Glutamate Carboxypeptidase II (GCPII)-Targeted PET to Identify Muscle Denervation in Peripheral Nervous System Injuries

Management of peripheral nervous system (PNS) neuropathies, such as traumatic peripheral nerve injury (PNI), relies on accurate assessment of muscle denervation and recovery. Yet, the current gold-standard clinical test, needle electromyography (EMG), has multiple shortcomings that can complicate surgical treatment. Here, we introduce a noninvasive method for holistic evaluation of muscle denervation by utilizing positron emission tomography (PET) to quantify expression of prostate-specific membrane antigen (PSMA), also known as glutamate carboxypeptidase II (GCPII), within muscles. We identified that GCPII is persistently over-expressed in denervated muscles and that expression normalizes with muscle reinnervation. Leveraging this phenomenon, we used two PSMA/GCPII-PET agents that are FDA-approved for prostate cancer imaging, [18F]DCFPyL and [68Ga]PSMA-11, to detect muscle denervation and subsequent reinnervation in experimental models of PNI. We found that denervated muscle had approximately twice the uptake as innervated muscle on GCPII-PET/magnetic resonance (MR) imaging and GCPII-PET/computed tomography (CT), which persisted for at least 16 weeks after nerve injury without repair in rats and swine. GCPII-targeted uptake also declined to near baseline levels with muscle reinnervation after nerve repair. To assess clinical feasibility, we performed [18F]DCFPyL PET/CT in a patient who had sustained a unilateral radial nerve injury 15 weeks prior, and we observed elevations in denervated muscle uptake that mirrored our preclinical findings. Our consistent findings across species of increased GCPII-PET uptake in chronically denervated muscle and its decline with muscle reinnervation, along with the established safety profile of available GCPII-PET agents, support the promise of GCPII-PET as a rapidly translatable strategy for characterization and longitudinal monitoring of PNIs and non-traumatic PNS neuropathies.