Clinical and Experimental Studies of Cysteine Cathepsins and Their Inhibitors in Human Brain Tumors

Cystatin B increases autophagic flux by sustaining proteolytic activity of cathepsin B and fuels glycolysis in pancreatic cancer: CSTB orchestrates autophagy and glycolysis in PDAC

BACKGROUND

Both autophagy and glycolysis are essential for pancreatic ductal adenocarcinoma (PDAC) survival due to desmoplasia. We investigated whether targeting a hub gene which participates in both processes could be an efficient strategy for PDAC treatment.

METHODS

The expression pattern of glycolysis signatures (GS) and autophagy signatures (AS) and their correlation with cystatin B (CSTB) in PDAC were analysed. It was discovered how CSTB affected the growth, glycolysis, and autophagy of PDAC cells. We assessed competitive binding to cathepsin B (CTSB) between CSTB and cystatin C (CSTC) via immunoprecipitation (IP) and immunofluorescence (IF). Chromatin immunoprecipitation quantitative polymerase chain reaction (ChIP-qPCR) and luciferase reporter gene assays were used to unveil the mechanism underlying CSTB upregulation. The expression pattern of CSTB was examined in clinical samples and KrasG12D/+, Trp53R172H/+, Pdx1-Cre (KPC) mice.

RESULTS

GS and AS were enriched and closely associated in PDAC tissues. CSTB increased autophagic flux and provided substrates for glycolysis. CSTB knockdown attenuated the proliferation of PDAC cells and patient-derived xenografts. The liquid chromatography-tandem mass spectrometry assay indicated CSTB interacted with CTSB and contributed to the proteolytic activity of CTSB in lysosomes. IF and IP assays demonstrated that CSTB competed with CSTC to bind to CTSB. Mutation of the key sites of CSTB abolished the interaction between CSTB and CTSB. CSTB was highly expressed in PDAC due to H3K27acetylation and SP1 expression. High expression of CSTB in PDAC was observed in tissue microarray and patients' serum samples.

CONCLUSIONS

Our work demonstrated the tumorigenic roles of autophagy and glycolysis in PDAC. CSTB is a key role in orchestrating these processes to ensure energy supply of PDAC cells.

Cystatins in cancer progression: More than just cathepsin inhibitors

Cystatins are endogenous and reversible inhibitors of cysteine peptidases that are important players in cancer progression. Besides their primary role as regulators of cysteine peptidase activity, cystatins are involved in cancer development and progression through proteolysis-independent mechanisms. Mechanistic studies of cystatin function revealed that they affect all stages of cancer progression including tumor growth, apoptosis, invasion, metastasis and angiogenesis. Recently, the involvement of cystatins in the antitumor immune responses was reported. In this review, we discuss molecular mechanisms and clinical aspects of cystatins in cancer. Altered expression of cystatins in cancer resulting in harmful excessive cysteine peptidase activity has been a subject of several studies in order to find correlations with clinical outcome and therapy response. However, involvement in anti-tumor immune response and signaling cascades leading to cancer progression designates cystatins as possible targets for development of new anti-tumor drugs.

Inhibition of cathepsin L sensitizes human glioma cells to ionizing radiation in vitro through NF-κB signaling pathway

AIM

Cathepsin L, a lysosomal cysteine proteinase, is exclusively elevated in a variety of malignancies, including gliomas. In this study we investigated the relationship between cathepsin L and NF-κB, two radiation-responsive elements, in regulating the sensitivity of human glioma cells ionizing radiation (IR) in vitro.

METHODS

Human glioma U251 cells were exposed to IR (10 Gy), and the expression of cathepsin L and NF-κB was measured using Western blotting. The nuclear translocation of NF-κB p65 and p50 was analyzed with immunofluorescence assays. Cell apoptosis was examined with clonogenic assays. NF-κB transcription and NF-κB-dependent cyclin D1 and ATM transactivation were monitored using luciferase reporter and ChIP assays, respectively. DNA damage repair was investigated using the comet assay.

RESULTS

IR significantly increased expression of cathepsin L and NF-κB p65 and p50 in the cells. Furthermore, IR significantly increased the nuclear translocation of NF-κB, and NF-κB-dependent cyclin D1 and ATM transactivation in the cells. Knockdown of p65 did not change the expression of cathepsin L in IR-treated cells. Pretreatment with Z-FY-CHO (a selective cathepsin L inhibitor), or knockdown of cathepsin L significantly attenuated IR-induced nuclear translocation of NF-κB and cyclin D1 and ATM transactivation, and sensitized the cells to IR. Pretreatment with Z-FY-CHO, or knockdown of p65 also decreased IR-induced DNA damage repair and clonogenic cell survival, and sensitized the cells to IR.

CONCLUSION

Cathepsin L acts as an upstream regulator of NF-κB activation in human glioma cells and contributes to their sensitivity to IR in vitro. Inhibition of cathepsin L can sensitize the cells to IR.

IGFBP-4 anti-angiogenic and anti-tumorigenic effects are associated with anti-cathepsin B activity

Insulin-like growth factor-binding protein 4 (IGFBP-4/IBP-4) has potent IGF-independent anti-angiogenic and antitumorigenic effects. In this study, we demonstrated that these activities are located in the IGFBP-4 C-terminal protein fragment (CIBP-4), a region containing a thyroglobulin type 1 (Tg1) domain. Proteins bearing Tg1 domains have been shown to inhibit cathepsins, lysosomal enzymes involved in basement membrane degradation and implicated in tumor invasion and angiogenesis. In our studies, CIBP-4 was shown to internalize and co-localize with lysosomal-like structures in both endothelial cells (ECs) and glioblastoma U87MG cells. CIBP-4 also inhibited both growth factor-induced EC tubulogenesis in Matrigel and the concomitant increases in intracellular cathepsin B (CatB) activity. In vitro assays confirmed CIBP-4 capacity to block recombinant CatB activity. Biodistribution analysis of intravenously injected CIBP-4-Cy5.5 in a glioblastoma tumor xenograft model indicated targeted accumulation of CIBP-4 in tumors. Most importantly, CIBP-4 reduced tumor growth in this animal model by 60%. Pleiotropic anti-angiogenic and anti-tumorigenic activities of CIBP-4 most likely underlie its observed therapeutic potential against glioblastoma.

A novel photoaffinity-based probe for selective detection of cathepsin L active form

Detecting the active forms of proteases by using activity-based probes in complex proteomes has become an intensively investigated field of research over the past years because many pathogenic conditions involve alterations in protease activities. The detection of lysosomal cysteine proteases, the cathepsins, has mostly relied on the use of probes that incorporate reactive electrophilic moieties to modify a cysteine in the active site covalently. Here we report the first example of an activity-based probe that targets the cathepsins and incorporates a photoactivatable benzophenone group for covalent labelling. When tested on a set of five cathepsins (B, K, L, S and V), this probe selectively labelled the active site of cathepsin L. Furthermore, when tested on crude cell extracts, the probe specifically detected cathepsin L quantities as low as a few picomoles. This study suggests that photoaffinity labelling is a promising approach for developing highly selective and useful cathepsin L probes. In particular, this probe might allow the detection of small amounts of the secreted active cathepsin L form in the cellular microenvironment in vitro and ex vivo.

The regulation of cysteine cathepsins and cystatins in human gliomas

Cysteine cathepsins play an important role in shaping the highly infiltrative growth pattern of human gliomas. We have previously demonstrated that the activity of cysteine cathepsins is elevated in invasive glioblastoma (GBM) cells in vitro, in part due to attenuation of their endogenous inhibitors, the cystatins. To investigate this relationship in vivo, we established U87-MG xenografts in non-obese diabetic (NOD)/severe combined immunodeficiency (SCID)-enhanced green fluorescent protein (eGFP) mice. Here, tumor growth correlated with an elevated enzymatic activity of CatB both in the tumor core and at the periphery, whereas CatS and CatL levels were higher at the xenograft edge compared to the core. Reversely, StefB expression was detected in the tumor core, but it was generally absent in the tumor periphery, suggesting that down-regulation of this inhibitor correlates with in vivo invasion. In human GBM samples, all cathepsins were elevated at the tumor periphery compared to brain parenchyma. CatB was also typically associated with angiogenic endothelia and necrotic areas. StefB was mainly detected in the tumor core, whereas CysC and StefA were evenly distributed, reflecting the observations in the xenografts. However, at the mRNA level, no differences in cathepsins and cystatins were observed between the tumor center and the periphery in both human biopsies and xenografts. Interestingly, in human tumors, cathepsin and stefin transcript levels correlated with CD68 and CXCR4 levels, but not with epidermal growth factor receptor (EGFR). Moreover, we reveal for the first time that an elevated StefA mRNA level is a highly significant prognostic factor for patient survival.

Wild type p53-dependent transcriptional upregulation of cathepsin L expression is mediated by C/EBPα in human glioblastoma cells

Mutations in the tumor suppressor gene p53 are frequent in human glioblastomas. Similarly cathepsin L, a lysosomal cysteine protease, is overexpressed and secreted by most human tumors including glioblastomas. However, hitherto there is no information on whether or not the mutation(s) in the p53 gene affect(s) expression of this protease. Using human glioblastoma cell lines harboring wild type and mutant p53, we demonstrate here for the first time that only the wild type but not the mutant p53 upregulates cathepsin L expression. By transfection of promoter reporter constructs, site-directed mutagenesis and chip assays we have established that wild type p53 elevates the levels of cathepsin L in these cells. It does so directly by binding to the cathepsin L promoter and also indirectly by inducing the expression of C/EBPα, which is crucial for the transcription of this protease. In view of its role in tumorigenesis, angiogenesis and tumor cell invasion, increased expression of cathepsin L in glioblastoma cells harboring wild type p53 might confer invasive ability and growth advantage to these cells. Therefore, use of cathepsin L inhibitors could prove useful in the management of these tumors.

Differential role of cathepsins B and L in autophagy-associated cell death induced by arsenic trioxide in U87 human glioblastoma cells

Arsenic trioxide (arsenite) was the first chemotherapeutic drug to be described and is now being rediscovered in cancer treatment, including glioblastoma multiforme. Arsenite toxicity triggers autophagy in cancer cells, although final stages of the process involve executive caspases, suggesting an interplay between autophagic and apoptotic pathways that awaits to be explained at a molecular level. We evaluated the contribution of the lysosomal cathepsins (Cat) L and B, which are upregulated in glioblastomas, in the mechanism of arsenite toxicity in human glioblastoma cells. Arsenite treatment induced autophagosome formation and permeabilization of mitochondria, followed by caspase 3/7-mediated apoptosis. The autophagy inhibitor 3-methyladenine protected from arsenite toxicity, whereas bafilomycin A1 did not. Furthermore, arsenite significantly decreased CatB levels and selectively inhibited its cellular and recombinant protein activity, while not affecting CatL. However, downregulation of CatL greatly enhanced apoptosis by arsenite. Our results show that arsenite toxicity involves a complex interplay between autophagy and apoptosis in human glioblastoma cells and is associated with inhibition of CatB, and that this toxicity is highly exacerbated by simultaneous CatL inhibition. The latter points to a synergy that could be used in clinical treatment to lower the therapeutic dose, thus avoiding the toxic side effects of arsenite in glioblastoma management.

High expression of cathepsin B and plasminogen activator inhibitor type-1 are strong predictors of survival in glioblastomas

In contrast to pilocytic astrocytomas (WHO grade I gliomas) that are circumscribed and cured by surgical resection, invasion is a hallmark of grades II-IV gliomas. Proteases play a major role in the invasion process and correlations between glioma grading, survival and protease expression have been demonstrated. In this study, we have chosen to study using different technical approaches (Q-RT-PCR, in situ hybridization and immunohistochemistry) the expression of five molecules involved in extracellular matrix degradation (cathepsin B, MMP2, MMP9, uPA and PAI-1) in glioblastomas in order to determine their prognostic impact among grade IV gliomas. Pilocytic astrocytomas were used as controls. Q-RT-PCR showed that transcripts of uPA, PAI-1, cathepsin B and MMP9 were significantly more expressed in glioblastomas (n = 52), in comparison to pilocytic astrocytomas (n = 17) (P = 0.049, P < 0.0001, P = 0.03 and P < 0.0001, respectively). On both univariate and multivariate analyses, cathepsin B and PAI-1 were strong predictors of overall survival among the group of glioblastomas (P < 0.0001 and P = 0.01, respectively). Immunohistochemical expression of cathepsin B further confirmed its prognostic value in an independent cohort of patients with glioblastoma. In situ hybridization showed that uPA is detected at the invasive edge of glioblastomas, whereas PAI-1 is more abundant in microvascular proliferation and pseudo-palisading cells than at the infiltrative edges. These results suggest that cathepsin B and PAI-1 are important biomarkers for the stratification of glioblastoma patients with respect to survival.

Cathepsins B, L and cystatin C in cyst fluid of ovarian tumors

Introduction

In cancer, an extracellular and membrane bound localization of cathepsins contribute to the invasion of tumor cells at the basement membrane.

Methods

This is the first study that explored levels of cathepsins B (CatB), L (CatL) and their inhibitor cystatin C (CysC) in the cystic fluid (CF) of ovarian tumors (n = 110).

Results

CF contained considerable amounts of CatB, CatL and CysC. Remarkable differences in CatB and CatL and CysC CF levels were found between different histopathological tumor subtypes. Levels of CatB and CysC were significantly higher in CF of malignant serous tumors compared to those found in benign serous tumors (p = 0.010 and p = 0.001 respectively), whereas levels of CatL were significantly higher in CF of malignant mucinous tumors compared to those found in benign mucinous tumors (p = 0.035). CatB and CysC showed a strong correlation in the group of patients with malignant serous tumors (p < 0.001; R = 0.921) suggesting that the increase in CatB might be balanced by a corresponding increase in CysC.

Conclusion

Further studies are warranted to investigate cathepsins as possible prognostic biomarkers for the aggressiveness of ovarian cancer.

Post-translational regulation of cathepsin B, but not of other cysteine cathepsins, contributes to increased glioblastoma cell invasiveness in vitro

Cells that migrate away from a central tumour into brain tissue are responsible for inefficient glioblastoma treatment. This migratory behaviour depends partially on lysosomal cysteine cathepsins. Reportedly, the expression of cathepsins B, L and S gradually increases in the progression from benign astrocytoma to the malignant glioblastoma, although their specific roles in glioma progression have not been revealed. The aim of this study was to clarify their specific contribution to glioblastoma cell invasion. The differences between the matrix invading cells and non-invading core cells from spheroids derived from glioblastoma cell culture and from glioblastoma patients' biopsies, and embedded in type I collagen, have been studied at the mRNA, protein and cathepsin activity levels. Analyses of the two types of cells showed that the three cathepsins were up-regulated post-translationally, their specific activities increasing in the invading cells. The cystatin levels were also differentially altered, resulting in higher ratio of cathepsins B and L to stefin B in the invading cells. However, using specific synthetic inhibitors and silencing strategies revealed that only cathepsin B activity was involved in the invasion of glioblastoma cells, confirming previous notion of cathepsin B as tumour invasiveness biomarker. Our data support the concept of specific roles of cysteine cathepsins in cancer progression. Finally the study points out on the complexity of protease regulation and the need to include functional proteomics in the systems biology approaches to understand the processes associated with glioma invasion and progression.

Neural stem cell markers, nestin and musashi proteins, in the progression of human glioma: correlation of nestin with prognosis of patient survival

BACKGROUND

The IF protein nestin and the RNA-binding protein musashi are expressed by neural progenitor cells during CNS development. Their expression in glial tumors was evaluated by immunohistochemistry, and the histopathological scores correlated with levels of cysteine cathepsins that are known prognostic markers in several tumors.

METHODS

The levels of nestin, musashi, and cathepsins B and L were assessed by immunohistochemical analysis of biopsies from 87 patients with primary CNS tumors. To confirm the immunohistochemical data, nestin expression was analyzed by real-time PCR in 12 brain tumor biopsies. The exact location of nestin-positive cells was determined by mapping the distribution of nestin in a highly invasive human glioma xenograft model.

RESULTS

Immunostaining revealed nestin to be expressed in 95.8% and musashi in 80% of the patient biopsies. The total IHC score for nestin was significantly higher in high- than in low-grade tumors (P < .0001). No difference was observed for musashi (P = .11). Real-time PCR of nestin expression confirmed the immunohistochemical data. Nestin expression was shown to be a strong prognostic marker for decreased overall survival (P = .0001), whereas musashi expression has no prognostic significance. Moreover, nestin was shown by Cox regression analysis to be a stronger prognostic marker than cathepsins B and L. IHC staining of nestin in a xenograft model showed that its expression is localized mainly in the invasive tumor cells at the tumor periphery.

CONCLUSIONS

Nestin is shown to be a strong prognostic marker for glioma malignancy. The presented data links the invasive glioma cells to CNS precursor cells, indicating that the most malignant cells in the gliomas may well be closely related to the glioma stem cells.

Towards novel anti-cancer strategies based on cystatin function

Cystatins have recently emerged as important players in a multitude of physiological and patho-physiological settings that range from cell survival and proliferation, to differentiation, cell signaling and immunomodulation. This group of cysteine protease inhibitors forms a large super-family of proteins composed of one, two, three, and, in some species, more than three cystatin domains. Over the last 20 years or so, members of the cystatin super-family have been primarily explored with respect to their capacity to inhibit intracellular cysteine proteases. Yet, this classical mode of action does not fully explain their remarkably diverse biological functions. Due to the space limitations, the author will discuss here the most recent findings that suggest that some of the single-domain, cytoplasmic and cell-secreted cystatins may play important roles in the promotion or suppression of tumor growth, invasion and metastasis. Based on the present understanding of cystatin function, novel avenues for anti-cancer strategies are proposed.

Proteases and glioma angiogenesis

Angiogenesis, the process by which new branches sprout from existing vessels, requires the degradation of the vascular basement membrane and remodeling of the ECM in order to allow endothelial cells to migrate and invade into the surrounding tissues. Serine, metallo, and cysteine proteinases are 3 types of a family of enzymes that proteolytically degrade various components of extracellular matrix. These proteases release various growth factors and also increase adhesive molecules and signaling pathway molecules upon their activation, which plays a significant role in angiogenesis. Downregulation of these molecules by antisense/siRNA or synthetic inhibitors decreases the levels of these molecules, inhibits the release of growth factors, and decreases the levels of various signaling pathway molecules, thereby leading to the inhibition of angiogenesis. Furthermore, MMPs degrade specific substrates and release angiogenic inhibitors which inhibit angiogenesis. Downregulation of 2 molecules, such as uPA and uPAR, uPAR and MMP-9, or Cathepsin B and MMP-9, are more effective to inhibit angiogenesis rather than downregulation of single molecules. However, careful testing of these combinations are most important because multiple effects of these combinations play a significant role in angiogenesis.

Cysteine cathepsins in human cancer

Proteases play causal roles in the malignant progression of human tumors. This review centers on the roles in this process of cysteine cathepsins, i.e., peptidases belonging to the papain family (C1) of the CA clan of cysteine proteases. Cysteine cathepsins, most likely along with matrix metalloproteases (MMPs) and serine proteases, degrade the extracellular matrix, thereby facilitating growth and invasion into surrounding tissue and vasculature. Studies on tumor tissues and cell lines have shown changes in expression, activity and distribution of cysteine cathepsins in numerous human cancers. Molecular, immunologic and pharmacological strategies to modulate expression and activity of cysteine cathepsins have provided evidence for a causal role for these enzymes in tumor progression and invasion. Clinically, the levels, activities and localization of cysteine cathepsins and their endogenous inhibitors have been shown to be of diagnostic and prognostic value. Understanding the roles that cysteine proteases play in cancer could lead to the development of more efficacious therapies.

Cathepsin L in glioma progression: Comparison with cathepsin B

OBJECTIVE

Lysosomal cysteine cathepsins have been implicated in tumor progression. This study is aimed to reveal differential expression and compare the prognostic significance of cathepsins B and L in glioma patients.

METHODS

The histological slides of 82 patients with primary astrocytic tumors were reviewed. We evaluated the immunostaining of the cathepsins in tumor and endothelial cells.

RESULTS

Cathepsins B and L stained positive in 98 and 88% of cases, respectively. The total score was significantly higher in malignant than in benign tumors, both for cathepsin B (p<0.001) and for cathepsin L (p<0.01). The IHC score in endothelial cells in the malignant group was significantly higher only for cathepsin B (p<0.0001). Survival analysis indicated that in contrast to the prognostic significance of total cathepsin B and endothelial cells associated cathepsin B for shorter patients' survival, the prognostic role of cathepsin L was not confirmed.

CONCLUSION

Cathepsin L is preferentially expressed in tumor cells, increasing with glioma progression, but is not significantly associated with new vasculature of glioblastoma. In contrast to cathepsin B, cathepsin L has no prognostic impact, suggesting different roles of the two cathepsins in glioma progression.

Selective suppression of cathepsin L by antisense cDNA impairs human brain tumor cell invasion in vitro and promotes apoptosis

Invasion and metastasis of certain tumors are accompanied by increased mRNA protein levels and enzymatic activity of cathepsin L. Cathepsin L has also been suggested to play a role in the proteolytic cascades associated with apoptosis. To investigate the role of cathepsin L in brain tumor invasion and apoptosis, the human glioma cell line, IPTP, was stably transfected with full-length antisense and sense cDNA of cathepsin L. Down-regulation of cathepsin L by antisense cDNA significantly impaired (up to 70%) glioma cell invasion in vitro and markedly increased glioma cell apoptosis induced by staurosporine. Compared to control and parental cell lines, antisense down-regulation of cathepsin L was associated with an earlier induction of caspase-3 activity. Up-regulation of cathepsin L activity by sense cDNA was associated with reduced apoptosis and later induction of caspase-3 activity. Moreover, down-regulation of cathepsin L lowered the expression of antiapoptotic protein Bcl-2, whereas up-regulation increased the expression of Bcl-2, indicating that cathepsin L acts upstream of caspase-3. These data show that cathepsin L is an important protein mediating the malignancy of gliomas and its inhibition may diminish their invasion and lead to increased tumor cell apoptosis by reducing apoptotic threshold.

Increase of Anti-Metastatic Efficacy by Selectivity- But Not Affinity-Optimization of Synthetic Serine Protease Inhibitors

Although tumors frequently show elevated protease activities, the concept of anti-proteolytic cancer therapy has lost momentum after failure of clinical trials with broad-spectrum matrix metalloproteinase inhibitors. Thus we need to adapt our design strategies for protease inhibitors. Here, we employed a series of seven structurally fine-modulated and pharmacokinetically closely related synthetic 4-amidinobenzylamine-based inhibitors with distinct selectivity for prototypical serine proteases in a murine T cell lymphoma liver metastasis model. This in vivo screening revealed efficacy of urokinase inhibitors but no correlation between urokinase selectivity or affinity and anti-metastatic effect. In contrast, factor Xa-selective inhibitors were more potent, demonstrating factor Xa or a factor Xa-like serine protease likely to be more determinant in this model. Factor Xa selectivity, but not affinity, significantly improved anti-metastatic efficacy. For example, factor Xa inhibitors CJ-504 and CJ-510 exert similar affinity for factor Xa (K(i)=14 nM versus 8.8 nM) but CJ-504 was 70-fold more selective for factor Xa. This correlated with higher anti-metastatic efficacy (58.8% with CJ-504; 28.2% with CJ-510). Our results show that among the protease inhibitors employed that have affinities in the nanomolar range, the strategy of selectivity-optimization is superior to further improvement of affinity to significantly enhance anti-metastatic efficacy. This appreciation may be important for the future rational design of new anti-proteolytic agents for cancer therapy.

Cathepsins B and L are markers for clinically invasive types of meningiomas

OBJECTIVE

Meningiomas are benign neoplasms that derive from coverings of the brain. Approximately 10% of benign tumors progress into atypical, malignant tumors, thus constituting a subset of histopathologically benign tumors that are clinically invasive. The aim of this study was to evaluate cathepsins B and L and their inhibitors as new prognostic factors that could distinguish malignant from benign forms of meningiomas.

METHODS

Using immunohistochemical analysis and specific monoclonal antibodies, we evaluated the levels of cathepsins B and L and the levels of the endogenous cysteine proteinase inhibitors stefin A and cystatin C in 88 meningiomas. Immunohistochemical scores were determined as the sum of the frequency (0-3) and intensity (0-3) of immunolabeling of the tumor cells.

RESULTS

Of the 88 tumors studied, 67 were benign meningiomas and 21 were atypical meningiomas. Among the benign group, nine tumors had certain features of malignancy. These tumors were classified as border benign meningiomas, and the rest were classified as clear benign meningiomas. A high immunohistochemical score (4-6) for cathepsin B was more frequent in atypical tumors than in clear benign tumors (P < 0.001). Compared with clear benign tumors, higher cathepsin B immunohistochemical scores were found in atypical tumors (P < 0.001) and border benign tumors (P < 0.03). No statistical difference in immunohistochemical staining of cathepsin B was found between atypical meningiomas and border benign meningiomas. Higher expression of cathepsin L was found in atypical tumors as compared with clear benign tumors (P < 0.03), but it was not observed in border benign as compared with clear benign meningiomas. No immunostaining for stefin A and cystatin C was detected in any of the tumors.

CONCLUSION

We show that the levels of cathepsin B and cathepsin L antigens are significantly higher in invasive types of benign meningioma. Specifically, cathepsin B may be used as a diagnostic marker to distinguish histomorphologically benign but invasive meningiomas from histomorphologically clear benign tumors.