Zhong, Wei

Abstract Failure to repair radiation (RT)-induced DNA damage results in cell lethality, and combined treatment with DNA repair inhibitors can markedly enhance tumor control achieved with radiation. These inhibitors also can potentiate acute RT toxicities by suppressing DNA repair. Capitalizing on this normal tissue radiosensitizing effect, we determined effective radiosensitizing dosing regimens in mice for the ATM inhibitor WSD0628 and the DNAPK inhibitor WNC0901 in mice. Drugs were administered via oral gavage prior to each RT dose, and RT was delivered using an anterior/posterior 225 kVp beam. In an initial iteration of this model, various combinations of WSD0628 and RT were administered to cohorts of mice (n=5/group) and body weight was followed for 2 weeks. The resulting data were modeled to define the total dose of radiation estimated to cause 50% of mice to lose >20% body weight (D50). There was an inverse relationship between the WSD0628 and D50 doses: 0 mg/kg WSD0628/24.0 Gy (95% confidence interval (CI) 24.5–24.7); 0.25 mg/kg/19.2 Gy (95% CI 16.7–21.8); 1 mg/kg/13.7 Gy (95% CI 13.2–14.2); 2.5 mg/kg/11.0 Gy (95% CI 10.5–11.5); 5 mg/kg/11.3 Gy (95% CI 6.7–15.9) and 7.5 mg/kg/7.8 Gy (95% CI 7.8–7.9). Histological review of tongues from animals treated with 15 Gy RT (5Gy x 3) + 7.5 mg/kg WSD0628 demonstrated epithelial denudation and acute inflammation consistent with oral mucositis, while these features were not seen with the same dose as RT alone. Similar WSD0628 doses were evaluated in combination with 8 Gy supratentorial RT (via lateral beams) in orthotopic GBM43 PDX tumors. By treatment arm, the median time to a moribund state was: sham (29 days (d)), RT (39d), 1 mg/kg (42d), 2.5 mg/kg (49d), 5 mg/kg (65d), and 10 mg/kg (123d, overall p<0.0001). A second mucositis model was used for evaluation of WNC0901. Cohorts of 5 mice/group were treated with a set dose of RT (4Gy x 3) to the oral cavity alone and in combination with various doses of WNC0901, and the fraction of mice with >20% weight loss within 2 weeks was determined. The results of this study are as follows: placebo (0 of 5 mice with >20% weight loss); 15 mg/kg (3 of 5 mice); 25, 50, or 100 mg/kg (5 of 5 mice). Based on these data, we defined 25 mg/kg WNC0901 as the minimally effective dose and predicted that 50 mg/kg would provide robust radiosensitization. Consistent with this prediction, co-treatment of B16 melanoma flank tumor xenografts with RT (8Gy x 1) and WNC0901 (50 mg/kg) more than doubled the median tumor control duration (median 42 [range 24-45] days; time from implantation for tumor to exceed 1500 mm3) as compared to RT alone (24 [13-30] days) or sham treatment (17 [13-17] days; overall p<0.0001). This study describes how a radiation-induced oral mucositis model can be used to identify effective radiosensitizing regimens faster and with fewer resources than relying on tumor control studies alone. Citation Format: Danielle Burgenske, Darwin Garcia, Jiayan Le, Wenjuan Zhang, Sneha Rathi, Katrina K. Bakken, Lauren L. Ott, Zeng Hu, Brett L. Carlson, Ann Mladek, Jessica L. Abraham, Paul A. Decker, Matthew L . Kosel, Jeanette E. Eckel-Passow, William F. Elmquist, Wei Zhong, Jann N. Sarkaria. Radiation-induced oral mucositis to rapidly determine effective radiosensitizing dosing regimens for ATM and DNAPK inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr B090.

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 Ataxia Telangiectasia–mutated (ATM) inhibitors are being developed as radiosensitizers to improve the antitumor effects of radiotherapy, but ATM inhibition can also radiosensitize normal tissues. Therefore, understanding the elevated risk of normal tissue toxicities is critical for radiosensitizer development. This study focused on modeling the relationship between acute mucosal toxicity, radiation dose, fractionation schedule, and radiosensitizer exposure. The ATM inhibitor WSD0628 was combined with single or fractionated doses of radiation delivered to the oral cavity or esophagus of Friend Leukemia virus B (FVB) mice. The potentiation by WSD0628 was quantified by a sensitizer enhancement ratio (SER), which describes the changes in radiation tolerance for radiation combined with WSD0628 relative to radiation-only regimens. WSD0628 profoundly enhanced radiation-induced acute oral and esophageal toxicities. For oral mucosal toxicity, the enhancement by WSD0628 with 3 fractions of radiation resulted in an SER ranging from 1.3 (0.25 mg/kg) to 3.1 (7.5 mg/kg). For the 7.5 mg/kg combination, the SER increased with increasing number of fractions from 2.2 (1 fraction) to 4.3 (7 fractions) for oral toxicity and from 2.2 (1 fraction) to 3.6 (3 fractions) for esophageal toxicity, which reflects a loss of the normal tissue sparing benefit of fractionated radiation. These findings were used to develop a modified biologically effective dose model to determine alternative radiation schedules with or without WSD0628 that result in similar levels of toxicity. Successful radiosensitizer dose escalation to a maximally effective therapeutic dose will require careful deliberation of tumor site and reduction of radiation dose volume limits for organs at risk.