The Tumour Suppressor p53: from structure to drug discovery

Professor Sir Alan Fersht, FRS
Cambridge University and MRC Centre for Protein Engineering, Hills Road, Cambridge, CB2 0QH, UK

Abstract:
p53 is the major tumour suppressor.  If it and its pathways are active, it will cause programmed cell death of all cancer cells.  p53 is directly inactivated by mutation in some 50% of human cancers.  Some 30-40% of the mutations simply lower the stability of the core domain so it melts close to or below body temperature.  This opens the possibility of making small molecule drugs to reactivate the protein causing the death of cancer cells.  We have shown in principle that it is possible to reactivate p53 by small molecules that bind to and stabilise it.  To understand further the structure of the protein and hence the rational design of drugs, we are solving its structure at high resolution.  We are faced with twin problems: the tetrameric protein consists of 1572 residues, some of which are in well-structured domains but others are intrinsically disordered or natively unfolded; and the important core domain is intrinsically unstable and not well suited to systematic study. We have solved the structure of the core domain in solution by state-of-the-art NMR methods and found structural reasons for its instability. We have engineered a more stable variant, which is biologically active and have solved the crystal structures of oncogenic mutants in this framework. We solved the quaternary structure of the full-length tetrameric complex by combining high-resolution structural information on the folded individual domains with NMR, small angle x-ray scattering and electron microscopy, which should be a paradigm for solving other complex proteins that are involved in the cell cycle.  We are refining these structures to high resolution, and studying their complexes with partner proteins using a further mix of structural methods.

The mutation Y220C occurs in about 70,000 to 80,000 new cases of cancer per annum.  The mutant is highly destabilized and denatures rapidly at body temperature.  Our structural studies revealed that the mutation forms a surface cavity that appears a prime target for small molecules to bind to and stabilise the protein.  In silico design identified a series of molecules that might bind in the cavity.  We screened those and the second and third generation derivatives and found small compounds of drug-like properties that raise the melting temperature of the mutants and restore its activity.