Abstract 7127: An ATM inhibitor: ZN-B-2262 in combination with radiation/ADCs containing topoisomerase inhibitors for the treatment of solid tumors
Authors: Zhou Ding , Wang Zheng , Liu Yan (Pita) , Fu Tingting , Cheng Ziqiang (Zack) 
Published: March 2024

Background: ZN-B-2262 is a best-in-class, IND-approved, small molecule serine/threonine kinase receptor inhibitor targeting Ataxia Telangiectasia Mutated (ATM), which plays a key role in DNA damage response (DDR) associated with double-strand breaks (DSB). Radiotherapy (RT) and topoisomerase inhibition can directly cause DSB. ZN-B-2262 is expected to enhance the therapeutic effect of RT, or antibody drug conjugates (ADCs) containing topoisomerase inhibitors by suppressing DSB DNA repair and blocking checkpoint controls.

Methods: The inhibition of isolated recombinant ATM, ATR, mTOR, DNA-PK, PI3Kα, PI3Kβ, PI3Kδ and PI3Kγ enzymes was evaluated using In-Cell-Western assay to determine the effect of ZN-B-2262 on ATM enzyme activity by detecting phosp-KAP1 (Ser824) expression. The inhibition of phospho-ATM (Ser1981) was evaluated by ATM assay on HT29 cells using a High-Content Imaging System (HCS). Therapeutic efficacy, as measured by tumor growth inhibition (TGI), was evaluated using ZN-B-2262 in combination with DS-1062 (Trop2 ADC), irinotecan or RT in MDA-MB-468 triple negative breast cancer (TNBC), SW620 colorectal cancer, and Fadu head and neck squamous cell carcinoma (HNSCC) subcutaneous xenograft murine models, respectively. In addition, ZN-B-2262 was tested for Human Aldehyde Oxidase (AO) activity. Safety margins were determined based on the ratio of unbound AUC obtained from 28-day GLP animal toxicology studies and predicted human PK at efficacious dose.

Results: ZN-B-2262 exhibited strong inhibition against ATM with the IC50 at 4.4 nM. No inhibition effect was observed on other IKK family enzymes with IC50 value &gt;10 uM. ZN-B-2262 showed high inhibition activity on phosp-KAP1 with IC50 of 13.25 nM and on phospho-ATM with IC50 of 21.5 nM. In the MDA-MB-468 xenograft efficacy study, ZN-B-2262 combined with a clinically relevant dose of DS-1062 showed significantly superior tumor inhibition effects compared to DS-1062 alone. In the SW620 xenograft efficacy study, in combination with irinotecan, ZN-B-2262 showed synergistic tumor inhibition effects. In the Fadu xenograft efficacy study, ZN-B-2262 demonstrated synergistic anti-tumor activity when combined with RT. Sustained and enhanced anti-tumor efficacy was observed post withdrawal of ZN-B-2262 combined with RT, which was not observed after stopping treatment of RT alone. Based on 28-day GLP tox in rat and dog, the predicted human safety margin is 25- to 50-fold.

Conclusion: ZN-B-2262, in combination with ADCs containing topoisomerase inhibitors, (e.g., Dato-Dxd), or RT, is expected to be a best-in-class (possibly first-in-class) compound, for the treatment of solid tumors. In particular, ZN-B-2262 should demonstrate improved PK and minimal inter-patient PK variability compared to current ATM clinical candidates since ZN-B-2262 is not an AO substrate.

Citation Format: Ding Zhou, Zheng Wang, Yan (Pita) Liu, Tingting Fu, Ziqiang (Zack) Cheng. An ATM inhibitor: ZN-B-2262 in combination with radiation/ADCs containing topoisomerase inhibitors for the treatment of solid tumors [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 7127.