Clinical utility of kallikrein-related peptidases (KLK) in urogenital malignancies

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.

Prognostic impact of kallikrein-related peptidase transcript levels in prostate cancer

We aimed to study mRNA levels and prognostic impact of all 15 human kallikrein-related peptidases (KLKs) and their targets, proteinase-activated receptors (PARs), in surgically treated prostate cancer (PCa). Seventy-nine patients with localized grade group 2-4 PCas represented aggressive cases, based on metastatic progression during median follow-up of 11 years. Eighty-six patients with similar baseline characteristics, but no metastasis during follow-up, were assigned as controls. Transcript counts were detected with nCounter technology. KLK12 protein expression was investigated with immunohistochemistry. The effects of KLK12 and KLK15 were studied in LNCaP cells using RNA interference. KLK3, -2, -4, -11, -15, -10 and -12 mRNA, in decreasing order, were expressed over limit of detection (LOD). The expression of KLK2, -3, -4 and -15 was decreased and KLK12 increased in aggressive cancers, compared to controls (P < .05). Low KLK2, -3 and -15 expression was associated with short metastasis-free survival (P < .05) in Kaplan-Meier analysis. PAR1 and -2 were expressed over LOD, and PAR1 expression was higher, and PAR2 lower, in aggressive cases than controls. Together, KLKs and PARs improved classification of metastatic and lethal disease over grade, pathological stage and prostate-specific antigen combined, in random forest analyses. Strong KLK12 immunohistochemical staining was associated with short metastasis-free and PCa-specific survival in Kaplan-Meier analysis (P < .05). Knock-down of KLK15 reduced colony formation of LNCaP cells grown on Matrigel basement membrane preparation. These results support the involvement of several KLKs in PCa progression, highlighting, that they may serve as prognostic PCa biomarkers.

Biomarkers in Gynecologic Tumors

Gynecologic malignancies are one of the most frequent cancers amongst women. Biomarkers are crucial for the differential diagnosis of adnexal masses; however, their potential for diagnosis is limited. In the era of difficulty in ovarian cancer screening, novel biomarkers are defined, but CA125 still remains the most valuable one. Circulating tumor DNAs, DNA hypermethylation, metabolites, microRNAs, and kallikreins have recently turned out as ovarian cancer biomarkers and are being applied to clinical practice. For uterine cancer, genomic classification has now been described, it will be used as a prognostic tool. In this chapter, we describe ovarian, endometrial, and cervical cancer biomarkers in detail.

Stable flow-induced expression of KLK10 inhibits endothelial inflammation and atherosclerosis

Atherosclerosis preferentially occurs in arterial regions exposed to disturbed blood flow (d-flow), while regions exposed to stable flow (s-flow) are protected. The proatherogenic and atheroprotective effects of d-flow and s-flow are mediated in part by the global changes in endothelial cell (EC) gene expression, which regulates endothelial dysfunction, inflammation, and atherosclerosis. Previously, we identified kallikrein-related peptidase 10 (Klk10, a secreted serine protease) as a flow-sensitive gene in mouse arterial ECs, but its role in endothelial biology and atherosclerosis was unknown. Here, we show that KLK10 is upregulated under s-flow conditions and downregulated under d-flow conditions using in vivo mouse models and in vitro studies with cultured ECs. Single-cell RNA sequencing (scRNAseq) and scATAC sequencing (scATACseq) study using the partial carotid ligation mouse model showed flow-regulated Klk10 expression at the epigenomic and transcription levels. Functionally, KLK10 protected against d-flow-induced permeability dysfunction and inflammation in human artery ECs, as determined by NFκB activation, expression of vascular cell adhesion molecule 1 and intracellular adhesion molecule 1, and monocyte adhesion. Furthermore, treatment of mice in vivo with rKLK10 decreased arterial endothelial inflammation in d-flow regions. Additionally, rKLK10 injection or ultrasound-mediated transfection of Klk10-expressing plasmids inhibited atherosclerosis in Apoe-/- mice. Moreover, KLK10 expression was significantly reduced in human coronary arteries with advanced atherosclerotic plaques compared to those with less severe plaques. KLK10 is a flow-sensitive endothelial protein that serves as an anti-inflammatory, barrier-protective, and anti-atherogenic factor.

Multiplex enzyme activity imaging by MALDI-IMS of substrate library conversions

Enzymes are fundamental to biological processes and involved in most pathologies. Here we demonstrate the concept of simultaneously mapping multiple enzyme activities (EA) by applying enzyme substrate libraries to tissue sections and analyzing their conversion by matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS). To that end, we spray-applied a solution of 20 naturally derived peptides that are known substrates for proteases, kinases, and phosphatases to zinc-fixed paraffin tissue sections of mouse kidneys. After enzyme conversion for 5 to 120 min at 37 °C and matrix application, the tissue sections were imaged by MALDI-IMS. We could image incubation time-dependently 16 of the applied substrates with differing signal intensities and 12 masses of expected products. Utilizing inherent enzyme amplification, EA-IMS can become a powerful tool to locally study multiple, potentially even lowly expressed, enzyme activities, networks, and their pharmaceutical modulation. Differences in the substrate detectability highlight the need for future optimizations.

CD44, TGM2 and EpCAM as novel plasma markers in endometrial cancer diagnosis

Background

Endometrial cancer (EC) is the most common malignancy of the female reproductive tract. Despite years of research, the accurate screening strategy is still not available in this disease and it is usually diagnosed only after the clinical signs are present. The recent technological advances in analytical methodologies enabled detection of multiple molecules in one, small sample of biological materials. Such approach was undertaken in the presented study.

Methods

Concentrations of aldehyde dehydrogenase 1 family, member A1 (ALDH1A1), carbonic anhydrase IX (CA9), CD44, epithelial cell adhesion molecule (EpCAM), hepsin, kallikrein-6, mesothelin, midkine, neural cell adhesion molecule L1 (L1CAM), and transglutaminase 2 (TGM2) were measured using MAGPIX®System in plasma samples of 45 EC, 20 healthy controls and 11 patients with endometriosis.

Results

Significantly increased concentration in EC as compared to healthy controls were found in case of CD44 (p <  0.001), EpCAM (p = 0.033) and TGM2 (p <  0.001). EpCAM and mesothelin concentrations differed based on FIGO stages. Regression analysis revealed marker panels with high accuracy in detection of EC. The highest AUC 0.937 was attributed to the 3-marker panel of CD44/TGM2/EpCAM (84% sensitivity, 100% specificity), FIGO IA samples were discriminated from more advanced stages of EC with the mesothelin/grade 1 model featuring AUC of 0.911 (95.24% sensitivity, 78.26% specificity).

Conclusions

Novel plasma biomarkers presenting good accuracy in diagnosing EC were found with TGM2 reported for the first time as plasma marker. It was also revealed that endometriosis may share similarities in the pattern of markers alterations characteristic for EC.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5556-x) contains supplementary material, which is available to authorized users.

Characterization of kallikrein-related peptidase 4 (KLK4) mRNA expression in tumor tissue of advanced high-grade serous ovarian cancer patients

Overexpression of several members of the kallikrein-related peptidase (KLK) family, including KLK4, has been reported in ovarian cancer tissue, consistent with the fact that elevated levels of KLK protein are often also found in serum and in effusion fluids of ovarian cancer patients. In the present study, we quantitatively analyzed KLK4 tumor tissue mRNA expression levels in a homogeneous cohort including 138 patients of advanced high-grade serous ovarian cancer (FIGO stage III/IV). Age as well as ascites fluid volume were found to be significantly associated with KLK4 mRNA expression levels. In univariate Cox regression analysis, the clinical factors residual tumor mass and ascites fluid volume represented univariate predictors for both overall survival (OS) and progression-free survival (PFS). Furthermore, elevated KLK4 mRNA expression levels were significantly linked with reduced OS (p = 0.001), but not with PFS. The results concerning the association of KLK4 mRNA expression with OS were validated in a publicly available Affymetrix-based mRNA data set from The Cancer Genome Atlas (n = 252) applying the Kaplan-Meier Plotter tool (p = 0.047). In multivariable analyses, elevated KLK4 mRNA values turned out as an additional, independent predictive marker for shortened OS (p = 0.006), whereas residual tumor mass, but not ascites fluid volume, remained an independent indicator for both OS and PFS (p < 0.001 and p = 0.002, respectively). The results of the present study, obtained in a well-defined, homogenous cohort of patients afflicted with advanced high-grade serous ovarian cancer, are in line with previous reports describing high KLK4 levels as an unfavorable marker in ovarian cancer patients.

Aberrant upregulation of KLK10 promotes metastasis via enhancement of EMT and FAK/SRC/ERK axis in PDAC

Pancreatic Ductal Adenocarcinoma (PADC) metastasis is the leading cause of morality of this severe malignant tumor. Proteases are key players in the degradation of extracellular matrix which promotes the cascade of tumor metastasis. As a kind of serine proteases, the kallikrein family performs vital function on the cancer proteolysis scene, which have been proved in diverse malignant tumors. However, the specific member of kallikrein family and its function in PDAC remain unexplored. In this study, by data mining of GEO datasets, we have identified KLK10 is upregulated gene in PDAC. We found that KLK10 was significantly overexpressed in tissues of pancreatic intraepithelial neoplasia (PanIN) and PDAC from Pdx1-Cre; LSL-KrasG12D/+ mice (KC) and Pdx1-Cre; LSL-KrasG12D/+; LSL-Trp53R172H/+ mice (KPC) by immunohistochemical analysis. Moreover, KLK10 is extremely elevated in the PDAC tissues, especially that from the PDAC patients with lymphatic and distant metastasis. Aberrant KLK10 expression is significantly correlated with poor prognosis and shorter survival by univariable and multivariable analysis. Functionally, knockdown of KLK10 observably inhibits invasion and metastatic phenotype of PDAC cells in vitro and metastasis in vivo. In addition, blockade of KLK10 attenuates epithelial-mesenchymal transition and activation of FAK-SRC-ERK signaling, which explains the mechanism of KLK10 in promoting metastasis. Collectively, KLK10 should be considered as a promising biomarker for diagnosis and potential target for therapy in PDAC.

Diagnostic and prognostic biomarker potential of kallikrein family genes in different cancer types

Purpose

The aim of this study was to compare and contrast the expression of all members of the Kallikrein (KLK) family of genes across 15 cancer types and to evaluate their utility as diagnostic and prognostic biomarkers.

Results

Severe alterations were found in the expression of different Kallikrein genes across various cancers. Interestingly, renal clear cell and papillary carcinomas have similar kallikrein expression profiles, whereas, chromophobe renal cell carcinoma has a unique expression profile. Several KLK genes have excellent biomarker potential (AUC > 0.90) for chromophobe renal cell carcinoma (KLK2, KLK3, KLK4, KLK7, KLK15), renal papillary carcinoma (KLK1, KLK6, KLK7), clear cell renal cell carcinoma (KLK1, KLK6), thyroid carcinoma (KLK2, KLK4, KLK13, KLK15) and colon adenocarcinoma (KLK6, KLK7, KLK8, KLK10). Several KLK genes were significantly associated with mortality in clear cell renal cell carcinoma (KLK2: HR = 1.69; KLK4: HR = 1.63; KLK8: HR = 1.71; KLK10: HR = 2.12; KLK11: HR = 1.76; KLK14: HR = 1.86), papillary renal cell carcinoma (KLK6: HR = 3.38, KLK7: HR = 2.50), urothelial bladder carcinoma (KLK5: HR = 1.89, KLK6: HR = 1.71, KLK8: HR = 1.60), and hepatocellular carcinoma (KLK13: HR = 1.75).

Methods

The RNA-seq gene expression data were downloaded from The Cancer Genome Atlas (TCGA). Statistical analyses, including differential expression analysis, receiver operating characteristic curves and survival analysis (Cox proportional-hazards regression models) were performed.

Conclusions

A comprehensive analysis revealed the changes in the expression of different KLK genes associated with specific cancers and highlighted their potential as a diagnostic and prognostic tool.

Advanced high-grade serous ovarian cancer: inverse association of KLK13 and KLK14 mRNA levels in tumor tissue and patients' prognosis

PURPOSE

Gene expression of a variety of the 15 members of the KLK serine protease family is dysregulated in ovarian cancer. We aimed at determining the clinical relevance of KLK13 and KLK14 mRNA expression in tumor tissues of a homogeneous patient cohort afflicted with advanced high-grade serous ovarian cancer (FIGO stage III/IV).

METHODS

mRNA expression levels of KLK13 and KLK14 were assessed by quantitative PCR in tumor tissue of 91 patients and related with clinical factors and patients' outcome.

RESULTS

There was no significant association of KLK13 and KLK14 mRNA expression with the clinical factors ascitic fluid volume or residual tumor mass. In univariate Cox regression analysis, elevated KLK13 mRNA levels were significantly linked with shorter progression-free (PFS; hazard ratio [HR] = 1.97, P = 0.020) and overall survival (OS; HR = 1.81, P = 0.041). High KLK14 mRNA levels were significantly associated with prolonged PFS (HR = 0.44, P = 0.017) and showed a trend towards significance for OS (HR = 0.55, P = 0.070). In multivariable analysis, including the factors age, residual tumor mass, ascitic fluid volume, KLK13, and KLK14, both KLKs, apart from residual tumor mass, remained statistically independent predictive markers: patients with high KLK13 mRNA expression levels displayed a more than twofold increase risk for shorter PFS (HR = 2.14, P = 0.020) as well as OS (HR = 2.05, P = 0.028), whereas elevated KLK14 mRNA values were found to be significant for both, prolonged PFS (HR = 0.36, P = 0.007) and OS (HR = 0.46, P = 0.037).

CONCLUSION

These results indicate that in advanced high-grade serous ovarian cancer KLK13 may become proficient for tumor-supporting functions, whereas KLK14 may have adopted tumor-suppressing activity.

Discovery of Bladder Cancer-related Genes Using Integrative Heterogeneous Network Modeling of Multi-omics Data

In human health, a fundamental challenge is the identification of disease-related genes. Bladder cancer (BC) is a worldwide malignant tumor, which has resulted in 170,000 deaths in 2010 up from 114,000 in 1990. Moreover, with the emergence of multi-omics data, more comprehensive analysis of human diseases become possible. In this study, we propose a multi-step approach for the identification of BC-related genes by using integrative Heterogeneous Network Modeling of Multi-Omics data (iHNMMO). The heterogeneous network model properly and comprehensively reflects the multiple kinds of relationships between genes in the multi-omics data of BC, including general relationships, unique relationships under BC condition, correlational relationships within each omics and regulatory relationships between different omics. Besides, a network-based propagation algorithm with resistance is utilized to quantize the relationships between genes and BC precisely. The results of comprehensive performance evaluation suggest that iHNMMO significantly outperforms other approaches. Moreover, further analysis suggests that the top ranked genes may be functionally implicated in BC, which also confirms the superiority of iHNMMO. In summary, this study shows that disease-related genes can be better identified through reasonable integration of multi-omics data.

Tissue kallikrein-related peptidase 4 (KLK4), a novel biomarker in triple-negative breast cancer

Triple-negative breast cancer (TNBC), lacking the steroid hormone receptors ER and PR and the oncoprotein HER2, is characterized by its aggressive pattern and insensitivity to endocrine and HER2-directed therapy. Human kallikrein-related peptidases KLK1-15 provide a rich source of serine protease-type biomarkers associated with tumor growth and cancer progression for a variety of malignant diseases. In this study, recombinant KLK4 protein was generated and affinity-purified KLK4-directed polyclonal antibody pAb587 established to allow localization of KLK4 protein expression in tumor cell lines and archived formalin-fixed, paraffin-embedded TNBC tumor tissue specimens. For this, KLK4 protein expression was assessed by immunohistochemistry in primary tumor tissue sections (tissue microarrays) of 188 TNBC patients, mainly treated with anthracycline- or CMF-based polychemotherapy. KLK4 protein is localized in the cytoplasm of tumor and stroma cells. In this patient cohort, elevated stroma cell KLK4 expression, but not tumor cell KLK4 expression, is predictive for poor disease-free survival by univariate analysis (hazard ratio: 2.26,p=0.001) and multivariable analysis (hazard ratio: 2.12,p<0.01). Likewise, univariate analysis revealed a trend for statistical significance of elevated KLK4 stroma cell expression for overall survival of TNBC patients as well.

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.

Quantification of Human Kallikrein-Related Peptidases in Biological Fluids by Multiplatform Targeted Mass Spectrometry Assays

Human kallikrein-related peptidases (KLKs) are a group of 15 secreted serine proteases encoded by the largest contiguous cluster of protease genes in the human genome. KLKs are involved in coordination of numerous physiological functions including regulation of blood pressure, neuronal plasticity, skin desquamation, and semen liquefaction, and thus represent promising diagnostic and therapeutic targets. Until now, quantification of KLKs in biological and clinical samples was accomplished by enzyme-linked immunosorbent assays (ELISA). Here, we developed multiplex targeted mass spectrometry assays for the simultaneous quantification of all 15 KLKs. Proteotypic peptides for each KLK were carefully selected based on experimental data and multiplexed in single assays. Performance of assays was evaluated using three different mass spectrometry platforms including triple quadrupole, quadrupole-ion trap, and quadrupole-orbitrap instruments. Heavy isotope-labeled synthetic peptides with a quantifying tag were used for absolute quantification of KLKs in sweat, cervico-vaginal fluid, seminal plasma, and blood serum, with limits of detection ranging from 5 to 500 ng/ml. Analytical performance of assays was evaluated by measuring endogenous KLKs in relevant biological fluids, and results were compared with selected ELISAs. The multiplex targeted proteomic assays were demonstrated to be accurate, reproducible, sensitive, and specific alternatives to antibody-based assays. Finally, KLK4, a highly prostate-specific protein and a speculated biomarker of prostate cancer, was unambiguously detected and quantified by immunoenrichment-SRM assay in seminal plasma and blood serum samples from individuals with confirmed prostate cancer and negative biopsy. Mass spectrometry revealed exclusively the presence of a secreted isoform and thus unequivocally resolved earlier disputes about KLK4 identity in seminal plasma. Measurements of KLK4 in either 41 seminal plasma or 58 blood serum samples revealed no statistically significant differences between patients with confirmed prostate cancer and negative biopsy. The presented multiplex targeted proteomic assays are an alternative analytical tool to study the biological and pathological roles of human KLKs.

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.

Urothelial cancer gene regulatory networks inferred from large-scale RNAseq, Bead and Oligo gene expression data

BACKGROUND

Urothelial pathogenesis is a complex process driven by an underlying network of interconnected genes. The identification of novel genomic target regions and gene targets that drive urothelial carcinogenesis is crucial in order to improve our current limited understanding of urothelial cancer (UC) on the molecular level. The inference of genome-wide gene regulatory networks (GRN) from large-scale gene expression data provides a promising approach for a detailed investigation of the underlying network structure associated to urothelial carcinogenesis.

METHODS

In our study we inferred and compared three GRNs by the application of the BC3Net inference algorithm to large-scale transitional cell carcinoma gene expression data sets from Illumina RNAseq (179 samples), Illumina Bead arrays (165 samples) and Affymetrix Oligo microarrays (188 samples). We investigated the structural and functional properties of GRNs for the identification of molecular targets associated to urothelial cancer.

RESULTS

We found that the urothelial cancer (UC) GRNs show a significant enrichment of subnetworks that are associated with known cancer hallmarks including cell cycle, immune response, signaling, differentiation and translation. Interestingly, the most prominent subnetworks of co-located genes were found on chromosome regions 5q31.3 (RNAseq), 8q24.3 (Oligo) and 1q23.3 (Bead), which all represent known genomic regions frequently deregulated or aberated in urothelial cancer and other cancer types. Furthermore, the identified hub genes of the individual GRNs, e.g., HID1/DMC1 (tumor development), RNF17/TDRD4 (cancer antigen) and CYP4A11 (angiogenesis/ metastasis) are known cancer associated markers. The GRNs were highly dataset specific on the interaction level between individual genes, but showed large similarities on the biological function level represented by subnetworks. Remarkably, the RNAseq UC GRN showed twice the proportion of significant functional subnetworks. Based on our analysis of inferential and experimental networks the Bead UC GRN showed the lowest performance compared to the RNAseq and Oligo UC GRNs.

CONCLUSION

To our knowledge, this is the first study investigating genome-scale UC GRNs. RNAseq based gene expression data is the data platform of choice for a GRN inference. Our study offers new avenues for the identification of novel putative diagnostic targets for subsequent studies in bladder tumors.

OVSCORE - a validated score to identify ovarian cancer patients not suitable for primary surgery

Following primary debulking surgery, the presence of a residual tumor mass is one of the most important prognostic factors in ovarian cancer. In a previous study, we established the OVSCORE, an algorithm to predict surgical outcome, based on the clinical factors of nuclear grading and ascitic fluid volume, plus the cancer biomarkers, kallikrein-related peptidases (KLKs), KLK6 and KLK13. In the present study, OVSCORE performance was tested in an independent ovarian cancer patient cohort consisting of 87 patients. The impact of KLKs, KLK5, 6, 7 and 13 and other clinical factors on patient prognosis and outcome was also evaluated. The OVSCORE proved to be a strong and statistically significant predictor of surgical success in terms of area under the receiver operating characteristic curve (ROC AUC, 0.777), as well as positive and negative predictive value in this independent study group. KLK6 and 13 individually did not show clinical relevance in this cohort, but two other KLKs, KLK5 and KLK7, were associated with advanced FIGO stage, higher nuclear grade and positive lymph node status. In the multivariate Cox regression analysis for overall survival (OS), KLK7 had a protective impact on OS. This study confirms the role of KLKs in ovarian cancer for surgical success and survival, and validates the novel OVSCORE algorithm in an independent collective. As a key clinical application, the OVSCORE could aid gynecological oncologists in identifying those ovarian cancer patients unlikely to benefit from radical surgery who could be candidates for alternative therapeutic approaches.

Predictions for the future of kallikrein-related peptidases in molecular diagnostics

Kallikrein-related peptidases (KLKs) form a cancer-related ensemble of serine proteases. This multigene family hosts the most widely used cancer biomarker that is PSA-KLK3, with millions of tests performed annually worldwide. The present report provides an overview of the biomarker potential of the extended KLK family (KLK1-KLK15) in various disease settings and envisages approaches that could lead to additional KLK-driven applications in future molecular diagnostics. Particular focus is given on the inclusion of KLKs into multifaceted cancer biomarker panels that provide enhanced diagnostic, prognostic and/or predictive accuracy in several human malignancies. Such panels have been described so far for prostate, ovarian, lung and colorectal cancers. The role of KLKs as biomarkers in non-malignant disease settings, such as Alzheimer's disease and multiple sclerosis, is also commented upon. Predictions are given on the challenges and future directions regarding clinically oriented KLK research.

Metastasis of ovarian cancer is mediated by kallikrein related peptidases

Ovarian cancer, in particular epithelial ovarian cancer (EOC), is commonly diagnosed when the tumor has metastasized into the abdominal cavity with an accumulation of ascites fluid. Combining histopathology and genetic variations, EOC can be sub-grouped into Type-I and Type-II tumors, of which the latter are more aggressive and metastatic. Metastasis and chemoresistance are the key events associated with the tumor microenvironment that lead to a poor patient outcome. Kallikrein-related peptidases (KLKs) are aberrantly expressed in EOC, in particular, in the more metastatic Type-II tumors. KLKs are a family of 15 serine proteases that are expressed in diverse human tissues and involved in various patho-physiological processes. As extracellular enzymes, KLKs function in the hydrolysis of growth factors, proteases, cell membrane bound receptors, adhesion proteins, and cytokines initiating intracellular signaling pathways and their downstream events. High KLK levels are differentially associated with the prognosis of ovarian cancer patients, suggesting that they not only have application as biomarkers but also function in disease progression, and therefore are potential therapeutic targets. Recent studies have demonstrated the function of these proteases in promoting and/or suppressing the invasive behavior of ovarian cancer cells in metastasis in vitro and in vivo. Both conventional cell culture methods and three-dimensional platforms have been applied to mimic the ovarian cancer microenvironment of patients, such as the solid stromal matrix and ascites fluid. Here we summarize published studies to provide an overview of our understanding of the role of KLKs in EOC, and to lay the foundation for future research directions.