Seprase, a membrane-type serine protease, has different expression patterns in intestinal- and diffuse-type gastric cancer

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.

Comprehensive analysis of the oncogenic and immunological role of FAP and identification of the ceRNA network in human cancers

Fibroblast activation protein-alpha (FAP) is a transmembrane serine protease involving in tissue remodeling. Previous studies report that FAP is highly expressed in certain tumors and participated in oncogenesis. However, there is still lack of systematic and in-depth analysis of FAP based on clinical big data. Here, we comprehensively map the FAP expression profile, prognostic outcome, genetic alteration, immune infiltration across over 30 types of human cancers through multiple datasets including TCGA, CPTAC, and cBioPortal. We find that FAP is up-regulated in most cancer types, and increased FAP expression is associated with advanced pathological stages or poor prognosis in several cancers. Furthermore, FAP is significantly correlated with the infiltration of cancer-associated fibroblasts, macrophages, myeloid dendritic cells, as well as endothelia cells. Immunosuppressive checkpoint proteins or cytokines expression, microsatellite instability and tumor mutational burden analysis also indicate the regulation role of FAP in tumor progression. Gene enrichment analysis demonstrates that ECM-receptor interaction as well as extracellular matrix and structure process are linked to the potential mechanism of FAP in tumor pathogenesis. The ceRNA network is also constructed and identified the involvement of LINC00707/hsa-miR-30e-5p/FAP, LINC02535/hsa-miR-30e-5p/FAP, LINC02535/hsa-miR-30d-5p/FAP, as well as AC026356.1/hsa-miR-30d-5p/FAP axis in tumor progression. In conclusion, our study offers new insights into the oncogenic and immunological role of FAP from a pan-cancer perspective, providing new clues for developing novel targeted anti-tumor strategies.

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.

Bioluminescence imaging of fibroblast activation protein-alpha in vivo and human plasma with highly sensitive probe

Fibroblast activation protein-alpha (FAPα) has emerged as a biomarker of tumor stromal fibroblasts. FAP was overexpressed in stromal fibroblasts of human malignancies and positively correlated with the depth of tumor invasion, lymphatic metastasis, distant metastases, high TNM stage and poor prognosis. However, the circulating FAP levels in the plasma of gastric cancer patients and the relationship between FAP levels and gastric cancer remain unknown. Moreover, probes with super selectivity, extremely high sensitivity, and excellent performance in quantitative detection are still lacking. Herein, we developed the bioluminescent probe BL-FAP for sensitive detection and imaging of endogenous FAP in gastric cancer cells and tissues and plasma from gastric cancer patients. The probe exhibited the high signal-to-noise ratio (15000∼fold), the excellent selectivity (FAP/DPP IV ratio and FAP/PREP ratio = 50000∼ fold), and the high sensitivity (18.1 pg/mL). BL-FAP facilitates monitoring of endogenous FAP in living cells and nude mice bearing MGC-803-luc tumors. More importantly, this probe was successfully applied to the measurement of FAP activity levels in plasma from gastric cancer patients for the first time. A significant enhancement in FAP levels was observed in patients with gastric cancer, suggesting that the FAP level may be a potential diagnostic parameter for gastric cancer.

Superiority of 68Ga-FAPI PET/CT scan in detecting additional lesions compared to 18FDG PET/CT scan in breast cancer

PURPOSE

We compared the ability of 68Ga-FAPI PET//CT with 18FDG PET/CT imaging techniques to detect additional lesions in breast cancer patients that may affect further chemotherapy options.

METHODS

A total of 48 patients with breast cancer underwent concurrent 68Ga-FAPI-04 and 18FDG PET/CT regardless of whether they had received chemotherapy or not in the last month before imaging. Both modalities were compared according to various parameters: clinical/pathological features, number of lesions detected, activity uptake (SUVmax), and the effect on the evaluation of response to treatment in the post-chemotherapy group.

RESULTS

This retrospective study included 48 patients with breast cancer (mean age 53.3 ± 11.7 years; IDC 89.6%; ILC 10.4%). In the comparison of both modalities, no statistical significance was obtained in terms of the pathological characteristics of the patients. More lesions were demonstrated in all categorized regions in 68Ga-FAPI PET/CT imaging with higher uptake values compared to 18FDG PET/CT in this study. In the treatment response evaluation of the post-chemotherapy group, 12 cases (12/24) who were evaluated as PMR, CMR, or SD according to 18FDG PET/CT results were later accepted as PD due to newly detected lesions in complementary 68Ga-FAPI PET/CT imaging and treatment of patients was managed accordingly by clinicians.

CONCLUSION

It was determined that 68Ga-FAPI PET/CT was superior to 18FDG PET/CT in terms of accuracy and it was thought that 68Ga-FAPI PET/CT could be utilized as an additional complementary imaging to 18FDG PET/CT. Moreover, 68Ga-FAPI PET/CT, with its significant theranostic potential, could become a key element in predicting the pathological response of breast cancer patients in further researches.

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.

The Role of Fibroblast Activation Protein Ligands in Oncologic PET Imaging

Fibroblast activation protein inhibitor emerges as a novel and highly promising agent for diagnostic and possibly theranostic application in various malignant and non-malignant diseases. FAPI impresses with its selective expression in several pathologies, ligand induced internalization, and presence in a large variety of malignancies. Current studies indicate that FAPI is equal or even superior to the current standard oncological tracer fluorodeoxyglucose in several oncological diseases. It seems to present lower background activity, stronger uptake in tumorous lesions and thus sharper contrasts. For improved comprehension of fibroblast activation, protein expression and clinicopathologic conditions, further studies are of essence.

[SP13786 Inhibits the Migration and Invasion of Lung Adenocarcinoma Cell A549 by Supressing Stat3-EMT via CAFs Exosomes]

背景与目的

成纤维细胞活化蛋白（fibroblast activation protein, FAP）是肿瘤相关成纤维细胞（cancer-associated fibroblasts, CAFs）的表面标志物之一，与CAFs的恶性表征关系密切，SP13786是FAP的特异性小分子抑制剂。本研究探讨SP13786作用于CAFs后，CAFs外泌体（exosomes, exo）对A549细胞迁移、侵袭的影响与机制。

方法

原代提取CAFs和癌旁成纤维细胞（peri-tumer fibroblasts, PTFs）；MTT实验检测不同浓度SP13786对CAFs增殖的影响；聚合物沉淀法提取PTFs-exo、CAFs-exo以及CAFs+SP13786-exo。将A549细胞设对照组、PTFs组、CAFs组及CAFs+SP13786组并分别以等体积的DMEM、PTFs-exo、CAFs-exo及CAFs+SP13786-exo孵育细胞。激光共聚焦实验检测A549细胞摄取外泌体的情况；免疫荧光、免疫组化和Western blot方法检测α平滑肌肌动蛋白（alpha-smooth muscle actin, α-SMA）、FAP在PTFs和CAFs中的表达及E-cadherin、N-cadherin、Slug、Stat3、P-Stat3在各组A549细胞中的表达；划痕实验和Transwell实验检测各组细胞的迁移和侵袭能力。

结果

免疫荧光、免疫组化和Western blot结果均显示α-SMA、FAP在CAFs中高表达，在PTFs中低表达（P < 0.05），表明从肺腺癌组织和癌旁组织中分别成功获得了CAFs和PTFs。MTT实验测得SP13786对于CAFs细胞的半数抑制浓度（50% inhibitory concentration, IC₅₀）约为3.3 nmol/L。免疫组化和Western blot结果显示与CAFs组相比，CAFs+SP13786组的α-SMA与FAP的表达显著降低（P < 0.05），说明抑制FAP可以显著降低CAFs的恶性表征。激光共聚焦结果显示外泌体能够被A549细胞所摄取。划痕实验与Transwell实验显示SP13786可抑制CAFs-exo对A549细胞迁移和侵袭的促进作用（P < 0.05）。与CAFs组比较，SP13786组A549细胞E-cadherin表达增多，N-cadherin与Slug表达降低（P < 0.05）；免疫荧光与Western blot显示SP13786组A549细胞的P-Stat3较CAFs组明显降低（P < 0.05），而总Stat3无显著差异。Stat3的特异性抑制剂WP1066明显抑制CAFs组A549细胞上皮间质转化（epithelial-mesenchymal transition, EMT），P-Stat3显著降低（P < 0.05），而加入WP1066后再加入SP13786-exo，P-Stat3未见进一步减低，EMT的抑制亦未见显著变化（P > 0.05）。

结论

FAP的小分子特异性抑制剂SP13786通过影响CAFs外泌体间接抑制A549细胞的迁移、侵袭，其可能机制是抑制Stat3的磷酸化从而影响A549细胞的EMT。

The role of fibroblast activation protein in health and malignancy

Fibroblast activation protein-α (FAP) is a type-II transmembrane serine protease expressed almost exclusively to pathological conditions including fibrosis, arthritis, and cancer. Across most cancer types, elevated FAP is associated with worse clinical outcomes. Despite the clear association between FAP and disease severity, the biological reasons underlying these clinical observations remain unclear. Here we review basic FAP biology and FAP's role in non-oncologic and oncologic disease. We further explore how FAP may worsen clinical outcomes via its effects on extracellular matrix remodeling, intracellular signaling regulation, angiogenesis, epithelial-to-mesenchymal transition, and immunosuppression. Lastly, we discuss the potential to exploit FAP biology to improve clinical outcomes.

The application of the fibroblast activation protein α-targeted immunotherapy strategy

Cancer immunotherapy has primarily been focused on attacking tumor cells. However, given the close interaction between tumor cells and cancer-associated fibroblasts (CAFs) in the tumor microenvironment (TME), CAF-targeted strategies could also contribute to an integrated cancer immunotherapy. Fibroblast activation protein α (FAP α) is not detectible in normal tissues, but is overexpressed by CAFs and is the predominant component of the stroma in most types of cancer. FAP α has both dipeptidyl peptidase and endopeptidase activities, cleaving substrates at a post-proline bond. When all FAP α-expressing cells (stromal and cancerous) are destroyed, tumors rapidly die. Furthermore, a FAP α antibody, FAP α vaccine, and modified vaccine all inhibit tumor growth and prolong survival in mouse models, suggesting FAP α is an adaptive tumor-associated antigen. This review highlights the role of FAP α in tumor development, explores the relationship between FAP α and immune suppression in the TME, and discusses FAP α as a potential immunotherapeutic target.

Fibroblast activation protein-α promotes the growth and migration of lung cancer cells via the PI3K and sonic hedgehog pathways

A characteristic of the epithelial-to-mesenchymal transition in cancer cells is the upregulation of mesenchymal markers. Fibroblast activation protein α (FAPα) is predominantly expressed by stromal fibroblasts. Previous studies have demonstrated that FAPα is also expressed by certain epithelium-derived cancer cells and is involved in the regulation of certain signaling pathways. One of our previous studies showed that FAPα promoted the proliferation of breast cancer cells via the phosphatidylinositol-3-kinase (PI3K) signaling pathway. In the present study, the A549 adenocarcinoma (AC) and SK-MES-1 squamous cell carcinoma (SCC) lung cancer cell lines were transfected with FAPα. The FAPα-expressing SK-MES-1 cells exhibited an increased growth rate, whereas the FAPα-expressing A549 cells exhibited a similar growth rate, compared with respective empty vector-transfected control cells. Electric cell-substrate impedance sensing (ECIS)-based attachment and wound-healing assays showed that the overexpression of FAPα markedly increased the adhesive and migratory properties of the SK-MES-1 cells but not those of the A549 cells. Additionally, inhibitors of focal adhesion kinase, agonist-induced phospholipase C, neural Wiskott-Aldrich syndrome protein, extracellular signal-regulated kinase, Rho-associated protein kinase, PI3K, and sonic hedgehog (SHH) were used to evaluate the interaction between FAPα and signaling pathways. Only the inhibitors of SHH and PI3K inhibited the increased motility of the FAPα-expressing SK-MES-1 cells. Western blot analysis confirmed the activation of PI3K/AKT and SHH/GLI family zinc finger 1 signaling in the FAPα-expressing SK-MES-1 cells. These results revealed that FAPα promoted the growth, adhesion and migration of lung SCC cells. In addition, FAPα regulated lung cancer cell function, potentially via the PI3K and SHH pathways. Further investigations are required to examine the role of FAPα in lung AC cells.

Expression levels of seprase/FAPα and DPPIV/CD26 in epithelial ovarian carcinoma

Dipeptidyl peptidase IV (DPPIV; also known as cluster of differentiation 26) and the surface-expressed protease, seprase [also known as fibroblast activation protein alpha (FAPα)], are able to degrade the extracellular matrix; therefore, they are involved in malignant cell invasion and metastasis. However, the prognostic implications of their overexpression in carcinomas remain controversial. The aim of the present study was to investigate the expression and potential prognostic effects of DPPIV and seprase in cases of ovarian carcinoma. Immunohistochemical analysis (IHC) was performed to assess the protein expression of DPPIV and seprase/FAPα in 199 patients (malignant epithelial ovarian cancer, 128; borderline ovarian tumors, 41; and benign ovarian tumors, 30). In addition, in situ hybridization was used to detect the mRNA expression levels of DPPIV and seprase in 86 malignant epithelial ovarian cancer samples. IHC revealed positive staining for seprase and DPPIV proteins in 110/128 (85.94%) and 106/128 (82.81%) patients with ovarian cancer, respectively. Seprase and DPPIV protein expression was associated with lymph node metastasis and the International Federation of Gynecology and Obstetrics stage. By contrast, no significant correlation was detected between the proteins and the patient age or histological grade and type of tumor. Immunostaining was stronger in the cancerous tissues compared with the borderline and benign tissues. Increased levels of seprase, but not DPPIV, were significantly associated with a shorter disease-free survival (P=0.033). Further analysis revealed that 96.5 (83/86) and 97.67% (84/86) of the malignant epithelial ovarian cancer samples stained positively for seprase and DPPIV mRNA, respectively. Therefore, DPPIV and seprase may be involved in the development of ovarian cancer, and that they are potential predictive markers of epithelial ovarian carcinoma.

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.

FAP-α (Fibroblast activation protein-α) is involved in the control of human breast cancer cell line growth and motility via the FAK pathway

BACKGROUND

Fibroblast Activation Protein alpha (FAP-α) or seprase is an integral membrane serine peptidase. Previous work has not satisfactorily explained both the suppression and promotion effects that have been observed in cancer. The purpose of this work was to investigate the role of FAP-α in human breast cancer. Expression of FAP-α was characterized in primary tumour samples and in cell lines, along with the effects of FAP-α expression on in vitro growth, invasion, attachment and migration. Furthermore the potential interaction of FAP-α with other signalling pathways was investigated.

RESULTS

FAP-α was significantly increased in patients with poor outcome and survival. In vitro results showed that breast cancer cells over expressing FAP-α had increased growth ability and impaired migratory ability. The growth of MDA-MB-231 cells and the adhesion and invasion ability of both MCF-7 cells and MDA-MB-231 cells were not dramatically influenced by FAP-α expression. Over-expression of FAP-α resulted in a reduction of phosphorylated focal adhesion kinase (FAK) level in both cells cultured in normal media and serum-free media. An inhibitor to FAK restored the reduced motility ability of both MCF-7exp cells and MDA-MB-231exp cells and prevented the change in phosphorylated FAK levels. However, inhibitors to PI3K, ERK, PLCΥ, NWASP, ARP2/3, and ROCK had no influence this.

CONCLUSIONS

FAP-α in significantly associated with poor outcome in patients with breast cancer. In vitro, FAP-α promotes proliferation and inhibits migration of breast cancer cells, potentially by regulating the FAK pathway. These results suggest FAP-α could be a target for future therapies.

Targeting inhibition of fibroblast activation protein-α and prolyl oligopeptidase activities on cells common to metastatic tumor microenvironments

Fibroblast activation protein (FAP), a membrane prolyl-specific proteinase with both dipeptidase and endopeptidase activities, is overexpressed by reactive stromal fibroblasts during epithelial-derived cancer growth. FAP digests extracellular matrix as tissue is remodeled during cancer expansion and may also promote an immunotolerant tumor microenvironment. Recent studies suggest that nonspecific FAP inhibitors suppress human cancer xenografts in mouse models. Prolyl oligopeptidase (POP), another prolyl-specific serine proteinase, is also elevated in many cancers and may have a regulatory role in angiogenesis promotion. FAP and POP cell-associated activities may be targets for diagnosis and treatment of various cancers, but their accessibilities to highly effective specific inhibitors have not been shown for cells important to cancer growth. Despite their frequent simultaneous expression in many cancers and their overlapping activities toward commonly used substrates, precise, separate measurement of FAP or POP activity has largely been ignored. To distinguish each of the two activities, we synthesized highly specific substrates and inhibitors for FAP or POP based on amino acid sequences surrounding the scissile bonds of their respective putative substrates. We found varying amounts of FAP and POP protein and activities on activated fibroblasts, mesenchymal cells, normal breast cells, and one breast cancer cell line, with some cells exhibiting more POP than FAP activity. Replicating endothelial cells (ECs) expressed POP but not FAP until tubulogenesis began. Targeting FAP-positive cells, especially mesenchymal stem cells and cancer-associated fibroblasts for inactivation or destruction, and inhibiting POP-producing EC may abrogate stromal invasion and angiogenesis simultaneously and thereby diminish cancer growth.

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.

Seprase: an overview of an important matrix serine protease

Seprase or Fibroblast Activation Protein (FAP) is an integral membrane serine peptidase, which has been shown to have gelatinase activity. Seprase has a dual function in tumour progression. The proteolytic activity of Seprase has been shown to promote cell invasiveness towards the ECM and also to support tumour growth and proliferation. Seprase appears to act as a proteolytically active 170-kDa dimer, consisting of two 97-kDa subunits. It is a member of the group type II integral serine proteases, which includes dipeptidyl peptidase IV (DPPIV/CD26) and related type II transmembrane prolyl serine peptidases, which exert their mechanisms of action on the cell surface. DPPIV and Seprase exhibit multiple functions due to their abilities to form complexes with each other and to interact with other membrane-associated molecules. Localisation of these protease complexes at cell surface protrusions, called invadopodia, may have a prominent role in processing soluble factors and in the degradation of extracellular matrix components that are essential to the cellular migration and matrix invasion that occur during tumour invasion, metastasis and angiogenesis.

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.

Activation of EDTA-resistant gelatinases in malignant human tumors

Among the many proteases associated with human cancer, seprase or fibroblast activation protein alpha, a type II transmembrane glycoprotein, has two types of EDTA-resistant protease activities: dipeptidyl peptidase and a 170-kDa gelatinase activity. To test if activation of gelatinases associated with seprase could be involved in malignant tumors, we used a mammalian expression system to generate a soluble recombinant seprase (r-seprase). In the presence of putative EDTA-sensitive activators, r-seprase was converted into 70- to 50-kDa shortened forms of seprase (s-seprase), which exhibited a 7-fold increase in gelatinase activity, whereas levels of dipeptidyl peptidase activity remained unchanged. In malignant human tumors, seprase is expressed predominantly in tumor cells as shown by in situ hybridization and immunohistochemistry. Proteins purified from experimental xenografts and malignant tumors using antibody- or lectin-affinity columns in the presence of 5 mmol/L EDTA were assayed for seprase activation in vivo. Seprase expression and activation occur most prevalently in ovarian carcinoma but were also detected in four other malignant tumor types, including adenocarcinoma of the colon and stomach, invasive ductal carcinoma of the breast, and malignant melanoma. Together, these data show that, in malignant tumors, seprase is proteolytically activated to confer its substrate specificity in collagen proteolysis and tumor invasion.

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.

The protease complex consisting of dipeptidyl peptidase IV and seprase plays a role in the migration and invasion of human endothelial cells in collagenous matrices

Dipeptidyl peptidase IV (DPP4/CD26) and seprase/fibroblast activation protein alpha are homologous type II transmembrane, homodimeric glycoproteins that exhibit unique prolyl peptidase activities. Human DPP4 is ubiquitously expressed in epithelial and endothelial cells and serves multiple functions in cleaving the penultimate positioned prolyl bonds at the NH(2) terminus of a variety of physiologically important peptides in the circulation. Recent studies showed a linkage between DPP4 and down-regulation of certain chemokines and mitogenic growth factors, and degradation of denatured collagens (gelatin), suggesting a role of DPP4 in the cell invasive phenotype. Here, we found the existence of a novel protease complex consisting of DPP4 and seprase in human endothelial cells that were activated to migrate and invade in the extracellular matrix in vitro. DPP4 and seprase were coexpressed with the three major protease systems (matrix metalloproteinase, plasminogen activator, and type II transmembrane serine protease) at the cell surface and organize as a complex at invadopodia-like protrusions. Both proteases were colocalized at the endothelial cells of capillaries, but not large blood vessels, in invasive breast ductal carcinoma in vivo. Importantly, monoclonal antibodies against the gelatin-binding domain of DPP4 blocked the local gelatin degradation by endothelial cells in the presence of the major metallo- and serine protease systems that modified pericellular collagenous matrices and subsequent cell migration and invasion. Thus, we have identified a novel mechanism involving the DPP4 gelatin-binding domain of the DPP4-seprase complex that facilitates the local degradation of the extracellular matrix and the invasion of the endothelial cells into collagenous matrices.

Dipeptide proline diphenyl phosphonates are potent, irreversible inhibitors of seprase (FAPα)

Dipeptidyl peptidase IV (DPP-IV) and seprase belong to a small group of membrane-bound, proline-specific serine proteases, the serine integral membrane proteases (SIMPs). Whilst DPP-IV is the most exhaustively studied peptidase in this class, relatively less is known about the inhibitor/substrate specificity of its close homolog seprase. Additionally, whereas, DPP-IV expression is largely ubiquitous, seprase expression is restricted to tumour and tissue remodelling sites in vivo. Consequently, the highly restricted expression and distribution of seprase potentially make it an excellent therapeutic target for the modulation of neoplastic invasion and metastasis. Against this background, we now wish to report on the design, synthesis, and kinetic testing of a series of dipeptide proline diphenyl phosphonates, against DPP-IV and seprase. The most potent inhibitor of DPP-IV and seprase was found to be Gly-ProP(OPh)2, which exhibited overall second-order rate constants of inactivation of 5.24 x 105 M-1 min-1 and 1.06 x 104 M-1 min-1 against DPP-IV and seprase, respectively. Both proteases displayed differing profiles of susceptibility towards the other members of the series of inhibitors synthesised. In addition, Gly-ProP(OPh)2 and Tyr-ProP(OPh)2 were found to exert a considerable, dose-dependent anti-invasive effect on the LOX melanoma cell line, in vitro.

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.

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.

Seprase promotes rapid tumor growth and increased microvessel density in a mouse model of human breast cancer

Seprase is a cell surface serine protease that is expressed to high levels by invading human breast carcinoma cells. To investigate the role of seprase in breast cancer, MDA MB-231 human mammary adenocarcinoma cells were engineered to express active seprase to high levels. All cells grow rapidly in cell culture. But differences are discovered when the cells are tested for tumorigenicity, growth, and microvessel density by implantation into the mammary fat pads of female severe combined immunodeficient mice. Control transfectants that do not express seprase grow slowly whereas cells that express seprase to high levels form fast-growing tumors that are highly vascular. Microvessel density is elevated in tumors of two different lines of seprase transfectants to 146 +/- 67.4 and 144 +/- 33.42 vessels/mm(2) as compared with 50.5 +/- 12.9 vessels/mm(2) for tumors of control-transfected cells that do not express seprase. Seprase-expressing cells are better able to attract blood vessels and exhibit rapid tumor growth.

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

Seprase is a membrane-bound serine proteinase with gelatinase activity, which may be involved in cancer invasion and metastasis. We examined seprase expression in colorectal cancer specimens obtained from 109 patients. Seprase immunoreactivity was found in cancer cells and adjacent stromal cells. Immunoblotting showed higher levels of seprase protein in colorectal cancer tissue than in normal colorectal tissue. A semiquantitative assessment of the immunohistochemistry results revealed a significant correlation between seprase expression and lymph node metastasis. These results suggested that an abundant expression of seprase in colorectal cancer tissue is associated with lymph node metastasis.