Fluorescent Macromolecular Sensors of Enzymatic Activity for In Vivo Imaging - Progress in Molecular Biology and Translational Science - page 349

1. INTRODUCTION
Fluorescence-based imaging and detection strategies have been a
mainstay of basic and preclinical research for over four decades. This is in
large part due to the cost-effectiveness, safety, and sensitivity of these tech-
niques (usually requiring only nanomolar concentrations of dyes while
yielding micrometer to nanometer microscopic resolution in single cells
as well as in tissue samples).
In parallel, an increasing number of fluorescent and bioluminescent mole-
cules (optical imaging probes) have become available and these are allowing in-
vestigation of ever more complex biological phenomena, such as genomic
regulation, signal transduction, cell excitability, and stem cell generation and dif-
ferentiation. Although many of the currently available fluorescent probes were
primarily developed for in vitro and in situ studies using fluorescence microscopy
and fluorescence-based screening assays, a growing number are being developed
specifically for in vivo applications such as cell tracking and monitoring both nor-
mal and pathological processes in animal models. Success in these endeavors has
spurred interest in the use of fluorescence imaging for detecting human disease.
In particular, enzyme-sensing fluorescent reporters have been used for detecting
a number of different pathologies in animal models and hold great promise in the
detection and treatment of human diseases, especially those exhibiting an in-
flammatory component (i.e., atherosclerosis, cancer, and osteoarthritis). The
continued development and improvement of optical detectors, along with
the increasing availability of high-specificity, biologically safe fluorescent probes,
has made transition of fluorescence-based imaging of enzyme activity to the
clinical arena a plausible endeavor.
This chapter discusses some of the important research that has brought this
experimental modality closer to clinical application and describes the com-
pounds that are most likely to have relevance and feasibility for transition into
clinical practice with emphasis given to fluorescent reporters of enzymatic
activity.
2. ENZYME ACTIVITY AND DYSREGULATION
AS A PREDICTOR OF DISEASE
Strategies aimed at imaging and detecting enzyme activity have sub-
stantial potential for aiding in the diagnosis and prognosis of a wide range of
diseases. Ample evidence exist showing that dysregulation of enzymatic