Current Medicinal Chemistry - Volume 21, Issue 8, 2014

Pancreatic ductal adenocarcinoma (PDAC) occurs in the majority of cases with early locoregional spread and distant metastases at diagnosis, leading to dismal prognosis and limited treatment options. Traditional cytotoxic chemotherapy provides only modest benefit to patients with PDAC. Identification of different molecular pathways, overexpressed in pancreatic cancer cells, has provided the opportunity to develop targeted therapies (monoclonal antibodies and small-molecule inhibitors) and peculiar new class of taxanes with a crucial therapeutic role in this cancer setting. A phase III trial has shown that erlotinib in combination with gemcitabine was clinically irrelevant and skin toxicity can be a positive prognostic factor. Moreover, the combination of cetuximab or erlotinib with radiotherapy in advanced pancreatic cancer has shown to be synergistic and a reversal of radio-resistance has been suggested by inhibition of VEGF/EGFR pathway. To overcome EGFR-inhibition therapy resistance several alternative pathways targets are under investigation (IGF- 1R, MMPs, Hedgehog proteins, m-TOR, MEK, COX-2) and provide the rationale for clinical use in phase II/III studies. Also nab-paclitaxel, a new taxanes class, uses high pancreatic albumin-binding protein SPARC levels to act in cancer cells with a less toxic and more effective dose with respect to classic taxanes. Understanding of molecular pathogenesis of pancreatic adenocarcinoma continues to expand. However, many promising data in preclinic and phase I/II trials did not yield promise in phase III trials, suggesting that identification of predictive biomarkers for these new agents is mandatory. The knowledge of biologic and molecular aspects of pancreatic cancer can be the basis for future therapeutic developments.

The onset of hepatocellular carcinoma (HCC) is related to the development of non-neoplastic liver disease, such as viral infections and cirrhosis. Even though patients with chronic liver diseases undergo clinical surveillance for early diagnosis of HCC, this cancer is often diagnosed in advanced stage. In this case locoregional treatment is not possible and systemic therapies are the best way to control it. Until now sorafenib, a Raf and multi-kinase inhibitor has been the best, choice to treat HCC systemically. It showed a survival benefit in multicenter phase III trials. However the proper patient setting to treat is not well defined, since the results in Child-Pugh B patients are conflicting. To date various new target drugs are under developed and other biological treatments normally indicated in other malignancies are under investigation also for HCC. These strategies aim to target the different biological pathways implicated in HCC development and progression. The target drugs studied in HCC include anti-VEGF and anti-EGFR monoclonal antibodies, tyrosine kinase inhibitors and mTOR inhibitors. The most important challenge is represented by the best integration of these drugs with standard treatments to achieve improvement in overall survival and quality of life.

The receptor tyrosine kinase mesenchymal-epithelial transition factor (c-Met) plays a pivotal role in regulation of cell proliferation and migration. Abnormal expression of c-Met has been associated with poor prognosis in several cancer types, including upper gastrointestinal malignancies. Moreover, c-Met interaction with multiple signalling pathways involved in tumor growth and invasive/metastatic phenotype has gained substantial attention in the last few years, suggesting the therapeutic potential of this target. This has led to the development and evaluation of a number of c-Met inhibitors. Here we describe the critical role of the HGF/c-Met pathway in cancer, as well as the preclinical and clinical investigations on c-Met inhibitors in solid tumors, with particular emphasis on recent findings with small-molecule inhibitors in gastrointestinal cancers. Clinical trials with several of these novel inhibitors have been encouraging and one of them, crizotinib (dual c-Met/ALK inhibitor), has recently been approved for lung cancers with ALK-rearrangement. There are accumulating evidences on the therapeutic potential of this and other c-Met inhibitors for the treatment of other malignancies, such as gastric and pancreatic cancers. These inhibitors might be used in combination with chemotherapy as well as with other biological agents, in order to overcome different resistance mechanisms. However, further studies are needed to identify determinants of the activity of c-Met inhibitors, through the analysis of genetic and environmental alterations affecting c-Met and parallel pro-cancer pathways. These studies will be critical to improve the efficacy and selectivity of current and future anticancer strategies targeting c-Met.

Oesophageal cancer is the sixth cause of cancer-related death worldwide. Nowadays radiochemotherapy (RTCT) plays a central role in the treatment settings of such disease. Evaluation of molecular targeted therapies is an attractive opportunity for the management of oesophageal, GEJ and gastric cancers to improve outcomes as for other primary tumours. Clinical trials focused on the potential of many molecular targeted agents included in CT schedules, and also on the possibility, efficacy and tolerance of their use combined with RT. This review will focus on the over 15 more promising agents studied in combination with RT for esophagogastric tumour, describing the mechanism and target of action, evidences and potential future role on over 50 trials evaluated. Mechanisms of action, studies and evidences about Human Epidermal Growth Factor type 2 Targeting Agents (one of the more promising), Epidermal Growth Factor’s Receptor Inhibitors (nowadays showing a lower potential than expected), Vascular Endothelial Growth Factor Inhibitors, Mesenchymal Epithelial Transition Factor, Hepatocyte Growth Factor and other targeting agents are reviewed.

Primary gastric non-Hodgkin’s lymphomas (PG-NHL) are the most common extranodal lymphomas, representing between 47% and 74% of all gastrointestinal lymphoma cases. In Western countries two histological types, diffuse large B-cell (DLBC) NHL and mucosa-associated lymphoid tissue (MALT) NHL, are more frequently represented, accounting for the majority of gastric tumors after adenocarcinoma. For several years treatment of these PG lymphomas consisted of surgery, chemotherapy and radiotherapy, alone or in combination. In the last two decades however, advances in our understanding of their pathogenesis and biology have changed the treatment strategy, at least as regards the early stages of disease. In addition to making tumor regression possible through the eradication of Helicobacter pylori, which is considered the main pathogenic agent, this understanding has also provided a solid rationale to assess the efficacy of targeted therapy, namely of drugs which interfere with specific molecules expressed by tumor cells or are involved in key growth pathways of these lymphomas. In particular, rituximab, a monoclonal anti-CD20 antibody, radioimmunotherapy, the first-generation proteasome inhibitor bortezomib and lenalidomide have been evaluated. Despite significant antitumor activity in this subset of NHL and manageable toxicity, many questions still remain however about the optimal dose, the best administration schedule and their combination with conventional chemotherapy. This review focuses on the pathogenesis of PG-MALT and DLBC lymphomas, and discusses the results of clinical trials on the impact of new agents on prognosis and survival in these patients, considering also potential new therapautic targets.

Advanced enteropancreatic (EP) neuroendocrine tumors (NETs) can be treated with several different therapies, including chemotherapy, biotherapy, and locoregional treatments. Over the last few decades, impressive progress has been made in the biotherapy field. Three main druggable molecular targets have been studied and developed in terms of therapy: somatostatin receptor (sstr), mammalian target of rapamycin (mTOR), and angiogenic factors. In particular, research has moved from the old somatostatin analogs (SSAs), such as octreotide (OCT) and lanreotide (LAN), specifically binding to the sstr-2, to the newer pasireotide (PAS), which presents a wider sstr spectrum. Over the last ten years, several molecular targeted agents (MTAs) have been studied in phase II trials, and very few of them have reached phase III. The mTOR inhibitor everolimus and the multitargeted inhibitor sunitinib have been approved for clinical use by the FDA and EMA in advanced well/moderately-differentiated (WD, MD) progressive pancreatic neuroendocrine tumors (PNETs), on the basis of the positive results of two international large randomized phase III trials vs. placebo. Bevacizumab has been studied in a large US phase III trial vs. interferon (IFN)-alfa2b, and results are pending. In this review, the biological and clinical aspects of MTAs introduced into clinical practice or which are currently in an advanced phase of clinical investigation are addressed.

Gastric cancer represents one of the most common cancer worldwide. Unfortunately, the majority of patients present in advanced stage and outcome still remains poor with high mortality rate despite decreasing incidence and new diagnostic and therapeutic strategies. Although utility of classical chemotherapy agents has been widely explored, advances have been slow and the efficacy of these agents has reached a plateau of median overall survival not higher than 12 months. Therefore, researchers focused their attention on better understanding molecular biology of carcinogenesis and deeper knowledge of the cancer cell phenotype, as well on development of rationally designed drugs that would target specific molecular aberrancies in signal transduction pathways. These targets include cell surface receptors, circulating growth and angiogenic factors and other molecules involved in downstream intracellular signaling pathways, including receptor tyrosine kinases. However, therapeutic advances in gastric cancer are not so encouraging when compared to other solid organ malignancies such as breast and colorectal cancer. This article reviews the role of targeted agents in gastric cancer as single-agent therapy or in combination regimens, including their rational and emerging mechanism of action, current and emerging data. We focused our attention mainly on published phase III studies, therefore cornerstone clinical trials with trastuzumab and bevacizumab have been largely discussed. Phase III studies presented in important international meetings are also reviewed as well phase II published studies and promising new therapies investigated in preclinical or phase I studies. Today, in first-line treatment only trastuzumab has shown significantly increased survival in combination with chemotherapy, whereas ramucirumab as single agent resulted effective in progressing patients, but - despite several disappointing results - these are the proof of principle that targeting the proper molecular aberration is the best way for implementing outcome of therapy.

Antivascular approaches aim to cause rapid and catastrophic shutdown in the vascular function of the tumour, leading to extensive tumour cell death. Tumour vascular disrupting agents (VDAs) are a new class of cancer therapies that target the existing vasculature of tumours, taking advantage of the relative instability of tumour vasculature and its supporting structures. Treatment with VDAs induces a rapid collapse and regression of tumour vessels, with a consequent deprivation of blood and oxygen which leads to ischemic or hemorrhagic necrosis of the tumour. In this review, an overview of the most recently developed vascular disrupting agents is reported, focusing on the biological effects exerted by these compounds on endothelial cells and tumour vasculature, potentially effective in the treatment of several malignancies including upper gastrointestinal tumours. In particular, we have focused on the antimitotic agent combretastatin and its numerous synthetic analogues such as combretastatin A-4-phosphate, OXI4503, and AVE8062, and on the colchicine analogue ZD6126.

DEAD-box RNA helicase DDX3 is a well-known host factor that inhibits hepatitis B viral proliferation and boosts innate immune responses via TANK-binding kinase 1 (TBK1)/IKKε-mediated and/or interferon (IFN)-β promoter stimulator-1 (IPS-1)-mediated IFN-β induction. Previously, we demonstrated the anti-hepatitis B activity of Rg3 via stimulation of TRAF6/TAK1 degradation and inhibition of JNK/AP-1 signaling. To determine the effects of Rg3 on innate immunity, an IFN-β promoter assay was performed. Rg3 ameliorated IFN-β expression via upregulation of both the TBK1/IKKε pathway and DDX3 expression. In addition, Rg3 induced the phosphorylation of IRF3 and its translocation into nucleus, which is a key molecule to induction of IFN-β expression. To evaluate the molecular mechanism of Rg3 on DDX3 expression, the DDX3 promoter (-1406/+105) was subjected to luciferase assay and ChIP analysis. p53 phosphorylation resulted in upregulation of DDX3 expression, which enhanced DDX3 promoter transactivation activity. Transient transfection with wild-type p53 increased DDX3 promoter activity in Hep3B cells which have null mutant of p53, whereas knockdown p53 by si-p53 reduced DDX3 promoter activity in HepG2.2.15 and HepG2 cells, respectively. Rg3- mediated phosphorylation of p53 resulted in inhibition of Akt phosphorylation, which in turn reduced MDM2-mediated p53 degradation. An Akt inhibitor augmented DDX3 promoter activity and reduced the secretion of hepatitis B surface antigen. Our data indicate that Rg3 enhances innate immunity by inducing IFN-β expression through upregulation of DDX3 promoter activity via p53-mediated transactivation and activation of the TBK1/IKKε/IRF3 pathway.

Protein damage mediated by oxidation has been associated with aging and age-related diseases, in particular neurodegenerative diseases. The protein that is known to be one of the major targets of oxidative stress is glyceraldehyde- 3-phosphate dehydrogenase. GAPDH is believed to play a key role in certain neurodegenerative disorders, such as Alzheimer’s, Parkinson’s, and Huntington’s diseases. Several recent studies have suggested that a wide range of variety of polyphenols including resveratrol may have neuroprotective effects. Here, we present data that clearly indicate the prooxidative properties of resveratrol and tiron in the inactivation of GAPDH induced by the superoxide anion generated via xanthine oxidase mediated oxidation of xanthine. Generated in the studied system tiron and resveratrol radicals are much more efficient in the inactivation of GAPDH than the superoxide anion alone. The analysis of CD spectra of protein exposed to the tiron and resveratrol radicals revealed little effect on the secondary structure of GAPDH. In both cases reduction of α-helical structure was followed by the increase in β-sheet conformation. Thus, the most probable mechanism of inactivation of GAPDH in the studied system is oxidation of cysteine residues in the catalytic center of the enzyme. Finally, molecular modeling of the resveratrol - GAPDH and tiron - GAPDH complexes showed potential binding sites for those antioxidants with binding affinity -45 kcal/mol and -48 kcal/mol respectively.