Psammaplin A as a general activator of cell-based signaling assays via HDAC inhibition and studies on some bromotyrosine derivatives

Abstract

The Wnt signaling pathway regulates cell growth and development in metazoans, and is therefore of interest for drug discovery. By screening a library of 5,808 pre-fractionated marine extracts in a cellbased Wnt signaling assay, several signaling activators and inhibitors were observed. LCMS based fractionation rapidly identified an active compound from Pseudoceratina purpurea as psammaplin A, a known HDAC inhibitor. Other HDAC inhibitors similarly activated signaling in this assay, indicating HDAC inhibitors will be identified through many cell-based reporter assays. In a large scale analysis of P. purpurea, three previously undescribed bromotyrosine based natural products were identified; the structure of one of these was confirmed by synthesis. Additionally, three other derivatives of psammaplin A were prepared: a mixed disulfide and two sulfinate esters. Finally, evidence to support a structural reassignment of psammaplin I from a sulfone to the isomeric sulfinate ester is presented.

WLS-dependent secretion of WNT3A requires Ser209 acylation and vacuolar acidification

“…To better characterize specific steps in Wnt secretion, we developed a multi-step cell-based assay using human HEK293 cells containing a stably integrated luciferase reporter under the control of eight tandem repeats of the superTOPFlash promoter (STF cells) (McCulloch et al, 2009;Xu et al, 2004). The initial screen used STF cells that, in addition, stably overexpress murine WNT3A and, therefore, have high levels of active -catenin readily assessible by firefly luciferase activity.…”

Biological targets and mechanisms of action of natural products from marine cyanobacteria

“…For example, psammaplin A was identified as a modulator of the Wnt signaling pathway. 117 Rather than acting on the signaling pathway itself, the activity of psammaplin A was due to significant transcriptional activity. 117 This was observed in the case of largazole in the screening of inhibitors for ubiquitin activating enzyme (E1) using mink lung epithelial cell line (Kip16) stably expressing the N-terminal GFP-p27 fusion.…”

“…117 Rather than acting on the signaling pathway itself, the activity of psammaplin A was due to significant transcriptional activity. 117 This was observed in the case of largazole in the screening of inhibitors for ubiquitin activating enzyme (E1) using mink lung epithelial cell line (Kip16) stably expressing the N-terminal GFP-p27 fusion. 118 Largazole showed nanomolar potency for GFP-p27 stabilization, however, E1 inhibition was observed at high micromolar concentration.…”

Discovery and Mechanism of Natural Products as Modulators of Histone Acetylation

“…HDAC inhibitors were also identified in pathway-based screens for target genes (i.e., p21 ) or for modulators of protein signaling pathways such as Wnt that could be indirectly affected by HDACs, via downstream cellular effects [47, 48]. The p21 protein is a negative regulator of the cell cycle that is commonly downregulated in cancers and is inducible following treatment with HDAC inhibitors.…”