1993 Volume 46 Issue 7 Pages 1069-1075
R1128 B (l, 3, 6-trihydroxy-8-n-butylanthraquinone), a new antibiotic produced by Streptomyces sp. No. 1128, inhibited estrogen binding to its receptor. The IC50 value of R1128B for partially purified rat uterine cytosol receptor was 1.2×10-7 M. However, the IC50 value of Rl 128 B against androgen-receptor binding was about 50-fold greater than that against estrogen-receptor binding. Rl 128 B was a competitive inhibitor against estrogen-receptor binding. R1128 B inhibited the growth of estrogen-responsive human mammary adenocarcinoma MCF-7 cells in soft agar. This inhibition, however, was reversed when estradiol was added to the culture medium. Rl 128 B showed antitumor activities against MCF-7 both xenografted to nude mice and implanted in subrenal capsule of mice (SRC assay). The potency of R1128 B was about 8-fold lower than that of tamoxifen both in vitro and in vivo.
