SB 612111 hydrochloride Anti LT therapy by LO inhibition has

Anti-LT therapy by 5-LO inhibition has been hampered by occurring liver toxicities by Zileuton or the clinical phase II compound Atreleuton [36], [37] However both compounds possess a thiophene as well as an N-hydroxyurea moiety. These features could be linked with reactive thiophene intermediates [38], [39] and redox cycling via electron transfer [40] potentially leading to the toxicity stated above. Indeed, there is no declaration of a class effect concerning liver toxicity by 5-LO inhibition per se[36]. The new lead compounds represent novel scaffolds with high efficacy in various in vitro assays. They circumvent bioactivation liabilities by eliminating a metabolic hot spot with the C5 methylated thiazole moiety [41], [42] as well as the above-mentioned 2,6 dialkylation. Taken together, based on our in vitro data, unsubstituted aminophenolic derivatives achieve their high potency partly by covalent binding to C159 and C418 of r5-LO. The poor potency of the compounds in intact SB 612111 hydrochloride could be explained by GSH trapping. This thiol reactivity may also be an explanation for the observed cytotoxicity of unsubstituted compounds (cf[19]). Nonetheless, the identification of novel small molecules targeting C159 and C418 of 5-LO may provide the basis for novel 5-LO drug discovery approaches specifically targeting these cysteine residues. Here, basic approaches can already be seen by another study in our group (Maucher et al., submitted data). The methylation motif of the lead compounds ST-1853 and ST-1906 on the other hand led to higher potencies in intact cells. Here, we could show that the structural motif of the two lead compounds prevented covalent modification of r5-LO as well as phase II metabolism (glucuronidation) while maintaining reducing properties. ST-1853 and ST-1906 displayed a high potency in physiologically relevant assays together with high specificity against related enzymes. Adding the moderate in vitro metabolism and non-cytotoxicity, they present well-balanced, most favorable characteristics that demand for further preclinical screening as anti-inflammatory drug candidates.
Conflict of interests
Acknowledgements We thank Anja Vogel, Astrid Brüggerhoff, and Sven George for expert technical assistance, Michael Hörnig for mutation of r5-LO, and Olof Rådmark for the pT3-5-LO plasmid. The study was supported by Else Kröner-Fresenius-Stiftung (TRIP, Dr. Hans Kröner-Graduiertenkolleg), LOEWE OSF, Fonds der Chemischen Industrie, LOEWE TMP and Fraunhofer-Projektgruppe für Translationale Medizin und Pharmakologie (TMP), Deutsche Forschungsgemeinschaft DFG (SFB 1039, Sachbeihilfe MA-5825/1-1, and INST 208/664-1) and the European COST Actions CA15135 and CM1207.
Introduction 5-Lipoxygenase (5-LO) catalyzes the initial two steps in the biosynthesis of leukotrienes from arachidonic acid. Leukotrienes represent a group of eicosanoids which are implicated in various pathological processes such as inflammation and cancerogenesis [1]. 5-LO is mainly expressed in various leukocytes such as polymorphonuclear leukocytes, monocytes/macrophages, mast cells, dendritic cells and B-lymphocytes, whereas platelets, endothelial cells and erythrocytes are 5-LO negative [1]. The 5-LO gene expression is regulated on epigenetic, transcriptional as well as post-transcriptional level. The promoter region contains eight GC-boxes and lacks canonical TATA and CAT boxes, thus resembling promoters of typical house-keeping genes [2]. Five of the eight GC-boxes are arranged in tandem arrays and are recognized by the transcription factors SP1 and EGR-1, respectively [3,4]. As mentioned above, basal 5-LO promoter activity is also controlled by epigenetic mechanism such as DNA methylation. In 5-LO negative U937 cells the GC-rich 5-LO promoter core region is strongly methylated which suppresses its activity [5]. No promoter methylation is observed in 5-LO positive cells like the human monocytic cell line Mono Mac 6 [5].