Current Drug Targets - Volume 18, Issue 8, 2017

10.2174/138945011808170504184719

The multidrug resistance (MDR) phenotype accounts for the poor response of cholangiocarcinoma to available antitumor drugs. This is an important limitation to the use of pharmacological approaches, both as adjuvant therapies and for treating advanced CCA when surgical removal is not possible. MDR is the result of a complex combination of defense mechanisms against toxic compounds already present in cholangiocytes, which play a role in the physiology of these cells by protecting the biliary epithelium from the toxins reaching the biliary tree with the blood that perfuses this tissue, or that are secreted by hepatocytes into bile, to which cholangiocytes are exposed. These mechanisms of chemoresistance (MOC) are also present, usually with enhanced efficacy, in tumors derived from cholangiolar cells. The present review article is an update of the state-of-the-art regarding the MOC involved in the poor response of CCA to antitumor drugs. These MOC have been classified as: changes in the amount of drug in the cells due to decreased uptake (MOC-1a) or enhanced efflux (MOC-1b); altered proportions between prodrug, active drug and inactive metabolites (MOC-2); changes in the molecular targets of antitumor drugs (MOC-3); an enhanced ability of tumor cells to repair drug-induced DNA damage (MOC-4), and an impaired apoptosis/survival balance (MOC-5).

Primary sclerosing cholangitis (PSC) is a biliary disease characterized by liver inflammation and death of cholangiocytes which, in turn, drive to fibrosis, cirrhosis and functional alterations of the liver. PSC is also associated with an increased risk of developing cholangiocarcinoma. To date, the etiopathogenesis of PSC is still not completely understood, although a genetic predisposition in association to environmental factors contribute to immune-mediated liver damage. The lack of such knowledge is responsible for the failure of most available therapies. At this time, many studies are evaluating potential approaches that could have a positive impact on the progression of the disease. This review aims to provide a summary of present and past therapeutic approaches for PSC.

Persistent exposure of biliary epithelial cells (i.e., cholangiocytes) to diverse factors such as disordered immunity, genetic alterations, ischemia, toxic compounds and/or infectious agents leads to a chronic portal inflammatory response which eventually progresses to biliary fibrosis. This stage is characterized by increased production and deposition of scar-forming extracellular matrix proteins (ECM), in particular fibrillar collagen types I and III, but including other ECM constituents such as elastin and fibrillin-1, both components of elastic fibers. The major cellular mediators responsible for collagen deposition are activated hepatic stellate cells (HSCs) and to a lesser extent, portal myofibroblasts, which are activated by soluble inflammatory mediators (i.e., cytokines, growth factors) and extracellular matrix components. Unless the underlying cause of biliary injury can be effectively treated, these processes may ultimately lead to decompensated cirrhosis and can also provide ideal microenvironments for the development and growth of primary tumors. Recent evidence indicates that fibrosis is a dynamic and potentially reversible process. As the curative options for most chronic biliary diseases remain limited to transplantation, there is an urgent need to clarify the molecular pathways involved in the development of biliary fibrosis and identify new therapeutic targets. In this review we describe the cellular and molecular regulators that orchestrate the cholangiocyte /myofibroblast cross-talk and identify the signaling processes that are most promising for therapeutic targeting.

Cholestasis is the main pathogenic event in a wide range of genetic or acquired disorders of bile acid synthesis or bile flow, resulting in intrahepatic and systemic accumulation of bile acids. In turn, augmented levels of bile acids lead to hepatocellular injury and progressive liver damage, eventually culminating in fibrosis and end-stage liver disease. In the injured cholestatic liver, apoptosis has long been recognized as a direct consequence of bile acid-mediated injury. It is now apparent that inflammation and necrosis play an equal or even more prevalent role. Ursodeoxycholic acid is the mainstream treatment for several cholestatic syndromes, but has limited efficacy in certain circumstances. With the notion that miRNAs play key roles in basic biological processes and that their deregulation is common in human liver disease, prospective use of miRNAs as either therapeutic targets or disease biomarkers is now being increasingly documented. Deciphering the exact contribution of each player is crucial for directing efforts toward finding much needed novel therapeutic strategies for cholestasis.

Cholangiocarcinoma (CCA) is a heterogeneous group of dysplastic disorders affecting the biliary epithelium. It is the second most common primary liver tumor which accounts for around 3% of all gastrointestinal cancers. CCA is very deadly due to its aggressiveness, late diagnosis and high chemoresistance. The incidence is increasing worldwide and the therapeutic options are very limited. Radiotherapy, chemotherapy, surgery and/or liver transplantation may be indicated in patients who meet certain criteria, but chances of success are low. There is therefore increasing interest in understanding the molecular mechanisms involved in the pathogenesis of this cancer type and in identifying new targets for therapy. Current strategies are based on targeting key signaling pathways involved in proliferation, survival, apoptosis and migration. In this review, the most relevant molecular mechanisms involved in the pathogenesis of CCA are discussed and the main preclinical and clinical studies are highlighted. Moreover, future directions in basic and clinical research are indicated.

Polycystic liver diseases (PLD) are a group of genetic disorders initiated by mutations in several PLD-related genes and characterized by the presence of multiple cholangiocyte-derived hepatic cysts that progressively replace liver tissue. PLD co-exists with Autosomal Dominant Polycystic Kidney Disease (ADPKD) and Autosomal Recessive PKD as well as occurs alone (i.e., Autosomal Dominant Polycystic Liver Disease [ADPLD]). PLD associated with ADPKD and ARPKD belong to a group of disorders known as cholangiociliopathies since many disease-causative and disease-related proteins are expressed in primary cilia of cholangiocytes. Aberrant expression of these proteins in primary cilia affects their structures and functions promoting cystogenesis. Current medical therapies for PLD include symptomatic management and surgical interventions. To date, the only available drug treatment for PLD patients that halt disease progression and improve quality of life are somatostatin analogs. However, the modest clinical benefits, need for long-term maintenance therapy, and the high cost of treatment justify the necessity for more effective treatment options. Substantial evidence suggests that experimental manipulations with components of the signaling pathways that influence cyst development (e.g., cAMP, intracellular calcium, receptor tyrosine kinase, transient receptor potential cation channel subfamily V member 4 (TRPV4) channel, mechanistic target of rapamycin (mTOR), histone deacetylase (HDAC6), Cdc25A phosphatase, miRNAs and metalloproteinases) attenuate growth of hepatic cysts. Many of these targets have been evaluated in pre-clinical trials suggesting their value as potential new therapies. This review outlines the current clinical and preclinical treatment strategies for PLD.

Cilia are microtubule-based organelles, which are ubiquitously expressed in epithelial cells. Cholangiocytes, the epithelial cells lining the biliary tree, have primary cilia extending from their apical plasma membrane into the ductal lumen, where the cilia function as multisensory organelles transducing environmental cues into the cell interior. The decrease or loss of primary cilia has been described in several malignancies, including cholangiocarcinoma, suggesting that the loss of cilia is a common occurrence in neoplastic transformation. In this short review, we describe the expression of cilia in several cancers, explore the mechanisms and consequences of ciliary loss, and discuss the potential use of the primary cilia as therapeutic targets.

Historically, the word cancer is derived from the Latin cancer, as the red swollen arteries near a tumor reminded the physician Galenus and his fellow Romans of a red crab. Currently, cancer remains the disease to beat as it remains a leading cause of death worldwide (WHO). Tumors do not simply consist of cancer cells, as they can recruit normal cells, which will form the tumor-associated stroma. These stromal cells together with the extracellular matrix, constitute the tumor microenvironment. Reciprocal communication between tumor-associated stromal cells and cancer cells is important for the induction of epithelial-to-mesenchymal transition and invasion. A detailed knowledge of this communication can spark the development of novel therapeutic strategies aimed at tackling yet unaddressed regulators of invasion and thus metastasis. Therefore, this review will focus not only on epithelial-to-mesenchymal transition and invasion, but also on communication between tumor cells, in particular colon cancer cells, and their stroma, with a primordial focus on cancer-associated fibroblasts, and lastly this review will discuss how this communication can affect the cancer cell’s ability to invade its surroundings and form metastases.

Obesity, an impending global pandemic, is not being effectively controlled by current measures such as lifestyle modifications, bariatric surgery or available medications. Its toll on health and economy compels us to look for more effective measures. Fortunately, the advances in biology and molecular technology have been in our favour for delineating new pathways in the pathophysiology of obesity and have led to subsequent development of new drug targets. Development of antiobesity drugs has often been riddled with problems in the past. Some of the recently approved drugs for pharmacotherapy of obesity have been lorcaserin, phentermine/topiramate and naltrexone/ bupropion combinations. Several promising new targets are currently being evaluated, such as amylin analogues (pramlintide, davalintide), leptin analogues (metreleptin), GLP-1 analogues (exenatide, liraglutide, TTP-054), MC4R agonists (RM-493), oxyntomodulin analogues, neuropeptide Y antagonists (velneperit), cannabinoid type-1 receptor blockers (AM-6545), MetAP2 inhibitors (beloranib), lipase inhibitors (cetilistat) and anti-obesity vaccines (ghrelin, somatostatin, Ad36). Many of these groups of drugs act as “satiety signals” while others act by antagonizing orexigenic signals, increasing fat utilisation and decreasing absorption of fats. Since these targets act through various pathways, the possibility of combined use of two or more classes of these drugs unlocks numerous therapeutic avenues. Hence, the dream of personalized management of obesity might be growing closer to reality.