DESIGN AND DEVELOPMENT OF NEAR-INFRARED FLUORESCENT PROBES FOR SENSING pH, HYPOXIA AND PEROXYNITRITE

Abstract

pH and hypoxia levels are two important diagnostic biomarkers in biological systems and abnormal levels will cause many diseases. The metabolism and transportation of peroxynitrite in biological systems involve a series of important enzymes and proteins. Peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. As a result, it is very important to detect and evaluate the levels of pH, hypoxia, and peroxynitrite in vivo to study the functionality of enzymes and provide practical applications for cancer diagnosis and therapy. Fluorescence detection and imaging offer a sensitive non-invasive method because it provides clear images of cellular three-dimensional structures, and can illustrate cellular multiple overlapping structures simultaneously, and enable image-guided surgery. However, it is challenging to design fluorescent probes with good fluorescence signals, low background noise, and multifunctional detection capability. In order to overcome these drawbacks, we have designed and synthesized a series of excellent fluorescent probes to detect pH, hypoxia, and peroxynitrite with good fluorescence signals, fast responses, low background noise, and multifunctional detection capabilities. The probes combine advantages of near-infrared imaging such as low fluorescence background interference, less photodamage to cells and tissues, and deep-tissue penetration with ratiometric imaging, this latter aspect reduces systematic errors with solely intensity-based fluorescent probes caused by fluctuations in the excitation light source, variations in probe concentrations, and different probe compartmental localizations. We have developed a new backbone for making near-infrared fluorescent probes. This new backbone has a reactive chlorine group for modifying the detectors. Based on this new backbone, we introduced a pH-responsive detector to prepare three pH-sensitive near-infrared fluorescent probes with high fluorescence quantum yields. We designed and synthesized a series of fluorescent probes on detecting hypoxia level. The nitro group was introduced directly in the conjugation system of the fluorophore, which make it fast response and ultra-sensitive. Additionally, by changing the electron-withdrawing abilities of the substitution group on 9-position of acridine moiety, the fluorescent probes show a significant different detection limit and sensitivity towards nitroreducatse. For third project, we developed a fluorescent probe responding to peroxynitrite. The probe contains a near-infrared fluorophore and a coumarin moiety and connected through a conjugated triple bond linker. The ester group of the coumarin moiety in the conjugation system can enhance the sensitivity of the ONOO- detection. For the fourth project, we developed multi-response fluorescent probe. This