Cytotoxicity of etidronic acid to human breast cancer cells.

INTRODUCTION Bisphosphonates have been used to treat Paget's disease, osteoporosis, and cancer metastases to the bone. The cancer chemotherapeutic potential of a first-generation bisphosphonate, etidronic acid, was evaluated by using MCF-7 human breast cancer cells. METHODS In vitro cytotoxicity of etidronic acid to MCF-7 cells was estimated on the basis of clonogenicity assays, while cell cycle effects were determined by using flow cytometry. Mutagenicity of etidronic acid was detected by using denaturing high-pressure liquid chromatography analysis of cellular DNA amplified by PCR with primers for exons 5 through 8 of the human p53 gene. RESULTS A 24-hour treatment with etidronic acid (10 mM) with or without strontium chloride was cytototoxic to MCF-7 cells. Etidronic acid caused a decrease in the S-phase population and an increase in the G2/M population. Mutations in the p53 gene were detected in MCF-7 cells treated with etidronic acid. Strontium chloride was not cytotoxic to cells. CONCLUSIONS Cytotoxicity of etidronic acid to breast cancer cells may complement its inhibitory effects on bone resorption at the site of bone metastasis. Within the cell cycle, late S-phase cells are the most radioresistant, while cells at the G2/M border are the most sensitive. Therefore the decrease in S-phase population with corresponding increase in G2/M would make the cells more radiosensitive. This may be useful if etidronic acid were combined with radioactive strontium (89Sr, metastron) or external-beam radiotherapy for treating bone metastases. Tumor cells that survive etidronic acid treatment may acquire drug resistance because of mutations in the p53 tumor-suppressor gene.