Pancreatic stellate cells: Aiding and abetting pancreatic cancer progression

Tumour-stromal interactions have now been acknowledged to play a major role in pancreatic cancer (PC) progression. The abundant collagenous stroma is produced by a specific cell type in the pancreas-the pancreatic stellate cell (PSC). Pancreatic stellate cells (PSCs) are a unique resident cell type of pancreas and with a critical role in both healthy and diseased pancreas. Accumulating evidence indicates that PSCs interact closely with cancer cells as well as with other cell types of the stroma such as immune cells, endothelial cells and neuronal cells, to set up a growth permissive microenvironment for pancreatic tumours, which facilitates local tumour growth as well as distant metastasis. Consequently, recent work in the field has focused on the development of novel therapeutic approaches targeting the stroma to inhibit PC progression. Such a multi-pronged approach targeting both tumour and stromal elements of PC has been successfully applied in pre-clinical settings. The challenge now is to translate the pre-clinical findings into the clinical setting to achieve better outcomes for pancreatic cancer patients.

Targeting the HGF/c-MET pathway in advanced pancreatic cancer: a key element of treatment that limits primary tumour growth and eliminates metastasis

Background

Stromal–tumour interactions facilitate pancreatic cancer (PC) progression. The hepatocyte growth factor (HGF)/c-MET pathway is upregulated in PC and mediates the interaction between cancer cells and stromal pancreatic stellate cells (PSCs). This study assessed the effect of HGF/c-MET inhibition plus gemcitabine (G) on the progression of advanced PC.

Methods

Orthotopic PC was produced by implantation of luciferase-tagged human cancer cells + human PSCs into mouse pancreas. Tumours were allowed to develop without treatment for 4 weeks. Mice were then treated for 6 weeks with one of the following: IgG, G, HGF inhibitor (Hi), c-MET inhibitor (Ci), Hi + Ci, Hi + G, Ci + G, or Hi + Ci + G.

Results

Bioluminescence imaging showed similar tumour sizes in all mice at the initiation of treatments. Triple therapy (Hi + Ci + G): (1) completely eliminated metastasis; (2) significantly reduced tumour size as assessed by bioluminescence and at necropsy; (3) significantly reduced proliferating cancer cell density and stem cell marker DCLK1 expression in tumours. In vitro 3D culture studies supported our in vivo findings.

Conclusion

Even at an advanced disease stage, a two-pronged approach, targeting (a) HGF/c-MET with relevant inhibitors and (b) cancer cells with chemotherapy, completely eliminated metastasis and significantly decreased tumour growth, suggesting that this is a promising treatment approach for PC.

Hepatocyte growth factor inhibition: a novel therapeutic approach in pancreatic cancer

BACKGROUND

Pancreatic stellate cells (PSCs, which produce the stroma of pancreatic cancer (PC)) interact with cancer cells to facilitate PC growth. A candidate growth factor pathway that may mediate this interaction is the HGF-c-MET pathway.

METHODS

Effects of HGF inhibition (using a neutralising antibody AMG102) alone or in combination with gemcitabine were assessed (i) in vivo using an orthotopic model of PC, and (ii) in vitro using cultured PC cells (AsPC-1) and human PSCs.

RESULTS

We have shown that human PSCs (hPSCs) secrete HGF but do not express the receptor c-MET, which is present predominantly on cancer cells. HGF inhibition was as effective as standard chemotherapy in inhibiting local tumour growth but was significantly more effective than gemcitabine in reducing tumour angiogenesis and metastasis. HGF inhibition has resulted in reduced metastasis; however, interestingly this antimetastatic effect was lost when combined with gemcitabine. This suggests that gemcitabine treatment selects out a subpopulation of cancer cells with increased epithelial-mesenchymal transition (EMT) and stem-cell characteristics, as supported by our findings of increased expression of EMT and stem-cell markers in tumour sections from our animal model. In vitro studies showed that hPSC secretions induced proliferation and migration, but inhibited apoptosis, of cancer cells. These effects were countered by pretreatment of hPSC secretions with a HGF-neutralising antibody but not by gemcitabine, indicating a key role for HGF in PSC-PC interactions.

CONCLUSIONS

Our studies suggest that targeted therapy to inhibit stromal-tumour interactions mediated by the HGF-c-MET pathway may represent a novel therapeutic approach in PC that will require careful modelling for optimal integration with existing treatment modalities.

Key role of pancreatic stellate cells in pancreatic cancer

Pancreatic stellate cells (PSCs) are responsible for producing the collagenous stroma in pancreatic cancer. Findings from the majority of in vitro and in vivo studies to date indicate that PSCs interact with cancer cells as well as with other cellular elements in the stroma including immune cells, endothelial cells and neuronal cells to set up a growth permissive microenvironment for pancreatic tumours. However, two recent studies reporting a protective effect of myofibroblasts in pancreatic cancer have served to remind researchers of the possibility that the role of PSCs in this disease may be context and time-dependent, such that any possible early protective role of PSCs is subverted in later stages by the ability of cancer cells to turn PSCs into cancer-promoting aides. This concept is supported by the development in recent years of several novel therapeutic approaches targeting the stroma that have been successfully applied in pre-clinical settings to inhibit disease progression. A multi-pronged approach aimed at tumour cells as well as stromal elements may be the key to achieving better clinical outcomes in patients with pancreatic cancer.

Alcohol and cigarette smoke components activate human pancreatic stellate cells: implications for the progression of chronic pancreatitis

BACKGROUND

Chronic pancreatitis, a known complication of alcohol abuse, is characterized histopathologically by prominent fibrosis. Pancreatic stellate cells (PSCs) are responsible for producing this fibrous tissue in chronic pancreatitis and are activated by alcohol. Progression of alcoholic chronic pancreatitis (as assessed by calcification and fibrosis) is thought to be facilitated by concurrent smoking, but the mechanisms are unknown. This study aimed to (a) determine whether human PSCs (hPSCs) and rat PSCs express nicotinic acetylcholine receptors (nAChRs), which are known to bind 2 important components of cigarette smoke, namely nicotine and nicotine-derived nitrosamine ketone (NNK), and (b) examine the effects of cigarette smoke components in the presence and absence of alcohol on PSC activation in vitro.

METHODS

Western blotting was used to detect the presence of nAChRs in primary cultures of PSCs. Clinically relevant concentrations of cigarette smoke components (either cigarette smoke extract [CSE], NNK, or nicotine) ± ethanol (EtOH) were used to treat primary cultures of PSCs, and stellate cell activation was assessed by cell migration, proliferation, collagen production, and apoptosis.

RESULTS

We demonstrate, for the first time, that PSCs express nAChRs (isoforms α3, α7, β, ε) and that the expression of the α7 isoform in hPSCs is induced by CSE + EtOH. We also provide novel findings that PSCs are activated by CSE and NNK (both alone and in combination with EtOH) as evidenced by an increase in cell migration and/or proliferation. Further, we demonstrate that activation of PSCs by CSE + EtOH and NNK + EtOH may be mediated via nAChRs on the cells.

CONCLUSIONS

PSCs are activated by clinically relevant concentrations of cigarette smoke components (CSE and NNK), alone and in combination with EtOH. Thus, in alcoholics who smoke, progression of pancreatic fibrosis may be facilitated by the combined effects of alcohol and cigarette smoke components on hPSC behavior.

Pancreatic cancer and its stroma: A conspiracy theory

Pancreatic cancer is characterised by a prominent desmoplastic/stromal reaction that has received little attention until recent times. Given that treatments focusing on pancreatic cancer cells alone have failed to significantly improve patient outcome over many decades, research efforts have now moved to understanding the pathophysiology of the stromal reaction and its role in cancer progression. In this regard, our Group was the first to identify the cells (pancreatic stellate cells, PSCs) that produced the collagenous stroma of pancreatic cancer and to demonstrate that these cells interacted closely with cancer cells to facilitate local tumour growth and distant metastasis. Evidence is accumulating to indicate that stromal PSCs may also mediate angiogenesis, immune evasion and the well known resistance of pancreatic cancer to chemotherapy and radiotherapy. This review will summarise current knowledge regarding the critical role of pancreatic stellate cells and the stroma in pancreatic cancer biology and the therapeutic approaches being developed to target the stroma in a bid to improve the outcome of this devastating disease.

The role of the hepatocyte growth factor/c-MET pathway in pancreatic stellate cell-endothelial cell interactions: antiangiogenic implications in pancreatic cancer

Activated cancer-associated human pancreatic stellate cells (CAhPSCs, which produce the collagenous stroma of pancreatic cancer [PC]) are known to play a major role in PC progression. Apart from inducing cancer cell proliferation and migration, CAhPSCs have also been implicated in neoangiogenesis in PC. However, the mechanisms mediating the observed angiogenic effects of CAhPSCs are unknown. A candidate pathway that may be involved in this process is the hepatocyte growth factor (HGF)/c-MET pathway and its helper molecule, urokinase-type plasminogen activator (uPA). This study investigated the effects of CAhPSC secretions on endothelial cell function in the presence and absence of HGF, c-MET and uPA inhibitors. HGF levels in CAhPSC secretions were quantified using ELISA. CAhPSC secretions were then incubated with human microvascular endothelial cells (HMEC-1) and angiogenesis assessed by quantifying HMEC-1 tube formation and proliferation. CAhPSC-secreted HGF significantly increased HMEC-1 tube formation and proliferation; notably, these effects were downregulated by inhibition of HGF, its receptor c-MET and uPA. Phosphorylation of p38 mitogen-activated protein kinase was downregulated during inhibition of the HGF/c-MET pathway, whereas phosphatidylinositol-3 kinase and ERK1/2 remained unaffected. Our studies have shown for the first time that CAhPSCs induce proliferation and tube formation of HMEC-1 and that the HGF/c-MET pathway plays a major role in this induction. Given that standard antiangiogenic treatment targeting vascular endothelial growth factor has had limited success in the clinical setting, the findings of the current study provide strong support for a novel, alternative antiangiogenic approach targeting the HGF/c-MET and uPA pathways in PC.