1. Multispectral Photoacoustic Imaging of Tumor Protease Activity with a Gold Nanocage-Based Activatable Probe
Cheng Liu, Shiying Li, Yanjuan Gu, Huahua Xiong, Wing-Tak Wong, Lei Sun Mol Imaging Biol. 2018 Dec;20(6):919-929. doi: 10.1007/s11307-018-1203-1.
Purpose: Tumor proteases have been recognized as significant regulators in the tumor microenvironment, but the current strategies for in vivo protease imaging have tended to focus on the development of a probe design rather than the investigation of a novel imaging strategy by leveraging the imaging technique and probe. Herein, it is the first report to investigate the ability of multispectral photoacoustic imaging (PAI) to estimate the distribution of protease cleavage sites inside living tumor tissue by using an activatable photoacoustic (PA) probe. Procedures: The protease MMP-2 is selected as the target. In this probe, gold nanocages (GNCs) with an absorption peak at ~ 800 nm and fluorescent dye molecules with an absorption peak at ~ 680 nm are conjugated via a specific enzymatic peptide substrate. Upon enzymatic activation by MMP-2, the peptide substrate is cleaved and the chromophores are released. Due to the different retention speeds of large GNCs and small dye molecules, the probe alters its intrinsic absorption profile and produces a distinct change in the PA signal. A multispectral PAI technique that can distinguish different chromophores based on intrinsic PA spectral signatures is applied to estimate the signal composition changes and indicate the cleavage interaction sites. Finally, the multispectral PAI technique with the activatable probe is tested in solution, cultured cells, and a subcutaneous tumor model in vivo. Results: Our experiment in solution with enzyme ± inhibitor, cell culture ± inhibitor, and in vivo tumor model with administration of the developed probe ± inhibitor demonstrated the probe was cleaved by the targeted enzyme. Particularly, the in vivo estimation of the cleavage site distribution was validated with the result of ex vivo immunohistochemistry analysis. Conclusions: This novel synergy of the multispectral PAI technique and the activatable probe is a potential strategy for the distribution estimation of tumor protease activity in vivo.
2. Development of a small-molecule-based activatable photoacoustic probe
Takayuki Ikeno, Kenjiro Hanaoka, Yasuteru Urano Methods Enzymol. 2021;657:1-19. doi: 10.1016/bs.mie.2021.06.041. Epub 2021 Jul 19.
Photoacoustic (PA) imaging is an emerging imaging modality that combines the advantages of optical imaging and ultrasound imaging. In particular, activatable PA probes, which visualize the presence or the activity of target molecules in terms of a change of the PA signal, are useful tools for functional imaging. In this chapter, we describe the development of small-molecule-based activatable PA probes, focusing on the design and synthesis of PA-MMSiNQ, our recently developed activatable PA probe for HOCl. We also describe the protocols used for evaluation of PA-MMSiNQ with a UV-vis spectrometer and a PA imaging microscope.
3. Activatable Fluorescent-Photoacoustic Integrated Probes with Deep Tissue Penetration for Pathological Diagnosis and Therapeutic Evaluation of Acute Inflammation in Mice
Wenxiu Li, Rong Li, Rui Chen, Sixin Ai, Huayong Zhu, Ling Huang, Weiying Lin Anal Chem. 2022 Jun 7;94(22):7996-8004. doi: 10.1021/acs.analchem.2c01048. Epub 2022 May 23.
Inflammation is associated with many diseases, so the development of an excellent near infrared fluorescent (NIRF) and photoacoustic (PA) dual-modality probe is crucial for the accurate diagnosis and efficacy evaluation of inflammation. However, most of the current NIRF/PA scaffolds are based on repurposing existing fluorescent dye platforms that exhibit non-optimal properties for both NIRF and PA signal outputs. Herein, we developed a novel dye scaffold QL-OH by optimizing the NIRF and PA signal of classical hemicyanine dyes. Based on this optimized dye, we developed the first NIRF/PA dual-mode carbon monoxide (CO) probe QL-CO for noninvasive and sensitive visualization of CO levels in deep inflammatory lesions in vivo. The novel probe QL-CO exhibited rapid and sensitive NIRF775/PA730 dual activation responses toward CO. In addition, the CO-activated probe QL-CO was successfully used for the diagnosis of inflammation and evaluation of anti-inflammation drug efficacy in living mice though the NIRF/PA dual-mode imaging technology for the first time. More importantly, the probe QL-CO could accurately locate the deep inflammatory lesion tissues (≈1 cm) in mice and obtain 3D PA diagnostic images with deep penetration depth and spatial resolution. Therefore, the new NIRF/PA dual-mode probe QL-CO has high potential for deep-tissue diagnosis imaging of CO in vivo. These findings may provide a new tool and approach for future research and diagnosis of CO-associated diseases.
