A28
Inhibition of MDM2: a safe strategy in the presence of mutant p53?
Patricia Roxburgh, Patricia Muller, Karen Vousden
The Beatson Institute for Cancer Research, Glasgow, UK
Background
p53 is a tumour suppressor gene which is mutated in 50% of cancers, in most cases leading to the expression of a mutant p53 protein. Wild type p53 efficiently inhibits cell proliferation, and under normal conditions this activity is controlled by MDM2, a p53-binding protein that ubiquitinates and subsequently targets p53 for degradation. MDM2 also targets mutant p53 for degradation.
HLI373 and Nutlin are MDM2 inhibitors that prevent MDM2-dependent degradation of p53. This is an attractive approach to activate p53 function in tumours expressing wild type p53, where treatment with the inhibitors leads to an increase in p53 protein levels and activity. However, there are concerns about the effects of these inhibitors on tissues expressing mutant p53. Mutant p53 has been shown to drive invasion, and in transgenic mice expressing mutant p53, deletion of Mdm2 results in the stabilisation of mutant p53 and a gain-of-function metastatic phenotype. Our aim is therefore to study the effects of HLI373 and Nutlin on both wild type and mutant p53 function.
Method
We have established a series of cell lines in which we can simultaneously investigate stabilisation of wild type and mutant p53. Using these cells, we are studying the effect of HLI373 or Nutlin on the expression, stability and ubiquitination of p53. The effects of both compounds on p53 activity are also being characterised, including the expression of p53 targets, cell cycle arrest and cell migration and motility.
Results
We initially determined the optimal working dose and time for HLI373 and Nutlin treatment based on stabilisation of wild type p53, increased p21 expression and cellular senescence. Preliminary data has confirmed a stabilisation of mutant p53 by HLI373 and Nutlin. The effects of these drugs on p53 levels and function in vivo is also being examined.
Conclusion
HLI373 and Nutlin stabilise both wild type and mutant p53. We are now investigating the effects of the compounds on mutant p53-dependent migration and invasion in the presence and absence of wild type p53.
