Pharmacological targeting of nonsense mutant TP53 and PTEN in cancer

The TP53 tumor suppressor gene encodes p53 and is inactivated by mutations in around half of all human tumors. Approximately 11% of TP53 mutations are nonsense mutations, resulting in the premature termination of translation and the production of truncated and non-functional p53 proteins. Aminoglycosides such as G418 are known to induce translational readthrough, a process in which the ribosome overcomes the stop signal introduced by a nonsense mutation and translates full-length protein. However, the clinical use of aminoglycosides is restricted due to severe side effects. We have demonstrated that combination treatments with proteasome inhibitors or compounds that disrupt the binding of p53 to the ubiquitin ligase MDM2 can synergistically enhance the levels of fulllength p53, improving the efficacy of readthrough compared to aminoglycosides alone. These combinations were proven to produce at least partially active fulllength p53, as shown by the suppression of cell growth and the induction of cell death. In parallel, chemical library screenings led to the discovery of two novel compounds, C47 and C61, showing readthrough activity and synergizing with G418 and eRF3 degraders CC-885 and CC-90009, respectively. Remarkably, C47 also exhibit readthrough activity for nonsense mutant phosphatase and tensin homolog (PTEN), expanding the scope for targeted cancer therapies. Furthermore, we have identified the 5-fluorouracil (5-FU) metabolite 5-Fluorouridine (FUr) as a potent readthrough-inducing compounds capable restoring full-length p53 expression in cells harboring nonsense mutant TP53. In vivo studies further substantiated the capability of FUr to reinstate full-length p53 expression in human tumor xenografts with TP53 R213X nonsense mutations. Finally, the first Trp53 R210X nonsense mutant knock-in mouse model has been generated. R210X corresponds to human TP53 R213X. Observations on tumor development, lifespan and other phenotypic traits in these mice provide valuable insights into the impact of TP53 nonsense mutation in a multi-organ system. These results also provide a platform for the preclinical evaluation of novel therapeutic strategies for targeting nonsense mutant TP53.

In summary, these findings offer a multi-faceted approach towards understanding TP53 nonsense mutations and advancing targeted cancer therapy through pharmacological induction of translational readthrough. The discovery of novel readthrough inducing compounds, the application of combination therapy in translational readthrough, the discovery of a novel therapeutic application for 5- FU and its metabolite FUr, as well as the generation of a novel animal model collectively set the stage for the further development of personalized treatments for patients with tumors harboring nonsense mutant TP53.

List of scientific papers

I. Synergistic rescue of nonsense mutant tumor suppressor p53 by combination treatment with aminoglycosides and Mdm2 inhibitors. Meiqiongzi Zhang*, Angelos Heldin*, Mireia Palomar-Siles, Susanne Öhlin, Vladimir J. N. Bykov and Klas G. Wiman. Frontiers in Oncology. (2018), 7:323. *Authors contributed equally.
https://doi.org/10.3389/fonc.2017.00323

II. Novel compounds that synergize with aminoglycoside G418 or eRF3 degraders for translational readthrough of nonsense mutant TP53 and PTEN. Angelos Heldin, Matko Cancer*, Mireia Palomar-Siles*, Meiqiongzi Zhang, Susanne Öhlin, Anna Mariani, Alexander Sun-Zhang, Jianping Liu, Vladimir J.N. Bykov and Klas G. Wiman. RNA Biology. (2023), 20:368. *Authors contributed equally.
https://doi.org/10.1080/15476286.2023.2222250

III. Translational readthrough of nonsense mutant TP53 by mRNA incorporation of 5-Fluorouridine. Mireia Palomar-Siles, Angelos Heldin, Meiqiongzi Zhang, Charlotte Strandgren, Viktor Yurevych, Jip T. van Dinter, Sem A. G. Engels, Damon A. Hofman, Susanne Öhlin, Birthe Meineke, Vladimir J. N. Bykov, Sebastiaan van Heesch and Klas G. Wiman. Cell Death & Disease. (2022), 13:997.
https://doi.org/10.1038/s41419-022-05431-2

IV. A novel tumor-prone mouse model harboring the Trp53R210X nonsense mutation. Charlotte Strandgren, Angelos Heldin, Susanne Öhlin and Klas G. Wiman. [Manuscript]