CYP1 INDUCTION, BINDING TO THE HEPATIC AROMATIC HYDROCARBON RECEPTOR AND MUTAGENICITY OF A SERIES OF 11-ALKOXY CYCLOPENTA[A]PHENANTHREN-17-ONES - A STRUCTURE-ACTIVITY RELATIONSHIP

A series of four 11-alkoxy cyclopenta[a]phenanthren-17-ones, ranging from the methoxy to the butoxy derivative, has been synthesised in order to investigate the effect of the size of the 11-substituent on the mutagenicity and ability of these compounds to induce hepatic CYP1 activity in rats. The latter was monitored by using as diagnostic probes methoxy and ethoxy-resorufin, and immunologically in Western blots employing anti-CYP1A1 antibodies. All four members of the series induced both CYP1A1 and CYP1A2 activities and apoprotein levels, but the methoxy- and ethoxy-CPP-17-ones were clearly the most potent. Of the four isomers, only 11-methoxy-CPP-17-one displaced H-3-TCDD from the cytosolic Ah receptor. Similarly only 11-methoxy-CPP-17-one elicited a positive mutagenic response in the Ames test in the presence of an Aroclor 1254-induced activation system. The relevance of these findings to the carcinogenicity of these compounds in the mouse skin painting model is discussed.