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.

METHODOLOGY/PRINCIPAL FINDINGS:

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/SIGNIFICANCE:

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: Janice García-Quiroz, Rocío García-Becerra, David Barrera, Nancy Santos, Euclides Avila, David Ordaz-Rosado, Mariana Rivas-Suárez, Ali Halhali, Pamela Rodríguez, Armando Gamboa-Domínguez, Heriberto Medina-Franco, Javier Camacho, Fernando Larrea, Lorenza Díaz
• Journal: PloS one (PLoS One) Vol. 7 Issue 9 Pg. e45063 ( 2012) ISSN: 1932-6203 [Electronic] United States
• PMID: 22984610 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antineoplastic Agents
• Calcium Channel Agonists
• Ether-A-Go-Go Potassium Channels
• KCNH1 protein, human
• Ki-67 Antigen
• Receptors, Calcitriol
• Astemizole
• Steroid Hydroxylases
• CYP24A1 protein, human
• Vitamin D3 24-Hydroxylase
• Calcitriol

Topics

• Antineoplastic Agents (pharmacology)
• Astemizole (pharmacology)
• Blotting, Western
• Breast Neoplasms (genetics, metabolism, pathology)
• Calcitriol (pharmacology)
• Calcium Channel Agonists (pharmacology)
• Cell Line, Tumor
• Cell Proliferation (drug effects)
• Dose-Response Relationship, Drug
• Down-Regulation (drug effects)
• Drug Synergism
• Ether-A-Go-Go Potassium Channels (genetics, metabolism)
• Female
• Gene Expression Regulation, Neoplastic (drug effects)
• Humans
• Immunohistochemistry
• Ki-67 Antigen (genetics, metabolism)
• Models, Genetic
• Receptors, Calcitriol (genetics, metabolism)
• Reverse Transcriptase Polymerase Chain Reaction
• Steroid Hydroxylases (genetics, metabolism)
• Tumor Cells, Cultured
• Up-Regulation (drug effects)
• Vitamin D3 24-Hydroxylase