Abstract 658: Triple-negative breast cancer sensitization to anti-metabolite chemotherapy utilizing PARP inhibiting olaparib

Abstract Triple Negative Breast Cancer (TNBC) is one of the most aggressive breast cancer subtypes as it grows faster than typical invasive carcinoma, leading to poor prognosis and an increased chance of recurrence. It lacks three key hormone receptors, estrogen, progesterone, and HER2 receptors, eliminating the efficacy of receptor-targeted therapies. The first line of treatment is the use of combination chemotherapies given at Maximum Tolerated Dosage (MTD) but this typically leads to higher toxicity and systemic side effects. We investigate Olaparib (OLA) and Gemcitabine (GEM) as a dual chemotherapy. OLA is an FDA-approved PARP inhibitor, facilitating single-stranded DNA breakage by preventing PARP from replacing excised nucleotides. GEM is an anti-metabolite that prevents cancerous cells from continuing mitosis and increasing apoptosis by taking the place of the nucleotide cytidine in the DNA during replication, leading to cell cycle arrest. We propose sensitizing TNBC to GEM by using OLA at lower doses than MTD while causing significant TNBC tumor cell death compared to the drug alone.We used EO771 cells (syngeneic to C57BL/6 mice) to evaluate GEM and OLA. Cells (100, 000/well) were plated in 24-well plates and treated with 0, 10, or 30 nM GEM, OLA, or combinations thereof. Crystal violet staining was used to visualize viable cells, which were quantified by absorbance at 550 nm. RNA extracted from 500, 000 cells/well in 6-well plates was analyzed via qPCR for stress and cytokine-related gene expression. GEM at 30 nM was more effective than at 10 nM, especially in combination with OLA (10 or 30 nM). Phase-contrast microscopy revealed significant cytotoxicity and cellular detachment with combined treatments, particularly GEM30/OLA10 and GEM30/OLA30. GEM 30/OLA 10 and GEM 30/OLA 30 showed the most significant cell death in response to combined chemotherapy. GEM 30/OLA 10 interestingly exhibited a slightly lower cell viability percentage than GEM 30/OLA 30. GEM30/OLA10 was the most effective combination tested, reducing TNF-α expression and cell viability while minimizing toxicity. The dual combinations suggest that GEM effectively disrupts DNA synthesis and drives single-stranded breakage. Future studies should include in vivo analyses of the tumor microenvironment, ELISAs for protein validation, and additional cell viability assays, such as MTT or XTT, to confirm these findings. Citation Format: Joshua C. Doloff, Amanda Rakoski, Abigail Yoo. Triple-negative breast cancer sensitization to anti-metabolite chemotherapy utilizing PARP inhibiting olaparib. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 658.