Proliferative responses of epithelial cells to 8‐bromo‐cyclic AMP and to a phorbol ester change during breast Pathogenesis

Abstract

We have explored the relationship of changes in proliferative responses of human mammary epithelial cells to a phorbol ester (TPA) and to 8‐Br‐cAMP, which modulate the activities of protein kinases A and C (PKA and PKC), with breast tumour progression. Treatment with TPA had no effect on nontumorigenic cell lines established from human fibrocystic biopsies and apparently normal tissue around a tumour. In contrast, TPA strongly inhibited the proliferation of numerous human tumorigenic breast cell lines. Treatment with 8‐Br‐cAMP decreased the proliferation of all studied nontumorigenic and tumorigenic cell lines. We have also studied the effect of TPA and 8‐Br‐cAMP on growth of epithelial cells in short‐term culture obtained from surgical human mammary biopsies with different states of breast disease. Both drugs enhanced growth of normal breast cells but had no significant effects on cells from biopsies with benign breast disease. In contrast, all examined cuitures from breast cancer biopsies were strongly inhhited by 8‐Br‐cAMP. Otherwise, TPA had an inhibitory effect only in the case of invasive ductal carcinoma of grade III. Malignant Ha‐ras‐transformation of nontumorigenic TPA‐insensitive breast HBL‐100 cells induced an inhibitory effect of TPA. In addition, a TPA‐insensitive MCF7 clone was much less tumorigenic in athymic mice than the parental strain shown to be inhibited by TPA. These data suggest that the two intracellular transduction pathways change at different stages of breast pathogenesis. Alterations in the PKA pathway are early events and are probably important to cell immortalization but do not necessarily lead to malignant development. In contrast, changes in PKC pathway are rather later events associated with advanced malignant transformation.