Molecular imaging is broadly defined as the characterization and measurement of biological processes in living animals, model systems and humans at the cellular and molecular level, using remote imaging detection methods, such as PET/SPECT, MRI and optical imaging (bioluminescence, fluorescence). The overall goal is to advance our understanding of biology and medicine through noninvasive in vivo investigation of gene expression and molecular interactions in the context of the whole organism.
Genetically-encoded imaging reporters introduced into cells and transgenic animals enable noninvasive, longitudinal studies of dynamic biological processes in intact cells and living animals. The most common reporters include firefly luciferase (bioluminescence imaging), green fluorescence protein (fluorescence imaging), Herpes simplex virus-1 thymidine kinase (positron emission tomography) and variants with enhanced spectral and kinetic properties optimized for use in vivo. When cloned into promoter/enhancer sequences or engineered into fusion proteins, imaging reporters enable fundamental processes such as transcriptional regulation, signal transduction cascades, protein-protein interactions, oncogenic transformation, cell trafficking and targeted drug action to be temporally and spatially registered in vivo.
We focus on three lines of investigation in molecular imaging research. We have developed reporter genes and imaging tools for investigating NF-kB signaling, mTOR pathway protein-protein interactions, drug targeting and transcriptional regulation in vivo using bioluminescence and PET. The multidrug resistance P-glycoprotein, a 170 kDa plasma membrane protein encoded by the human multidrug resistance gene (MDR1), functions as an energy-dependent efflux pump of many potent chemotherapeutic drugs in cancer as well as b-amyloid at the blood brain barrier. We have synthesized imaging agents that are recognized as transport substrates by the P-glycoprotein at tracer concentrations to study regulation and transport function of P-glycoprotein and homologous transporters in cancer and Alzheimer's disease. We have also explored the rapid and efficient delivery of fluorescent and radioactive complexes to the cell interior. Membrane permeant peptide conjugates incorporating novel transduction peptide sequences and appropriate motifs for chelating technetium or rhenium and conjugating optical probes have been synthesized and validated as targeted transmembrane delivery vehicles.
Spying on biology with both injectable or genetically-encoded imaging reporters provides new insight into target-specific molecular and regulatory machinery within the contextual environment of the whole animal.
