Paclitaxel resistance and multicellular spheroid formation are induced by kallikrein-related peptidase 4 in serous ovarian cancer cells in an ascites mimicking microenvironment

Cancer-mesothelial and cancer-macrophage interactions in the ovarian cancer microenvironment

The metastatic ovarian cancer microenvironment is characterized by an intricate interaction network between cancer cells and host cells. This complex heterotypic cancer-host cell crosstalk results in an environment that promotes cancer cell metastasis and treatment resistance, leading to poor patient prognosis and survival. In this review, we focus on two host cell types found in the ovarian cancer microenvironment: mesothelial cells and tumor-associated macrophages. Mesothelial cells make up the protective lining of organs in the abdominal cavity. Cancer cells attach and invade through the mesothelial monolayer to form metastatic lesions. Crosstalk between mesothelial and cancer cells can contribute to metastatic progression and chemotherapy resistance. Tumor-associated macrophages are the most abundant immune cell type in the ovarian cancer microenvironment with heterogeneous subpopulations exhibiting protumor or antitumor functions. Macrophage reprogramming toward a protumor or antitumor state can be influenced by chemotherapy and communication with cancer cells, resulting in cancer cell invasion and treatment resistance. A better understanding of cancer-mesothelial and cancer-macrophage crosstalk will uncover biomarkers of metastatic progression and therapeutic targets to restore chemotherapy sensitivity.

Current and emerging biomarkers in ovarian cancer diagnosis; CA125 and beyond

Ovarian cancer (OC) is one of the most common causes of cancer-related death in women worldwide. Its five-year survival rates are worse than the two most common gynecological cancers, cervical and endometrial. This is because it is asymptomatic in the early stages and usually detected in the advanced metastasized stage. Thus, survival is increasingly dependent on timely diagnosis. The delay in detection is contributed partly by the occurrence of non-specific clinical symptoms in the early stages and the lack of effective biomarkers and detection approaches. This underlines the need for biomarker identification and clinical validation, enabling earlier diagnosis, effective prognosis, and response to therapy. Apart from the traditional diagnostic biomarkers for OC, several new biomarkers have been delineated using advanced high-throughput molecular approaches in recent years. They are currently being clinically evaluated for their true diagnostic potential. In this chapter, we document the commonly utilized traditional screening markers and recently identified emerging biomarkers in OC diagnosis, focusing on secretory and protein biomarkers. We also briefly reviewed the recent advances and prospects in OC diagnosis.

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.

Role of Serine Proteases at the Tumor-Stroma Interface

During tumor development, invasion and metastasis, the intimate interaction between tumor and stroma shapes the tumor microenvironment and dictates the fate of tumor cells. Stromal cells can also influence anti-tumor immunity and response to immunotherapy. Understanding the molecular mechanisms that govern this complex and dynamic interplay, thus is important for cancer diagnosis and therapy. Proteolytic enzymes that are expressed and secreted by both cancer and stromal cells play important roles in modulating tumor-stromal interaction. Among, several serine proteases such as fibroblast activation protein, urokinase-type plasminogen activator, kallikrein-related peptidases, and granzymes have attracted great attention owing to their elevated expression and dysregulated activity in the tumor microenvironment. This review highlights the role of serine proteases that are mainly derived from stromal cells in tumor progression and associated theranostic applications.

Angiogenesis-related non-coding RNAs and gastrointestinal cancer

Gastrointestinal (GI) cancers are among the main reasons for cancer death globally. The deadliest types of GI cancer include colon, stomach, and liver cancers. Multiple lines of evidence have shown that angiogenesis has a key role in the growth and metastasis of all GI tumors. Abnormal angiogenesis also has a critical role in many non-malignant diseases. Therefore, angiogenesis is considered to be an important target for improved cancer treatment. Despite much research, the mechanisms governing angiogenesis are not completely understood. Recently, it has been shown that angiogenesis-related non-coding RNAs (ncRNAs) could affect the development of angiogenesis in cancer cells and tumors. The broad family of ncRNAs, which include long non-coding RNAs, microRNAs, and circular RNAs, are related to the development, promotion, and metastasis of GI cancers, especially in angiogenesis. This review discusses the role of ncRNAs in mediating angiogenesis in various types of GI cancers and looks forward to the introduction of mimetics and antagonists as possible therapeutic agents.

Carboplatin sensitivity in epithelial ovarian cancer cell lines: The impact of model systems

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy in North America, underscoring the need for the development of new therapeutic strategies for the management of this disease. Although many drugs are pre-clinically tested every year, only a few are selected to be evaluated in clinical trials, and only a small number of these are successfully incorporated into standard care. Inaccuracies with the initial in vitro drug testing may be responsible for some of these failures. Drug testing is often performed using 2D monolayer cultures or 3D spheroid models. Here, we investigate the impact that these different in vitro models have on the carboplatin response of four EOC cell lines, and in particular how different 3D models (polydimethylsiloxane-based microfluidic chips and ultra low attachment plates) influence drug sensitivity within the same cell line. Our results show that carboplatin responses were observed in both the 3D spheroid models tested using apoptosis/cell death markers by flow cytometry. Contrary to previously reported observations, these were not associated with a significant decrease in spheroid size. For the majority of the EOC cell lines (3 out of 4) a similar carboplatin response was observed when comparing both spheroid methods. Interestingly, two cell lines classified as resistant to carboplatin in 2D cultures became sensitive in the 3D models, and one sensitive cell line in 2D culture showed resistance in 3D spheroids. Our results highlight the challenges of choosing the appropriate pre-clinical models for drug testing.

PAR2 induces ovarian cancer cell motility by merging three signalling pathways to transactivate EGFR

BACKGROUND AND PURPOSE

Specific cellular functions mediated by GPCRs are often associated with signalling through a particular G protein or β-arrestin. Here, we examine signalling through a GPCR, protease-activated receptor 2 (PAR2), in a high-grade serous ovarian cancer cell line (OV90).

EXPERIMENTAL APPROACH

Human ovarian cancer tissues (n = 1,200) and nine human ovarian cancer cell lines were assessed for PAR2 expression. PAR2 signalling mechanisms leading to cell migration and invasion were dissected using cellular assays, western blots, CRISPR-Cas9 gene knockouts, pharmacological inhibitors of PAR2 and downstream signalling proteins in OV90 cancer cells.

KEY RESULTS

PAR2 was significantly overexpressed in clinical ovarian cancer tissues and in OV90 ovarian cancer cells. PAR2 agonists, an endogenous protease (trypsin) and a synthetic peptide (2f-LIGRL-NH₂ ), induced migration and invasion of OV90 ovarian cancer cells through activating a combination of Gα_q/11 , Gα_12/13 and β-arrestin1/2, but not Gα_s or Gα_i . This novel cooperative rather than parallel signalling resulted in downstream serial activation of Src kinases, then transactivation of epidermal growth factor receptor (EGFR), followed by downstream MEK-ERK1/2-FOS/MYC/STAT3-COX2 signalling. Either a PAR2 antagonist (I-191), CRISPR-Cas9 gene knockouts (PAR2 or Gα proteins or β-arrestin1/2), or inhibitors of each downstream protein attenuated human ovarian cancer cell motility.

CONCLUSION AND IMPLICATIONS

This study highlights a novel shared signalling cascade, requiring each of Gα_q/11 , Gα_12/13 and β-arrestin1/2 for PAR2-induced ovarian cancer cell migration and invasion. This mechanism controlling a cellular function is unusual in not being linked to a specific individual G protein or β-arrestin-mediated signalling pathway.

Functional balance between Tcf21-Slug defines cellular plasticity and migratory modalities in high grade serous ovarian cancer cell lines

Cellular plasticity and transitional phenotypes add to complexities of cancer metastasis that can be initiated by single cell epithelial to mesenchymal transition (EMT) or cooperative cell migration (CCM). Our study identifies novel regulatory cross-talks between Tcf21 and Slug in mediating phenotypic and migration plasticity in high-grade serous ovarian adenocarcinoma (HGSC). Differential expression and subcellular localization associate Tcf21, Slug with epithelial, mesenchymal phenotypes, respectively; however, gene manipulation approaches identify their association with additional intermediate phenotypic states, implying the existence of a multistep epithelial-mesenchymal transition program. Live imaging further associated distinct migratory modalities with the Tcf21/Slug status of cell systems and discerned proliferative/passive CCM, active CCM and EMT modes of migration. Tcf21-Slug balance identified across a phenotypic spectrum in HGSC cell lines, associated with microenvironment-induced transitions and the emergence of an epithelial phenotype following drug exposure. Phenotypic transitions and associated functionalities following drug exposure were affirmed to ensue from occupancy of Slug promoter E-box sequences by Tcf21. Our study effectively provides a framework for understanding the relevance of ovarian cancer plasticity as a function of two transcription factors.

Uncoupling Traditional Functionalities of Metastasis: The Parting of Ways with Real-Time Assays

The experimental evaluation of metastasis overly focuses on the gain of migratory and invasive properties, while disregarding the contributions of cellular plasticity, extra-cellular matrix heterogeneity, niche interactions, and tissue architecture. Traditional cell-based assays often restrict the inclusion of these processes and warrant the implementation of approaches that provide an enhanced spatiotemporal resolution of the metastatic cascade. Time lapse imaging represents such an underutilized approach in cancer biology, especially in the context of disease progression. The inclusion of time lapse microscopy and microfluidic devices in routine assays has recently discerned several nuances of the metastatic cascade. Our review emphasizes that a complete comprehension of metastasis in view of evolving ideologies necessitates (i) the use of appropriate, context-specific assays and understanding their inherent limitations; (ii) cautious derivation of inferences to avoid erroneous/overestimated clinical extrapolations; (iii) corroboration between multiple assay outputs to gauge metastatic potential; and (iv) the development of protocols with improved in situ implications. We further believe that the adoption of improved quantitative approaches in these assays can generate predictive algorithms that may expedite therapeutic strategies targeting metastasis via the development of disease relevant model systems. Such approaches could potentiate the restructuring of the cancer metastasis paradigm through an emphasis on the development of next-generation real-time assays.

Overview of tissue kallikrein and kallikrein-related peptidases in breast cancer

The kallikrein family comprises tissue kallikrein and 14 kallikrein-related peptidases (KLKs) recognized as a subgroup of secreted trypsin- or chymotrypsin-like serine proteases. KLKs are expressed in many cellular types where they regulate important physiological activities such as semen liquefaction, immune response, neural development, blood pressure, skin desquamation and tooth enamel formation. Tissue kallikrein, the oldest member and kinin-releasing enzyme, and KLK3/PSA, a tumor biomarker for prostate cancer are the most prominent components of the family. Additionally, other KLKs have shown an abnormal expression in neoplasia, particularly in breast cancer. Thus, increased levels of some KLKs may increase extracellular matrix degradation, invasion and metastasis; other KLKs modulate cell growth, survival and angiogenesis. On the contrary, KLKs can also inhibit angiogenesis and produce tumor suppression. However, there is a lack of knowledge on how KLKs are regulated in tumor microenvironment by molecules present at the site, namely cytokines, inflammatory mediators and growth factors. Little is known about the signaling pathways that control expression/secretion of KLKs in breast cancer, and further how activation of PAR receptors may contribute to functional activity in neoplasia. A better understanding of these molecular events will allow us to consider KLKs as relevant therapeutic targets for breast cancer.

Kallikrein-related peptidase 6 orchestrates astrocyte form and function through proteinase activated receptor-dependent mechanisms

Kallikrein-related peptidase 6 (Klk6) is the most abundant serine proteinase in the adult central nervous system (CNS), yet we know little regarding its physiological roles or mechanisms of action. Levels of Klk6 in the extracellular environment are dynamically regulated in CNS injury and disease positioning this secreted enzyme to affect cell behavior by potential receptor dependent and independent mechanisms. Here we show that recombinant Klk6 evokes increases in intracellular Ca2+ in primary astrocyte monolayer cultures through activation of proteinase activated receptor 1 (PAR1). In addition, Klk6 promoted a condensation of astrocyte cortical actin leading to an elongated stellate shape and multicellular aggregation in a manner that was dependent on the presence of either PAR1 or PAR2. Klk6-evoked changes in astrocyte shape were accompanied by translocation of β-catenin from the plasma membrane to the cytoplasm. These data are exciting because they demonstrate that Klk6 can influence astrocyte plasticity through receptor-dependent mechanisms. Furthermore, this study expands our understanding of the mechanisms by which kallikreins can contribute to neural homeostasis and remodeling and point to both PAR1 and PAR2 as new therapeutic targets to modulate astrocyte form and function.

Long non-coding RNA LINC01314 represses cell migration, invasion, and angiogenesis in gastric cancer via the Wnt/β-catenin signaling pathway by down-regulating KLK4

Background

In recent years, gastric cancer (GC) has become a major cause of mortality among various malignancies worldwide with high incidence rates. Long non-coding RNA (lncRNAs) may serve as oncogenes and tumor suppressors in cancers. Therefore, we investigated the effect of LINC01314 on the development of GC cells in relation to the Wnt/β-catenin signaling pathway.

Methods

Microarray data analysis was conducted to screen GC-related differentially expressed lncRNAs, followed by determination of the binding interaction between LINC01314 and kallikrein 4 (KLK4). Human GC cell line SGC-7901 was treated with over-expressed or silenced LINC01314 or KLK4 to investigate the mechanism LINC01314 affecting GC cellular activities. The levels of KLK4, Wnt-1, β-catenin, cyclin D1, N-cadherin and E-cadherin were measured, and cell invasion and migration were evaluated. Next, the tumor weight, micro-vessel density (MVD) and the expression of VEGF-C and VEGFR-3 in transplanted tumors were measured.

Results

LINC01314 was poorly expressed in GC cells and KLK4 was revealed to be a direct target gene of LINC01314. Overexpressed LINC01314 or silencing of KLK4 led to inhibited GC cell migration and invasion, corresponding to decreased Wnt-1, β-catenin, cyclin D1 and N-cadherin while increased E-cadherin. Also, in response to over-expression of LINC01314 or silencing of KLK4, tumor weight and the MVD of transplanted tumors were reduced and angiogenesis was suppressed, which was indicated by down-regulated positive expression of VEGF-C and VEGFR-3.

Conclusion

The findings indicated that over-expression of LINC01314 down-regulated KLK4 to inhibit the activation of the Wnt/β-catenin signaling pathway, thus suppressing migration, invasion, and angiogenesis in GC cells, which provides new insight for the treatment of GC.

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.

Reversing platinum resistance in ovarian cancer multicellular spheroids by targeting Bcl-2

Purpose

Peritoneal metastasis is the most common pathway for the spread of ovarian cancer. Ovarian cancer cells in ascites prefer to aggregate into the more chemoresistant multicellular spheroids (MCSs), leading to treatment failure and disease recurrence. We previously established a suspension MCS model of ovarian cancer cells in vitro and found that the MCS cells acquired drug resistance to cisplatin. In the present study, we aimed to uncover the underlying mechanism of the platinum resistance of MCS and the potential targets to reverse the drug resistance.

Materials and methods

MCS models were established for the phenotypic studies, including proliferation, invasion, migration, drug resistance, apoptosis assays, and signaling pathway analysis. The key molecule, Bcl-2, was screened by profile analysis and validated by Western blotting. siRNA was used to verify the anti-cisplatin-induced apoptosis effect of Bcl-2. The Bcl-2 inhibitor, ABT-737, was used for improving the sensitivity of MCS to cisplatin. The 50% inhibitory concentrations (IC50) were measured by viability assays treated with different concentrations of cisplatin. Flow cytometry and Western blotting were used for quantification of drug-induced apoptosis.

Results

The ovarian cancer MCS showed a proliferation-stagnant but invasive phenotype when resuspended. When treated with cisplatin, MCS cells showed much higher viability, with significantly fewer apoptotic cells than the adherent cells. Levels of Bcl-2 were upregulated in ovarian cancer ascitic cells and MCS cells. Bcl-2 knockdown by siRNA or blockage by ABT-737 enhanced the cisplatin-induced apoptosis and reduced the 50% inhibitory concentrations of cisplatin for MCS by 58.5% and 88.2%, respectively.

Conclusion

The upregulated Bcl-2 contributes to cisplatin resistance in our MCS model and targeting it sensitizes the MCS to cisplatin treatment. This provides us a preliminary treatment method for ovarian cancer peritoneal metastasis.

Kallikrein-related peptidases 4, 5, 6 and 7 regulate tumour-associated factors in serous ovarian cancer

BACKGROUND

Tissue kallikrein-related peptidases 4, 5, 6 and 7 (KLK4-7) strongly increase the malignancy of ovarian cancer cells. Deciphering their downstream effectors, we aimed at finding new potential prognostic biomarkers and treatment targets for ovarian cancer patients. KLK4-7-transfected (OV-KLK4-7) and vector-control OV-MZ-6 (OV-VC) ovarian cancer cells were established to select differentially regulated factors.

METHODS

With three independent approaches, PCR arrays, genome-wide microarray and proteome analyses, we identified 10 candidates (MSN, KRT19, COL5A2, COL1A2, BMP5, F10, KRT7, JUNB, BMP4, MMP1). To determine differential protein expression, we performed western blot analyses, immunofluorescence and immunohistochemistry for four candidates (MSN, KRT19, KRT7, JUNB) in cells, tumour xenograft and patient-derived tissues.

RESULTS

We demonstrated that KLK4-7 clearly regulates expression of MSN, KRT19, KRT7 and JUNB at the mRNA and protein levels in ovarian cancer cells and tissues. Protein expression of the top-upregulated effectors, MSN and KRT19, was investigated by immunohistochemistry in patients afflicted with serous ovarian cancer and related to KLK4-7 immunoexpression. Significant positive associations were found for KRT19/KLK4, KRT19/KLK5 and MSN/KLK7.

CONCLUSION

These findings imply that KLK4-7 exert key modulatory effects on other cancer-related genes and proteins in ovarian cancer. These downstream effectors of KLK4-7, MSN and KRT19 may represent important therapeutic targets in serous ovarian cancer.

The Role of Tumor Microenvironment in Chemoresistance: 3D Extracellular Matrices as Accomplices

BACKGROUND

The functional interplay between tumor cells and their adjacent stroma has been suggested to play crucial roles in the initiation and progression of tumors and the effectiveness of chemotherapy. The extracellular matrix (ECM), a complex network of extracellular proteins, provides both physical and chemicals cues necessary for cell proliferation, survival, and migration. Understanding how ECM composition and biomechanical properties affect cancer progression and response to chemotherapeutic drugs is vital to the development of targeted treatments.

METHODS

3D cell-derived-ECMs and esophageal cancer cell lines were used as a model to investigate the effect of ECM proteins on esophageal cancer cell lines response to chemotherapeutics. Immunohistochemical and qRT-PCR evaluation of ECM proteins and integrin gene expression was done on clinical esophageal squamous cell carcinoma biopsies. Esophageal cancer cell lines (WHCO1, WHCO5, WHCO6, KYSE180, KYSE 450 and KYSE 520) were cultured on decellularised ECMs (fibroblasts-derived ECM; cancer cell-derived ECM; combinatorial-ECM) and treated with 0.1% Dimethyl sulfoxide (DMSO), 4.2 µM cisplatin, 3.5 µM 5-fluorouracil and 2.5 µM epirubicin for 24 h. Cell proliferation, cell cycle progression, colony formation, apoptosis, migration and activation of signaling pathways were used as our study endpoints.

RESULTS

The expression of collagens, fibronectin and laminins was significantly increased in esophageal squamous cell carcinomas (ESCC) tumor samples compared to the corresponding normal tissue. Decellularised ECMs abrogated the effect of drugs on cancer cell cycling, proliferation and reduced drug induced apoptosis by 20⁻60% that of those plated on plastic. The mitogen-activated protein kinase-extracellular signal-regulated kinase (MEK-ERK) and phosphoinositide 3-kinase-protein kinase B (PI3K/Akt) signaling pathways were upregulated in the presence of the ECMs. Furthermore, our data show that concomitant addition of chemotherapeutic drugs and the use of collagen- and fibronectin-deficient ECMs through siRNA inhibition synergistically increased cancer cell sensitivity to drugs by 30⁻50%, and reduced colony formation and cancer cell migration.

CONCLUSION

Our study shows that ECM proteins play a key role in the response of cancer cells to chemotherapy and suggest that targeting ECM proteins can be an effective therapeutic strategy against chemoresistant tumors.

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.

Organotypic 3D Models of the Ovarian Cancer Tumor Microenvironment

Ovarian cancer progression involves multifaceted and variable tumor microenvironments (TMEs), from the in situ carcinoma in the fallopian tube or ovary to dissemination into the peritoneal cavity as single cells or spheroids and attachment to the mesothelial-lined surfaces of the omentum, bowel, and abdominal wall. The TME comprises the tumor vasculature and lymphatics (including endothelial cells and pericytes), in addition to mesothelial cells, fibroblasts, immune cells, adipocytes and extracellular matrix (ECM) proteins. When generating 3D models of the ovarian cancer TME, researchers must incorporate the most relevant stromal components depending on the TME in question (e.g., early or late disease). Such complexity cannot be captured by monolayer 2D culture systems. Moreover, immortalized stromal cell lines, such as mesothelial or fibroblast cell lines, do not always behave the same as primary cells whose response in functional assays may vary from donor to donor; 3D models with primary stromal cells may have more physiological relevance than those using stromal cell lines. In the current review, we discuss the latest developments in organotypic 3D models of the ovarian cancer early metastatic microenvironment. Organotypic culture models comprise two or more interacting cell types from a particular tissue. We focus on organotypic 3D models that include at least one type of primary stromal cell type in an ECM background, such as collagen or fibronectin, plus ovarian cancer cells. We provide an overview of the two most comprehensive current models—a 3D model of the omental mesothelium and a microfluidic model. We describe the cellular and non-cellular components of the models, the incorporation of mechanical forces, and how the models have been adapted and utilized in functional assays. Finally, we review a number of 3D models that do not incorporate primary stromal cells and summarize how integration of current models may be the next essential step in tackling the complexity of the different ovarian cancer TMEs.

High-throughput 3-dimensional culture of epithelial ovarian cancer cells as preclinical model of disease

BACKGROUND

Recent reports have identified distinct genomic patterns in ovarian carcinoma, including proliferative and mesenchymal-like groups, with worse outcome. The exact mechanisms driving the onset and progression of these tumors are still poorly understood. Additionally, researchers are concerned about the correct subtype stratification of the available cell line models, and the exploration of alternatives to monolayer culture. Identification of biomarkers to stratify cell lines, characterization of important processes as epithelial-mesenchymal transition (EMT), and the use of three-dimensional (3D) cultures as alternative models could be useful for cell line classification.

METHODS AND RESULTS

In this work, we present a descriptive analysis of 16 commonly used ovarian cancer cell lines. We have studied their morphology in 2- and 3D culture, and their response to cisplatin, observing in the majority of them an increased resistance in 3D. We have also performed an immunohistochemical analysis for proliferation marker Ki-67, and EMT related markers to establish phenotypes. Epithelial cells tend to show higher proliferative rates, and mesenchymal cells show an increase in EMT related markers, especially when cultured in 3D conditions.

CONCLUSIONS

We have stated the complex heterogeneity of ovarian cancer models, resembling primary tumors, agreeing with the argument that the cell line model for in vitro experiments must be carefully chosen. Our results also support that tridimensional culture could be a very helpful alternative in ovarian cancer research. Regarding EMT, a very important process for the development of this disease, some related biomarkers might be further characterized for their role in this disease development.

Ascitic fluid from advanced ovarian cancer patients compromises the activity of receptor tyrosine kinase inhibitors in 3D cell clusters of ovarian cancer cells

Ovarian cancer patients in the advanced stages of the disease show clinical ascites, which is associated with a poor prognosis. There is limited understanding of the effect of ascitic fluid on ovarian cancer cells and their response to anticancer drugs. We investigated the antitumour effects of EGFR/Her-2 (canertinib) and c-Met (PHA665752) inhibitors in a 3D cell model of three ovarian cancer lines. Single and combined inhibitor treatments affected cell growth of OVCAR-5 and SKOV-3 cell lines but not OV-90 cell line. Growth reduction was correlated with the down expression of PCNA, EGFR, HER-2, c-MET, ERK and AKT and their phosphorylation status in cells in growth factor supplemented media. However, these effects were not re-producible in OVCAR-5 and SKOV-3 cell lines when they were exposed to ascitic fluid obtained from three ovarian cancer patients. Serum albumin and protein components in the ascitic fluids may reduce the cellular uptake of the inhibitors.

Multiplicity of acquired cross-resistance in paclitaxel-resistant cancer cells is associated with feedback control of TUBB3 via FOXO3a-mediated ABCB1 regulation

Acquired drug resistance is a primary obstacle for effective cancer therapy. The correlation of point mutations in class III β-tubulin (TUBB3) and the prominent overexpression of ATP-binding cassette P-glycoprotein (ABCB1), a multidrug resistance gene, have been protruding mechanisms of resistance to microtubule disruptors such as paclitaxel (PTX) for many cancers. However, the precise underlying mechanism of the rapid onset of cross-resistance to an array of structurally and functionally unrelated drugs in PTX-resistant cancers has been poorly understood. We determined that our established PTX-resistant cancer cells display ABCB1/ABCC1-associated cross-resistance to chemically different drugs such as 5-fluorouracil, docetaxel, and cisplatin. We found that feedback activation of TUBB3 can be triggered through the FOXO3a-dependent regulation of ABCB1, which resulted in the accentuation of induced PTX resistance and encouraged multiplicity in acquired cross-resistance. FOXO3a-directed regulation of P-glycoprotein (P-gp) function suggests that control of ABCB1 involves methylation-dependent activation. Consistently, transcriptional overexpression or downregulation of FOXO3a directs inhibitor-controlled protease-degradation of TUBB3. The functional PI3K/Akt signaling is tightly responsive to FOXO3a activation alongside doxorubicin treatment, which directs FOXO3a arginine hypermethylation. In addition, we found that secretome factors from PTX-resistant cancer cells with acquired cross-resistance support a P-gp-dependent association in multidrug resistance (MDR) development, which assisted the FOXO3a-mediated control of TUBB3 feedback. The direct silencing of TUBB3 reverses induced multiple cross-resistance, reduces drug-resistant tumor mass, and suppresses the impaired microtubule stability status of PTX-resistant cells with transient cross-resistance. These findings highlight the control of the TUBB3 response to ABCB1 genetic suppressors as a mechanism to reverse the profuse development of multidrug resistance in cancer.

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.

Kallikrein-related peptidase 4 induces cancer-associated fibroblast features in prostate-derived stromal cells

The reciprocal communication between cancer cells and their microenvironment is critical in cancer progression. Although involvement of cancer‐associated fibroblasts (CAF) in cancer progression is long established, the molecular mechanisms leading to differentiation of CAFs from normal fibroblasts are poorly understood. Here, we report that kallikrein‐related peptidase‐4 (KLK4) promotes CAF differentiation. KLK4 is highly expressed in prostate epithelial cells of premalignant (prostatic intraepithelial neoplasia) and malignant lesions compared to normal prostate epithelia, especially at the peristromal interface. KLK4 induced CAF‐like features in the prostate‐derived WPMY1 normal stromal cell line, including increased expression of alpha‐smooth muscle actin, ESR1 and SFRP1. KLK4 activated protease‐activated receptor‐1 in WPMY1 cells increasing expression of several factors (FGF1, TAGLN, LOX, IL8, VEGFA) involved in prostate cancer progression. In addition, KLK4 induced WPMY1 cell proliferation and secretome changes, which in turn stimulated HUVEC cell proliferation that could be blocked by a VEGFA antibody. Importantly, the genes dysregulated by KLK4 treatment of WPMY1 cells were also differentially expressed between patient‐derived CAFs compared to matched nonmalignant fibroblasts and were further increased by KLK4 treatment. Taken together, we propose that epithelial‐derived KLK4 promotes tumour progression by actively promoting CAF differentiation in the prostate stromal microenvironment.

High levels of the AR-V7 Splice Variant and Co-Amplification of the Golgi Protein Coding YIPF6 in AR Amplified Prostate Cancer Bone Metastases

BACKGROUND

The relation between androgen receptor (AR) gene amplification and other mechanisms behind castration-resistant prostate cancer (CRPC), such as expression of constitutively active AR variants and steroid-converting enzymes has been poorly examined. Specific aim was to examine AR amplification in PC bone metastases and to explore molecular and functional consequences of this, with the long-term goal of identifying novel molecular targets for treatment.

METHODS

Gene amplification was assessed by fluorescence in situ hybridization in cryo-sections of clinical PC bone metastases (n = 40) and by PCR-based copy number variation analysis. Whole genome mRNA expression was analyzed using H12 Illumina Beadchip arrays and specific transcript levels were quantified by qRT-PCR. Protein localization was analyzed using immunohistochemistry and confocal microscopy. The YIPF6 mRNA expression was transiently knocked down and stably overexpressed in the 22Rv1 cell line as representative for CRPC, and effects on cell proliferation, colony formation, migration, and invasion were determined in vitro. Extracellular vesicles (EVs) were isolated from cell cultures using size-exclusion chromatography and enumerated by nanoparticle tracking analysis. Protein content was identified by LC-MS/MS analysis. Blood coagulation was measured as activated partial thromboplastin time (APTT). Functional enrichment analysis was performed using the MetaCore software.

RESULTS

AR amplification was detected in 16 (53%) of the bone metastases examined from CRPC patients (n = 30), and in none from the untreated patients (n = 10). Metastases with AR amplification showed high AR and AR-V7 mRNA levels, increased nuclear AR immunostaining, and co-amplification of genes such as YIPF6 in the AR proximity at Xq12. The YIPF6 protein was localized to the Golgi apparatus. YIPF6 overexpression in 22Rv1 cells resulted in reduced cell proliferation and colony formation, and in enhanced EV secretion. EVs from YIPF6 overproducing 22Rv1 cells were enriched for proteins involved in blood coagulation and, accordingly, decreased the APTT in a dose-dependent fashion.

CONCLUSIONS

AR amplified CRPC bone metastases show high AR-V7 expression that probably gives resistance to AR-targeting drugs. Co-amplification of the Golgi protein coding YIPF6 gene with the AR may enhance the secretion of pro-coagulative EVs from cancer cells and thereby stimulate tumor progression and increase the coagulopathy risk in CRPC patients. Prostate 77: 625-638, 2017. © 2017 Wiley Periodicals, Inc.

Mechanisms and Targets Involved in Dissemination of Ovarian Cancer

Ovarian carcinoma is associated with the highest death rate of all gynecological tumors. On one hand, its aggressiveness is based on the rapid dissemination of ovarian cancer cells to the peritoneum, the omentum, and organs located in the peritoneal cavity, and on the other hand, on the rapid development of resistance to chemotherapeutic agents. In this review, we focus on the metastatic process of ovarian cancer, which involves dissemination of, homing to and growth of tumor cells in distant organs, and describe promising molecular targets for possible therapeutic intervention. We provide an outline of the interaction of ovarian cancer cells with the microenvironment such as mesothelial cells, adipocytes, fibroblasts, endothelial cells, and other stromal components in the context of approaches for therapeutic interference with dissemination. The targets described in this review are discussed with respect to their validity as drivers of metastasis and to the availability of suitable efficient agents for their blockage, such as small molecules, monoclonal antibodies or antibody conjugates as emerging tools to manage this disease.

Direct and indirect mechanisms of KLK4 inhibition revealed by structure and dynamics

The kallikrein-related peptidase (KLK) family of proteases is involved in many aspects of human health and disease. One member of this family, KLK4, has been implicated in cancer development and metastasis. Understanding mechanisms of inactivation are critical to developing selective KLK4 inhibitors. We have determined the X-ray crystal structures of KLK4 in complex with both sunflower trypsin inhibitor-1 (SFTI-1) and a rationally designed SFTI-1 derivative to atomic (~1 Å) resolution, as well as with bound nickel. These structures offer a structural rationalization for the potency and selectivity of these inhibitors, and together with MD simulation and computational analysis, reveal a dynamic pathway between the metal binding exosite and the active site, providing key details of a previously proposed allosteric mode of inhibition. Collectively, this work provides insight into both direct and indirect mechanisms of inhibition for KLK4 that have broad implications for the enzymology of the serine protease superfamily, and may potentially be exploited for the design of therapeutic inhibitors.

PLGA nanoparticle encapsulation reduces toxicity while retaining the therapeutic efficacy of EtNBS-PDT in vitro

Photodynamic therapy regimens, which use light-activated molecules known as photosensitizers, are highly selective against many malignancies and can bypass certain challenging therapeutic resistance mechanisms. Photosensitizers such as the small cationic molecule EtNBS (5-ethylamino-9-diethyl-aminobenzo[a]phenothiazinium chloride) have proven potent against cancer cells that reside within acidic and hypoxic tumour microenvironments. At higher doses, however, these photosensitizers induce "dark toxicity" through light-independent mechanisms. In this study, we evaluated the use of nanoparticle encapsulation to overcome this limitation. Interestingly, encapsulation of the compound within poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PLGA-EtNBS) was found to significantly reduce EtNBS dark toxicity while completely retaining the molecule's cytotoxicity in both normoxic and hypoxic conditions. This dual effect can be attributed to the mechanism of release: EtNBS remains encapsulated until external light irradiation, which stimulates an oxygen-independent, radical-mediated process that degrades the PLGA nanoparticles and releases the molecule. As these PLGA-encapsulated EtNBS nanoparticles are capable of penetrating deeply into the hypoxic and acidic cores of 3D spheroid cultures, they may enable the safe and efficacious treatment of otherwise unresponsive tumour regions.

Mesothelial cells interact with tumor cells for the formation of ovarian cancer multicellular spheroids in peritoneal effusions

Epithelial ovarian cancer (EOC) dissemination is primarily mediated by the shedding of tumor cells from the primary site into ascites where they form multicellular spheroids that rapidly lead to peritoneal carcinomatosis. While the clinical importance and fundamental role of multicellular spheroids in EOC is increasingly appreciated, the mechanisms that regulate their formation and dictate their cellular composition remain poorly characterized. To investigate these important questions, we characterized spheroids isolated from ascites of women with EOC. We found that in these spheroids, a core of mesothelial cells was encased in a shell of tumor cells. Analysis further revealed that EOC spheroids are dynamic structures of proliferating, non-proliferating and hypoxic regions. To recapitulate these in vivo findings, we developed a three-dimensional co-culture model of primary EOC and mesothelial cells. Our analysis indicated that, compared to the OVCAR3 cell line, primary EOC cells isolated from ascites as well as mesothelial cells formed compact spheroids. Analysis of heterotypic spheroid microarchitecture revealed a structure that grossly resembles the structure of spheroids isolated from ascites. Cells that formed compact spheroids had elevated expression of β1 integrin and low expression of E-cadherin. Addition of β1 integrin blocking antibody or siRNA-mediated downregulation of β1 integrin resulted in reduced tightness of the spheroids. Interestingly, the loss of MUC16 and E-cadherin expression resulted in the formation of more compact spheroids. Therefore, our findings support the heterotypic nature of spheroids from malignant EOC ascites. In addition, our data describe an unusual link between E-cadherin expression and less compact spheroids. Our data also emphasize the role of MUC16 and β1 integrin in EOC spheroid formation.

Kallikrein-related peptidases (KLKs) and the hallmarks of cancer

The kallikrein-related peptidases (KLKs) represent the largest family of serine proteases within the human genome and are expressed in various tissues. Although they regulate several important physiological functions, KLKs have also been implicated in numerous pathophysiological processes, including cancer. Growing evidence describing the deregulation of KLK expression and secretion, as well as activation in various malignancies, has uncovered their potential as mediators of cancer progression, biomarkers of disease and as candidate therapeutic targets. The diversity of signalling pathways and proteolytic cascades involving KLKs and their downstream targets appears to affect cancer biology through multiple mechanisms, including those related to the hallmarks of cancer. The aim of this review is to provide an update on the importance of KLK-driven molecular pathways in relation to cancer cell traits associated with the hallmarks of cancer and to highlight their potential in personalized therapeutics.

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

INTRODUCTION

Tissue kallikrein and the kallikrein-related peptidases (KLKs) constitute a family of 15 homologous secreted serine proteases with trypsin- or chymotrypsin-like activities, which participate in a broad spectrum of physiological procedures. Deregulated expression and/or activation of the majority of the family members have been reported in several human diseases, thereby making KLKs ideal targets for therapeutic intervention.

AREAS COVERED

In the present review, we summarize the role of KLKs in normal human physiology and pathology, focusing on prostate cancer and skin diseases. Furthermore, we discuss the recent advances in the development of KLK-based therapies. A great number of diverse engineered KLKs inhibitors with improved potency, selectivity and immunogenicity have been synthesized by redesigning examples that are endogenous and naturally occurring. Moreover, encouraging results have been documented using KLKs-based vaccines and immunotherapies, as well as KLKs-mediated activation of pro-drugs. Finally, KLKs-targeting aptamers and KLKs-based imaging tools represent novel approaches towards the exploitation of KLKs' therapeutic value.

EXPERT OPINION

The central/critical roles of KLK family in several human pathologies highlight KLKs as attractive molecular targets for developing novel therapeutics.

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.

Identifying microRNA-mRNA regulatory network in gemcitabine-resistant cells derived from human pancreatic cancer cells

Pancreatic cancer is unresectable in over 80 % of patients owing to difficulty in early diagnosis. Chemotherapy is the most frequently adopted therapy for advanced pancreatic cancer. The development of drug resistance to gemcitabine (GEM), which is always used in standard chemotherapy, often results in therapeutic failure. However, the molecular mechanisms underlying the gemcitabine resistance remain unclear. Therefore, we sought to explore the microRNA-mRNA network that is associated with the development of gemcitabine resistance and to identify molecular targets for overcoming the gemcitabine resistance. By exposing SW1990 pancreatic cancer cells to long-term gemcitabine with increasing concentrations, we established a gemcitabine-resistant cell line (SW1990/GEM) with a high IC50 (the concentration needed for 50 % growth inhibition, 847.23 μM). The mRNA and microRNA expression profiles of SW1990 cells and SW1990/GEM cells were determined using RNA-seq analysis. By comparing the results in control SW1990 cells, 507 upregulated genes and 550 downregulated genes in SW1990/GEM cells were identified as differentially expressed genes correlated with gemcitabine sensitivity. Gene ontology (GO) analysis showed that the differentially expressed genes were related to diverse biological processes. The upregulated genes were mainly associated with drug response and apoptosis, and the downregulated genes were correlated with cell cycle progression and RNA splicing. Concurrently, the differentially expressed microRNAs, which are the important player in drug resistance development, were also examined in SW1990/GEM cells, and 56 differential microRNAs were identified. Additionally, the expression profiles of selected genes and microRNAs were confirmed by using Q-PCR assays. Furthermore, combining the differentially expressed microRNAs and mRNAs as well as the predicted targets for these microRNAs, a core microRNA-mRNA regulatory network was constructed, which included hub microRNAs, such as hsa-miR-643, hsa-miR-4644, hsa-miR-4650-5p, hsa-miR-4455, hsa-miR-1261, and hsa-miR-3676. The predicted targets of these hub microRNAs in the microRNA-mRNA network were also observed in the identified differential genes. As a result, a differential gene and microRNA expression pattern was constructed in gemcitabine-resistant pancreatic cancer cells. Therefore, these data may be useful for the detection and treatment of drug resistance in pancreatic cancer patients, and the microRNA-mRNA network-based analysis is expected to be more effective and provides deep insights into the molecular mechanism of drug resistance.

The first potent diphenyl phosphonate KLK4 inhibitors with unexpected binding kinetics

We report the first highly potent and selective small-molecule KLK4 inhibitors, showing surprising reversible binding kinetics.

Engineered microenvironments provide new insights into ovarian and prostate cancer progression and drug responses

Tissue engineering technologies, which have originally been designed to reconstitute damaged tissue structure and function, can mimic not only tissue regeneration processes but also cancer development and progression. Bioengineered approaches allow cell biologists to develop sophisticated experimentally and physiologically relevant cancer models to recapitulate the complexity of the disease seen in patients. Tissue engineering tools enable three-dimensionality based on the design of biomaterials and scaffolds that re-create the geometry, chemistry, function and signalling milieu of the native tumour microenvironment. Three-dimensional (3D) microenvironments, including cell-derived matrices, biomaterial-based cell culture models and integrated co-cultures with engineered stromal components, are powerful tools to study dynamic processes like proteolytic functions associated with cancer progression, metastasis and resistance to therapeutics. In this review, we discuss how biomimetic strategies can reproduce a humanised niche for human cancer cells, such as peritoneal or bone-like microenvironments, addressing specific aspects of ovarian and prostate cancer progression and therapy response.

KLK-targeted Therapies for Prostate Cancer

Alternative treatments are urgently needed for prostate cancer, especially to address the aggressive metastatic castration-resistant disease. Proteolytic enzymes are involved in cancer growth and progression. The prostate produces several proteases, the most abundant ones being two members of the kallikrein-related peptidase (KLK) family, prostate-specific antigen (PSA) and KLK2. Despite the wide use of PSA as a clinical marker, the function(s) of PSA and other KLKs in prostate cancer are poorly known. Hypothetic roles of KLKs in prostate cancer include activities that may both promote and inhibit cancer growth and metastasis, including the antiangiogenic activity of PSA. Thus it may be possible to control prostate cancer growth by modulating the proteolytic activities of KLKs. PSA and KLK2 are especially attractive targets for prostate cancer treatment because of their proposed roles in tumor development and inhibition of angiogenesis in combination with their prostate selective expression. So far the number of molecules affecting selectively the activity of KLKs is limited and none of these are used to treat prostate cancer. Prodrugs that, after cleavage of the peptide part by PSA or KLK2, release active drug molecules, and PSA-targeted therapeutic vaccines have already been tested clinically in humans and the first results have been encouraging. Although KLKs are attractive targets for prostate cancer treatment, much remains to be done before their potential can be fully elucidated. The objective of this review is to address the current state of the KLKs as novel therapeutic targets for prostate cancer treatment.

Proteomic and other analyses to determine the functional consequences of deregulated kallikrein-related peptidase (KLK) expression in prostate and ovarian cancer

Rapidly developing proteomic tools are improving detection of deregulated kallikrein-related peptidase (KLK) expression, at the protein level, in prostate and ovarian cancer, as well as facilitating the determination of functional consequences downstream. MS-driven proteomics uniquely allows for the detection, identification, and quantification of thousands of proteins in a complex protein pool, and this has served to identify certain KLKs as biomarkers for these diseases. In this review, we describe applications of this technology in KLK biomarker discovery and elucidate MS-based techniques that have been used for unbiased, global screening of KLK substrates within complex protein pools. Although MS-based KLK degradomic studies are limited to date, they helped to discover an array of novel KLK substrates. Substrates identified by MS-based degradomics are reported with improved confidence over those determined by incubating a purified or recombinant substrate and protease of interest, in vitro. We propose that these novel proteomic approaches represent the way forward for KLK research, in order to correlate proteolysis of biological substrates with tissue-related consequences, toward clinical targeting of KLK expression and function for cancer diagnosis, prognosis, and therapies.

The multiple facets of drug resistance: one history, different approaches

Some cancers like melanoma and pancreatic and ovarian cancers, for example, commonly display resistance to chemotherapy, and this is the major obstacle to a better prognosis of patients. Frequently, literature presents studies in monolayer cell cultures, 3D cell cultures or in vivo studies, but rarely the same work compares results of drug resistance in different models. Several of these works are presented in this review and show that usually cells in 3D culture are more resistant to drugs than monolayer cultured cells due to different mechanisms. Searching for new strategies to sensitize different tumors to chemotherapy, many methods have been studied to understand the mechanisms whereby cancer cells acquire drug resistance. These methods have been strongly advanced along the years and therapies using different drugs have been increasingly proposed to induce cell death in resistant cells of different cancers. Recently, cancer stem cells (CSCs) have been extensively studied because they would be the only cells capable of sustaining tumorigenesis. It is believed that the resistance of CSCs to currently used chemotherapeutics is a major contributing factor in cancer recurrence and later metastasis development. This review aims to appraise the experimental progress in the study of acquired drug resistance of cancer cells in different models as well as to understand the role of CSCs as the major contributing factor in cancer recurrence and metastasis development, describing how CSCs can be identified and isolated.

Modeling platinum sensitive and resistant high-grade serous ovarian cancer: development and applications of experimental systems

High-grade serous ovarian cancer remains the most common sub-type of ovarian cancer and, characterized by high degrees of genomic instability and heterogeneity, is typified by a transition from early response to acquired resistance to platinum-based chemotherapy. Conventional models for the study of ovarian cancer have been largely limited to a set of relatively poorly characterized immortalized cell lines and recent studies have called into question the validity of some of these as reliable models. Here, we review new approaches and models systems that take into account advances in our understanding of ovarian cancer biology and advances in the technology available for their generation and study. We discuss primary cell models, 2D, 3D, and organotypic models, and “paired” sample approaches that capture the evolution of chemotherapy failure within single cases. We also overview new methods for non-invasive collection of representative tumor material from blood samples. Adoption of such methods and models will improve the quality and clinical relevance of ovarian cancer research.

Culture models to define key mediators of cancer matrix remodeling

High grade serous epithelial ovarian cancer (HG-SOC) is one of the most devastating gynecological cancers affecting women worldwide, with a poor survival rate despite clinical treatment advances. HG-SOC commonly metastasizes within the peritoneal cavity, primarily to the mesothelial cells of the omentum, which regulate an extracellular matrix rich in collagens type I, III, and IV along with laminin, vitronectin, and fibronectin. Cancer cells depend on their ability to penetrate and invade secondary tissue sites to spread, however a detailed understanding of the molecular mechanisms underlying these processes remain largely unknown. Given the high metastatic potential of HG-SOC and the associated poor clinical outcome, it is extremely important to identify the pathways and the components of which that are responsible for the progression of this disease. In vitro methods of recapitulating human disease processes are the critical first step in such investigations. In this context, establishment of an in vitro “tumor-like” micro-environment, such as 3D culture, to study early disease and metastasis of human HG-SOC is an important and highly insightful method. In recent years, many such methods have been established to investigate the adhesion and invasion of human ovarian cancer cell lines. The aim of this review is to summarize recent developments in ovarian cancer culture systems and their use to investigate clinically relevant findings concerning the key players in driving human HG-SOC.

Function and clinical relevance of kallikrein-related peptidases and other serine proteases in gynecological cancers

Gynecological cancers, including malignant tumors of the ovaries, the endometrium and the cervix, account for approximately 10% of tumor-associated deaths in women of the Western world. For screening, diagnosis, prognosis, and therapy response prediction, the group of enzymes known as serine (Ser-)proteases show great promise as biomarkers. In the present review, following a summary of the clinical facts regarding malignant tumors of the ovaries, the endometrium and the cervix, and characterization of the most important Ser-proteases, we thoroughly review the current state of knowledge relating to the use of proteases as biomarkers of the most frequent gynecological cancers. Within the Ser-protease group, the kallikrein-related peptidase (KLK) family, which encompasses a subgroup of 15 members, holds particular promise, with some acting via a tumor-promoting mechanism and others behaving as protective factors. Further, the urokinase-type plasminogen activator (uPA) and its inhibitor PAI-1 (plasminogen activator inhibitor-1) seem to play an unfavorable role in gynecological tumors, while down-regulation of high-temperature requirement proteins A 1, 2 and 3 (HtrA1,2,3) is associated with malignant disease and cancer progression. Expression/activity levels of other Ser-proteases, including the type II transmembrane Ser-proteases (TTSPs) matriptase, hepsin (TMPRSS1), and the hepsin-related protease (TMPRSS3), as well as the glycosyl-phosphatidylinositol (GPI)-anchored Ser-proteases prostasin and testisin, may be of clinical relevance in gynecological cancers. In conclusion, proteases are a rich source of biomarkers of gynecological cancer, though the enzymes' exact roles and functions merit further investigation.

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.

Hydrogel Microwell Arrays Allow the Assessment of Protease-Associated Enhancement of Cancer Cell Aggregation and Survival

Current routine cell culture techniques are only poorly suited to capture the physiological complexity of tumor microenvironments, wherein tumor cell function is affected by intricate three-dimensional (3D), integrin-dependent cell-cell and cell-extracellular matrix (ECM) interactions. 3D cell cultures allow the investigation of cancer-associated proteases like kallikreins as they degrade ECM proteins and alter integrin signaling, promoting malignant cell behaviors. Here, we employed a hydrogel microwell array platform to probe using a high-throughput mode how ovarian cancer cell aggregates of defined size form and survive in response to the expression of kallikreins and treatment with paclitaxel, by performing microscopic, quantitative image, gene and protein analyses dependent on the varying microwell and aggregate sizes. Paclitaxel treatment increased aggregate formation and survival of kallikrein-expressing cancer cells and levels of integrins and integrin-related factors. Cancer cell aggregate formation was improved with increasing aggregate size, thereby reducing cell death and enhancing integrin expression upon paclitaxel treatment. Therefore, hydrogel microwell arrays are a powerful tool to screen the viability of cancer cell aggregates upon modulation of protease expression, integrin engagement and anti-cancer treatment providing a micro-scaled yet high-throughput technique to assess malignant progression and drug-resistance.

MicroRNA-200c overexpression inhibits tumorigenicity and metastasis of CD117+CD44+ ovarian cancer stem cells by regulating epithelial-mesenchymal transition

Background

Cancer stem cells (CSCs) are believed to be ‘seed cell’ in cancer recurrence and metastasis. MicroRNAs (miRNAs) can play an important role in the progression of primary tumor towards metastasis by regulating the epithelial-mesenchymal transition (EMT). The goal of this study was to investigate the effect of miRNA-200c overexpression on the EMT, tumorigenicity and metastasis of epithelial ovarian cancer (EOC) CSCs.

Methods

The EOC CD117⁺CD44⁺CSCs were isolated from the human ovarian cancer cell line SKOV3 by using a magnetic-activated cell sorting system, and the lentivirus miR-200c transduced CSCs were then selected for the study. The assays of colony forming, wound healing, cellular migration in vitro and tumor progression in vivo were performed.

Results

The miR-200c expression was reduced in the CD117⁺CD44⁺CSCs compared with the non-CD117⁺CD44⁺CSCs. However, the stable overexpression of the miR-200c in the CD117⁺CD44⁺CSCs resulted in a significant down-regulation of ZEB-1 and the Vimentin expression, an upregulation of the E-cadherin expression as well as a decrease of colony forming, migratory and invasion in vitro. Importantly, the miR-200c overexpression significantly inhibited the CD117⁺CD44⁺CSCs xenograft growth and lung metastasis in vivo in nude mice by inhibition of the EMT. In addition, the down-regulation of ZEB-1 showed the same efficacy as the miR-200c overexpression in the CD117⁺CD44⁺CSCs.

Conclusion

These findings from this study suggest that the miR-200c overexpression may be considered a critical approach for the EOC CD117⁺CD44⁺CSCs in clinical trials.

A bioengineered 3D ovarian cancer model for the assessment of peptidase-mediated enhancement of spheroid growth and intraperitoneal spread

Cancer-associated proteases promote peritoneal dissemination and chemoresistance in malignant progression. In this study, kallikrein-related peptidases 4, 5, 6, and 7 (KLK4-7)-cotransfected OV-MZ-6 ovarian cancer cells were embedded in a bioengineered three-dimensional (3D) microenvironment that contains RGD motifs for integrin engagement to analyze their spheroid growth and survival after chemotreatment. KLK4-7-cotransfected cells formed larger spheroids and proliferated more than controls in 3D, particularly within RGD-functionalized matrices, which was reduced upon integrin inhibition. In contrast, KLK4-7-expressing cell monolayers proliferated less than controls, emphasizing the relevance of the 3D microenvironment and integrin engagement. In a spheroid-based animal model, KLK4-7-overexpression induced tumor growth after 4 weeks and intraperitoneal spread after 8 weeks. Upon paclitaxel administration, KLK4-7-expressing tumors declined in size by 91% (controls: 87%) and showed 90% less metastatic outgrowth (controls: 33%, P < 0.001). KLK4-7-expressing spheroids showed 53% survival upon paclitaxel treatment (controls: 51%), accompanied by enhanced chemoresistance-related factors, and their survival was further reduced by combination treatment of paclitaxel with KLK4/5/7 (22%, P = 0.007) or MAPK (6%, P = 0.006) inhibition. The concomitant presence of KLK4-7 in ovarian cancer cells together with integrin activation drives spheroid formation and proliferation. Combinatorial approaches of paclitaxel and KLK/MAPK inhibition may be more efficient for late-stage disease than chemotherapeutics alone as these inhibitory regimens reduced cancer spheroid growth to a greater extent than paclitaxel alone.