The colony-forming ability of HeLa cells that survived an initial dose of X-irradiation proved abnormally sensitive to lucanthone. Surviving cells gradually regained normal resist ance to lucanthone treatment, which implied that lucanthone was acting to inhibit a postradiation repair process. Enhance ment of cell killing by lucanthone was comparable in degree to that induced by actinomycin D, with which it shares many properties. Lucanthone merits further study as a possible adjunct in clinical

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... radiation therapy, since it is a relatively safe drug which has been widely used for many years in the treat ment of human schistosomiasis.