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EBioMedicine. 2019 Jun;44:419-430. doi: 10.1016/j.ebiom.2019.05.035. Epub 2019 May 22.

The BET inhibitor JQ1 attenuates double-strand break repair and sensitizes models of pancreatic ductal adenocarcinoma to PARP inhibitors.

Author information

1
Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 1670 University Blvd, Birmingham, AL, USA.
2
Department of Pathology, Division of Anatomic Pathology, University of Alabama at Birmingham, NP3551 North Pavilion UAB Hospital, Birmingham, AL, USA; The Birmingham Veterans Administration Medical Center, 700 19(th) St S, Birmingham, AL, USA.
3
Department of Radiation Oncology, University of Alabama at Birmingham, Hazelrig Salter Radiation Oncology Center, 1700 6(th) Avenue S, Birmingham, AL, USA.
4
Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA.
5
Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 1670 University Blvd, Birmingham, AL, USA. Electronic address: kyoon@uab.edu.

Abstract

BACKGROUND:

DNA repair deficiency accumulates DNA damage and sensitizes tumor cells to PARP inhibitors (PARPi). Based on our observation that the BET inhibitor JQ1 increases levels of DNA damage, we evaluated the efficacy of JQ1 + the PARPi olaparib in preclinical models of pancreatic ductal adenocarcinoma (PDAC). We also addressed the mechanism by which JQ1 increased DNA damage.

METHODS:

The effect of JQ1 + olaparib on in vivo tumor growth was assessed with patient-derived xenograft (PDX) models of PDAC. Changes in protein expression were detected by immunohistochemistry and immunoblot. In vitro growth inhibition and mechanistic studies were done using alamarBlue, qRT-PCR, immunoblot, immunofluorescence, ChIP, and shRNA knockdown assays.

FINDINGS:

Tumors exposed in vivo to JQ1 had higher levels of the DNA damage marker γH2AX than tumors exposed to vehicle only. Increases in γH2AX was concomitant with decreased expression of DNA repair proteins Ku80 and RAD51. JQ1 + olaparib inhibited the growth of PDX tumors greater than either drug alone. Mechanistically, ChIP assays demonstrated that JQ1 decreased the association of BRD4 and BRD2 with promoter loci of Ku80 and RAD51, and shRNA data showed that expression of Ku80 and RAD51 was BRD4- and BRD2-dependent in PDAC cell lines.

INTERPRETATION:

The data are consistent with the hypothesis that JQ1 confers a repair deficient phenotype and the consequent accumulation of DNA damage sensitizes PDAC cells to PARPi. Combinations of BET inhibitors with PARPi may provide a novel strategy for treating PDAC. FUND: NIH grants R01CA208272 and R21CA205501; UAB CMB T32 predoctoral training grant.

KEYWORDS:

BET bromodomain inhibitor (BETi); DNA double-strand break repair proteins; DNA repair and damage; PARP inhibitor (PARPi); Pancreatic cancer; Patient-derived xenograft model

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