Cathepsins B and D Activity and Activity Ratios in Normal Ovaries, Benign Ovarian Neoplasms, and Epithelial Ovarian Cancer

Current insights into the metastasis of epithelial ovarian cancer - hopes and hurdles

BACKGROUND

Ovarian cancer is the most lethal gynecologic cancer and the fifth leading cause of cancer-related mortality in women worldwide. Despite various attempts to improve the diagnosis and therapy of ovarian cancer patients, the survival rate for these patients is still dismal, mainly because most of them are diagnosed at a late stage. Up to 90% of ovarian cancers arise from neoplastic transformation of ovarian surface epithelial cells, and are usually referred to as epithelial ovarian cancer (EOC). Unlike most human cancers, which are disseminated through blood-borne metastatic routes, EOC has traditionally been thought to be disseminated through direct migration of ovarian tumor cells to the peritoneal cavity and omentum via peritoneal fluid. It has recently been shown, however, that EOC can also be disseminated through blood-borne metastatic routes, challenging previous thoughts about ovarian cancer metastasis.

CONCLUSIONS

Here, we review our current understanding of the most updated cellular and molecular mechanisms underlying EOC metastasis and discuss in more detail two main metastatic routes of EOC, i.e., transcoelomic metastasis and hematogenous metastasis. The emerging concept of blood-borne EOC metastasis has led to exploration of the significance of circulating tumor cells (CTCs) as novel and non-invasive prognostic markers in this daunting cancer. We also evaluate the role of tumor stroma, including cancer associated fibroblasts (CAFs), tumor associated macrophages (TAMs), endothelial cells, adipocytes, dendritic cells and extracellular matrix (ECM) components in EOC growth and metastasis. Lastly, we discuss therapeutic approaches for targeting EOC. Unraveling the mechanisms underlying EOC metastasis will open up avenues to the design of new therapeutic options. For instance, understanding the molecular mechanisms involved in the hematogenous metastasis of EOC, the biology of CTCs, and the detailed mechanisms through which EOC cells take advantage of stromal cells may help to find new opportunities for targeting EOC metastasis.

PDMS-PMOXA-Nanoparticles Featuring a Cathepsin B-Triggered Release Mechanism

Background: It was our intention to develop cathepsin B-sensitive nanoparticles for tumor-site-directed release. These nanoparticles should be able to release their payload as close to the tumor site with a decrease of off-target effects in mind. Cathepsin B, a lysosomal cysteine protease, is associated with premalignant lesions and invasive stages of cancer. Previous studies have shown cathepsin B in lysosomes and in the extracellular matrix. Therefore, this enzyme qualifies as a trigger for such an approach. Methods: Poly(dimethylsiloxane)-b-poly(methyloxazoline) (PDMS-PMOXA) nanoparticles loaded with paclitaxel were formed by a thin-film technique and standard coupling reactions were used for surface modifications. Despite the controlled release mechanism, the physical properties of the herein created nanoparticles were described. To characterize potential in vitro model systems, quantitative polymerase chain reaction and common bioanalytical methods were employed. Conclusions: Stable paclitaxel-loaded nanoparticles with cathepsin B digestible peptide were formed and tested on the ovarian cancer cell line OVCAR-3. These nanoparticles exerted a pharmacological effect on the tumor cells suggesting a release of the payload.

FRET Imaging of Enzyme-Responsive HPMA Copolymer Conjugate

Fluorescence resonance energy transfer (FRET) is applied to investigate the enzyme-responsive payload release from a macromolecular therapeutic. The donor Cy5 is attached to the N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer backbone and the acceptor Cy7 is bound to the termini of enzyme-sensitive peptide side chains. Upon exposure to an enzyme, the bond between the peptide and Cy7 is cleaved, thereby leading to the loss of FRET signal. This enzyme response is visualized at the cell, tissue and whole-body levels. The in vitro results demonstrate that high expression of cathepsin B in tumor cells induces effective release of the drug model from conjugates resulting in a high concentration of payload inside tumor cells. The in vivo and ex vivo images show that the conjugate releases drug model faster in the ovarian tumor than in the normal tissues. The information will enhance the understanding of enzyme-responsive polymer carriers and help to shape their design.

Lessons learned from imaging mouse ovarian tumors: the route of probe injection makes a difference

Patients with ovarian cancer often develop small metastatic lesions in their peritoneal cavities. Fluorescent-imaging probes that can highlight these small lesions have significant value for guiding procedures and treatment decisions. In this animal study, we demonstrated that intraperitoneal (IP) delivery of a protease-sensitive fluorescent probe resulted in the labeling of all tumors regardless of their sizes with low background signals in organs. Conversely, intravenous (IV) injections of the probe resulted in high signals in most organs and large tumors (>5 mm) but not in any of the small lesions (<2 mm).

Combined in vivo molecular and anatomic imaging for detection of ovarian carcinoma-associated protease activity and integrin expression in mice

Most patients with epithelial ovarian cancer (EOC) experience drug-resistant disease recurrence. Identification of new treatments is a high priority, and preclinical studies in mouse models of EOC may expedite this goal. We previously developed methods for magnetic resonance imaging (MRI) for tumor detection and quantification in a transgenic mouse model of EOC. The goal of this study was to determine whether three-dimensional (3D) fluorescence molecular tomography (FMT) and fluorescent molecular imaging probes could be effectively used for in vivo detection of ovarian tumors and response to therapy. Ovarian tumor-bearing TgMISIIR-TAg mice injected with fluorescent probes were subjected to MRI and FMT. Tumor-specific probe retention was identified in vivo by alignment of the 3D data sets, confirmed by ex vivo fluorescent imaging and correlated with histopathologic findings. Mice were treated with standard chemotherapy, and changes in fluorescent probe binding were detected by MRI and FMT. Ovarian tumors were detected using probes specific for cathepsin proteases, matrix metalloproteinases (MMPs), and integrin α(v)β(3). Cathepsin and integrin α(v)β(3) probe activation and retention correlated strongly with tumor volume. MMP probe activation was readily detected in tumors but correlated less strongly with tumor volume. Tumor regression associated with response to therapy was detected and quantified by serial MRI and FMT. These results demonstrate the feasibility and sensitivity of FMT for detection and quantification of tumor-associated biologic targets in ovarian tumors and support the translational utility of molecular imaging to assess functional response to therapy in mouse models of EOC.

Multi-conformation 3D QSAR study of benzenesulfonyl-pyrazol-ester compounds and their analogs as cathepsin B inhibitors

Cathepsin B has been found being responsible for many human diseases. Inhibitors of cathepsin B, a ubiquitous lysosomal cysteine protease, have been developed as a promising treatment for human diseases resulting from malfunction and over-expression of this enzyme. Through a high throughput screening assay, a set of compounds were found able to inhibit the enzymatic activity of cathepsin B. The binding structures of these active compounds were modeled through docking simulation. Three-dimensional (3D) quantitative structure-activity relationship (QSAR) models were constructed using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) based on the docked structures of the compounds. Strong correlations were obtained for both CoMFA and CoMSIA models with cross-validated correlation coefficients (q²) of 0.605 and 0.605 and the regression correlation coefficients (r²) of 0.999 and 0.997, respectively. The robustness of these models was further validated using leave-one-out (LOO) method and training-test set method. The activities of eight (8) randomly selected compounds were predicted using models built from training set of compounds with prediction errors of less than 1 unit for most compounds in CoMFA and CoMSIA models. Structural features for compounds with improved activity are suggested based on the analysis of the CoMFA and CoMSIA contour maps and the property map of the protein ligand binding site. These results may help to provide better understanding of the structure-activity relationship of cathepsin B inhibitors and to facilitate lead optimization and novel inhibitor design. The multi-conformation method to build 3D QSAR is very effective approach to obtain satisfactory models with high correlation with experimental results and high prediction power for unknown compounds.

QSAR models for predicting cathepsin B inhibition by small molecules--continuous and binary QSAR models to classify cathepsin B inhibition activities of small molecules

Cathepsin B is a potential target for the development of drugs to treat several important human diseases. A number of inhibitors targeting this protein have been developed in the past several years. Recently, a group of small molecules were identified to have inhibitory activity against cathepsin B through high throughput screening (HTS) tests. In this study, traditional continuous and binary QSAR models were built to classify the biological activities of previously identified compounds and to distinguish active compounds from inactive compounds for drug development based on the calculated molecular and physicochemical properties. Strong correlations were obtained for the continuous QSAR models with regression correlation coefficients (r²) and cross-validated correlation coefficients (q²) of 0.77 and 0.61 for all compounds, and 0.82 and 0.68 for the compound set excluding 3 outliers, respectively. The models were further validated through the leave-one-out (LOO) method and the training-test set method. The binary models demonstrated a strong level of predictability in distinguishing the active compounds from inactive compounds with accuracies of 0.89 and 0.94 for active and inactive compounds, respectively, in non-cross-validated models. Similar results were obtained for the cross-validated models. Collectively, these results demonstrate the models’ ability to discriminate between active and inactive compounds, suggesting that the models may be used to pre-screen compounds to facilitate compound optimization and to design novel inhibitors for drug development.

Computational analysis of the cathepsin B inhibitors activities through LR-MMPBSA binding affinity calculation based on docked complex

Cathepsin B, a ubiquitous lysosomal cysteine protease, is involved in many biological processes related to several human diseases. Inhibitors targeting the enzyme have been investigated as possible diseases treatments. A set of 37 compounds were recently found active in a high throughput screening assay to inhibit the catalytic activity of Cathepsin B, with chemical structures and biological test results available to the public in the PubChem BioAssay Database (AID 820). In this study, we compare these experimental activities to the results of theoretical predictions from binding affinity calculation with a LR-MM-PNSA approach based on docked complexes. Strong correlations (r(2) = 0.919 and q(2) = 0.887 for the best) are observed between the theoretical predictions and experimental biological activity. The models are cross-validated by four independent predictive experiments with randomly split compounds into training and test sets. Our results also show that the results based on protein dimer show better correlations with experimental activity when compared to results based on monomer in the in silico calculations.

Trial of the cysteine cathepsin inhibitor JPM-OEt on early and advanced mammary cancer stages in the MMTV-PyMT-transgenic mouse model

Recent data suggest proteases of the papain-like cysteine cathepsin family as molecular targets for cancer therapy. Here, we report the treatment of polyoma middle T oncogene-induced breast cancers in mice with the cell-permeable broad-spectrum cysteine cathepsin inhibitor JPM-OEt. Up to 100 mg/kg inhibitor was intraperitoneally injected once per day in two trials on early and advanced cancers. In both trials, transient delays in tumour growth were observed. However, at the endpoint of both experiments no significant differences in tumour weights, histopathology and lung metastasis were found between the inhibitor and the control group. The invasive strand formation of collagen I-embedded tumour cell spheroids generated from primary tumours of inhibitor-treated mice in the early cancer trial could be inhibited in vitro by JPM-OEt; a result arguing against induction of resistance to the inhibitor. Measurement of cysteine cathepsin activities in tissue extracts after intraperitoneal injection of JPM-OEt revealed effective inhibition of cysteine cathepsins in pancreas, kidneys and liver, while activities in mammary cancers and in lungs were not significantly affected. We conclude that the pharmacokinetic properties of JPM-OEt, which result in poor bioavailability, may prohibit its use for stand-alone treatment of solid mammary cancers and their lung metastases.

Identification of novel bovine cumulus cell molecular markers predictive of oocyte competence: functional and diagnostic implications

The present study was undertaken to discover molecular markers in bovine cumulus cells predictive of oocyte competence and to elucidate their functional significance. Differences in RNA transcript abundance in cumulus cells harvested from oocytes of adult versus prepubertal animals (a model of poor oocyte quality) were identified by microarray analysis. Four genes of interest encoding for the lysosomal cysteine proteinases cathepsins B, S, K, and Z and displaying greater transcript abundance in cumulus cells surrounding oocytes harvested from prepubertal animals were chosen for further investigation. Greater mRNA abundance for such genes in cumulus cells of prepubertal oocytes was confirmed by real-time RT-PCR. Elevated transcript abundance for cathepsins B, S, and Z also was observed in cumulus cells surrounding adult metaphase II oocytes that developed to the blastocyst stage at a low percentage following parthenogenetic activation versus those that developed at a high percentage. Functional significance of cumulus cell cathepsin expression to oocyte competence was confirmed by treatment of cumulus-oocyte complexes during in vitro oocyte maturation with a cell-permeable cysteine proteinase (cathepsin) inhibitor. Inhibitor treatment decreased apoptotic nuclei in the cumulus layer and enhanced development of parthenogenetically activated and in vitro-fertilized adult oocytes to the blastocyst stage. Stimulatory effects of inhibitor treatment during meiotic maturation on subsequent embryonic development were not observed when oocytes were matured in the absence of cumulus cells. The present results support a functional role for cumulus cell cathepsins in compromised oocyte competence and suggest that cumulus cell cathepsin mRNA abundance may be predictive of oocyte quality.

Endometrial carcinoma expresses an increased cathepsin B/D ratio

OBJECTIVES

Cathepsins B and D belong to a family of proteases involved in tumor invasion and metastasis. As such they may function as biomarkers for the aggressiveness of a given tumor. We examined the enzymatic activity of these proteins as well as the cellular and extracellular distribution of cathepsins B and D.

METHODS

39 snap frozen tissue samples were assayed for activity fluorometrically with cathepsin-specific peptide substrates in combination with specific inhibitors. 4 groups were established: benign tissue, stage I/grade 1, stage i/grade 3, and stage IIIC/any grade. IHC staining for cathepsin B with the percentage of counterstained enzyme calculated from each specimen.

RESULTS

A significantly increased level of cathepsin B activity was seen in malignant tissue specimens when compared to benign tissue. The cathepsin B/D ratio confirmed and was required to detect the significance of this distinction for each malignant group when compared to benign samples. There were no differences in cathepsin B or D expression detected between the various malignant groups. IHC staining for cathepsin B was more diffuse in the malignant tissues.

CONCLUSIONS

Malignant endometrium displays increased cathepsin B activity when compared benign samples. The cathepsin B/D ratio is increased for each of the malignant groups studied when compared directly to benign endometrium. The cathepsin B/D ratio cannot be utilized to distinguish the stage or grade between any of the malignant groups studied. This ratio may serve to distinguish malignant from benign tumor samples and may be a constitutive change in the malignant transformation.