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