title: Genistein potentiates the growth inhibitory effects of 1,25-dihydroxyvitamin D3 in DU145 human prostate cancer cells: role of the direct inhibition of CYP24 enzyme activity.
abstract: In a search for improved therapies for prostate cancer, we investigated the effect of genistein in combination with 1alpha-25-dihydroxyvitamin D3 [1,25(OH)2D3], on the growth of DU145 human prostate cancer cells. DU145 cells were very resistant to the growth inhibitory action of 1,25(OH)2D3 or genistein when administered individually. However, the combination caused a significant growth inhibition seen at lower concentrations of both agents. 1,25(OH)2D3 induces the expression of the CYP24 gene, which codes for the enzyme that initiates the catabolism of 1,25(OH)2D3. We showed for the first time that genistein at low doses (50-100 nM) directly inhibited CYP24 at the enzyme level. Addition of genistein to mitochondrial preparations inhibited CYP24 enzyme activity in a noncompetitive manner. CYP24 inhibition by genistein increased the half-life of 1,25(OH)2D3 thereby augmenting the homologous up-regulation of the vitamin D receptor (VDR) both at the mRNA and protein levels. Genistein co-treatment enhanced 1,25(OH)2D3-mediated transactivation of the vitamin D responsive reporters OC-Luc and OP-Luc transfected into DU145 cells. Consistent with the growth inhibition due to the combination treatment, significant changes in the expression of genes involved in growth arrest and apoptosis were seen. We conclude that genistein potentiates the antiproliferative actions of 1,25(OH)2D3 in DU145 cells by two mechanisms: (i) an increase in the half-life of 1,25(OH)2D3 due to the direct inhibition of CYP24 enzyme activity and (ii) an amplification of the homologous up-regulation of VDR. Together these two effects lead to a substantial enhancement of the cellular responses to the growth inhibitory and pro-apoptotic signaling by 1,25(OH)2D3.
authors.affiliation: Department of Medicine, Division of Endocrinology, Stanford University School of Medicine, 300 Pasteur Dr, Stanford, CA 94305, USA.
authors.forename: Srilatha
authors.initials: S
authors.lastname: Swami
authors.forename: Aruna V
authors.initials: AV
authors.lastname: Krishnan
authors.forename: Donna M
authors.initials: DM
authors.lastname: Peehl
authors.forename: David
authors.initials: D
authors.lastname: Feldman
mesh_terms: D016588:Anticarcinogenic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects*; D019833:Genistein / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000201:enzymology*; D018167:Receptors, Calcitriol / Q000096:biosynthesis; D015398:Signal Transduction / Q000528:radiation effects; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D016588:Anticarcinogenic Agents; D018167:Receptors, Calcitriol; C118756:dihydroxy-vitamin D3; D014807:Vitamin D; D019833:Genistein; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase