Process of hepatic metastasis from pancreatic cancer: biology with clinical significance

Molecular mechanisms of pancreatic cancer liver metastasis: the role of PAK2

Background

Pancreatic cancer remains an extremely malignant digestive tract tumor, posing a significant global public health burden. Patients with pancreatic cancer, once metastasis occurs, lose all hope of cure, and prognosis is extremely poor. It is important to investigate liver metastasis of Pancreatic cancer in depth, not just because it is the most common form of metastasis in pancreatic cancer, but also because it is crucial for treatment planning and prognosis assessment. This study aims to delve into the mechanisms of pancreatic cancer liver metastasis, with the goal of providing crucial scientific groundwork for the development of future treatment methods and drugs.

Methods

We explored the mechanisms of pancreatic cancer liver metastasis using single-cell sequencing data (GSE155698 and GSE154778) and bulk data (GSE71729, GSE19279, TCGA-PAAD). Initially, Seurat package was employed for single-cell data processing to obtain expression matrices for primary pancreatic cancer lesions and liver metastatic lesions. Subsequently, high-dimensional weighted gene co-expression network analysis (hdWGCNA) was used to identify genes associated with liver metastasis. Machine learning algorithms and COX regression models were employed to further screen genes related to patient prognosis. Informed by both biological understanding and the outcomes of algorithms, we meticulously identified the ultimate set of liver metastasis-related gene (LRG). In the study of LRG genes, various databases were utilized to validate their association with pancreatic cancer liver metastasis. In order to analyze the effects of these agents on tumor microenvironment, we conducted an in-depth analysis, including changes in signaling pathways (GSVA), cell differentiation (pseudo-temporal analysis), cell communication networks (cell communication analysis), and downstream transcription factors (transcription factor activity prediction). Additionally, drug sensitivity analysis and metabolic analysis were performed to reveal the effects of LRG on gemcitabine resistance and metabolic pathways. Finally, functional experiments were conducted by silencing the expression of LRG in PANC-1 and Bx-PC-3 cells to validate its influence to proliferation and invasiveness on PANC-1 and Bx-PC-3 cells.

Results

Through a series of algorithmic filters, we identified PAK2 as a key gene promoting pancreatic cancer liver metastasis. GSVA analysis elucidated the activation of the TGF-beta signaling pathway by PAK2 to promote the occurrence of liver metastasis. Pseudo-temporal analysis revealed a significant correlation between PAK2 expression and the lower differentiation status of pancreatic cancer cells. Cell communication analysis revealed that overexpression of PAK2 promotes communication between cancer cells and the tumor microenvironment. Transcription factor activity prediction displayed the transcription factor network regulated by PAK2. Drug sensitivity analysis and metabolic analysis revealed the impact of PAK2 on gemcitabine resistance and metabolic pathways. CCK8 experiments showed that silencing PAK2 led to a decrease in the proliferative capacity of pancreatic cancer cells and scratch experiments demonstrated that low expression of PAK2 decreased invasion capability in pancreatic cancer cells. Flow cytometry reveals that PAK2 significantly inhibited apoptosis in pancreatic cancer cell lines. Molecules related to the TGF-beta pathway decreased with the inhibition of PAK2, and there were corresponding significant changes in molecules associated with EMT.

Conclusion

PAK2 facilitated the angiogenic potential of cancer cells and promotes the epithelial-mesenchymal transition process by activating the TGF-beta signaling pathway. Simultaneously, it decreased the differentiation level of cancer cells, consequently enhancing their malignancy. Additionally, PAK2 fostered communication between cancer cells and the tumor microenvironment, augments cancer cell chemoresistance, and modulates energy metabolism pathways. In summary, PAK2 emerged as a pivotal gene orchestrating pancreatic cancer liver metastasis. Intervening in the expression of PAK2 may offer a promising therapeutic strategy for preventing liver metastasis of pancreatic cancer and improving its prognosis.

Analysis of Risk Factors for Distant Metastasis of Pancreatic Ductal Adenocarcinoma without Regional Lymph Node Metastasis and a Nomogram Prediction Model for Survival

Background

Negative regional lymph nodes do not indicate a lack of distant metastasis. A considerable number of patients with negative regional lymph node pancreatic cancer will skip the step of regional lymph node metastasis and directly develop distant metastasis.

Methods

We retrospectively analyzed the clinicopathological characteristics of patients with negative regional lymph node pancreatic cancer and distant metastasis in the Surveillance, Epidemiology, and End Results database from 2010 to 2015. Multivariate logistic analysis and Cox analysis were used to determine the independent risk factors that promoted distant metastasis and the 1-, 2-, and 3-year cancer-specific survival in this subgroup.

Results

Sex, age, pathological grade, surgery, radiotherapy, race, tumor location, and tumor size were significantly correlated with distant metastasis (P < 0.05). Among these factors, pathological grade II and above, tumor site other than the pancreatic head, and tumor size >40 mm were independent risk factors for distant metastasis; age ≥60 years, tumor size ≤21 mm, surgery, and radiation were protective factors against distant metastasis. Age, pathological grade, surgery, chemotherapy, and metastasis site were identified as predictors of survival. Among them, age ≥40 years, pathological grade II and above, and multiple distant metastasis were considered independent risk factors for cancer-specific survival. Surgery and chemotherapy were considered protective factors for cancer-specific survival. The prediction performance of the nomogram was significantly better than that of the traditional American Joint Committee on Cancer tumor, node, metastasis staging system. We also established an online dynamic nomogram calculator, which can predict the survival rate of patients at different follow-up time points.

Conclusion

Pathological grade, tumor location, and tumor size were independent risk factors for distant metastasis in pancreatic ductal adenocarcinoma with negative regional lymph nodes. Older age, smaller tumor size, surgery, and radiotherapy were protective factors against distant metastasis. A new nomogram that was constructed could effectively predict cancer-specific survival in pancreatic ductal adenocarcinoma with negative regional lymph nodes and distant metastasis. Furthermore, an online dynamic nomogram calculator was established.

Liver-Metastasis-Related Genes are Potential Biomarkers for Predicting the Clinical Outcomes of Patients with Pancreatic Adenocarcinoma

It is widely acknowledged that metastasis determines the prognosis of pancreatic adenocarcinoma (PAAD), and the liver is the most primary distant metastatic location of PAAD. It is worth exploring the value of liver-metastasis-related genetic prognostic signature (LM-PS) in predicting the clinical outcomes of PAAD patients post R0 resection. We collected 65 tumors and 165 normal pancreatic data from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression project (GTEx), respectively. Differentially expressed genes (DEGs) between primary tumor and normal pancreatic samples were intersected with DEGs between primary tumor samples with liver metastasis and those without new tumor events. The intersected 45 genes were input into univariate Cox regression analysis to identify the prognostic genes. Thirty-three prognostic liver-metastasis-related genes were identified and included in least absolute shrinkage and selection operator (LASSO) analysis to develop a seven-gene LM-PS, which included six risk genes (ANO1, FAM83A, GPR87, ITGB6, KLK10, and SERPINE1) and one protective gene (SMIM32). The PAAD patients were grouped into low- and high-risk groups based on the median value of risk scores. The LM-PS harbored an independent predictive ability to distinguish patients with a high-risk of death and liver metastasis after R0 resection. Moreover, a robust prognostic nomogram based on LM-PS, the number of positive lymph nodes, and histologic grade were established to predict the overall survival of PAAD patients. Besides, a transcription factor‐microRNA coregulatory network was constructed for the seven LM-PS genes, and the immune infiltration and genomic alterations were systematically explored in the TGCA-PAAD cohort.

YEATS2 is a target of HIF1α and promotes pancreatic cancer cell proliferation and migration

Hypoxia is involved in the development of pancreatic cancer (PC). The responses of hypoxia-associated genes and their regulated mechanisms are largely unknown. In this study, through bioinformatic analysis and quantitative real-time polymerase chain reaction, the YEATS domain containing 2 (YEATS2) was determined to be a key hypoxia-associated gene. It was increased in PC cells under hypoxia, upregulated in PC tissues, and predicted poor outcome. YEATS2 inhibition decreased the proliferation and migration of PC cells under both normoxia and hypoxia in vitro as well as proliferation and metastasis in vivo. We found that hypoxia-inducible factor 1α (HIF1α) regulated the expression of YEATS2 via binding to the hypoxia response element (HRE) of YEATS2 and coexpressed with YEATS2 in PC tissues. Overexpression of YEATS2 blocked the inhibitory effects of HIF1α silence on PC cell proliferation and migration under hypoxia. Collectively, our study revealed that YEATS2 is a target gene of HIF1α and promotes PC development under hypoxia.

MiR-137 promotes anoikis through modulating the AKT signaling pathways in Pancreatic Cancer

Anoikis resistance is a fundamental feature of the survival of metastatic cancer cells during cancer progression. However, the mechanisms underlying anoikis resistance in pancreatic cancer (PC) are still unclear. MicroRNA-137 (miR-137) is a tumor suppressor that inhibits the proliferation and invasion of cancer cells through targeting multiple oncogenes. However, the effects and molecular mechanism of miR-137 on anoikis of PC are still unclear. Here we demonstrated that miR-137 was downregulated after the induction of anoikis model in time dependent. Function assays revealed that miR-137 promoted the pancreatic cancer cells anoikis in vitro and vivo. According to bioinformation analysis of clinical databases, we predicted that paxillin (PXN) was a target of miR-137. Further, TCGA analysis revealed that PXN was closely associated with the development of PC. Through loss-of-function studies, we demonstrated that PXN was a functional target of miR-137 on anoikis of PC cells. Moreover, we found that PXN promoted the activation of the AKT signaling pathways which was involving in the cancer cells anoikis. Together, our findings reveal that miR-137 plays a novel role during anoikis and may serve as a potential target for the detection and treatment of PC.

Tumor associated neutrophils promote the metastasis of pancreatic ductal adenocarcinoma

The aim of this study was to investigate the role of tumor-associated neutrophils (TANs) in the metastasis of pancreatic ductal adenocarcinoma (PDAC), to explore the regulation of TANs, and to determine the mechanisms governing the metastasis of PDAC. The correlation between neutrophils and the patient's clinical pathological data was first evaluated. Then, the effects of neutrophils on the invasion of PDAC were analyzed using a combination of conditioned media, direct and indirect coculture of human peripheral blood neutrophils, and PDAC cell lines (Panc-1, MiaPaCa-2 and AsPC-1). The cytokines secreted by neutrophils were detected through ELISA. TAN density was significantly correlated with poor metastasis-free survival (P < .05). Through coculture, it was found that the effect of neutrophils on pancreatic cancer cells was dependent on concentration, and a high concentration of neutrophils showed a lethal effect, while a low concentration of neutrophils primarily promoted the migration ability of cancer cells. The results of the wound-healing assay, the Transwell invasion assay, and laser confocal microscopy confirmed the promoting effect and indicated that the effect of neutrophils toward cancer cells may function indirectly by releasing a series of cytokines. The results of ELISA show that this effect may be achieved through the secretion of a large amount of TNF-α and TGF-β1 by neutrophils. Our study indicated that neutrophils may increase the metastasis of PDAC by releasing a series of cell cytokines, such as TNF-α and TGF-β1.

Extracellular matrix proteins in metastases to the liver - Composition, function and potential applications

The rising evidence of the tumor microenvironment (TME) and its role in cancer have made this an area of increased research efforts. The focus is both on the primary tumor but also on the metastatic setting. The TME though, does not only consist of the non-malignant cells of a tumor, but also of the acellular compartment: The Extracellular Matrix (ECM). The liver is a common organ for metastasis of many cancers and for some of these cancers' liver surgery is a standard treatment with long-term cure, whereas for other cancers not considered meaningful. Blood supply and anatomical reasons plays one part for the establishment of liver metastasis. It is however a well-known fact that the "soil" of a metastatic organ is of utter importance in the process of metastasis. The "soil" consists of the TME where the ECM is a critical and active part. This review focuses what is known about the normal ECM of the human liver, what is known about ECM proteins in human liver metastasis, challenges of studying the ECM in liver metastases and lastly, potential applications of this field of knowledge.

Metastasis-associated fibroblasts promote angiogenesis in metastasized pancreatic cancer via the CXCL8 and the CCL2 axes

The characteristic desmoplastic stroma of pancreatic ductal adenocarcinoma (PDAC) is a key contributor to its lethality. This stromal microenvironment is populated by cancer-associated fibroblasts (CAFs) that interact with cancer cells to drive progression and chemo-resistance. Research has focused on CAFs in the primary tumour but not in metastases, calling into question the role of analogous metastasis-associated fibroblasts (MAFs). We infer a role of MAFs in murine hepatic metastases following untargeted treatment with the anti-angiogenic drug sunitinib in vivo. Treated metastases were smaller and had fewer stromal cells, but were able to maintain angiogenesis and metastasis formation in the liver. Furthermore, sunitinib was ineffective at reducing MAFs alongside other stromal cells. We speculate that cancer cells interact with MAFs to maintain angiogenesis and tumour progression. Thus, we tested interactions between metastatic pancreatic cancer cells and fibroblasts using in vitro co-culture systems. Co-cultures enhanced fibroblast proliferation and induced angiogenesis. We identify carcinoma-educated fibroblasts as the source of angiogenesis via secretions of CXCL8 (aka IL-8) and CCL2 (aka MCP-1). Overall, we demonstrate that metastasis-associated fibroblasts have potential as a therapeutic target and highlight the CXCL8 and CCL2 axes for further investigation.

The Systemic-immune-inflammation Index Independently Predicts Survival and Recurrence in Resectable Pancreatic Cancer and its Prognostic Value Depends on Bilirubin Levels: A Retrospective Multicenter Cohort Study

OBJECTIVE

Our aim was to determine the prognostic significance of the systemic-immune-inflammation index (SIII) in patients with resectable pancreatic cancer, using cancer-specific survival as the primary outcome.

BACKGROUND

Pancreatic cancer is associated with a dysfunctional immune system and poor prognosis. We examined the prognostic significance of the SIII in patients with resectable pancreatic ductal adenocarcinoma (PDAC) and the effects of bilirubin on this index.

METHODS

We retrospectively assessed all pancreatic resections performed between 2004 and 2015 at 4 tertiary referral centers to identify pathologically confirmed PDAC patients. Baseline clinicopathologic characteristics, preoperative laboratory values such as absolute neutrophil, lymphocyte, and platelet counts, C-reactive protein, albumin, bilirubin, and CA19-9 levels, and also follow-up information, were collected. The associations of the calculated inflammatory indices with outcome were both internally and externally validated.

RESULTS

In all, 590 patients with resectable PDAC were included. The discovery and validation cohort included 170 and 420 patients, respectively. SIII >900 [hazard ratio (HR) 2.32, 95% confidence interval (CI) 1.55-3.48], lymph node ratio (HR 3.75, 95% CI 2.08-6.76), and CA19.9 >200 kU/L (HR 1.62, 95% CI 1.07-2.46) were identified as independent predictors of cancer-specific survival. Separate model analysis confirmed that preoperative SIII contributed significantly to prognostication. However, SIII appeared to lose its prognostic significance in patients with bilirubin levels above 200 μmol/L.

CONCLUSIONS

SIII is an independent predictor of cancer-specific survival and recurrence in patients with resectable PDAC. SIII may lose its prognostic significance in patients with high bilirubin levels. Properly designed prospective studies are needed to further confirm this hypothesis.

K-RAS Mutant Gene Found in Pancreatic Juice Activated Chromatin From Peri-ampullary Adenocarcinomas

External pancreatic duct stents inserted after resection of pancreatic head tumors provide unique access to pancreatic juice analysis of genetic and metabolic components that may be associated with peri-ampullary tumor progression. For this pilot study, portal venous blood and pancreatic juice samples were collected from 17 patients who underwent pancreaticoduodenectomy for peri-ampullary tumors. Portal vein circulating tumor cells (CTC) were isolated by high-speed fluorescence-activated cell sorting (FACS) and analyzed by quantitative reverse transcription polymerase chain reaction (RT-PCR) for K-RAS exon 12 mutant gene expression (K-RASmut). DNA, chromatin, and histone acetylated active chromatin were isolated from pancreatic juice samples by chromatin immunoprecipitation (ChIP) and the presence of K-RASmut and other cancer-related gene sequences detected by quantitative polymerase chain reaction (PCR) and ChIP-Seq. Mutated K-RAS gene was detectable in activated chromatin in pancreatic juice secreted after surgical resection of pancreatic, ampullary and bile duct carcinomas and directly correlated with the number of CTC found in the portal venous blood (P = .0453). ChIP and ChIP-Seq detected acetylated chromatin in peri-ampullary cancer patient juice containing candidate chromatin loci, including RET proto-oncogene, not found in similar analysis of pancreatic juice from non-malignant ampullary adenoma. The presence of active tumor cell chromatin in pancreatic juice after surgical removal of the primary tumor suggests that viable cancer cells either remain or re-emerge from the remnant pancreatic duct, providing a potential source for tumor recurrence and cancer relapse. Therefore, epigenetic analysis for active chromatin in pancreatic juice and portal venous blood CTC may be useful for prognostic risk stratification and potential identification of molecular targets in peri-ampullary cancers.

Prognostic value of pretreatment systemic immune-inflammation index in patients with gastrointestinal cancers

BACKGROUND

Numerous studies have reported the relationship between systemic immune-inflammation index (SII) and prognosis in gastrointestinal (GI) cancers, but no consensus has been reached. We aimed to systematically evaluate the prognostic value of SII in patients with GI cancers.

METHODS

Relevant published papers regarding the prognostic value of SII in patients with GI cancers were obtained from a number of electronic databases. The overall hazard ratios and the corresponding 95% confidence intervals (95% CIs) were calculated using a fixed or random effects model to assess the relationship between SII and prognosis through Stata SE 12.0.

RESULTS

A total of 24 eligible published articles with 9,626 patients were included. From the pooled results, we found that high SII indicated worse overall survival (OS) in patients with GI cancers (HR = 1.52, 95%CI: 1.29-1.74). And patients with high SII had poorer disease-free survival (HR: 2.28, 95% CI: 1.46-3.10), time to recurrence (HR: 1.70, 95% CI: 1.11-2.30), and recurrence-free survival (HR: 1.60, 95% CI: 1.19-2.00) when compared with those with low SII values.

CONCLUSIONS

SII might serve as a noninvasive and powerful tool for predicting survival outcome in patients with GI cancers.

Efficacy of transcatheter arterial chemoembolization for liver metastases arising from pancreatic cancer

PURPOSE

The aim of the study was to evaluate the efficacy of transcatheter arterial chemoembolization (TACE) in treating patients with liver metastases from pancreatic cancer, and explore the prognostic risk factors.

RESULTS

Three of the 27 patients were totally recovered, and 12 were partially alleviated. The total efficacy rate was 55.6% (15/27). The median survival time was 13.6 months, and the 0.5-, 1-, 2-, 3-, and 5-year survival rates were 70.4% (19/27), 48.1% (13/27), 22.2% (6/27), 14.8 (4/27), 11.1% (3/27), respectively. None of the groups showed any severe complications. Univariate analysis showed that pathological type, concomitant therapies for liver metastasis, vascular supply, CA199 levels and extrahepatic metastasis were related to prognosis (P < 0.05). Multivariate analysis indicated that pancreatic cancer pathology and extrahepatic metastasis were independent risk factors influencing patients' prognosis (χ2 = 13.182, 17.989, P < 0.05).

METHODS

The clinical records of 27 patients with lliver metastases from pancreatic cancer diagnosed at the First Affiliated Hospital of Zhejiang University between May 2009 and May 2015 were retrospectively analyzed. The short-term and long-term efficacy and toxic side effects of TACE were observed. The prognostic risk factors were analyzed using Cox (proportional hazards) regression model.

CONCLUSION

TACE is an effective therapy for treating liver metastases from pancreatic malignancy. Pathological type and extrahepatic metastasis of pancreatic tumor are independent risk factors for patients' prognosis. The prognosis of patients with liver metastasis from pancreatic neuroendocrine neoplasm is superior to that of extrahepatic metastasis.

Conversion of epithelial-to-mesenchymal transition to mesenchymal-to-epithelial transition is mediated by oxygen concentration in pancreatic cancer cells

Tumor metastasis is accompanied by a two-stage process of epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET). Currently, the exact mechanisms underlying EMT-MET conversion are unclear. In the present study, the mechanisms by which primary sites (hypoxic) and homing sites (normoxic or hyperoxic) participate in EMT-MET conversion were evaluated. Pancreatic cancer cells were grown under different oxygenation conditions. Cell morphology and epithelial (E)-cadherin and vimentin expression were examined. Transwell chambers were used to examine tumor invasiveness, and scratch assays were performed to examine cell migration. Reverse transcription-polymerase chain reaction and western blot analysis were used to quantitate the mRNA and protein expression of E-cadherin, vimentin, Snail and hypoxia-inducible factor (HIF)-1α. BxPc-3 and Panc-1 cells grown under hypoxic conditions demonstrated increased partial EMT, reduced E-cadherin expression, and increased vimentin expression, compared with cells grown under normoxic or hyperoxic conditions. Cells grown under hypoxic conditions also indicated increased migration and invasiveness. HIF-1α mRNA and protein expression was increased in cells grown under hypoxic conditions. These changes were reversed when a specific inhibitor of the HIF-1α receptor was used to block HIF-1α signaling. Differences in oxygen concentration at primary sites and homing sites are important in the EMT-MET process, and the underlying mechanism may involve HIF-1α-Snail signaling.

ITGA1 is a pre-malignant biomarker that promotes therapy resistance and metastatic potential in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has single-digit 5-year survival rates at <7%. There is a dire need to improve pre-malignant detection methods and identify new therapeutic targets for abrogating PDAC progression. To this end, we mined our previously published pseudopodium-enriched (PDE) protein/phosphoprotein datasets to identify novel PDAC-specific biomarkers and/or therapeutic targets. We discovered that integrin alpha 1 (ITGA1) is frequently upregulated in pancreatic cancers and associated precursor lesions. Expression of ITGA1-specific collagens within the pancreatic cancer microenvironment significantly correlates with indicators of poor patient prognosis, and depleting ITGA1 from PDAC cells revealed that it is required for collagen-induced tumorigenic potential. Notably, collagen/ITGA1 signaling promotes the survival of ALDH1-positive stem-like cells and cooperates with TGFβ to drive gemcitabine resistance. Finally, we report that ITGA1 is required for TGFβ/collagen-induced EMT and metastasis. Our data suggest that ITGA1 is a new diagnostic biomarker and target that can be leveraged to improve patient outcomes.

Complement component 1, q subcomponent binding protein (C1QBP) in lipid rafts mediates hepatic metastasis of pancreatic cancer by regulating IGF-1/IGF-1R signaling

Pancreatic cancer shows a remarkable predilection for hepatic metastasis. Complement component 1, q subcomponent binding protein (C1QBP) can mediate growth factor-induced cancer cell chemotaxis and distant metastasis by activation of receptor tyrosine kinases. Coincidentally, insulin-like growth factor-1 (IGF-1) derived from the liver and cancer cells itself has been recognized as a critical inducer of hepatic metastasis. However, the mechanism underlying IGF-1-dependent hepatic metastasis of pancreatic cancer, in which C1QBP may be involved, remains unknown. In the study, we demonstrated a significant association between C1QBP expression and hepatic metastasis in patients with pancreatic cancer. IGF-1 induced the translocation of C1QBP from cytoplasm to lipid rafts and further drove the formation of CD44 variant 6 (CD44v6)/C1QBP complex in pancreatic cancer cells. C1QBP interacting with CD44v6 in lipid rafts promoted phosphorylation of IGF-1R and thus activated downstream PI3K and MAPK signaling pathways which mediated metastatic potential of pancreatic cancer cells including proliferation, apoptosis, invasion, adhesion and energy metabolism. Furthermore, C1QBP knockdown suppressed hepatic metastasis of pancreatic cancer cells in nude mice. We therefore conclude that C1QBP in lipid rafts serves a key regulator of IGF-1/IGF-1R-induced hepatic metastasis from pancreatic cancer. Our findings about C1QBP in lipid rafts provide a novel strategy to block IGF-1/IGF-1R signaling in pancreatic cancer and a reliable premise for more efficient combined modality therapies.

Prometastatic mechanisms of CAF-mediated EMT regulation in pancreatic cancer cells

Tumor metastasis are accompanied by the EMT (epithelial-mesenchymal transition)-MET (mesenchymal-epithelial transition) two-step process. In this study, we investigated the importance of cancer associated fibroblasts (CAF) in the process. First, the primary cultures of isolated pancreatic CAF, fibroblasts of normal pancreatic tissues (NF), and normal hepatic stellate cells (HSF) were identified and verified via the expression of α-SMA and vimentin. Using an indirect three-dimensional co-culture model, the morphological changes were observed by light microscopy and laser scanning confocal microscopy. The invasive and migration capacity of pancreatic cancer cells was determined by Transwell chamber migration assay or scratch assay. The mRNA and protein expression levels of E-cadherin, vimentin, and Gli1 were determined by RT-PCR and western blotting. Primary cultures of isolated CAF, NF, HSF showed satisfactory growth with active proliferation. Indirect co-culture with CAF, BxPc-3 and Panc-1 cells showed significant partial EMT, reduced E-cadherin expression, and enhanced vimentin expression as compared with the single culture and NF/HSF co-culture groups, with corresponding increases in migratory and invasive capacities. PCR and western blotting results showed that mRNA and protein expression levels of Gli1 in CAF and Snail in cancer cells were increased. This process could be reversed by inhibition of hedgehog (HH) signaling in CAF. In the tumor microenvironment, activation of CAF is the key event in mediating partial EMT, and its mechanism may be associated with paracrine action after activation of HH signaling in CAF.

Liver metastases: Microenvironments and ex-vivo models

The liver is a highly metastasis-permissive organ, tumor seeding of which usually portends mortality. Its unique and diverse architectural and cellular composition enable the liver to undertake numerous specialized functions, however, this distinctive biology, notably its hemodynamic features and unique microenvironment, renders the liver intrinsically hospitable to disseminated tumor cells. The particular focus for this perspective is the bidirectional interactions between the disseminated tumor cells and the unique resident cell populations of the liver; notably, parenchymal hepatocytes and non-parenchymal liver sinusoidal endothelial, Kupffer, and hepatic stellate cells. Understanding the early steps in the metastatic seeding, including the decision to undergo dormancy versus outgrowth, has been difficult to study in 2D culture systems and animals due to numerous limitations. In response, tissue-engineered biomimetic systems have emerged. At the cutting-edge of these developments are ex vivo 'microphysiological systems' (MPS) which are cellular constructs designed to faithfully recapitulate the structure and function of a human organ or organ regions on a milli- to micro-scale level and can be made all human to maintain species-specific interactions. Hepatic MPSs are particularly attractive for studying metastases as in addition to the liver being a main site of metastatic seeding, it is also the principal site of drug metabolism and therapy-limiting toxicities. Thus, using these hepatic MPSs will enable not only an enhanced understanding of the fundamental aspects of metastasis but also allow for therapeutic agents to be fully studied for efficacy while also monitoring pharmacologic aspects and predicting toxicities. The review discusses some of the hepatic MPS models currently available and although only one MPS has been validated to relevantly modeling metastasis, it is anticipated that the adaptation of the other hepatic models to include tumors will not be long in coming.