Damnacanthal Is a Highly Potent, Selective Inhibitor of p56lck Tyrosine Kinase Activity

Abstract

Damnacanthal, an anthraquinone isolated from a plant extract, was found to be a potent, selective inhibitor of p56lck tyrosine kinase activity. The structure, potency, and selectivity of damnacanthal were confirmed by independent synthesis and testing. Damnacanthal exhibited an IC50 of 17 nM for inhibition of p56lck autophosphorylation and an IC50 of 620 nM for phosphorylation of an exogenous peptide by p56lck. Damnacanthal had > 100-fold selectivity for p56lck over the serine/threonine kinases, protein kinase A and protein kinase C, and > 40-fold selectivity for p56lck over four receptor tyrosine kinases. It also demonstrated modest (7-20-fold), but highly statistically significant, selectivity for p56lck over the homologous enzymes p60src and p59fyn. Mechanistic studies demonstrated that damnacanthal was competitive with the peptide binding site, but mixed noncompetitive with the ATP site. Although damnacanthal contains a potentially reactive aldehyde moiety, equilibrium dialysis experiments demonstrated that significant amine formation between damnacanthal and amines occurred only at high concentrations of reactants. However, damnacanthal appeared to bind nonspecifically to membrane lipids and was not active in whole cell tyrosine kinase assays. Damnacanthal is the most potent, selective inhibitor of p56lck tyrosine kinase activity described to date and may represent the starting point for the identification of novel, selective inhibitors of p56lck which are active in whole cell as well as in cell-free systems.

.ALPHA.-Glucosidase Inhibitors from Garcinia brevipedicellata (Clusiaceae)

“…The hexane and CH 2 Cl 2 -soluble fractions obtained from the acetone extract was subjected to repeated chromatography on silica gel column to afford four new depsidones, brevipsidones A-D (1-4) along with damnacanthal, 20) scopoletin 21) and a mixture of stigmasterol and b-sitosterol. 9 Hz, H-9) suggested a tetrasubstituted A-ring and a total substituted B ring.…”

The C terminus of T cell‐specific adapter protein (TSAd) is necessary for TSAd‐mediated inhibition of Lck activity

“…To further substantiate that Lck may phosphorylate TSAd, we incubated Jurkat T cells that had been transiently transfected with TSAd overnight in medium containing the Lck-specific inhibitor damnacanthal [28]. In damnacanthal-treated resting cells, tyrosine phosphorylation of TSAd was clearly reduced, as was phosphorylation of all other cellular substrates (Fig.…”

Cell-based chemical genetic screen identifies damnacanthal as an inhibitor of HIV-1 Vpr induced cell death

“…Dam was first isolated from noni fruit, a traditional Tahaitian fruit commonly used as a folk medicine by Polynesians for over 2000 years [27]. It has been reported that Dam reverts the morphology of K-ras transformed cells to normal one [28] and that Dam inhibits p56lck tyrosine kinase in in vitro kinase assay [29]. Dam inhibited Vpr induced cell growth cessation by twofold with more than 7 standard deviations from untreated Vpr infected cells (Fig.1 B & C).…”