Pteridine reductase (PTR1) is essential for salvage of pterins by parasitic trypanosomatids and is a target for the development of improved therapies. To identify inhibitors of Leishmania major and Trypanosoma cruzi PTR1, we combined a rapid-screening strategy using a folate-based library with structure-based design. Assays were carried out against folate-dependent enzymes including PTR1, dihydrofolate reductase (DHFR), and thymidylate synthase. Affinity profiling determined selectivity and specificity of a series of quinoxaline and 2,4-diaminopteridine derivatives, and nine compounds showed greater activity against parasite enzymes compared with human enzymes. Compound 6a displayed a Ki of 100 nM toward LmPTR1, and the crystal structure of the LmPTR1:NADPH:6a ternary complex revealed a substrate-like binding mode distinct from that previously observed for similar compounds. A second round of design, synthesis, and assay produced a compound (6b) with a significantly improved Ki (37 nM) against LmPTR1, and the structure of this complex was also determined. Biological evaluation of selected inhibitors was performed against the extracellular forms of T. cruzi and L. major, both wild-type and overexpressing PTR1 lines, as a model for PTR1-driven antifolate drug resistance and the intracellular form of T. cruzi. An additive profile was observed when PTR1 inhibitors were used in combination with known DHFR inhibitors, and a reduction in toxicity of treatment was observed with respect to administration of a DHFR inhibitor alone. The successful combination of antifolates targeting two enzymes indicates high potential for such an approach in the development of previously undescribed antiparasitic drugs.antitrypanosomatid agents ͉ antifolates ͉ drug discovery P rotozoan parasites of the order Kinetoplastida are the causal agents of serious human diseases, including African sleeping sickness, Chagas' disease, and leishmaniasis. There is an urgent need for new, more effective drugs targeting these neglected diseases, because those in current use are toxic, expensive, and often difficult to administer. The problem is compounded by an increase in drug resistance and lack of progress in drug development. Only a single new effective treatment has been developed in the last 25 years, Miltefosine (hexadecylphosphocholine), recently approved in India (1).Enzymes involved in the provision and use of reduced folate cofactors such as dihydrofolate reductase (DHFR) and thymidylate synthase (TS) are valued drug targets for the treatment of bacterial infections (2), cancer (3), and certain parasitic diseases, notably malaria (4). DHFR catalyzes the two-step reduction of folate to tetrahydrofolate, which is then transformed to N 5 ,N 10 -methylene tetrahydrofolate and is used by TS as a methyl donor and reducing agent in the conversion of 2Ј-deoxyuridine-5Ј-monophosphate to 2Ј-deoxythymidine-5Ј-monophosphate. Inhibition of DHFR or TS reduces the cellular pool of 2Ј-deoxythymidine-5Ј-monophosphate, impairing DNA replication and resulting ...
Discovered in late 1960, azoles are heterocyclic compounds class which constitute the largest group of available antifungal drugs. Particularly, the imidazole ring is the chemical component that confers activity to azoles. Triazoles are obtained by a slight modification of this ring and similar or improved activities as well as less adverse effects are reported for triazole derivatives. Consequently, it is not surprising that benzimidazole/benzotriazole derivatives have been found to be biologically active. Since benzimidazole has been widely investigated, this review is focused on defining the place of benzotriazole derivatives in biomedical research, highlighting their versatile biological properties, the mode of action and Structure Activity Relationship (SAR) studies for a variety of antimicrobial, antiparasitic, and even antitumor, choleretic, cholesterol-lowering agents.
Since 1940s, Quinoxaline 1,4-dioxides (QdNO's) are known as potent antibacterial agents, and subtherapeutic levels have been used to promote growth and improve efficiency of feed conversion in animal feed. They have also shown a selective cytotoxicity against hypoxic cells present in solid tumours. Furthermore, recent studies have put in evidence that QdNO's are endowed with antitubercular, antiprotozoal and anticandida activities. On the other hand, several authors have reported about photoallergic and mutagenic effects of some derivatives. QdNO's may also cause the development of antibiotic-resistant bacteria and influence the horizontal transfer of virulence genes between bacteria. In this review article we report the biological properties, the mode of action and Structure Activity Relationship (SAR) studies of the QdNO derivatives. Furthermore, some cytogenetic and genotoxic effects, classical and more recent method of synthesis, the quinoxaline 1,4-dioxides, and some of their most important reactions, were also reported.
The upregulation of pteridine reductase (PTR1) is a major contributor to antifolate drug resistance in Leishmania spp., as it provides a salvage pathway that bypasses dihydrofolate reductase (DHFR) inhibition. The structure-based optimization of the PTR1 inhibitor methyl-1-[4-(2,4-diaminopteridin-6-ylmethylamino)benzoyl]piperidine-4-carboxylate (1) led to the synthesis of a focused compound library which showed significantly improved selectivity for the parasite's folate-dependent enzyme. When used in combination with pyrimethamine, a DHFR inhibitor, a synergistic effect was observed for compound 5b. This work represents a step forward in the identification of effective antileishmania agents.
Many viral pathogens encode the motor proteins named RNA helicases which display various functions in genome replication. General strategies to design specific and selective drugs targeting helicase for the treatment of viral infections could act via one or more of the following mechanisms: inhibition of the NTPase activity, by interferences with ATP binding and therefore by limiting the energy required for the unwinding and translocation, or by allosteric mechanism and therefore by stabilizing the conformation of the enzyme in low helicase activity state; inhibition of nucleic acids binding to the helicase; inhibition of coupling of ATP hydrolysis to unwinding; inhibition of unwinding by sterically blocking helicase translocation.
Recently, by in vitro screening studies, it has been reported that several benzotriazole, imidazole, imidazodiazepine, phenothiazine, quinoline, anthracycline, triphenylmethane, tropolone, pyrrole, acridone, small peptide, and Bananin derivatives are endowed with helicase inhibition of pathogen viruses belonging to Flaviviridae, Coronaviridae, and Picornaviridae families.
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