Abstract 7237: Peptide-mRNA complex mediated restoration of BRCA-1 tumor suppressor function in BRCA-1 mutated cancers as a new therapeutic strategy

Abstract BRCA1 and BRCA-2 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 (10% of BC) and from epigenetically silenced BRCA-1 (30% of sporadic BC) are associated with a lack of expression and/or function of BRCA-1, which induces genomic instability. Herein, we describe a new potent strategy combining mRNAs with a tumor selective peptide nanocarrier, to selectively rescue BRCA-1 function as potential therapeutic approach in cancers. Proprietary BRCA-1 derived mRNA were complexed with proprietary short amphipathic peptides and the resulting nanoparticles were evaluated on several breast cancer cells, harboring different BRCA-1 alterations. Sensitivity to Veliparib (PARPi) following the nanoparticle treatments were evaluated on PARPI resistant and PARPi sensitive cells. The recruitment of RAD51 to sites of double stranded DNA break was quantified by immunofluorescence. In-vivo efficacy of varying sequences of BRCA-1 mRNA-peptide nanoparticles (2. 0 mg/kg, weekly, IV; ADGN-901, -902, -903) and veliparib (50mg/kg, daily, oral) were evaluated on breast cancer (HCC1937-BRCA-1 deficient, PARPi resistant) mouse xenografts. We showed that ADGN-901 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 inhibits proliferation 60% of all cells harboring defects in BRCA-1. Interestingly, ADGN-901 and ADGN-903 were able to resensitize the PARPi resistant cells to veliparib inhibition. We demonstrated that ADGN-903 restores BRCA-1 function in homologous recombination. ADGN-903 prevents RAD51 recruitment to the damage site by reducing RAD51 protein level as well as formation of RAD51 foci following irradiation. IV administration of ADGN-901 and ADGN-903 (2. 0 mg/kg) had a strong inhibitory effect on HCC-1937 tumor growth while ADGN-902 and veliparib were inactive. ADGN-901 reduced tumor growth by 95% and ADGN-903 abolished tumor growth with strong tumor regressions. ADGN-901 and ADGN-903, were also evaluated on large tumors of about 500-600 mm3 and were highly effective in preventing further progression and achieving shrinkage of large tumors. ADGN-901 and ADGN-903 treatments are well tolerated, without inducing clinical toxicity. BRCA-1 mRNA-peptide nanoparticles are effective in rescuing BRCA-1 function and inducing tumor regressions in BRCA-1 altered breast cancer cells and tumors. Our study provides a proof-of-concept that restoration of wild type BRCA-1 expression could be a potent therapeutic strategy for BRCA-1 altered tumors whether or not they are PARPi resistant. Citation Format: Gilles Divita, Audrey Grunenberger, Léa Cabrera, Nathalie Durany, Neil Desai. Peptide-mRNA complex mediated restoration of BRCA-1 tumor suppressor function in BRCA-1 mutated cancers as a new therapeutic strategy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 7237.