[Purine and pyrimidine nucleoside phosphorylases - remarkable enzymes still not fully understood]. / Nukleozydowe fosforylazy purynowe i pirymidynowe - niezwykle enzymy ciagle nie do konca rozszyfrowane.

Purine and pyrimidine nucleoside phosphorylases catalyze the reversible phosphorolytic cleavage of the glycosidic bond of purine and pyrimidine nucleosides, and are key enzymes of the nucleoside salvage pathway. This metabolic route is the less costly alternative to the de novo synthesis of nucleosides and nucleotides, supplying cells with these important building blocks. Interest in nucleoside phosphorylases is not only due to their important role in metabolism of nucleosides and nucleotides, but also due to the potential medical use of the enzymes (all phosphorylases in activating prodrugs - nucleoside and nucleic base analogs, high-molecular mass purine nucleoside phosphorylases in gene therapy of some solid tumors) and their inhibitors (as selective immunosuppressive, anticancer and antiparasitic agents, and preventing inactivation of other nucleoside drugs). Phosphorylases are also convenient tools for efficient enzymatic synthesis of otherwise inaccessible nucleoside analogues. In this paper the contribution of Professor David Shugar and some of his colleagues and coworkers in studies of these remarkable enzymes carried out over nearly 40 years is discussed on the background of global research in this field.

[Thymidylate synthase-catalyzed reaction mechanism]. / Mechanizm reakcji katalizowanej przez syntaze tymidylanowa.

Thymidylate synthase ThyA (EC 2.1.1.45;-encoded by the Tyms gene), having been for 60 years a molecular target in chemotherapy, catalyses the dUMP pyrimidine ring C(5) methylation reaction, encompassing a transfer of one-carbon group (the methylene one, thus at the formaldehyde oxidation level) from 6R-N5,10-methylenetetrahydrofolate, coupled with a reduction of this group to the methyl one, with concomitant generation of 7,8-dihydrofolate and thymidylate. New facts are presented, concerning (i) molecular mechanism of the catalyzed reaction, including the substrate selectivity mechanism, (ii) mechanism of inhibition by a particular inhibitor, N4-hydroxy-dCMP, (iii) structural properties of the enzyme, (iv) cellular localization, (v) potential posttranslational modifications of the enzyme protein and their influence on the catalytic properties and (vi) non-catalytic activities of the enzyme.

[The specific enzyme inhibitors for potential therapeutic use]. / Specyficzne inhibitory enzymów o potencjalnym zastosowaniu terapeutycznym.

Therapy for hepatitis C virus (HCV) initially consisted on administering ribavirin - having a broad spectrum of action - and pegylated interferon, and was only effective in 40-50% of patients. Appropriate was to find effective inhibitors of viral replication e.g. by inhibition of a viral enzyme, NTPase/helicase required in the process of translation and RNA replication of the HCV. We developed methods of synthesis of many compounds belonging to different groups - derivatives of nucleosides, benzotriazole, benzimidazole, tropolone and epirubicine. Some of the derivatives inhibit HCV helicase activity at low concentrations and reduces replication of the viral RNA in subgenomic replicon system. In the process of HCV replication casein kinase CK2 plays an important role. It regulates the level of phosphorylation of HCV protein NS5A, which affects the production of infectious virions of HCV. Effective and selective inhibitors of kinase CK2 could be of use in the treatment of HCV in combination with other drugs. CK2 kinase phosphorylates approximately 300 proteins that affect the growth, differentiation, proliferation or apoptosis. Elevated CK2 kinase activity has been observed in several types of cancer and other diseases, therefore, inhibitors of this enzyme are potential therapeutic importance, particularly for anti-cancer treatment. Research carried out in collaboration with prof. Shugar led to the synthesis of one of the most selective inhibitors of this enzyme which is 4,5,6,7-tetrabromo-1H-benzotriazole, used for the study of the role of kinase CK2 in a number of metabolic processes in tumor cells.

[Contribution of a halogen bond to binding of halogenated ligands by protein kinases]. / Rola wiazania halogenowego w oddzialywaniu halogenowanych ligandów z kinazami bialkowymi.

This article presents a brief overview of recent studies on the phenomena of halogen bonding, most of which have been done for the last 15 years in the collaboration with Prof. David Shugar. All these investigations concern reliable estimation of the thermodynamic contribution of a halogen bond to protein-ligand interactions.

Milestones in Parkinson's disease therapeutics.

In the mid-1980s, the treatment of Parkinson's disease was quite exclusively centered on dopatherapy and was focusing on dopamine systems and motor symptoms. A few dopamine agonists and a monoamine oxidase B inhibitor (selegiline) were used as adjuncts in advanced Parkinson's disease. In the early 2010s, levodopa remains the gold standard. New insights into the organization of the basal ganglia paved the way for deep brain stimulation, especially of the subthalamic nucleus, providing spectacular improvement of drug-refractory levodopa-induced motor complications. Novel dopamine agonists (pramipexole, ropinirole, rotigotine), catecholmethyltransferase inhibitors (entacapone), and monoamine oxidase B inhibitors (rasagiline) have also been developed to provide more continuous oral delivery of dopaminergic stimulation in order to improve motor outcomes. Using dopamine agonists early, before levodopa, proved to delay the onset of dyskinesia, although this is achieved at the price of potentially disabling daytime somnolence or impulse control disorders. The demonstration of an antidyskinetic effect of the glutamate antagonist amantadine opened the door for novel nondopaminergic approaches of Parkinson's disease therapy. More recently, nonmotor symptoms (depression, dementia, and psychosis) have been the focus of the first randomized controlled trials in this field. Despite therapeutic advances, Parkinson's disease continues to be a relentlessly progressive disorder leading to severe disability. Neuroprotective interventions able to modify the progression of Parkinson's disease have stood out as a failed therapeutic goal over the last 2 decades, despite potentially encouraging results with compounds like rasagiline. Newer molecular targets, new animal models, novel clinical trial designs, and biomarkers to assess disease modification have created hope for future therapeutic interventions.

Preclinical discovery of apixaban, a direct and orally bioavailable factor Xa inhibitor.

Apixaban (BMS-562247; 1-(4-methoxyphenyl)-7-oxo-6-(4-(2-oxopiperidin-1-yl)phenyl)-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-c]pyridine-3-carboxamide), a direct inhibitor of activated factor X (FXa), is in development for the prevention and treatment of various thromboembolic diseases. With an inhibitory constant of 0.08 nM for human FXa, apixaban has greater than 30,000-fold selectivity for FXa over other human coagulation proteases. It produces a rapid onset of inhibition of FXa with association rate constant of 20 µM⁻¹/s approximately and inhibits free as well as prothrombinase- and clot-bound FXa activity in vitro. Apixaban also inhibits FXa from rabbits, rats and dogs, an activity which parallels its antithrombotic potency in these species. Although apixaban has no direct effects on platelet aggregation, it indirectly inhibits this process by reducing thrombin generation. Pre-clinical studies of apixaban in animal models have demonstrated dose-dependent antithrombotic efficacy at doses that preserved hemostasis. Apixaban improves pre-clinical antithrombotic activity, without excessive increases in bleeding times, when added on top of aspirin or aspirin plus clopidogrel at their clinically relevant doses. Apixaban has good bioavailability, low clearance and a small volume of distribution in animals and humans, and a low potential for drug-drug interactions. Elimination pathways for apixaban include renal excretion, metabolism and biliary/intestinal excretion. Although a sulfate conjugate of Ο-demethyl apixaban (O-demethyl apixaban sulfate) has been identified as the major circulating metabolite of apixaban in humans, it is inactive against human FXa. Together, these non-clinical findings have established the favorable pharmacological profile of apixaban, and support the potential use of apixaban in the clinic for the prevention and treatment of various thromboembolic diseases.

Chemical biology of natural indolocarbazole products: 30 years since the discovery of staurosporine.

Staurosporine was discovered at the Kitasato Institute in 1977 while screening for microbial alkaloids using chemical detection methods. It was during the same era that protein kinase C was discovered and oncogene v-src was shown to have protein kinase activity. Staurosporine was first isolated from a culture of Actinomyces that originated in a soil sample collected in Mizusawa City, Japan. Thereafter, indolocarbazole compounds have been isolated from a variety of organisms. The biosynthesis of staurosporine and related indolocarbazoles was finally elucidated during the past decade through genetic and biochemical studies. Subsequently, several novel indolocarbazoles have been produced using combinatorial biosynthesis. In 1986, 9 years since its discovery, staurosporine and related indolocarbazoles were shown to be nanomolar inhibitors of protein kinases. They can thus be viewed as forerunners of today's crop of novel anticancer drugs. The finding led many pharmaceutical companies to search for selective protein kinase inhibitors by screening natural products and through chemical synthesis. In the 1990s, imatinib, a Bcr-Abl tyrosine kinase inhibitor, was synthesized and, following human clinical trials for chronic myelogenous leukemia, it was approved for use in the USA in 2001. In 1992, mammalian topoisomerases were shown to be targets for indolocarbazoles. This opened up new possibilities in that indolocarbazole compounds could selectively interact with ATP-binding sites of not only protein kinases but also other proteins that had slight differences in ATP-binding sites. ABCG2, an ATP-binding cassette transporter, was recently identified as an important new target for indolocarbazoles.

Neuro- and cardioprotective effects of blockade of nitric oxide action by administration of methylene blue.

Methylene blue (MB), generic name methylthioninium (C(16)H(18)ClN(3) S . 3H(2)O), is a blue dye synthesized in 1876 by Heinrich Caro for use as a textile dye and used in the laboratory and clinically since the 1890s, with well-known toxicity and pharmacokinetics. It has experimentally proven neuroprotective and cardioprotective effects in a porcine model of global ischemia-reperfusion in experimental cardiac arrest. This effect has been attributed to MB's blocking effect on nitric oxide synthase and guanylyl cyclase, the latter blocking the synthesis of the second messenger of nitric oxide. The physiological effects during reperfusion include stabilization of the systemic circulation without significantly increased total peripheral resistance, moderately increased cerebral cortical blood flow, a decrease of lipid peroxidation and inflammation, and less anoxic tissue injury in the brain and the heart. The last two effects are recorded as less increase in plasma concentrations of astroglial protein S-100beta, as well as troponin I and creatine kinase isoenzyme MB, respectively.

MGMT inhibitors--The Trinity College-Paterson Institute experience, a chemist's perception.

The DNA repair protein, O(6)-alkylguanine-DNA alkyltransferase (MGMT) can confer resistance to the cancer chemotherapeutic effects of the class of DNA damaging drugs generally referred to as the O(6)-alkylating agents. Inactivation of MGMT is thus a practical approach to improving the efficacy of such agents. An account is given of the collaboration between groups at Trinity College, Dublin and the Paterson Institute, Manchester which led to the development of the MGMT inactivating drug, Patrin (PaTrin-2, Lomeguatrib). The development of a simpler method of synthesis of O(6)-arylmethylguanines opened up the way to make a series of O(6)-heteroalkylmethyl analogues of the archetypal MGMT pseudosubstrate, O(6)-methylguanine. Of these, the furfuryl and thenyl compounds were the most active against recombinant Human MGMT in an in vitro assay. The 4-bromothenyl derivative was chosen for clinical trial as the most active compound. The MGMT active site tolerates O(6)-substituted guanines where the side chain can be quite large, but does not tolerate those with an aromatic or heteroaromatic ring with an 'ortho' substituent.

Pharmacophore identification: the case of the ser/thr protein phosphatase inhibitors.

This review provides a chronological account of the identification and refinement of the pharmacophore for inhibition of two key serine/threonine protein phosphatases, PP1 and PP2A. The dramatic impact of natural product isolation, molecular modeling, analogue design, biochemical studies, and crystallography on the evolution of the pharmacophore will be described.

Camptothecin and taxol: historic achievements in natural products research.

The research team of Dr. Monroe E. Wall and Dr. Mansukh C. Wani of Research Triangle Institute discovered two first-in-class life-saving chemotherapeutic agents. Camptothecin, first isolated and identified from Camptotheca acuminata, was found to kill cancer cells uniquely via topoisomerase I poisoning. Presently, two first-generation analogues of camptothecin are used to treat ovarian, colorectal, and small-cell lung cancers, and several second-generation analogues are in clinical trials. Taxol, first isolated and identified by Wall and Wani from Taxus brevifolia, was found to inhibit cancer cell growth via the stabilization of microtubules. In 1992, taxol was approved for refractory ovarian cancer and today is used against breast and non-small cell lung cancers and in Kaposi's sarcoma. While there have been numerous reviews of these molecules individually, this review offers an integrated account of the research team of "Wall and Wani" and the significance of their discoveries to chemistry, biology, and clinical medicine.

L-S,R-buthionine sulfoximine: historical development and clinical issues.

L-S,R-buthionine sulfoximine (L-S,R BSO) is a potent specific inhibitor of gamma-glutamylcysteine synthetase, the rate-limiting step in glutathione (GSH) biosynthesis. GSH is an important component of tumor drug resistance based on a strong association and recent transfection studies. Depletion of intracellular GSH by BSO significantly enhances the cytotoxicity of many cytotoxic agents, principally alkylating agents and platinating compounds but also irradiation and anthracyclines. Phase I clinical trials of BSO + melphalan (L-PAM)have been carried out and observed little toxicity with BSO alone and increased myelosuppression with BSO + L-PAM. Consistent and profound (< 10% of control) GSH depletion was observed in serial determinations of tumor GSH levels in patients receiving continuous infusion (CI) BSO. Evidence of clinical activity has been observed in patients with alkylating or platinating agent-refractory tumors. Phase II evaluation of CI BSO with L-PAM is in progress.

Camptothecin and taxol: from discovery to clinic.

Camptothecin (CPT) and taxol are secondary metabolites found in the stembark of Camptotheca acuminata, a native of China, and Taxus brevifolia, found in the northwest Pacific coastal region of the USA, respectively. The compounds were isolated through bioassay-guided fractionation of various extracts and through chromatographic fractions. Their unique and hitherto unknown structures were elucidated by nuclear magnetic resonance, mass spectrometry and X-ray analysis. Both compounds have unique mechanisms of antitumor activity; CPT uniquely inhibits an enzyme, topoisomerase I, involved in DNA replication, while taxol binds to a protein, tubulin, thus inhibiting cell division. Taxol has been called the best new anticancer agent developed from natural products, showing particular efficacy against ovarian cancer. CPT and analogs singly or combined with cisplatinum show efficacy against solid tumors, breast, lung, and colorectal, which hitherto have been unaffected by most cancer chemotherapeutic agents.