The Novel Imidazopyridine 2-[2-(4-Methoxy-pyridin-2-yl)-ethyl]-3H-imidazo[4,5-b]pyridine (BYK191023) Is a Highly Selective Inhibitor of the Inducible Nitric-Oxide Synthase

Abstract

We have identified imidazopyridine derivatives as a novel class of NO synthase inhibitors with high selectivity for the inducible isoform. 2-[2-(4-Methoxy-pyridin-2-yl)-ethyl]-3H-imidazo [4,5-b]pyridine (BYK191023) showed half-maximal inhibition of crudely purified human inducible (iNOS), neuronal (nNOS), and endothelial (eNOS) NO synthases at 86 nM, 17 M, and 162 M, respectively. Inhibition of inducible NO synthase was competitive with L-arginine, pointing to an interaction of BYK191023 with the catalytic center of the enzyme. In radioligand and surface plasmon resonance experiments, BYK191023 exhibited an affinity for iNOS, nNOS, and eNOS of 450 nM, 30 M, and Ͼ500 M, respectively. Inhibition of cellular nitrate/nitrite synthesis in RAW, rat mesangium, and human embryonic kidney 293 cells after iNOS induction showed 40-to 100-fold higher IC 50 values than at the isolated enzyme, in agreement with the much higher L-arginine concentrations in cell culture media and inside intact cells. BYK191023 did not show any toxicity in various rodent and human cell lines up to high micromolar concentrations. The inhibitory potency of BYK191023 was tested in isolated organ models of iNOS (lipopolysaccharide-treated and phenylephrine-precontracted rat aorta; IC 50 ϭ 7 M), eNOS (arecaidine propargyl esterinduced relaxation of phenylephrine-precontracted rat aorta; IC 50 Ͼ 100 M), and nNOS (field-stimulated relaxation of phenylephrine-precontracted rabbit corpus cavernosum; IC 50 Ͼ 100 M). These data confirm the high selectivity of BYK191023 for iNOS over eNOS and nNOS found at isolated enzymes. In summary, we have identified a new highly selective iNOS inhibitor structurally unrelated to known compounds and L-arginine. BYK191023 is a valuable tool for the investigation of iNOS-mediated effects in vitro and in vivo.NO synthases are enzymes responsible for the generation of nitric oxide from the amino acid L-arginine (for review, see Alderton et al., 2001). Two classes of enzymes exist, which differ in their activation profile and their capacity to generate NO. Once expressed the inducible NO synthase (iNOS) is active for prolonged periods and produces micromolar concentrations of NO over longer periods. The iNOS expression is stimulated in various cell types by proinflammatory signals and is involved in immune defense against invading pathogens (Stuehr et al., 1991;Schmidt and Walter, 1994;Moncada and Higgs, 1995). The constitutively expressed enThese studies were supported in part by grants SFB 553 C15 and SFB 432 B6 from the Deutsche Forschungsgemeinschaft (to S.S.).Article, publication date, and citation information can be found at

Glioma Stem Cell Proliferation and Tumor Growth Are Promoted by Nitric Oxide Synthase-2

“…Penetration of the BBB by 1400W is limited (Rebello et al, 2002), thus prompting the selection of alternative NOS2 inhibitors for BBB penetration (Figure S6A). The more lipophilic NOS2 inhibitor, BYK191023 (Strub et al, 2006) exhibited similar efficacy as 1400W for inhibition of CD133+ GSC growth in vitro (Figure S6B). However, BYK191023 possesses more suitable characteristics for BBB penetration, so it was therefore considered ideal for application in the intracranial glioma model.…”

“…BYK191023 could be a strong candidate for clinical evaluation as it possesses the following desirable characteristics: 1) exhibits at least 1000 fold selectivity for NOS2 over NOS1 and NOS3 (MacMicking et al, 1995; Strub et al, 2006), 2) adheres to “Lipinski’s rules of five” for optimal pharmacokinetics and bioavailability (Lipinski et al, 2001), 3) is sufficiently lipophilic for BBB penetration (i.e., LogP 1.84), and 4) decreases GSC growth and survival in vitro and in vivo . In combination with the minimal toxic potential for NOS2 inhibition in humans and the effective anti-GSC activity demonstrated in our investigations, the data provided here will hopefully serve as an impetus for evaluation of NOS2-directed therapies as a component of multimodal treatment regimens for human glioma.…”

Inducible nitric oxide synthase: Regulation, structure, and inhibition

“…An unconventional pyridine derivative is imidazopyridine 25 (BYK191023), which was discovered in 2005 in a high-throughput screen. 171 Two years later it was determined to be a competitive, time-dependent, irreversible inhibitor in the presence of NADPH, likely causing the loss of heme. 172 Highly selective for iNOS (in enzyme assays, cells, and isolated organ systems), 25 was also tested in several animal models.…”

Stimulation of brain nicotinic acetylcholine receptors activates adrenomedullary outflow via brain inducible NO synthase‐mediated S‐nitrosylation

“…In the present study, due to the lack of highly selective inhibitors of eNOS, we used a highly selective iNOS inhibitor BYK191023 and a selective nNOS inhibitor 3‐bromo‐7‐nitroindazole. BYK191023 exhibits IC 50 values of 86, 17 000 and 162 000 nM for iNOS, nNOS and eNOS respectively (Strub et al, ). On the other hand, 3‐bromo‐7‐nitroindazole exhibits IC 50 values of 0.29, 0.17 and 0.86 μM for iNOS, nNOS and eNOS respectively (Bland‐Ward and Moore, ).…”