Background and purpose: Breast cancer, the most common cancer in women in most countries, is a highly stressful disease. Catecholamines released during stress bind to adrenoceptors and we have recently described a 2 -adrenoceptors in human breast cell lines, linked to enhanced cell proliferation. The purpose was to assess the in vivo effects of compounds acting on a 2 -adrenoceptors in a reliable model of breast cancer. Experimental approach: The expression of a 2 -adrenoceptors was confirmed by immunocytochemistry, immunofluorescence and reverse transcription-PCR in the mouse mammary tumour cell line MC4-L5. Proliferation was assessed by [3 H]thymidine incorporation and tumours were measured daily. Apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated dUTP digoxigenin nick-end labelling. Key results: Incubation for 2 days with a 2 -adrenoceptor agonists (clonidine and dexmedetomidine) significantly enhanced proliferation of the mouse mammary tumour cell line MC4-L5. These agonists also significantly stimulated tumour growth of the progestin-dependent tumour C4-HD even in the presence of medroxyprogesterone acetate (MPA). In every tumour tested (C4-HD, CC4-2-HD and CC4-3-HI), regardless of MPA sensitivity, clonidine significantly enhanced tumour growth in the absence of MPA. The a 2 -adrenoceptor antagonists, yohimbine and rauwolscine, completely reversed the effects of clonidine. However, the group receiving yohimbine alone showed a nonsignificant but constant increase in tumour growth, whereas rauwolscine alone diminished tumour growth significantly, behaving as a reverse agonist. In CC4-3-HI tumours, rauwolscine treatment enhanced apoptosis and diminished the mitotic index, whereas clonidine had the inverse effect. Conclusions and implications: a 2 -Adrenoceptor agonists enhanced tumour growth and rauwolscine behaved in vivo as a reverse agonist, suggesting that it may be tested for adjuvant treatment.

BACKGROUND AND PURPOSEb-Adrenoceptors are expressed in human and experimental animal breast cancer cells. However, the effect of the agonists and antagonists reported on cell proliferation and tumour growth was paradoxical, precluding their utilization as possible adjuvant therapy, mainly in the cases of refractory tumours. EXPERIMENTAL APPROACH KEY RESULTSb2-Adrenoceptor expression was confirmed in the mouse and human cells tested. Cell proliferation was increased by adrenaline (by a2-adrenoceptor action) and decreased in every tested cell line by the b-adrenoceptor agonist isoprenaline and the b2-adrenoceptor agonist salbutamol. Isoprenaline and salbutamol reduced tumour growth in every tumour tested (mouse C4-HD and CC4-3-HI and human IBH-4, IBH-6 and MDA-MB-231 cell lines growing as xenografts in nude mice). These effects were reversed by the b-adrenoceptor antagonist propranolol. The a2-adrenoceptor antagonist rauwolscine and the b2-adrenoceptor agonist salbutamol were equally effective in diminishing tumour growth. ERK 1/2 activation analysed in IBH-4 tumours correlated with tumour growth, with the b-adrenoceptor agonists decreasing its activation. Inhibition of ERK 1/2 phosphorylation in vitro was mainly mediated by the PKA pathway. CONCLUSIONS AND IMPLICATIONSIn our experimental models, the b-adrenoceptor agonists inhibited breast cancer cell proliferation and tumour growth, probably mediated by inhibition of ERK 1/2 phosphorylation. The b-adrenoceptor agonists were as effective as the a2-adrenoceptor antagonist rauwolscine, providing possible novel adjuvant treatments for breast cancer.

Epinephrine and Norepinephrine, typically released during stress bind to nine different adrenoceptors (AR) which classically control the cardiovascular and respiratory systems. New targets were described for the many agonists and antagonists developed for these AR, as the central nervous system. During the last three decades, AR expression and action on the mammary gland/breast were extensively investigated. In the cow mammary gland, good milkability was associated with low density of beta(2)-AR and high density of alpha(2)-AR. In the rat normal mammary gland, beta-AR are expressed in the epithelial cells, alveoli, ducts, and adipocytes showing an exquisite regulation by steroid hormones and prolactin. In rat dimethylbenz(a)anthracene (DMBA) tumors, a close correlation was observed between tumor growth and beta-AR concentration. beta(2)-AR were described in numerous human cell lines and breast tumors. The action of beta-adrenergic compounds on cell proliferation is contradictory. While some authors found that beta-agonists significantly inhibit cancer cell proliferation and tumor growth in mice, others described a significant reduction in DNA synthesis by beta-blockers. Also, positive effects of beta-AR on human carcinoma cell migration have been described. alpha(2)-AR are expressed in human breast cancer and non-cancer cell lines, their stimulation being associated with increased cell proliferation. In vivo clonidine increased tumor growth and alpha (2)-adrenergic antagonists completely reversed this effect. When administered alone, rauwolscine inhibited tumor growth behaving as an inverse agonist. Therefore, the numerous adrenergic beta- and alpha-AR agonists or antagonists could prove to be unexpected therapeutic options for mammary gland/ breast and mainly breast cancer.