Incorporation of S-9 activation into an ER-alpha transactivation assay

We evaluated the feasibility of incorporating an exogenous metabolic activa ting system into an estrogen receptor-a transactivation assay. 17 beta-estr adiol (E2), and the proestrogenic pesticide methoxychlor (MXC) were evaluat ed for activity in the presence and absence of Aroclor-1254 induced rat liv er S-9 fractions. Both E2 and MXC responded consistently in the assay with average EC50 values of 9.6 x 10(-11) M and 1.2 X 10(-5) M, respectively. In the presence of a 0.1% S-9 fraction, the EC50 for E2 was increased to 1.4 x 10(-9) M and that for MXC decreased to 4.9 X 10(-7) M, with both compound s demonstrating increased secondary metabolite formation as evidenced by HP LC analysis. Consistent with these data, metabolites of E2 and MXC exhibite d decreased and increased potencies, respectively, in the assay system rela tive to the parent molecules. S-9 was compatible with the MCF-7 reporter as say and has the potential to enhance detection of proestrogenic materials. (C) 2000 Elsevier Science Inc. All rights reserved.