Generation of angiostatin-like fragments from plasminogen by prostate-specific antigen

Predictive value of kallikrein forms and β-microseminoprotein in blood from patients with evidence of detectable levels of PSA after radical prostatectomy

PURPOSE

To determine whether β-microseminoprotein or any of the kallikrein forms in blood-free, total or intact PSA or total hK2-predict metastasis in patients with evidence of detectable levels of PSA in blood after radical prostatectomy.

METHOD

We determined marker concentrations in blood from 173 men treated with radical prostatectomy and evidence of detectable levels of PSA in the blood (PSA ≥ 0.05) after surgery between 2014 and 2015 and at least 1 year after any adjuvant therapy. We used Cox regression to determine whether any marker was associated with metastasis using both univariate and multivariable models that included standard clinical predictors.

RESULTS

Overall, 42 patients had metastasis, with a median follow-up of 67 months among patients without an event. The levels of intact and free PSA and free-to-total PSA ratio were significantly associated with metastasis. Discrimination was highest for free PSA (c-index: 0.645) and free-to-total PSA ratio (0.625). Only free-to-total PSA ratio remained associated with overall metastasis (either regional or distant) after including standard clinical predictors (p = 0.025) and increased discrimination from 0.686 to 0.697. Similar results were found using distant metastasis as an outcome (p = 0.011; c-index increased from 0.658 to 0.723).

CONCLUSION

Our results provide evidence that free-to-total PSA ratio can risk stratifying patients with evidence of detectable levels of PSA in blood after RP. Further research is warranted on the biology of prostate cancer markers in patients with evidence of detectable levels of PSA in blood after radical prostatectomy. Our findings on the free-to-total ratio for predicting adverse oncologic outcomes need to be validated in other cohorts.

Remodelling of the tumour microenvironment by the kallikrein-related peptidases

Kallikrein-related peptidases (KLKs) are critical regulators of the tumour microenvironment. KLKs are proteolytic enzymes regulating multiple functions of bioactive molecules including hormones and growth factors, membrane receptors and the extracellular matrix architecture involved in cancer progression and metastasis. Perturbations of the proteolytic cascade generated by these peptidases, and their downstream signalling actions, underlie tumour emergence or blockade of tumour growth. Recent studies have also revealed their role in tumour immune suppression and resistance to cancer therapy. Here, we present an overview of the complex biology of the KLK family and its context-dependent nature in cancer, and discuss the different therapeutic strategies available to potentially target these proteases.

KLK3 in the Regulation of Angiogenesis-Tumorigenic or Not?

In this focused review, we address the role of the kallikrein-related peptidase 3 (KLK3), also known as prostate-specific antigen (PSA), in the regulation of angiogenesis. Early studies suggest that KLK3 is able to inhibit angiogenic processes, which is most likely dependent on its proteolytic activity. However, more recent evidence suggests that KLK3 may also have an opposite role, mediated by the ability of KLK3 to activate the (lymph)angiogenic vascular endothelial growth factors VEGF-C and VEGF-D, further discussed in the review.

Granzymes in cardiovascular injury and disease

Chronic inflammation and impaired wound healing play important roles in the pathophysiology of cardiovascular diseases. Moreover, the aberrant secretion of proteases plays a critical role in pathological tissue remodeling in chronic inflammatory conditions. Human Granzymes (Granule secreted enzymes - Gzms) comprise a family of five (GzmA, B, H, K, M) cell-secreted serine proteases. Although each unique in function and substrate specificities, Gzms were originally thought to share redundant, intracellular roles in cytotoxic lymphocyte-induced cell death. However, an abundance of evidence has challenged this dogma. It is now recognized, that individual Gzms exhibit unique substrate repertoires and functions both intracellularly and extracellularly. In the extracellular milieu, Gzms contribute to inflammation, vascular dysfunction and permeability, reduced cell adhesion, release of matrix-sequestered growth factors, receptor activation, and extracellular matrix cleavage. Despite these recent findings, the non-cytotoxic functions of Gzms in the context of cardiovascular disease pathogenesis remain poorly understood. Minimally detected in tissues and bodily fluids of normal individuals, GzmB is elevated in patients with acute coronary syndromes, coronary artery disease, and myocardial infarction. Pre-clinical animal models have exemplified the importance of GzmB in atherosclerosis, aortic aneurysm, and cardiac fibrosis as animals deficient in GzmB exhibit reduced tissue remodeling, improved disease phenotypes and increased survival. Although a role for GzmB in cardiovascular disease is described, further work to elucidate the mechanisms that underpin the remaining human Gzms activity in cardiovascular disease is necessary. The present review provides a summary of the pre-clinical and clinical evidence, as well as emerging areas of research pertaining to Gzms in tissue remodeling and cardiovascular disease.

Beyond the biomarker role: prostate-specific antigen (PSA) in the prostate cancer microenvironment

The prostate-specific antigen (PSA) blood test is the accepted biomarker of tumor recurrence. PSA levels in serum correlate with disease progression, though its diagnostic accuracy is questionable. As a result, significant progress has been made in developing modified PSA tests such as PSA velocity, PSA density, 4Kscore, PSA glycoprofiling, Prostate Health Index, and the STHLM3 test. PSA, a serine protease, is secreted from the epithelial cells of the prostate. PSA has been suggested as a molecular target for prostate cancer therapy due to the fact that it is not only active in prostate tissue but also has a pivotal role on prostate cancer signaling pathways including proliferation, invasion, metastasis, angiogenesis, apoptosis, immune response, and tumor microenvironment regulation. Here, we summarize the current standing of PSA in prostate cancer progression as well as its utility in prostate cancer therapeutic approaches with an emphasis on the role of PSA in the tumor microenvironment.

Differential roles of protease isoforms in the tumor microenvironment

Alternative splicing of precursor mRNA is a key mediator of gene expression regulation leading to greater diversity of the proteome in complex organisms. Systematic sequencing of the human genome and transcriptome has led to our understanding of how alternative splicing of critical genes leads to multiple pathological conditions such as cancer. For many years, proteases were known only for their roles as proteolytic enzymes, acting to regulate/process proteins associated with diverse cellular functions. However, the differential expression and altered function of various protease isoforms, such as (i) anti-apoptotic activities, (ii) mediating intercellular adhesion, and (iii) modifying the extracellular matrix, are evidence of their specific contribution towards shaping the tumor microenvironment. Revealing the alternative splicing of protease genes and characterization of their protein products/isoforms with distinct and opposing functions creates a platform to understand how protease isoforms contribute to specific cancer hallmarks. Here, in this review, we address cancer-specific isoforms produced by the alternative splicing of proteases and their distinctive roles in the tumor microenvironment.

Prognostic and diagnostic role of PSA immunohistochemistry: A tissue microarray study on 21,000 normal and cancerous tissues

To assess the prognostic and diagnostic utility of PSA immunostaining, tissue microarrays containing 17,747 prostate cancers, 3,442 other tumors from 82 different (sub) types and 608 normal tissues were analyzed at two different antibody concentrations (1:100 and 1:800). In normal tissues, PSA expression was limited to prostate epithelial cells. In prostate cancers, PSA staining was seen in 99.9–100% (1:800–1:100) primary tumors, 98.7–99.7% of advanced recurrent cancers, in 84.6–91.4% castration resistant cancers, and in 7.7–18.8% of 16 small cell carcinomas. Among extraprostatic tumors, PSA stained positive in 0–3 (1:800-1:100) of 19 osteosarcomas, 1-2 of 34 ovarian cancers, 0-2 of 35 malignant mesotheliomas, 0–1 of 21 thyroid gland carcinomas and 0–1 of 26 large cell lung cancers. Reduced staining intensity and loss of apical staining were strongly linked to unfavorable tumor phenotype and poor prognosis (p < 0.0001 each). This was all the more the case if a combined “PSA pattern score” was built from staining intensity and pattern. The prognostic impact of the “PSA pattern score” was independent of established pre- and postoperative clinico-pathological prognostic features. In conclusion, PSA immunostaining is a strong prognostic parameter in prostate cancer and has high specificity for prostate cancer at a wide range of antibody dilutions.

The kallikrein-related peptidase family: Dysregulation and functions during cancer progression

Cancer is the second leading cause of death with 14 million new cases and 8.2 million cancer-related deaths worldwide in 2012. Despite the progress made in cancer therapies, neoplastic diseases are still a major therapeutic challenge notably because of intra- and inter-malignant tumour heterogeneity and adaptation/escape of malignant cells to/from treatment. New targeted therapies need to be developed to improve our medical arsenal and counter-act cancer progression. Human kallikrein-related peptidases (KLKs) are secreted serine peptidases which are aberrantly expressed in many cancers and have great potential in developing targeted therapies. The potential of KLKs as cancer biomarkers is well established since the demonstration of the association between KLK3/PSA (prostate specific antigen) levels and prostate cancer progression. In addition, a constantly increasing number of in vitro and in vivo studies demonstrate the functional involvement of KLKs in cancer-related processes. These peptidases are now considered key players in the regulation of cancer cell growth, migration, invasion, chemo-resistance, and importantly, in mediating interactions between cancer cells and other cell populations found in the tumour microenvironment to facilitate cancer progression. These functional roles of KLKs in a cancer context further highlight their potential in designing new anti-cancer approaches. In this review, we comprehensively review the biochemical features of KLKs, their functional roles in carcinogenesis, followed by the latest developments and the successful utility of KLK-based therapeutics in counteracting cancer progression.

Anti-angiogenic activity of PSA-derived peptides

BACKGROUND

PSA is a biomarker for diagnosis and management of prostate cancer. PSA is known to have anti-tumorigenic activities, however, the physiological role of PSA in prostate tumor progression is not well understood.

METHODS

Five candidate peptides identified based upon computer modeling of the PSA crystal structure and hydrophobicity were synthesized at >95% purity. The peptides in a linear form, and a constrained form forced by a di-sulfide bond joining the two ends of the peptide, were investigated for anti-angiogenic activity in HUVEC.

RESULTS

None of the five PSA-mimetic peptides exhibited PSA-like serine protease activity. Two of the peptides demonstrated significant anti-angiogenic activity in HUVEC based on (i) inhibition of cell migration and invasion; (ii) inhibition of tube formation in Matrigel; (iii) anti-angiogenic activity in a sprouting assay; and (iv) altered expression of pro- and anti-angiogenic growth factors. Constrained PSA-mimetic peptides had greater anti-angiogenic activity than the corresponding linearized form. Complexing of PSA with ACT eliminated PSA enzymatic activity and reduced anti-angiogenic activity. In contrast, ACT had no effect on the anti-angiogenic effects of the linear or constrained PSA-mimetic peptides. Modeling of the ACT-PSA complex demonstrated ACT sterically blocks the anti-angiogenic activity of the two bioactive peptides.

CONCLUSIONS

The interaction of a hydrophilic domain on the surface of the PSA molecule with a target on the cell membrane of prostate endothelial and epithelial cells was responsible for the anti-angiogenic or anti-tumorigenic activity of PSA: enzymatic activity was not associated with anti-angiogenic effects. Furthermore, since PSA and ACT are both expressed within the human prostate tissue microenvironment, the balance of their expression may represent a mechanism for endogenous regulation of tissue angiogenesis.

Kallikrein-Related Peptidases in Prostate Cancer: From Molecular Function to Clinical Application

Prostate cancer is a leading contributor to male cancer-related deaths worldwide. Kallikrein-related peptidases (KLKs) are serine proteases that exhibit deregulated expression in prostate cancer, with KLK3, or prostate specific antigen (PSA), being the widely-employed clinical biomarker for prostate cancer. Other KLKs, such as KLK2, show promise as prostate cancer biomarkers and, additionally, their altered expression has been utilised for the design of KLK-targeted therapies. There is also a large body of in vitro and in vivo evidence supporting their role in cancer-related processes. Here, we review the literature on studies to date investigating the potential of other KLKs, in addition to PSA, as biomarkers and in therapeutic options, as well as their current known functional roles in cancer progression. Increased knowledge of these KLK-mediated functions, including degradation of the extracellular matrix, local invasion, cancer cell proliferation, interactions with fibroblasts, angiogenesis, migration, bone metastasis and tumour growth in vivo, may help define new roles as prognostic biomarkers and novel therapeutic targets for this cancer.

Proteolytic activity of prostate-specific antigen (PSA) towards protein substrates and effect of peptides stimulating PSA activity

Prostate-specific antigen (PSA or kallikrein-related peptidase-3, KLK3) exerts chymotrypsin-like proteolytic activity. The main biological function of PSA is the liquefaction of the clot formed after ejaculation by cleavage of semenogelins I and II in seminal fluid. PSA also cleaves several other substrates, which may explain its putative functions in prostate cancer and its antiangiogenic activity. We compared the proteolytic efficiency of PSA towards several protein and peptide substrates and studied the effect of peptides stimulating the activity of PSA with these substrates. An endothelial cell tube formation model was used to analyze the effect of PSA-degraded protein fragments on angiogenesis. We showed that PSA degrades semenogelins I and II much more efficiently than other previously identified protein substrates, e.g., fibronectin, galectin-3 and IGFBP-3. We identified nidogen-1 as a new substrate for PSA. Peptides B2 and C4 that stimulate the activity of PSA towards small peptide substrates also enhanced the proteolytic activity of PSA towards protein substrates. Nidogen-1, galectin-3 or their fragments produced by PSA did not have any effect on endothelial cell tube formation. Although PSA cleaves several other protein substrates, in addition to semenogelins, the physiological importance of this activity remains speculative. The PSA levels in prostate are very high, but several other highly active proteases, such as hK2 and trypsin, are also expressed in the prostate and may cleave protein substrates that are weakly cleaved by PSA.

PSMA/PSA ratio evaluated by immunohistochemistry may improve diagnosis of prostate cancer

Prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) measured in serum are not fully satisfactory as biomarkers of prostate cancer (PC). Results obtained in this article indicated that PSMA/PSA ratio evaluated by immunohistochemistry in normal prostate (NP), benign prostatic hyperplasia (BPH), and PC at the individual level could be a useful tool for diagnosis and prognosis of PC. PSMA and PSA were equally expressed in NP and the PSMA/PSA ratio was 1.22 ± 0.15. Data also indicated that PSMA/PSA ratio fluctuates in BPH and PC compared to NP. In BPH, the PSMA/PSA ratio was around 0.47 ± 0.02, whereas it's significantly increased in PC, about 4.95 ± 0.83. In parallel, the highest PSMA/PSA ratio was associated with high intratumoral angiogenesis in PC patients with (PSMA+,PSA+) profile.

Plasminogen activators are involved in angiostatin generation in vivo in benign and malignant ovarian tumor cyst fluids

In many tumor types, angiogenesis is the net result of pro- and anti-angiogenic mediators and correlated with metabolic activity, growth, and degree of malignancy. One of the first discovered anti-angiogenic compounds is angiostatin, a proteolytic fragment of plasminogen. The requirements for in vivo angiostatin generation have not yet been determined. We investigated the levels of plasminogen and angiostatin by western blotting and of components of the plasminogen activator complex by ELISA in cyst fluid derived from benign and malignant ovarian tumors. Fluid samples from functional ovarian follicles, dermoid cysts and endometriotic lesions were evaluated separately. When no or minimal amounts of plasminogen were present in the cyst fluids, angiostatin was generally absent as well, irrespective of plasminogen activator concentrations. When plasminogen was present, the degree of conversion of plasminogen to angiostatin was significantly correlated with the level of uPA, and, to a lesser extent, to the tPA level. However, angiostatin was also found in a number of cyst fluid samples with minimal or no plasminogen activators, suggesting the involvement of other angiostatin generating proteases in these samples. Conversely, no angiostatin was observed in a number of cyst fluid samples containing both plasminogen and plasminogen activators. The presence of an inhibitor of the enzymatic activity of uPA and/or tPA, like PAI-1, may explain this finding. Our data show that plasminogen activators are clearly involved in in vivo angiostatin formation in ovarian cysts. Most likely, however, other proteases, as well as inhibitors of plasminogen activators, are involved as well.

Human tissue kallikreins 3 and 5 can act as plasminogen activator releasing active plasmin

Human tissue kallikreins (KLKs) are a group of serine proteases found in many tissues and biological fluids and are differentially expressed in several specific pathologies. Here, we present evidences of the ability of these enzymes to activate plasminogen. Kallikreins 3 and 5 were able to induce plasmin activity after hydrolyzing plasminogen, and we also verified that plasminogen activation was potentiated in the presence of glycosaminoglycans compared with plasminogen activation by tPA. This finding can shed new light on the plasminogen/plasmin system and its involvement in tumor metastasis, in which kallikreins appear to be upregulated.

Pseudopeptides with a centrally positioned alkene-based disulphide bridge mimetic stimulate kallikrein-related peptidase 3 activity

First successful pseudopeptides of the KLK3-activating bicyclic peptide “C-4” are reported.

Platelet-associated angiogenesis regulating factors: a pharmacological perspective

Platelets, in addition to maintaining hemostasis, also stimulate angiogenesis by generating and releasing, upon activation, factors that promote the growth of new blood vessels. To date, at least 20 angiogenesis-regulating factors have been identified in platelets, including both promoters and inhibitors. Platelet-derived angiogenesis regulators promote angiogenesis during wound healing, tumor growth, and in response to ischemia. Within platelets, angiogenesis regulators are primarily stored in α-granules, but are also found in the cytosol or derived from membrane lipids. Their release can be inhibited pharmacologically by anti-platelet agents, which consequently suppress platelet-stimulated angiogenesis. Several years ago, our research group discovered that platelets generate the angiogenesis inhibitor angiostatin independent of the activation state of platelets, and that platelet-derived angiostatin serves to limit the angiogenesis-stimulating effects of platelets. In this review, we summarize the current knowledge of platelet-associated angiogenesis regulators, how they impact angiogenesis, and how they are controlled pharmacologically.

Enzymatic activity of free-prostate-specific antigen (f-PSA) is not required for some of its physiological activities

BACKGROUND

Prostate specific antigen (PSA) is a well known biomarker for early diagnosis and management of prostate cancer. Furthermore, PSA has been documented to have anti-angiogenic and anti-tumorigenic activities in both in vitro and in vivo studies. However, little is known about the molecular mechanism(s) involved in regulation of these processes, in particular the role of the serine-protease enzymatic activity of PSA.

METHODS

Enzymatic activity of PSA isolated directly from seminal plasma was inhibited specifically (>95%) by incubation with zinc2+ . Human umbilical vein endothelial cells (HUVEC) were utilized to compare/contrast the physiological effects of enzymatically active versus inactive PSA.

RESULTS

Equimolar concentrations of enzymatically active PSA and PSA enzymatically inactivated by incubation with Zn2+ had similar physiological effects on HUVEC, including inhibiting the gene expression of pro-angiogenic growth factors, like VEGF and bFGF, and up-regulation of expression of the anti-angiogenic growth factor IFN-γ; suppression of mRNA expression for markers of blood vessel development, like FAK, FLT, KDR, TWIST-1; P-38; inhibition of endothelial tube formation in the in vitro Matrigel Tube Formation Assay; and inhibition of endothelial cell invasion and migration properties.

DISCUSSION

Our data provides compelling evidence that the transcriptional regulatory and the anti-angiogenic activities of human PSA are independent of the innate enzymatic activity.

Tumor angiogenesis as a target for dietary cancer prevention

Between 2000 and 2050, the number of new cancer patients diagnosed annually is expected to double, with an accompanying increase in treatment costs of more than $80 billion over just the next decade. Efficacious strategies for cancer prevention will therefore be vital for improving patients' quality of life and reducing healthcare costs. Judah Folkman first proposed antiangiogenesis as a strategy for preventing dormant microtumors from progressing to invasive cancer. Although antiangiogenic drugs are now available for many advanced malignancies (colorectal, lung, breast, kidney, liver, brain, thyroid, neuroendocrine, multiple myeloma, myelodysplastic syndrome), cost and toxicity considerations preclude their broad use for cancer prevention. Potent antiangiogenic molecules have now been identified in dietary sources, suggesting that a rationally designed antiangiogenic diet could provide a safe, widely available, and novel strategy for preventing cancer. This paper presents the scientific, epidemiologic, and clinical evidence supporting the role of an antiangiogenic diet for cancer prevention.

The discovery of compounds that stimulate the activity of kallikrein-related peptidase 3 (KLK3)

Kallikrein-related peptidase 3 (KLK3), also known as prostate-specific antigen (PSA), is the most useful biomarker for prostate cancer (PCa). KLK3 is suggested to play a role in regulating cancer growth through anti-angiogenic activity in vivo and in vitro. This feature, together with its specificity for prostate tissue, makes KLK3 an intriguing target for the design of new therapies for PCa. 3D pharmacophores for KLK3-stimulating compounds were generated based on peptides that bind specifically to KLK3 and increase its enzymatic activity. As a result of pharmacophore-based virtual screening, four small, drug-like compounds with affinity for KLK3 were discovered and validated by capillary differential scanning calorimetry. One of the compounds also stimulated the activity of KLK3, and is therefore the first published small molecule with such an activity.

Matrix metalloproteinase-19 inhibits growth of endothelial cells by generating angiostatin-like fragments from plasminogen

Background

Angiogenesis is the process of forming new blood vessels from existing ones and requires degradation of the vascular basement membrane and remodeling of extracellular matrix (ECM) in order to allow endothelial cells to migrate and invade into the surrounding tissue. Matrix metalloproteinases (MMPs) are considered to play a central role in the remodeling of basement membranes and ECM. However, MMPs contribute to vascular remodeling not only by degrading ECM components. Specific MMPs enhance angiogenesis via several ways; they help pericytes to detach from vessels undergoing angiogenesis, release ECM-bound angiogenic growth factors, expose cryptic pro-angiogenic integrin binding sites in the ECM, generate promigratory ECM component fragments, and cleave endothelial cell-cell adhesions. MMPs can also negatively influence the angiogenic process through generating endogenous angiogenesis inhibitors by proteolytic cleavage. Angiostatin, a proteolytic fragment of plasminogen, is one of the most potent antagonists of angiogenesis that inhibits migration and proliferation of endothelial cells. Reports have shown that metalloelastase, pancreas elastase, plasmin reductase, and plasmin convert plasminogen to angiostatin.

Results

We report here that MMP-19 processes human plasminogen in a characteristic cleavage pattern to generate three angiostatin-like fragments with a molecular weight of 35, 38, and 42 kDa. These fragments released by MMP-19 significantly inhibited the proliferation of HMEC cells by 27% (p = 0.01) and reduced formation of capillary-like structures by 45% (p = 0.05) compared with control cells. As it is known that angiostatin blocks hepatocyte growth factor (HGF)-induced pro-angiogenic signaling in endothelial cells due to structural similarities to HGF, we have analyzed if the plasminogen fragments generated by MMP-19 interfere with this pathway. As it involves the activation of c-met, the receptor of HGF, we could show that MMP-19-dependent processing of plasminogen decreases the phosphorylation of c-met.

Conclusion

Altogether, MMP-19 exhibits an anti-angiogenic effect on endothelial cells via generation of angiostatin-like fragments.

TRP channels in prostate cancer: the good, the bad and the ugly?

During the last decade, transient receptor potential (TRP) channels emerge as key proteins in central mechanisms of the carcinogenesis such as cell proliferation, apoptosis and migration. Initial studies showed that expression profile of some TRP channels, notably TRP melastatin 8 (TRPM8), TRP vanilloid 6 (TRPV6),TRP canonical (TRPC6) and TRPV2, is changing during the development and the progression of prostate cancer towards the hormone-refractory stages. The link between the change in expression levels and the functional role of these channels in prostate cancer is step by step being elucidated. These recent advances are here described and discussed.

Co-expression and impact of prostate specific membrane antigen and prostate specific antigen in prostatic pathologies

BACKGROUND

The present study was undertaken to relate the co-expression of prostate-associated antigens, PSMA and PSA, with the degree of vascularization in normal and pathologic (hyperplasia and cancer) prostate tissues to elucidate their possible role in tumor progression.

METHODS

The study was carried out in 6 normal, 44 benign prostatic hyperplastic and 39 cancerous human prostates. Immunohistochemical analysis were performed using the monoclonal antibody CD34 to determine the angiogenic activity, and the monoclonal antibodies 3E6 and ER-PR8 to assess PSMA and PSA expression, respectively.

RESULTS

In our study we found that in normal prostate tissue, PSMA and PSA were equally expressed (3.7 ± 0.18 and 3.07 ± 0.11). A significant difference in their expression was see in hyperplastic and neoplastic prostates tissues (16.14 ± 0.17 and 30.72 ± 0.85, respectively) for PSMA and (34.39 ± 0.53 and 17.85 ± 1.21, respectively) for PSA. Study of prostate tumor profiles showed that the profile (PSA+, PSMA-) expression levels decreased between normal prostate, benign prostatic tissue and primary prostate cancer. In the other hand, the profile (PSA-, PSMA+) expression levels increased from normal to prostate tumor tissues. PSMA overexpression was associated with high intratumoral angiogenesis activity. By contrast, high PSA expression was associated with low angiogenesis activity.

CONCLUSION

These data suggest that these markers are regulated differentially and the difference in their expression showed a correlation with malignant transformation. With regard to the duality PSMA-PSA, this implies the significance of their investigation together in normal and pathologic prostate tissues.

Prostate-specific antigen levels are associated with arterial stiffness in essential hypertensive patients

INTRODUCTION

Prostate-specific antigen (PSA) has been recently related to cardiovascular system in a multifactorial way. Arterial stiffness is a independent predictor of cardiovascular events and is involved in the pathogenesis of hypertension. The aim of the present study was to investigate whether PSA values, are associated with arterial stiffness indices in patients with essential arterial hypertension.

METHODS

The study comprised 150 consecutive male patients (mean age 60 years) with uncomplicated never-treated essential hypertension. All patients underwent a complete clinical and laboratory evaluation, including measurement of PSA levels. Aortic stiffness and arterial wave reflection assessment was made by using carotid-femoral (PWVc-f) pulse wave velocity and aortic augmentation index corrected for heart rate (AIx75). Patients with prostate cancer or benign prostate hyperplasia (PSA > 4 ng/mL) were excluded from the study.

RESULTS

PSA was positively associated with waist-to-hip ratio (r = 0.235, P = 0.04), PWVc-f (r = 0.426, P < 0.001), AIx75 (r = 0.264, P = 0.001), and high sensitivity C-reactive protein (hsCRP; r = 0.376, P < 0.001). In categorization to PSA quartiles, patients in the higher quartile presented with higher waist-to hip ratio (P = 0.009), PWVc-f (P < 0.00001), AIx75 (P < 0.001) and hsCRP (P < 0.001) values. In multivariate analysis after adjustment for various confounders PSA remained a significant determinant of PWVc-f values (beta [SE] = 0.477 [0.13], R(2) = 0.405, P < 0.001).

CONCLUSION

The present study points towards an association between PSA levels and aortic stiffness in untreated essential hypertensive males. Potential causal relationships between PSA and arterial stiffness remain to be further explored.

Kallikrein-related peptidase 13 (KLK13) gene expressional status contributes significantly in the prognosis of primary gastric carcinomas

OBJECTIVES

Gastric cancer is a fatal human malignancy with poor prognosis. Modifications in gene expression, including those of the kallikrein-related peptidase family, have been portrayed in gastric carcinogenesis. Given KLK13 involvement in human malignancies, we aimed to uncover its prognostic strength in stomach cancer.

DESIGN AND METHODS

Quantitative analysis of KLK13 profiles was accomplished in human gastric cancer cells and in a statistically significant sample size of stomach tissue specimens with the development of the highly sensitive real-time PCR methodology.

RESULTS

Decreased KLK13 expression was demonstrated in cancerous compared with their matching non-malignant pairs (p=0.002) and in poorly differentiated gastric tumors (p=0.029). KLK13-positive patients were shown to live considerably longer (p=0.014) and with low risk of disease recurrences (p=0.043).

CONCLUSIONS

This is the first study disclosing the possible clinical utility of KLK13 as a new tumor biomarker capable of predicting a favorable outcome for gastric cancer patients.

Functional intersection of the kallikrein-related peptidases (KLKs) and thrombostasis axis

A large body of emerging evidence indicates a functional interaction between the kallikrein-related peptidases (KLKs) and proteases of the thrombostasis axis. These interactions appear relevant for both normal health as well as pathologies associated with inflammation, tissue injury, and remodeling. Regulatory interactions between the KLKs and thrombostasis proteases could impact several serious human diseases, including neurodegeneration and cancer. The emerging network of specific interactions between these two protease families appears to be complex, and much work remains to elucidate it. Complete understanding how this functional network resolves over time, given specific initial conditions, and how it might be controllably manipulated, will probably contribute to the emergence of novel diagnostics and therapeutic agents for major diseases.

Cloning, expression and in vitro evaluation of recombinant canine Tum5, an angiostatic domain of mammalian type IV collagen

The process of new blood vessel formation within and around neoplastic tissue, termed angiogenesis, is a significant factor in the development, progression and metastasis of malignant tumours in all species. A major cause of death in cancer patients is the development of treatment-resistant metastatic disease, which may be avoided by therapies that target the genetically stable population of vascular endothelial cells within tumours. Tumstatin is a small protein formed by the cleavage of the alpha-3 subunit of the non-collagenous domain of mammalian type IV collagen. Recombinant human Tumstatin has been shown to have potent angiostatic properties in vitro and in vivo. Tumstatin is a potent initiator of apoptosis and inhibits the proliferation and migration of vascular endothelial cells in cell culture. Recently, a fragment of Tumstatin, termed Tum5, has been shown to have biologic activity similar to the parent compound. The systemic administration of angiostatic proteins like Tum5 may result in the remission of established tumours, while preventing or delaying the onset of clinically detectable metastasis. Recombinant canine Tum5 (cTum5) was cloned and its protein expression induced in a prokaryotic vector. The resulting cTum5 protein caused dose-dependent inhibition of vascular endothelial cells in vitro, which appears to be mediated through apoptosis.

Antiangiogenic properties of prostate-specific antigen (PSA)

The prostate produces high levels of prostate-specific antigen (PSA, also known as kallikrein-related peptidase 3, KLK3), which is a potential target for tumor imaging and treatment. Although serum PSA levels are elevated in prostate cancer, PSA expression is lower in malignant than in normal prostatic epithelium and it is further reduced in poorly differentiated tumors. PSA has been shown to inhibit angiogenesis both in in vitro and in vivo models. In this review we focus on our recent studies concerning the mechanism of the antiangiogenic function of PSA. We have recently shown that the antiangiogenic activity of PSA is related to its enzymatic activity. Inactive PSA isoforms do not have antiangiogenic activity as studied by a human umbelical vein endothelial cell (HUVEC) tube formation model. Furthermore, inhibition of PSA, either by a monoclonal antibody or small molecule inhibitors abolishes the effect of PSA, while a peptide that stimulates the activity of PSA enhances the antiangiogenic effect. We have analyzed changes in gene expression associated with the PSA induced reduction of tube formation in the HUVEC model. Several small changes were observed and they were found to be opposite to those associated with tube formation. Taken together, these studies suggest that PSA exerts antiantiogenic activity related to its enzymatic activity. Thus it might be associated with the slow growth of prostate cancer.

Prostate-specific antigen kallikrein: from prostate cancer to cardiovascular system

Prostate-specific antigen (PSA), considered only an established marker for the detection of prostate cancer, has been identified as a member (hK3) of the human kallikrein family of serine proteases and now, it is known that PSA is not specific to prostate, semen, and gender. Increased PSA serum levels have been reported also in cardiovascular patients and both elevated as well as diminished PSA have been reported during acute myocardial infarction (AMI). Preliminary observations have concluded that when elevation of prostate-specific antigen occurs during AMI, it seems to relate to a higher occurrence of major adverse cardiac events and that coronary lesions are frequent and often more severe than when a diminution of PSA occurs. Large studies need to be done to confirm these preliminary results but the journey of PSA could be longer than expected.

Reflections on the tissue kallikrein and kallikrein-related peptidase family – from mice to men – what have we learnt in the last two decades?

The genes encoding the kininogenase, glandular tissue kallikrein, in rodents and man were first described in the mid-1980s. Remarkably, they appeared to be part of a much larger highly conserved family of genes (GK) in rodents, but only had two paralogs in man. This discrepancy was not rectified until the late 1990s/2000 with the identification of a cluster of 12 more kallikrein-related (KLK) genes in the human 19q13 locus and the subsequent identification of their rodent homologs. Interestingly, there are remarkable similarities in expression patterns, hormonal regulation and functional attributes of the old (GK) and new (KLK) families which underscore the evolutionary conservation across these loci and species. This historical perspective focuses on the lessons learned from earlier studies on the rodentGKgene families and the striking similarities of some attributes, yet uniqueness, of others. These earlier findings have all contributed to the current status of the KLK serine peptidase-encoding gene family as an exciting source of new biomarkers and therapeutic targets.

The Tissue Kallikrein Family of Serine Proteases: Functional Roles in Human Disease and Potential as Clinical Biomarkers

Prostate specific antigen (PSA) or human kallikrein 3 (hK3) has long been an effective biomarker for prostate cancer. Now, other members of the tissue kallikrein (KLK) gene family are fast becoming of clinical interest due to their potential as prognostic biomarkers. particularly for hormone dependent cancers. The tissue kallikreins are serine proteases that are encoded by highly conserved multi-gene family clusters in rodents and humans. The rat and mouse loci contain 10 and 25 functional genes, respectively, while the human locus at 19q 13.4 contains 15 genes. The structural organization and size of these genes are similar across species; all genes have 5 coding exons that encode a prepro-enzyme. Although the physiological activators of these zymogens have not been described, in vitro biochemical studies show that some kallikreins can auto-activate and others can activate each other, suggesting that the kallikreins may participate in an enzymatic cascade similar to that of the coagulation cascade. These genes are expressed, to varying degrees, in a wide range of tissues suggesting a functional involvement in a diverse range of physiological and pathophysiological processes. These include roles in normal skin desquamation and psoriatic lesions, tooth development, neural plasticity, and Alzheimer's disease (AD). Of particular interest is the expression of many kallikreins in prostate, ovarian, and breast cancers where they are emerging as useful prognostic indicators of disease progression.

Development of peptides specifically modulating the activity of KLK2 and KLK3

The prostate produces several proteases, the most abundant ones being kallikrein-related peptidase 3 (KLK3, PSA) and KLK2 (hK2), which are potential targets for tumor imaging and treatment. KLK3 expression is lower in malignant than in normal prostatic epithelium and it is further reduced in poorly differentiated tumors, in which the expression of KLK2 is increased. KLK3 has been shown to inhibit angiogenesis, whereas KLK2 may mediate tumor growth and invasion by participating in proteolytic cascades. Thus, it may be possible to control prostate cancer growth by modulating the proteolytic activity of KLK3 and KLK2. We have developed peptides that very specifically stimulate the activity of KLK3 or inhibit that of KLK2. Using these peptides we have established peptide-based methods for the determination of enzymatically active KLK3. The first-generation peptides are unstable in vivo and are rapidly cleared from the circulation. Currently we are modifying the peptides to make them suitable for in vivo applications. We have been able to considerably improve the stability of KLK2-binding peptides by cyclization. In this review we summarize the possible roles of KLK3 and KLK2 in prostate cancer and then concentrate on the development of peptides that modulate the activity of these proteases.

Novel small molecule inhibitors for prostate-specific antigen

BACKGROUND

Prostate-specific antigen (PSA or KLK3) has been shown to inhibit angiogenesis, but it might also have tumor promoting activities. Thus, it may be possible to modulate prostate cancer growth by stimulating or inhibiting the activity of PSA. To this end we have previously identified peptides that stimulate the activity of PSA. As peptides have several limitations as drug molecules, we screened a chemical library to find drug-like compounds that could be used to modulate the function(s) of PSA.

METHODS

Almost 50,000 compounds were analyzed for their ability to modulate PSA activity towards a fluorescent PSA-substrate. The ability of the most active compounds to affect the anti-angiogenic activity of PSA was analyzed by human umbilical vein endothelial cell (HUVEC) tube formation assay.

RESULTS

In the initial screening we identified two compounds that inhibited PSA activity. Based on these, similar compounds were selected and tested for activity to define structure-activity relationships. Several compounds with micromolar IC50-values were found, but they were not entirely specific towards PSA, e.g., they inhibited chymotrypsin, which has similar substrate specificity as PSA. However, it was possibly to improve the selectivity of the compounds towards PSA by small structural changes. These compounds inhibited the anti-angiogenic activity of PSA in the HUVEC model, proving that the proteolytic activity of PSA is essential for inhibition of angiogenesis.

CONCLUSIONS

We found several PSA inhibitors that could be useful tools for studying the role of PSA in cancer models and in normal physiology as showed in angiogenesis model.

Structural characterization and anti-angiogenic properties of prostate-specific antigen isoforms in seminal fluid

BACKGROUND

The prostate produces high levels of prostate-specific antigen (PSA), which has been shown to exert anti-angiogenic properties and thus might slow down prostate tumor growth. It has been suggested that the protease activity of PSA is not needed for its anti-angiogenic function. We have previously shown that seminal fluid contains both active and inactive, internally cleaved forms of PSA. The precise structural differences between these isoforms and their function are not known.

METHODS

To elucidate the structures, we purified PSA from seminal fluid and separated it by anion-exchange chromatography into six different isoforms, which were characterized by mass spectrometry. The anti-angiogenic activity of these PSA-isoforms was analyzed by human umbilical vein endothelial cell (HUVEC) tube formation assay.

RESULTS

The enzymatically active PSA-isoforms had an intact peptide moiety but could be separated into three isoforms based on differences in glycosylation. The major isoform contained PSA with a biantennary carbohydrate with terminal sialic acids on both antennae. The other active isoforms showed significant carbohydrate heterogeneity, containing one or no sialic acid. The inactive isoforms were internally cleaved at several different positions, but the fragments were held together by disulphide bonds. The enzymatic activity of PSA correlated with its inhibitory effect on the endothelial cell tube formation and the inhibition was dose-dependent at physiological concentrations, whereas enzymatically inactive internally cleaved PSA-isoforms had no effect.

CONCLUSIONS

Our results show that the anti-angiogenic effect of PSA is based on its proteolytic activity.

Gene expression changes associated with the anti-angiogenic activity of kallikrein-related peptidase 3 (KLK3) on human umbilical vein endothelial cells

Kallikrein-related peptidase 3 (KLK3, also known as prostate-specific antigen, PSA) is a chymotrypsin-like kallikrein that has anti-angiogenic properties. We have previously shown in a human umbilical vein endothelial cell (HUVEC) model that the anti-angiogenic effect of KLK3 is related to its enzyme activity. However, the mechanism of this effect remains to be clarified. To this end, we used a DNA microarray to study KLK3-induced changes in gene expression associated with reduction of HUVEC tube formation. Among the 41 000 genes studied, 311 were differentially expressed between control and KLK3-treated cells. These changes were enriched in several pathways, including those associated with proteasome, ubiquitin-mediated proteolysis, focal adhesion and regulation of the actin cytoskeleton. Furthermore, the changes were opposite to those previously described to occur during tubulogenesis. In conclusion, our results show that KLK3 induces gene expression changes in HUVECs. Although these changes might be relevant for the mechanism by which KLK3 exerts its anti-angiogenic activity, it cannot be judged from the present results whether they reflect the primary mechanism mediating the effect of KLK3 or are secondary to morphogenic differentiation.

New insights into the functional mechanisms and clinical applications of the kallikrein-related peptidase family

The Kallikrein-related peptidase (KLK) family consists of fifteen conserved serine proteases that form the largest contiguous cluster of proteases in the human genome. While primarily recognized for their clinical utilities as potential disease biomarkers, new compelling evidence suggests that this family plays a significant role in various physiological processes, including skin desquamation, semen liquefaction, neural plasticity, and body fluid homeostasis. KLK activation is believed to be mediated through highly organized proteolytic cascades, regulated through a series of feedback loops, inhibitors, auto-degradation and internal cleavages. Gene expression is mainly hormone-dependent, even though transcriptional epigenetic regulation has also been reported. These regulatory mechanisms are integrated with various signaling pathways to mediate multiple functions. Dysregulation of these pathways has been implicated in a large number of neoplastic and non-neoplastic pathological conditions. This review highlights our current knowledge of structural/phylogenetic features, functional role and regulatory/signaling mechanisms of this important family of enzymes.

Effect of Chronic Prostatitis on Angiogenic Activity and Serum Prostate Specific Antigen Level in Benign Prostatic Hyperplasia

The aim of this study was to evaluate the effect of chronic inflammatory pathology on the angiogenic activity in benign prostatic hyperplasia (BPH). Besides the presence of a relationship between serum prostate specific antigen (PSA) values and microvessel density (mvd), the intensity and extent (widespread or focal) of tissue PSA expression was also examined. The distribution of 30 cases according to the diagnosis groups was as follows: group 1, nine cases with prostatic adenocarcinoma; group 2, 10 cases with BPH and chronic prostatitis; group 3, 11 cases with BPH. The biopsy materials obtained by tru-cut biopsy (five cases) and transurethral resection (25 cases) were evaluated retrospectively. The evaluation of angiogenesis was made by CD34 immune marker, while the analysis of immunohistochemical tissue PSA expression was verified by PSA immune marker. Serum PSA levels and other clinical parameters were obtained from the clinical files of the patients. The mean age of the patients was 68 +/- 3 years (range, 48-83 years). The difference between the mean mvd values of the groups was statistically significant (chi2 = 10.492, p = 0.005). Group 1 showed higher mean mvd value than the other two groups. Although group 2 showed higher mean mvd value than group 3, the difference was not statistically significant (p = 0.863). There was no correlation between the mean mvd and serum PSA levels in any group. The intensity of PSA expression in prostate specimens was different in all groups. Maximum cases in group 3 showed high tissue PSA expression (chi2 = 12.442, p = 0.014). In group 1, there was a significant relationship between the intensity of PSA expression and the mean mvd (U = 1, p = 0.032). In group 2, a statistically significant correlation was noted between the mean serum PSA levels and the widespread occurrence of PSA expression (U = 0, p = 0.017). In the present study, we determined that chronic prostatitis had no effect on mvd in BPH cases. The correlation between tissue PSA expression and mvd was contradictory to the reports in the literature. Analyses in larger series are needed to prove the presence of a probable effect of chronic prostatitis on angiogenesis.

No association between polymorphism in the vascular endothelial growth factor gene at position -460 and sporadic prostate cancer in the Turkish population

The development and progression of prostate cancer (PCa) has biologically and genetically remained a mystery. A man's risk of developing PCa is influenced by both genetic and environmental factors. Angiogenic cytokines like vascular endothelial growth factor (VEGF) play a pivotal role in tumor angiogenesis. Single nucleotide polymorphisms in angiogenesis-dependent genes affect the sensibility of cancer development and progression. Therefore, we hypothesized a potential association between DNA sequence variations in VEGF -460 gene region and sporadic PCa patients in the Turkish population. 133 sporadic PCa patients and 157 healthy controls were studied. Genotypes were determined by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis. The distribution of genotype and allele frequencies of the polymorphism did not yield a statistically significant difference between patients and controls (P>0.05). Furthermore, classification of patients by tumor-lymph nodes-metastasis (TNM), Gleason Scores (GS) and serum prostate-specific antigen (PSA) levels did not show significant differences among the VEGF -460 C>T genotypes (P>0.05). This is the first demonstration showing that the VEGF -460 C>T polymorphism in men is not associated with sporadic PCa in the Turkish population.

Expression and Functional Characterization of the Cancer-related Serine Protease, Human Tissue Kallikrein 14

Human tissue kallikrein 14 (KLK14) is a novel extracellular serine protease. Clinical data link KLK14 expression to several diseases, primarily cancer; however, little is known of its (patho)-physiological role. To functionally characterize KLK14, we expressed and purified recombinant KLK14 in mature and proenzyme forms and determined its expression pattern, specificity, regulation, and in vitro substrates. By using our novel immunoassay, the normal and/or diseased skin, breast, prostate, and ovary contained the highest concentration of KLK14. Serum KLK14 levels were significantly elevated in prostate cancer patients compared with healthy males. KLK14 displayed trypsin-like specificity with high selectivity for P1-Arg over Lys. KLK14 activity could be regulated as follows: 1) by autolytic cleavage leading to enzymatic inactivation; 2) by the inhibitory serpins alpha1-antitrypsin, alpha2-antiplasmin, antithrombin III, and alpha1-antichymotrypsin with second order rate constants (k(+2)/Ki) of 49.8, 23.8, 1.48, and 0.224 microM(-1) min(-1), respectively, as well as plasminogen activator inhibitor-1; and 3) by citrate and zinc ions, which exerted stimulatory and inhibitory effects on KLK14 activity, respectively. We also expanded the in vitro target repertoire of KLK14 to include collagens I-IV, fibronectin, laminin, kininogen, fibrinogen, plasminogen, vitronectin, and insulin-like growth factor-binding proteins 2 and 3. Our results indicate that KLK14 may be implicated in several facets of tumor progression, including growth, invasion, and angiogenesis, as well as in arthritic disease via deterioration of cartilage. These findings may have clinical implications for the management of cancer and other disorders in which KLK14 activity is elevated.

Phase I safety, pharmacokinetic and pharmacodynamic studies of 2-methoxyestradiol alone or in combination with docetaxel in patients with locally recurrent or metastatic breast cancer

PURPOSE

We report the first phase I trials of 2-methoxyestradiol (2ME2, Panzem Capsules, EntreMed, Rockville, MD), alone and in combination with docetaxel, in patients with metastatic breast cancer (MBC).

PATIENTS AND METHODS

In Trial 001, 2ME2 monotherapy was administered orally once (200-1000 mg/d, cohorts 1-5) or twice daily (200-800 mg/q12h, cohorts 6-9) for 28 days followed by a 14-day observation period, continuously thereafter. In Trial 002, docetaxel 35 mg/m(2) was administered weekly for four of six weeks for a maximum six cycles; 2ME2 (200-1000 mg/d) was given orally once daily for 28 days followed by a 13-day observation period in cycle one, continuously thereafter. In both trials, responding or stable patients continued 2ME2 until progression.

RESULTS

Trial 001 enrolled 31 patients; there were no objective responses. Trial 002 enrolled 15 patients; ORR was 20% including one CR. There were no Grade IV toxicities; MTD was not reached in either study. When combined with docetaxel, three patients had significant transaminase elevations that returned to normal with continued treatment (in two of three patients). There was significant inter-patient variability and extensive metabolism to 2-methoxyestrone (2ME1). Steady-state AUC and trough concentrations of 2ME2 increased linearly up to 400-600 mg/d; doses above 400-600 mg/d did not increase 2ME2 levels. The target trough concentration (3-25 ng/mL) was not attained. Combined administration did not alter docetaxel or 2ME2 pharmacokinetics.

CONCLUSION

2ME2, alone or in combination with docetaxel, was well tolerated in patients with MBC but systemic exposure remained below the expected therapeutic range.

The role of kallikrein-related peptidases in prostate cancer: potential involvement in an epithelial to mesenchymal transition

Several members of the kallikrein-related peptidase family of serine proteases have proteolytic activities that may affect cancer progression; however, the in vivo significance of these activities remains uncertain. We have demonstrated that expression of PSA or KLK4, but not KLK2, in PC-3 prostate cancer cells changed the cellular morphology from epithelial to spindle-shaped, markedly reduced E-cadherin expression, increased vimentin expression and increased cellular migration. These changes are indicative of an epithelial to mesenchymal transition (EMT), a process important in embryonic development and cancer progression. The potential novel role of kallikrein-related peptidases in this process is the focus of this brief review.

Characterization of human kallikreins 6 and 10 in ascites fluid from ovarian cancer patients

OBJECTIVES

Human kallikreins 6 (hK6) and 10 (hK10) are secreted serine proteases. We previously found that hK6 and hK10 are highly overexpressed in epithelial ovarian tumors and demonstrated that serum levels of hK6 and hK10 are valuable biomarkers for ovarian cancer diagnosis and prognosis. Our aim is to purify and characterize these two kallikreins from ascites fluid of ovarian cancer patients.

METHODS

Protein concentrations of hK6 and hK10 in ovarian cancer ascites fluids were measured with ELISA-type immunoassays. hK6 and hK10 were purified from the ascites fluids with immunoaffinity columns, followed by reverse-phase high performance liquid chromatography. Purified hK6 and hK10 were then subjected to N-terminal sequencing. Enzymatic analyses were performed with synthetic fluorogenic peptides.

RESULTS

hK6 and hK10 were present in ovarian cancer ascites fluid at concentrations ranging from 0.2-571 and 0.7-220 microg/l, respectively. The majority of hK6 and hK10 in the ascites fluids were present in the free (uncomplexed) form. Both hK6 and hK10 purified from the ascites fluid were zymogens with a molecular mass of 30 kDa. Purified hK6 exhibited trypsin-like enzymatic activity, whereas no enzymatic activity was observed for purified hK10. The enzymatic activity of hK6 could be suppressed by a neutralizing monoclonal antibody.

CONCLUSIONS

The majority of hK6 secreted by the ovarian tumor cells into the ascites fluid are present in the uncomplexed, zymogen form, possessing weak trypsin-like enzymatic activity. All hK10 present in ovarian cancer ascites fluids are in the uncomplexed, zymogen form and have no detectable enzymatic activity.