Thioholgamides: Thioamide-Containing Cytotoxic RiPP Natural Products

Thioviridamide is a structurally unique ribosomally synthesized and post-translationally modified peptide that contains several thioamide bonds and is active against a number of cancer cell lines. In the search for naturally occurring thioviridamide analogs, we employed genome mining that led to the identification of several related gene clusters. Chemical screening followed by cultivation and isolation yielded thioholgamides A and B, two new additions to the thioviridamide family with several amino acid substitutions, a different N-capping moiety, and with one less thioamide bond. Thioholgamides display improved cytotoxicity in the submicromolar range against a range of cell lines and an IC₅₀ of 30 nM for thioholgamide A against HCT-116 cells. Herein, we report the isolation and structural elucidation of thioholgamides A and B, a proposed biosynthetic cluster for their production, and their bioactivities against a larger panel of microorganisms and cancer cell lines.