Abstract 701: Preclinical data of a novel DNA-PK inhibitor in combination with radiation therapy shows promise in the treatment of established GBM and lung carcinoma cell lines

Abstract

Abstract Radiation therapy (RT) is a cornerstone of oncologic therapy for the majority of solid malignancies, and unrepaired DNA double-strand breaks are responsible for radiation-induced cytotoxicity. RT-induced DNA lesions can be repaired by multiple mechanisms including homologous recombination (HR) and non-homologous end joining (NHEJ), and disruption of either of these pathways can enhance cytotoxicity. A key component of the NHEJ pathway is the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), and loss of kinase activity can significantly increase radiosensitivity. Herein we describe the results of our medicinal chemistry campaign to develop a potent and selective DNA-PKcs inhibitor, WNC0901. WNC0901 inhibits DNA-PKcs kinase activity in a cell free system with an IC50 of 0.071 nM and demonstrated at least 30-fold higher sensitivity than other family members (ATM, ATR, mTOR, PI3K). WNC0901 has limited aldehyde oxidase (AO) liability with a T1/2 >2000 min in liver cytosol and is stable for over 120 minutes in the presence and absence of an AO inhibitor. A preliminary pharmacokinetic analysis in wista han rat (IV=2mg/kg, PO=20mg/kg) demonstrated 116% apparent absolute oral bioavailability, 2.6 hour terminal half-life, 33.0 mL/min/kg clearance, and a 2.6% unbound brain-to-plasma partition coefficient (Kpuu). WNC0901 also had favorable pharmacokinetic properties in beagle dog (IV=2mg/kg, PO=20mg/kg) with moderate clearance (8.5 mL/min/kg), high apparent absolute oral bioavailability (131%) with good exposure (AUC=36092 h*ng/mL), moderate half-life (4.28 h), and low protein binding (74.3% fraction unbound). The volume of distribution was moderate in both species (Vss = 1.32 L/kg in wistar han rat and 1.87 L/kg in beagle dog). In cell culture, WNC0901 inhibited autophosphorylation of DNA-PKcs in HT29 cells irradiated with 10 Gy with an IC50 of 32.7 nM and robustly inhibited autophosphorylation in both U251 glioma and A549 lung cancer cell lines at 300 nM in combination with 5Gy. In a clonogenic assay, 5Gy irradiation (10% survival) combined with 100nM WNC0901 demonstrated modestly enhanced cell killing (1.5% survival), and maximal effects were seen at 300nM (0.04% survival, p<0.01). Similar radiosensitizing effects with 300 nM WNC0901 were seen in the A549 cell line (0.2% survival with combination compared to 19% with 5Gy alone, p<0.01). In summary, WNC0901 inhibits DNA-PK kinase activity and provides potent radiosensitization in a GBM and lung cancer cell line. Future studies will assess the combination of WNC0901 and RT in GBM patient-derived xenograft models in vivo. Citation Format: Ann C. Mladek, Danielle L. Burgenske, William F. Elmquist, Wei Zhong, Jann N. Sarkaria. Preclinical data of a novel DNA-PK inhibitor in combination with radiation therapy shows promise in the treatment of established GBM and lung carcinoma cell lines [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 701.