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Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy


BRCA1 and BRCA2 are important for DNA double-strand break repair by homologous recombination1, and mutations in these genes predispose to breast and other cancers2. Poly(ADP-ribose) polymerase (PARP) is an enzyme involved in base excision repair, a key pathway in the repair of DNA single-strand breaks3. We show here that BRCA1 or BRCA2 dysfunction unexpectedly and profoundly sensitizes cells to the inhibition of PARP enzymatic activity, resulting in chromosomal instability, cell cycle arrest and subsequent apoptosis. This seems to be because the inhibition of PARP leads to the persistence of DNA lesions normally repaired by homologous recombination. These results illustrate how different pathways cooperate to repair damage, and suggest that the targeted inhibition of particular DNA repair pathways may allow the design of specific and less toxic therapies for cancer.

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Figure 1: Depletion or inhibition of PARP1 selectively reduces the viability of BRCA1- and BRCA2-deficient ES cells.
Figure 2: DSB formation and repair after exposure to PARP inhibitor.
Figure 3: PARP inhibition selectively blocks the growth of BRCA2-deficient tumours in vivo.
Figure 4: A model for the selective effects of PARP inhibition on cells lacking wild-type BRCA1 and BRCA2.


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We thank Cancer Research UK, Breakthrough Breast Cancer and the Mary-Jean Mitchell Green Foundation for financial support. We thank I. Titley for help with FACS analysis, A. McCarthy and J. Williamson for help with chromosome spreads, E. Witt for western blot analysis, E. Iorns for real-time PCR analysis and M. Zdzienicka for V-C8 and V-C8 BAC cells. We also thank the Maybridge Chemical Company for their help in the design and synthesis of the PARP inhibitors.

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Correspondence to Graeme C. M. Smith or Alan Ashworth.

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Competing interests

G.C.M.S., N.M.B.M., I.H., C.K. and K.J.D. are employees of KuDOS Pharmaceuticals Ltd. S.P.J. is the scientific founder and Chief Scientific Officer of KuDOS Pharmaceuticals Ltd. A patent application has been submitted by KuDOS and the Institute of Cancer Research based on these results.

Supplementary information

Supplementary Figures S1-S4

Supplementary Figure S1 describes the novel PARP inhibitor compounds used in this study. Supplementary Figure S2 shows a clonogenic experiment illustrating the rapid and irreversible effects of PARP inhibitors. Supplementary Figure S3 describes clonogenic experiments using Chinese Hamster Ovary and MCF7 cells and PARP inhibitors. Supplementary Figure S4 shows metaphase spreads, γH2AX assays and Rad51 assays. (PPT 1258 kb)

Supplementary Data

This file contains Supplementary Table S1, Supplementary Methods, Supplementary Figure Legends and additional references. (RTF 41 kb)

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Farmer, H., McCabe, N., Lord, C. et al. Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy. Nature 434, 917–921 (2005).

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