title: Astemizole synergizes calcitriol antiproliferative activity by inhibiting CYP24A1 and upregulating VDR: a novel approach for breast cancer therapy.
abstract: BACKGROUND
  Calcitriol antiproliferative effects include inhibition of the oncogenic ether-à-go-go-1 potassium channel (Eag1) expression, which is necessary for cell cycle progression and tumorigenesis. Astemizole, a new promising antineoplastic drug, targets Eag1 by blocking ion currents. Herein, we characterized the interaction between calcitriol and astemizole as well as their conjoint antiproliferative action in SUM-229PE, T-47D and primary tumor-derived breast cancer cells.
  
  
  RESULTS
  Molecular markers were studied by immunocytochemistry, Western blot and real time PCR. Inhibitory concentrations were determined by dose-response curves and metabolic activity assays. At clinically achievable drug concentrations, synergistic antiproliferative interaction was observed between calcitriol and astemizole, as calculated by combination index analysis (CI <1). Astemizole significantly enhanced calcitriol's growth-inhibitory effects (3-11 folds, P<0.01). Mean IC(20) values were 1.82 ± 2.41 nM and 1.62 ± 0.75 µM; for calcitriol (in estrogen receptor negative cells) and astemizole, respectively. Real time PCR showed that both drugs alone downregulated, while simultaneous treatment further reduced Ki-67 and Eag1 gene expression (P<0.05). Astemizole inhibited basal and calcitriol-induced CYP24A1 and CYP3A4 mRNA expression (cytochromes involved in calcitriol and astemizole degradation) in breast and hepatoma cancer cells, respectively, while upregulated vitamin D receptor (VDR) expression.
  
  
  CONCLUSIONS
  Astemizole synergized calcitriol antiproliferative effects by downregulating CYP24A1, upregulating VDR and targeting Eag1. This study provides insight into the molecular mechanisms involved in astemizole-calcitriol combined antineoplastic effect, offering scientific support to test both compounds in combination in further preclinical and clinical studies of neoplasms expressing VDR and Eag1. VDR-negative tumors might also be sensitized to calcitriol antineoplastic effects by the use of astemizole. Herein we suggest a novel combined adjuvant therapy for the management of VDR/Eag1-expressing breast cancer tumors. Since astemizole improves calcitriol bioavailability and activity, decreased calcitriol dosing is advised for conjoint administration.
authors.affiliation: Departamento de Biología de la Reproducción, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, México, DF, México.
authors.forename: Janice
authors.initials: J
authors.lastname: García-Quiroz
authors.forename: Rocío
authors.initials: R
authors.lastname: García-Becerra
authors.forename: David
authors.initials: D
authors.lastname: Barrera
authors.forename: Nancy
authors.initials: N
authors.lastname: Santos
authors.forename: Euclides
authors.initials: E
authors.lastname: Avila
authors.forename: David
authors.initials: D
authors.lastname: Ordaz-Rosado
authors.forename: Mariana
authors.initials: M
authors.lastname: Rivas-Suárez
authors.forename: Ali
authors.initials: A
authors.lastname: Halhali
authors.forename: Pamela
authors.initials: P
authors.lastname: Rodríguez
authors.forename: Armando
authors.initials: A
authors.lastname: Gamboa-Domínguez
authors.forename: Heriberto
authors.initials: H
authors.lastname: Medina-Franco
authors.forename: Javier
authors.initials: J
authors.lastname: Camacho
authors.forename: Fernando
authors.initials: F
authors.lastname: Larrea
authors.forename: Lorenza
authors.initials: L
authors.lastname: Díaz
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D016589:Astemizole / Q000494:pharmacology*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002117:Calcitriol / Q000494:pharmacology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000235:genetics / Q000378:metabolism; D008957:Models, Genetic; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D000970:Antineoplastic Agents; D002120:Calcium Channel Agonists; D051638:Ether-A-Go-Go Potassium Channels; C496884:KCNH1 protein, human; D019394:Ki-67 Antigen; D018167:Receptors, Calcitriol; D016589:Astemizole; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol