ABSTRACT
The tumour suppressor p53 is the most frequently mutated gene in human cancer. Reactivation of mutant p53 by small molecules is an exciting potential cancer therapy. Although several compounds restore wild-type function to mutant p53, their binding sites and mechanisms of action are elusive. Here computational methods identify a transiently open binding pocket between loop L1 and sheet S3 of the p53 core domain. Mutation of residue Cys124, located at the centre of the pocket, abolishes p53 reactivation of mutant R175H by PRIMA-1, a known reactivation compound. Ensemble-based virtual screening against this newly revealed pocket selects stictic acid as a potential p53 reactivation compound. In human osteosarcoma cells, stictic acid exhibits dose-dependent reactivation of p21 expression for mutant R175H more strongly than does PRIMA-1. These results indicate the L1/S3 pocket as a target for pharmaceutical reactivation of p53 mutants.
Subject(s)
Computational Biology/methods , Mutant Proteins/chemistry , Mutant Proteins/metabolism , Tumor Suppressor Protein p53/chemistry , Tumor Suppressor Protein p53/metabolism , Apoptosis Regulatory Proteins/metabolism , Aza Compounds/pharmacology , Binding Sites , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , Cell Line, Tumor , Cyclin-Dependent Kinase Inhibitor p21/genetics , Cyclin-Dependent Kinase Inhibitor p21/metabolism , Cysteine/genetics , Heterocyclic Compounds, 4 or More Rings/chemistry , Heterocyclic Compounds, 4 or More Rings/pharmacology , Humans , Molecular Dynamics Simulation , Oxepins/chemistry , Oxepins/pharmacology , Protein Stability/drug effects , Protein Structure, Secondary , Protein Structure, Tertiary , Proto-Oncogene Proteins/metabolism , Reproducibility of Results , Structure-Activity Relationship , Transcription, Genetic/drug effects , Tumor Suppressor Protein p53/geneticsABSTRACT
AMPA receptors form a major subdivision of the glutamate receptor family that mediates excitatory synaptic transmission in the brain. Currents through AMPA receptors can be up- or down-regulated by compounds that allosterically modulate receptor kinetics through binding sites distinct from that for glutamate. One of those modulators is the benzothiadiazide IDRA-21 which has been reported to enhance synaptic transmission and be effective in behavioral tests, but typically requires threshold concentrations of at least 100 microM to be active in vitro. In this study, new benzothiadiazides were developed with IDRA-21 as lead compound and examined for their potency in modulating AMPA receptor kinetics. A significant increase in drug affinity was obtained by alkyl substitution at the 5'-position of IDRA-21; substitutions at other positions of the benzothiadiazide core generally did not yield a further gain in affinity and in some cases abolished drug binding. The 5'-ethyl derivative exhibited an EC(50) value in the order of 22 microM which represents about a 30-fold gain in affinity over that of IDRA-21. The EC(50) value is comparable to that of cyclothiazide, the most potent benzothiadiazide drug, but the effects on AMPA receptors differed substantially between these two compounds in that the 5'-ethyl derivative of IDRA-21 greatly increased the binding affinity for receptor agonists whereas cyclothiazide is known to reduce agonist binding. The structure--activity relationships reported here thus offer to provide new insights how receptor kinetics is linked to particular aspects of receptor--drug interactions.
