α2-Adrenoceptors Enhance Cell Proliferation and Mammary Tumor Growth Acting Through both the Stroma and the Tumor Cells

A.      Bruzzone; C.      Perez Pinero; P.      Rojas; M.      Romanato; H.      Gass; C.      Lanari; I.      A. Luthy

Abstract

We have previously described enhanced human breast cancer cell proliferation and mouse mammary tumor growth induced by α2-adrenergic agonists, associated with α2-adrenoceptor (α2-AR) expression in epithelial cells. The aim of the present work was to assess if stromal fibroblasts can contribute to this effect. α2-AR expression was assessed by immunocytochemistry and immunohistochemistry, cell proliferation by [3H]- Thymidine incorporation and tumor growth by measuring with caliper. All tested mouse and human fibroblasts expressed at least two α2-AR subtypes and α2-adrenergic agonists enhanced fibroblast proliferation. In vivo, the α2-adrenergic agonist clonidine significantly enhanced tumor growth. The α2- adrenergic antagonist rauwolscine reversed this effect, but when administered alone, significantly inhibited tumor growth. Clonidine significantly stimulated cell proliferation in the epithelial-enriched fraction, the cancer associated fibroblastenriched fraction and the co-culture of both fractions in primary cultures from both tumors (IBH-4 and IBH-6). Rauwolscine reversed clonidine stimulation in every fraction. However, when incubated alone, the inhibitory effect was observed in fractions from IBH-4 tumors but not from IBH-6 tumors. These experiments show that fibroblasts from tumor stroma are also influenced by α2-adrenergic compounds through the α2-ARs expressed in these cells. Moreover, the α2-adrenergic antagonist rauwolscine could eventually block in both epithelial and stromal cells, the mitogenic effect of catecholamines released during stress, providing a potential additional treatment for breast cancer patients. Chemists synthesizing adrenergic compounds should consider their action in breast cancer patients.

Keywords: Clonidine, rauwolscine, adrenoceptors, mammary tumor, carcinoma-associated fibroblasts, breast cancer, fibroblast MC4-L4F, Dexmedetomidine, G protein coupled receptors, Dulbecco's modified Eagle's medium