Porphyrins and Hydroporphyrins for In Vivo Bioimaging

Abstract

This chapters provides an overview of the recent applications of tetrapyrrolic macrocycles for in vivo fluorescence imaging. Recently, porphyrinic compounds have been used as theranostic agents for photodynamic therapy (PDT) or photothermal therapy. They have also been used as multimodal imaging agents, a way to combine fluorescence photoacoustic imaging, positron emission tomography (PET), magnetic resonance imaging (MRI), and ultrasound imaging. The simple porphyrin derivatives typically possess low fluorescence brightness and short absorption wavelengths. However, structural modifications allow for a great improvement of these properties and tailor them for deep tissue applications. Thus, benzoporphyrins, strongly conjugated hydroporphyrin arrays, as well as hydroporphyrins (i.e., partially saturated porphyrin derivatives) show optical properties adequate for in vivo fluorescence imaging. Specifically, hydroporphyrins have been broadly used for simultaneous cancer treatment and multimodal imaging. Synthetic bacteriochlorins can be used as fluorescent probes for multicolor fluorescence-guided surgery. Benzoporphyrins and lanthanide porphyrinic complexes have been applied for in vivo oxygen sensing and as theranostic agents for PDT and multimodal imaging, respectively. Considerable efforts have been devoted to formulation of nanostructures containing hydroporphyrins. Nanoscience enables new modes for delivering, targeting, and activating fluorescent hydroporphyrins, as well as more efficient combination of fluorescence with other imaging and therapeutic modalities.