Pancreatic cancer: molecular pathogenesis and new therapeutic targets

Chemoprevention strategies for pancreatic cancer

Pancreatic cancer has a poor prognosis and is often diagnosed at an advanced stage, which makes it difficult to treat. The low survival rate of patients with pancreatic cancer points towards an increased need for novel therapeutic and chemopreventive strategies and also early detection of this disease. Increased consumption of fruits and vegetables has been associated with a reduced risk of pancreatic cancer. Synthetic and natural, diet-derived bioactive compounds have been evaluated as pancreatic cancer chemopreventive agents and have demonstrated various degrees of efficacy in cellular and in vivo animal models. Some chemopreventive agents (for example, curcumin or resveratrol) have also been reported to sensitize pancreatic cancer cells to standard chemotherapeutic drugs (for example, gemcitabine or erlotinib), which suggests that chemopreventive agents could potentially be used as potentiators of standard chemotherapy. Few clinical trials of pancreatic cancer chemopreventive agents have been completed and some are in early phases. Further development of pancreatic cancer chemopreventive agents may prove to be tremendously valuable for individuals at high risk of developing pancreatic cancer and patients who present with premalignant lesions. This Review discusses the current state of the pancreatic cancer chemoprevention field and highlights the challenges ahead.

Neurotransmitter receptors as central regulators of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has a near 100% mortality because it is generally detected at an advanced stage and responds poorly to existing therapeutics. This review summarizes current evidence suggesting important roles of neurotransmitter receptors in the regulation of this malignancy. Experimental evidence indicates that the alpha(7)-nicotinic acetylcholine receptor (alpha(7)nAChR) stimulates PDAC via stress neurotransmitter-mediated activation of beta-adrenergic signaling while the alpha(4)beta(2)nAChR inhibits PDAC via GABA-mediated inhibition of adenylyl cyclase activation. In analogy to molecular mechanisms that govern nicotine addiction, chronic exposure to nicotine or its nitrosated derivative nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone render the stimulatory alpha(7)nAChR hyperactive while desensitizing the inhibitory alpha(4)beta(2)nAChR. Accordingly, PDAC intervention strategies should include the diagnosis of unphysiological neurotransmitter levels and aim to restore any imbalance in stimulatory and inhibitory neurotransmitters.

Gankyrin promotes the proliferation of human pancreatic cancer

Previous studies in our laboratory have suggested that gankyrin expression is correlated with a malignant phenotype in colorectal cancer. Here, we investigated the possible role of gankyrin in pancreatic carcinogenesis. Gankyrin expression was significantly increased in pancreatic cancer compared to non-cancerous tissues. This expression significantly enhanced cancer cell proliferation and growth in vitro and in vivo. Suppression of gankyrin downregulated cyclin A, cyclin D1, cyclin E, CDK2, CDK4, PCNA and p-Rb but upregulated p27, Rb and p53. However, gankyrin overexpression led to opposite results. Thus, gankyrin could enhance pancreatic cancer cell proliferation by promoting cell cycle progression and p53 degradation.

A phase I study of the biomodulation of capecitabine by docetaxel and gemcitabine (mGTX) in previously untreated patients with metastatic adenocarcinoma of the pancreas

BACKGROUND

Pancreas cancer remains a formidable challenge. We report the first prospective analysis of the 3-drug combination of gemcitabine (G), docetaxel (T) and capecitabine (X) (mGTX) with schedule modification to maximize biomodulation of X.

METHODS

We conducted a dose escalation study of mGTX in first-line treatment of metastatic pancreas cancer using three dose levels (DL 1-3). Patients received docetaxel on days 1 and 8, gemcitabine on days 8 and 15, and capecitabine on days 8 through 21. Gemcitabine dose was fixed at 750 mg/m² over 75 min, capecitabine was given twice daily and escalated from 500 to 650 mg/m² at DL2 and docetaxel increased from 30 to 36 mg/m² at DL3.

RESULTS

Twenty-one patients (18 evaluable) were enrolled in the study. MTD was reached at DL3 and one DLT was observed at DL2 (prolonged neutropenia). The most common grade 3/4 toxicities were leukopenia (29%) and neutropenia (29%) and fatigue (25%). Tumor growth control rate was 80% (11% PR; 69% SD lasting at least 3 months). Median progression-free-survival was 5.8 months (95% CI 2.7, 10.6) and median overall survival was 7.4 months (95% CI 3.8 16.8). CA 19-9 decreased by at least 50% from baseline in half the patients.

CONCLUSION

mGTX demonstrates acceptable tolerability with interesting activity in patients with pancreatic cancer. The recommended doses for phase II studies are docetaxel 36 mg/m² days 1 and 8, gemcitabine 750 mg/m² over 75 min days 8 and 15, and capecitabine 625 mg/m² twice daily days 8 through 21.

c-FLIP degradation mediates sensitization of pancreatic cancer cells to TRAIL-induced apoptosis by the histone deacetylase inhibitor LBH589

Great efforts have been made to develop novel and efficacious therapeutics against pancreatic cancer to improve the treatment outcomes. Tumor-necrosis factor-related apoptosis-inducing ligand (TRAIL) is such a therapeutic cytokine with selective killing effect toward malignant cells. However, some human pancreatic cancers are intrinsically resistant to TRAIL-mediated apoptosis or therapy. In this study, we have shown that the histone deacetylase inhibitor LBH589 can synergize with TRAIL to augment apoptosis even in TRAIL-resistant cells. LBH589 decreased c-FLIP levels in every tested cell line and survivin levels in some of the tested cell lines. Enforced expression of ectopic c-FLIP, but not survivin, abolished the cooperative induction of apoptosis by the combination of LBH589 and TRAIL, indicating that c-FLIP downregulation plays a critical role in LBH589 sensitization of pancreatic cancer cells to TRAIL. Moreover, LBH589 decreased c-FLIP stability and the presence of the proteasome inhibitor MG132 prevented c-FLIP from reduction by LBH589. Correspondingly, we detected increased levels of ubiqutinated c-FLIP in LBH589-treated cells. These data thus indicate that LBH589 promotes ubiqutin/proteasome-mediated degradation of c-FLIP, leading to downregulation of c-FLIP. Collectively, LBH589 induces c-FLIP degradation and accordingly sensitizes pancreatic cancer cells to TRAIL-induced apoptosis, highlighting a novel therapeutic regimen against pancreatic cancer.

Effects of thymoquinone in the expression of mucin 4 in pancreatic cancer cells: implications for the development of novel cancer therapies

Pancreatic cancer is one of the most lethal cancers in the world, as it continues to be resistant to any therapeutic approaches. The high molecular weight glycoprotein mucin 4 (MUC4) is aberrantly expressed in pancreatic cancer and contributes to the regulation of differentiation, proliferation, metastasis, and the chemoresistance of pancreatic cancer cells. The absence of its expression in the normal pancreatic ductal cells makes MUC4 a promising target for novel cancer therapeutics. Natural products have been widely investigated as potential candidates in cancer therapies, and thymoquinone (TQ), extracted from the seeds of Nigella sativa, has shown excellent antineoplastic properties in some systems. In the present study, we evaluated the effect of TQ on pancreatic cancer cells and specifically investigated its effect on MUC4 expression. The MUC4-expressing pancreatic cancer cells FG/COLO357 and CD18/HPAF were incubated with TQ, and in vitro functional assays were done. The results obtained indicate that treatment with TQ downregulated MUC4 expression through the proteasomal pathway and induced apoptosis in pancreatic cancer cells by the activation of c-Jun NH(2)-terminal kinase and p38 mitogen-activated protein kinase pathways. In agreement with previous studies, the decrease in MUC4 expression correlated with an increase in apoptosis, decreased motility, and decreased migration of pancreatic cancer cells. MUC4 transient silencing studies showed that c-Jun NH(2)-terminal kinase and p38 mitogen-activated protein kinase pathways are activated in pancreatic cancer cells, indicating that the activation of these pathways by TQ is directly related to the MUC4 downregulation induced by the drug. Overall, TQ has potential for the development of novel therapies against pancreatic cancer.

Inhibition of MLK3 Decreases Proliferation and Increases Antiproliferative Activity of Epidermal Growth Factor Receptor (EGFR) Inhibitor in pancreatic cancer cell Lines

Pancreatic adenocarcinoma is associated with advanced presentation and poor survival. Currently approved therapies have minimal effect on patient survival. Pancreatic adenocarcinomas have a high incidence of activated K-RAS, which may confer resistance to epidermal growth factor receptor (EGFR) inhibitors. Mixed lineage kinase-3 (MLK3) is a MAP3K that activates multiple MAPK pathways. The role of MLK3 in the pathophysiology and resistance to therapy of pancreatic adenocarcinoma has not been investigated. MLK3 is over expressed in pancreatic cancer cell lines compared to an immortalized pancreatic epithelial cell line. The requirement of MLK3 for cell proliferation and survival of pancreatic cancer cell lines, PANC-1 and MiaPaCa-2, was investigated using RNA interference (siRNA) and MLK inhibitor, K252a, alone or in conjunction with the EGFR inhibitor, Compound 56. Ablation of expression of MLK3 via siRNA-mediated gene silencing and pharmacological inhibition of MLK3 by K252a each decreased cell viability in both pancreatic cancer cell lines, with a concurrent decrease in the activation of ERK, JNK and AKT. Concomitant inhibition of EGFR and MLK3 induced apoptosis, as evidenced by increased cleavage of PARP and caspase-3. These results suggest that MLK3 plays an important role in survival and proliferation of pancreatic cancer cell lines and that inhibition of MLK3 may enhance the therapeutic efficacy of EGFR inhibitors in the treatment of pancreatic cancer.

Pancreatic cancer organotypic cultures

Pancreatic cancer, the fourth most common cause of cancer-related death, is a devastating disease with poor prognosis. Over the last four decades, no effective new treatments have been developed for this cancer. As a result, its prognosis has remained unchanged. Appropriate cancer models, representing all aspects of pancreatic cancer, will enhance our understanding of its biology. In this review we discuss the evolution and merit of organotypic culture models. These co-culture in vitro systems of cancer and stromal cells grown within, or on top of, reconstituted extracellular matrix gels model pancreatic cancer more realistically than 2D systems. Different methodologies are discussed which enable interrogation of various hypotheses examining the tumour-stroma cross-talk. Thus this validated organotypic culture model provides a system, which can be easily manipulated and used to test (novel) treatment options targeting the cancer, the stromal compartment or both, in a physiologically relevant environment. The big challenge for future research is to expand this model further so that its mimicry of the human tumour is more robust. This will increase our understanding of the biology of this aggressive tumour; ultimately resulting in improved therapies and, therefore, a better prognosis.