We report the design testing and in vivo application of pH sensitive contrast brokers designed specifically for Cerenkov imaging. is usually observed. METHODS Mono and di-18F-labeled derivatives of phenolsulfonphthalein (phenol red) and chromophores and is generalizable to any functional dye that absorbs at suitable wavelengths. pH probes for CI. We report 18F-radiolabeling of CP and PR derivatives (Physique 1) in vitro testing and in vivo measurement of pH in a mouse model of urinary alkalinization. The theory of selective bandwidth quenching is usually exhibited intermolecularly using PP mixed with 18F-FDG and intramolecularly using fluorinated PR and CP. The quenching is usually shown to be reversible and pH dependent. Finally 18F-labeled CP is used to estimate pH in the bladders of mice treated with acetazolamide a carbonic anhydrase inhibitor. Ratiometric imaging is employed at different wavelengths to determine absolute pH values in vivo. These results provide methods for multispectral optical imaging of nonfluorescent molecules with the potential for dual measurement of function and location using radiolabeled probes. Physique 1 Chemical structures of the pH indicators MATERIALS AND METHODS All reagents were purchased from Sigma-Aldrich unless otherwise stated. 18F-FDG and 18F-NaF were obtained from the Cyclotron Facility at the University of Pennsylvania. 18 labeling Labeling was performed using a custom-made electrophilic fluorination unit as previously described (of CR has also been shown in vivo using nanoparticles (37). However intramolecular quenching would ultimately be more useful as it would require a single contrast injection. As a result 18F-DFPR a derivative of the pH indicator commonly used in cell culture was synthesized. Quenching could be now observed in both the 515-575 nm and the target bandwidth of 575-650 nm. Although 18F-DFPR could effectively quench CR a relatively small difference in emission was observed between acidic and basic forms. Thus we synthesized 18F-MFCP and found that it outperformed 18F-DFPR and PP in the magnitude of quenching in the target bandwidth. In addition selectively quenching a targeted bandwidth it was critical that this sensors be switchable in order to accurately reflect the surrounding environment. The Betulinic acid sequential addition of base and acid to 18F-MFCP led to stepwise quenching and restoration of CI respectively. While 18F-MFCP exhibited the highest potential as an in vivo probe we also investigated PP+18F-FDG Betulinic acid and 18F-DFPR and found that they were both capable of switching. These results indicate that it is possible to rapidly monitor pH changes dynamically in the Betulinic acid extracellular tumor space of the tumor microenvironment. In vivo experiments were carried out using 18F-MFCP in Betulinic acid a mouse model of urinary alkalization. Acetazolamide is usually a carbonic anhydrase inhibitor that is used to treat metabolic and respiratory alkalosis. In doing so it causes blood acidification and urinary alkalization. The latter property along with the collection of small molecule Rabbit polyclonal to PPP1CB. radiopharmaceuticals in urine due to renal clearance provided a model to test how well 18F-MFCP reports on in vivo pH. Using a pH meter mouse urine pH was measured to be 6.2±0.1 in controls and 8.5±0.2 in acetazolamide treated animals. Optical Betulinic acid images of the bladder obtained following 18F-MFCP administration showed a clear difference in CR output between the two experimental conditions whereas no difference in PET signal was seen. Control animals exhibited a brighter signal than acetazolamide treated animals with the greatest difference seen in the open and 575-650 nm filter images. Following imaging expelled urine from acetazolamide treated animals was dark purple (not shown) indicating further that this urine was basic as measured by 18F-MFCP. When ROIs around the bladder were quantified the differences were not significant unless ratios were taken relative to the invariant signal at 810-875 nm. Using the ratiometric method it is possible for 18F-MFCP to report on absolute pH. We constructed a normalized pH response curve using in vitro 18F-MFCP data by taking the ratio of emission at 575-650 to 810-875 nm. When the same ratios from the control and acetazolamide treated mice were plotted around the pH response curve the CR values correlated well although they tended to lie above.