DETECTION AND CHARACTERIZATION OF 9-ANTHRON-10-YL RADICALS FORMED BY ANTIPSORIATIC AND TUMOR-PROMOTING 9-ANTHRONES IN AQUEOUS BUFFERS

Certain 1,8-dihydroxy-9-anthrones have been used for the topical treatment of psoriasis for over seventy-five years. The therapeutic usefulness of these compounds is limited, however, by side effects including severe skin inflammation and staining. Antipsoriatic 9-anthrones are also tumor promoters in mouse skin. The chemical mechanisms underlying the biological properties of 9-anthrones are believed to involve the generation of free radical products such as 9-anthron-10-yl radicals or secondary oxygen radicals such as O2.- or OH.. However, the specific role that 9-anthron-10-yl radicals may play in mediating the biological effects of 9-anthrones is uncertain because these species have not been detected in biological systems. In the present study we have used the EPR spin trapping technique to demonstrate for the first time the formation of the 1,8-dihydroxy-9-anthron-10-yl radical in aqueous buffers. Additionally, in order to gain information concerning the role of 9-anthron-10-yl radicals in tumor promotion and antipsoriatic activities, we have used this technique to investigate the formation of these radical species by a series of 9-anthrones of known tumor-promoting and antipsoriatic activities. All of the 9-anthrones studied formed spin adducts with 3,5-dibromo-4-nitrosobenzenesulfonic acid in aqueous buffers. The formation of these adducts was pH-dependent, being favored at alkaline pH. The results demonstrate that the ability to form 9-anthron-10-yl radicals in aqueous buffers is a common, but not exclusive, property of tumor-promoting and antipsoriatic anthrones and suggest that other factors may also be important for producing the biological effects of these compounds.