Combined effects of the bisphosphonate, zoledronic acid and the aromatase inhibitor letrozole on breast cancer cells in vitro: evidence of synergistic interaction.
BACKGROUND
Aromatase inhibitors are widely used in the treatment of oestrogen receptor-positive post-menopausal breast cancer. These patients may also be receiving the bisphosphonate, zoledronic acid (ZA) to prevent bone loss or reduce skeletal morbidity in the setting of advanced disease. The potential biological interaction of these two drugs in breast cancer has not been assessed.


METHODS
Aromatase-expressing breast cancer cells were treated with letrozole and ZA either simultaneously or in sequence, and the resulting apoptosis was assessed by staining with Hoechst 33342 and propidium iodide and examined using a fluorescent inverted Leica DMIRB microscope and a UV filter.


RESULTS
We found that letrozole and ZA induce levels of apoptosis in breast cancer cells in vitro that are significantly greater compared with treatment with each drug alone. However, this potentially, synergistic relationship is drug-sequence dependent, occurring only when cells are treated with letrozole, followed by ZA. The converse sequence, or administering drugs simultaneously, induces levels of apoptosis no greater than each drug alone.


CONCLUSIONS
Owing to the enhanced anti-tumour efficacy of sequential drug administration, our findings may indicate that, for post-menopausal women who require treatment with letrozole, ZA should also be considered.
Neville-Webbe
H L
HL
Academic Unit of Clinical Oncology, Cancer Research Centre, Weston Park Hospital, Sheffield, UK. h.l.neville-webbe@sheffield.ac.uk
Coleman
R E
RE
Holen
I
I
D000465:Algorithms; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D047072:Aromatase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D050071:Bone Density Conservation Agents / Q000008:administration & dosage / Q000494:pharmacology; D001943:Breast Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004164:Diphosphonates / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D004357:Drug Synergism; D005260:Female; D006801:Humans; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D000077289:Letrozole; D009570:Nitriles / Q000008:administration & dosage / Q000494:pharmacology*; D014230:Triazoles / Q000008:administration & dosage / Q000494:pharmacology*; D000077211:Zoledronic Acid
D047072:Aromatase Inhibitors; D050071:Bone Density Conservation Agents; D004164:Diphosphonates; D007093:Imidazoles; D009570:Nitriles; D014230:Triazoles; D000077211:Zoledronic Acid; D000077289:Letrozole