Abstract A095: Targeting protein-DNA interactions in the DNA damage response: Lead identification and optimization for novel inhibitors of RPA and Ku
Authors: Turchi John , Pawelczak Katherine S , Gavande Navnath , VanderVere-Carozza Pamela S 
Published: March 2020

Abstract
Recent advances in our understanding of the mechanisms of the cellular response to DNA damage (DDR) have opened up an exciting array of opportunities to treat human cancer. The majority of drug discovery efforts have focused on the DDR kinases, ATM, ATR and DNA-PK, each of which is activated in response to different types of DNA damage or genomic perturbations. We have taken the novel approach of drugging this pathway by targeting the DNA binding proteins Replication protein A (RPA) and Ku, which are required to activate the ATR and DNA-PK kinases, respectively. Chemical inhibition of the DNA binding activity functionally abrogates kinase activity and provides a novel mechanism by which DDR kinases can be blocked. The identification of a potent inhibitor of the Ku-DNA interactions was gleaned from a specificity screen and was found to effectively block the Ku-DNA interaction and this inhibits DNA-PK phosphorylation activity. We identified a series of moieties and optimized pharmacophore for potent and specific inhibition of Ku and demonstrate cellular inhibition of Ku DNA binding and DNA-PK activity. Third generation Ku inhibitors were developed to optimize for cellular bioavailability and are able to sensitize cells to DNA double strand break inducing agents, consistent with the role of DNA-PK in the non-homologous end joining repair pathway. We initially identified a series of RPA-DNA interaction inhibitors from an in vitro high throughput screen. Extensive SAR was conducted to optimize for potency, specificity and physicochemical properties and led to the promotion of a lead candidate. We have determined the mechanism of action for single agent anti-cancer activity and combination activity involves chemical exhaustion of RPA. In vivo analysis of the lead candidate in pre-clinical models of lung and ovarian cancer has led to the advancement of a clinical candidate and represent a first in class RPA inhibitor poised for clinical advancement. Together, these data demonstrate the ability to chemically target structure specific protein-DNA interactions. The molecules synthesized to inhibit these interactions share some common features, but can be optimized to obtain high potency and specificity. In addition, chemical modifications can be employed to allow cellular and in vivo bioavailability while retaining potent inhibitory activity. These data reveal the potential to target a new range of macromolecular interactions to expand the anticancer armamentarium to protein-DNA interactions.
Citation Format: John Turchi, Katherine S Pawelczak, Navnath Gavande, Pamela S VanderVere-Carozza. Targeting protein-DNA interactions in the DNA damage response: Lead identification and optimization for novel inhibitors of RPA and Ku [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A095. doi:10.1158/1535-7163.TARG-19-A095