This proposal describes the development of hyperpolarized-129Xenon (HP-Xe)-based probes for magnetic resonance imaging (MRI) of two biomarkers of inflammation and brain injury, the peripheral benzodiazepine receptor (PBR) and the neurotrophic protein, S100B. Molecular imaging (MI) is an emerging discipline that tries to non-invasively visualize specific biomolecules in living organisms and has many medical applications with immense commercial potential. For example, MI-based biomarkers will allow for better treatment of disease through earlier and more precise diagnosis. In addition, they will help to shorten pre-clinical and clinical drug-development protocols by more sensitively and quantitatively measuring the biological actions of new medications. The sensitivity of positron emission tomography (PET) and single photon emission computed tomography (SPECT) have led to the widespread use of these technologies for imaging specific bio-molecules in vivo. However, PET and SPECT have very poor spatial resolution (mm-cm) and use probes containing short-lived radioactive isotopes which emit tissue damaging ionizing radiation. MRI, on the other hand, utilizes relatively harmless radio-waves to image living organisms at close to cellular resolution (25-100 <m), but its use in MI has been hampered by low sensitivity: conventional MRI is limited to detecting probe concentrations of 10-3-10-5 M while the majority of biological targets are present at concentrations of 10-6-10-12 M in the body. In contrast, PET can detect probes at 10-9-10-12 M. Here we plan to develop the first in vivo application of a recently outlined technique that couples HP-Xe-based MRI, a technology pioneered by Mitchel Albert, one of the investigators in this proposal, to Xe biosensors which are chemical constructs consisting of a molecular Xe cage linked to a ligand that binds to the desired cellular target. Further signal amplification is produced by a recently described manipulation termed HP-129Xe chemical exchange saturation transfer (HYPERCEST): HP-129Xe molecules that diffuse through the cage are specifically depolarized. This new technology is predicted to i) retain the spatial resolution of MRI, ii) have exquisite molecular specificity including the ability to distinguish between free probe and probe that is specifically complexed to the target. Studies conducted over the last 15 years have demonstrated that the PBR and S100B are sensitive and potent biomarkers for inflammation and "active" brain pathology and injury. The studies suggest that the probes that we are developing could serve as a powerful diagnostic agent for conditions as diverse as atherosclerosis, Alzheimer's disease, multiple sclerosis, Parkinson's disease and traumatic brain injury. Here we propose to synthesize and subsequently validate these probes in a rodent model of brain injury. PUBLIC HEALTH RELEVANCE: We are proposing to synthesize probe molecules that can be used in conjunction with magnetic resonance imaging (MRI) to non-invasively take very high resolution pictures of the distribution of proteins called peripheral benzodiazepine receptors (PBR) and S100B in the tissues and brains of human patients. It has been previously demonstrated that examining the distribution of PBR and S100B in this manner will help us to better diagnose, monitor progression of and treat serious diseases such as multiple sclerosis, atherosclerosis, Alzheimer's disease and Parkinson's disease.