Liu, Lily

Abstract Radiation is a cornerstone of glioblastoma (GBM) treatment, however, the majority of tumors progress within the radiation field due to inherent radiotherapy (RT) resistance. The integration of highly potent radiosensitizers, such as the ATM inhibitors AZD1390 or WSD0628, could reverse resistance and significantly improve local control of these tumors. However, the achievable brain tumor exposure of these inhibitors may be limited by drug exposure in skin and mucosa, leading to enhanced radiation toxicity. To support the clinical development of WSD0628, we developed pharmacokinetic (PK)-efficacy models to help interpret ongoing PK analyses. A model based on in vitro cell studies was based on the in vitro observations that 30 nM WSD0628 provided maximum ATM inhibition and the extent of radiosensitization was directly related to the duration of drug incubation after irradiation, up to a maximum of 24 hours. The unbound WSD0628 concentration, measured by rapid equilibrium dialysis, was 66% of the total concentration in cell culture media, and was used to define an optimal radiosensitizing target of 20 nM free WSD0628 for 4 to 24 hours. Previous PK analyses showed that the free, unbound fraction (fu) of WSD0628 in plasma and brain tumor tissue are 0.02 and 0.054, respectively, and the brain tumor-to-plasma ratio is 0.32 in GBM43 patient-derived xenografts (PDXs). From these data, a total drug level of 1160 nM in plasma is predicted to achieve unbound drug levels above the 20 nM WSD0628 target unbound concentration. To validate this prediction, parallel in vivo dose-ranging studies were performed in orthotopic PDXs. Mice with orthotopic GBM43 were randomized to treatment with RT (8 Gy x1) alone or in combination with a range of WSD0628 doses. RT combined with 0.25 mg/kg and 1 mg/kg WSD0628 had no impact on survival, compared to RT alone, while median survival increased by 1.3-fold for RT combined with 2.5 mg/kg, 1.7-fold with 5 mg/kg, and 3.2-fold with 10 mg/kg WSD0628. A similar dose-response was observed in an M12 melanoma brain metastasis PDX. Based on PK modeling of these drug doses, 2.5 mg/kg dosing will maintain total WSD0628 plasma levels above 1160 nM for 11.9 hours, 5 mg/kg for 23.6 hours, and 10 mg/kg for 40 hours. Taken together, we have developed a model to predict efficacious dosing of a brain tumor based on the free drug hypothesis, which allows integration of multiple aspects of in vitro modeling with measured drug levels in animal models to predict total plasma levels associated with robust sensitizing effects. Assuming similar tissue to plasma partitioning in human GBM, this model could be directly applied to interpret the ongoing Phase 1 PK analysis of WSD0628 in recurrent GBM. Citation Format: Ann Catherine Mladek, Juhee Oh, Sneha Rathi, Lily Liu, Danielle M. Burgenske, Brett L. Carlson, Katrina K. Bakken, Lauren L. Ott, Zeng Hu, Wei Zhong, William F. Elmquist, Jann N. Sarkaria. Modeling pharmacokinetics and efficacy of the ATM inhibitor WSD0628 in GBM and melanoma metastasis PDX models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4629.

Abstract Background The ataxia-telangiectasia mutated (ATM) protein coordinates the cellular response to therapeutic radiation, and ATM inhibitors can potentially enhance the efficacy of radiation in otherwise radiation-resistant tumors. Methods The small molecule ATM kinase inhibitor WSD0628 was specifically designed for enhanced distribution across the blood-brain barrier to more effectively treat glioblastoma (GBM) and brain metastases in combination with radiation therapy (RT). GBM and brain metastasis patient-derived xenograft models were used to understand target inhibition, radiosensitization, inhibition of the DNA damage response, and in vivo efficacy. Results Initial in vitro characterization of WSD0628 demonstrates a high level of selectivity across kinase families, limited aldehyde oxidase liability, and low risk of hERG interactions. Consistent with a central role for ATM in radiation response, WSD0628 blocked radiation-induced signaling and enhanced radiosensitivity in U251 glioma cells and brain tumor PDXs GBM120 and M12. In comparison to control or RT alone in orthotopic PDXs, the combination of WSD0628 with RT markedly prolonged median survival—GBM12 (19, 55, and 408 days, respectively); GBM43 (26, 44, and 143 days, respectively); GBM120 (51, 89, and 231 days, respectively); M12 (17, 39, and 190 days, respectively). Pharmacokinetic and pharmacodynamic testing after treatment in orthotopic GBM43 tumors showed inhibitory levels of WSD0628 and a reduction of γH2AX foci in the combination-treated tumors. Conclusions Collectively, these results suggest a promising role for WSD0628 in combination with RT in brain tumors and provide the rationale for an ongoing Phase 0/1A clinical trial testing this combination in recurrent GBM.

Abstract Glioblastoma (GBM) are inherently resistant to radiation therapy (RT), and development of radiosensitizers is one strategy to overcome this limitation. Repair of DNA double strand breaks induced by RT are mediated by the protein kinase Ataxia Telangiectasia mutated (ATM). In this study, the novel ATM inhibitor WSD-0628 was evaluated in combination with RT using GBM and melanoma models. In vitro evaluation of 10uM WSD-0628 binding to a panel of potential drug targets, including receptors, ion channels, enzymes, and transporters, indicated a satisfactory safety profile with low risk for off-target liability. WSD-0628 potently inhibits ATM-mediated phosphorylation of the DNA damage response protein KAP1 in MCF-7 cells at sub-nanomolar (nM) concentrations (IC50 0.42nM) in comparison to much less potent inhibition of the related kinases ATR (phosphorylation of CHK1, IC50 742nM) or DNA-PKcs (auto-phosphorylation of DNA-PK, IC50 169nM) in HT29 cells assessed by ELISA. In U251 GBM cells, 30 nM WSD-0628 potently inhibited RT-induced phospho-KAP1 and robustly reduced clonogenic survival by 5-fold when combined with 5 Gy irradiation (combination vs RT alone, p<0.01). Similar potent radiosensitizing effects were seen in a melanoma brain metastasis PDX line M12 (10nM WSD-0628+IR-5Gy 1% survival vs 5% survival with IR-5Gy alone. p<0.01), and the SV-40 transformed astrocyte line SVG-A (10nM WSD-0628 + IR-2.5Gy survival 0.2% vs 15% with IR-2.5Gy alone. p<0.01). Evaluation of the pharmacokinetic profile of WSD-0628 in mice 2h after a single 5 mg/kg oral dose reveals a high level of free drug availability in the brain (34nM) and in the CSF (50nM) with little to no Pgp/BCRP substrate liability. An initial in vivo dose finding study in orthotopic GBM43 PDX yielded significant benefit with WSD-0628 at either 5 or 10 mg/kg PO daily when combined with radiation (2Gy QD for 5 days); Median survival for sham RT (29d) or RT alone (34d) were significantly different from RT combinations with 5 mg/kg (54d) and 10 mg/kg (73d; p<0.01 for both dose levels), although the higher dose combination was poorly tolerated with body weight loss between 15-20% one week after RT completion. Dosing of WSD-0628 (7.5 mg/kg PO, QD) given just before and 24h after a single dose of RT (12.5Gy) in mice with orthotopic M12 was well tolerated and provided robust radiosensitizing effects with median survival for combination treatment of over 180d vs 17d for control and 49d with RT alone groups (combination vs RT alone, p=0.04). Collectively, these results suggest a promising role for WSD-0628 in combination with RT in GBM and melanoma metastatic to the brain. Citation Format: Ann Mladek Tuma, Wei Zhong, Lily Liu, Danielle M. Burgenske, Brett L. Carlson, Katrina K. Bakken, Zeng Hu, Margaret A. Connors, Jann N. Sarkaria. WSD-0628, a novel brain penetrant ATM inhibitor, radiosensitizes GBM and melanoma patient derived xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3305.