Preliminary Imaging Studies of the Kappa Opioid Receptors in Schizophrenia and their Relationship to Dopamine Function

Despite clinical and preclinical evidence suggesting a potential role for the kappa dynorphin system in schizophrenia, there are no rigorous in vivo investigations of this system in schizophrenia. We propose a multimodal imaging study to obtain information about the availability of kappa opioid receptors (KOR) in striatum in schizophrenia and explore its relationship to dopaminergic function measured in the same subjects, with a neuromelanin sensitive MRI (NM-MRI) scan. We recently validated NM-MRI as a measure of neuromelanin concentration and a marker of dopaminergic function, demonstrating a significant relationship between NM signal in the substantia nigra and Positron Emission Tomography measures of dopamine release capacity in the striatum. In this proposal 10 antipsychotic-drug naïve patients with schizophrenia and 10 demographically matched healthy controls will undergo a PET scan with [18F]LY2459989, a selective KOR antagonist radiotracer, and a NM-MRI scan to obtain in the same subjects a measure of KOR availability in the striatum and neuromelanin in the substantia nigra. We expect that groups will differ on both measures, and that upregulation of KOR will relate to higher neuromelanin in patients with SCZ. This pilot study will inform the design of a much larger study and provide POC for biomarker- driven investigations of KOR antagonists in schizophrenia by providing in vivo molecular measures and a link between KOR and dopamine dysfunction. This may ultimately provide support for advancing new therapeutic testing of specific KOR antagonists, informed by the use of potential biomarkers that we will probe here, the KOR and NM-MRI, to enhance the design and selection of patients with schizophrenia that could be targeted. New therapies are badly needed in this disease, particularly for patients in whom first-line D2-based treatments do not produce full remission of symptoms. Alternative or additional therapies to D2 drugs will improve the quality of life for patients suffering from this devastating disease.