Multicomponent Reactions for de Novo Synthesis of BODIPY Probes: In Vivo Imaging of Phagocytic Macrophages

Abstract

Multicomponent reactions are excellent tools to generate complex structures with broad chemical diversity and fluorescent properties. Herein we describe the adaptation of the fluorescent BODIPY scaffold to multicomponent reaction chemistry with the synthesis of BODIPY adducts with high fluorescence quantum yields and good cell permeability. From this library we identified one BODIPY derivative (PhagoGreen) as a low-pH sensing fluorescent probe that enabled imaging of phagosomal acidification in activated macrophages. The fluorescence emission of PhagoGreen was proportional to the degree of activation of macrophages and could be specifically blocked by bafilomycin A, an inhibitor of phagosomal acidification. PhagoGreen does not impair the normal functions of macrophages and can be used to image phagocytic macrophages in vivo.

Kinetic analysis of superparamagnetic iron oxide nanoparticles in the liver of body-temperature-controlled mice using dynamic susceptibility contrast magnetic resonance imaging and an empirical mathematical model

“…Another method to observe the phagocytic activity of Kupffer cells in vivo is fluorescence imaging method using fluorescence probes [35]. This method, however, has some problems such as self-induced fluorescence and the difficulty of observing deep tissues due to photon attenuation by light scattering in living tissues.…”

Modern Synthetic Avenues for the Preparation of Functional Fluorophores

“…Multifunctional fluorescent polymers for avidin and bovine serum albumin conjugation were prepared through an Ugi MCR in combination with a controlled reversible addition–fragmentation chain‐transfer polymerization (Figure 2 G) 12. An example of the applicability of Ugi 4‐CRs to functionalize fluorophores for optical imaging was reported by our group 13. We described the preparation of a fluorescent isocyanide–BODIPY core and its derivatization using different MCRs.…”

Optical Windows for Imaging the Metastatic Tumour Microenvironment in vivo

“…Several activatable molecular probes have been designed to track tumour or stromal cells as well as to provide a direct readout of cellular or enzymatic activity (Figure 2). These include fluorescently labelled inhibitors or quenched peptides to image protease activity (e.g., matrix metalloproteases in cancer cells or fibroblast activation protein in cancer-associated fibroblasts [10]), fluorescent probes activated by myeloperoxidase for monitoring activated neutrophils and alveolar macrophages in the lungs [11], or pH-sensitive probes for imaging phagocytic macrophages in vivo [12]. …”

“…(A) Peptide sequences can be conjugated to quenched fluorophores to produce activatable molecular probes that emit fluorescence only after cleavage by specific proteins (e.g., fibroblast activating protein) [10]; (B) an internally-quenched fluorophore (SNAPF), which reacts with hypochlorite (OCl − ) produced by the myeloperoxidase enzyme, allows the monitoring of activated neutrophils in the lung by fluorescence imaging [11]; (C) PhagoGreen is a pH-sensitive BODIPY fluorophore for imaging phagocytic macrophages in vivo [12]. …”