Functionalized Near-Infrared Cyanine Dyes for Fluorescence Imaging and Diagnostics

The utilization of fluorescent cyanine dyes that emit within the near-infrared window significantly enhances biological imaging due to enhanced light penetration and minimal background fluorescence. This thesis describes efforts to develop new classes of functionalized cyanine dyes for imaging and diagnostics. Chapter 1 provides an overview of cyanine dye structure and the major concepts underlying the rational design of bioresponsive fluorescent cyanine probes. The development of heptamethine cyanine probes for imaging hypoxic cancer cells is described in Chapters 2 and 3. A first generation probe (Chapter 2) included a reactive p-nitrobenzyl group that produced "turn on" fluorescence when it entered hypoxic cells. A second-generation version (Chapter 3) has additional appendages that optimize the probe photophysics for eventual operation in living subjects. The probe design in Chapter 4 is a functionalized cyanine dye with targeting ligands that enhance affinity for receptors on the surface of cancer cells in culture and within tumor spheroids. A comparison of mono- versus tri-valent targeting systems found the tri-valent version to exhibit greater cell imaging contrast. In Chapter 5, esterase-responsive near-infrared probes are harnessed for photodynamic therapy of cancer cells. One molecular platform was a heptamethine cyanine probe that showed dual activation of fluorescence and singlet oxygen production. A second esterase-responsive near-infrared probe was a derivative of 5-aminoevulinic acid and found to produce high amounts of protoporphyrin IX in cancer cells for more effective photodynamic therapy. Chapter 6 turns to the topic of fluorescence sensing and describes a fluorescent ratiometric supramolecular tandem assay for detecting phosphatase and phytase enzymes. The study capitalizes on the selective binding of a calixpyridiniumn quencher molecule to a polyanionic pyrene fluorophore with no binding to a cationic near-infrared pentamethine cyanine. The three-component system enabled the creation of ratiometric fluorescence enzyme assays that detected the presence of alkaline phosphatase and phytase.