Abstract C102: mRNA-mediated restoration of BRCA-1 tumor suppressor function prevents tumor growth and reverses resistance to PARP inhibitors in triple-negative breast cancers
Authors: DIVITA Gilles , Grunenberger Audrey , Cabrera Léa , Durany Nathalie , Boularache Khadidja , Josserand Veronique , Desai Neil 
Published: December 2023

Abstract
BRCA1 and BRCA2 proteins are involved in the repair of DNA damage such as double-strand breaks during S and G2 phases, by intervening in homologous recombination (HR) steps. Breast cancers arising from BRCA-1 mutation carriers, up to 10% BC, are associated with a lack of expression and/or function of BRCA-1 protein, which induces genomic instability. Considering the major role of BRCA1 gene in DNA repair process, therapeutic approaches using cytotoxic agents such as the platinum and PARP inhibitors are used as treatments. However, hypersensitivity to PARPi is limited in the clinic by acquired resistance after restoration of HR. We have developed a new potent strategy combining mRNAs with a tumor selective nanocarrier, to selectively rescue BRCA-1 functions and restore PARPi sensitivity, as potential therapeutic approach in cancers. ADGN-technology is based on short amphipathic peptides that form stable neutral nanoparticles with mRNA. ADGN-901, -902 , -903 nanoparticles containing mRNA derived from BRCA-1 were evaluated on breast cancer cells, harboring different BRCA-1 deletion and mutations. Cell proliferation, cell cycle level and apoptosis activation were determined by flow cytometry and Tunel assay. BRCA-1 and RAD51 protein levels were evaluated by western blot. Sensitivity to Veliparib (PARPi) following ADGN-mRNA treatment was evaluated on PARPI resistance and PARPi sensitive cells. The recruitment of RAD51 to sites of double stranded DNA break was quantified by immunofluorescence. In-vivo efficacy of IV-administered ADGN-BRCA NPs (2.0 mg/kg) was evaluated on breast (HCC1937-BRCA-1 deficient, PARPi resistant) cancer mouse xenografts. We have selected specific mRNA sequences encoding for different domains of BRCA-1 protein. We showed than ADGN-901 mediated rescue of BRCA-1 wild type expression inhibits the proliferation of BRCA-1 deficient cell lines from 20 to 60% depending on the type of BRCA-1 alterations. ADGN-902, specifically reduces the proliferation of cells expressing N-terminal truncated BRCA-1, by 50 to-60% and ADGN-903 markedly delay (&gt;60%) the growth of all cells harboring defect in BRCA-1. In contrast, no significant cytotoxicity related to vehicle was observed. ADGN-901 and ADGN-903 resensitize the resistant cells to PARPi Veliparib inhibition. We demonstrated that the expression of domain of BRCA-1 encoded by ADGN-903 mRNA, appears to prevent RAD51 recruitment to the damage site by reducing RAD51 protein level as well as formation of RAD51 foci following irradiation. Intravenous-administration ADGN-901 and ADGN-903 (2.0mg/kg) prevented HCC-1937 tumor growth. ADGN-901 reduced tumor growth by 95% and ADGN-903 resulted in a tumor regression of 50%. ADGN-901 and ADGN-903 treatments are well tolerated, without inducing clinical toxicity. ADGN-BRCA nanoparticles are effective in rescuing BRCA-1 functions in Breast cancer cells. Our study provides a proof-of-concept that restoration of the expression of the wild type form of BRCA-1 could be combined together with PARP inhibition for potent combinatorial cancer treatment.
Citation Format: Gilles DIVITA, Audrey Grunenberger, Léa Cabrera, Nathalie Durany, Khadidja Boularache, Veronique Josserand, Neil Desai. mRNA-mediated restoration of BRCA-1 tumor suppressor function prevents tumor growth and reverses resistance to PARP inhibitors in triple-negative breast cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C102.