Dysregulated expression or activation of
matrix metalloproteinases (
MMPs) is observed in many kinds of life-threatening diseases. Therefore,
MMP imaging-for example, with radiolabeled
MMP inhibitors (MMPIs)-potentially represents a valuable tool for clinical diagnostics using noninvasive single photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging. Despite numerous preclinical imaging approaches, translation to a clinical setting has not yet been successful. We introduce and oppose three potential radiofluorinated
MMP-targeted imaging probes, modified by the introduction of pentamethine cyanine (
Cy5)
dyes and therefore containing both radio- as well as fluorescent label with respect to their capability to assess
MMP activity in vivo by means of scintigraphic (PET) and/or fluorescent (NIRF) imaging. New hybrid MMPI tracer candidates, structurally based on radiofluorinated pyrimidine-2,4,6-triones (
barbiturates) from previous approaches, were synthesized by convenient two-step syntheses. In the first step,
Cy5 dyes, varying in the number of sulfonate groups (nSO3- = 1, 2, or 4) and bearing an additional "clickable"
alkyne moiety, were coupled to the
barbiturate MMPI by
amide formation. In the second step, the [18F]
fluoride radiolabel was introduced into the resulting
Cy5 dye conjugates by "radio-click" chemistry. Biodistribution studies of these hybrid tracer candidates were assessed and compared in C57BL/6 mice by PET as well as fluorescence imaging.
MMP activity was imaged in a
MMP-positive mouse model of
irritant contact dermatitis (ICD) by PET and sequential fluorescence reflectance imaging (FRI), respectively. In vivo data were validated by scintillation counting,
gelatin zymography, and
MMP-histology. Three new potential hybrid
MMP imaging probes were prepared, differing essentially in the number of sulfonate groups, introduced by
Cy5 dye components. Although the hydrophilicity of these compounds was substantially increased, 10a (nSO3- = 1) and 10b (nSO3- = 2) were still rapidly eliminated via unfavorable hepatobiliary pathways, as observed in earlier approaches. Only 11 (nSO3- = 4) showed delayed in vivo clearance and a shift towards higher renal elimination. In the chosen mouse model of ICD, only 11 (nSO3- = 4) significantly accumulated in the inflamed mouse ear, which could be precisely visualized by means of PET and FRI.