In vitro and in vivo evaluation of the caspase-3 substrate-based radiotracer [(18)F]-CP18 for PET imaging of apoptosis in tumors.

Purpose: A novel caspase-3 substrate-based probe [(18)F]-CP18 was evaluated as an in vivo positron emission tomography (PET) imaging agent for monitoring apoptosis in tumors.

Methods: Uptake of [(18)F]-CP18 in cell assays and tumors was measured. Caspase-3/7 activities in cell lysates and tumor homogenates were determined.

[(18)F]T807, a novel tau positron emission tomography imaging agent for Alzheimer's disease.

Objective: We wished to develop a highly selective positron emission tomography (PET) imaging agent targeting PHF-tau in human Alzheimer's disease (AD) brains.

Methods: To screen potential tau binders, human AD brain sections were used as a source of native paired helical filament (PHF)-tau and Aβ rather than synthetic tau aggregates or Aβ fibrils generated in vitro to measure the affinity and selectivity of [(18)F]T807 to tau and Aβ. Brain uptake and biodistribution of [(18)F]T807 in mice were also tested.

A highly selective and specific PET tracer for imaging of tau pathologies.

Senile plaques and neurofibrillary tangles are prominent neuropathological hallmarks in Alzheimer's disease and are considered to be targets for therapeutic intervention as well as biomarkers for diagnostic in vivo imaging agents. While there are a number of amyloid-β positron emission tomography (PET) tracers currently in different stages of clinical development and commercialization, there have been very few reports on imaging agents selectively targeting tau aggregates. In search of [18F]-PET tracers that possess great binding affinity and selectivity toward tau tangles, we tested more than 900 compounds utilizing a unique screening process.

Transduction of proteins into intact neutrophils.

Neutrophils and related phagocytic leukocytes are notoriously difficult to transfect, making the introduction of proteins into these cells for biological studies problematic. We describe here two methods that have been successfully used to introduce proteins into intact primary human neutrophils while maintaining normal functional responses. The first utilizes a lipid-based reagent that transports proteins into intact neutrophils.

Signaling requirements for translocation of P-Rex1, a key Rac2 exchange factor involved in chemoattractant-stimulated human neutrophil function.

PI 3,4,5-trisphosphate [PI(3,4,5)P3; PIP3]-dependent Rac exchanger 1 (P-Rex1) is a Rac-specific guanine nucleotide exchange factor abundant in neutrophils and myeloid cells. As a selective catalyst for Rac2 activation, P-Rex1 serves as an important regulator of human neutrophil NADPH oxidase activity and chemotaxis in response to a variety of extracellular stimuli. The exchange activity of P-Rex1 is synergistically activated by the binding of PIP3 and betagamma subunits of heterotrimeric G proteins in vitro, suggesting that the association of P-Rex1 with membranes is a prerequisite for cellular activation.

Regulation of the phagocyte NADPH oxidase by Rac GTPase.

Phagocytic leukocytes generate reactive oxygen species important for the killing of invading microorganisms. The source of these oxidants is the NADPH oxidase, a tightly controlled multicomponent enzyme made up of a membrane-associated catalytic moiety and cytosolic regulatory components that must assemble to form the active oxidase. The phagocyte NADPH oxidase was the first mammalian system shown to be directly regulated by a Rac GTPase.

Critical role of proline-rich tyrosine kinase 2 in reversion of the adhesion-mediated suppression of reactive oxygen species generation by human neutrophils.

Neutrophils act as the first line of innate immune defense against invading microorganisms during infection and inflammation. The tightly regulated production of reactive oxygen species (ROS) through activation of NADPH oxidase is a major weapon used by neutrophils and other phagocytic leukocytes to combat such pathogens. Cellular adhesion signals play important physiological roles in regulating the activation of NADPH oxidase and subsequent ROS formation.

The molecular basis for adhesion-mediated suppression of reactive oxygen species generation by human neutrophils.

Human neutrophil adherence to ECMs induces an initial inhibition of stimulated reactive oxygen species (ROS) formation, followed by an enhanced phase of oxidant production. The initial integrin-mediated suppression of ROS constitutes a mechanism to prevent inappropriate tissue damage as leukocytes migrate to inflammatory sites. The Rac2 guanosine 5'-triphosphatase (GTPase) is a critical regulatory component of the phagocyte NADPH oxidase.

Nitration of PECAM-1 ITIM tyrosines abrogates phosphorylation and SHP-2 binding.

Platelet-endothelial cell adhesion molecule-1 (PECAM-1) is a cell adhesion molecule with a cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) that, when phosphorylated, binds Src homology 2 domain-containing protein-tyrosine phosphatase (SHP-2). PECAM-1 is expressed at endothelial cell junctions where exposure to inflammatory intermediates may result in post-translational amino acid modifications that affect protein structure and function. Reactive nitrogen species (RNS), which are produced at sites of inflammation, nitrate tyrosine residues, and several proteins modified by tyrosine nitration have been found in diseased tissue.