H2O2-responsive liposomal nanoprobe for photoacoustic inflammation imaging and tumor theranostics via in vivo chromogenic assay

Development of Photoacoustic Probes for in Vivo Molecular Imaging

Photoacoustic (PA) imaging is an emerging, non-invasive imaging modality that encompasses attributes of both optical and ultrasound imaging. Because of the combination of optical excitation and acoustic detection, PA imaging enables high contrast and high resolution within deep tissue (centimeter depths). Recent advances in PA probe development have allowed for stimulus-responsive imaging in a variety of biological models with implications for basic, translational, and clinical sciences. This perspective highlights recent progress in the development of PA probes and their application to live-animal molecular imaging.

Enhancing hydrophilicity of photoacoustic probes for effective ratiometric imaging of hydrogen peroxide

Hydrogen peroxide (H₂O₂) plays a significant role in regulating the redox balance in the living body.

Manganese Dioxide Coated WS2 @Fe3 O4 /sSiO2 Nanocomposites for pH-Responsive MR Imaging and Oxygen-Elevated Synergetic Therapy

Recently, the development of multifunctional theranostic nanoplatforms to realize tumor-specific imaging and enhanced cancer therapy via responding or modulating the tumor microenvironment (TME) has attracted tremendous interests in the field of nanomedicine. Herein, tungsten disulfide (WS₂ ) nanoflakes with their surface adsorbed with iron oxide nanoparticles (IONPs) via self-assembly are coated with silica and then subsequently with manganese dioxide (MnO₂ ), on to which polyethylene glycol (PEG) is attached. The obtained WS₂ -IO/S@MO-PEG appears to be highly sensitive to pH, enabling tumor pH-responsive magnetic resonance imaging with IONPs as the pH-inert T2 contrast probe and MnO₂ as the pH-sensitive T1 contrast probe. Meanwhile, synergistic combination tumor therapy is realized with such WS₂ -IO/S@MO-PEG, by utilizing the strong near-infrared light and X-ray absorbance of WS₂ for photothermal therapy (PTT) and enhanced cancer radiotherapy (RT), respectively, as well as the ability of MnO₂ to decompose tumor endogenous H₂ O₂ and relieve tumor hypoxia to further overcome hypoxia-associated radiotherapy resistance. The combination of PTT and RT with WS₂ -IO/S@MO-PEG results in a remarkable synergistic effect to destruct tumors. This work highlights the promise of developing multifunction nanocomposites for TME-specific imaging and TME modulation, aiming at precision cancer synergistic treatment.

Fluorescence and photoacoustic dual-mode imaging of tumor-related mRNA with a covalent linkage-based DNA nanoprobe

A fluorescence and photoacoustic dual-mode DNA nanoprobe based on covalent linkage was developed for detecting tumor-associated mRNA.

Nanoparticle-triggered in situ catalytic chemical reactions for tumour-specific therapy

This tutorial review highlights the progress and future development of nanoparticle-triggered in situ catalytic chemical reactions for tumour-specific therapy.

Erythrocyte-Membrane-Coated Prussian Blue/Manganese Dioxide Nanoparticles as H2O2-Responsive Oxygen Generators To Enhance Cancer Chemotherapy/Photothermal Therapy

Because of the nontargeting release of anticancer drugs, conventional chemotherapy results in serious side effects and poor therapeutic outcomes. In addition, hypoxia situation in the tumor microenvironment also promotes the growth and metastasis of tumors. Multifunctional nanocarriers with stimuli-activation and hypoxia-relieving properties can help overcome some of these limitations. In this study, we have constructed a nanocarrier which is named PBMn-DOX@RBC. A Prussian blue/manganese dioxide (PBMn) nanoparticle is used as an oxygen precursor or catalyzer for H₂O₂ activation, and a red blood cell (RBC) membrane is used to increase the loading capacity of doxorubicin (DOX) and prolong the circulation time in vivo. H₂O₂ is overproduced in tumor tissues and tumor cells. It can be used as a stimulus to activate drug release. In the presence of H₂O₂, the hypoxia inside the tumors is relieved by the administration of PBMn-DOX@RBC. The generated oxygen disrupts the RBC coated on the surface of PBMn, which accelerates the release of DOX. RBCs also prolong the circulation time of the nanometer system in vivo. By combining the photothermal therapy (PTT) and chemotherapy, the tumor growth inhibition mediated by PBMn-DOX@RBC is further enhanced. PBMn-DOX@RBC fulfills the demands to relieve tumor hypoxia and enhance cancer chemotherapy/PTT.

Antiferromagnetic Pyrite as the Tumor Microenvironment-Mediated Nanoplatform for Self-Enhanced Tumor Imaging and Therapy

Several decades of research have identified the specific tumor microenvironment (TME) to develop promising nanotheranostics, such as pH-sensitive imaging, acidity-sensitive starving therapy, and hydrogen peroxide-activated chemotherapy, etc. Herein, a novel TME-mediated nanoplatform employing antiferromagnetic pyrite nanocubes is presented, exploiting the intratumoral, overproduced peroxide for self-enhanced magnetic resonance imaging (MRI) and photothermal therapy (PTT)/chemodynamic therapy (CDT). Through the activation of excessive peroxide in the tumor microenvironment, pyrite can lead to in situ surface oxidation and generate hydroxyl radicals to kill tumor cells (i.e., CDT). The increase of the valence state of surface Fe significantly promotes the performance of MRI accompanied by CDT. Furthermore, the localized heat by photothermal treatment can accelerate the intratumoral Fenton process, enabling a synergetic PTT/CDT. To our best knowledge, this is the first study to use the TME-response valence-variable strategy based on pyrite for developing a synergetic nanotheranostic, which will open up a new dimension for the design of other TME-based anticancer strategies.

A bioreducible N-oxide-based probe for photoacoustic imaging of hypoxia

Hypoxia occurs when limited oxygen supply impairs physiological functions and is a pathological hallmark of many diseases including cancer and ischemia. Thus, detection of hypoxia can guide treatment planning and serve as a predictor of patient prognosis. Unfortunately, current methods suffer from invasiveness, poor resolution and low specificity. To address these limitations, we present Hypoxia Probe 1 (HyP-1), a hypoxia-responsive agent for photoacoustic imaging. This emerging modality converts safe, non-ionizing light to ultrasound waves, enabling acquisition of high-resolution 3D images in deep tissue. HyP-1 features an N-oxide trigger that is reduced in the absence of oxygen by heme proteins such as CYP450 enzymes. Reduction of HyP-1 produces a spectrally distinct product, facilitating identification via photoacoustic imaging. HyP-1 exhibits selectivity for hypoxic activation in vitro, in living cells, and in multiple disease models in vivo. HyP-1 is also compatible with NIR fluorescence imaging, establishing its versatility as a multimodal imaging agent.

Hypoxia is a hallmark of many diseases including cancer and ischemia, and detection can be invasive and of low resolution and specificity. Here the authors show a hypoxia probe that converts non-ionizing light to ultrasound, which enables the acquisition of high-resolution 3D images in deep tissue.

Nanoparticle Regrowth Enhances Photoacoustic Signals of Semiconducting Macromolecular Probe for In Vivo Imaging

Smart molecular probes that emit deep-tissue penetrating photoacoustic (PA) signals responsive to the target of interest are imperative to understand disease pathology and develop innovative therapeutics. This study reports a self-assembly approach to develop semiconducting macromolecular activatable probe for in vivo imaging of reactive oxygen species (ROS). This probe comprises a near-infrared absorbing phthalocyanine core and four poly(ethylene glycol) (PEG) arms linked by ROS-responsive self-immolative segments. Such an amphiphilic macromolecular structure allows it to undergo an ROS-specific cleavage process to release hydrophilic PEG and enhance the hydrophobicity of the nanosystem. Consequently, the residual phthalocyanine component self-assembles and regrows into large nanoparticles, leading to ROS-enhanced PA signals. The small size of the intact macromolecular probe is beneficial to penetrate into the tumor tissue of living mice, while the ROS-activated regrowth of nanoparticles prolongs the retention along with enhanced PA signals, permitting imaging of ROS during chemotherapy. This study thus capitalizes on stimuli-controlled self-assembly of macromolecules in conjunction with enhanced heat transfer in large nanoparticles for the development of smart molecular probes for PA imaging.

Ratiometric photoacoustic imaging of endoplasmic reticulum polarity in injured liver tissues of diabetic mice

As one of the complications of diabetes, liver injury results in significant hazards. Therefore, accurately diagnosing diabetes-induced liver injury beforehand is crucial for the warning and treatment of hepatic diseases. Diabetes-induced liver injury can cause changes in the microstructure and morphology of liver tissue, leading to changes in the hydrophilic and hydrophobic domains in the endoplasmic reticulum (ER), which is closely associated with changes in cellular ER polarity. So, differences in the ER polarity can indicate the degree of diabetes-induced liver injury. Herein, we develop a new fluorescent and photoacoustic dual-mode probe, ER-P, for detection of the ER polarity of liver tissue in normal and diabetic mice. Upon excitation with a 633 nm laser, ER-P showed increasing fluorescence intensity at 800 nm accompanying a decline in the polarity. Due to its polarity-sensitivity, ER-P was utilized for confocal fluorescence imaging in live cells, and the results demonstrate that ER-P can exclusively accumulate in the ER and indicate an increase in the polarity during ER stress. Importantly, ER-P displayed different absorbance intensities at 700 nm and 800 nm in different polarity environments because of intramolecular charge transfer. The photoacoustic intensity ratios between 700 nm and 800 nm will enable quantification of polarity to be achieved. The ratiometric photoacoustic imaging data demonstrate that the polarity of the liver tissue of diabetic mice is higher than that of the liver tissue of normal mice. Meanwhile, after treatment with the antidiabetic drug metformin, diabetic mice exhibit a reduced polarity environment in their liver tissue. The proposed study may serve as a new approach for the early diagnosis and therapeutic evaluation of diabetes-induced liver injury.

Broadband Absorbing Semiconducting Polymer Nanoparticles for Photoacoustic Imaging in Second Near-Infrared Window

Photoacoustic (PA) imaging holds great promise for preclinical research and clinical practice. However, most studies rely on the laser wavelength in the first near-infrared (NIR) window (NIR-I, 650-950 nm), while few studies have been exploited in the second NIR window (NIR-II, 1000-1700 nm), mainly due to the lack of NIR-II absorbing contrast agents. We herein report the synthesis of a broadband absorbing PA contrast agent based on semiconducting polymer nanoparticles (SPN-II) and apply it for PA imaging in NIR-II window. SPN-II can absorb in both NIR-I and NIR-II regions, providing the feasibility to directly compare PA imaging at 750 nm with that at 1064 nm. Because of the weaker background PA signals from biological tissues in NIR-II window, the signal-to-noise ratio (SNR) of SPN-II resulted PA images at 1064 nm can be 1.4-times higher than that at 750 nm when comparing at the imaging depth of 3 cm. The proof-of-concept application of NIR-II PA imaging is demonstrated in in vivo imaging of brain vasculature in living rats, which showed 1.5-times higher SNR as compared with NIR-I PA imaging. Our study not only introduces the first broadband absorbing organic contrast agent that is applicable for PA imaging in both NIR-I and NIR-II windows but also reveals the advantages of NIR-II over NIR-I in PA imaging.

Leveraging H2 O2 Levels for Biomedical Applications

Hydrogen peroxide (H₂ O₂ )-responsive materials have been employed as drug delivery or diagnostic systems to treat or detect diseases with abnormal oxidative stress. A number of H₂ O₂ -responsive systems have been developed, and they have achieved great progress in controlled drug delivery for disease treatment. However, pathological sites with elevated H₂ O₂ level, such as cancer and inflammation, have their own characteristics; therefore the material structures and the subsequent formulations should be reasonably designed to acquire maximized therapeutic effects. In this progress report, we overview the development of H₂ O₂ -responsive functional groups for constructing H₂ O₂ -responsive formulations, as well as the guidance for designing suitable formulations to treat each specific pathological condition. The challenges and perspectives in this field are also discussed.