Defining the role of persistent DNA bridges in tumor-intrinsic immune activation in hereditary breast and ovarian cancer - PROJECT SUMMARY
Chromosome segregation errors such as persistent DNA bridges accelerate genome instability, a hallmark of
cancer. These toxic DNA lesions occur at a higher frequency in hereditary breast and ovarian cancer (HBOC)
cells with DNA repair deficiencies, and thus defective genome maintenance. PARP inhibitors (PARPi) cause
targeted tumor cell death in BRCA-mutant HBOC and have been suggested to further increase the frequency of
DNA bridges in cultured BRCA-mutant cells. Despite the therapeutic promise of PARPi, BRCA-deficient cancers
develop acquired resistance to this therapy. Recent studies show that immunotherapies can prevent or delay
PARPi resistance in HBOC tumors; however, the mechanisms by which PARPi synergizes with immunotherapies
remain poorly defined. My preliminary data shows that PARPi treatment leads to coating of persistent DNA
bridges with the innate immune DNA sensor cGAS in BRCA-mutant cells, which coincides with increased type I
interferon signaling. I hypothesize that PARPi-induced persistent DNA bridges are central to the mechanism of
PARPi cytotoxicity and synergy with immunotherapies, therefore requiring rigorous further study to identify
strategies that maximize the therapeutic potential of PARPi treatment in DNA repair-deficient tumors. The
overall objective of this proposal is to thus define the mechanisms by which PARPi-induced persistent
DNA bridges lead to tumor-intrinsic immune activation in HBOC. The proposed research will investigate
this objective in two specific aims. Aim 1 will define the structure and nuclear integrity of PARPi-induced
persistent bridges by use of transposase-mediated fluorescence imaging, immunofluorescence, live-cell
imaging, and correlative light and electron microscopy. How these factors affect cGAS-STING activation will be
assessed using immunoblotting, RT-qPCR, and enzyme immunoassays. Aim 2 will establish persistent DNA
bridges and bulky anaphase bridges as potential predictive biomarkers that reflect DNA repair defects,
chromosome segregation failure, and subsequent cGAS-STING activation in PARPi olaparib-treated BRCA-
mutant breast cancer. I will leverage digital images of hematoxylin and eosin (H&E)-stained samples and perform
immunohistochemistry staining on a tissue microarray of de-identified, paired clinical samples before and during
olaparib treatment, which will be interrogated in the context of ongoing phospho-STING staining. Defining the
interplay between chromosomal instability-driven immune activation and tumor response to PARPi will be a first
step towards improved HBOC treatment. This proposal will be completed in a supportive, collaborative, and
interdisciplinary environment that will allow me to perform fundamental and translational cancer biology research.
This training will advance my experimental design, rigorous data analysis, and technical skills in molecular
biology, high-resolution microscopy, and cytopathology. My training plan also provides ample opportunities to
improve oral presentation, writing, teaching, and mentorship skills to prepare me for a successful career as an
academic cancer biologist leading a research group to mentor and train the next generation of scientists.