Introduction/Background
The development of novel PET radiotracers and therapeutic strategies requires thorough in vivo characterization before first-in-human studies. This is particularly challenging for targets such as misfolded proteins (e.g., alpha-synuclein, tau, amyloid-beta), where low target density and off-target binding can limit radioligand specificity and sensitivity, or for more complex biologics that have multiple simultaneous therapeutic targets. Non-human primate (NHP) imaging represents an important translational step between preclinical research and clinical studies, owing to the close anatomical and physiological similarities between primates and humans. Furthermore, NHP models of disease provide opportunities to evaluate novel drugs and therapeutic approaches under conditions that approximate human pathology. This presentation highlights the contribution of NHP PET imaging to radiotracer development, therapy evaluation and clinical translation.

Methods
Selected examples of NHP PET studies will illustrate approaches used to evaluate novel radiotracers and candidate therapies. These include dynamic PET imaging combined with anatomical imaging, kinetic modelling, pharmacological blocking or displacement studies to assess target specificity, longitudinal imaging in disease models to monitor pathology and treatment response, and whole-body imaging for biodistribution and radiation dosimetry.

Results
NHP PET studies provide valuable information on brain and organ uptake, pharmacokinetics, target specificity and quantification. They support the selection of appropriate analysis approaches and outcome measures, contribute to imaging protocol optimization, and help identify potential species-related differences (particularly rodents) in preparation for human studies.

In disease models, PET enables the in vivo assessment of longitudinal pathological processes, target engagement and therapeutic response, supporting the selection of promising drug candidates and dosing regimens at a very early stage of development. Whole-body imaging and dosimetry further contribute to the safety assessment required for clinical translation.

Conclusion
NHP PET imaging provides a valuable translational framework for radiotracer and drug development, providing data at a critical and less costly preclinical stage. By combining molecular imaging, quantitative pharmacokinetic assessment and novel therapeutic evaluation in relevant animal models, it generates critical information to guide preclinical decision-making and support the design of early-phase clinical trials.