Biocell - Comparison of the affinity of different compounds to alpha2-adrenergic receptors in MCF-7 cells, including catecholestrogens

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Summary *

COMPARISON OF THE AFFINITY OF DIFFERENT COMPOUNDS TO ALPHA2-ADRENERGIC RECEPTORS IN MCF-7 CELLS, INCLUDING CATECHOLESTROGENS. Pérez C, Chiesa l, and Lüthy lA. We have described the presence of alpha2 adrenoceptors on MCF-7 cells by RT-PCR and binding to tritiated specific antagonist rauwolscine. These receptors were associated to increased cell proliferation. However, the specificity of these receptors has not yet been established and the objective of the present work is then to study this specificity. Cells at confluence were incubated during 30 min. with 5 nM [3H]-Rauwolcine in the presence or absence of increasing concentrations of several non-labeled compounds. The specific alpha2-adrenergic antagonists yohimbine and rauwolcine showed high affinity for the receptor, with an EC50 of displacement of O.0509 nM and 15 nM respectively, while the specific agonist clonidine showed much less affinity with an EC50 of 2.54 uM. The natural adrenergic compounds epinephrine and norepinephrine were able to displace tritiated rauwolscine with an EC50 of 1.84 uM and 0.603 nM respectively. The a1-antagonist with high affinity for AR-alpha1, prazosin had an EC50 of 41.7 nM. The AR-beta isoproterenol did not exert any displacement at physiological concentrations. Of great importance was the finding that catecholestrogens are also able to bind to the alpha2-AR. 20H-estradiol and 20H-estrone exhibited an EC50 similar to the alpha2-adrenergic compounds (0.784 uM and 0.407 nM). 40H-estrone had an EC50 of 25.2 nM while 40H-estradiol did not show any affinity for the receptor. This work completes the characterization of RA-alpha2 on human breast cancer cells MCF-7 in culture. Moreover, interactions between catecholestrogens and RA-alpha2 are described for the first time. Information provided by the agent in SIGEVA