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

Brain tumors represent 9% of all tumors and 25% of tumors in children and their incidence is increasing. Annually, five to six patients per 100,000 inhabitants are diagnosed with primary brain tumors and four to five undergo surgery for the most malignant form of brain tumors, glioblastoma multiforme, which originates from glial cells. This means that about 75% of brain tumors are already at the most malignant stage at the time of diagnosis. According to the WHO classification, tumors of neuroepithelial tissues comprise several histological types including astrocytic tumors (1). Pilocytic astrocytoma (WHO grade I) is the least malignant subtype. Low grade (WHO II) astrocytoma (A) infiltrates the tissue of origin without necessarily forming a bulky tumor mass; it has a survival time of about 10 years. Anaplastic (high-grade) astrocytoma (WHO III, AA) is characterized by an increasing rate of proliferation and mitosis and cellular pleiomorphism, with the vast majority of patients dying 2-3 years after surgery. These tumors often dedifferentiate into the highest stage of malignancy, glioblastoma multiforme (GBM), with a typically high proliferation of endothelial cells, necrosis, and a survival of only several months. GBM may also develop de novo from differentiated astrocytes, usually with a short clinical history (1, 2). The treatment of these tumors is constituted mainly by surgery and irradiation. However, because of its widespread local invasion it is very difficult to remove the tumor completely, resulting in frequent recurrences followed by death within several months. New prognostic markers, particularly for low-grade brain tumors, are needed for possible chemopreventive strategies. Proteolytic enzymes are among the proposed new prognostic factors for many types of tumors, including carcinomas and melanoma (3). This is mainly due to the fact that their increased expression plays a functional role in tumor cell migration and metastasis. Among these enzymes are also lysosomal cysteine proteinases, such as cathepsins B, L and H (4). However, it has been demonstrated that in breast (5, 6) and lung (7) carcinoma grade of malignancy and prognostic significance also depend on a balance between such enzymes and their endogenous inhibitors. The major intracellular inhibitors of cysteine proteinases are stefins A and B and altered expression of these two inhibitors has been reported in various types of malignancies (4, 8). There is limited information available on the role and prognostic relevance of cysteine proteinases including Cat B and the stefins in brain tumors (reviewed in 10). The first aim of our study was therefore to measure cathepsin B (Cat B) and its most potent intracellular inhibitor, stefin A (St A), in a series of 100 patients with brain tumors. Twenty-three (23) patients had benign tumors and 73 had malignant tumors of various histological types, including seven cases of AA and 58 cases of GBM. Immunohistochemical (IHC) staining was performed as described (9) with antibodies for Cat B (MAb 3E1) and St A (MAb C5/2) obtained from KRKA, d.d. , Ljubljana, Slovenia IHC score was determined separately for tumor cells, macrophages and endothelial cells and represented the sum of the frequency (0-3) and intensity (0-3) of staining. The overall IHC score (0-12) represented the sum of the scores in tumor and endothelial cells. It was related to other histological The International Journal of Biological Markers / Vol. 15 no. 1, pp. 90-93 © Wichtig Editore, 2000