Development of a Squaraine-Based Molecular Probe for Dual-Modal <i>in Vivo</i> Fluorescence and Photoacoustic Imaging
Yong Dae Park, Jam-Eon Park, Hyeon Sik Kim, Seung-Hyeon Choi, Jung Eun Park, Jongho Jeon, Seung‐Hwan Park
Abstract
Dual-modular imaging approaches combining near-infrared (NIR) fluorescence (FLI) and photoacoustic imaging (PAI) require suitable contrast agents to produce dual-modular signals. Although nanoparticles have been used to develop PAI agents, small molecule-based imaging agents have not been extensively studied, highlighting the need to design new fluorophores with an enhanced multifunctional ability. Thus, in this study, we designed a novel squaraine (SQ)-based dye and reported its rational preparation and conjugation with a cancer targeting peptide. Specifically, benzoindole-derived SQ (BSQ) showed strong absorption and fluorescence properties at above 650 nm under aqueous conditions, with a maximum absorption and emission at 665 and 680 nm, respectively. Moreover, PA signal scanning experiments revealed a maximum signal intensity in the range 680–700 nm. BSQ was also conjugated with cyclic arginine–glycine–aspartic acid (cRGD) to improve its active targeting ability for the αvβ3 integrin, which is overexpressed in various cancer and angiogenic cells. A series of in vitro, in vivo, and ex vivo FLI studies showed that the cRGD conjugated BSQ (BSQ–RGD2) successfully stained and targeted αvβ3 integrin-overexpressing tumor cells and xenografts, which were clearly visualized by FLI and PAI. Therefore, BSQ–RGD2 can successfully be applied to dual-modular imaging of the specific biomarker in living animals.