Abstract 5977: Discovery and preclinical validation of [11C]AZ3391: A first in class blood-brain barrier permeable, subtype selective PARP-1 PET radioligand

Abstract

Abstract Positron emission tomography (PET) is a molecular imaging technique used to study the distribution of radiolabeled tracer molecules in vivo in a non-invasive fashion. We here report the discovery and preclinical validation of a novel PET tracer for PARP1. Its exquisite selectivity and high contrast in vivo opens up unique opportunities for exploring target engagement and relationships between drug exposure in plasma and PARP1 occupancy during clinical development of PARP1 inhibitors. AZ3391 was identified as a PET radioligand candidate from our medicinal chemistry program investigating novel PARP1 selective inhibitors and radiolabeled with carbon-11 (t1/2=20.4 min) for a series of in vitro and in vivo imaging experiments. Using in vitro autoradiography, dense binding of [11C]AZ3391 was observed in tissues known to be rich in PARP1 (eg tumour xenograft; NHP and human brain cerebellum). [11C]AZ3391 binding was completely abolished by the inclusion of a high concentration of Olaparib or AZD5305 in the incubate, thus demonstrating specific binding to PARP1 in vitro. Following intravenous injection of [11C]AZ3391 in non-human primates, high binding was observed in organs known to express PARP1, eg brain, spleen and bone marrow. The radioactivity in these organs could be blocked in a dose-dependent manner after pre-treatment with increasing doses of AZD9574 (up to 0.05 mg/kg), thus demonstrating specific binding to PARP1 in vivo. This set of preclinical data supports further development of [11C]AZ3391 as a tool to assess drug induced PARP1 engagement in patients. Citation Format: Peter Johnström, Jeffrey Johannes, Andy Pike, Zsolt Cselényi, Magnus Schou. Discovery and preclinical validation of [11C]AZ3391: A first in class blood-brain barrier permeable, subtype selective PARP-1 PET radioligand [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 5977.