Inhibiting MDM2/P53 protein-protein interaction
Therapeutic rationale
The p53 tumour suppressor protein plays an established key role in regulating cellular responses to different stress situations by upregulating the transcription of genes that are involved in cell cycle arrest and/or apoptosis. The activity and stability of p53 is modulated by the Mdm2 protein by binding to the transactivation domain of p53. Amplification of the Mdm2 gene has been reported in approximately 7% of all tumours, and in 30% of all osteosarcomas and soft tissue tumours. The inhibition of the Mdm2/p53 protein-protein interaction has become a well-validated drug target since the discovery of the first small molecule inhibitor, Nutlin, by researchers at Roche. In addition, the crystal structure of the Mdm2/p53 complex has provided structural insights in the molecular requirements for small molecule compounds to be able to interfere with the Mdm2/p53 interaction.
Drug-like inhibitors of the Mdm2/p53 interaction
Two diverse drug-like chemical classes of small molecule compounds have been identified as inhibitors of the Mdm2/p53 protein-protein interaction using Silicos' proprietary Cosmos™ technology platform. The compounds belonging to the first class A have two stereocenters, but the number of different stereoisomers is however reduced from the theoretical four to only two due to an imposed cis/trans substitution pattern in the compounds. It is anticipated that resolution of the relative enantiomers will result in a concomitant further increase in activity. The class B compounds do not contain any stereocenters. Measured using a homogeneous time resolved fluorescence (HTRF) protein-protein interaction assay using a GST-His fusion protein as control, both sets include compounds that inhibit the Mdm2/p53 interaction in low micromolar IC50 concentrations. A significant amount of structure-activity data is available for one of the series, and this information is consistent with the available binding models of the compounds docked into the p53-binding pocket of Mdm2. Efficient synthetic routes have been developed for both chemical classes to allow easy modification of substituents at different positions on the molecules. Furthermore, for both chemical classes there are structural and synthetic opportunities available to introduce functional moieties for optimisation of the pharmacokinetic and solubility properties without interfering with the respective binding capabilities.
Figure 1. (Left) A model of the proposed binding mode of SIL-43 (white surface) in the p53-binding pocket of Mdm2. (Right) Dose response curve of SIL-43. Red points are from the Mdm2/p53 interaction, blue points denote the GST-His control.