A reductively convertible nickel phthalocyanine precursor as a biological thiol-responsive turn-on photoacoustic contrast agent.

A nickel phthalocyanine precursor bearing poly(ethylene glycol) as a turn-on contrast agent for photoacoustic imaging was prepared. The water-soluble polymeric chains were smoothly eliminated through thiol-mediated reductive aromatization in cancer cells, enabling the detection of endogenous biological thiols in vitro and in vivo.

An activator-induced quencher-detachment-based turn-on probe with a cationic substrate moiety for acetylcholinesterase.

We report a choline ester-grafted turn-on fluorescence probe to detect acetylcholinesterase (AChE) in living cells. The AChE-mediated hydrolysis of the choline ester moiety producing carboxylate initiates the activation of the Cy5 fluorophore quenched by an intramolecular nucleophilic mercapto group. The probe has the advantages of high AChE affinity and low cytotoxicity.

Aluminum naphthalocyanine conjugate as an MMP-2-activatable photoacoustic probe for in vivo tumor imaging.

Matrix metalloproteinase-2 (MMP-2), which is one of MMPs family, is known as an extracellular gelatinase controlling cancer cell adhesion, growth, and metastasis. Because of the great interest in MMP-2 activity, the detailed protocols for evaluating MMP-2-responsive contrast agents, especially photoacoustic probes for in vivo use, are helpful for researchers in the field. We here describe the detailed synthetic procedure of MMP-2-activatable photoacoustic probe AlNc-pep-PEG consisting of aluminum naphthalocyanine, MMP-2-responsive peptide sequence, and poly(ethylene glycol), which has recently been developed in our research group. The detailed measurement protocol of photoacoustic signal intensity in vitro and in vivo by using in-house built photoacoustic signal measurement system and photoacoustic imaging apparatus are also summarized.

MMP-2-Activatable Photoacoustic Tumor Imaging Probes Based on Al- and Si-Naphthalocyanines.

Enzyme-activatable photoacoustic probes are powerful contrast agents to visualize diseases in which a specific enzyme is overexpressed. In this study, aluminum and silicon naphthalocyanines (AlNc and SiNc, respectively) conjugated with matrix metalloprotease-2 (MMP-2)-responsive PLGLAG peptide sequence and poly(ethylene glycol) (PEG) as an axial ligand were designed and synthesized. AlNc-peptide-PEG conjugates AlNc-pep-PEG formed dimeric species interacting with each other through face-to-face H-aggregation in water, while SiNc-based conjugates SiNc-pep-PEG hardly interacted with each other because of the two bulky hydrophilic axial ligands. Both conjugates formed spherical nanometer-sized self-assemblies in water, generating photoacoustic waves under near-infrared photoirradiation. The treatment of MNc-peptide-PEG conjugates (M = Al, Si) with MMP-2 smoothly induced the cleavage of the PLGLAG sequence to release the hydrophilic PEG moiety, resulting in the aggregation of MNcs. By comparing the PA signal intensity changes at 680 and 760 nm, the photoacoustic signal intensity ratios were shown to be enhanced by 3-5 times after incubation with MMP-2. We demonstrated that MNc-peptide-PEG conjugates (M = Al, Si) could work as activatable photoacoustic probes in the in vitro experiment of MMP-2-overexpressed cell line HT-1080 as well as the in vivo photoacoustic imaging of HT-1080-bearing mice.

pH-Activatable Cyanine Dyes for Selective Tumor Imaging Using Near-Infrared Fluorescence and Photoacoustic Modalities.

Photoacoustic (PA) imaging is an emerging molecular imaging modality that complements fluorescence imaging and enables high resolution within deep tissue. Fluorescence/PA multimodality imaging would be a powerful technique to extract more comprehensive information from targets than traditional single-modality imaging. In this paper, we developed a new pH-activatable sensor, CypHRGD, which is applicable to both fluorescence and PA detection. CypHRGD was derived from our previous near-infrared pH-sensing platform, in which substitution with a bulky phenyl group and functionalization with a cRGD peptide remarkably improved the sensor's biocompatibility with attenuated dye aggregation. The multimodality imaging applications of CypHRGD were demonstrated in cultured cells and cancer-xenografted mice with rapid kinetics and high sensitivity and specificity, which relies on cRGD-facilitated tumor targeting, probe accumulation and subsequent activation in the acidic organelles after endocytosis.