Effect of digoxin on DNA synthesis and cell viability in human breast tumour tissue in organ culture.

10 biopsy specimens of primary breast tumours from 10 patients were classified histopathologically into 8 ductal carcinomas and 2 lobular carcinomas. Portions of tumour of approximately 1 mm3 were cultured in Medium 199 buffered with 20 mM Hepes for 48 h with or without addition of digoxin at concentrations from 1-2 ng/ml to 10-20 micrograms/ml of culture medium. Measurement of DNA synthesis by [3H]-thymidine incorporation, DNA analysis and histological examination showed that 5 biopsy specimens demonstrated epithelial cell survival in culture. These cultures were significantly (p less than 0.001) affected by digoxin at concentrations above 10-20 ng/ml, with suppression of [3H]-thymidine incorporation and reduced epithelial cell viability. Parallel studies on 5 biopsy specimens of DMBA-induced rat mammary carcinomas showed no effects of digoxin up to 10 micrograms/ml of culture medium. These studies indicate the possibility of this class of drug being of use in growth suppression of breast tumours.