Molecular mechanisms of pancreatic cancer and potential targets of treatment

Update on the management of pancreatic cancer: Surgery is not enough

Pancreatic ductal adenocarcinoma (PDAC) represents the fourth cause of death in cancer and has a 5-year survival of < 5%. Only about 15% of the patients present with a resectable PDAC with potential to undergo “curative” surgery. After surgery, local and systemic recurrence, is though very common. The median survival of resected patients with adjuvant chemotherapy after surgery is only 20-23 mo. This underscores the significant need to improve PDAC management strategies. Increased survival rate is dependent on new breakthroughs in our understanding of not at least tumor biology. The aim of this review is to update and comment on recent knowledge concerning PDAC biology and new diagnostics and treatment modalities. One fundamental approach to improve survival rates is by earlier and improved diagnosis of the disease. In recent years, novel blood-based biomarkers have emerged based on genetic, epigenetic and protein changes in PDAC with very promising results. For biomarkers to enter clinical practice they need to have been developed using adequate control groups and provide high sensitivity and specificity and by this identify patients at risk already in a pre-symptomatic stage. Another way to improve outcomes, is by employing neoadjuvant treatments thereby increasing the number of resectable cases. Novel systemic treatment regimes like FOLFIRINOX and nab-paclitaxel have demonstrated improvements in prolonging survival in advanced cases, but long-term survival is still scarce. The future improved understanding of PDAC biology will inevitably render new treatment options directed against both the cancer cells and the surrounding microenvironment.

Pancreatic stellate cells promotes the perineural invasion in pancreatic cancer

Perineural invasion is a prominent characteristic of pancreatic cancer. Pancreatic cancer has an extremely high incidence of perineural invasion which has been associated with poor survival. Early studies mostly focus on the interaction between cancer cells and nerves. Recently, the effect of pancreatic stellate cells in progression of pancreatic cancer has been paid more attention. Both in vitro studies and in vivo ones revealed that pancreatic stellate cells can enhance the proliferation, migration and invasion of pancreatic cancer cells. Pancreatic stellate cells can also regulate the expression and effect of molecules involved in perineural invasion. In addition, pancreatic stellate cells seems to associated with the generation of neuronal plasticity in pancreatic cancer. Herein the hypothesis that pancreatic stellate cells play a potential role in promote the perineural invasion in pancreatic cancer through three mechanisms. One is that pancreatic stellate cells enhance the proliferation, migration and invasion directly through releasing a variety of stimuli and providing a suitable microenvironment. Pancreatic stellate cells also regulate the expression and effects of molecules involved in perineural invasion such as nerve growth factor. Another is that pancreatic stellate cells induce neuronal plasticity, which makes nerves more vulnerable to be invaded. We can conclude that pancreatic stellate cells play a central role in regulating the perineural invasion process by producing different effects on cancer cells and nerve. To inhibit the activity of pancreatic stellate cells or block the interaction between pancreatic stellate cells and cancer cells or nerve tissue might reduce the perineural invasion in pancreatic cancer.

Invasive markers identified by gene expression profiling in pancreatic cancer

BACKGROUND

Molecular profiling has proven utility as a diagnostic and predictive tool in clinical oncology. However, a clinically relevant gene expression profile in pancreatic cancer remains elusive.

METHODS

Primary and metastatic pancreatic cancer cell lines (BxPC-3 and AsPC-1), were stimulated with phorbol-12-myristate 13-acetate (PMA), a known inducer of cell invasion. Affymetrix gene expression microarray analysis was performed, comparing gene expression to unstimulated controls. Differential expression was identified using ArrayAssist, and confirmed using quantitative real-time PCR. Bioinformatic analysis was performed using Pathway Studio and GOstat. The derived gene expression was further validated in fresh frozen pancreatic tumour samples. The ability of the derived 3 gene expression markersto differentiate between pancreatic adenocarcinoma (PDAC) and other neoplasms, and its association with clinicopathological variables was examined.

RESULTS

PMA-induced significant changes in cell line gene expression, from which distinctive 3 potential invasive markers were derived. Expression of these genes, uPA, MMP-1 and IL1-R1 was confirmed in human pancreatic tumours, and was found to differentiate PDAC from other pancreatic neoplasms. The expression of IL1-R1 in PDAC is a novel finding. We found that the expression of MMP-1 was associated with high-grade PDAC (p = 0.035, Wilcoxon rank sum).

CONCLUSION

We have identified three potential invasive markers, uPA, MMP-1 and IL1-R1, whose gene expression may differentiate PDAC from other pancreatic neoplasms, and potentially reflect a more invasive phenotype.

Pancreatic cancer: the role of pancreatic stellate cells in tumor progression

Pancreatic ductal adenocarcinoma is an aggressive and highly lethal disease frequently characterized by a dense stromal or desmoplastic response. Accumulating evidence exists that tumor desmoplasia plays a central role in disease progression and that e.g. activated pancreatic stellate cells (PSCs) are responsible for the excess matrix production. The mechanisms underlying the tumor versus stroma interplay are complex. Pancreatic cancer cells release mitogenic and fibrogenic stimulants, such as transforming growth factor β(1), platelet-derived growth factor (PDGF), sonic hedgehog, galectin 3, endothelin 1 and serine protease inhibitor nexin 2, all of which may promote the activated PSC phenotype. Stellate cells in turn secrete various factors, including PDGF, stromal-derived factor 1, epidermal growth factor, insulin-like growth factor 1, fibroblast growth factor, secreted protein acidic and rich in cysteine, matrix metalloproteinases, small leucine-rich proteoglycans, periostin and collagen type I that mediate effects on tumor growth, invasion, metastasis and resistance to chemotherapy. This review intends to shed light on the mechanisms by which PSCs in the stroma influence pancreatic cancer development. The increased understanding of this interaction will be of potential value in designing new modalities of targeted therapy. and IAP.

Gemcitabine chemoresistance in pancreatic cancer: molecular mechanisms and potential solutions

Ductal pancreatic adenocarcinoma is associated with a very poor prognosis and most patients are given palliative care. Chemotherapy in the form of gemcitabine has been found to reduce disease-related pain, and the otherwise frequently occurring weight changes, to increase Karnofsky performance status and quality of life and has also resulted in a modest improvement in survival time. The intracellular uptake of gemcitabine is dependent on nucleoside transporters, predominantly human equilibrative nucleoside transporter-1 (hENT-1), which is over-expressed in human pancreatic adenocarcinoma cells. Cellular resistance to gemcitabine can be intrinsic or acquired during gemcitabine treatment. One of the mechanisms is a decrease in hENT-1 expression. Modifications of gemcitabine not rendering it dependent on the nucleoside transporter may be a successful future mode of chemotherapy treatment, and determination of the nucleoside receptor status at the time of diagnosis could potentially also contribute to a more targeted therapy in the future.