Small-molecule inhibitor of p53 binding to mitochondria protects mice from gamma radiation

Abstract

p53-dependent apoptosis contributes to the side effects of cancer treatment, and genetic or pharmacological inhibition of p53 function can increase normal tissue resistance to genotoxic stress1,2,3,4,5,6. It has recently been shown that p53 can induce apoptosis through a mechanism that does not depend on transactivation but instead involves translocation of p53 to mitochondria7,8,9,10,11,12,13. To determine the impact of this p53 activity on normal tissue radiosensitivity, we isolated a small molecule named pifithrin-μ (PFTμ, 1) that inhibits p53 binding to mitochondria by reducing its affinity to antiapoptotic proteins Bcl-xL and Bcl-2 but has no effect on p53-dependent transactivation. PFTμ has a high specificity for p53 and does not protect cells from apoptosis induced by overexpression of proapoptotic protein Bax or by treatment with dexamethasone (2). PFTμ rescues primary mouse thymocytes from p53-mediated apoptosis caused by radiation and protects mice from doses of radiation that cause lethal hematopoietic syndrome. These results indicate that selective inhibition of the mitochondrial branch of the p53 pathway is sufficient for radioprotection in vivo.

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Figure 1: Principles of using a lentivirus-based readout system for screening inhibitors of p53-mediated apoptosis.
Figure 2: Effects of PFTμ on p53-dependent and p53-independent apoptosis.
Figure 3: Lack of effect of PFTμ on p53-dependent transactivation.
Figure 4: PFTμ interferes with p53 protein binding to mitochondria.
Figure 5: PFTμ protects mouse thymocytes (in vitro) and mice (in vivo) from gamma irradiation–induced death.

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Acknowledgements

We thank P. Chumakov, A. Almasan and M. Oren for providing recombinant constructs. This work was supported by grant CA75179 to A.V.G., CA103283 grant to Quark Biotech, Inc. and contract HHSN261200422015C to Cleveland BioLabs, Inc. from the US National Institutes of Health.

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Authors

Contributions

E.S. generated data, performed data analyses and prepared the manuscript; S.S. generated data and performed data analyses; P.G.K. generated data and performed data analyses; O.B.C. managed part of the work; I.P., I.S., D.A.B. and L.G.B. generated data; R.M.M. performed data analysis; R.S. organized the research and performed data analysis; E.A.K. generated data, performed data analyses, prepared the manuscript and organized the research; and A.V.G. performed data analyses, prepared the manuscript and managed the project overall.

Corresponding authors

Correspondence to Elena A Komarova or Andrei V Gudkov.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Effect of PFTμ (10 μM) on staurosporine-induced cell death in H1299 and HeLa cells. (PDF 91 kb)

Supplementary Fig. 2

Effect of PFTμ (0.1–10 μM) on Fas-, TNF- and staurosporine-induced apoptosis in human lung fibroblasts WI38. (PDF 91 kb)

Supplementary Fig. 3

Effect of PFTμ on TNF-induced activation of NFκB. (PDF 90 kb)

Supplementary Fig. 4

PFTμ (10 μM) does not affect the p53-mediated transactivation of promoters of Bax, Hdm2 and Cyclin G genes. (PDF 117 kb)

Supplementary Fig. 5

Lack of effect of PFTμ (10 μM) on viability of p53-null mouse thymocytes treated with 10 Gy of gamma radiation (estimated by Trypan blue uptake assay 24 h after irradiation). (PDF 90 kb)

Supplementary Fig. 6

A single intraperitoneal injection of 40 mg kg−1 of body weight of PFTμ did not change survival or dynamic of death of mice treated with 11 Gy of gamma radiation. (PDF 90 kb)

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Strom, E., Sathe, S., Komarov, P. et al. Small-molecule inhibitor of p53 binding to mitochondria protects mice from gamma radiation. Nat Chem Biol 2, 474–479 (2006). https://doi.org/10.1038/nchembio809

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