Decline in protease activities with age in the nematode Caenorhabditis elegans

The activities of 3 lysosomal proteases in the nematode Caenorhabditis elegans are markedly lower in older animals. The aspartyl protease cathepsin D declines about 10-fold from day 3 (early adulthood) to day 11 (near the mean lifespan); this reflects a net decline in the amount of cathepsin D antigen. The specific activity of the thiol protease cathepsin Ce1 declines about 2.5-fold over the same period, and the specific activity of the thiol protease cathepsin Ce2 declines about 8-fold. The activity of a new non-lysosomal protease, designated cathepsin CeX, is invariant with age. The data are consistent with the hypothesis that reduced protease activity in older animals may cause a decline in the rate of protein turnover with age, but do not prove this hypothesis.     

Destructive potential of the aspartyl protease cathepsin D in MHC class II-restricted antigen processing

Whether specific proteases influence MHC class II antigen presentation is still not clearly defined. Cathepsin D, one of the most abundant lysosomal proteases, is thought to be dispensable for MHC class II antigen presentation, yet in vitro digestions of antigen substrates with endosomes/lysosomes from antigen-presenting cells sometimes reveal a dominant role for pepstatin-sensitive aspartyl proteases of which cathepsin D is the major representative. We tested whether the aspartyl protease substrate myoglobin requires cathepsin D activity for presentation to T cells. Surprisingly, in dendritic cells (DC) lacking cathepsin D, presentation of two different myoglobin T cell epitopes was enhanced rather than hindered. This paradox is resolved by the finding that pepstatin-sensitive myoglobin processing activity persists in lysosomes from cathepsin D-null DC and that this reduced activity, most likely due to cathepsin E, is closer to the optimum level required for myoglobin antigen presentation. Our results indicate redundancy among lysosomal aspartyl proteases and show that while processing activities can be productive for MHC class II T cell epitope generation at one level, they can become destructive above an optimal level.     

Involvement of cathepsin D during tail regression in tadpoles of the common Indian tree frog, Polypedates maculatus (Anura: Rhacophoridae)

Cathepsin D, an aspartyl protease, plays a key role in the metabolic degradation of intracellular proteins in an acidic milieu of lysosomes. Proteolysis plays an essential role in anuran tail regression and a wide variety of thyroid hormone induced proteolytic enzymes have been reported to be involved in the regressing tail. The present study describes the trend of specific activity of cathepsin D in the tail of different developmental stages and immunohistochemical localization of cathepsin D during degradation of various tail tissues in the tadpoles of Polypedates maculatus. Cathepsin D has been found to be involved in the degradation of major tail tissues such as epidermis, muscle, spinal cord, notochord cells and blood cells in the regressing tail. Interestingly, it has also been found to be involved in the pre-regressing tail prior to visible tail regression. In addition, melanocytes have been described to be associated with degradation of different tail tissues.     

The role of proteolytic enzymes in cancer invasion and metastasis

The production of metastasis appears to involve a number of different proteases including the urokinase form of plasminogen activator, cathepsin B, cathepsin D and various metalloproteases. Early data implicating these proteases in metastasis were mostly indirect and based on correlation studies in animal models. More recent work, using specific protease inhibitors and antibodies against proteases to block experimental metastasis, have provided more direct evidence that proteases play a role in cancer spread. In addition, transfection of genes encoding certain proteases increases the metastatic phenotype of the recipient cells. In human tumours, a number of different proteases also correlate with metastatic potential. It is concluded that certain proteases may be new prognostic markers in cancer as well as new targets for anti-metastatic therapy.     

Impact of impurities on IC50 values of P450 inhibitors

During early drug discovery, the synthetic pathways for test compounds are not well defined and impurities in the test compounds are inevitable. Compounds undergo serial screening tests at this stage to assess their biological activities and drug-like properties. Impurities in the test compounds can produce false positive results and therefore complicate the interpretation of data. P450 inhibition is one of the screens used in the early drug discovery process to assess the potential of drug-drug interactions caused by the inhibition of P450 enzymes. The impact of impurities on P450 inhibition has not been investigated. In this study, the impact of impurities on CYP2D6 IC(50) values was evaluated using model compounds. Cimetidine was chosen as the test compound. Quinidine, fluoxetine, fluvoxamine, and ibuprofen were chosen to represent impurities as they inhibit CYP2D6 to varying degrees. The IC(50) values of these model impurities for CYP2D6 were 0.11 μM, 0.98 μM, 13.4 μM, and >100 μM, respectively. Impurities with potent CYP2D6 inhibition, such as quinidine, can significantly decrease the apparent IC(50) value for the mixture. With the addition of only 2% quinidine to cimetidine (mol/mol), the apparent IC(50) value of cimetidine decreased from 98 μM to 4.4 μM. With the addition of 10% quinidine, the apparent IC(50) decreased to 1.04 μM. Such a significant decrease in apparent IC(50) values can produce a false alert and cause the inappropriate elimination of good compounds at an early stage. Impur6ities with low inhibitory potential, such as fluvoxamine and ibuprofen, did not cause a significant change in apparent IC(50) values. An impurity can have a similar effect on the IC(50) values for inhibition of other biological activities. The effect of an impurity on apparent IC(50) values can be predicted by using a simulation curve if the potency of the impurity is characterized.     

Dissimilar attenuation of Candida albicans virulence properties by human immunodeficiency virus type 1 protease inhibitors.

The secreted aspartyl proteinase (Sap) of Candida albicans, which is believed to represent an important virulence factor of this opportunistic yeast, and the human immunodeficiency virus type 1 (HIV-1) protease, which is obligatory for the production of infectious virions, both belong to the same family of aspartyl proteinases. We have previously shown that the HIV-1 protease inhibitor Indinavir directly inhibits secretion and proteinase activity of Sap in a dose-dependent manner. Furthermore, at very high concentrations, viability of C. albicans is markedly reduced by Indinavir, indicating that HIV-1 protease inhibitors may possess antifungal activity. We thus proposed that these drugs may add to the resolution of mucosal candidiasis in HIV-1 infected subjects. We have now compared three different HIV-1 protease inhibitors. The rank order of Sap inhibition, already significant at 0.1 mg/ml for all protease inhibitors, was Ritonavir > Indinavir > Saquinavir. However, the cross-reactivity of Ritonavir to pepsin was also more pronounced compared with the other two. Indinavir did not affect Candida viability at concentrations up to 1 mg/ml, in line with our previous study. In contrast, at this concentration Saquinavir was even fungicidal as assessed by three different viability assays (colony formation assay, MTT assay, propidium iodide staining) whereas Ritonavir significantly affected the mitochondrial activity only (MTT assay). No influence on Candida viability was observed for any of the three at concentrations of 0.1 mg/ml or lower. It remains to be examined whether HIV-1 protease inhibitors or derivatives thereof may be suitable for in vivo therapy of subjects suffering from mucosal candidiasis resistant to current antimycotics.     

Synthesis and biological evaluation of 2-, 3-, and 4-acylaminocinnamyl-N-hydroxyamides as novel synthetic HDAC inhibitors

A new series of 2-, 3-, and 4-acylaminocinnamyl-N-hydroxyamides 1-3 have been prepared, and their anti-HDAC (against maize HD2, HD1-B, and HD1-A enzymes) activities have been assessed. Cinnamyl-hydroxyamides bearing acylamino substituents at the C2 position of the benzene ring (compounds 1a-g) showed very low HDAC inhibiting activities, with IC(50) values in the high micromolar range. By shifting the same acylamino groups from C2 to C3 (compounds 2a-g) as well as C4 (compounds 3a-f) position of the benzene ring, a number of highly potent HDAC inhibitors have been obtained. In the anti-HD2 assay 3c (IC(50) = 11 nM) was the most potent compound, being >11600-, 4.5-, and 10-fold more potent than sodium valproate, SAHA, and HC-toxin, respectively, and showing the same activity as trapoxin. HD1-B and HD1-A assays have been performed to screen the inhibitory action of 1-3 against mammalian class I (HD1-B) and class II (HD1-A) HDAC homologous enzymes. From the corresponding IC(50) data, a selectivity ratio has been calculated. In general, compounds 1-3 showed no or little selectivity towards the class II homologue HD1-A, the most selective being 2a with class II selectivity ratio = 4.3. About the inhibitory potency, the 4-(2-naphthoylamino)cinnamyl-N-hydroxyamide 3f showed the highest inhibiting effect against the two enzymes (IC(50-HD1-B) = 36 nM; IC(50-HD1-A) = 42 nM). Selected 2 and 3 compounds will be evaluated to determine their antiproliferative and cyto differentiating activities on HL-60 cells.     

Inhibitory activity of Drynariae rhizoma extracts on cathepsin having bone resorption activity

Effects of traditional Korean (Hanbang) medicine, Drynariae rhizoma (DR), on the protease activity of bone loss-initiation in rats and mice were investigated. Ethanol extracts-DR (EE-DR) and water extracts-DR (WE-DR) were identified as potent inhibitor of cathepsins K and L. The original WE-DR inhibits cathepsins K and L with IC50 values of 3.7 microg/ml and 4.5 microg/ml, respectively. EE-DR was more potent than that of WE-DR, because the inhibitions of cathepsin K and L increased to 0.5 microg/ml and 0.8 microg/ml, respectively. The EE-DR was proved to be the most potent. EE-DR was found to be a potent inhibitor of cathepsins K with a Ki value of 5.0 microg/ml for cathepsin K. The activity was increased by 10-fold when the assay is performed in the presence of glutathione at pH 7.0, which favors the formation of a GSH thiolate anion. Thus, it is suggested that this increase in potency is probably due to an enhanced chemical reactivity of the extract mixtures toward the thiolate of the active site of the enzyme. WE-DR exhibited time-dependet inhibition which allowed us to determine the association and dissociation rate constants with cathepsin K. Finally, EE-DR inhibits bone resorption in an in vitro assay involving mouse osteoclasts and bovine bone with an IC50 value of 70 microg/ml. WE-DR represents a new herbal formulation inhibiting cathepsin K and L activity and proteolysis of bone collagen. These results strongly suggest that DR is effective for preventing the development of bone loss induced by cathepsin K. This result also suggested that the DR is effective for bone resorptive action in bone cells.     

Proteases involved in the metabolic degradation of human interleukin-1beta by rat kidney lysosomes.

The in vitro metabolic degradation of human interleukin (IL)-1beta was studied using lysates of rat kidney lysosomes, and proteases involved in the degradation were identified. In the study of IL-1beta degradation, fluorescein isothiocyanate (FITC)-labeled IL-1beta was used as a substrate. The maximal degradation of IL-1beta occurred at pH 3.0, and the reaction was proportional to the lysosomal protein concentration and time of incubation. The degradation was stimulated by the addition of L-cysteine. The reaction was not inhibited by phenylmethanesulfonyl fluoride or EDTA, indicating that serine proteases or metalloproteases do not play a major role in the degradation process. N-Ethylmaleimide, leupeptin and E-64, inhibitors of thiol protease, inhibited the degradation of IL-1beta, by 59%-70%. Pepstatin A, an inhibitor of carboxyl protease, inhibited the degradation by 58%. Combinations of thiol and carboxyl protease inhibitors nearly completely inhibited the degradation. Bio-Gel P-10 gel filtration chromatography of in vitro reactants confirmed the ability of lysosomal proteases to degrade IL-1beta and revealed four to five peaks of degradation products. Taken together, these results indicate that thiol protease and carboxyl protease play an important role in the IL-1beta degradation process by kidney lysosomes. Leupeptin and E-64 dose dependently inhibited both cathepsin B and cathepsin L activities, and pepstatin A strongly inhibited cathepsin D activity in rat kidney lysosomes. The present results suggest that cathepsin B, cathepsin L, and cathepsin D in kidney lysosomes are involved in the metabolic degradation of human IL-1beta.     

Immunological similarity between Schistosoma and bovine cathepsin D

IgG antibodies from sera of rabbits immunized with a mixture of three synthetic peptides of highly conserved surface-exposed sequences between Schistosoma japonicum and S. mansoni cathepsin D, and a rabbit anti-bovine cathepsin D serum strongly recognized a 45 kDa molecule on immunoblots of adult S. mansoni worm saline extracts (AWSE). This recognition was abolished by immunoadsorption with two of the three selected peptides. The anti-peptide antibodies fixed onto Protein A-Sepharose specifically immunoprecipitated a S. mansoni AWSE component that was able to degrade bovine hemoglobin at pH 3.8. This reaction was inhibited by 7 microM pepstatin A, a classical aspartyl protease inhibitor, suggesting that the parasite cathepsin D was immunoprecipitated. The anti-peptide antibodies also recognized on a dot-blot assay a purified, commercially obtained bovine cathepsin D preparation but not the purified human counterpart. On the other hand, the anti-bovine cathepsin D serum recognized the two above-mentioned schistosome peptides. In addition, S. mansoni-infected patient sera recognized on immunoblots the bovine but not the human cathepsin D. These results, together with a comparative analysis of the selected peptide sequence regions between the schistosome and the two mammal enzymes, allowed us to pinpoint to one amino acid the cross-reactivity between parasite and bovine cathepsin D and the lack of it with human cathepsin D. This difference might be of relevance for immunodiagnosis.     

Isolation, partial purification and some properties of two acid proteases from adult Dirofilaria immitis

Two acid proteases were isolated from the soluble extracts of adult Dirofilaria immitis, the filarial heartworm of canines. Activity of these proteases was detected using 3H-labeled bovine alpha-casein as substrate, and they were designated Fp-I and Fp-II in order of their elution from a CM-cellulose column. The molecular weight of partially purified Fp-I was approximately 170000, and it was active between pH 4.6-5.8. The activity of Fp-I doubled in the presence of various sulfhydryl reagents at 5 mM, and it was inhibited 50-60% by the sulfhydryl inhibitors p-hydroxymercuribenzoate and iodoacetate at 1 mM, the heavy metal chelating agent o-phenanthroline at 1 mM and the peptide aldehyde protease inhibitors pepstatin (10 microM), leupeptin, antipain and chymostatin (50 microM). The molecular weight of the more extensively purified Fp-II is approximately 48000. This protease was active between pH 2.6-3.4 and was highly sensitive to inhibition by pepstatin (80% inhibition at 10 nM). Fp-II was not significantly affected by sulfhydryl reagents, sulfhydryl inhibitors, metal chelating agents or peptide aldehyde protease inhibitors other than pepstatin. These properties of dirofilarial Fp-II resemble those of mammalian cathepsin D.     

Changes of skeletal muscle proteases activities during a chronic low-frequency stimulation period

Modifications of muscular contractile patterns by chronic low-frequency stimulation induce structural, physiological, and biochemical transformations in fast-twitch fibers that cause them to act like slow-twitch muscle. During this transformation many changes in protein pattern appear and the proteolytic system may be involved in those changes. The activities of cathepsin L, B, H, D, the level of cystatin, as well as the calpain activity in rabbit fast-twitch muscle have been compared with those of slow-twitch muscle. The results show that fast-twitch muscle has lower cathepsin activities and higher calpain activities than slow-twitch muscle. Chronic low-frequency stimulation was applied for 24 days to fast-twitch muscles and changes in proteases and protease inhibitors (cystatin and calpastatin) were studied. After 7-14 days of stimulation, lysosomal cathepsin L, B, and D and cytoplasm calpain and proteosome activities increased several-fold. Involvement of the phagocyte cells in the protein fiber turnover was minimal. Although the turnover of contractile proteins during muscle electrostimulation takes place in synchrony with changes in the muscle proteolytic system, the stimulation period used did not attain the total transformation from fast- to slow-twitch muscle proteolytic pattern.     

4-Aryl-4H-chromene-3-carbonitrile derivatives: evaluation of Src kinase inhibitory and anticancer activities

Src kinase mutations and/or overexpression have been implicated in the development of a number of human cancer including colon, breast, and lung cancers. Thus, designing potent and selective Src kinase inhibitors as anticancer agents is a subject of major interest. A series of 4-aryl substituted derivatives of 2-amino-7-dimethylamino-4H-chromene-3-carbonitrile were synthesized using one-pot reaction of appropriate substituted aromatic aldehydes, malononitrile, and 3-(dimethylamino)phenol in the presence of piperidine. All 23 compounds were evaluated for inhibition of Src kinase and cell proliferation in human colon adenocarcinoma (HT-29) and leukemia (CCRF-CEM) cell lines. Among the tested compounds, 2-chlorophenyl- (4c), 3-nitrophenyl- (4h), 4-trifluoromethyphenyl- (4i), and 2,3-dichlorophenyl- (4k) substituted chromenes showed Src kinase inhibitory effect with IC(50) values of 11.1-18.3 μM. Compound 4c was relatively selective against Src (IC(50) = 11.1 μM), when compared with selected kinases, epidermal growth factor receptor (EGFR, IC(50) > 300 μM), C-terminal Src kinase (Csk, IC(50) = 101.7 μM), and lymphocyte-specific protein tyrosine kinase (Lck, IC(50) = 46.8 μM). 3-Chlorophenyl substituted thiazole (4v) and 2-chlorophenylsubstituted thiazole (4u) chromene derivatives inhibited the cell proliferation of HT-29 and CCRF-CEM by 80% and 50% respectively, at a concentration of 50 μM. The data indicate that 4H-chromene-3-carbonitrile scaffold has the potential to be optimized further for designing more potent Src kinase inhibitors and/or anticancer lead compounds.     

Destructive proteolysis by cysteine proteases in antigen presentation of ovalbumin

Most native antigens require digestion by acidic proteases in order to be recognized in the context of major histocompatibility complex class II by T helper cells (Th). We have studied the roles of three different acidic proteases, cathepsin D, cathepsin B and cathepsin L, in the processing of ovalbumin (OVA) for presentation in the context of I-A^d. We report that digestion of OVA in vitro with the aspartyl protease cathepsin D generates the epitope OVA_322–336, which is recognized by I-A^d-restricted OVA-specific Th in the presence of paraformaldehyde-fixed antigen-presenting cells (APC). In contrast, digestion of OVA with the cysteine proteases cathepsin B and L not only failed to generate an epitope, but also destroyed OVA_322–336. In the presence of fixed APC expressing I-A^d, OVA_322–336 was protected from destructive proteolysis by cathepsin L. These results illustrate the dependence of epitope selection on the intracellular proteolytic environment in APC, and suggest that mechanisms must exist for protection of epitopes from destructive proteolysis in the processing compartments.     

Anti-HIV-1 activity of antiviral compounds, as quantitated by a focal immunoassay in CD4+ HeLa cells and a plaque assay in MT-4 cells

The inhibitory effects of a series of antiviral compounds on human immunodeficiency virus type 1 (HIV-1) were evaluated in a plaque assay (PA) in MT-4 cells and a focal immunoassay (FIA) in CD4+ HeLa cells. Similar 50% inhibitory concentrations (IC50) were obtained for the sulfated polysaccharides when measured by PA or FIA: the IC50 values of dextran sulfate and pentosan polysulfate were 0.8 microgram/ml and 0.35 microgram/ml, respectively. Also, comparable IC50 values (ranging from 1.42 to 2.71 microM) were obtained for purine 2',3'-dideoxyribosides (i.e. DDA, DDI and DDG) when evaluated by PA or FIA. In contrast, the IC50 values of pyrimidine 2',3'-dideoxyribosides were invariably 4- to 10-fold lower when monitored by PA than FIA: the IC50s of AZT, D4T and DDC in the PA were 0.015, 0.094 and 0.038 microM, respectively, and in the FIA were 0.062 microM, 0.29 microM and 0.46 microM, respectively. The differential anti-HIV-1 activities found with AZT, D4T and DDC in the PA and FIA systems may at least be related in part to differences in the metabolism of the compounds (i.e. phosphorylation by thymidine kinase or 2'-deoxycytidine kinase) between MT-4 and CD4+ HeLa cells. The novel anti-HIV-1 compounds tetrahydro-imidazo[4,5,1-jk][1,4]-benzodiazepin-2(1H)-thione (TIBO) derivatives, R82150 and R82913, and the acyclouridine derivative 1-[(2-hydroxyethoxy)methyl]-6-phenylthiothymine (HEPT) were also more inhibitory to HIV-1 in the PA than FIA system. The IC50 values of R82150, R82913 and HEPT, as based on PA, were 0.005, 0.003 and 0.79 microM, respectively. Their IC50 values, as based on FIA, were 0.020 microM, 0.015 microM and 3.77 microM, respectively. The TIBO derivatives emerged as the most effective HIV-1 inhibitors of the compounds tested whether assayed by PA or FIA.     

Antiallergic activity profile in vitro of RHC 2963 and related compounds

RHC 2963 (7-methyl-pyrido (3',2':4,5)-thieno (3,2-d)-1,2,3 triazine-4(3H)-one and 20 related compounds have been investigated for their antiallergic activities in 3 in vitro models of anaphylaxis and for their effects on cyclic nucleotide phosphodiesterases (cNUC-PDE) from purified rat mast cells (RMC). Nine compounds were potent (I50 less than or equal to 80 microM) inhibitors of antigen-induced release of histamine (AIR) from RMC, 2 compounds inhibited anti-IgE-induced release of histamine from human basophils (I50 less than or equal to 60 microM) and one compound inhibited AIR from guinea pig lung slices (I50 = 55 microM). RHC 2963 was 18 times more potent than disodium cromoglycate (DSCG) as inhibitor of AIR from RMC and had an activity profile identical to that of DSCG in the following respects: loss of inhibitory activity with increasing preincubation time, tachyphylactic properties and inability to inhibit non-immunologic release of histamine induced by compound 48/80. Neither RHC 2963 nor DSCG had any effect on anti-IgE-induced release of histamine from human basophils or IgG1-mediated release of histamine from guinea pig lung. Twelve of the compounds in this chemical series were more potent than theophylline as inhibitors of cyclic AMP and/or cyclic GMP phosphodiesterase (PDE) from RMC. Paired regression analysis of the I50 values for inhibition of AIR and cNUC-PDE from RMC revealed no statistically significant correlation between the inhibition of AIR and inhibition of cAMP- or cGMP-PDE. We conclude: (1) RHC 2963 and some of the related compounds are potent inhibitors of immunologic release of histamine from RMC with a mechanism of action similar to that of DSCG, and (2) inhibition of cAMP- or cGMP-PDE by these compounds is not the biochemical mechanism by which they inhibit AIR from RMC.     

Potential biomarkers for differentiation of benign prostatic hyperplasia and prostate cancer

This study aims to evaluate the role of free/total prostate-specific antigen (PSA) ratio, serum total sialic acid level and cathepsin D activity in the differentiation of prostate cancer and benign prostatic hyperplasia (BPH). The study looked at 100 patients with BPH, 75 patients with organ-confined or locally advanced prostate cancer, and a control group of 50 healthy volunteers. Prostate cancer patients showed significantly higher total sialic acid level and cathepsin D activity and lower free/total PSA ratio than those in the BPH group. The results suggest that combined measurement of serum total sialic acid and/or cathepsin D activity with free/total PSA ratio could serve as a useful adjunct to conventional diagnostics for the differentiation of prostate cancer and BPH.     

Prognostic value of cathepsin D in breast cancer: comparison of immunohistochemical and immunoradiometric detection methods.

AIM: To test whether immunoradiometric or immunohistochemical detection of lysosomal protease cathepsin D in breast cancer is more predictive of outcome. METHODS: Tumour tissues from 270 primary breast cancer patients were evaluated for the expression of cathepsin D using immunohistochemistry (IH; paraffin embedded tissues) and an immunoradiometric assay (IRMA; cytosol from frozen tissues). Immunohistochemical scores were based on immunoreaction in tumour cells and tumour associated macrophages. RESULTS: IRMA values (cut off 40 fmol/mg cell protein) correlated significantly with IH values. Recorded incidences of positive immunoreaction in tumour cells using two different cut off values were 52% and 35%, respectively. Macrophages stained positive in 31% of tissues. Combined evaluation of tumour cells and macrophages resulted in positivity rates of 59% and 48%, respectively. Node status was the only variable found to correlate with cathepsin D expression. IH results correlated significantly with clinical outcome (median observation time 68 months) in node negative patients (n = 120) but not in node positive patients (n = 145). Cathepsin D positivity as measured by IRMA was not related to clinical outcome in either group. On multivariate analysis in the node negative group, IH detection of cathepsin D appeared to be the only independent factor indicating prognosis. For node positive patients, tumour grade, size, and receptor status were of prognostic relevance. CONCLUSIONS: Because of the simple methodology and the minimal amount of tissue used for analysis, immunohistochemistry was preferred to immunoradiometry for cathepsin D measurement; it also provided more predictive data with respect to prognosis.