Inhibition of cancer cell growth by calcium channel antagonists in the athymic mouse

• Published in: Cancer research (Baltimore) Vol. 52; no. 9; pp. 2413 - 2418
• Main Authors: TAYLOR, J. M, SIMPSON, R. U
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01-05-1992
• Subjects: Amlodipine; Animals; antagonists; Antineoplastic agents; Biological and medical sciences; Breast Neoplasms - blood; Breast Neoplasms - pathology; calcium; Calcium - blood; Calcium - pharmacology; Calcium Channel Blockers - pharmacology; carcinoma; Cell Division - drug effects; cells; channels; Chemotherapy; Culture Media; Diltiazem - pharmacology; DNA, Neoplasm - metabolism; Drug Screening Assays, Antitumor; growth; inhibition; Medical sciences; Mice; Mice, Nude; Nifedipine - analogs & derivatives; Nifedipine - pharmacology; Pharmacology. Drug treatments; Tumor Cells, Cultured; Verapamil - pharmacology; Cell proliferation; Calcium antagonist; Oral administration; Malignant tumor; Dihydropyridine derivative; Hypercalcemia; Mammary gland diseases; In vivo; Metabolic disorder; Chemotherapy; Experimental disease; Treatment; Animal; Established cell line; Mammary gland; Inhibition
• ISSN: 0008-5472; 1538-7445

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.