Selective agonists of estrogen receptors (ER) alpha and beta in a murine breast cancer model.

SOLDATI R; GOROSTIAGA MA; MOLLER F; VOLLMER G; LANARI C

San Diego, EEUU

Congreso; Advances in Breast Cancer Research- AACR; 2007

American Association of Cancer Research

Selective agonists of estrogen receptors (ER) alpha and beta in a murine breast cancer model. Soldati Rocío, Gorostiaga María, Möller Frank, Vollmer Günter, Lanari Claudia. The role of estrogen receptors (ER) in mammary gland and breast cancer is controversially discussed. Estrogens control transcriptional responses through binding to two different nuclear ERs, alpha (ERα) and beta (ERβ). Both receptors bind to 17β–estradiol (E2) with the same affinity although they can differentially activate certain promoter elements thereby inducing different biological responses. It has been reported that ERα mediates proliferative responses while ERβ modulates the ERa mediated responses in the mammary gland in an inhibitory fashion.We have developed an experimental model in wich murine ductal mammary carcinomas express ERα and ERβ as well as progesterone receptors (PR). These tumors (C4HI) may regress completely following estrogen treatment and in primary cultures E2 inhibits cell proliferation. Paradoxically, the cell lines developed from these tumors have a different estrogen responsiveness and they are stimulated by E2 behaving like MCF-7 human breast cancer cells. As both ER isoforms are expressed in tumors and the in cell lines, we decided to investigate whether this differential responsiveness could be driven by the different ER isoforms. Thus, the aim of this study was to evaluate the effect of the ERα selective agonist: 4,4’,4’’-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT)  and the ERβ selective agonist: (4-hydroxy-phenyl)-propionitrile (DPN), in primary cultures of the C4-HI tumor and in the MC4-L2 cell line. The effect of the pure agonists and of E2 was evaluated on cell proliferation, on expression of ERα and PR as well as on the expression of the antiapoptotic gene clusterin. Cell proliferation was evaluated by 3H-thymidine uptake using the agonists in a range of concentrations from 0,01nM to 100nM[MSOffice1] . PPT and DPN showed similar effects and similar to those induced by 1 nM E2. The three compounds were inhibitory for C4-HI and stimulatory for MC4-L2, showing in each case a clear dose respone pattern. However, the effect of PPT was stronger than the effect of DPN.Accordingly, real time PCR studies revealed an up regulation of mRNA of clusterin in MC4-L2 cells treated with 100nM PPT or DPN  and a downregulation in C4-HI cells similarly treated for 24 hs (p<0.001).  Both compounds and E2 induced an increase in PR and a decrease in ERα expression evaluated by inmunofluoresence and by western blots in C4HI. In summary, these results indicate that the differential effects of E2 in the investigated tumors and in the cell lines regarding induction of stimulatory or inhibitory signals are not related to differences in the ER isoforms involved. The reason for this differing response pattern still remains to be elucidated. However, we can conclude that ERα is mediating inhibitory signals in breast cancer growth.  [MSOffice1]Always from low dose to high dose