Substituted quinolines as noncovalent proteasome inhibitors

Abstract

Screening of a library of diverse heterocyclic scaffolds identified substituted quinolines as inhibitors of the human proteasome. The heterocyclic library was prepared via a novel titanium-catalyzed multicomponent coupling reaction, which rendered a diverse set of isoxazoles, pyrimidines, pyrroles, pyrazoles and quinolines. SAR of the parent lead compound indicated that hydrophobic residues on the benzo-moiety significantly improved potency. Lead compound 25 inhibits the chymotryptic-like proteolytic activity of the proteasome (IC50 5.4μM), representing a new class of nonpeptidic, noncovalent proteasome inhibitors.

Keywords: Inhibitors; Noncovalent; Proteasome; Quinolines.

Figure 1

Structures of covalent, peptidic proteasome inhibitors bortezomib, and noncovalent, nonpeptidic proteasome inhibitors PI-083, Chloroquine, 5AHQ and substituted quinolines.

Figure 2

Titanium catalyzed multicomponent coupling reaction to form pyridines, isoxazoles, pyrazoles, and quinolines, as examples.

Figure 3

(A) Quinoline 7 inhibits the CT-L and Casp-L activity of the human proteasome. Fluorogenic substrates Suc-LLVY-AMC, Z-ARR-AMC and Z-LLE-AMC were used to measure CT-L, T-L and Casp-L activities of purified human 20S proteasome particles. The maximum increase in fluorescence per minute was used to calculate specific activities of each sample. (B) Lineweaver–Burk plot using SucLLVY-AMC consistent with a model of ‘mixed-type inhibition’. Undetectable proteasome activity was observed at the lowest amount of substrate thus these values are omitted in the L–B plot.

Figure 4

NF-κB-luc HeLa cells were unstimulated/stimulated with 25 ng/mL TNF-α in the absence or presence of quinoline 7 in 1% DMSO. Fold-induction (%) of the Luciferase activity, normalized for all samples to TNF- α stimulation, is shown. Data shown is an average of 2 independent experiments. *Statistically significant from the vehicle + TNF control (one-way ANOVA n = 4).