Abstract IA006: Multifaceted effects of DNA damage response inhibitors on radiation responses of glioblastoma and the normal brain
Authors: Chalmers Anthony J. 
Published: January 2024

Abstract
PARP inhibitors (PARPi) and ATM inhibitors (ATMi) enhance radiation sensitivity in multiple cancer models, both in vitro and in vivo. Our observation that the radiosensitizing properties of PARPi are most pronounced in rapidly proliferating cells is reflected in early phase clinical trial data showing exacerbation of acute radiation toxicity in rapidly proliferating tissues such as oropharyngeal and esophageal mucosa. Lack of radiosensitization in late responding, slowly proliferating normal tissues indicates that PARPi may be more effectively combined with radiation therapy (RT) in patients with brain tumors. ATMi are much more potent radiosensitizers than PARPi but less is known about their impact on normal tissue toxicity since they have only recently progressed to the clinic, although preclinical in vivo data are encouraging. We are evaluating the oral PARPi olaparib and the oral ATMi AZD1390 in combination with RT +/- temozolomide (TMZ) in the treatment of glioblastoma (GBM), the most prevalent and most aggressive primary brain tumor. Patients with GBM experience very poor outcomes in terms of both median survival (c.1 year) and neurocognitive decline, which is caused primarily by RT. Early phase testing of the olaparib-RT combination is underway in three populations of patients with newly diagnosed GBM. Patients aged &gt;65 with MGMT unmethylated GBM are being recruited to a randomized, placebo-controlled phase II study (PARADIGM, ISRCTN52658296) after a phase I dose escalation study showed that olaparib (200 mg twice daily) was extremely well tolerated when combined with brain irradiation (40 Gray in 15#). Good performance status patients aged under 70 are being recruited to PARADIGM-2 (ISRCTN51253312) which comprises two parallel phase I dose escalation studies: patients with MGMT unmethylated tumors are receiving daily olaparib with RT (60 Gy in 30#) without TMZ, while patients with MGMT methylated tumors are receiving intermittent olaparib with standard chemoradiation. AZD1390 is being evaluated in a first-in-human phase I dose escalation study (NCT03423628) in combination with re-irradiation (35 Gy in 10#) in patients with recurrent GBM, and with first-line radical radiotherapy (60 Gy in 30#) in patients with newly diagnosed, MGMT unmethylated GBM. In parallel, we are undertaking preclinical studies to investigate the impact of PARPi and ATMi on RT induced neurotoxicity. In vivo imaging studies support the emerging concept that RT induced neuroinflammation is important in the pathogenesis of neurotoxicity, and we have generated preliminary behavioral data indicating that both PARPi and ATMi can alleviate the neurotoxic effects of RT. Ongoing experiments are defining the roles of microglia, astrocytes and neurogenesis in this phenomenon. We will present these diverse datasets in the context of our hypothesis that combining PARPi or ATMi with RT has potential to improve outcomes for GBM patients by enhancing tumor control while simultaneously suppressing neuroinflammation and alleviating RT related neurocognitive decline.
Citation Format: Anthony J. Chalmers. Multifaceted effects of DNA damage response inhibitors on radiation responses of glioblastoma and the normal brain [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr IA006.