Abstract 514: Potentiation ofPARP inhibitor activity in <i>BRCA</i> -wildtype breast cancer cell lines by 2-hydroxyflavanone.

Abstract Background: 2-hydroxyflavanone (2HF) is citrus derived compound which has demonstrated in vitro anticancer activity against multiple malignancies. Its presence inhibits RLIP, a protein encoded by RALBP1 gene which functions as an ATP dependent efflux pump for glutathione-electrophile conjugates, oxidative and alkylating intermediates and, mediates epidermal growth factor receptor endocytosis. Thus RLIP promotes oncogenesis with growth modulation and ability to resist chemotherapy with glutathione mediated xenobiotic efflux. Reduced RLIP expression by 2HF reduces spontaneous carcinogenesis in p53 null mouse models, indicating its utility in tumors with DNA repair-deficiency. BRCA1, BRCA2, and PALB2 are the pivotal genes involved in homologous recombination (HR) mutation which can be targeted by poly(ADP-ribose) polymerase pathway (PARP) inhibitors. Through this study we assessed the effects of PARP inhibitor AZD2461 alone and in combination with 2HF on cell viability of MDA-MB-231 and MCF-7 breast cancer cell lines. Methods: Expression of mRNA of BRCA1, BRCA2 and PALB2 genes was assessed in MDA-MB-231 (triple negative) and MCF-7 (ER+) breast cancer cell lines after exposure to 2HF and LNA by using quantification cycle in Polymerase chain reaction. LDH release at 72 hours was measured and compared with controls in cells treated with 2HF or AZD2461 alone or in combination. Cytotoxicity was measured using absorbance of reduced WST-8 produced by the viable cells. Results: RLIP depletion by 2HF reduced the expression of mRNA of HR genes BRCA1, BRCA2, and PALB2 to 2% - 20% of the level of untreated controls. PARP inhibitor induced LDH release with incremental dose of 2HF at 10, 20 and 40 µM, with greatest cytotoxic effects at 40 µM 2HF (p &amp;lt; 0.001). Addition of 2HF to PARP inhibitor AZD2461 increased cell lysis in MCF-7 and MDA-MB-231 cells, however only diminished cell viability in MCF-7 but not in MDA-MB-231. Discussion: PARP inhibitors are very effective in tumors with HRD mutation, however their utility is limited in subjects with mutations involving non HRD pathways. RALBP1 inhibition with 2HF decreases the expression of gene involved in HR pathway thus stimulating a transcriptomic environment that is similar to HRD mutated cells. 2HF could thus sensitize BRCA-wildtype ER+ and possibly triple negative breast cancers to PARP inhibitors. This potentially has clinical application among patients who may benefit from PARP inhibitors outside of current indications such as BRCA or HRD deficient mutations. Through this work, we look forward to inspire more work on clinical exploration of 2HF with PARP inhibitors. Citation Format: Harshit Khosla, Sharda P. Singh, Chhanda Bose, Sharad S. Singhal, Sanjay Awasthi. Potentiation ofPARP inhibitor activity in BRCA-wildtype breast cancer cell lines by 2-hydroxyflavanone [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 514.