The critical role of circular RNAs in drug resistance in gastrointestinal cancers

Nowadays, drug resistance (DR) in gastrointestinal (GI) cancers, as the main reason for cancer-related mortality worldwide, has become a serious problem in the management of patients. Several mechanisms have been proposed for resistance to anticancer drugs, including altered transport and metabolism of drugs, mutation of drug targets, altered DNA repair system, inhibited apoptosis and autophagy, cancer stem cells, tumor heterogeneity, and epithelial-mesenchymal transition. Compelling evidence has revealed that genetic and epigenetic factors are strongly linked to DR. Non-coding RNA (ncRNA) interferences are the most crucial epigenetic alterations explored so far, and among these ncRNAs, circular RNAs (circRNAs) are the most emerging members known to have unique properties. Due to the absence of 5' and 3' ends in these novel RNAs, the two ends are covalently bonded together and are generated from pre-mRNA in a process known as back-splicing, which makes them more stable than other RNAs. As far as the unique structure and function of circRNAs is concerned, they are implicated in proliferation, migration, invasion, angiogenesis, metastasis, and DR. A clear understanding of the molecular mechanisms responsible for circRNAs-mediated DR in the GI cancers will open a new window to the management of GI cancers. Hence, in the present review, we will describe briefly the biogenesis, multiple features, and different biological functions of circRNAs. Then, we will summarize current mechanisms of DR, and finally, discuss molecular mechanisms through which circRNAs regulate DR development in esophageal cancer, pancreatic cancer, gastric cancer, colorectal cancer, and hepatocellular carcinoma.

Girdin regulates the proliferation and apoptosis of pancreatic cancer cells via the PI3K/Akt signalling pathway

Girdin functions as an Akt phosphorylation enhancer (APE), which expedites the proliferation and survival of many types of tumours. However, the influence of Girdin on pancreatic cancer and the underlying molecular mechanisms have yet to be uncovered. Hence, in the present study, we sought to elucidate the function of Girdin in pancreatic cancer malignancy, particularly its role in pancreatic cancer cell proliferation, migration and apoptosis. Immunohistochemistry (IHC) was used to evaluate Girdin expression in pancreatic cancer tissues and to analyse its correlation with pathological grade. Girdin expression was further validated in pancreatic cancer cell lines (AsPC-1, BxPC-3 and PANC-1), and human pancreatic ductal epithelial (HPNE) cells were used as a control. Recombinant adenovirus vectors containing Girdin-siRNA were constructed to inhibit Girdin expression and were used in subsequent experiments to determine the effects of Girdin silencing on pancreatic cancer cells. Girdin silencing suppressed pancreatic cancer cell proliferation and induced pancreatic cancer cell apoptosis in vitro and in vivo. According to the results of further mechanistic investigations, Girdin may regulate cell processes through the phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) signalling pathway to exert additive effects on pancreatic cancer.

Application of non-invasive low strength pulsed electric field to EGCG treatment synergistically enhanced the inhibition effect on PANC-1 cells

Traditional therapies for pancreatic cancer are usually expensive and likely to cause side effects, and most patients have the risk of recurrence and suffering pain. Here, we investigated combination treatment of epigallocatechin-3-gallate (EGCG) and non-invasive low strength pulsed electric field (PEF) on the human pancreatic cell line PANC-1. Cells were cultured in various concentrations of EGCG and exposed to trains of PEF. The results showed that the low strength PEF alone or single treatment with low concentration of EGCG did not obviously affect the cell proliferation and migration in PANC-1. However, the EGCG-induced inhibitions of cell viability and migration ability in PANC-1 were dramatically enhanced by the further exposure of low strength PEF (60 V/cm). In particular, the same combination treatment caused less inhibition of cell viability in non-malignant HEK293 cells. We also found the combination treatment significantly decreased the ratio of Bcl-2/Bax protein and increased caspase activity in PANC-1 cells, resulting in the promotion of apoptotic responses, evidenced by chromatin condensation. The findings of the present study reveal the synergistic reactions in the combination treatment may severely disturb mitochondria, enhance the intrinsic pathway transduction, and effectively induce apoptosis; moreover, the migration and invasion of PANC-1 cancer cells were also significantly suppressed. Since normal cells are less sensitive to this combination treatment, and the non-invasive PEF could be modified to focus on a specific location, this treatment may serve as a promising method for anti-cancer therapy.

New therapeutic directions for advanced pancreatic cancer: cell cycle inhibitors, stromal modifiers and conjugated therapies

INTRODUCTION

Pancreatic adenocarcinoma is a devastating malignancy with an extremely poor prognosis. These tumors progress rapidly and somewhat silently with few specific symptoms and are relatively resistant to chemotherapeutic agents. Many agents, including cell cycle inhibitors, are under development for the treatment of this cancer for which there are disappointingly few treatment options. Areas covered: Here we outline the existing approved treatments for advanced pancreatic disease and discuss a range of novel therapies currently under development including cell cycle inhibitors, stromal modifiers and conjugated therapies. We also describe the current state of the pancreatic cancer therapeutics market both past and future. Expert opinion: Despite the recent explosion of novel therapies with an array of unique targets, the core treatment of pancreatic cancer still with traditional cytotoxic agents with a few exceptions. However, as these novel treatments move through the pipeline, we are hopeful that there will soon be a number of effective options for patients with advanced pancreatic cancer.

FBW7 increases the chemosensitivity of pancreatic cancer cells to gemcitabine through upregulation of ENT1

F-box and WD repeat domain-containing 7 (FBW7) has been characterized as a tumor suppressor, and its mutation or decreased expression has been observed in many types of human cancers. Our recent studies have uncovered that in pancreatic cancer, the KRAS mutation decreased FBW7 expression through phosphorylation and subsequent ubiquitination. Moreover, FBW7 inhibited aerobic glycolysis in pancreatic cancer via induction of thioredoxin-interacting protein (TXNIP), a mitochondrial localized tumor suppressor. The roles of FBW7 in anti-apoptosis and drug resistance via proteosomal degradation of myeloid cell leukemia-1 (MCL-1), which is an anti-apoptotic factor have been reported. However, the role of FBW7 in the chemotherapeutic resistance of pancreatic cancer to gemcitabine has seldom been reported. In the present study, we demonstrated that overexpression of FBW7 in pancreatic cancer cells rendered increased sensitivity to gemcitabine. Mechanistically, FBW7 promoted gemcitabine sensitivity via upregulation of equilibrative nucleoside transporter 1 (ENT1) at the protein level rather than the transcriptional level. In depth analysis demonstrated that the ENT1 protein level could be increased by lysosome inhibition. Taken together, our results demonstrated that FBW7 could be a target for improving the therapeutic efficacy of gemcitabine by induction of ENT1.

Intratumoral heterogeneity of the therapeutical response to gemcitabine and metformin

Cancer heterogeneity and microenvironmental aspects within a tumor are considered key factors influencing resistance of carcinoma cells to distinct chemotherapeutical agents. We evaluated a high concentration of metformin in combination with gemcitabine on a syngeneic orthotopic mouse model using 6606PDA cells. We observed reduced tumor size and reduced cancer cell proliferation after three weeks of chemotherapy with either compound and noticed an additive effect between gemcitabine and metformin on tumor weight. Interestingly, distinct areas of the carcinoma responded differently to either compound. Metformin inhibited the proliferation of cancer cells close to the desmoplastic reaction, whereas gemcitabine inhibited the proliferation of cancer cells mainly 360-570 μm distant to the desmoplastic reaction. Indeed, co-culture of pancreatic stellate cells with 6606PDA, 7265PDA or MIA PaCa-2 cells increased gemcitabine resistance. Metformin resistance, however, was increased by high glucose concentration in the medium. Other factors such as hypoxia or the pH of the medium had no influence on gemcitabine or metformin induced inhibition of cancer cell proliferation. These data demonstrate a spatial heterogeneity in drug resistance within pancreatic adenocarcinomas and that microenvironmental aspects such as supply of glucose and the presence of pancreatic stellate cells regulate cancer cell sensitivity towards metformin or gemcitabine.

Drug metabolism and pancreatic cancer

Pancreatic cancer remains a fatal disease in the majority of patients. The era of personalized medicine is upon us: customizing therapy according to each patient's individual cancer. Potentially, therapy can be targeted at individuals who would most likely have a favorable response, making it more efficacious and cost effective. This is particularly relevant for pancreatic cancer, which currently portends a very poor prognosis. However, there is much to be done in this field, and more studies are needed to bring this concept to reality.

Ramucirumab for the treatment of gastric cancers, colorectal adenocarcinomas, and other gastrointestinal malignancies

INTRODUCTION

The use of antiangiogenic strategy in the treatment of advanced colorectal cancers has been largely evidence-based. More recently, novel vascular endothelial growth factor receptor (VEGFR) inhibitors have been studied in other gastrointestinal diseases. Ramucirumab, a recombinant monoclonal antibody that binds to VEGFR2 extracellular domain with a much greater affinity compared to its natural ligand, showed second-line effectiveness for patients with gastric or colorectal carcinomas.

AREAS COVERED

We perform a narrative literature review. The aims of our work are to recall the current evidence of its efficacy in the treatment of gastric, hepatocellular and colorectal cancers and to present the ongoing studies enrolling gastrointestinal cancer patients in which ramucirumab is being tested. Expert commentary: The landscape of angiogenesis-inhibition for the treatment of GI malignancies is rapidly evolving. The results of the REGARD and RAINBOW trials renewed the interest for antiangiogenic agents in gastric cancer and determined a swift change in the treating paradigm for this disease. Accordingly, ramucirumab was shown to be effective in pretreated colorectal cancer patients and it is being tested in other gastrointestinal malignancies.

The need for effective pancreatic cancer detection and management: a biomarker-based strategy

Pancreatic cancer (Pa) is generally a very aggressive disease, with few effective approaches available for early diagnosis or therapy. These factors, combined with the aggressiveness and chemoresistance of Pa, results in a bleak outcome post-diagnosis. Cancer-related biomarkers have established capabilities for diagnosis, prognosis and screening and can be exploited to aid in earlier less-invasive diagnosis and optimization of targeted therapies. Pa has only one US FDA-approved biomarker, CA19-9, which has significant limitations. Hence, it is vital that novel biomarkers are identified and validated to diagnose, treat, control and monitor Pa. This review focuses on existing and potential Pa-associated markers and discusses how they may be applied in cohort for improved management of Pa.

A novel schedule of erlotinib/capecitabine (7/7) as salvage therapy in previously treated advanced pancreatic adenocarcinoma: a case series

BACKGROUND

The objective of this study was to report a case series on the efficacy and safety of capecitabine 7/7 schedule combined with erlotinib (CAP-ERL) in patients with advanced pancreatic cancer (APC) who have failed prior therapies.

METHODS

We retrospectively evaluated 13 patients with locally advanced or metastatic pancreatic cancer previously treated with gemcitabine or oxaliplatin-irinotecan-based first-line regimens. Treatment consisted of capecitabine (Xeloda) at a flat dose of 1000 mg orally twice daily on days 1-7 out of 14 days (7/7 schedule) and erlotinib (Tarceva) 100 mg orally once daily until unacceptable toxicity or disease progression. Tumor assessments were repeated every two cycles (8 weeks) and serum tumor markers were measured every 4 weeks.

RESULTS

All patients (median age: 63 years; 7 female/3 male) had various previous lines of treatments of chemotherapies. Median number of cycles with CAP-ERL was 4 (range 2-12). The overall response rate was 20%. CA19-9 was reduced more than 25% in 40% patients. The median overall survival and progression-free survival from the start of CAP-ERL were 4.5 months (range 3-7.5) and 2 months (range 1.5-4), respectively. The most common grade 3 toxicities included hand-foot syndrome, nausea, vomiting, diarrhea, rash, and fatigue.

CONCLUSIONS

Our result suggests that the combination of a fixed low dose of CAP-ERL 7/7 schedule was tolerated with manageable toxicity and showed encouraging activity as salvage treatment in patients with refractory APC with ECOG performance status 0-2. Further prospective studies are warranted to evaluate this combination.

Hereditary Pancreatic Cancer Syndromes

Despite decades of scientific and clinical research, pancreatic ductal adenocarcinoma (PDAC) remains a lethal malignancy. The clinical and pathologic features of PDAC, specifically the known environmental and genetic risk factors, are reviewed here with special emphasis on the hereditary pancreatic cancer (HPC) syndromes. For these latter conditions, strategies are described for their identification, for primary and secondary prevention in unaffected carriers, and for disease management in affected carriers. Nascent steps have been made toward personalized medicine based on the rational use of screening, tumor subtyping, and targeted therapies; these have been guided by growing knowledge of HPC syndromes in PDAC.