The p53 gene is a tumour suppressor gene, in other words its activity stops the formation of tumours. It is therefore a key protein in the cell’s defence against cancer. Mutations in p53 are found in most tumour types, and so contribute to the complex network of molecular events leading to tumour formation. This tumour suppressor is in fact mutationally inactivated in around 50% of human cancers. Approximately onethird of the mutations lower the melting temperature of the protein, leading to its rapid denaturation. Small molecules that bind to those mutants and stabilize them could be effective anticancer drugs. One mutation (Y220C), which occurs in around 75,000 new cancer cases per annum, creates a surface cavity that destabilizes the protein, at a site that is not functional.
Researchers from the Centre for Protein Engineering at the Medical Research Council Centre in Cambridge have succeeded in designing a series of binding molecules from an in silico analysis of the crystal structure using virtual screening and rational drug design. One of them, a carbazole derivative (PhiKan083), binds to the cavity with a dissociation constant of approximately 150μM. It raises the melting temperature of the mutant and slows down its rate of denaturation. Using Diamond, the group has solved the crystal structure of the protein–PhiKan083 complex at 1.5 Å resolution. The structure implicates key interactions between the protein and ligand and conformational changes that occur on binding, which will provide a basis for lead optimization.
Andreas Joerger is responsible for the crystallographic aspects of the project.
“We have demonstrated that the site of mutation in the oncogenic Y220C mutant is a druggable target and the binding molecule PhiKan083 binds to it with a reasonable affinity. The crystal structure of the complex will be a starting point for further rounds of drug design and refinement. Because the site of mutation is distant from regions of the protein that are functionally important, it is an excellent target for drug stabilization therapy. In the longer term, and with further experimental time at Diamond, there is every possibility that an anticancer drug could be developed for the Y220C mutant using compounds that bind more tightly than the current lead.”
Andreas Joerger, Medical Research Council
Targeted rescue of a destabilized mutant of p53 by an in silico screened drug, Frank M. Boeckler, Andreas C. Joerger, Gaurav Jaggi,Trevor J. Rutherford, Dmitry B. Veprintsev, and Alan R. Fersht. PNAS July 29, 2008 vol. 105 no. 30 10360.
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