Cytotoxic Anthracycline Metabolites from a Recombinant Streptomyces

The C7 (C9 or C10)- O-l-rhodosamine-bearing anthracycline antibiotic cytorhodins and their biosynthetic intermediates were recently isolated from Streptomyces sp. SCSIO 1666. Cosmid p17C4 from the Streptomyces lydicus genomic library, which harbors both the biosynthetic genes for l-rhodinose (or 2-deoxy-l-fucose) and its glycosyltransferase (encoded by slgG), was introduced into SCSIO 1666 to yield the recombinant strain Streptomyces sp. SCSIO 1666/17C4. Chemical investigations of this strain's secondary metabolic potential revealed the production of different anthracyclines featuring C7- O-l-rhodinose (or 2-deoxy-l-fucose) instead of the typically observed l-rhodosamine. Purification of the fermentation broth yielded 12 new anthracycline antibiotics including three new ε-rhodomycinone derivatives, 1, 4, and 8, nine new β-rhodomycinone derivatives, 2, 3, 5-7, and 9-12, and three known compounds, l-rhodinose-l-rhodinose-l-rhodinoserhodomycinone (13), ε-rhodomycinone (14), and γ-rhodomycinone (15). All compounds were characterized on the basis of detailed spectroscopic analyses and comparisons with previously reported data. These compounds exhibited cytotoxicity against a panel of human cancer cell lines. Significantly, compounds 4 and 13 displayed pronounced activity against HCT-116 as characterized by IC₅₀ values of 0.3 and 0.2 μM, respectively; these IC₅₀ values are comparable to that of the positive control epirubicin.