Functional imaging of proteolysis: stromal and inflammatory cells increase tumor proteolysis

The underlying basement membrane is degraded during progression of breast and colon carcinoma. Thus, we imaged degradation of a quenched fluorescent derivative of basement membrane type IV collagen (DQ-collagen IV) by living human breast and colon tumor spheroids. Proteolysis of DQ-collagen IV by HCT 116 and HKh-2 human colon tumor spheroids was both intracellular and pericellular. In contrast, proteolysis of DQ-collagen IV by BT20 human breast tumor spheroids was pericellular. As stromal elements can contribute to proteolytic activities associated with tumors, we also examined degradation of DQ-collagen IV by human monocytes/macrophages and colon and breast fibroblasts. Fibroblasts themselves exhibited a modest amount of pericellular degradation. Degradation was increased 4-17-fold in cocultures of fibroblasts and tumor cells as compared to either cell type alone. Inhibitors of matrix metalloproteinases, plasmin, and the cysteine protease, cathepsin B, all reduced degradation in the cocultures. Monocytes did not degrade DQ-collagen IV; however, macrophages degraded DQ-collagen IV intracellularly. In coculture of tumor cells, fibroblasts, and macrophages, degradation of DQ-collagen IV was further increased. Imaging of living tumor and stromal cells has, thus, allowed us to establish that tumor proteolysis occurs pericellularly and intracellularly and that tumor, stromal, and inflammatory cells all contribute to degradative processes.     

Cathepsin B inhibitors: Further exploration of the nitroxoline core

Human cathepsin B is a cysteine protease with many house-keeping functions, such as intracellular proteolysis within lysosomes. Its increased activity and expression have been strongly associated with many pathological processes, including cancers. We present here the design and synthesis of novel derivatives of nitroxoline as inhibitors of cathepsin B. These were prepared either by omitting the pyridine part, or by modifying positions 2, 7, and 8 of nitroxoline. All compounds were evaluated for their ability to inhibit endopeptidase and exopeptidase activities of cathepsin B. For the most promising inhibitors, the ability to reduce extracellular and intracellular collagen IV degradation was determined, followed by their evaluation in cell-based in vitro models of tumor invasion. The presented data show that we have further defined the structural requirements for cathepsin B inhibition by nitroxoline derivatives and provided additional knowledge that could lead to non-peptidic compounds with usefulness against tumor progression.     

Peptidomimetic 2-cyanopyrrolidines as potent selective cathepsin L inhibitors

Cathepsins have been found to have important physiological roles. The implication of cathepsin L in various types of cancers is well established. In a search for selective cathepsin L inhibitors as anticancer agents, a series of 2-cyanoprrolidine peptidomimetics, carrying a nitrile group as warhead, were designed. Two series of compounds, one with a benzyl moiety and a second with an isobutyl moiety at P₂ position of the enzyme were synthesized. The synthesized compounds were evaluated for inhibitory activity against human cathepsin L and cathepsin B. Although, none of the compounds showed promising inhibitory activity, (E)N-{(S)1-[(S)2-cyano-1-pyrrolidinecarbonyl]-3-methylbutyl}-2,3-diphenylacrylamide (24) with an isobutyl moiety at P₂ was found to show selectivity as a cathepsin L inhibitor (Ki 5.3 μM for cathepsin L and Ki > 100 μM for cathepsin B). This compound could act as a new lead for the further development of improved inhibitors within this inhibitor type.     

NBCn1 and NHE1 expression and activity in ΔNErbB2 receptor-expressing MCF-7 breast cancer cells: Contributions to pHi regulation and chemotherapy resistance

Altered pH-regulatory ion transport is characteristic of many cancers; however, the mechanisms and consequences are poorly understood. Here, we investigate how a truncated, constitutively active ErbB2 receptor (ΔNErbB2) common in breast cancer impacts on the Na⁺/H⁺-exchanger NHE1 and the Na⁺,HCO₃⁻-cotransporter NBCn1 in MCF-7 human breast cancer cells and address the roles of these transporters in chemotherapy resistance. Upon ΔNErbB2 expression, mRNA and protein levels of NBCn1, yet not of NHE1, increased several-fold, and the localization of both transporters was altered paralleling extensive morphological changes. The rate of pH_i recovery after acid loading increased by 50% upon ΔNErbB2 expression. Knockdown and pharmacological inhibition confirmed the involvement of both NHE1 and NBCn1 in acid extrusion. NHE1 inhibition or knockdown sensitized ΔNErbB2-expressing cells to cisplatin-induced programmed cell death (PCD) in a caspase-, cathepsin-, and reactive oxygen species-dependent manner. NHE1 inhibition augmented cisplatin-induced caspase activity and lysosomal membrane permeability followed by cysteine cathepsin release. In contrast, NBCn1 inhibition attenuated cathepsin release and had no net effect on viability. These findings warrant studies of NHE1 as a potential target in breast cancer and demonstrate that in spite of their similar transport functions, NHE1 and NBCn1 serve different functions in MCF-7 cells.     

Fluorescent microplate assay for cancer cell-associated cathepsin B.

Cathepsin B and in particular cell-surface and secreted cathepsin B has been implicated in the invasive and metastatic phenotype of numerous types of cancer. We describe here a method to easily survey cancer cell lines for cathepsin B activity using the highly selective substrate Z-Arg-Arg-AMC. Intact human U87 glioma cells hydrolyze Z-Arg-Arg-AMC with a Km of 460 microM at pH 7.0 and 37 degrees C. This is nearly the same as the Km of 430 microM obtained with purified cathepsin B assayed under the same conditions. The pericellular (i.e. both cell-surface and released) cathepsin B activity was inhibited by the cysteine protease inhibitors E-64, leupeptin, Mu-Np2-HphVS-2Np, Mu-Leu-HpHVSPh and the cathepsin B selective inhibitor Mu-Tyr(3,5 I2)-HphVSPh with IC50 values similar to those observed for the inhibition of purified human liver cathepsin B. Other human cancer cell lines with measurable pericellular cathepsin B activity included HT-1080 fibrosarcoma, MiaPaCa pancreatic, PC-3 prostate and HCT-116 colon. Cathepsin B activity correlated with protein levels of cathepsin B as determined by immunoblot analysis. Pericellular cathepsin B activity was also detected in the rat cell lines MatLyLu prostate and Mat B III adenocarcinoma and in the murine lines B16a melanoma and Lewis lung carcinoma. The ability to determine pericellular cathepsin B activity will be useful in selecting appropriate cell lines for use in vivo when analyzing the effects of inhibiting cathepsin B activity on tumor growth and metastasis.     

2,3-Dihydroquinazolin-4(1H)-one derivatives as potential non-peptidyl inhibitors of cathepsins B and H

A direct correlation between cathepsin expression–cancer progression and elevated levels of cathepsins due to an imbalance in cellular inhibitors-cathepsins ratio in inflammatory diseases necessitates the work on the identification of potential inhibitors to cathepsins. In the present work we report the synthesis of some 2,3-dihydroquinazolin-4(1H)-ones followed by their evaluation as cysteine protease inhibitors in general and cathepsin B and cathepsin H inhibitors in particular. 2,3-Dihydroquinazolin-4(1H)-ones, synthesized by the condensation of anthranilamide and carbonyl compound in presence of PPA-SiO₂ catalyst, were characterized by spectral analysis. The designed compounds were screened as inhibitors to proteolysis on endogenous protein substrates. Further, a distinct differential pattern of inhibition was obtained for cathepsins B and H. The inhibition was more to cathepsin B with K_i values in nanomolar range. However, cathepsin H was inhibited at micromolar concentration. Maximum inhibition was shown by compounds, 1e and 1f for cathepsin B and compounds 1c and 1f for cathepsin H. The synthesized compounds were established as reversible inhibitors of cathepsins B and H. The results were also compared with the energy of interaction between enzyme active site and compounds using iGemdock software.     

TFPI‐2 silencing increases tumour progression and promotes metalloproteinase 1 and 3 induction through tumour‐stromal cell interactions

Tissue factor pathway inhibitor‐2 (TFPI‐2) is a potent inhibitor of plasmin which activates matrix metalloproteinases (MMPs) involved in degradation of the extracellular matrix. Its secretion in the tumour microenvironment makes TFPI‐2 a potential inhibitor of tumour invasion and metastasis. As demonstrated in aggressive cancers, TFPI‐2 is frequently down‐regulated in cancer cells, but the mechanisms involved in the inhibition of tumour progression remained unclear. We showed in this study that stable TFPI‐2 down‐regulation in the National Cancer Institute (NCI)‐H460 non‐small cell lung cancer cell line using specific micro interfering micro‐interfering RNA promoted tumour progression in a nude mice orthotopic model that resulted in an increase in cell invasion. Moreover, TFPI‐2 down‐regulation enhanced cell adhesion to collagen IV and laminin via an increase in α₁ integrin on cell surface, and increased MMP expression (mainly MMP‐1 and ‐3) contributing to cancer cell invasion through basement membrane components. This study also reveals for the first time that pulmonary fibroblasts incubated with conditioned media from TFPI‐2 silencing cancer cells exhibited increased expression of MMPs, particularly MMP‐1, ‐3 and ‐7, that are likely involved in lung cancer cell invasion through the surrounding stromal tissue, thus enhancing formation of metastases.     

Intracellular and extracellular cathepsin B facilitate invasion of MCF-10A neoT cells through reconstituted extracellular matrix in vitro

Lysosomal cysteine proteinase cathepsin B is implicated in remodeling the extracellular matrix, a crucial step in the process of tumor cell invasion. In this study the contributions of intracellular and extracellular cathepsin B activities in the invasion of ras-transformed human breast epithelial cells, MCF-10A neoT, were assessed using specific cathepsin B neutralizing monoclonal antibody (Mab) 2A2, together with other general and specific cysteine proteinase inhibitors. We showed that the degradation of extracellular matrix by living MCF-10A neoT cells was predominantly intracellular, as imaged by confocal assays using quenched fluorescent substrate DQ-collagen IV. CA-074, a membrane-impermeable cathepsin B-selective inhibitor and its membrane-permeable analogue CA-074Me showed similar inhibition of invasion at 10 microM, i.e., 24.9 and 27.0%, respectively. Neutralizing monoclonal antibody exhibited a significantly higher inhibitory effect, decreasing invasion at 0.5 microM by 42.7%. Tumor cells may internalize monoclonal antibody; therefore, 2A2 Mab could impair both the intracellular and the extracellular fractions of cathepsin B activity. However, both 2A2 Mab and cathepsin B-selective inhibitors were less potent than the general cysteine proteinase inhibitors chicken cystatin and E-64, indicating that other cysteine proteinases, presumably cathepsin L, are involved in invasion. Our results show that intracellular and extracellular cathepsin B activity contribute to in vitro invasion of MCF-10A neoT cells and suggest that inhibitors capable of impairing both fractions have a potential as new anticancer drugs.     

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

Abstract 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.     

Live-cell imaging demonstrates extracellular matrix degradation in association with active cathepsin B in caveolae of endothelial cells during tube formation

Localization of proteases to the surface of endothelial cells and remodeling of the extracellular matrix (ECM) are essential to endothelial cell tube formation and angiogenesis. Here, we partially localized active cathepsin B and its cell surface binding partners, S100A/p11 (p11) of the annexin II heterotetramer (AIIt), to caveolae of human umbilical vein endothelial cells (HUVEC). Via a live-cell proteolysis assay, we observed that degradation products of quenched-fluorescent (DQ)-proteins (i.e. gelatin and collagen IV) colocalized intracellularly with caveolin-1 (cav-1) of HUVEC grown in either monolayer cultures or in vitro tube formation assays. Activity-based probes that bind covalently to active cysteine cathepsins and degradation products of DQ-collagen IV partially localized to intracellular vesicles that contained cav-1 and active cysteine cathepsins. Biochemical analyses revealed that the distribution of active cathepsin B in caveolar fractions increased during in vitro tube formation. Pro-uPA, uPAR, MMP-2 and MMP-14, which have been linked with cathepsin B to ECM degradation pathways, were also found to increase in caveolar fractions during in vitro tube formation. Our findings are the first to demonstrate through live-cell imaging ECM degradation in association with active cathepsin B in caveolae of endothelial cells during tube formation.     

Participation of intracellular cysteine proteinases, in particular cathepsin B, in degradation of collagen in periosteal tissue explants

The involvement of cysteine proteinases in the degradation of soft connective tissue collagen was studied in cultured periosteal explants. Using cysteine proteinase inhibitors that were active intracellularly or extracellularly (Ep453 and Ep475, respectively), it was shown that over-all collagen degradation, as measured by the release of hydroxyproline, decreased significantly on inhibition of the intracellular pool of cysteine proteinases by Ep453. This inhibitor also induced an accumulation of intracellular fibrillar collagen in fibroblasts, indicating a decreased degradation of phagocytosed collagen. The extracellular inhibitor, Ep475, had minor or no effects.Histochemical analysis using a substrate for the cysteine proteinases cathepsins B and L revealed a high level of enzyme activity, which was completely blocked in explants preincubated with a selective intracellular inhibitor of cathepsin B, Ca074-Mc. Moreover, the cathepsin B inhibitor strongly affected collagen degradation, decreasing the release of hydroxyproline and increasing the accumulation of phagocytosed collagen. These effects were comparable or slightly stronger than those found with the general intracellular inhibitor (Ep453). Taken together, these data strongly suggest that intracellular cysteine proteinases, in particular cathepsin B, play an important role in the digestion of soft connective tissue collagen.     

Identification of Small Molecule Inhibitors of Jumonji AT-rich Interactive Domain 1B (JARID1B) Histone Demethylase by a Sensitive High Throughput Screen

JARID1B (also known as KDM5B or PLU1) is a member of the JARID1 family of histone lysine demethylases responsible for the demethylation of trimethylated lysine 27 in histone H3 (H3K4me3), a mark for actively transcribed genes. JARID1B is overexpressed in several cancers, including breast cancer, prostate cancer, and lung cancer. In addition, JARID1B is required for mammary tumor formation in syngeneic or xenograft mouse models. JARID1B-expressing melanoma cells are associated with increased self-renewal character. Therefore, JARID1B represents an attractive target for cancer therapy. Here we characterized JARID1B using a homogeneous luminescence-based demethylase assay. We then conducted a high throughput screen of over 15,000 small molecules to identify inhibitors of JARID1B. From this screen, we identified several known JmjC histone demethylase inhibitors, including 2,4-pyridinedicarboxylic acid and catechols. More importantly, we identified several novel inhibitors, including 2-4(4-methylphenyl)-1,2-benzisothiazol-3(2H)-one (PBIT), which inhibits JARID1B with an IC₅₀ of about 3 μm in vitro. Consistent with this, PBIT treatment inhibited removal of H3K4me3 by JARID1B in cells. Furthermore, this compound inhibited proliferation of cells expressing higher levels of JARID1B. These results suggest that this novel small molecule inhibitor is a lead compound that can be further optimized for cancer therapy.     

Quinazolinone derivatives as inhibitors of homologous recombinase RAD51

RAD51 is a vital component of the homologous recombination DNA repair pathway and is overexpressed in drug-resistant cancers, including aggressive triple negative breast cancer (TNBC). A proposed strategy for improving therapeutic outcomes for patients is through small molecule inhibition of RAD51, thereby sensitizing tumor cells to DNA damaging irradiation and/or chemotherapy. Here we report structure-activity relationships for a library of quinazolinone derivatives. A novel RAD51 inhibitor (17) displays up to 15-fold enhanced inhibition of cell growth in a panel of TNBC cell lines compared to compound B02, and approximately 2-fold increased inhibition of irradiation-induced RAD51 foci formation. Additionally, compound 17 significantly inhibits TNBC cell sensitivity to DNA damage, implying a potentially targeted therapy for cancer treatment.     

Cathepsin G-induced malignant progression of MCF-7 cells involves suppression of PAF signaling through induced expression of PAFAH1B2

Breast cancer is primarily classified into ductal and lobular types, as well as into noninvasive and invasive cancer. Invasive cancer involves lymphatic and hematogenous metastasis. In breast cancer patients with distant metastases, a neutrophil-derived serine protease; cathepsin G (Cat G), is highly expressed in breast cancer cells. Cat G induces cell migration and multicellular aggregation of MCF-7 human breast cancer cells; however, the mechanism is not clear. Recently, platelet-activating factor (PAF)-acetylhydrolase (PAF-AH), the enzyme responsible for PAF degradation, was reported to be overexpressed in some tumor types, including pancreatic and breast cancers. In this study, we investigated whether PAF-AH is involved in Cat G-induced aggregation and migration of MCF-7 cells. We first showed that Cat G increased PAF-AH activity and elevated PAFAH1B2 expression in MCF-7 cells. The elevated expression of PAFAH1B2 was also observed in human breast cancer tissue specimens by immunohistochemical analysis. Furthermore, knockdown of PAFAH1B2 in MCF-7 cells suppressed the cell migration and aggregation induced by low concentrations, but not high concentrations, of Cat G. Carbamoyl PAF (cPAF), a nonhydrolyzable PAF analog, completely suppressed Cat G-induced migration of MCF-7 cells. In addition, PAF receptor (PAFR) inhibition induced cell migration of MCF-7 cells even in the absence of Cat G, suggesting that Cat G suppresses the activation of PAFR through enhanced PAF degradation due to elevated expression of PAFAH1B2 and thereby induces malignant phenotypes in MCF-7 cells. Our findings may lead to a novel therapeutic modality for treating breast cancer by modulating the activity of Cat G/PAF signaling.     

Discovery of novel cathepsin inhibitors with potent anti-metastatic effects in breast cancer cells

It is still challenging to determine the potential targets of natural products, which is essential for further drug research and development. Due to its novel mechanism of action of inducing autophagy effects in breast cancer cells, asperphenamate has received our considerable attention. However, its unknown target inevitably impedes further study. In our previous work, the target enzyme of asperphenamate was predicted as cathepsin by the natural product consensus pharmacophore strategy. Then, asperphenamate and its three derivatives were chosen to study in detail by molecular docking calculations with AutoDock 4 suite. The docking results showed the three derivatives interacted more tightly with either cathepsin L or cathepsin S than with asperphenamate. The ortho-benzyloxyl phenylacetyl derivative 1 and p-toluenesulfonyl derivative 3 showed similar interactions with cathepsin L and adopted a better geometric shape within the binding pocket than did the N-CBZ-piperidyl analog 2. On the other hand, compound 2 formed more hydrogen bonds than 1 and 3 to make it tightly bind within cathepsin S. The cathepsin inhibitory activity assay verified the molecular simulation results. Compound 2 was remarkably less active than 1 and 3 against cathepsin L. However, compound 2 showed the strongest potency against cathepsin S with IC₅₀ of 13.12 ± 0.29 μM. Considering that cathepsin S plays a vital role in the process of metastasis in breast cancer cells, the inhibitory effect of 2 on migration and invasion was further studied in human breast cancer MDA-MB-231 cells by wound healing and transwell chamber assays. The results illustrated that 2 exhibited an apparent inhibitory ability to the metastasis of MDA-MB-231 cells. Next, 2 will be chosen as a lead compound to develop novel double functional chemotherapeutic agents with both novel mechanisms of action against apoptosis-resistant cancer cells, such as inducing autophagy and inhibiting cancer metastasis.     

Design,synthesis and biological evaluation of pyrimidine derivatives as novel CDK2 inhibitors that induce apoptosis and cell cycle arrest in breast cancer cells

Cyclin-dependent kinase 2 (CDK2) plays a key role in eukaryotic cell cycle progression which could facilitate the transition from G1 to S phase. The dysregulation of CDK2 is closely related to many cancers. CDK2 is utilized as one of the most studied kinase targets in oncology. In this article, 24 benzamide derivatives were designed, synthesized and investigated for the inhibition activity against CDK2. Our results revealed that the compound 25 is a potent CDK2 inhibitor exhibiting a broad spectrum anti-proliferative activity against several human breast cancer cells. Additionally, compound 25 could block cell cycle at G0 or G1 and induce significant apoptosis in MDA-MB-468 cells. These findings highlight a rationale for further development of CDK2 inhibitors to treat human breast cancer.     

Activation of the P2X7 receptor induces migration of glial cells by inducing cathepsin B degradation of tissue inhibitor of metalloproteinase 1

The P2X₇ receptor is an ion‐gated channel, which is activated by high extracellular concentrations of adenosine triphosphate (ATP). Activation of P2X₇ receptors has been shown to induce neuroinflammatory changes associated with several neurological conditions. The matrix metalloproteinases (MMPs) are a family of endopeptidases that have several functions including degradation of the extracellular matrix, cell migration and modulation of bioactive molecules. The actions of MMPs are prevented by a family of protease inhibitors called tissue inhibitors of metalloproteinases (TIMPs). In this study, we show that ATP‐treated glial cultures from neonatal C57BL/6 mice release and increase MMP‐9 activity, which is coupled with a decrease in release of TIMP‐1 and an increase in activated cathepsin B within the extracellular space. This process occurs independently of NLRP3‐inflammasome formation. Treatment with a P2X₇ receptor antagonist prevents ATP‐induced MMP‐9 activity, inhibition of active cathepsin B release and allows for TIMP‐1 to be released from the cell. We have shown that cathepsin B degrades TIMP‐1, and inhibition of cathepsin B allows for release of TIMP‐1 and inhibits MMP‐9 activity. We also present data that indicate that ATP or cell damage induces glial cell migration, which is inhibited by P2X₇ antagonism, depletion of MMP‐9 or inhibition of cathepsin B.     

Tellurium-based cysteine protease inhibitors: evaluation of novel organotellurium(IV) compounds as inhibitors of human cathepsin B

New organotellurium(IV) compounds with specific cysteine protease inhibitory activity were synthesized. Serine and aspartic protease activity were not affected by any of these compounds. All Te(IV) compounds tested exhibited high specific second-order constant for cathepsin B inactivation. Tellurium(IV) compound 6 was the best inhibitor of the series, showing a second-order constant of 36,000 M(-1)s(-1). This value is about 100-fold higher than the second-order rate for cysteine protease inactivation shown by the historic Te(IV) compound AS 101 (1). The inhibition was irreversible and time and concentration dependent; no saturation kinetics were observed, suggesting a direct bimolecular reaction. The results described in this paper show that the new organotellurium(IV) compounds are powerful inhibitors of cathepsin B, constituting promising potential anti-metastatic agents.     

Protein C inhibitor regulates both cathepsin L activity and cell-mediated tumor cell migration

Background

Protein C inhibitor (PCI) is a plasma serine protease inhibitor (serpin) that regulates several serine proteases in coagulation including thrombin and activated protein C. However, the physiological role of PCI remains under investigation. The cysteine protease, cathepsin L, has a role in many physiological processes including cardiovascular diseases, blood vessel remodeling, and cancer.

Methods and results

We found that PCI inhibits cathepsin L with an inhibition rate (k₂) of 3.0 × 10⁵ M⁻¹ s⁻¹. Whereas, the PCI P1 mutant (R354A) inhibits cathepsin L at rates similar to wild-type PCI, mutating the P2 residue results in a slight decrease in the rate of inhibition. We then assessed the effect of PCI and cathepsin L on the migration of human breast cancer (MDA-MB-231) cells. Cathepsin L was expressed in both the cell lysates and conditioned media of MDA-MB-231 cells. Wound-induced and transwell migration of MDA-MB-231 cells was inhibited by exogenously administered wtPCI and PCI P1 but not PCI P14 mutant. In addition, migration of MDA-MB-231 cells expressing wtPCI was significantly decreased compared to non-expressing MDA-MB-231 cells or MDA-MB-231 cells expressing the PCI P14 mutant. Downregulation of cathepsin L by either a specific cathepsin L inhibitor or siRNA technology also resulted in a decrease in the migration of MDA-MB-231 cells.

Conclusions

Overall, our data show that PCI regulates tumor cell migration partly by inhibiting cathepsin L.

General significance

Consequently, inhibiting cathepsin L by serpins like PCI may be a new pathway of regulating hemostasis, cardiovascular and metastatic diseases.