Studies toward the Unique Pederin Family Member Psymberin: Structure–Activity Relationships, Biochemical Studies, and Genetics Identify the Mode-of-Action of Psymberin

Abstract

Psymberin is the only member of the pederin natural product family that contains a dihydroisocoumarin side chain. Structural modifications of psymberin uncoupled inhibition of protein translation from cytotoxicity, suggesting that psymberin has more than one bioactivity. A forward genetic screen in Caenorhabditis elegans was conducted to identify the molecular target(s) of psymberin. Multiple independent psymberin-resistant mutants were isolated, each containing the same point mutation in a gene encoding a ribosomal protein. However, a psymberin-resistant mutant strain bearing this mutation was not cross-resistant to the pederin family member mycalamide A, which binds to the archaeal form of the same protein. Thus, two pederin family members likely differ in how they bind the same molecular target. The accumulation of psymberin in cells was sensitive to the stereochemistry of the amide side chain at C4 or C8 and the presence of the dihydroisocoumarin side chain. The observation that psymberin diastereomers or dihydroisocoumarin-truncated analogs lose all cytotoxic activity while retaining the ability to inhibit protein translation in a cell-free in vitro assay can be explained in the context of these differential cell uptake issues. Finally, we also demonstrate that the blistering activity associated with pederin and other members of the family is not due to their protein synthesis inhibiting activity. Unlike pederin and mycalamide, psymberin does not display irritant or blistering activity.

Irciniastatin A Induces Potent and Sustained Activation of Extracellular Signal-Regulated Kinase and Thereby Promotes Ectodomain Shedding of Tumor Necrosis Factor Receptor 1 in Human Lung Carcinoma A549 Cells

“…8,9) Additionally, genetic studies with Caenorhabditis elegans show that irciniastatin A primarily targets the ribosome. 10) Cell-surface tumor necrosis factor (TNF) receptor 1 is processed into its soluble form by TNF-α-converting enzyme (TACE), also referred to as a disintegrin and metalloproteinase 17. 11) We have previously shown that three translation inhibitors, i.e., acetoxycycloheximide, cytotrienin A and deoxynivalenol, rapidly induced the ectodomain shedding of TNF receptor 1 in human lung carcinoma A549 cells.…”

Studies toward the Unique Pederin Family Member Psymberin: Full Structure Elucidation, Two Alternative Total Syntheses, and Analogs

“…Here, we describe the synthesis of psymberin analogs that were useful for the structure-function and mode-of-action studies that will be detailed in a subsequent article. 13 The terminal olefin of 1 is distinct from the exocyclic double bond present in other pederin family members. In the subsequent article, we demonstrate that the homoallylic ether in pederin is responsible for the irritant/blistering activity associated with this class of compounds.…”

“…In a subsequent article, we detail our biological investigations that led to the target identification of psymberin, and attributes that distinguish it from the pederin/mycalamide family of natural products. 13 …”

Predominately Uncultured Microbes as Sources of Bioactive Agents

“…Representative examples of these compounds have been synthesized by considerable numbers of organic chemists in the last 10 plus years. The following papers should be consulted by readers interested in the synthetic processes used (Jewett and Rawal, 2007; Jiang et al, 2007; Nishii et al, 2009; Wan et al, 2011; Wu et al, 2011, 2012; Mosey and Floreancig, 2012; Floreancig, 2014; Uesugi et al, 2015). Of these, the review by Mosey and Floreancig (2012) gives a relatively thorough overview of the isolation, biological activities, and medicinal chemistry of these agents.…”