title: Inhibition of cancer cell growth by calcium channel antagonists in the athymic mouse.
abstract: The calcium channel antagonists (CCAs) amlodipine, diltiazem, and verapamil inhibited HT-39 human breast cancer cell proliferation in a concentration-dependent manner. The apparent 50% inhibitory dose values were 1.5 microM for the dihydropyridine amlodipine, 5 microM for the benzothiazapine diltiazem, and 10 microM for the phenylalkylamine verapamil. Amlodipine treatment caused a rapid concentration-dependent decrease of intracellular calcium concentration in the HT-39 cell line. Addition of 1 microM amlodipine had no effect on intracellular calcium levels, 3 microM amlodipine lowered intracellular calcium levels in the HT-39 cells by 13.7%, and 10 microM amlodipine lowered intracellular calcium levels by 33.2%. Also, lowering medium calcium levels from 2.0 mM to 0.5 microM resulted in a rapid 41.3% decrease in intracellular calcium and a concomitant 60% inhibition of HT-39 cell DNA synthesis. When HT-39 cells were transplanted into athymic mice, marked hypercalcemia developed. Serum calcium levels from control mice were 8.3 +/- 0.6 mg/dl (mean +/- SE; n = 4); those from tumor-bearing mice were 11.3 +/- 0.08 mg/dl (mean +/- SE; n = 17). Blood calcium levels correlated directly with tumor size (r = 0.91, P less than 0.01). We examined the capacity of three CCAs to specifically inhibit HT-39 tumor growth in vivo. One week after inoculation of HT-39 cells, mice were acclimated to vehicle or 0.1 mg/day amlodipine, 1.0 mg/day diltiazem, or 1.0 mg/day verpamil, in their drinking water, for 7 days. Oral administration of the dihydropyridine amlodipine (0.35 mg/day) for 10 days inhibited HT-39 breast tumor growth by 83.5 +/- 20.1% (mean +/- SE). Oral administration of diltiazem (3.5 mg/day) inhibited HT-39 breast tumor growth rate by 46.5 +/- 6.6% over a 2-week measurement period, and verapamil (3.5 mg/day) inhibited tumor growth rate by 68.2 +/- 9.7% (mean +/- SE). The CCAs had no effect on mouse body weight or gross organ morphology at the concentrations used. Lack of depolarization-induced calcium fluxes in the HT-39 cell line suggests that these cells do not express voltage-operated calcium channels. Thus, our study correlates an effect of amlodipine to lower intracellular calcium levels, by a mechanism not known at present, with its effect to inhibit HT-39 cell proliferation. These findings are important since they demonstrate that amlodipine and other CCAs with known pharmacodynamics and side effects act to blunt breast tumor progression in vivo.
authors.affiliation: Department of Pharmacology, University of Michigan, Ann Arbor 48109-0626.
authors.forename: J M
authors.initials: JM
authors.lastname: Taylor
authors.forename: R U
authors.initials: RU
authors.lastname: Simpson
mesh_terms: D017311:Amlodipine; D000818:Animals; D001943:Breast Neoplasms / Q000097:blood / Q000473:pathology*; D002118:Calcium / Q000097:blood* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D003470:Culture Media; D004273:DNA, Neoplasm / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology*; D004354:Drug Screening Assays, Antitumor; D051379:Mice; D008819:Mice, Nude; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D002121:Calcium Channel Blockers; D003470:Culture Media; D004273:DNA, Neoplasm; D017311:Amlodipine; D014700:Verapamil; D004110:Diltiazem; D009543:Nifedipine; D002118:Calcium