genetics of colon tumorigenesis, and provide important insights into the pathways of colorectal cancer development and might ultimately lead to more effective individually targeted cancer prevention strategies.

FAP-overexpressing fibroblasts produce an extracellular matrix that enhances invasive velocity and directionality of pancreatic cancer cells

BACKGROUND

Alterations towards a permissive stromal microenvironment provide important cues for tumor growth, invasion, and metastasis. In this study, Fibroblast activation protein (FAP), a serine protease selectively produced by tumor-associated fibroblasts in over 90% of epithelial tumors, was used as a platform for studying tumor-stromal interactions. We tested the hypothesis that FAP enzymatic activity locally modifies stromal ECM (extracellular matrix) components thus facilitating the formation of a permissive microenvironment promoting tumor invasion in human pancreatic cancer.

METHODS

We generated a tetracycline-inducible FAP overexpressing fibroblastic cell line to synthesize an in vivo-like 3-dimensional (3D) matrix system which was utilized as a stromal landscape for studying matrix-induced cancer cell behaviors. A FAP-dependent topographical and compositional alteration of the ECM was characterized by measuring the relative orientation angles of fibronectin fibers and by Western blot analyses. The role of FAP in the matrix-induced permissive tumor behavior was assessed in Panc-1 cells in assorted matrices by time-lapse acquisition assays. Also, FAP+ matrix-induced regulatory molecules in cancer cells were determined by Western blot analyses.

RESULTS

We observed that FAP remodels the ECM through modulating protein levels, as well as through increasing levels of fibronectin and collagen fiber organization. FAP-dependent architectural/compositional alterations of the ECM promote tumor invasion along characteristic parallel fiber orientations, as demonstrated by enhanced directionality and velocity of pancreatic cancer cells on FAP+ matrices. This phenotype can be reversed by inhibition of FAP enzymatic activity during matrix production resulting in the disorganization of the ECM and impeded tumor invasion. We also report that the FAP+ matrix-induced tumor invasion phenotype is β1-integrin/FAK mediated.

CONCLUSION

Cancer cell invasiveness can be affected by alterations in the tumor microenvironment. Disruption of FAP activity and β1-integrins may abrogate the invasive capabilities of pancreatic and other tumors by disrupting the FAP-directed organization of stromal ECM and blocking β1-integrin dependent cell-matrix interactions. This provides a novel preclinical rationale for therapeutics aimed at interfering with the architectural organization of tumor-associated ECM. Better understanding of the stromal influences that fuel progressive tumorigenic behaviors may allow the effective future use of targeted therapeutics aimed at disrupting specific tumor-stromal interactions.

Colorectal cancer cells activate adjacent fibroblasts resulting in FGF1/FGFR3 signaling and increased invasion

Cancer-associated fibroblasts expressing fibroblast activation protein (FAP) have been implicated in the invasive behavior of colorectal cancer. In this study, we use FAP expression as a marker of fibroblast activation and analyze the effect of activated fibroblasts on colorectal cancer migration and invasion in experimental cell studies. We also investigated the expression pattern of FAP in cancer-associated fibroblasts during transformation from benign to malignant colorectal tumors. In immunohistochemical analyses, FAP was expressed in fibroblasts in all colorectal cancer samples examined, whereas all normal colon, hyperplastic polyps, or adenoma samples were negative. In in vitro studies, conditioned medium from colon cancer cells, but not adenoma cells, activated fibroblasts by inducing FAP expression. These activated fibroblasts increased the migration and invasion of colon cancer cells in Boyden chamber experiments and in a three-dimensional cell culture model. We identify fibroblast growth factor 1/fibroblast growth factor receptor 3 (FGF1/FGFR-3) signaling as mediators leading to the increased migration and invasion. Activated fibroblasts increase their expression of FGF1, and by adding a fibroblast growth factor receptor inhibitor, as well as an FGF1-neutralizing antibody, we reduced the migration of colon cancer cells. Our findings provide evidence of a possible molecular mechanism involved in the cross talk between cancer cells and fibroblasts leading to cancer cell invasion.

Fibroblast activation protein-α promotes tumor growth and invasion of breast cancer cells through non-enzymatic functions

Fibroblast activation protein-α (FAP) is a cell surface, serine protease of the post-prolyl peptidase family that is expressed in human breast cancer but not in normal tissues. Previously, we showed that FAP expression increased tumor growth rates in a mouse model of human breast cancer. Here the role of the proteolytic activities of FAP in promoting tumor growth, matrix degradation and invasion was investigated. Mammary fat pads of female SCID mice were inoculated with breast cancer cells that express FAP and the mice treated with normal saline or Val-boroPro (talabostat); Glu-boroPro (PT-630); or 1-[[(3-hydroxy-1-adamantyl)amino]acetyl]-2-cyano-(S)-pyrrolidine (LAF-237) that inhibit prolyl peptidases. Other mice were injected with breast cancer cells expressing a catalytically inactive mutant of FAP and did not receive inhibitor treatment. PT-630 and LAF-237 did not slow growth of tumors produced by any of the three cell lines expressing FAP. Talabostat slightly decreased the growth rates of the FAP-expressing tumors but because PT-630 and LAF-237 did not, the growth retardation was likely not related to the inhibition of FAP or the related post-prolyl peptidase dipeptidyl peptidase IV. Breast cancer cells expressing a catalytically inactive mutant of FAP (FAP(S624A)) also produced tumors that grew rapidly. In vitro studies revealed that cells expressing wild type FAP or FAP(S624A) degrade extracellular matrix (ECM) more extensively, accumulate higher levels of matrix metalloproteinase-9 (MMP-9) in conditioned medium, are more invasive in type I collagen gels, and have altered signaling compared to control transfectants that do not express FAP and form slow growing tumors. We conclude that the proteolytic activity of FAP participates in matrix degradation, but other functions of the protein stimulate increased tumor growth.

Clinical implications and characteristics of factor forkhead box protein 3 in gastric cancer

Transcription factor forkhead box protein 3 (FOXP3) is a specific marker of naturally occurring regulatory T cells (Tregs). Recently, various reports have suggested that FOXP3 may represent a tumor escape mechanism in cancer cells apart from its roles in Tregs. In the present study, the clinical and biological characteristics of FOXP3 were evaluated in human gastric cancer. The expression and localization of FOXP3 in gastric cancer cell lines was analyzed to evaluate its cellular biological features. Sections of human gastric cancer specimens were stained using immunohistochemistry (IHC) to assess the relationship between FOXP3 expression and tumor differentiation, in order to identify its clinical characteristics in gastric cancer. Expression of FOXP3 mRNA and protein was found in four gastric cancer cell lines (AGS, SGC-7901, MKN-28 and MKN-45). IHC of the gastric cancer sections revealed that more than 56% of gastric cancers displayed nuclear or cytoplasmic FOXP3 staining. Furthermore, a linear relationship between the differentiation of the gastric cancer tissues and FOXP3 expression intensity was shown. IHC and confocal analysis showed that the expression of FOXP3 was mainly present in the nucleus of tumor cells in the tissues and cell lines. Thus, FOXP3 nuclear staining may be associated with the risk of poor tumor differentiation. Apart from the lymphocytes, no FOXP3 staining was noted in the normal gastric tissues and para-tumor tissues. The high frequency of FOXP3 expression in gastric cancer tissue is a significant finding in the investigation of tumor differentiation and immune escape. This mechanism provides a further understanding of gastric cancer and a novel therapeutic strategy is presented.

FOXP3 expression and clinical characteristics of hepatocellular carcinoma

AIM: To study the biological and clinical characteristics of transcription factor forkhead box protein 3 (FOXP3) in hepatocellular carcinoma (HCC).

METHODS: We analyzed the expression and localization of FOXP3 in HCC tissues and cell lines to evaluate its biological features. The relationship between FOXP3 staining and clinical risk factors of HCC was assessed to identify the clinical characteristics of FOXP3 in HCC.

RESULTS: The mRNA and protein expression of FOXP3 were found in some hepatoma cell lines. Immunohistochemical (IHC) analysis of HCC sections revealed that 48% of HCC displayed FOXP3 staining, but we did not find any FOXP3 staining in normal liver tissues and para-tumor tissues. IHC and Confocal analysis showed that the expressions of FOXP3 were mainly present in the nucleus and cytoplasm of tumor cells in tissues or cell lines. In HCC, the distribution of FOXP3 was similar to that of the cirrhosis, but not to the hepatitis B virus. Those findings implicate that FOXP3 staining seems to be associated with the high risk of HCC.

CONCLUSION: The clinical characteristics of FOXP3 in HCC warrants further studies to explore its functions and roles in the cirrhosis and development of HCC.

Using substrate specificity of antiplasmin-cleaving enzyme for fibroblast activation protein inhibitor design

Circulating antiplasmin-cleaving enzyme (APCE), a prolyl-specific serine proteinase, is essentially identical to membrane-inserted fibroblast activation protein (FAP) that is transiently expressed during epithelial-derived cancer growth. Human precursive alpha(2)-antiplasmin (Met-alpha(2)AP), the only known physiologic substrate for APCE, is cleaved N-terminally to Asn-alpha(2)AP that is rapidly cross-linked to fibrin and protects it from digestion by plasmin. Identifying a specific inhibitor of APCE/FAP continues to be intensely pursued. Recombinant FAP cleavage of peptide libraries of short amino acid sequences surrounding the scissile bond, -Pro(12)-Asn(13)-, indicated that P2 Gly and P1 Pro are required, just as we found for APCE. We examined cleavage of P4-P4' peptides, using 19 amino acid substitutions at each position and selected ones in P8-P5. K(m) values determined for peptide substrates showed that P7 Arg has the highest affinity for APCE. Peptide cleavage rate increased with Arg in P6 rather than P5 or native P7. Placing Arg in P4 or P8 reduced cleavage rates dramatically. Cleavage of substrates with extended peptide sequences before or after the scissile bond showed endopeptidase to be superior to dipeptidase activity for APCE. A substrate analogue inhibitor, Phe-Arg-(8-amino-3,6-dioxaoctanoic acid)-Gly-[r]-fluoropyrrolidide, inhibited APCE with a K(i) of 54 microM but not dipeptidyl peptidase IV even at 2 mM. The inhibitor also blocked cleavage of Met-alpha(2)AP with an IC(50) of 91 microM. Replacing Arg with Gly at the same distance from fluoropyrrolidide as P7 Arg is from P1 Pro reduced its inhibition of APCE approximately 10-fold. Results indicate that Arg at P5, P6, or P7 distances from P1 enhances affinity and efficiency of substrates or inhibitors toward APCE or FAP.

Elevation of seprase expression and promotion of an invasive phenotype by collagenous matrices in ovarian tumor cells

Tumor cells do not constitutively exhibit invasive activity, but rather, can be transiently induced to adhere and form lesions. We report here that the expression of seprase, a dominant EDTA-resistant gelatinase in malignant tumors, is dependent on tumor cell exposure to type I collagen gel (TICg). The induced seprase expression of ovarian tumor cells influences their collagen contraction and invasion capability. Importantly, tumor cells with reduced seprase expression, due to manipulation by RNA interference, showed a reduction of TICg contraction in the gel contractility assay, inhibition of tumor cell invasion through TICg as shown by a transwell migration assay and inhibition of peritoneal membrane tumor lesion in a mouse model. In addition, mAb C27, an antibody against beta1 integrin, which blocks cellular avidity to TICg, can induce seprase RNA expression and promote the invasive phenotype and metastatic potential of ovarian tumor cells. Thus, collagenous matrices in the tumor cell niche induce the expression of seprase and initiate tumor invasion and metastatic cascades.

FAP-alpha and uPA show different expression patterns in premalignant and malignant esophageal lesions

Fibroblast activation protein-alpha (FAP-alpha) and urokinase-type plasminogen activator (uPA) are serine proteases involved in cancer invasion and metastasis. The authors examined FAP-alpha and uPA expression in premalignant and malignant stages of esophageal adenocarcinoma by immunohistochemistry. Additionally, Western blotting was performed on fresh-frozen tissue samples. FAP-alpha and uPA were detected in metaplastic, dysplastic, and carcinoma cells, as well as in adjacent stroma. Stromal FAP-alpha expression was associated with depth of tumor invasion, while stromal uPA expression correlated with lymph node metastases in adenocarcinomas. Stromal uPA expression in cells with premalignant changes correlated with histological grading. Immunoblotting showed higher protease expression in carcinoma tissues than in normal esophageal epithelium. These results suggest that FAP-alpha and uPA expression in metaplastic, dysplastic, and esophageal cancer tissue is associated with neoplastic progression of esophageal lesions.

Fibroblast activation protein and its relationship to clinical outcome in pancreatic adenocarcinoma

OBJECTIVES

Given the extensive desmoplastic response associated with pancreatic adenocarcinoma, we hypothesized that the stromal protein fibroblast activation protein (FAP) would be highly expressed and associated with the presence of fibrosis and other clinical features.

METHODS

Paraffin-embedded pancreatic adenocarcinomas that were resected with curative intent from 1992 to 2003 were used for this study. Fibroblast activation protein expression by immunohistochemical analysis was evaluated both by intensity (0-3+) and percentage. Fibrosis was estimated as a percentage of each tumor specimen.

RESULTS

Ninety percent (63/70) of specimens demonstrated FAP expression. Expression was significantly more pronounced in tumor-associated myofibroblasts immediately adjacent to tumor than in surrounding tumor-associated myofibroblasts (P < 0.001). Lower FAP expression in adjacent tumor-associated myofibroblasts was associated with increased fibrosis (P = 0.02). Greater FAP expression in surrounding tumor-associated myofibroblasts was associated with an increased chance of having positive lymph nodes for all patients (P = 0.03) and a higher risk of tumor recurrence (P = 0.015) and death (P = 0.02) for patients who did not receive preoperative therapy.

CONCLUSIONS

Fibroblast activation protein is highly expressed in pancreatic adenocarcinoma, with greatest expression immediately adjacent to tumor. Higher FAP expression is associated with worse clinical outcome. The investigation of FAP inhibitors as a therapeutic strategy against pancreatic cancer should be considered.

Clinical implications of fibroblast activation protein in patients with colon cancer

PURPOSE

Human fibroblast activation protein (FAP)/seprase is a 97-kDa surface glycoprotein expressed on tumor associated fibroblasts in the majority of epithelial cancers including colon adenocarcinomas. FAP overexpression in human tumor cells has been shown to promote tumor growth in animal models, and clinical trials targeting FAP enzymatic activity have been initiated. The primary objective of this study was to evaluate the clinical significance of stromal FAP in human colon cancers by immunohistochemisty.

EXPERIMENTAL DESIGN

Sections of paraffin-embedded resected primary human colon cancer specimens from 1996 through 2001 within the Fox Chase Cancer Center tumor bank were stained with D8 antibody directed against FAP/seprase. Xenotransplanted human colorectal tumors in mice were examined similarly for stromal FAP in tumors of different sizes. Overall percentage of stromal FAP staining of the primary tumor was assessed semiquantitatively (0, 1+, 2+, 3+) and staining intensity was also graded (none, weak, intermediate, strong). Survival time and time to recurrence data were analyzed using Kaplan-Meier plots, log-rank tests, and Cox proportional hazards models.

RESULTS

One hundred thirty-eight patients with resected specimens were available for study (mean follow-up, 1,050 days) with 6 (4%) stage I, 52 (38%) stage II, 43 (31%) stage III, and 37 (27%) stage IV patients. FAP was detected in >93% of specimens. Semiquantitative staining was scored as 1+ in 28 (20%), 2+ in 52 (38%), and 3+ in 49 (35%). FAP staining intensity was graded as weak in 45 (33%), intermediate in 48 (35%), and dark in 36 (26%). Stromal FAP was found to correlate inversely with tumor stage (semiquantitative, P = 0.01; intensity, P = 0.009) and with tumor size of the tumor xenograft model (correlation coefficient, -0.61; P = 0.047), suggesting that stromal FAP may have a greater role in the early development of tumors. Furthermore, greater stromal FAP for patients with known metastatic disease was associated with a decreased survival.

CONCLUSION

Our data indicate that patients whose colon tumors have high levels of stromal FAP are more likely to have aggressive disease progression and potential development of metastases or recurrence. This study affirms the rationale for ongoing clinical investigations using FAP as a therapeutic target to disrupt FAP-driven tumor progression in patients with metastatic disease. It also suggests that the effects of FAP inhibition should be investigated in earlier-stage tumors, given its high levels and potential effect earlier in the course of the disease.

Effect of fibroblast activation protein and alpha2-antiplasmin cleaving enzyme on collagen types I, III, and IV

The circulating enzyme, alpha2-antiplasmin cleaving enzyme (APCE), has very similar sequence homology and proteolytic specificity as fibroblast activation protein (FAP), a membrane-bound proteinase. FAP is expressed on activated fibroblasts associated with rapid tissue growth as in embryogenesis, wound healing, and epithelial-derived malignancies, but not in normal tissues. Its presence on stroma suggests that FAP functions to remodel extracellular matrix (ECM) during neoplastic growth. Precise biologic substrates have not been defined for FAP, although like APCE, it cleaves alpha2-antiplasmin to a derivative more easily cross-linked to fibrin. While FAP has been shown to cleave gelatin, evidence for cleavage of native collagen, the major ECM component, remains indistinct. We examined the potential proteolytic effects of FAP or APCE alone and in concert with selected matrix metalloproteinases (MMPs) on collagens I, III, and IV. SDS-PAGE analyses demonstrated that neither FAP nor APCE cleaves collagen I. Following collagen I cleavage by MMP-1, however, FAP or APCE digested collagen I into smaller peptides. These peptides were analogous to, yet different from, those produced by MMP-9 following MMP-1 cleavage. Amino-terminal sequencing and mass spectrometry analyses of digestion mixtures identified several peptide fragments within the sequences of the two collagen chains. The proteolytic synergy of APCE in the cleavage of collagen I and III was not observed with collagen IV. We conclude that FAP works in synchrony with other proteinases to cleave partially degraded or denatured collagen I and III as ECM is excavated, and that derivative peptides might function to regulate malignant cell growth and motility.

Tumor stroma-associated antigens for anti-cancer immunotherapy

Immunotherapy has been widely investigated for its potential use in cancer therapy and it becomes more and more apparent that the selection of target antigens is essential for its efficacy. Indeed, limited clinical efficacy is partly due to immune evasion mechanisms of neoplastic cells, e.g. downregulation of expression or presentation of the respective antigens. Consequently, antigens contributing to tumor cell survival seem to be more suitable therapeutic targets. However, even such antigens may be subject to immune evasion due to impaired processing and cell surface expression. Since development and progression of tumors is not only dependent on cancer cells themselves but also on the active contribution of the stromal cells, e.g. by secreting growth supporting factors, enzymes degrading the extracellular matrix or angiogenic factors, the tumor stroma may also serve as a target for immune intervention. To this end several antigens have been identified which are induced or upregulated on the tumor stroma. Tumor stroma-associated antigens are characterized by an otherwise restricted expression pattern, particularly with respect to differentiated tissues, and they have been successfully targeted by passive and active immunotherapy in preclinical models. Moreover, some of these strategies have already been translated into clinical trials.

Antiplasmin-cleaving enzyme is a soluble form of fibroblast activation protein

Circulating antiplasmin-cleaving enzyme (APCE) has a role in fibrinolysis and appears structurally similar to fibroblast activation protein (FAP), a cell-surface proteinase that promotes invasiveness of certain epithelial cancers. To explore this potential relationship, we performed comparative structure/function analyses of the 2 enzymes. APCE from human plasma and recombinant FAP (rFAP) exhibited identical pH optima of 7.5, extinction coefficients (in(280 nm)(1%)) of 20.2 and 20.5, common sequences of tryptic peptides, and cross-reactivity with FAP antibody. APCE and rFAP are homodimers with monomeric subunits of 97 and 93 kDa. Only homodimers appear to have enzymatic activity, with essentially identical kinetics toward Met-alpha2-antiplasmin (Met-alpha2AP) and peptide substrates. APCE and rFAP cleave both Pro3-Leu4 and Pro12-Asn13 bonds of Met-alpha2AP, but relative kcat/Km values for Pro12-Asn13 are about 16-fold higher than for Pro3-Leu4. APCE and rFAP demonstrate higher kcat/Km values toward a peptide modeled on P4-P4' sequence surrounding the Pro12-Asn13 primary cleavage site than for Z-Gly-Pro-AMC and Ala-Pro-AFC substrates. These data support APCE as a soluble derivative of FAP and Met-alpha2AP as its physiologic substrate. Conversion of Met-alpha2AP by membrane or soluble FAP to the more easily fibrin-incorporable form, Asn-alpha2AP, may increase plasmin inhibition within fibrin surrounding certain neoplasms and have an impact on growth and therapeutic susceptibility.

Abrogation of fibroblast activation protein enzymatic activity attenuates tumor growth

Tumor-associated fibroblasts are functionally and phenotypically distinct from normal fibroblasts that are not in the tumor microenvironment. Fibroblast activation protein is a 95 kDa cell surface glycoprotein expressed by tumor stromal fibroblasts, and has been shown to have dipeptidyl peptidase and collagenase activity. Site-directed mutagenesis at the catalytic site of fibroblast activation protein, Ser624 --> Ala624, resulted in an approximately 100,000-fold loss of fibroblast activation protein dipeptidyl peptidase (DPP) activity. HEK293 cells transfected with wild-type fibroblast activation protein, enzymatic mutant (S624A) fibroblast activation protein, or vector alone, were inoculated subcutaneously into immunodeficient mouse to assess the contribution of fibroblast activation protein enzymatic activity to tumor growth. Overexpression of wild-type fibroblast activation protein showed growth potentiation and enhanced tumorigenicity compared with both fibroblast activation protein S624A and vector-transfected HEK293 xenografts. HEK293 cells transfected with fibroblast activation protein S624A showed tumor growth rates and tumorigenicity potential similar only to vector-transfected HEK293. In vivo assessment of fibroblast activation protein DPP activity of these tumors showed enhanced enzymatic activity of wild-type fibroblast activation protein, with only baseline levels of fibroblast activation protein DPP activity in either fibroblast activation protein S624A or vector-only xenografts. These results indicate that the enzymatic activity of fibroblast activation protein is necessary for fibroblast activation protein-driven tumor growth in the HEK293 xenograft model system. This establishes the proof-of-principle that the enzymatic activity of fibroblast activation protein plays an important role in the promotion of tumor growth, and provides an attractive target for therapeutics designed to alter fibroblast activation protein-induced tumor growth by targeting its enzymatic activity.

A novel human dendritic cell-derived C1r-like serine protease analog inhibits complement-mediated cytotoxicity

Trypsin-like serine proteases are involved in diverse biological processes such as complement activation, tissue remodeling, cellular migration, tumor invasion, and metastasis. Here we report a novel human C1r-like serine protease analog, CLSPa, derived from dendritic cells (DC). The 487-residue CLSPa protein contains a CUB domain and a serine protease domain, possessing characteristic catalytic triad but lacking typical activation/cleavage sequence. It shares great homology with complement C1r/C1s and mannose-associated serine proteases. CLSPa mRNA is widely expressed, especially abundant in placenta, liver, kidney, pancreas, and myeloid cells, which are a major resources of serine proteases. Upon stimulation by agonistic anti-CD40 Ab, TNF-alpha, or LPS, CLSPa mRNA expression was significantly up-regulated in monocytic cells and monocyte-derived immature DC. When overexpressed in 293T cells, CLSPa protein was synthesized into the culture supernatants as a secretory protein, which had an inhibitory effect on complement-mediated cytotoxicity to antibody-sensitized erythrocytes. However, CLSPa itself possesses little protease activity, but it plays an inhibitory role in other active protease catalytic processes. The identification of human CLSPa as a novel Clr-like protein might facilitate future investigation of the regulatory mechanism of CLSPa in complement pathways during inflammation.