Abstract 871: [18F]BMS-986192 as a novel PET imaging agent for assessment of PD-L1 expression in vivo
Authors: Smith Ralph A. , Donnelly David , Morin Paul E. , Lipovsek Dasa , Gokemeijer Jochem , Cohen Daniel , Kim Joonyoung , Pena Adrienne , Adelakun Olufemi , Wang Xi-Tao , Chow Patrick , Bonacorsi Samuel J. , Hayes Wendy 
Published: July 2017

Abstract
Objectives Inhibition of the Programmed Death Ligand-1 (PD-L1)/PD-1 interaction allows for potent anti-tumor activity and antibodies that disrupt this interaction have been approved for the treatment of multiple cancer types. PD-L1 expression has been investigated clinically as a potential biomarker to predict response to anti-PD-1/PD-L1 therapy. BMS-986192, an Adnectin with high affinity and specificity for human PD-L1, was selected in vitro from a complex library. Here we report the discovery and first preclinical evaluation of [18F]BMS-986192 as a PET imaging agent to detect PD-L1 expression in vivo.
Methods [18F]BMS-986192 was radiolabeled via copper-free click chemistry and assessed for its ability to detect PD-L1 expression. Tracer binding to human L2987 (PD-L1+) and HT-29 (PD-L1-) xenografts as well as human non-small cell lung cancer (NSCLC) tissue samples was assessed by autoradiography (ARG). Tracer binding was compared to PD-L1 expression assessed independently with anti-PD-L1 immunohistochemistry (IHC). In vivo performance of the tracer was also assessed by PET imaging in mice bearing bilateral L2987 and HT-29 xenografts, and tracer biodistribution was further assayed in these animals ex vivo by gamma counter. Finally, initial in vivo biodistribution and radiation dosimetry was measured by PET in cynomolgus monkey.
Results ARG studies showed increased [18F]BMS-986192 total binding to PD-L1(+) L2987 xenograft compared to PD-L1(-) HT-29 xenograft tissue. Radiotracer binding was higher in all tested human NSCLC tissue samples compared to xenografts. Dose-dependent blockade was seen in all PD-L1(+) tissues co-incubated with cold BMS-986192, and binding was unaffected by co-incubation with cold non-PD-L1 binding control. Visual comparison of tracer binding aligns closely with PD-L1 IHC both spatially as well as in intensity. Preferential accumulation of [18F]BMS-986192 was noted in PD-L1(+) L2987 compared to PD-L1(-) HT-29 xenografts in tumor-bearing mice. PET studies in cynomolgus monkeys confirmed binding to PD-L1(+) tissue (e.g. spleen) with minimal nonspecific background signal exclusive of primary clearance organs. Radiation dosimetry of [18F]BMS-986192 indicates an estimated single administration dose limit of 6.2 mCi for an average human subject.
Conclusions ARG, PET studies, and ex vivo measurements in rodent and cynomolgus monkey demonstrated sensitive and specific [18F]BMS-986192 binding to PD-L1. Low background signal in cynomolgus monkey in the context of endogenous PD-L1 expression further supports the potential of this tracer for sensitive detection of PD-L1(+) lesions in vivo. Radiation dosimetry suggests that [18F]BMS-986192 can be safely administered in human trials, with estimated absorbed radiation doses well within safe parameters for human administration. [18F]BMS-986192 has potential as a sensitive PD-L1 imaging agent for same-day imaging in patients.
Citation Format: Ralph A. Smith, David Donnelly, Paul E. Morin, Dasa Lipovsek, Jochem Gokemeijer, Daniel Cohen, Joonyoung Kim, Adrienne Pena, Olufemi Adelakun, Xi-Tao Wang, Patrick Chow, Samuel J. Bonacorsi, Wendy Hayes. [18F]BMS-986192 as a novel PET imaging agent for assessment of PD-L1 expression in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 871. doi:10.1158/1538-7445.AM2017-871