Abstract 7117: Convection enhanced delivery of a novel ATR inhibitor synergizes with systemic lomustine for improved treatment of glioblastoma

Abstract Developing effective strategies for treating glioblastoma (GBM), the most common and aggressive form of brain cancer, has been a long-standing challenge. Despite rigorous treatment regimens including surgical resection with concomitant radiotherapy and chemotherapy, the prognosis for this disease remains poor, largely due to tumor recurrence, resistance to conventional therapeutics, pharmacokinetic and brain delivery challenges, and dose-limiting toxicities of existing therapies. The DNA damage response and DNA repair mechanisms such as the ataxia telangiectasia and Rad3-related (ATR) pathway are key mediators of therapeutic responses, and recent studies have shown that targeting DNA repair proteins alongside standard-of-care options is a promising anti-tumor strategy. Here, we employ a combination approach using a next-generation macrocyclic ATR inhibitor, ATRIN-333, to sensitize GBM tumors to alkylators. We establish the potency of ATRIN-333 and report a robust synergistic interaction between it and the alkylator lomustine in GBM cell-based assays and in a murine flank tumor model. This combinatorial treatment was then applied to a mouse intracranial tumor model, where we utilized a convection enhanced delivery (CED) system combined with nanoparticle technology for direct intracranial administration of ATRIN-333. ATRIN-333 was successfully encapsulated into a novel polymeric nanoparticle formulation using poly (ethylene glycol) -co-poly (ethylene brassylate-co-dioxanone) (PEG-EB-co-DO). CED of both free and encapsulated ATRIN-333 potently sensitized intracranial GBM tumors to low-dose (5 mg/kg) systemically-delivered lomustine, reducing tumor size and conferring a substantial survival benefit compared to cohorts treated with lomustine or the ATR inhibitor alone. The combination approach was well tolerated by the mice, with no hematological toxicity observed as assessed by bone marrow analysis and blood cell counts. Our results demonstrate that ATR inhibitor/lomustine combination therapy, used in conjunction with a CED platform, is a powerful avenue for GBM treatment and a viable option for potential clinical implementation. Note: AJ and TL contributed equally to this work. Citation Format: Alexander Josowitz, Teresa Lee, Ranjini K. Sundaram, Jinal Pothupitiya, Eric J. Brown, Amrita Sule, Jason Beckta, Yongheng Wang, Joseph Vacca, Oren Gilad, Ranjit S. Bindra, W Mark Saltzman. Convection enhanced delivery of a novel ATR inhibitor synergizes with systemic lomustine for improved treatment of glioblastoma 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 (6Suppl): Abstract nr 7117.