Pleiotropic and evolutionally conserved components of transcription nuclear factor - NF-B play key roles in progression of various diseases by regulating expression of antiapoptotic and cytokine responsive genes  . We previously demonstrated that rapidly activating transcription factors (TF) can be detected by using sequence-specific self-quenched reporter probes (oligonucleotide-molecular sensors (ODN-MS), which ideally remain “silent” in the absence of activated TF but emit photons upon specific binding to them [3-5]. Recently we were investigating sensor-based optical imaging of early inflammation in the endocrine pancreas using type 1 diabetes (T1D) model because NF-κB activation is essential for determining the fate of pancreatic β-cells and hence the progression of T1D. Using an immunocompetent SKH1 mouse model of early stage T1D we showed that NF-κB activation was induced by low-dose streptozotocin (LD-STZ). ODNMS probes that carried near-infrared (NIR) fluorophores formed a complex with NF-κB subunits in in vitro assays and in situ after LD-STZ treatment. Imaging studies of pancreas (sections and isolated islets) were corroborated with electrophoresis mobility shift assays (EMSA). A higher specific NIR fluorescence intensity in nuclei and cytoplasm of islets from LD-STZ treated groups compared to non-treated control animals was observed. Our results demonstrate that: 1) the use of ODN-MS probes in non-fixed islets and tissue sections may be used for distinguishing differences in inflammatory pathway activation in animal models of early stage diabetes; 2) early, non-invasive detection of NF-κB in pancreatic islets may serve as a potential strategy for imaging of early T1D-mediated sustained pro-inflammatory changes in the endocrine pancreas.
Activatable fluorescent molecular probes are predominantly nonfluorescent in their inactivated state due to intramolecular quenching, but increase fluorescence yield significantly after enzyme-mediated hydrolysis of peptides. Continuous wave in vivo detection of these protease-activatable fluorophores in the heart, however, is limited by the inability to differentiate between activated and nonactivated fractions of the probe and is frequently complicated by large background signal from probe accumulation in the liver. Using a cathepsin-activatable near-infrared probe (PGC-800), we demonstrate here that fluorescence lifetime (FL) significantly increases in infarcted murine myocardial tissue (0.67 ns) when compared with healthy myocardium (0.59 ns) after 24 h. Furthermore, we show that lifetime contrast can be used to distinguish in vivo cardiac fluorescence from background nonspecific liver signal. The results of this study show that lifetime contrast is a helpful addition to preclinical imaging of activatable fluorophores in the myocardium by reporting molecular activity in vivo due to changes in intramolecular quenching. This characterization of FL from activatable molecular probes will be helpful for advancing in vivo imaging of enzyme activity.