Der Pharmacia Lettre
Abstract
Author(s): Sivakumar Annadurai, Natalia F. Krynetskaia, Manali S. Phadke, Evgeny Krynetskiy,
Daniel J. Canney
DNA-protein interactions regulate pivotal intracellular processes and thus provide an important
target for drug discovery efforts. Small molecules remain ineffective inhibitors of DNA binding
because of the lack of adequate high-throughput screening procedures, and the paucity of lead
molecules for drug design. High Mobility Group protein B1 (HMGB1) is a nuclear DNA-binding
protein with no known sequence specificity or enzymatic activity, which plays an important role
in chemotherapy-induced apoptosis, tissue regeneration, and inflammation. The natural
triterpene glycyrrhizin (GLA) has been reported to be a modest inhibitor of DNA-HMGB1
binding interactions, though the mechanism of inhibition remained unclear. In the present work,
we investigated inhibitory effects of GLA and its derivatives (carbenoxolone (CGA) and
potassium salt of glycyrrhetinate (GAK)) on DNA-binding activity of HMGB1. Using a newly
developed capillary electrophoresis mobility shift assay, we characterized binding of synthetic
DNA duplexes with recombinant human HMGB1. Dynamic light scattering and fluorometric
experiments demonstrated that the inhibitory effects of these triterpenes on DNA binding
depended on their ability to form supramolecular aggregates. GLA and GAK demonstrated
inhibitory effect on DNA-HMGB1 binding at concentrations exceeding CMC (100-150mM). GLA
inhibited DNA-HMGB1 binding with IC50 = 500 mM; 600 mM GAK showed 100% inhibition of
DNA-HMGB1 binding. In the presence of GLA, human lung carcinoma cells demonstrated more
than 300-fold increased viability when treated with chemotherapeutic drug cytarabine,
consistent with the GLA inhibitory activity. The results of our study demonstrated that molecules
capable of forming stable aggregates are potential modulators of DNA-protein binding and open
avenues to the development of novel classes of physiologically active compounds.
