New vitamin D receptor agonists with decreased metabolic stability

The aim of the study was the development of vitamin D receptor agonists with decreased metabolic stability for the topical treatment of psoriasis and related hyperproliferative skin diseases. Calcitriol analogues 1, 2, 3, all of which contain modifications in the side chain, were synthesized. The obtained analogues were full agonists when the induction of CD14 expression in HL-60 cells, the induction of 5-lipoxygenase activity in Mono Mac 6 cells, and the inhibition of phytohemagglutinin (PHA)-stimulated lymphocyte proliferation were studied. The EC(50) value of the most active compound 1 was 1.2 nM in the CD14 assay and 1 nM in the 5-lipoxygenase assay, whereas calcitriol gave EC(50) values in these assays of 3.7 and 9 nM, respectively. In the lymphocyte proliferation assay, compound 1 and calcitriol had IC(50) values of 0.3 and 2.8 nM, respectively. All three compounds had receptor binding affinities similar to that of calcitriol. The compounds showed a decreased metabolic stability in rat liver homogenates and had a 50-fold lower affinity for the vitamin D-binding protein than calcitriol, which suggests that calcitriol analogues are metabolized more rapidly after systemic uptake or application. When injected into rats, the analogues displayed an approximately 100-fold lower hypercalcemic effect than calcitriol. In summary, our study presents three new and potent vitamin D receptor agonists with interesting profiles for development as antipsoriatic drugs.