SELECTIVE LIGANDS FOR THE ANTIESTROGEN-BINDING SITES : SYNTHESIS, CHEMICAL AND BIOCHEMICAL STUDIES

Abstract

Nonsteroidal compounds, 3,4-diarylchrom-3-enes and 2-benzyl-3-arylbenzofurans. were synthesised and evaluated as selective ligands for the antiestrogen-binding sites. The key steps in the synthesis were reactions of isoflavanones or benzofuranones respectively with the arylorganometallic reagents followed by dehydration of the resulting carbinols. The synthesis of tamoxifen derivatives was also investigated. Chemical studies of some of the compounds were investigated via bromination, iodination, hydrogenation and hydrogenolysis. The compounds synthesised were evaluated for their binding affinity for the estrogen receptor (ER) and the antiestrogen-binding sites (AEBS) and for their effects on cell proliferation and cholesterol biosynthesis. Most of the compounds synthesised were selective for the AEBS, having negligible binding to the ER. Most bound to AEBS with equivalent or greater affinity than tamoxifen. These compounds were generally more active in inhibiti."lg [3H]thymidine incorporation in AEBS-containing ElA lymphoid cells and MCF7 human breast cancer cells than tamoxifen. The anti proliferative effect was dose dependent between 10-8M to 1 o-6 M. Some of these compounds had no effect on [3H]thymidine incorporation by an AEBS-deficient variant of the MCF7 cell line, RTx6 . The high affinity of these compounds for the AEBS and low affinity for the ER suggest that these compounds do not act through the ER but probably via interaction with the AEBS. This is further supported by the fact that these compounds have no antiprouferative effect on the RTx6 cell line, consistent with the view that the antiproliferative effect of these compounds is ER-independent and may involve the AEBS. Two of these compounds also significantly inhibited de novo cholesterol biosynthesis in ElA cells which lack ER in a manner which precedes their ability to cause cell death. It may be inferred that selective ligands of AEBS interfere with cholesterol biosynthesis and that this provides a possible explanation for the antiproliferative and cytotoxic activity of these compounds on mammalian cell lines. Thus the findings in this thesis of (1) selective and high affinity binding of 3,4 diarylchrom-3-enes and 2-benzyl-3-arylbenzofurans to AEBS; (2) their concentration dependent inhibition of [3H]thymidine incorporation by AEBS-containing cells; and (3) " their lack of antiproliferative effect in an AEBS-deficient cell line all suggest a functional role for AEBS in mediating the antigrowth effect of these compounds.