Directed Accumulation of Anticancer Depsipeptides by Characterization of Neoantimycins Biosynthetic Pathway and an NADPH-Dependent Reductase

Neoantimycins (NATs) are members of antimycin-types of depsipeptides with outstanding anticancer activities. We isolated NAT-A (1) and -F (2) from the fermentation extract of Streptomyces conglobatus. The NAT biosynthetic gene cluster (nat BGC) was identified by genome sequencing and bioinformatics analysis. nat BGC includes two nonribosomal peptide synthetase (NRPS) and one polyketide synthase (PKS) gene, and a gene cassette (10 genes), of which the encoded enzymes share high homology to the ones responsible for 3-formamidosalicylate (3-FAS) biosynthesis in the antimycin biosynthetic pathway. Heterologous expression of the partial nat BGC without the 3-FAS gene cassette in the antimycin producer, Streptomyces albus J1074, results in the production of 1 and 2, suggesting that the nat BGC indeed directs NATs biosynthesis. Targeted in-frame deletion of the reductase gene (natE) abolished the production of 1 and 2 but accumulated two NAT derivatives, the known NAT-H (3) and a new NAT-I (4). Biochemical verification demonstrated that the recombinant NatE indeed catalyzes an NADPH-dependent reaction of 3 or 4 to 1 or 2, respectively. Compound 3 presented significantly stronger activities against eight cancer cell lines than the ones using cisplatin, the clinical chemotherapy medicine. In particular, 3 displayed 559- and 57-fold higher activity toward human melanoma and cervix epidermoid carcinoma cells, respectively, compared with cisplatin. The new derivative, 4, was 1.5- to 10.9-fold more active than cisplatin toward five cancer cell lines. The evaluation of NATs biosynthesis depicted here will pave the way to generate new NAT derivatives through rational pathway engineering.