Abstract 5616: Targeting the DNA damage response sensor replication protein A for first in class cancer therapy
Authors: Pawelczak Katherine , VanderVere-Carozza Pamela , Jordan Matthew , Turchi John 
Published: March 2024

Abstract
The DNA Damage Response (DDR) is an integrated network of DNA repair and cell signaling pathways that are critical towards maintaining genomic stability. The most successful DDR targeted therapies inhibit the DNA damage sensor, PARP, a protein that recognizes single strand DNA (ssDNA) breaks as well as other DNA secondary structures induced by single strand gaps that can initiate chromosome instability and cell death. Building on the initial clinical success of PARP inhibitors, development of DDR targeted therapeutics has become increasingly popular, however, the clinical outcomes with these therapeutics have not met expectations and thus a new approach to targeting the DDR pathway is needed. NERx Biosciences has developed a novel strategy of targeting the DDR by intervening upstream of the DDR kinases and targeting specific DDR sensors. The human ssDNA binding protein, replication protein A (RPA), is a critical sensor for the DDR, serving to sense the ssDNA at replication forks that arise from replication stress (RS) and is a novel target for cancer therapy. We have discovered, developed, and characterized a novel small molecule RPA inhibitor (RPAi) NERx-329 that blocks the RPA-DNA interaction and elicits a state of chemical RPA exhaustion that results in in vivo anticancer activity. Extensive chemical optimization enabled in vitro and in vivo analyses to elucidate mechanism of action, cellular engagement, and therapeutic activity of RPA-targeted agents. Biochemical reconstitution of the ATR signaling pathway shows that NERx-329 disrupts ATR kinase activity, further suggesting a novel mechanism of action driven by RPA inhibition induced replication catastrophe. In vivo analysis reveals activity in a series of lung and ovarian patient derived xenograft models of human cancer. Single agent activity results in a tumor growth delay, which can be enhanced in combination therapy with DDR inhibitors as well as traditional DNA damaging cancer therapeutics. Data demonstrate that tumor growth observed in vivo is a function of NERx329 bioavailability and not development of a specific resistance mechanism. In an effort to identify formulations effective in enhancing oral bioavailability, we have pursued the development of Spray-dried dispersions (SDD). PK analysis reveal a dose-dependent substantial increase in CMAX and AUC, allowing for optimal dosing regimens for efficacy and safety studies. In addition, specific genetic predictors of RPAi sensitivity have been identified and results demonstrate specific genetic alterations increase RPAi activity in vitro and in vivo. NERx-329 represents the first clinically viable agent to target the DDR pathway by disrupting the RPA-DNA interaction and holds the potential for significant impact in cancer treatment.
Citation Format: Katherine Pawelczak, Pamela VanderVere-Carozza, Matthew Jordan, John Turchi. Targeting the DNA damage response sensor replication protein A for first in class cancer therapy [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(6_Suppl):Abstract nr 5616.