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Parsels LA, Karnak D, Parsels JD, Zhang Q, Vélez-Padilla J, Reichert ZR, Wahl DR, Maybaum J, O'Connor MJ, Lawrence TS, Morgan MA. PARP1 Trapping and DNA Replication Stress Enhance Radiosensitization with Combined WEE1 and PARP Inhibitors. Mol Cancer Res 2017; 16:222-232. [PMID: 29133592 DOI: 10.1158/1541-7786.mcr-17-0455] [Citation(s) in RCA: 91] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Revised: 10/30/2017] [Accepted: 11/06/2017] [Indexed: 12/21/2022]
Abstract
KRAS mutations in non-small cell lung cancer (NSCLC) cause increased levels of DNA damage and replication stress, suggesting that inhibition of the DNA damage response (DDR) is a promising strategy for radiosensitization of NSCLC. This study investigates the ability of a WEE1 inhibitor (AZD1775) and a PARP inhibitor (olaparib) to radiosensitize KRAS-mutant NSCLC cells and tumors. In addition to inhibiting the DDR, these small-molecule inhibitors of WEE1 and PARP induce DNA replication stress via nucleotide exhaustion and PARP trapping, respectively. As monotherapy, AZD1775 or olaparib alone modestly radiosensitized a panel of KRAS-mutant NSCLC lines. The combination of agents, however, significantly increased radiosensitization. Furthermore, AZD1775-mediated radiosensitization was rescued by nucleotide repletion, suggesting a mechanism involving AZD1775-mediated replication stress. In contrast, radiosensitization by the combination of AZD1775 and olaparib was not rescued by nucleosides. Whereas both veliparib, a PARP inhibitor that does not efficiently trap PARP1 to chromatin, and PARP1 depletion radiosensitized NSCLC cells as effectively as olaparib, which does efficiently trap PARP, only olaparib potentiated AZD1775-mediated radiosensitization. Taken together, these mechanistic data demonstrate that although nucleotide depletion is sufficient for radiosensitization by WEE1 inhibition alone, and inhibition of PARP catalytic activity is sufficient for radiosensitization by olaparib alone, PARP1 trapping is required for enhanced radiosensitization by the combination of WEE1 and PARP inhibitors.Implications: This study highlights DNA replication stress caused by nucleotide depletion and PARP1 trapping as an important mechanism of radiosensitization in KRAS-mutant tumors and supports further development of DNA replication as a therapeutic target. Mol Cancer Res; 16(2); 222-32. ©2017 AACR.
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Affiliation(s)
- Leslie A Parsels
- Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, Michigan
| | - David Karnak
- Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Joshua D Parsels
- Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Qiang Zhang
- Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, Michigan
| | | | - Zachery R Reichert
- Department of Hematology and Oncology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Daniel R Wahl
- Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Jonathan Maybaum
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Mark J O'Connor
- Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Cambridge, United Kingdom
| | - Theodore S Lawrence
- Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Meredith A Morgan
- Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, Michigan.
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