Kallikrein-related peptidases (KLKs) as emerging therapeutic targets: focus on prostate cancer and skin pathologies

Kallikrein-related peptidases: mechanistic understanding for potential therapeutic targeting in cancer

INTRODUCTION

Human kallikrein-related peptidases (KLKs) represent a subgroup of 15 serine endopeptidases involved in various physiological processes and pathologies, including cancer.

AREAS COVERED

This review aims to provide a comprehensive overview of the KLK family, highlighting their genomic structure, expression profiles and substrate specificity. We explore the role of KLKs in tumorigenesis, emphasizing their potential as biomarkers and therapeutic targets in cancer treatment. The dysregulated activity of KLKs has been linked to various malignancies, making them promising candidates for cancer diagnostics and therapy.

EXPERT OPINION

: Recent advancements in understanding the mechanistic pathways of KLK-related tumorigenesis offer new prospects for developing targeted cancer treatments. Expert opinion suggests that while significant progress has been made, further research is necessary to fully exploit KLKs' potential in clinical applications.

Kallikrein-related peptidase 10 predicts prognosis and mediates tumor immunomodulation in colorectal cancer

The incidence and mortality rates of colorectal cancer (CRC) have significantly increased in recent years. It has been shown that early diagnosis of CRC improves the five-year survival of patients compared to late diagnosis, as patients with stage I disease have a five-year survival rate as high as 90 %. Through bioinformatics analysis, we identified Kallikrein 10 (KLK10), a member of the Kallikrein family, as a reliable predictor of CRC progression, particularly in patients with early-stage CRC. Furthermore, single-cell analysis revealed that KLK10 was highly expressed in tumor and partial immune cells. Analysis of the biological functions of KLK10 using the Kyoto encyclopedia of genes and genomes and gene ontology indicated that KLK10 plays a role in the proliferation and differentiation of cancer cells, along with the maintenance of tumor function and immune regulation, explicitly by T cells and macrophages. EdU cell proliferation staining, plate clone formation assay, and cell scratch assay demonstrated that KLK10 inhibition by siRNA affected the proliferation and migration of CRC cells. Cell cycle detection by flow cytometry demonstrated that KLK10 inhibition led to cell cycle arrest in the G1 phase. In addition, the proportion of M1 and M2 macrophages in 45 tumor specimens was analyzed by immunohistochemistry, the proportion of CD4+ T cells and CD8+ T cells in plasma was identified by flow cytometry, and their correlation with KLK10 was analyzed. The effects of KLK10 on T cells and macrophages were verified in independent cell experiments. The results revealed that KLK10 also activates CD4+ T cells, mediating M2-type macrophage polarization.

Expression of anoctamin 7 (ANO7) is associated with poor prognosis and mucin 2 (MUC2) in colon adenocarcinoma: a study based on TCGA data

Colon adenocarcinoma (COAD) is the predominant type of colorectal cancer. Early diagnosis and treatment can significantly improve the prognosis of COAD patients. Anoctamin 7 (ANO7), an anion channel protein, has been implicated in prostate cancer and other types of cancer. In this study, we analyzed the expression of ANO7 and its correlation with clinicopathological characteristics among COAD patients using the Gene Expression Profiling Interactive Analysis 2 (GEPIA2) and the University of Alabama at Birmingham CANcer (UALCAN) databases. The GEPIA2, Kaplan-Meier plotter, and the Survival Genie platform were employed for survival analysis. The co-expression network and potential function of ANO7 in COAD were analyzed using GeneFriends, the Database for Annotation, Visualization and Integrated Discovery (DAVID), GeneMANIA, and Pathway Studio. Our data analysis revealed a significant reduction in ANO7 expression levels within COAD tissues compared to normal tissues. Additionally, ANO7 expression was found to be associated with race and histological subtype. The COAD patients exhibiting low ANO7 expression had lower survival rates compared to those with high ANO7 expression. The genes correlated with ANO7 were significantly enriched in proteolysis and mucin type O-glycan biosynthesis pathway. Furthermore, ANO7 demonstrated a direct interaction and a positive co-expression correlation with mucin 2 (MUC2). In conclusion, our findings suggest that ANO7 might serve as a potential prognostic biomarker and potentially plays a role in proteolysis and mucin biosynthesis in the context of COAD.

Association of Kallikrein Related Peptidase 3 (KLK3) gene with dermatophytosis in the UK biobank cohort

BACKGROUND

In a previous genome wide association study (GWAS) of UK Biobank (UKB) data, we identified one susceptibility locus, tubulointerstitial nephritis antigen (TINAG), with genome wide significance for dermatophytosis. We used genotype calls from file UKB22418. These data are derived directly from Affymetrix DNA microarrays but are missing many genotype calls. Using computationally efficient approaches, UKB has entered imputed genotypes into a second dataset, UKB22828, increasing the number of testable variants by over 100-fold to 96 million variants.

METHODS

In the current study, we used UKB imputed genotypes in UKB22828 to identify dermatophytosis susceptibility loci. To identify cases of dermatophytosis, we used ICD10 code B35, which covers tinea barbae, tinea capitis, tinea unguium, tinea manuum, tinea pedis, tinea corporis, tinea imbricata, tinea cruris, other dermatophytoses and dermatophytosis, unspecified. We used PLINK, a whole-genome association analysis toolset, to analyse the UKB22828 chromosome files.

RESULTS

GWAS summary (Manhattan) plot of the meta-analysis association statistics highlighted two susceptibility loci, TINAG and Kallikrein Related Peptidase 3 (KLK3), with genome wide significance for dermatophytosis. KLK3, also known as prostate specific antigen (PSA), belongs to a subclass of serine proteases with a variety of physiological functions.

CONCLUSION

KLK3 may be a dermatophytosis susceptibility gene. KLK3 could affect risk of dermatophytosis, since kallikreins are necessary for normal homeostasis of the skin.

The roles of proteases in prostate cancer

Since the proposition of the pro-invasive activity of proteolytic enzymes over 70 years ago, several roles for proteases in cancer progression have been established. About half of the 473 active human proteases are expressed in the prostate and many of the most well-characterized members of this enzyme family are regulated by androgens, hormones essential for development of prostate cancer. Most notably, several kallikrein-related peptidases, including KLK3 (prostate-specific antigen, PSA), the most well-known prostate cancer marker, and type II transmembrane serine proteases, such as TMPRSS2 and matriptase, have been extensively studied and found to promote prostate cancer progression. Recent findings also suggest a critical role for proteases in the development of advanced and aggressive castration-resistant prostate cancer (CRPC). Perhaps the most intriguing evidence for this role comes from studies showing that the protease-activated transmembrane proteins, Notch and CDCP1, are associated with the development of CRPC. Here, we review the roles of proteases in prostate cancer, with a special focus on their regulation by androgens.

The peptide woods are lovely, dark and deep: Hunting for novel cancer antigens

Harnessing the patient's immune system to control a tumor is a proven avenue for cancer therapy. T cell therapies as well as therapeutic vaccines, which target specific antigens of interest, are being explored as treatments in conjunction with immune checkpoint blockade. For these therapies, selecting the best suited antigens is crucial. Most of the focus has thus far been on neoantigens that arise from tumor-specific somatic mutations. Although there is clear evidence that T-cell responses against mutated neoantigens are protective, the large majority of these mutations are not immunogenic. In addition, most somatic mutations are unique to each individual patient and their targeting requires the development of individualized approaches. Therefore, novel antigen types are needed to broaden the scope of such treatments. We review high throughput approaches for discovering novel tumor antigens and some of the key challenges associated with their detection, and discuss considerations when selecting tumor antigens to target in the clinic.

Vaspin Alleviates Sepsis-Induced Cardiac Injury and Cardiac Inflammation by Inhibiting Kallikrein 7 in Mice

Background

Vaspin is an important adipokine that is involved in cardiovascular diseases. This study is aimed at investigating whether vaspin participates in sepsis-induced cardiac injury and explored the possible mechanism.

Methods

First, cecal ligation and puncture (CLP) and lipopolysaccharide (LPS) were used to establish a mouse model of sepsis, and cardiac vaspin expression was examined. In addition, after pretreatment with vaspin or phosphate-buffered saline (PBS), wild-type (WT) mice underwent CLP to establish a septic model and received sham as a control. Finally, WT mice and kallikrein 7 (KLK7-/-) mice were underwent CLP with or without vaspin pretreatment.

Results

Mice that underwent CLP and were administered LPS exhibited increased vaspin expression in both the heart and serum compared with sham- or saline-treated mice. In CLP mice, pretreatment with vaspin reduced mortality and alleviated the expression of cardiac injury markers and cardiac dysfunction. In addition, vaspin reduced the cardiac levels of CD45+ cells and CD68+ cells, alleviated the cardiac inflammatory response, and reduced cardiomyocyte apoptosis. The protective effects of vaspin on CLP mice were masked by the deletion of KLK7, which was demonstrated to be a downstream signal of vaspin.

Conclusions

Vaspin alleviates cardiac inflammation and plays a protective role in sepsis-induced cardiac injury by reducing KLK7 expression.

EPA Modulates KLK Genes via miR-378: A Potential Therapy in Prostate Cancer

It is known that miRNA-378a-3p (miR-378) could be induced by eicosapentaenoic acid (EPA), an omega-3 fatty acid. Herein, we first demonstrated how miR-378 exerts anti-prostate cancer (PCa) actions by influencing multiple target genes, including KLK2, KLK4, KLK6, and KLK14, which are implicated in PCa development, cell proliferation, and cell survival. Furthermore, these genes also correlate with androgen and mTOR signaling transduction, and are considered pivotal pathways for the onset and progression of PCa. In total, four PCa cell lines and eight pairing tissues (tumor vs. normal) from clinical PCa patients were included in the current study. The results showed high significance after EPA induced tumor cells containing higher expression levels of miR-378, and led the PCa cells having low cell viabilities, and they progressed to apoptosis when compared with normal prostate cells (p < 0.001). The findings indicated that EPA might become a potential therapy for PCa, especially because it is derived from the components of natural fish oil; it may prove to be a great help for solving the problem of castration-resistant prostate cancer (CRPC).

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.

SPINKs in Tumors: Potential Therapeutic Targets

The serine protease inhibitor Kazal type (SPINK) family includes SPINK1-14 and is the largest branch in the serine protease inhibitor family. SPINKs play an important role in pancreatic physiology and disease, sperm maturation and capacitation, Nager syndrome, inflammation and the skin barrier. Evidence shows that the unregulated expression of SPINK1, 2, 4, 5, 6, 7, and 13 is closely related to human tumors. Different SPINKs exhibit various regulatory modes in different tumors and can be used as tumor prognostic markers. This article reviews the role of SPINK1, 2, 4, 5, 6, 7, and 13 in different human cancer processes and helps to identify new cancer treatment targets.

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.

KLK8 promotes the proliferation and metastasis of colorectal cancer via the activation of EMT associated with PAR1

Kallikrein-related peptidase 8 (KLK8) acts as an oncogene or anti-oncogene in various tumours, and the abnormal expression of KLK8 is involved in the carcinogenesis of several tumours. However, the role of KLK8 in colorectal cancer (CRC) and the underlying mechanism remain largely unclear. In this study, the carcinogenic effect of KLK8 was determined via CCK-8 and colony formation assays in vitro and a xenograft model in nude mice in vivo. The metastasis-promoting effect of KLK8 was investigated with transwell migration and invasion assays and wound-healing assay in vitro and a metastasis model in nude mice in vivo. Bioinformatics analyses and mechanistic experiments were conducted to elucidate the molecular mechanism. Herein, we reported that KLK8 had a promotive effect on the proliferation, migration and invasion of RKO and SW480 cells. Epithelial-mesenchymal transition (EMT) played an important role in the promotive effects of KLK8 on CRC. In addition, protease-activated receptor-1 (PAR-1) antagonist SCH79797 but not protease-activated receptor-2 (PAR-2) antagonist FSLLRY-NH2 attenuated the proliferation, migration and invasion of KLK8-upregulated RKO and SW480 cells. PAR-1 antagonist SCH79797 reduced the tumour volume of xenograft model and decreased the metastatic nodules in the livers of metastasis model. Furthermore, SCH79797 could reverse the positive impact of KLK8 on the EMT process in CRC both in vitro and in vivo. Taken together, these findings demonstrated for the first time that KLK8 promoted EMT and CRC progression, and this effect might be, at least partly mediated by PAR1-dependent pathway.

The Tumor Proteolytic Landscape: A Challenging Frontier in Cancer Diagnosis and Therapy

In recent decades, dysregulation of proteases and atypical proteolysis have become increasingly recognized as important hallmarks of cancer, driving community-wide efforts to explore the proteolytic landscape of oncologic disease. With more than 100 proteases currently associated with different aspects of cancer development and progression, there is a clear impetus to harness their potential in the context of oncology. Advances in the protease field have yielded technologies enabling sensitive protease detection in various settings, paving the way towards diagnostic profiling of disease-related protease activity patterns. Methods including activity-based probes and substrates, antibodies, and various nanosystems that generate reporter signals, i.e., for PET or MRI, after interaction with the target protease have shown potential for clinical translation. Nevertheless, these technologies are costly, not easily multiplexed, and require advanced imaging technologies. While the current clinical applications of protease-responsive technologies in oncologic settings are still limited, emerging technologies and protease sensors are poised to enable comprehensive exploration of the tumor proteolytic landscape as a diagnostic and therapeutic frontier. This review aims to give an overview of the most relevant classes of proteases as indicators for tumor diagnosis, current approaches to detect and monitor their activity in vivo, and associated therapeutic applications.

A novel role of kallikrein-related peptidase 8 in the pathogenesis of diabetic cardiac fibrosis

Rationale: Among all the diabetic complications, diabetic cardiomyopathy, which is characterized by myocyte loss and myocardial fibrosis, is the leading cause of mortality and morbidity in diabetic patients. Tissue kallikrein-related peptidases (KLKs) are secreted serine proteases, that have distinct and overlapping roles in the pathogenesis of cardiovascular diseases. However, whether KLKs are involved in the development of diabetic cardiomyopathy remains unknown.The present study aimed to determine the role of a specific KLK in the initiation of endothelial-to-mesenchymal transition (EndMT) during the pathogenesis of diabetic cardiomyopathy.

Methods and Results-By screening gene expression profiles of KLKs, it was found that KLK8 was highly induced in the myocardium of mice with streptozotocin-induced diabetes. KLK8 deficiency attenuated diabetic cardiac fibrosis, and rescued the impaired cardiac function in diabetic mice. Small interfering RNA (siRNA)-mediated KLK8 knockdown significantly attenuated high glucose-induced endothelial damage and EndMT in human coronary artery endothelial cells (HCAECs). Diabetes-induced endothelial injury and cardiac EndMT were significantly alleviated in KLK8-deficient mice. In addition, transgenic overexpression of KLK8 led to interstitial and perivascular cardiac fibrosis, endothelial injury and EndMT in the heart. Adenovirus-mediated overexpression of KLK8 (Ad-KLK8) resulted in increases in endothelial cell damage, permeability and transforming growth factor (TGF)-β1 release in HCAECs. KLK8 overexpression also induced EndMT in HCAECs, which was alleviated by a TGF-β1-neutralizing antibody. A specificity protein-1 (Sp-1) consensus site was identified in the human KLK8 promoter and was found to mediate the high glucose-induced KLK8 expression. Mechanistically, it was identified that the vascular endothelial (VE)-cadherin/plakoglobin complex may associate with KLK8 in HCAECs. KLK8 cleaved the VE-cadherin extracellular domain, thus promoting plakoglobin nuclear translocation. Plakoglobin was required for KLK8-induced EndMT by cooperating with p53. KLK8 overexpression led to plakoglobin-dependent association of p53 with hypoxia inducible factor (HIF)-1α, which further enhanced the transactivation effect of HIF-1α on the TGF-β1 promoter. KLK8 also induced the binding of p53 with Smad3, subsequently promoting pro-EndMT reprogramming via the TGF-β1/Smad signaling pathway in HCAECs. The in vitro and in vivo findings further demonstrated that high glucose may promote plakoglobin-dependent cooperation of p53 with HIF-1α and Smad3, subsequently increasing the expression of TGF-β1 and the pro-EndMT target genes of the TGF-β1/Smad signaling pathway in a KLK8-dependent manner.

Conclusions: The present findings uncovered a novel pro-EndMT mechanism during the pathogenesis of diabetic cardiac fibrosis via the upregulation of KLK8, and may contribute to the development of future KLK8-based therapeutic strategies for diabetic cardiomyopathy.

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.

Surface loops of trypsin-like serine proteases as determinants of function

Trypsin and chymotrypsin-like serine proteases from family S1 (clan PA) constitute the largest protease group in humans and more generally in vertebrates. The prototypes chymotrypsin, trypsin and elastase represent simple digestive proteases in the gut, where they cleave nearly any protein. Multidomain trypsin-like proteases are key players in the tightly controlled blood coagulation and complement systems, as well as related proteases that are secreted from diverse immune cells. Some serine proteases are expressed in nearly all tissues and fluids of the human body, such as the human kallikreins and kallikrein-related peptidases with specialization for often unique substrates and accurate timing of activity. HtrA and membrane-anchored serine proteases fulfill important physiological tasks with emerging roles in cancer. The high diversity of all family members, which share the tandem β-barrel architecture of the chymotrypsin-fold in the catalytic domain, is conferred by the large differences of eight surface loops, surrounding the active site. The length of these loops alters with insertions and deletions, resulting in remarkably different three-dimensional arrangements. In addition, metal binding sites for Na+, Ca2+ and Zn2+ serve as regulatory elements, as do N-glycosylation sites. Depending on the individual tasks of the protease, the surface loops determine substrate specificity, control the turnover and allow regulation of activation, activity and degradation by other proteins, which are often serine proteases themselves. Most intriguingly, in some serine proteases, the surface loops interact as allosteric network, partially tuned by protein co-factors. Knowledge of these subtle and complicated molecular motions may allow nowadays for new and specific pharmaceutical or medical approaches.

Kallikrein-related peptidases in lung diseases

Human tissue kallikreins (KLKs) are 15 members of the serine protease family and are present in various healthy human tissues including airway tissues. Multiple studies have revealed their crucial role in the pathophysiology of a number of chronic, infectious and tumour lung diseases. KLK1, 3 and 14 are involved in asthma pathogenesis, and KLK1 could be also associated with the exacerbation of this inflammatory disease caused by rhinovirus. KLK5 was demonstrated as an influenza virus activating protease in humans, and KLK1 and 12 could also be involved in the activation and spread of these viruses. KLKs are associated with lung cancer, with up- or downregulation of expression depending on the KLK, cancer subtype, stage of tumour and also the microenvironment. Functional studies showed that KLK12 is a potent pro-angiogenic factor. Moreover, KLK6 promotes malignant-cell proliferation and KLK13 invasiveness. In contrast, KLK8 and KLK10 reduce proliferation and invasion of malignant cells. Considering the involvement of KLKs in various physiological and pathological processes, KLKs appear to be potential biomarkers and therapeutic targets for lung diseases.

Novel splice variants of the human kallikrein-related peptidases 11 (KLK11) and 12 (KLK12), unraveled by next-generation sequencing technology

Tissue kallikrein, kallikrein-related peptidases (KLKs), and plasma kallikrein form the largest group of serine proteases in the human genome, sharing many structural and functional characteristics. In this study, we describe the molecular cloning of four novel splice variants of the human KLK11 and KLK12 genes, discovered by combining 3' rapid amplification of cDNA ends (3' RACE), next-generation sequencing (NGS) technology, advanced bioinformatic analysis and Sanger sequencing. Expression analysis of these new transcripts in cell lines originating from 17 cancerous and two normal tissues revealed the expression pattern of each transcript. These novel KLK11 and KLK12 splice variants represent new potential cancer biomarkers.

The miRNA-kallikrein interaction: a mosaic of epigenetic regulation in cancer

The kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases with trypsin- and chymotrypsin-like activities. Dysregulated expression and/or aberrant activation of KLKs has been linked to various pathophysiological processes, including cancer. Many KLKs have been identified as potential cancer biomarkers. microRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression by pairing to the 3' untranslated region (UTR) of complimentary mRNA targets. miRNAs are dysregulated in many cancers, including prostate, kidney and ovarian cancers. Several studies have shown that miRNAs are involved in the post-transcriptional regulation of KLKs. However, recent evidence suggests that miRNAs can also act as downstream effectors of KLKs. In this review, we provide an update on the epigenetic regulation of KLKs by miRNAs. We also present recent experimental evidence that supports the regulatory role of KLKs on miRNA networks. The potential diagnostic and therapeutic applications of miRNA-kallikrein interactions are also discussed.

Mining human cancer datasets for kallikrein expression in cancer: the 'KLK-CANMAP' Shiny web tool

The dysregulation of the serine-protease family kallikreins (KLKs), comprising 15 genes, has been reportedly associated with cancer. Their expression in several tissues and physiological fluids makes them potential candidates as biomarkers and therapeutic targets. There are several databases available to mine gene expression in cancer, which often include clinical and pathological data. However, these platforms present some limitations when comparing a specific set of genes and can generate considerable unwanted data. Here, several datasets that showed significant differential expression (p<0.01) in cancer vs. normal (n=118), metastasis vs. primary (n=15) and association with cancer survival (n=21) have been compiled in a user-friendly format from two open and/or publicly available databases Oncomine and OncoLnc for the 15 KLKs. The data have been included in a free web application tool: the KLK-CANMAP https://cancerbioinformatics.shinyapps.io/klk-canmap/. This tool integrates, analyses and visualises data and it was developed with the R Shiny framework. Using KLK-CANMAP box-plots, heatmaps and Kaplan-Meier graphs can be generated for the KLKs of interest. We believe this new cancer KLK focused web tool will benefit the KLK community by narrowing the data visualisation to only the genes of interest.

Kallikrein-related peptidases represent attractive therapeutic targets for ovarian cancer

INTRODUCTION

Aberrant levels of kallikrein-related peptidases (KLK1-15) have been linked to cancer cell proliferation, invasion and metastasis. In ovarian cancer, the KLK proteolytic network has a crucial role in the tissue and tumor microenvironment. Publically available ovarian cancer genome and expression data from multiple patient cohorts show an upregulation of most KLKs. Areas covered: Here, we review the expression levels of all 15 members of this family in normal and ovarian cancer tissues, categorizing them into highly and moderately or weakly expressed KLKs, and their association with patient prognosis and survival. We summarize their tumor-biological functions determined in cell-based assays and xenograft models, further highlighting their suitability as cancer biomarkers and attractive candidates for drug development. Finally, we discuss some different pharmaceutical approaches, including peptide-based and small molecule inhibitors, cyclic peptides, depsipeptides, engineered natural inhibitors, antibodies, RNA/DNA-based aptamers, prodrugs, miRNA and siRNA. Expert opinion: In light of the results from clinical and tumor-biological studies, together with the available pharmaceutical tools, we suggest KLK4, KLK5, KLK6 and possibly KLK7 as preferred targets for inhibition in ovarian cancer.

Kallikrein-related peptidases and associated microRNAs as promising prognostic biomarkers in gastrointestinal malignancies

Gastrointestinal (GI) malignancies represent a wide spectrum of diseases of the GI tract and its accessory digestive organs, including esophageal (EC), gastric (GC), hepatocellular, pancreatic (PC) and colorectal cancers (CRC). Malignancies of the GI system are responsible for nearly 30% of cancer-related morbidity and approximately 40% of cancer-related mortality, worldwide. For this reason, the discovery of novel prognostic biomarkers that can efficiently provide a better prognosis, risk assessment and prediction of treatment response is an imperative need. Human kallikrein-related peptidases (KLKs) are a subgroup of trypsin and chymotrypsin-like serine peptidases that have emerged as promising prognosticators for many human types of cancer, being aberrantly expressed in cancerous tissues. The aberrant expression of KLKs in human malignancies is often regulated by KLK/microRNAs (miRNAs) interactions, as many miRNAs have been found to target KLKs and therefore alter their expression levels. The biomarker utility of KLKs has been elucidated not only in endocrine-related human malignancies, including those of the prostate and breast, but also in GI malignancies. The main purpose of this review is to summarize the existing information regarding the prognostic significance of KLKs in major types of GI malignancies and highlight the regulatory role of miRNAs on the expression levels of KLKs in these types of cancer.

Discovery of novel transcripts of the human tissue kallikrein (KLK1) and kallikrein-related peptidase 2 (KLK2) in human cancer cells, exploiting Next-Generation Sequencing technology

Tissue kallikrein, kallikrein-related peptidases (KLKs), and plasma kallikrein form the largest group of serine proteases in the human genome, sharing many structural and functional properties. Several KLK transcripts have been found aberrantly expressed in numerous human malignancies, confirming their prognostic or/and diagnostic values. However, the process of alternative splicing can now be studied in-depth due to the development of Next-Generation Sequencing (NGS). In the present study, we used NGS to discover novel transcripts of the KLK1 and KLK2 genes, after nested touchdown PCR. Bioinformatics analysis and PCR experiments revealed a total of eleven novel KLK transcripts (two KLK1 and nine KLK2 transcripts). In addition, the expression profiles of each novel transcript were investigated with nested PCR experiments using variant-specific primers. Since KLKs are implicated in human malignancies, qualifying as potential biomarkers, the quantification of the presented novel transcripts in human samples may have clinical applications in different types of cancer.

Molecular cloning of novel transcripts of human kallikrein-related peptidases 5, 6, 7, 8 and 9 (KLK5 - KLK9), using Next-generation sequencing

Alternative splicing of cancer-related genes is a common cellular mechanism accounting for cancer cell transcriptome complexity and affecting cell cycle control, proliferation, apoptosis, angiogenesis, invasion, and metastasis. In this study, we describe the discovery and molecular cloning of thirty novel transcripts of the human KLK5, KLK6, KLK7, KLK8 and KLK9 genes, using 3′ rapid amplification of cDNA ends (3′ RACE) and NGS technology, as well as their expression analysis in many established cell lines, originating from several distinct cancerous and normal tissues. Extensive bioinformatic analysis revealed novel splice variants of these five members of the KLK family, comprising entirely new exons, previously unknown boundaries of the already annotated exons (extensions and truncations) as well as alternative splicing events between these exons. Nested RT-PCR in a panel of human cell lines originating from seventeen cancerous and two normal tissues with the use of variant-specific pairs of primers was carried out for expression analysis of these novel splice variants, and Sanger sequencing of the respective amplicons confirmed our NGS results. Given that some splice variants of KLK family members possess clinical value, novel alternatively spliced transcripts appear as new candidate biomarkers for diagnostic and/or prognostic purposes and as targets for therapeutic strategies.

Multianalyte quantitative competitive PCR on optically encoded microspheres for an eight-gene panel related to prostate cancer

Nucleic acid-based tests have a profound impact in every medical discipline. Because multigene tests offer higher diagnostic accuracy and lower overall cost than single assays, they are especially useful for diseases, like prostate cancer, that present variability at the molecular level and diversity of available therapeutic interventions. We have developed a quantitative competitive PCR for an eight-gene panel, related to prostate cancer, that includes five genes of the human tissue kallikrein family (KLKs), prostate-specific membrane antigen (PSMA), prostate cancer antigen 3 (PCA3), and HPRT1 as a reference gene. Using PCR as a synthetic tool, a competitor was prepared for each target sequence containing the same primer binding sites as the target but differing in a short segment to enable discrimination by hybridization. The assay involves multiplex amplification of targets and competitors followed by a multiplex hybridization assay for the 16 amplification products. The assay was performed on optically encoded microspheres with oligonucleotide probes attached to their surface. The microspheres were analyzed rapidly (1 min) by flow cytometry. The signal ratio of the target and cognate competitor is a function of the target copy number in the sample prior to amplification. The multiplexing potential of the proposed method is much higher than real-time PCR and other end-point methods since there are 100 sets of commercially available microspheres.

Proteases and cytokines as mediators of interactions between cancer and stromal cells in tumours

Proteolytic enzymes are highly relevant in different processes of cancer progression. Their interplay with other signalling molecules such as cytokines represents important regulation of multicellular cross-talk. In this review, we discuss protease regulation mechanisms of cytokine signalling in various types of cancer. Additionally, we highlight the reverse whereby cytokines have an impact on protease expression in an autocrine and paracrine manner, representing complex feedback mechanisms among multiple members of these two protein families. The relevance of the protease-cytokine axis is illustrated in glioblastoma, where interactions between normal mesenchymal stem cells and cancer cells play an important role in this very malignant form of brain cancer.

Development of molecules stimulating the activity of KLK3 - an update

Kallikrein-related peptidase-3 (KLK3, known also as prostate-specific antigen, PSA) is highly expressed in the prostate. KLK3 possess antiangiogenic activity, which we have found to be related to its proteolytic activity. Thus, it may be possible to slow down the growth of prostatic tumors by enhancing this activity. We have developed peptides that enhance the proteolytic activity of KLK3. As these peptides are degraded in circulation and rapidly excreted, we have started to modify them and have succeeded in creating bioactive and more stable pseudopeptides. We have also identified small molecules stimulating the activity of KLK3, especially in synergy with peptides.

Downregulated KLK13 expression in bladder cancer highlights tumor aggressiveness and unfavorable patients' prognosis

PURPOSE

Despite recent research advantages on the molecular and subcellular background, bladder cancer (BlCa) remains a clinically neglected malignancy. This is strongly reflected by the generic approach of disease diagnosis and management. Additionally, patients' prognosis became a rather demanding task due to the great disease heterogeneity. Here, we aimed to evaluate, for the first time, the clinical value of KLK13 in BlCa.

METHODS

A total of 279 bladder specimens (137 tumors, 107 adjacent normal tissues and 35 healthy samples) were included. Total RNA was extracted, reverse transcribed, and KLK13 expression was assessed by quantitative real-time PCR.

RESULTS

KLK13 expression is significantly increased in bladder tumors compared to normal adjacent epithelium. However, reduced KLK13 expression is correlated with disease aggressiveness, including higher tumor stage and grade, and high-risk TaT1 tumors according to the EORTC stratification. Moreover, Kaplan-Meier and Cox regression analysis highlighted the prognostic value of the reduced KLK13 expression for the prediction of TaT1 patients' recurrence and shorter disease-free survival following TURBT. Finally, the combination of KLK13 expression with EORTC-risk stratification results to an improved prediction of TaT1 patients' outcome.

CONCLUSION

This first clinical study of KLK13 in BlCa reveals its deregulated expression in bladder tumors and highlights KLK13 as a promising marker for improving TaT1 patients' prognosis following treatment.