Relationship of anti-proliferative activity of TAS-108, a steroid anti-estrogen, and high expression of ERα in MCF7 cells.

Abstract

e11566 Background: TAS-108 is an anti-estrogen that binds to both ERα and ERβ and has potent anti-proliferative activity in vitro and in vivo assay. Recently, the phase II clinical study of TAS-108 showed that it has competitive clinical benefic with lower level of adverse effects. However, the effect of TAS-108 on molecular mechanism, including ER dimerization, remains largely uninvestigated. Methods: The plasmids containing ERα or ERβ fused with N- and C-terminal fragments of firefly luciferase were constructed for split luciferase complementation assays. The resulting plasmids were transfected in HEK293 cells for 24 hr and TAS-108 was added to the media for 6 hr. For RT-qPCR of AREG and TFF1 and proliferation assay, ERβ was transfected in MCF7 cells for 24hr. The proliferation level was determined by measuring the fluorescent level induced by Prestoblue reagent. Results: Using split luciferase complementation assay, we determined that TAS-108 induced ERα/β heterodimerization about 100-fold more potently than ERα/α homodimerization. Increasing the ERβ level by transfection in MCF7 cells (MCF7-ERβ), potency of TAS-108 was increased significantly; 30nM TAS-108 was suitable to block the E2 mediated increase of AREG and TFF1 expression and significantly decrease proliferation of MCF7-ERβ. Conclusions: Taken together, these data suggest that TAS-108 has a higher affinity for ERα/β heterodimerization than ERα/α homodimerization and TAS-108 shows more effective anti-proliferative activity by blocking the expression of E2-induced proliferative genes when coupled with increased levels of ERβ. These findings also underscore the molecular role of ERβ in the biology and suggest the possibility of the compound inducing ERα/β heterodimerization as anti-breast cancer drugs.