CB1151, a 20-epi analogue of 1,25-dihydroxyvitamin D3, exhibits anti-tumor effects by inhibiting MCF-7 cell growth (IC50: 0.82 nM).

CB1151 (0-100 nM; 5 days) inhibits MCF-7 cell growth, as assessed by [3H]-thymidine incorporation (IC50: 0.82 nM). CB1151 (0-100 nM; 40 hours) activates the IP9-type VD response element (EC50: 1.2 nM) and shows a stronger correlation with inhibition of proliferation compared to DR3-type elements (EC50: 3.2 nM) in MCF-7 cells transfected with the CAT reporter [1]. CB1151 exhibits a functional dissociation constant (Kdf) of 3.6 nM, indicating the ligand concentration that provides 50% of the protease-resistant VDR fragment [2].