New antitumor substances, BE-12406A and BE-12406B, produced by a streptomycete. I. Taxonomy, fermentation, isolation, physico-chemical and biological properties

New antitumor substances, designated BE-12406A and BE-12406B, were isolated from the culture broth of a streptomycete, strain BA 12406. The active principles were extracted from mycelium by methanol and successively purified by silica gel column chromatography and preparative TLC. BE-12406A and BE-12406B inhibited the growth of vincristine-resistant or doxorubicin-resistant P388 murine leukemia cell lines as well as their parent sensitive cell line. In in vivo experiments, BE-12406A inhibited the growth of S-180 murine ascites tumor.