Bacterial thioredoxin reductase inhibitors and methods for use thereof

Abstract

The mechanism of action of Ebselen differentiates between bacterial and mammalian thioredoxin reductase (TrxR). It displays fast oxidation of mammalian Trx and via the NADPH-TrxR catalyzed turnover of ebselen selenol with hydrogen peroxide, and therefore are mammalian antioxidants. Ebselen, and its diselenide, are strong competitive inhibitors of E. coli TrxR with Ki of 0.14 μM and 0.46 μM, respectively. E. coli mutants lacking glutathione reductase or glutathione were much more sensitive to inhibition by ebselen. Since either glutaredoxin or thioredoxin systems are electron donors to ribonucleotide reductase, ebselen targets primarily glutathione and glutaredoxin-negative bacteria, a class which includes major pathogens. Ebselen, and similar compounds are therefore useful as antibacterial agents, even for multiresistant strains. Two major pathogenic bacteria, which previously had not been known to be sensitive to ebselen, Mycobacterium tuberculosis (tuberculosis) and Helicobacter pylori (stomach ulcer and cancer), were shown to be excellent targets. Helicobacter pylori was also sensitive to ebsulfur.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the field of biologically active selenium and sulfur compounds, and more particularly to ebselen (or ebsulfur), its diselenide analog, and more generally to benzisoselenazole-3(2H)-one and derivatives thereof, salts thereof, pharmaceutical formulations thereof, and methods of use thereof.BACKGROUND OF THE INVENTION[0002]The thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH are together called the thioredoxin system, which serves as a hydrogen donor for ribonucleotide reductase and has a general powerful disulfide reductase activity (4, 5, 11, 13). The thioredoxin system is present in cells and in all forms of life (4, 5, 11, 13). Thioredoxin reductase (TrxR) is a dimeric FAD containing enzyme that catalyzes the reduction of its main protein substrate oxidized thioredoxin, to reduced thioredoxin at the expense of NADPH. The enzyme mechanism involves the transfer of reducing equivalents of NADPH to a redox active si...

AI Technical Summary

Benefits of technology

[0015]Ebselen, 2-phenyl-1,2-benzoisoselenazol-3(2H)-one, is an isoselenazol well known for its antioxidant and anti-inflammatory properties (1, 24) and is widely used in laboratories as peroxide reducing antioxidant in in vivo models and has been proved in clinical trails against acute ischemic stroke (2, 25-31). We have previously shown that ebselen and its diselenide are substrates for mammalian TrxR and efficient oxidants of reduced Trx forming the ebselen selenol, the active form of ebselen with its hydrogen peroxide reductase activity (3a,3b). The mechanism of antioxidant action of ebselen, together with its diselenide, was mainly through its interactions with the mammalian TrxR and Trx, providing the electrons for the reduction of hydrogen peroxide from NADPH (3a, 3b, 32) (FIG. 3). In the present invention we have discovered that ebselen, however, is not a substrate of E. coli TxrR, but instead it is a competitive inhibitor for the reduction of thioredoxin with a Ki of 0.15 μM. E. Coli mutants lacking a functional glutaredoxin system (glutathione reductase, GSH or glutaredoxin 1) were much more sensitive to inhibition by ebselen, which thereby will inhibit the essential enzyme ribonucleotide reductase (RNR) required for DNA synthesis. A main target of action of ebselen is the thioredoxin system. It follows that gram positive bacteria or other microorganisms lacking GSH will be particularly susceptible to ebselen. The present invention demonstrates that the well tolerated drug ebselen inhibits bacterial growth due to the large differences in structure and mechanism of the bacterial and mammalian thioredoxin reductases, establishing the drug as a novel chemotherapeutic principle.

[0017]Comparing the kinetic parameters of the interaction between the compounds and the two enzyme systems, provides better understanding of the chemical basis for the inhibition mechanism of ebselen and its diselenide towards the E. coli TrxR. This enhanced understanding of the principle chemical mechanism of ebselen diverse activity towards mammalian and E. coli TrxR is very important for the use of the drug and also for the development of effective antibiotic drugs based on same mechanism.

Problems solved by technology

The presently used drugs have limitations and resistant bacterial infections is an increasing problem as evident by development of vancomycin and methicillin resistant bacteria.

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