Abstract B028: Systemic and CNS distributional pharmacokinetics of WSD0628, a novel radiosensitizer: Implications for the treatment of brain tumors

Abstract Glioblastoma (GBM) is an aggressive and highly infiltrative brain tumor with poor prognosis. Radiation therapy induces DNA damage, and DNA damage response (DDR) pathways modulate resistance to radiation therapy. Inhibiting DDR pathways by targeting ATM, a key enzyme involved in the repair of DNA double strand breaks, leads to radiosensitization and enhances cytotoxicity. Clinical translation of radiosensitizers for GBM may be influenced by a lack of effective drug delivery across the blood brain barrier (BBB). The purpose of this study is to determine the key preclinical pharmacokinetic parameters and mechanisms that influence the CNS delivery of WSD0628, a novel ATM inhibitor. In vitro clonogenic survival assays using U251 GBM cells indicate that WSD0628 shows significant radiosensitization, with a 70% decrease in surviving colonies in the presence of 10nM or higher drug concentrations in combination with 2. 5 to 10 Gy radiation as compared to radiation alone. We evaluated the systemic pharmacokinetics and CNS distribution of WSD0628 in FVB wild-type mice and FVB mice lacking Pgp and Bcrp (Mdr1a/b−/−Bcrp1−/−, triple knockout) after a 1, 5, 10 mg/kg intravenous (IV) or oral (PO) dose. Clearance decreased with increase in dose and a greater than dose proportional increase in exposure was observed. WSD0628 is rapidly absorbed and is bioavailable after oral administration. Tissue distribution coefficients were determined as the ratio of exposure in tissue to plasma (Kp = AUCtissue/AUCplasma). Kp, brain was 0. 22 ± 0. 05, and Kp, spinal cord was 0. 30 ± 0. 09 in the wild-type mice. For wild-type mice, Kp, uu, brain was 0. 20 ± 0. 05 and Kp, uu, spinal cord was 0. 26 ± 0. 08, determined by correcting for binding to CNS tissues and plasma. The brain distribution of WSD0628 was only modestly increased (1. 4 times) in the triple knockout mice with Kp, brain of 0. 32 ± 0. 06 and Kp, spinal cord of 0. 41 ± 0. 08. Organ distribution of WSD0628 at steady-state was studied after intraperitoneal implantation of Alzet osmotic pumps primed to release WSD0628 at 7. 5 ug/hr for 25 hours. Tissue distribution coefficients, determined by organ-to-plasma steady-state concentration ratios, were highest for liver and kidneys, followed by heart, lungs and CNS. Survival studies conducted in mice bearing orthotopic GBM patient derived xenografts show a significant improvement in survival in mice receiving a combination of WSD0628 and radiation as compared to radiation alone. In conclusion, WSD0628 is a robust radiosensitizer and has moderate brain penetration that is not limited by the efflux transporters Pgp and Bcrp. Based on preliminary efficacy studies in mice, WSD0628 shows potential for treatment of GBM tumors. Evaluations are underway to determine tumor free concentrations and quantification of corresponding biomarkers. Combining this knowledge of PK of WSD0628 with the dynamics of the targeted biological pathway will inform a PK-PD-efficacy model and predict effective dosage regimens for future preclinical and clinical trials. Citation Format: Sneha Rathi, Ann Mladek, Zhiyi Xue, Ju-Hee Oh, Wenjuan Zhang, Wenqiu Zhang, Jiayan Le, Jann S. Sarkaria, William F. Elmquist. Systemic and CNS distributional pharmacokinetics of WSD0628, a novel radiosensitizer: Implications for the treatment of brain tumors abstract. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84 (5 Suppl₁): Abstract nr B028.