Evaluation of Microglial Activation in Schizophrenia Patients Stratified by C4 Complement Using [18F]DPA-714 PET Imaging

The primary objective of this study is to evaluate the correlation between **cortical neuro-inflammation** quantified by Positron Emission Tomography (PET) using [18F]DPA-714 and genetic determinants of C4 expression in patients with schizophrenia and healthy volunteers. This is clinically relevant as it may provide insights into the pathophysiological mechanisms underlying schizophrenia, potentially leading to improved diagnostic and therapeutic strategies.

Secondary objectives include:

• Assessing the correlation between cortical and subcortical markers in Magnetic Resonance Imaging (MRI), PET using [18F]DPA-714 neuro-inflammation markers, and genetic determinants of C4 expression in patients with schizophrenia and healthy volunteers.
• Evaluating the correlation between cortical neuro-inflammation and peripheral inflammation biomarkers, such as cytokine levels, C-reactive protein (CRP), and lipid anomalies.
• Investigating the correlation between cortical neuro-inflammation and clinical determinants of inflammation.

The clinical trial involves a study population comprising **male** and **female** participants aged between 18 and 55 years. The trial includes individuals diagnosed with **schizophrenia** according to DSM-5 criteria, as well as healthy volunteers. Participants are selected based on specific genetic markers, including the presence or absence of the HLA 8.1 AH haplotype. The study population is matched for age, sex, and HLA/C4 status. Participants are required to have efficient contraception if they are women of reproductive age. The trial does not involve a vulnerable population. The sponsor has not provided information regarding the total number of participants. Participants must be able to understand the research objectives and procedures, be affiliated with a social security scheme, and have a TSPO genotype that allows tracer fixation. All participants have signed a free and informed consent form.

The clinical trial is designed to evaluate the correlation between cortical neuro-inflammation and genetic determinants of C4 expression in patients with **schizophrenia** and healthy volunteers. This study employs a **randomized**, **double-blind**, and **controlled** methodology to ensure the reliability and validity of the results. The trial will utilize Positron Emission Tomography (PET) with the radiotracer **18F-DPA-714** to measure microglial activation in the brain. The trial is expected to run from June 2023 to September 2027, with participant involvement lasting up to one year.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to assess eligibility based on criteria such as age, diagnosis of schizophrenia according to DSM-5, and genetic markers. Following successful screening, participants will be randomized into groups. The study includes several follow-up visits to monitor the primary endpoint, which is the level of microglial activation, and secondary endpoints, including regional cortical thickness and subcortical brain connectivity. The end-of-study visit will conclude the participant's involvement, where final assessments and data collection will occur.

Participants are expected to remain in the study for its full duration unless specific conditions necessitate early termination. These conditions include adverse reactions to the investigational product, withdrawal of consent, or non-compliance with study protocols. The trial aims to provide comprehensive data on the relationship between neuro-inflammation and genetic factors in schizophrenia, contributing to the understanding of the disease's pathophysiology.

The clinical trial involves the use of the experimental medication **18F-DPA-714**, which is administered in the form of an **injection**. The active substance in this medication is **N,N-diethyl-2-(2-(4-(2[(18)F]-fluoroethoxy)phenyl)5,7dimethylpyrazolo[1,5a]pyrimidin-3-yl)acetamide**, a chemical compound. The medication is delivered via **intravenous injection**. The maximum daily dose and total dose for the treatment period is 200 MBq/ml, with the treatment period limited to a single day. The medication is not formulated for pediatric use and is not classified as an orphan drug. The administration of 18F-DPA-714 is intended to assess cortical neuro-inflammation in patients with schizophrenia using Positron Emission Tomography (PET).

In this study, no non-experimental treatments such as standard-of-care therapy, placebo, or comparator treatments are utilized. The focus is solely on the administration of the experimental medication, 18F-DPA-714. Participant compliance with the dosing schedule is monitored to ensure adherence to the protocol. The trial is conducted under the authorization of the relevant regulatory bodies, with the medication's use being authorized for the specific purpose of this clinical investigation.

Efficacy in this clinical trial will be assessed by evaluating the level of **microglial activation** in the brain using Positron Emission Tomography (PET) with [18F]DPA-714. This primary endpoint will be compared between groups based on the genotype of C4, weighted by the ancestral haplotype that carries it. Secondary endpoints include regional cortical thicknesses determined via anatomical MRI, and parameters of subcortical brain connectivity derived from diffusion MRI, such as fractional anisotropy, and resting functional MRI, such as functional connectivity. These will also be compared between groups according to the C4 genotype. Additionally, lipid abnormalities (cholesterol, serum triglycerides), blood glucose, peripheral markers of inflammation (CRP, cytokines), and clinical parameters (abdominal tension, abdominal girth) will be correlated with the level of microglial activation measured in PET.