Prognostic value of kallikrein-related peptidase 6 protein expression levels in advanced ovarian cancer evaluated by automated quantitative analysis (AQUA)

A potent, proteolysis-resistant inhibitor of kallikrein-related peptidase 6 (KLK6) for cancer therapy, developed by combinatorial engineering

Human tissue kallikrein (KLK) proteases are hormone-like signaling molecules with important functions in cancer pathophysiology. KLK-related peptidase 6 (KLK6), specifically, is highly up-regulated in several types of cancer, where its increased activity promotes cancer invasion and metastasis. This characteristic suggests KLK6 as an attractive target for therapeutic interventions. However, inhibitors that specifically target KLK6 have not yet been reported, possibly because KLK6 shares a high sequence homology and structural similarity with other serine proteases and resists inhibition by many polypeptide inhibitors. Here, we present an innovative combinatorial approach to engineering KLK6 inhibitors via flow cytometry-based screening of a yeast-displayed mutant library of the human amyloid precursor protein Kunitz protease inhibitor domain (APPI), an inhibitor of other serine proteases, such as anionic and cationic trypsins. On the basis of this screening, we generated APPI_{M17L,I18F,S19F,F34V} (APPI-4M), an APPI variant with a KLK6 inhibition constant (K_i ) of 160 pm and a turnover time of 10 days. To the best of our knowledge, APPI-4M is the most potent KLK6 inhibitor reported to date, displaying 146-fold improved affinity and 13-fold improved proteolytic stability compared with WT APPI (APPI_WT). We further demonstrate that APPI-4M acts as a functional inhibitor in a cell-based model of KLK6-dependent breast cancer invasion. Finally, the crystal structures of the APPI_WT/KLK6 and APPI-4M/KLK6 complexes revealed the structural and mechanistic bases for the improved KLK6 binding and proteolytic resistance of APPI-4M. We anticipate that APPI-4M will have substantial translational potential as both imaging agent and therapeutic.

Mass spectrometry based proteomics analyses in kallikrein-related peptidase research: implications for cancer research and therapy

INTRODUCTION

Kallikrein-related peptidases (KLKs) are a family of serine peptidases that are deregulated in numerous pathological conditions, with a multitude of KLK-mediated functional roles implicated in the progression of cancer. Advances in multidimensional mass spectrometry (MS)-based proteomics have facilitated the quantitative measurement of deregulated KLK expression in cancer, identifying certain KLKs, as well as their substrates, as potential cancer biomarkers. Areas covered: In this review, we discuss how these approaches have been utilized for KLK biomarker discovery and unbiased substrate determination in complex protein pools that mimic the in vivo extracellular microenvironment. Expert commentary: Although a limited number of studies have been performed, the quantity of information generated has greatly improved our understanding of the functional roles of KLKs in cancer progression. In addition, these data suggest additional means through which deregulated KLK expression may be targeted in cancer treatment, highlighting the potential therapeutic value of these state-of-the-art MS-based studies.

Stereotactic radiosurgery of early melanoma brain metastases after initiation of anti-CTLA-4 treatment is associated with improved intracranial control

BACKGROUND

Numerous studies suggest that radiation can boost antitumor immune response by stimulating release of tumor-specific antigens. However, the optimal timing between radiotherapy and immune checkpoint blockade to achieve potentially synergistic benefits is unclear.

MATERIAL AND METHODS

Multi-institutional retrospective analysis was conducted of ninety-nine metastatic melanoma patients from 2007 to 2014 treated with ipilimumab who later received stereotactic radiosurgery (SRS) for new brain metastases that developed after starting immunotherapy. All patients had complete blood count acquired before SRS. Primary outcomes were intracranial disease control and overall survival (OS).

RESULTS

The median follow-up time was 15.5months. In the MD Anderson cohort, patients who received SRS after 5.5months (n=20) of their last dose of ipilimumab had significantly worse intracranial control than patients who received SRS within 5.5months (n=51) (median 3.63 vs. 8.09months; hazard ratio [HR] 2.07, 95% confidence interval [CI] 1.03-4.16, p=0.041). OS was not different between the two arms. The improvement in intracranial control was confirmed in an independent validation cohort of 28 patients treated at Yale-New Haven Hospital. Circulating absolute lymphocyte count before SRS predicted for treatment response as those with baseline counts >1000/µL had reduced risk of intracranial recurrence compared with those with ≤1000/µL (HR 0.46, 95% CI 0.0.23-0.94, p=0.03).

CONCLUSIONS

In this multi-institutional study, patients who received SRS for new brain metastases within 5.5months after ipilimumab therapy had better intracranial disease control than those who received SRS later. Moreover, higher circulating lymphocyte count was associated with improved intracranial disease control.

Study of kallikrein-related peptidase 6 (KLK6) and its complex with α1-antitrypsin in biological fluids

BACKGROUND

Human kallikrein-related peptidase 6 (KLK6) is a member of the kallikrein family of serine proteases. KLK6 is synthesized as a preproenzyme, mainly in tissues of the central nervous system (CNS), and secreted as an inactive precursor. Serum KLK6 is a biomarker of unfavorable prognosis for ovarian cancer, but its sensitivity for early detection is relatively low. Differential glycosylation of KLK6 has been identified in ascites fluid obtained from ovarian cancer patients, suggesting the presence of unique KLK6 isoforms in biological samples.

METHODS

In the present study, we applied a two-step enrichment approach for KLK6 in ovarian cancer ascites, followed by mice immunization and production of monoclonal antibodies. Immunoaffinity techniques coupled to mass spectrometric methods were employed for hybridoma screening and target antigen identification.

RESULTS

We found that the main target of the newly-generated monoclonal antibodies target was the serine protease inhibitor α1-antitrypsin (A1AT). Additional experiments confirmed that A1AT is the main inhibitor of KLK6 in biological fluids. One new antibody (24ED138) was chosen to build a hybrid assay for the accurate quantification of the A1AT-KLK6 complex in biological samples. The aforementioned assay was evaluated with serum samples collected from patients with ovarian cancer (n=24) and normal donors (n=16) and showed slight improvement in sensitivity (~12%) compared to the standard in-house KLK6 assay.

CONCLUSIONS

We conclude that KLK6 is present in biological fluids either as free form, or bound to A1AT, and the bound form performs better than total KLK6 as a biomarker of ovarian carcinoma.

Clinical relevance of kallikrein-related peptidase 6 (KLK6) and 8 (KLK8) mRNA expression in advanced serous ovarian cancer

Most members of the kallikrein-related peptidase family have been demonstrated to be dysregulated in ovarian cancer and modulate tumor growth, migration, invasion, and resistance to chemotherapy. In the present study, we assessed the mRNA expression levels of KLK6 and KLK8 by quantitative PCR in 100 patients with advanced serous ovarian cancer FIGO stage III/IV. A pronounced correlation between KLK6 and KLK8 mRNA expression (rs = 0.636, p < 0.001) was observed, indicating coordinate expression of both peptidases. No significant associations of clinical parameters with KLK6, KLK8, and a combined score KLK6+KLK8 were found. In univariate Cox regression analysis, elevated mRNA levels of KLK6 were significantly linked with shortened overall survival (OS) (hazard ratio [HR] = 2.07, p = 0.007). While KLK8 values were not associated with patients' outcome, high KLK6+KLK8 values were significantly associated with shorter progression-free survival (HR = 1.82, p = 0.047) and showed a trend towards significance in the case of OS (HR = 1.82, p = 0.053). Strikingly, in multivariable analysis, elevated KLK6 mRNA values, apart from residual tumor mass, remained an independent predictive marker for poor OS (HR = 2.33, p = 0.005). As KLK6 mRNA and protein levels correlate, KLK6 may represent an attractive therapeutic target for potent and specific inhibitors of its enzymatic activity.

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.

Kallikrein-related peptidase 6 regulates epithelial-to-mesenchymal transition and serves as prognostic biomarker for head and neck squamous cell carcinoma patients

Background

Dysregulated expression of Kallikrein-related peptidase 6 (KLK6) is a common feature for many human malignancies and numerous studies evaluated KLK6 as a promising biomarker for early diagnosis or unfavorable prognosis. However, the expression of KLK6 in carcinomas derived from mucosal epithelia, including head and neck squamous cell carcinoma (HNSCC), and its mode of action has not been addressed so far.

Methods

Stable clones of human mucosal tumor cell lines were generated with shRNA-mediated silencing or ectopic overexpression to characterize the impact of KLK6 on tumor relevant processes in vitro. Tissue microarrays with primary HNSCC samples from a retrospective patient cohort (n = 162) were stained by immunohistochemistry and the correlation between KLK6 staining and survival was addressed by univariate Kaplan-Meier and multivariate Cox proportional hazard model analysis.

Results

KLK6 expression was detected in head and neck tumor cell lines (FaDu, Cal27 and SCC25), but not in HeLa cervix carcinoma cells. Silencing in FaDu cells and ectopic expression in HeLa cells unraveled an inhibitory function of KLK6 on tumor cell proliferation and mobility. FaDu clones with silenced KLK6 expression displayed molecular features resembling epithelial-to-mesenchymal transition, nuclear β-catenin accumulation and higher resistance against irradiation. Low KLK6 protein expression in primary tumors from oropharyngeal and laryngeal SCC patients was significantly correlated with poor progression-free (p = 0.001) and overall survival (p < 0.0005), and served as an independent risk factor for unfavorable clinical outcome.

Conclusions

In summary, detection of low KLK6 expression in primary tumors represents a promising tool to stratify HNSCC patients with high risk for treatment failure. These patients might benefit from restoration of KLK6 expression or pharmacological targeting of signaling pathways implicated in EMT.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0381-6) contains supplementary material, which is available to authorized users.

Kallikrein family proteases KLK6 and KLK7 are potential early detection and diagnostic biomarkers for serous and papillary serous ovarian cancer subtypes

Background

Early detection of ovarian cancer remains a challenge due to widespread metastases and a lack of biomarkers for early-stage disease. This study was conducted to identify relevant biomarkers for both laparoscopic and serum diagnostics in ovarian cancer.

Methods

Bioinformatics analysis and expression screening in ovarian cancer cell lines were employed. Selected biomarkers were further validated in bio-specimens of diverse cancer types and ovarian cancer subtypes. For non-invasive detection, biomarker proteins were evaluated in serum samples from ovarian cancer patients.

Results

Two kallikrein (KLK) serine protease family members (KLK6 and KLK7) were found to be significantly overexpressed relative to normal controls in most of the ovarian cancer cell lines examined. Overexpression of KLK6 and KLK7 mRNA was specific to ovarian cancer, in particular to serous and papillary serous subtypes. In situ hybridization and histopathology further confirmed significantly elevated levels of KLK6 and KLK7 mRNA and proteins in tissue epithelium and a lack of expression in neighboring stroma. Lastly, KLK6 and KLK7 protein levels were significantly elevated in serum samples from serous and papillary serous subtypes in the early stages of ovarian cancer, and therefore could potentially decrease the high “false negative” rates found in the same patients with the common ovarian cancer biomarkers human epididymis protein 4 (HE4) and cancer antigen 125 (CA-125).

Conclusion

KLK6 and KLK7 mRNA and protein overexpression is directly associated with early-stage ovarian tumors and can be measured in patient tissue and serum samples. Assays based on KLK6 and KLK7 expression may provide specific and sensitive information for early detection of ovarian cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-014-0109-z) contains supplementary material, which is available to authorized users.

Kallikrein-related peptidase-6 (KLK6) mRNA expression is an independent prognostic tissue biomarker of poor disease-free and overall survival in colorectal adenocarcinoma

Members of the family of tissue kallikrein and kallikrein-related peptidases possess important prognostic value in cancer. Moreover, the oncogenic role of kallikrein-related peptidase-6 (KLK6) in colorectal cancer has been well documented so far. This study investigated the prognostic value of KLK6 mRNA expression as a molecular tissue biomarker in colorectal adenocarcinoma. For this purpose, KLK6 mRNA expression was studied in 110 primary colorectal adenocarcinomas and 39 paired noncancerous colorectal specimens. A dramatic upregulation of KLK6 mRNA expression was observed in colorectal tumors. KLK6 mRNA overexpression was associated with high depth of tumor invasion, presence of distant metastases, and tumor-node-metastasis (TNM) stage of patients. Furthermore, KLK6 mRNA expression was shown to predict poor disease-free and overall survival independently of patient gender, age, tumor size, location, histological subtype, grade, venous invasion, lymphatic invasion, TNM stage, radiotherapy, and chemotherapy treatment. Moreover, Kaplan-Meier survival analysis revealed that colorectal adenocarcinoma patients with negative regional lymph nodes (N0) and those without distant metastases (M0) harboring KLK6 mRNA-positive colorectal tumors tended to relapse and die earlier than N0 and M0 patients with KLK6 mRNA-negative colorectal adenocarcinoma. Thus, KLK6 mRNA expression could be considered as an independent, unfavorable molecular prognostic biomarker in colorectal adenocarcinoma, with additional prognostic value in patients without regional or distant metastases.

Secretome and degradome profiling shows that Kallikrein-related peptidases 4, 5, 6, and 7 induce TGFβ-1 signaling in ovarian cancer cells

Kallikrein‐related peptidases, in particular KLK4, 5, 6 and 7 (4–7), often have elevated expression levels in ovarian cancer. In OV‐MZ‐6 ovarian cancer cells, combined expression of KLK4–7 reduces cell adhesion and increases cell invasion and resistance to paclitaxel. The present work investigates how KLK4–7 shape the secreted proteome (“secretome”) and proteolytic profile (“degradome”) of ovarian cancer cells. The secretome comparison consistently identified >900 proteins in three replicate analyses. Expression of KLK4–7 predominantly affected the abundance of proteins involved in cell–cell communication. Among others, this includes increased levels of transforming growth factor β‐1 (TGFβ‐1). KLK4–7 co‐transfected OV‐MZ‐6 cells share prominent features of elevated TGFβ‐1 signaling, including increased abundance of neural cell adhesion molecule L1 (L1CAM). Augmented levels of TGFβ‐1 and L1CAM upon expression of KLK4–7 were corroborated in vivo by an ovarian cancer xenograft model. The degradomic analysis showed that KLK4–7 expression mostly affected cleavage sites C‐terminal to arginine, corresponding to the preference of kallikreins 4, 5 and 6. Putative kallikrein substrates include chemokines, such as growth differentiation factor 15 (GDF 15) and macrophage migration inhibitory factor (MIF). Proteolytic maturation of TGFβ‐1 was also elevated. KLK4–7 have a pronounced, yet non‐degrading impact on the secreted proteome, with a strong association between these proteases and TGFβ‐1 signaling in tumor biology.

Expression of KLK4, 5, 6, and 7 yields subtle secretome and degradome alterations.

Pro‐ and anti‐tumorigenic proteins are affected.

TGFβ‐1 signaling is elevated.

Degradomic analysis supports cell‐contextual KLK activity.

Potential substrates of KLK4–7 have been identified.

Common variation in Kallikrein genes KLK5, KLK6, KLK12, and KLK13 and risk of prostate cancer and tumor aggressiveness

The human tissue Kallikrein family consists of 15 genes with the majority shown to be differentially expressed in cancers and/or indicators of cancer prognosis. We sought to elucidate the role of common genetic variation in four of the Kallikrein genes, KLK5, KLK6, KLK12, and KLK13, in prostate cancer risk and tumor aggressiveness. Genotyping of all 22 tagging single nucleotide polymorphisms (tagSNPs) in the KLK5, KLK6, KLK12, and KLK13 genes was performed in approximately 1,000 prostate cancer cases and 1,300 male controls from Australia. Data from any positive results were also accessed for 1,844 cases and 1,886 controls from a previously published prostate cancer genome-wide association study set from the United Kingdom. For one SNP in KLK12, rs3865443, there was evidence for association with prostate cancer risk of similar direction and magnitude in the replication set to that seen in the Australian cohort. We conducted genotyping of a further 309 prostate cancer cases, and combined analyses revealed an increased risk of prostate cancer for carriers of the rare homozygous genotype for rs3865443 (OR 1.28, 95% CI 1.04-1.57; P = 0.018). No other tagSNPs in the KLK5, KLK6, and KLK13 genes were consistently associated with prostate cancer risk or tumor aggressiveness. Analysis of a combined sample of 3,153 cases and 3,199 controls revealed the KLK12 tagSNP rs3865443 to be marginally statistically significantly associated with risk of prostate cancer. Considering the total number of SNPs investigated in this study, this finding should be interpreted cautiously and requires additional validation from very large datasets such as those of the Prostate Cancer Association group to investigate cancer associated alterations (PRACTICAL) Consortium.

Correlation of hK6 expression with tumor recurrence and prognosis in advanced gastric cancer

Background

Human kallikrein gene 6 (KLK6) is a member of the human kallikrein gene family (Kallikreins, KLKs). Human kallikrein-related peptidase 6 (hK6) is a trypsin-like serine protease encoded by the KLK6, has been reported to be highly expressed in several cancers including gastric cancer. In this study, we investigated the the correlation of hK6 expression with clinicopathological characteristics, tumor recurrence and prognosis in advanced gastric carcinoma after curative resection.

Methods

We retrospectively analyzed the clinical data of 129 cases advanced gastric cancer after curative gastrectomy. The expression of hK6 in advanced gastric cancer tissues compared to adjacent noncancerous tissues were examined, and the relationship between hK6 expression and clinicopathological characteristics was evaluated. In additional, these patients were followed up to investigate the relationship between hK6 expression and the survival time.

Results

The positive rate of hK6 expression was significantly higher in advanced gastric cancer tissue, than that in adjacent noncancerous and gastric ulcer tissues (36.5%, 33.3%, respectively, P < 0.001). There was a close relationship between hK6 expression and TNM stage (P = 0.005), vascular invasion (P = 0.037) and perineural invasion (P = 0.035). Furthermore, patients with hK6 positive showed significantly higher recurrence and poorer prognosis than those with hK6 negative. Multivariate analysis showed that hK6 expression was a significant independent factor for tumor recurrence and overall survival.

Conclusion

hK6 is overexpressed in advanced gastric cancer tissues. Its clinical utility may be used as an unfavorable indicator in predicting tumor recurrence and prognosis for advanced gastric cancer after operation. This study also suggests that hK6 might be a potential therapeutic target for gastric cancer.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/8558403578787206

Decreased expression of kallikrein-related peptidase 13: possible contribution to metastasis of human oral cancer

The human kallikrein-related peptidase family is comprised of 15 serine protease genes on chromosome 19q13.4. Our previous microarray analyses showed that the gene kallikrein-related peptidase 13 (KLK13) was down-regulated in oral squamous cell carcinoma (OSCC) cell lines. We evaluated the expression status of KLK13 in primary OSCCs and performed functional molecular experiments in OSCC cell lines. In 102 primary tumors studied, KLK13 expression significantly (P < 0.05) decreased compared with matched normal counterparts. Interestingly, KLK13-negative cases correlated significantly (P < 0.05) with regional lymph node metastasis. In vitro, cells overexpressing KLK13 (oeKLK13) had decreased invasiveness and motility and up-regulation of adhesion molecules (E-cadherin, α-catenin, β-catenin, junction plakoglobin, plakophilin4, desmocollin2, desmoglein3, and desmoplakin) compared with control cells. A rescue experiment that transfected oeKLK13 cells with siRNA against KLK13 restored invasiveness and migration activities with down-regulated adhesion molecules. Based on our results, we concluded that KLK13 may play an important role in regulating cellular migration and invasiveness, making the loss of KLK13 a potential biomarker for early detection of lymph node metastasis in OSCCs.

Optimizing molecular-targeted therapies in ovarian cancer: the renewed surge of interest in ovarian cancer biomarkers and cell signaling pathways

The hallmarks of ovarian cancer encompass the development of resistance, disease recurrence and poor prognosis. Ovarian cancer cells express gene signatures which pose significant challenges for cancer drug development, therapeutics, prevention and management. Despite enhancements in contemporary tumor debulking surgery, tentative combination regimens and abdominal radiation which can achieve beneficial response rates, the majority of ovarian cancer patients not only experience adverse effects, but also eventually relapse. Therefore, additional therapeutic possibilities need to be explored to minimize adverse events and prolong progression-free and overall response rates in ovarian cancer patients. Currently, a revival in cancer drug discovery is devoted to identifying diagnostic and prognostic ovarian cancer biomarkers. However, the sensitivity and reliability of such biomarkers may be complicated by mutations in the BRCA1 or BRCA2 genes, diverse genetic risk factors, unidentified initiation and progression elements, molecular tumor heterogeneity and disease staging. There is thus a dire need to expand existing ovarian cancer therapies with broad-spectrum and individualized molecular targeted approaches. The aim of this review is to profile recent developments in our understanding of the interrelationships among selected ovarian tumor biomarkers, heterogeneous expression signatures and related molecular signal transduction pathways, and their translation into more efficacious targeted treatment rationales.

The physiology and pathobiology of human kallikrein-related peptidase 6 (KLK6)

The human kallikrein-related peptidase 6 (KLK6) gene belongs to the 15-member kallikrein (KLK) gene family mapping to chromosome 19q13.3-13.4. Encoding for an enzyme with trypsin-like properties, KLK6 can degrade components of the extracellular matrix. The successful utilisation of another KLK member (KLK3/PSA) for prostate cancer diagnosis has led many to evaluate KLK6 as a potential biomarker for other cancer and diseased states. The observed dysregulated expression in cancers, neurodegenerative diseases and skin conditions has led to the discovery that KLK6 participates in other cellular pathways including inflammation, receptor activation and regulation of apoptosis. Moreover, the improvements in high-throughput genomics have not only enabled the identification of sequence polymorphisms, but of transcript variants, whose functional significances have yet to be realised. This comprehensive review will summarise the current findings of KLK6 pathophysiology and discuss its potential as a viable biomarker.

Genomic instability and copy-number heterogeneity of chromosome 19q, including the kallikrein locus, in ovarian carcinomas

Many tissue kallikrein (KLK) genes and proteins are candidate diagnostic, prognostic and predictive biomarkers for ovarian cancer (OCa). We previously demonstrated that the KLK locus (19q13.3/4) is subject to copy-number gains and structural rearrangements in a pilot study of cell lines and ovarian cancer primary tissues, shown to overexpress KLK gene family members. To determine the overall frequency of genomic instability and copy-number changes, a retrospective study was conducted using formalin-fixed paraffin embedded (FFPE) tissues. Eighty-one chemotherapy naïve serous OCas were examined using 3-colour fluorescence in situ hybridization (FISH) to identify structural and numerical changes on 19q, including the KLK locus; in addition to immunohistochemistry (IHC) for KLK6, which has been shown to be overexpressed in OCa. The KLK locus was subject to copy-number changes in ∼83% of cases: net gain in 51%, net loss in 30% and amplified in 2%; and found to be chromosomally unstable (p < 0.001). All cases showed a wide range of immuoreactivity for KLK6 by IHC. Although no strong correlation could be found with copy-number, the latter was contributing factor to the observed KLK6 protein overexpression. Moreover, univariate and multivariate analyses showed an association between the net loss of the KLK locus and longer disease-free survival. Interestingly, FISH analyses indicated that chromosome 19q was subjected to structural rearrangement in 62% of cases and was significantly correlated to tumor grade (p < 0.001). We conclude that numerical and structural aberrations of chromosome 19q, affect genes including the KLK gene members, may contribute to ovarian carcinoma progression and aggressiveness.

Prognostic value and biological role of the kallikrein-related peptidases in human malignancies

Cancer is a substantial health problem for the populations of the Western world. The discovery of new molecular biomarkers for diagnosis, prognosis and monitoring patients' response to therapy can aid in combating this complicated disease. The human kallikrein-related peptidases (human tissue kallikreins [KLKs]) are encoded by a continuous multigene family, located on chromosomal region 19q13.3-4. KLK3 (prostate-specific antigen) is the most efficient cancer biomarker ever employed. KLK genes are expressed abnormally in various malignancies, where they affect cancer-cell growth and metastasis. Their deregulated expression pattern, often associated with various clinicopathological characteristics of cancer patients, can be exploited, solely or within multiparametric panels, as a prognostic biomarker. Recent data illustrate that discernible molecular modulations of KLKs, occurring as a result of cancer cells' treatment with antitumor agents, may serve as new potential biomarkers, possibly predicting patients' treatment response. It is believed that KLKs might be employed in future clinical practice as novel and effective tumor markers.

Three dysregulated miRNAs control kallikrein 10 expression and cell proliferation in ovarian cancer

BACKGROUND

Kallikrein-related peptidases (KLKs) are a family of serine proteases that have been shown to be dysregulated in several malignancies including ovarian cancer. The control of kallikrein genes and their physiological function in cancer is not well understood. We hypothesized that microRNAs (miRNAs) represent a novel mechanism for post-transcriptional control of KLK expression in cancer.

METHODS

We first analysed miRNA expression in ovarian cancer in silico. A total of 98 miRNAs were reported to have altered expression in ovarian cancer. Three of these miRNAs were predicted to target KLK10. We experimentally verified the predicted miR-KLK10 interaction using two independent techniques, a luciferase assay with a construct containing the KLK10 3' untranslated region (UTR), pMIR-KLK10, and measuring KLK10 protein levels after transfection with miRNA.

RESULTS

When we co-transfected cells with pMIR-KLK10 and either let-7f, miR-224, or mR-516a, we saw decreased luciferase signal, suggesting that these miRNAs can target KLK10. We then examined the effect of these three miRNAs on KLK10 protein expression and cell growth. Transfection of all miRNAs, let-7f, miR-224, and miR-516a led to a decrease in protein expression and cellular growth. This effect was shown to be dose dependent. The KLK10 protein levels were partially restored by co-transfecting let-7f and its inhibitor. In addition, there was a slight decrease in KLK10 mRNA expression after transfection with let-7f.

CONCLUSION

Our results confirm that KLKs can be targeted by more than one miRNA. Increased expression of certain miRNAs in ovarian cancer can lead to decreased KLK protein expression and subsequently have a negative effect on cell proliferation. This dose-dependent effect suggests that a 'tweaking' or 'fine-tuning' mechanism exists in which the expression of one KLK can be controlled by multiple miRNAs. These data together suggest that miRNA may be used as potential therapeutic options and further studies are required.

KLK6 and KLK13 predict tumor recurrence in epithelial ovarian carcinoma

Background:

The human kallikrein-related peptidase family consists of 15 genes. Twelve of these genes are overexpressed in ovarian cancer and may represent potential markers for diagnosis, prognosis, and/or response to treatment. The aim of this study was to determine the prognostic significance of kallikrein-related peptidase 6 (KLK6) and kallikrein-related peptidase 13 (KLK13) in epithelial ovarian cancer by quantifying gene expression levels with tumour pathology and patient survival data.

Methods:

Total RNA was isolated from 106 patients diagnosed with primary ovarian cancer, as well as 8 normal ovary controls. Samples were analysed by quantitative real-time PCR for KLK6 and KLK13 expression. Correlation between kallikrein gene expression and clinical characteristics was evaluated with the χ²-test. Survival analysis was performed using Kaplan–Meier and Cox proportional hazards regression models.

Results:

Expression levels of both KLK6 and KLK13 mRNA were significantly increased in invasive cancers relative to normal ovaries (P=0.002 and 0.039 respectively). High KLK6 and KLK13 expression was an indicator of poor prognosis, with patients having a shorter recurrence-free survival (P=0.002 and 0.027 respectively). High KLK6 expression was also significantly associated with lower overall survival (P=0.011). When subjected to multivariate analysis, patients with either high KLK6 or KLK13 were 3- and 2.2-fold, respectively, more likely to have a recurrence than patients with low kallikrein expression.

Conclusion:

These data show increased mRNA expression of KLK6 and KLK13 in ovarian cancer compared to normal ovarian tissues. High KLK6 or KLK13 expression in primary ovarian tumours can significantly predict prognosis in terms of recurrence-free survival and overall survival. In all, this study shows KLK6 and KLK13 as potential biomarkers and may be therapeutic targets for treatment of ovarian cancer.