Targeted Degradation of Mutant p53 Reverses the Pro-oncogenic Dominant-Negative Effect.

p53 is a transcription factor that functions as a tumor suppressor and the active unit of which is a tetramer. Nearly all cancers inactivate the p53 pathway, primarily through missense mutations in TP53. Most mutant p53 proteins lose their function and often exhibit increased protein stability. In addition to this loss of function, mutant p53 can drive oncogenicity through a dominant-negative effect by forming mixed tetramers with wild-type (WT) p53 to inhibit its activity. The study in this issue of Cancer Research by Klemm and colleagues provides definitive evidence for the mechanism by which mutant p53 inactivates WT p53 function. The p53R248Q mutant has a longer half-life than WT p53, resulting in an approximate ratio of 3 or 4 mutant molecules to every WT molecule. This imbalance facilitates the dominant-negative effect, which can be overcome either by exogenously increasing WT p53 levels or by selectively degrading mutant p53. In experiments whereby mutant p53 was degraded using a degron-tagged construct combined with iberdomide as a molecular glue, remarkable therapeutic efficacy was observed when this approach was used in combination with an MDM2 inhibitor. This work paves the way for therapeutic strategies that aim to degrade mutant p53 proteins in cases in which a WT TP53 allele is retained. See related article by Klemm et al., p. 1978.