Current Medicinal Chemistry - Volume 23, Issue 2, 2016

Peptidyl arginine deiminases (PADs) are a small group of isozymes that convert Arg residues on the surface of proteins into citrulline residues, typically as a part of posttranslational processing. PADs are present in most of the tissues, and the isozyme distribution is tissue-specific. In the past 15 years, it is becoming apparent that PADs are either upregulated or their catalytic activity is enhanced in certain disease conditions, including neurological diseases. In particular, hypercitrullinated proteins and elevated PAD activities are discovered in neurodegenerative conditions such as multiple sclerosis, Alzheimer’s disease etc. This review article reviews the status of PAD enzymes as targets in neurodegenerative conditions, and briefly outlines the efforts in medicinal chemistry to identify PAD inhibitors for the treatment of various neurodegenerative conditions.

Cardiovascular diseases (CVD) are the leading cause of mortality worldwide. It is widely accepted that oxidative stress plays a key role in their development and progression; hence oxidative damage might be abrogated by antioxidants. Polyphenols are phytochemicals showing extensively studied antioxidant properties in-vivo. Most representative sources of these compounds include fruits, greens, nuts, herbs, cocoa, tea and coffee. Epidemiological evidence suggests an association between the consumption of polyphenol-rich vegetables and the reduction of cardiovascular disease prevalence. This fact could be related to the anti-inflammatory, antithrombotic and vasodilatory effects of polyphenols. Even though these biological effects could be mainly attributed to the antioxidant activity of polyphenols, other pharmacological mechanisms should also be considered. The latter could comprise direct anti-inflammatory effects, modulation of intracellular signaling and gene expression, improvement of nitric oxide homeostasis, as well as platelet antiaggregation. However, it is noticeable that protocols of interventions to evaluate the properties of polyphenols have failed to show the same positive results reported from observational studies. At present, a controversy exists regarding the actual effectiveness of polyphenols in preventing cardiovascular diseases. Therefore, an improvement of the available knowledge about polyphenol pharmacokinetics, together with a better understanding of the mechanisms of action of these compounds, could be of great benefit. Thus, a rational support for the development of interventional designs could provide reliable evidence on the actual role of polyphenols in CVD prevention.

The PDE4 enzyme has been proven to be a versatile drug target for therapeutics to treat diverse disease conditions such as asthma, COPD, diabetes, Huntington’s disease, and various other inflammatory disorders. The treatment of COPD is the most studied utility for PDE4 inhibitors due to their ability to inhibit inflammatory cell responses. Roflumilast is the only approved drug belonging to this class to treat COPD and has shown significant results in the treatment of asthmatic patients. This perspective highlights the pharmacological details of roflumilast and cilomilast. Moreover, efforts have been made to justify the superiority of roflumilast over cilomilast by detailed comparison of their pharmacological, pharmacokinetic, pharmacodynamic properties and structural features. Several other molecules, with promising PDE4 inhibitory activity have also been highlighted. Commonly associated side effects with this class of compounds, their management, and future direction towards the development of PDE4 inhibitors with improved therapeutic index are the focus of this perspective. More emphasis has been given towards the future development strategies to limit the side effects such as emesis and to achieve better benefit to risk ratio.

ROS1 is a pivotal transmembrane receptor protein tyrosine kinase which regulates several cellular processes like apoptosis, survival, differentiation, proliferation, cell migration, and transformation. There is increasing evidence supporting that ROS1 plays an important role in different malignancies including glioblastoma, colorectal cancer, gastric adenocarcinoma, inflammatory myofibroblastic tumor, ovarian cancer, angiosarcoma, and non small cell lung cancer; thus, ROS1 has become a potential drug discovery target. ROS1 shares about 49% sequence homology with ALK primary structure; therefore, wide range of ALK kinase inhibitors have shown in vitro inhibitory activity against ROS1 kinase. After Crizotinib approval by FDA for the management of ALK-rearranged lung cancer, ROS1-positive tumors have been focused. Although significant advancements have been achieved in understanding ROS1 function and its signaling pathways plus recent discovery of small molecules modulating ROS1 protein, a vital need of medicinal chemistry efforts is still required to produce selective and potent ROS1 inhibitors as an important therapeutic strategy for different human malignancies. This review focuses on the current knowledge about different scaffolds targeting ROS1 rearrangements, methods to synthesis, and some biological data about the most potent compounds that have delivered various scaffold structures.

The Amaryllidaceae occupies a privileged status amongst medicinal plants in having delivered the Alzheimer’s drug galanthamine to the clinical market. Following its resounding success, there have been several positive indicators for the emergence of an anticancer drug from the family due to the potent antiproliferative activities manifested by several of its alkaloid constituents. Of these, the phenanthridones such as pancratistatin hold most promise as potential chemotherapeutics having succumbed to various phases of clinical trials. Other cytotoxic targets of the Amaryllidaceae are to be found within the lycorane and crinane groups, as exemplified by crinine and lycorine. Although the molecular targets of these alkaloids still remain elusive, much effort has gone into understanding their mode of action in cancer cells. Recent findings have shown that the apoptotic pathway may be a key factor in cancer cell death instigated by Amaryllidaceae alkaloids. As such, this review seeks to: (a) examine the apoptotic effects of Amaryllidaceae alkaloids in cancer cells; (b) explore the molecular basis to these effects; and (c) provide a pharmacophoric rationale in support of these activities.

Nasopharyngeal carcinoma (NPC) is a cancer of the nasopharyngeal epithelium with distinct geographical, ethnic and racial distribution. Several genetic, ethnic and environmental risk factors, have been implicated in nasopharyngeal pathogenesis and of significance, is the Epstein - Barr virus (EBV)- latent infection observed in most patients. Patients with NPC are typically diagnosed only in advanced stages due to non-specific symptoms, and hence, they respond poorly to therapy. Currently, low survival rates, severe complications, tumour metastasis and recurrence following chemo-radiotherapy, delineate the need for better therapeutic options to combat the disease. Recent studies have shown that epigenetic mechanisms such as DNA methylation, histone modifications and microRNAs, which are altered in the EBV genome as well as in the host cells, may underlie the initiation and progression of NPC. Histone acetylation and deacetylation which are mediated by enzymes, namely histone acetyl transferases (HATs) and histone deacetylases (HDACs), are known to regulate gene expression and several cellular processes. HDACs are also involved in maintaining the EBV latent cycle and thus, HDAC inhibitors (HDACi) are potent inducers of EBV reactivation, which is critical for the expression of the lytic proteins, thereby providing novel targets for therapy, as well as mediating enhanced killing of cancer cells, when used alone or along with additional anti-cancer agents in EBV associated malignancies. Recently, three FDA- approved HDACi have been used for the treatment of T-cell lymphoma, while several others are in clinical trials, making histone modifications excellent candidates for targeted therapy. In this review, we summarize the epigenetic mechanisms altered in NPC, with a focus on histone modifications for targeted therapy.