Targeting Ribonucleotide Reductase to Overcome Olaparib Resistance in TNBC
Poster Number
16A
Faculty Mentor Name
Jesika S Faridi
Research or Creativity Area
Health Sciences
Abstract
Breast cancer is the second leading cause of cancer-related death worldwide. Triple-negative breast cancer (TNBC) is particularly one of the most aggressive and therapeutically challenging subtypes due to the absence of hormone receptors (estrogen and progesterone receptors) and HER2 expression. PARP (Poly ADP polymerase) inhibitors, such as olaparib, exhibit clinical efficacy in BRCA 1/2 mutated TNBC patients by causing synthetic lethality through DNA repair mechanisms. However, the emergence of resistance to Olaparib significantly limits its long-term therapeutic benefit. Ribonucleotide reductase (RR), the rate-limiting enzyme that converts ribonucleotides into deoxyribonucleotides for DNA synthesis, plays a critical role in cell proliferation. Notably, the RRM2 subunit of RR is upregulated in TNBC and has been implicated in acquired drug resistance. Didox (3,4-dihydroxybenzohydroxamic acid), an RR inhibitor with iron-chelating and free radical scavenging properties, represents a potential strategy to target this resistance mechanism.
Purpose
This study investigates whether the inhibition of RRM2 using Didox can improve Olaparib efficacy and alleviate the resistance in TNBC models. We hypothesize that combining Didox with Olaparib will deplete intracellular deoxyribonucleotide (dNTP) pools, increase replication stress, and potentiate DNA damage. To test this, four TNBC cell lines (MDA-MB-231, MDA-MB-468, MDA-MB-436, and HCC1937), representing both BRCA wild-type and BRCA-mutant backgrounds, were utilized. Cytotoxic effects of Olaparib and Didox were assessed using MTS-based IC₅₀ determination, followed by combination index analysis using the Chou–Talalay method to evaluate potential drug synergy.
Results
MDA-MB-436 (BRCA1-mutant) cells exhibited high sensitivity to Olaparib, whereas MDA-MB-468 and MDA-MB-231 (BRCA1 wild-type) cells were relatively resistant. Didox showed moderate cytotoxicity as a single agent but significantly enhanced Olaparib sensitivity in resistant cell lines. Proliferation assays demonstrated marked synergistic effects following 7 days of combination treatment. Western blot analyses revealed that PARP inhibition induced DNA damage stress and upregulated RRM2 expression, suggesting a compensatory survival mechanism. Furthermore, combined treatment with Didox and Olaparib resulted in increased markers of DNA damage, indicating that RRM2 inhibition augments PARP inhibitor efficacy in TNBC models. Importantly, the differential sensitivity across cell lines highlights both responsive and resistant phenotypes.
Significance
This study aims at a novel combinatorial therapeutic strategy targeting RRM2 to overcome PARP inhibitor resistance in TNBC. By demonstrating that Didox enhances Olaparib efficacy through increased replication stress and DNA damage, these findings offer a mechanistic rationale for dual targeting of DNA repair and nucleotide synthesis pathways.
Location
University of the Pacific, DeRosa University Center
Start Date
24-4-2026 11:00 AM
End Date
24-4-2026 2:00 PM
Targeting Ribonucleotide Reductase to Overcome Olaparib Resistance in TNBC
University of the Pacific, DeRosa University Center
Breast cancer is the second leading cause of cancer-related death worldwide. Triple-negative breast cancer (TNBC) is particularly one of the most aggressive and therapeutically challenging subtypes due to the absence of hormone receptors (estrogen and progesterone receptors) and HER2 expression. PARP (Poly ADP polymerase) inhibitors, such as olaparib, exhibit clinical efficacy in BRCA 1/2 mutated TNBC patients by causing synthetic lethality through DNA repair mechanisms. However, the emergence of resistance to Olaparib significantly limits its long-term therapeutic benefit. Ribonucleotide reductase (RR), the rate-limiting enzyme that converts ribonucleotides into deoxyribonucleotides for DNA synthesis, plays a critical role in cell proliferation. Notably, the RRM2 subunit of RR is upregulated in TNBC and has been implicated in acquired drug resistance. Didox (3,4-dihydroxybenzohydroxamic acid), an RR inhibitor with iron-chelating and free radical scavenging properties, represents a potential strategy to target this resistance mechanism.
