Resistance to therapy caused by intragenic deletion in BRCA2

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Abstract

Cells with loss of BRCA2 function are defective in homologous recombination (HR) and are highly sensitive to inhibitors of poly(ADP-ribose) polymerase (PARP)1,2, which provides the basis for a new therapeutic approach. Here we show that resistance to PARP inhibition can be acquired by deletion of a mutation in BRCA2. We derived PARP-inhibitor-resistant (PIR) clones from the human CAPAN1 pancreatic cancer cell line, which carries the protein-truncating c.6174delT frameshift mutation. PIR clones could form DNA-damage-induced RAD51 nuclear foci and were able to limit genotoxin-induced genomic instability, both hallmarks of a competent HR pathway. New BRCA2 isoforms were expressed in the resistant lines as a result of intragenic deletion of the c.6174delT mutation and restoration of the open reading frame (ORF). Reconstitution of BRCA2-deficient cells with these revertant BRCA2 alleles rescued PARP inhibitor sensitivity and HR deficiency. Most of the deletions in BRCA2 were associated with small tracts of homology, and possibly arose from error-prone repair caused by BRCA2 deficiency3,4. Similar ORF-restoring mutations were present in carboplatin-resistant ovarian tumours from c.6174delT mutation carriers. These observations have implications for understanding drug resistance in BRCA mutation carriers as well as in defining functionally important domains within BRCA2.

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Figure 1: PIR CAPAN1 clones.
Figure 2: BRCA2 expression in PIR clones.
Figure 3: Expression of new mutant BRCA2 isoforms restores KU0058948 resistance and increases HR in BRCA2 deficient cells.
Figure 4: Identification of BRCA2 ORF-restoring mutations in carboplatin-resistant tumours in BRCA2 c.6174delT mutation carriers.

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Acknowledgements

We thank M. Jasin and N. Siaud for providing the VC8-DR-GFP cell line, G. Smith and N. Martin for the provision of KU0058948, and S. Swift, A. Smith and K. Savage for technical support. This work was funded by Breakthrough Breast Cancer and Cancer Research UK. S.L.E. is a C. J. Martin Fellow and is supported by the National Health and Medical Research Council of Australia.

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Correspondence to Alan Ashworth.

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Competing interests

Authors A.A. and C.J.L. are inventors on patents held jointly with KuDOS/AstraZeneca relating to the use of PARP inhibitors. They may benefit financially from these under the Institute of Cancer Research’s Rewards to Inventors scheme.

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Edwards, S., Brough, R., Lord, C. et al. Resistance to therapy caused by intragenic deletion in BRCA2. Nature 451, 1111–1115 (2008) doi:10.1038/nature06548

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