Baumycin A1

A potent angiogenesis-inhibitory compound TAN-1120 was found to be produced by a Streptomyces species isolated from a soil sample. The producing organism was characterized as a new subspecies of S. triangulatus and named S. triangulatus subsp. angiostaticus subsp. nov. due to its specific ability to produce the compound. This substance was isolated as a red powder by a combination of organic solvent extraction, silica gel column chromatography and preparative HPLC using an ODS column. Its structure was elucidated by chemical reactions and spectral analyses to be a new baumycin-group anthracycline. Reduction of TAN-1120 gave two compounds, a deoxy derivative and baumycin A1. TAN-1120 showed remarkably potent angiostatic activity in two conventional angiogenesis assay systems in vivo, while doxorubicin and daunomycin had far weaker activity. It strongly inhibited proliferation of vascular endothelial cells did not prevent capillary cord formation in vitro by the endothelial cells on extracellular matrix-coated plates. TAN-1120 is one of the most potent angiostatic agents reported.

An aclacinomycin A-resistant subline of mouse lymphoblastoma L5178Y cells was isolated by successive treatment of tumor-bearing mice with the antibiotic. IC50 (50% growth inhibition) in culture was observed at a drug concentration of 0.22 micrograms/ml, which was ca. 11 times higher than IC50 for the parental cells. The resistant cell line exhibited cross resistance to mitomycin C, actinomycin D, macromomycin, auromomycin, vinblastine, cytochalasin B, and other anthracyclines: daunorubicin, adriamycin, 4'-O-tetrahydropyranyladriamycin, baumycins A1 and A2, aclacinomycins B and Y, MA144-S1, 1-deoxypyrromycin, cinerubin A, musettamcyin, and pyrromycin. The 1-deoxy group of anthracyclines showed higher degree of cross resistance than the 1-hydroxy group. No significant cross resistance was found with bleomycin A2, neothramycin and blasticidin S. The resistance to aclacinomycin A and cross resistance to adriamycin were also demonstrated by the method of uridine incorporation. The accumulation or retention studies with [3H]adriamycin revealed that the resistance may be due to decreased uptake and increased efflux of the antibiotic in the resistant cells.

The effects of various new anthracycline antibiotics on DNA and RNA synthesis were studied using DNA polymerase I (EC 2.7.7.7), RNA polymerase (EC 2.7.7.6) obtained from Escherichia coli and reverse transcriptase obtained from avian myeloblastosis virus. Aclacinomycin A, its analogues, baumycins A1 and A2, adriamycin and daunomycin showed potent inhibitory effects on these polymerases, with calf thymus DNA as template, with IC50 values of 10-30 microM. With poly(rA) x d(pT)10 as template for reverse transcriptase, aclacinomycin A and daunomycin showed IC50 values higher than 500 microM. Baumycins B1, B2, C1, and C2 showed high IC50 values on three polymerases. Addition of excess template DNA to the reaction mixture reversed the inhibitory effect of anthracyclines. Addition of calf thymus DNA to anthracyclines caused a bathochromic and hypochromic change in the visible spectrum. Apparent binding constant for aclacinomycin A, its analogues, and adriamycin were in the range of (1-2) X 10(6) M-1. Aclacinomycin A and adriamycin also bind to heat denatured DNA, but not strongly to yeast RNA. From these results, the structure-activity relationships of new anthracyclines on DNA binding and polymerase reactions are discussed.