Mini Reviews in Medicinal Chemistry - Volume 15, Issue 1, 2015

Extracellular nucleotides and nucleosides are signalling molecules acting in all tissues and organs, including the central nervous system (CNS). A wide variety of effects, exerted by ecto-purines, requires that their levels, and ATP in particular, must be precisely controlled. Under physiological conditions, concentration of ecto-purines is regulated by a complex cascade of ecto-enzymes, including ecto-NTPDases (nucleoside triphosphate diphosphohydrolases), ecto-NPPs (nucleotide pyrophosphohydrolases/phosphodiesterases), ectoalkaline phosphatases, and ecto-5’nucleotidase. Adenylate kinase, transferring the phosphate moiety between nucleotides, also plays a role in controlling ecto-purines concentration. Disturbances in the elements of purinergic pathway within the CNS underlie the induction and amplification of many neurological pathologies. ATP released in bulk from the cells, and not degraded by less efficient or dysfunctional ecto-nucleotidases, triggers excitotoxic damage and neuro-inflammation in the brain tissue. High ATP concentration activating specific receptors has been shown to be involved in various disorders throughout CNS, including brain injury and ischemia, neuro-inflammation, epilepsy as well as neuropathic pain and migraine. Taking the above mentioned influence of ATP into consideration, the modulation of ecto-NTPDase activity or its site-targeted delivery seems a good therapeutic method. The availability of effective brain-targeted drug-delivery system is one of the most significant challenges facing potential NTPDase-based treatment of CNS disorders. The application of genetically engineered stem cells as carrier vehicles offers a promising strategy for the efficient delivery of the enzyme to CNS tissues.

Ecto-nucleotidases are nucleotide metabolizing enzymes that are divided into four different families; nucleoside triphosphate diphosphohydrolases (NTPDases), ecto-5′-nucleotidase (ecto-5′-NT), nucleotide pyrophosphatase/phosphodiesterases (NPPs), and alkaline phosphatases (APs). These enzymes are responsible for the hydrolysis of nucleotidases (nucleoside 5′-triphosphates, 5′-diphosphates and 5′-monophosphates). Ecto-nucleotidases modulate P1- and P2-receptor-mediated signaling. Alterations in extracellular nucleotide and adenosine level can increase or decrease P1 and P2 activity. Potent and selective ligands for certain ectonucleotidase are important as pharmacological tools to investigate the (patho)physiological roles of these enzymes. Furthermore, such ligands are required to study their potential as novel drugs, e.g., as immunomodulatory agents, for the treatment of cancer, cardiovascular or central nervous system disorders. Hence, this review aims to provide an overview of ecto-nucleotidases inhibitors developed so far.

Ecto-5’-nucleotidase (e5NT) hydrolyzes extracellular nucleotides and contributes to purinergic signaling. e5NT is implicated in a variety of pathological states including immunological diseases and cancer and represents an emerging drug target. Herein, we review structural and computational studies that have helped to better understand ligand binding characteristics and mechanistic features of the enzyme and led to the identification of new classes of e5NT inhibitors.

Alkaline phosphatase (AP, EC 3.1.3.1.) is a metalloenzyme that belongs to a family of ectonucleotidases. The other members of ectonucleotidase family are ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases), ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) and ecto-5-nucleotidase (e5NT). These ectonucleotidases are responsible for hydrolyzing extracellular nucleotides to nucleosides including adenosine. Many of these extracellular nucleotides and adenosine are important signaling molecules that act on their respective receptors (adenosine activated P1 receptor; nucleotide activated P2 receptor, each having many sub-types) and are therefore responsible for triggering cellular responses that lead to important physiological and immunological changes. A dedicated, concerted cohort of ectonucleotidases is responsible for controlling the availability of these extracellular signaling molecules at their respective receptors. Inhibitors of these ectonucleotidases provide the means by which these cellular processes can be modulated. This mini review has been written in the wake of mounting evidence of potential therapeutic benefits associated with inhibition of alkaline phosphatases and aims to provide prolific leads to design more potent and selective AP inhibitors.

Modern research in drug discovery from medicinal plants involves a multidimensional approach combining botanical, phytochemical, biochemical combinatorial chemistry and bioassay-guided fractionation approaches. Natural sources continue to provide an alternative as pharmacological leads against various devastating diseases such as diabetes, CVD, cancer etc. Nowadays, there is enormous requirement of safe and effective drugs in the world. This has prompted scientists to revert back towards natural resources as a potential source of therapeutics for treatment and management of such chronic and fatal diseases. However, there are certain serious challenges and limitations in this field including scale up and commercialization of active compounds which allow only one in thousand lead molecules to be developed as drug. A systematic and scientific approach is an essential requirement for drug development from natural resource. This mini review provides an overview of the methods involved in natural product research starting from crude plant extract to bioactive pharmacological lead. Moreover, it also discusses the limitations of working concerning the bioactivity of medicinal plants.

Organophosphate (OP) pesticides and nerve agents are responsible for suicidal and accidental poisonings. The acute toxicity of nerve agents leads to progressive inhibition of the enzyme acetylcholinesterase (AChE) by phosphylation of serine residue at the active site of gorge. The recent massive destruction of Syrian civilians by nerve gas sarin, has again renewed the research attention of global science fraternity towards nerve agents, their mode of action and most prominently their therapeutic treatment. This review is principally focused on nerve agent intoxication. The common approach to deal with OP-intoxication is, application of antimuscarinic drug (atropine), anticonvulsant drug (diazepam) and clinically used oximes (pralidoxime, trimedoxime, obidoxime and asoxime). However, the existing therapeutic approach is arguable and has several failings to cure all kinds of nerve agent poisonings. Considering this issue, numerous oximes have been synthesized and screened through various in-vitro and in-vivo studies in last decade to overcome the downsides. At present, only a few oximes (bis pyridinum-oximes) exhibit sound efficacy against selective OPs. In spite of extensive efforts, till date no oxime is available as a universal antidote against all the classes of OPs. This review is centered on the recent developments and structural modification of AChE reactivators against nerve agent toxicity. In particular, a deeper look has been taken into chemical modifications of the reactivators by incorporation of different structural moieties targeted towards the increased reactivation affinity and improved blood brain barrier (BBB) penetration.

Cancer has become a serious concern in public health. Harmful side effects and multidrug resistance of traditional chemotherapy have prompted urgent needs for novel anticancer drugs or therapeutic approaches. Anticancer peptides (ACPs) have become promising molecules for novel anticancer agents because of their unique mechanism and several extraordinary properties. Most α-helical ACPs target the cell membrane, and interactions between ACPs and cell membrane components are believed to be the key factor in the selective killing of cancer cells. In this review, we focus on the exploitation of the structure and function of α-helical ACPs, including the distinction between cancer and normal cells, the proposed anticancer mechanisms, and the influence of physicochemical parameters of α-helical ACPs on the biological activities and selectivity against cancer cells. In addition, the design and modification methods to optimize the cell selectivity of α-helical ACPs are considered. Furthermore, the suitability of ACPs as cancer therapeutics is discussed.