Nargenicin
A1(1) is an antibacterial macrolide with
effective activity against various Gram-positive bacteria, including
methicillin-resistant Staphylococcus aureus. Due
to the promising properties of this compound in inhibiting cell proliferation,
immunomodulation, and the cell protective effect, there has been significant
interest in this molecule. Recently, the biosynthetic gene cluster
(BGC) of 1 was reported from Nocardia argentinesis and Nocardia arthritidis. In addition, two crucial
enzymes involved in the formation of the core decalin moiety and postmodification
of the decalin moiety by an ether bridge were characterized. This
study reports on the BGC of 1 from Nocardia sp. CS682. In addition, the direct capture and heterologous expression
of nar BGC from Nocardia sp. CS682
in Streptomyces venezuelae led to the production
of 1. Further metabolic profiling of wild type, Nocardia sp. CS682 in optimized media (DD media) resulted
in the isolation of two acetylated derivatives, 18-O-acetyl-nodusmicin and 18-O-acetyl-nargenicin. The
post-PKS modification pathway in biosynthesis of 1 was
also deciphered by identifying intermediates and/or in vitro enzymatic reactions of NgnP1, NgnM, and NgnO3. Different novel analogues
of 1, such as compound 6, compound 7, 23-demethyl 8,13-deoxy-nodusmicin (8), 23-demethyl
8,13-deoxynargenicin (9), 8,13-deoxynodusmicin (10), and 8,13-deoxynargenicin (11), were also
characterized, which extended our understanding of key post-PKS modification
steps during the biosynthesis of 1. In addition, the
antimicrobial and anticancer activities of selected analogues were
also evaluated, whereas compound 9 was shown to exhibit
potent antitumor activity by induction of G2/M cell cycle arrest,
apoptosis, and autophagy.