Thèse de la Paillasse au Cerveau l'Imagerie Tep du Récepteur P2y12 pour Décoder la Neuroinflammation H/F Doctorat.Gouv.Fr

Établissement : Université Paris-Saclay GS Santé et médicaments École doctorale : Innovation thérapeutique : du fondamental à l'appliqué Laboratoire de recherche : Laboratoire d'Imagerie Biomédicale Multimodale Paris-Saclay Direction de la thèse : Alexandra WINKELER ORCID 0000000333972570 Début de la thèse : 2026-12-01 Date limite de candidature : 2026-10-31T23:59:59 Le récepteur P2Y12 (P2Y12R) a été identifié comme un biomarqueur d'imagerie TEP particulièrement prometteur pour évaluer l'état fonctionnel de la microglie, étant plus spécifique des cellules que les ligands TSPO et moins sensible à la variabilité génétique. Cependant, le rôle de ce récepteur reste mal compris, et le développement de traceurs TEP est entravé par la faible perméabilité de la barrière hémato-encéphalique (BHE) et d'importantes différences inter-espèces en ce qui concerne la disponibilité et l'affinité des récepteurs. Au cours des cinq dernières années, près d'une dizaine de ligands candidats pour le récepteur P2Y12 ont été radiomarqués, mais seuls quelques-uns ont atteint une disponibilité cérébrale suffisante. Ce projet de thèse se concentre sur le positionnement du récepteur P2Y12 en tant que biomarqueur clé de la microglie homéostatique anti-inflammatoire, tout en validant de nouveaux radioligands TEP conçus pour cette cible très prometteuse. Dans ce cadre, le doctorant évaluera les profils d'expression de P2Y12R dans différents contextes pathologiques. Parallèlement, il mettra en oeuvre un pipeline standardisé de développement/validation de ligands, allant des essais in vitro, de l'autoradiographie, à l'imagerie in vivo chez différentes espèces (des rongeurs aux primates non humains), au cours duquel les ligands P2Y12R existants et nouvellement développés seront comparés afin d'identifier les plus performantes. L'objectif final est une meilleure compréhension du P2Y12R en tant que biomarqueur microgliale, et de faire progresser un radioligand hautement spécifique, capable de franchir efficacement la BHE, et adapté à un usage clinique, offrant ainsi un nouvel outil puissant pour surveiller la neuroinflammation dans les maladies neurologiques et neurodégénératives. Neurodegenerative and neurological disorders trigger a neuroinflammatory response within the central nervous system (CNS), aiming to limit damage and promote repair. Microglia, the resident immune cells of the CNS, continuously monitor their environment under homeostatic conditions. During neuroinflammation, however, they become activated and can exert either beneficial or detrimental effects depending on their activation state. Classically activated microglia drive pro-inflammatory responses, while alternatively activated microglia contribute to anti-inflammatory signaling, tissue remodeling, and repair. Because of their pivotal role in neuroinflammation, microglia are of major interest as targets for quantitative localization and in vivo imaging of neuroinflammatory processes.
The ability to image microglial activation states in patients would therefore represent a critical advance for both diagnosis and therapy monitoring, surpassing current ligands targeting the 18-kDa translocator protein-a PET biomarker used to date that suffers from low cell specificity.
The purinergic P2Y12 receptor (P2RY12), a G protein-coupled receptor, is exclusively expressed by homeostatic and anti-inflammatory microglia in the CNS (1-3). This makes it one of the most promising targets for imaging changes in microglial activation. However, radioligand development is complex because of limited or no brain penetration (4). Consequently, only a few PET radioligands for P2Y12R have been developed to date; amongst these are those developed by our group at UMR BioMaps (CEA-JOLIOT), in collaboration with MIRCen (CEA-JACOB) and the Pharmaceutical Institute at the University of Bonn (5, 6).
Our group, in line with other studies, has shown that preclinical validation of P2Y12R PET radioligands using animal models is complicated by significant species differences in the ligand-P2Y12R interactions, despite a more than 80% homology of the receptor across all species (6, 7). As a consequence, in vitro and in vivo humanized models are used during preclinical validation, such as the one developed at MIRCen. Nevertheless, the high variability in the experimental approaches makes it difficult to compare the reported ligand characteristics, such as affinity values, across different studies. To enable rigorous comparison of P2Y12R radioligands across laboratories and accelerate clinical translation, standardized in vitro and in vivo assays are essential.
This PhD project therefore aims to 1. setup a standardized pipeline of in vitro to in vivo humanized models that allows a systematic evaluation of currently available (and potential novel) brain-permeable P2Y12R PET radioligands, in parallel to 2. particular focus on species-dependent ligand-receptor interactions (human, mouse, rat, and potentially non-human primates). This latter allows the application of the ligands in preclinical models, with the aim for a better understanding of P2RY12 expression in different pathologies through the use of animal models and the possibility to investigate therapeutic strategies in vivo.
Ultimately, this work will guide the selection or development of the most suitable radioligand for clinical translation, enabling the specific imaging of differentially activated microglia.
This project directly contributes to the CEA's strategic theme Technology for tomorrow's medicine and leverages the SHFJ's unique translational PET imaging platform as well as the molecular biology and viral production platform of MIRCen.
This PhD project aims to:
1. Investigate the potential of P2RY12 radioligands to quantify the dynamics of P2RY12 expression during disease. This first objective requires the use of animal disease models. Thus, our understanding of interspecies receptor variations (human, rat, mouse, non-human primate) and their impact on ligand binding is essential, and will be studied by
i. Characterizing the binding properties of available and newly developed P2Y12R ligands in vitro.
ii. Assessing autoradiographic binding patterns in rodent and humanized brain tissues to evaluate specificity and regional distribution.
2. Evaluate in vivo PET imaging performance of candidate ligands in rodents and non-human primates, focusing on pharmacokinetics (PK).
3. Select a lead P2RY12 ligand suitable for clinical translation to image microglial activation states in patients.
Methodology
- In vitro studies with the aim to compare ligand affinities and selectivity across species:
o Generate cell lines stably expressing human, rat, and mouse P2RY12, based on previous achievements for the hP2RY12.
o Perform receptor-binding assays (saturation, competition) in cell lines expressing human, rat, and mouse P2RY12
- Autoradiography with the aim to map binding distribution on brain tissue and assess non-specific binding.
o Evaluate radioligand binding on brain tissue sections from rodent disease & humanized rat models, as well as human samples (when available).
- In vivo PET imaging with the aim to evaluate PK
o Evaluate PK of promising ligands in healthy and subsequently pathological rodent models (e.g., Alzheimer's disease).
o Use the humanized rat model to evaluate translation potential of the ligand.
o Extend successful ligands with translational potential to non-human primates for further pharmacokinetic profiling and quantification.
- Data integration and comparison:
o Benchmark in-house ligands against published candidates under standardized conditions through cross-validation of in vitro, autoradiographic, and in vivo findings.
o Discussion & exchange with radiopharmaceuticians on the potential for clinical application