Selective inhibition of cyclooxygenase‐2 (COX‐2) by 1α,25‐dihydroxy‐16‐ene‐23‐yne‐vitamin D 3 , a less calcemic vitamin D analog

Inducible cyclooxygenase‐2 (COX‐2) has been implicated to play a role in inflammation and carcinogenesis and selective COX‐2 inhibitors have been considered as anti‐inflammatory and cancer chemopreventive agents. 1α,25‐dihydroxyvitamin D 3 (1α,25(OH) 2 D 3 ), the active hormonal form of vitamin D 3 also has been considered to be a cancer chemopreventive agent in addition to its important role in maintaining calcium homeostasis. Based on these observations, we studied the direct effect of 1α,25(OH) 2 D 3 and one of its less calcemic synthetic analogs, 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 on the activity of both COX‐1 and COX‐2 in an in vitro enzyme assay. Preliminary data indicated that both 1α,25(OH) 2 D 3 and 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 inhibited selectively the activity of COX‐2 with no effect on the activity of COX‐1. Out of the two compounds, 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 was found to be more effective with an IC 50 of 5.8 nM. Therefore, the rest of the experiments were performed using 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 only. 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 inhibited the proliferation of lipopolysaccharide (LPS) stimulated mouse macrophage cells (RAW 264.7) with a reduction in the expression of COX‐2 along with other inflammatory mediators like inducible nitric oxide synthase (iNOS) and interleukin‐2 (IL‐2). Furthermore, 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 also inhibited carrageenan induced inflammation in an air pouch of a rat and effectively reduced the expression of COX‐2, iNOS, and IL‐2 in the tissues of the same air pouch. In both cases, 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 did not show any effect on the expression of COX‐1. In summary, our results indicate that 1α,25(OH) 2 ‐16‐ene‐23‐yne‐D 3 , a less calcemic vitamin D analog, exhibits potent anti‐inflammatory effects and is a selective COX‐2 inhibitor. J. Cell. Biochem. 104: 1832–1842, 2008. © 2008 Wiley‐Liss, Inc.