# Defining the Roles of BRCA2 and RAD51 in PARPi Response

> **NIH NIH R01** · YALE UNIVERSITY · 2024 · $69,049

## Abstract

PROJECT SUMMARY
PARP inhibitors (PARPi) hold tremendous therapeutic potential because of their selectivity for cells lacking
functional BRCA1, BRCA2, and other homology-directed repair (HDR) genes. However, as with other targeted
therapies, resistance to PARPi frequently arises, underscoring the unmet need to elucidate how PARPi cause
cell death in BRCA mutant but not normal cells. Individual PARPi may act through distinct mechanisms, either
by “trapping” PARP-DNA complexes, or by inhibiting repair of single-stranded (ssDNA) nicks that are
subsequently converted to double-stranded breaks (DSBs). Moreover, patients may exhibit differential drug
sensitivity depending on the specific causative BRCA gene mutation. Defining this fundamental landscape will
be critical to better predict responders/non-responders as well as the durability of patient response to PARPi.
Historically, a detailed, mechanistic study of how mutations in BRCA2 influence genome integrity has been
hampered by the immense challenge of manipulating and purifying this large protein. Recently, we have
overcome these challenges, allowing us to leverage a combination of in vitro biochemical assays and cellular
assays to pinpoint how individual pathogenic or targeted mutations influence specific functionalities including:
DNA binding, replication fork protection, RAD51 nucleoprotein filament formation, and RAD51-mediated DNA
strand invasion. In addition to applying these techniques to interrogate the explicit biochemical function(s)
compromised by pathogenic BRCA2 mutations, we will assess sensitivity to PARPi with strong, intermediate,
or weak trapping activity (e.g. Talazoparib, Olaparib, and Veliparib, respectively). Lastly, we will investigate the
function(s) reconstituted by “reversion” mutations identified in patients with PARPi-resistant tumors, which may
independently identify functional attributes necessary for PARPi sensitivity. Our long-term goal is to unveil the
molecular consequences of PARPi treatment that necessitate processing by BRCA2, RAD51, and other HDR
proteins. Our central hypothesis is that by elucidating how BRCA2 and RAD51 mechanistically overcome
PARPi-mediated toxicity, we will provide the necessary framework to understand how PARPi resistance can
develop in patients. Our hypothesis is based on compelling preliminary data illustrating the specific functions
of BRCA2 and RAD51 in response to PARPi. Thus, our rationale, to reveal the mechanism(s) that underlie
PARPi-mediated toxicity, will vertically advance knowledge surrounding the HDR response to PARPi, and
ultimately, improve clinical management of BRCA patients. In aim 1, we will utilize patient derived BRCA2
reversion alleles in our isogenic human cell models to interrogate what specific function(s) have been
“reactivated” to promote resistance to PARPi. In aim 2, we will determine how BRCA2 and RAD51 catalyze
the removal or bypass of PARPi trapped lesions using purified proteins and relevant model DNA sub...

## Key facts

- **NIH application ID:** 10977463
- **Project number:** 3R01CA270788-03S1
- **Recipient organization:** YALE UNIVERSITY
- **Principal Investigator:** Ryan Brown Jensen
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $69,049
- **Award type:** 3
- **Project period:** 2022-06-07 → 2025-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10977463

## Citation

> US National Institutes of Health, RePORTER application 10977463, Defining the Roles of BRCA2 and RAD51 in PARPi Response (3R01CA270788-03S1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10977463. Licensed CC0.

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