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Park PH , Yamamoto TM , Li H , Alcivar AL , Xia B , Wang Y , Bernhardy AJ , Turner KM , Kossenkov AV , Watson ZL , Behbakht K , Casadei S , Swisher EM , Mischel PS , Johnson N , Bitler BG
Amplification of the mutation-carrying BRCA2 allele promotes RAD51 loading and PARP inhibitor resistance in the absence of reversion mutations
Mol Cancer Ther. 2020 Feb 1;19(2) :602-613
PMID: 31575654    PMCID: PMC7007853    URL: https://www.ncbi.nlm.nih.gov/pubmed/31575654
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Patients harboring germline Breast Cancer susceptibility genes 1 and 2 (BRCA1/2) mutations are predisposed to developing breast, pancreatic, and ovarian cancers. BRCA2 plays a critical role in homologous recombination DNA repair and deleterious mutations in BRCA2 confer sensitivity to poly(ADP-ribose) polymerase (PARP) inhibition. Recently, the PARP inhibitors olaparib and rucaparib were FDA approved for the treatment of metastatic breast cancer and recurrent ovarian cancer patients with mutations in BRCA1/2. Despite their initial anti-tumor activity, the development of resistance limits the clinical utility of PARP inhibitor therapy. Multiple resistance mechanisms have been described, including reversion mutations that restore the reading frame of the BRCA2 gene. In this study, we generated olaparib and rucaparib resistant BRCA2 mutant Capan1 cell lines. We did not detect secondary reversion mutations in the olaparib or rucaparib resistant clones. Several of the resistant clones had gene duplication and amplification of the mutant BRCA2 allele, with a corresponding increase in expression of a truncated BRCA2 protein. In addition, homologous recombination (HR)-mediated DNA repair was rescued, as evidenced by the restoration of RAD51 foci formation. Using mass spectrometry, we identified Disruptor Of Telomeric silencing 1-Like (DOT1L), as an interacting partner of truncated BRCA2. RNA-interference-mediated knockdown of BRCA2 or DOT1L was sufficient to re-sensitize cells to olaparib. The results demonstrate that independent of a BRCA2 reversion mutation amplification of a mutant-carrying BRCA2 contributes to PARP inhibitor resistance.
1538-8514 Park, Pyoung Hwa Yamamoto, Tomomi M Li, Hua Alcivar, Allen L ORCID: https://orcid.org/0000-0001-6251-5016 Xia, Bing Wang, Yifan Bernhardy, Andrea J Turner, Kristen M Kossenkov, Andrew V Watson, Zachary L ORCID: https://orcid.org/0000-0001-9425-1449 Behbakht, Kian Casadei, Silvia ORCID: https://orcid.org/0000-0003-2619-5662 Swisher, Elizabeth M ORCID: https://orcid.org/0000-0003-2331-0434 Mischel, Paul S Johnson, Neil Bitler, Benjamin G Journal Article United States R00 CA194318/CA/NCI NIH HHS/ P30 CA010815/CA/NCI NIH HHS/ R50 CA211199/CA/NCI NIH HHS/ R01 CA214799/CA/NCI NIH HHS/ P30 CA046934/CA/NCI NIH HHS/ Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. Mol Cancer Ther. 2020 Feb;19(2):602-613. doi: 10.1158/1535-7163.MCT-17-0256. Epub 2019 Oct 1