Design, synthesis and evaluation of 2-aryl quinoline derivatives against 12R-lipoxygenase (12R-LOX): Discovery of first inhibitor of 12R-LOX

The 12R-lipoxygenase (12R-LOX), a (non-heme) iron-containing metalloenzyme belonging to the lipoxygenase (LOX) family catalyzes the conversion of arachidonic acid (AA) to its key metabolites. Studies suggested that 12R-LOX plays a critical role in immune modulation for the maintenance of skin homeostasis and therefore can be considered as a potential drug target for psoriasis and other skin related inflammatory diseases. However, unlike 12-LOX (or 12S-LOX) the enzyme 12R-LOX did not receive much attention till date. In our effort, the 2aryl quinoline derivatives were designed, synthesized and evaluated for the identification of potential inhibitors of 12R-hLOX. The merit of selection of 2-aryl quinolines was assessed by in silico docking studies of a representative compound (4a) using the homology model of 12R-LOX. Indeed, in addition to participating in Hbonding with THR628 and LEU635 the molecule formed a hydrophobic interaction with VAL631. The desired 2aryl quinolines were synthesized either via the Claisen-Schmidt condensation followed by one-pot reductioncyclization or via the AlCl3 induced heteroarylation or via the O-alkylation approach in good to high (82-95%) yield. When screened against human 12R-LOX (12R-hLOX) in vitro four compounds (e.g. 4a, 4d, 4e and 7b) showed encouraging (>45%) inhibition at 100 mu M among which 7b and 4a emerged as the initial hits. Both the compounds showed selectivity towards 12R-hLOX over 12S-hLOX, 15-hLOX and 15-hLOXB and concentration dependent inhibition of 12R-hLOX with IC50 = 12.48 +/- 2.06 and 28.25 +/- 1.63 mu M, respectively. The selectivity of 4a and 7b towards 12R-LOX over 12S-LOX was rationalized with the help of molecular dynamics simulations. The SAR (Structure-Activity Relationship) within the present series of compounds suggested the need of a ohydroxyl group on the C-2 phenyl ring for the activity. The compound 4a and 7b (at 10 and 20 mu M) reduced the hyper-proliferative state and colony forming potential of IMQ-induced psoriatic keratinocytes in a concentration dependent manner. Further, both compounds decreased the protein levels of Ki67 and the mRNA expression of IL-17A in the IMQ-induced psoriatic-like keratinocytes. Notably, 4a but not 7b inhibited the production of IL-6 and TNF-alpha in the keratinocyte cells. In the preliminary toxicity studies (i.e. teratogenicity, hepatotoxicity and heart rate assays) in zebrafish both the compounds showed low safety (<30 mu M) margin. Overall, being the first identified inhibitors of 12R-LOX both 4a and 7b deserve further investigations.

Automated summary

The lipoxygenase enzyme 12R-LOX plays a critical role in immune modulation and can be a potential drug target for skin related inflammatory diseases. In this study, 2-aryl quinoline derivatives were designed and synthesized as inhibitors of 12R-LOX. Compound 4a and 7b emerged as potential inhibitors, showing selectivity towards 12R-LOX.