ABSTRACT
Protein-protein interactions (PPIs) governing the recognition of substrates by E3 ubiquitin ligases are critical to cellular function. There is significant therapeutic potential in the development of small molecules that modulate these interactions; however, rational design of small molecule enhancers of PPIs remains elusive. Herein, we report the prospective identification and rational design of potent small molecules that enhance the interaction between an oncogenic transcription factor, ß-Catenin, and its cognate E3 ligase, SCFß-TrCP. These enhancers potentiate the ubiquitylation of mutant ß-Catenin by ß-TrCP in vitro and induce the degradation of an engineered mutant ß-Catenin in a cellular system. Distinct from PROTACs, these drug-like small molecules insert into a naturally occurring PPI interface, with contacts optimized for both the substrate and ligase within the same small molecule entity. The prospective discovery of 'molecular glue' presented here provides a paradigm for the development of small molecule degraders targeting hard-to-drug proteins.
Subject(s)
Small Molecule Libraries/analysis , Small Molecule Libraries/pharmacology , Ubiquitin-Protein Ligases/metabolism , HEK293 Cells , Humans , Phosphorylation/drug effects , Protein Binding/drug effects , Proteolysis/drug effects , Small Molecule Libraries/chemistry , Substrate Specificity/drug effects , Ubiquitination/drug effects , beta Catenin/metabolism , beta-Transducin Repeat-Containing Proteins/metabolismABSTRACT
2-Amino-7-substituted benzoxazole analogs were identified by HTS as inhibitors of RSK2. Molecular modeling and medicinal chemistry techniques were employed to explore the SAR for this series with a focus of improving in vitro and target modulation potency and physicochemical properties.
Subject(s)
Benzoxazoles/chemistry , Protein Kinase Inhibitors/chemistry , Ribosomal Protein S6 Kinases, 90-kDa/antagonists & inhibitors , Benzoxazoles/chemical synthesis , Benzoxazoles/metabolism , Binding Sites , Crystallography, X-Ray , Humans , Molecular Dynamics Simulation , Protein Binding , Protein Kinase Inhibitors/chemical synthesis , Protein Structure, Tertiary , Ribosomal Protein S6 Kinases, 90-kDa/metabolism , Structure-Activity RelationshipABSTRACT
UNLABELLED: The p90 ribosomal S6 kinase (RSK) family of serine/threonine kinases is expressed in a variety of cancers and its substrate phosphorylation has been implicated in direct regulation of cell survival, proliferation, and cell polarity. This study characterizes and presents the most selective and potent RSK inhibitors known to date, LJH685 and LJI308. Structural analysis confirms binding of LJH685 to the RSK2 N-terminal kinase ATP-binding site and reveals that the inhibitor adopts an unusual nonplanar conformation that explains its excellent selectivity for RSK family kinases. LJH685 and LJI308 efficiently inhibit RSK activity in vitro and in cells. Furthermore, cellular inhibition of RSK and its phosphorylation of YB1 on Ser102 correlate closely with inhibition of cell growth, but only in an anchorage-independent growth setting, and in a subset of examined cell lines. Thus, RSK inhibition reveals dynamic functional responses among the inhibitor-sensitive cell lines, underscoring the heterogeneous nature of RSK dependence in cancer. IMPLICATIONS: Two novel potent and selective RSK inhibitors will now allow a full assessment of the potential of RSK as a therapeutic target for oncology.
