Mithramycin SK, a novel antitumor drug with improved therapeutic index, mithramycin SA, and demycarosyl-mithramycin SK: three new products generated in the mithramycin producer Streptomyces argillaceus through combinatorial biosynthesis.
To gain initial structure-activity relationships regarding the highly functionalized pentyl side chain attached at C-3 of mithramycin (MTM), we focused on a post-polyketide synthase (post-PKS) tailoring step of the MTM biosynthesis by Streptomyces argillaceus ATCC 12956, which was proposed to be catalyzed by ketoreductase (KR) MtmW. In this last step of the MTM biosynthesis, a keto group of the pentyl side chain is reduced to a secondary alcohol, and we anticipated the generation of an MTM derivative with an additional keto group in the 3-side chain. Insertional inactivation of mtmW, a gene located ca. 8 kb downstream of the mithramycin-PKS genes, yielded an S. argillaceus mutant, which accumulated three new mithramycin analogues, namely mithramycin SA, demycarosyl-mithramycin SK, and mithramycin SK (MTM-SK). The structures of these three compounds confirmed indirectly the proposed role of MtmW in MTM biosynthesis. However, the new mithramycin derivatives bear unexpectedly shorter 3-side chains (ethyl or butyl) than MTM, presumably caused by nonenzymatic rearrangement or cleavage reactions of the initially formed pentyl side chain with a reactive beta-dicarbonyl functional group. The major product, MTM-SK, was tested in vitro against a variety of human cancer cell lines, as well as in an in vitro toxicity assay, and showed an improved therapeutic index, in comparison to the parent drug, MTM.
Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 907 Rose Street, Lexington, Kentucky 40536-0082, USA.
Lily L
LL
Remsing
Ana M
AM
González
Mohammad
M
Nur-e-Alam
M José
MJ
Fernández-Lozano
Alfredo F
AF
Braña
Uwe
U
Rix
Marcos A
MA
Oliveira
Carmen
C
Méndez
José A
JA
Salas
Jürgen
J
Rohr
D000903:Antibiotics, Antineoplastic / Q000096:biosynthesis* / Q000494:pharmacology; D002240:Carbohydrate Sequence; D020650:Combinatorial Chemistry Techniques; D004354:Drug Screening Assays, Antitumor; D020868:Gene Silencing; D006801:Humans; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D008926:Plicamycin / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000494:pharmacology; D013302:Streptomyces / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D014312:Trisaccharides / Q000096:biosynthesis / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000903:Antibiotics, Antineoplastic; D014312:Trisaccharides; D010088:Oxidoreductases; D008926:Plicamycin