TITLE:
The PARP-1 Inhibitor Olaparib Causes Retention of γ-H2AX Foci in BRCA1 Heterozygote Cells Following Exposure to Gamma Radiation
AUTHORS:
Emma C. Bourton, Piers N. Plowman, Amanda J. Harvey, Sheba Adam Zahir, Christopher N. Parris
KEYWORDS:
BRCA1; BRCA2; Heterozygote; Radiosensitivity; PARP Inhibitor; Gamma-H2AX; Imaging Flow Cytometry
JOURNAL NAME:
Journal of Cancer Therapy,
Vol.4 No.11A,
December
17,
2013
ABSTRACT:
A novel treatment for
cancer patients with homozygous deletions of BRCA1 and BRCA2 is to use
drugs that inhibit the enzyme poly(ADP-ribose) polymerase (PARP). Specific
inhibition of PARP-1 can induce synthetic lethality in irradiated cancer cells
while theoretically leaving normal tissue unaffected. We recently demonstrated
in a cell survival assay that lymphoblastoid cells with mono-allelic mutations
of BRCA1 were hypersensitive to gamma
radiation in the presence of the PARP-1 inhibitor Olaparib compared to normal
cells and mono-allelic BRCA2 cells. To determine if the enhanced
radiation sensitivity was due to a persistence of DNA strand breaks, we
performed γ-H2AX foci analysis in cells derived
from two normal individuals, three heterozygous BRCA1 and three heterozygous BRCA2
cell lines. Cells were exposed to 2 Gy gamma radiation in the presence or
absence of 5 μM Olaparib. Using immunofluorescence and imaging flow cytometry, foci were
measured in untreated cells and at 0.5, 3, 5 and 24 hours post-irradiation. In
all lymphoblastoid cells treated with 2 Gy gamma radiation, there was a
predictable induction of DNA strand breaks, with a modest but significant retention
of foci over 24 hours in irradiated cells treated with Olaparib (ANOVA P , in mono-allelic BRCA1 cells, there was a failure to fully repair
DNA double-strand breaks (DSB) in the presence of Olaparib, evidenced by a
significant retention of foci at 24 hours’ post irradiation (t-Test P These data show that the cellular
hypersensitivity of mono-allelic BRCA1
lymphoblastoid cells to gamma radiation in the presence of the Olaparib is due
to the retention of
DNA DSB. These data may indicate that patients with inherited mutations in the BRCA1 gene treated with radiotherapy
and PARP-1 inhibitors may experience elevated radiation-associated normal
tissue toxicity.