Excretable IR-820 for in vivo NIR-II fluorescence cerebrovascular imaging and photothermal therapy of subcutaneous tumor

Upconversion NIR-II fluorophores for mitochondria-targeted cancer imaging and photothermal therapy

NIR-II fluorophores have shown great promise for biomedical applications with superior in vivo optical properties. To date, few small-molecule NIR-II fluorophores have been discovered with donor-acceptor-donor (D-A-D) or symmetrical structures, and upconversion-mitochondria-targeted NIR-II dyes have not been reported. Herein, we report development of D-A type thiopyrylium-based NIR-II fluorophores with frequency upconversion luminescence (FUCL) at ~580 nm upon excitation at ~850 nm. H4-PEG-PT can not only quickly and effectively image mitochondria in live or fixed osteosarcoma cells with subcellular resolution at 1 nM, but also efficiently convert optical energy into heat, achieving mitochondria-targeted photothermal cancer therapy without ROS effects. H4-PEG-PT has been further evaluated in vivo and exhibited strong tumor uptake, specific NIR-II signals with high spatial and temporal resolution, and remarkable NIR-II image-guided photothermal therapy. This report presents the first D-A type thiopyrylium NIR-II theranostics for synchronous upconversion-mitochondria-targeted cell imaging, in vivo NIR-II osteosarcoma imaging and excellent photothermal efficiency.

Sequential Release Platform of Heparin and Urokinase with Dual Physical (NIR-II and Bubbles) Assistance for Deep Venous Thrombosis

Disability and even death from acute thrombosis remain a grave menace to public health. At present, the traditional drugs represented by urokinase (UK) in clinical thrombolysis can cause side effects of bleeding when the dosage is excess. Therefore, a more effective and safer method of thrombolysis is urgently needed. In this paper, a multifunctional dual-drug sequential release thrombolysis platform (UK-UH@PDA@HMSNs) consisting of polydopamine (PDA)-modified hollow mesoporous silicon (HMSNs) loading with UK and unfractionated heparin (UH) was constructed with a double physical assistance (NIR-II and bubbles). With the aid of near infrared-II (NIR-II, 1064 nm, 1.0 W cm^-2) laser, the photothermal effect of PDA could be motivated to facilitate the UH release, thereby accelerating the dissolution of thrombus. Afterward, the local hyperthermia effect could expedite the phase transition of l-menthol in HMSNs to generate bubbles to promote the release of UK, thereby realizing the sequential release of two thrombolytic drugs. Importantly, this method deftly conquered the inherent obstacle that UK and UH cannot be combined directly. In vivo and in vitro experiments proved that the thrombolytic efficiency of UK-UH@PDA@HMSNs stimulated by NIR-II was nearly 3 times than that of UK alone. Collectively, the proposed dual physical assistance and sequential dual-drug delivery system significantly improved the efficiency of thrombolysis under the premise of limiting drug doses; the risk of death from intracranial hemorrhage thus could be decreased radically.

Incorporation of Planar Blocks into Twisted Skeletons: Boosting Brightness of Fluorophores for Bioimaging beyond 1500 Nanometer

The brightness of organic fluorescence materials determines their resolution and sensitivity in fluorescence display and detection. However, strategies to effectively enhance the brightness are still scarce. Conventional planar π-conjugated molecules display excellent photophysical properties as isolated species but suffer from aggregation-caused quenching effect when aggregated owing to the cofacial π-π interactions. In contrast, twisted molecules show high photoluminescence quantum yield (Φ_PL) in aggregate while at the cost of absorption due to the breakage in conjugation. Therefore, it is challenging to integrate the strong absorption and high solid-state Φ_PL, which are two main indicators of brightness, into one molecule. Herein, we propose a molecular design strategy to boost the brightness through the incorporation of planar blocks into twisted skeletons. As a proof-of-concept, twisted small-molecule TT3-oCB with larger π-conjugated dithieno[3,2-b:2',3'-d]thiophene unit displays superb brightness at the NIR-IIb (1500-1700 nm) than that of TT1-oCB and TT2-oCB with smaller thiophene and thienothiophene unit, respectively. Whole-body angiography using TT3-oCB nanoparticles presents an apparent vessel width of 0.29 mm. Improved NIR-IIb image resolution is achieved for femoral vessels with an apparent width of only 0.04 mm. High-magnification through-skull microscopic NIR-IIb imaging of cerebral vasculature gives an apparent width of ∼3.3 μm. Moreover, the deeply located internal organ such as bladder is identified with high clarity. The present molecular design philosophy embodies a platform for further development of in vivo bioimaging.

Visible-near infrared-II skull optical clearing window for in vivo cortical vasculature imaging and targeted manipulation

Skull optical clearing window permits us to perform in vivo cortical imaging without craniotomy, but mainly limits to visible (vis)-near infrared (NIR)-I light imaging. If the skull optical clearing window is available for NIR-II, the imaging depth will be further enhanced. Herein, we developed a vis-NIR-II skull optical clearing agents with deuterium oxide instead of water, which could make the skull transparent in the range of visible to NIR-II. Using a NIR-II excited third harmonic generation microscope, the cortical vasculature of mice could be clearly distinguished even at the depth of 650 μm through the vis-NIR-II skull clearing window. The imaging depth after clearing is close to that without skull, and increases by three times through turbid skull. Furthermore, the new skull optical clearing window promises to realize NIR-II laser-induced targeted injury of cortical single vessel. This work enhances the ability of NIR-II excited nonlinear imaging techniques for accessing to cortical neurovasculature in deep tissue.

Contrast-Enhanced Multispectral Photoacoustic Imaging for Irregular Hepatectomy Navigation: A Pilot Study

Irregular hepatectomy plays a prominent role in the treatment of small hepatocellular carcinoma (HCC) patients with severe cirrhosis and localized liver metastasis. In clinical practices, intraoperative tumor boundaries delineation facilitates to accomplish tumor resection with negative margin, remarkably decreasing the recurrence rates. Currently, ultrasound (US) and ICG fluorescence-guided surgery has been used for intraoperative navigation in irregular hepatectomy, but insufficient specificity results in a limited prevalence. Inspired by the high resolution of photoacoustic (PA) imaging and established clinical efficacy of ¹⁸F-Alfatide that is specific for integrin α_vβ₃-overexpressed tumors, we herein developed a fluorescent analogue IR820-E[c(RGDfK)]₂, and a proof-of-concept intraoperative multispectral PA imaging navigation for precise irregular hepatectomy using hand-held PA/US imaging system. An integrin α_vβ₃-targeted fluorescent contrast agent IR820-E[c(RGDfK)]₂ was designed, synthesized, and characterized. In vitro studies were performed to determine optical and PA properties, affinity and specificity and biocompatibility. Multispectral PA imaging, the optimal imaging time point and contrast, multispectral PA imaging-guided irregular hepatectomy, pharmacokinetics, and safety profile were evaluated in subcutaneous and orthotopic HCC tumor models. Ex vivo macroscopic three-dimensions (3D) PA imaging with IR820-E[c(RGDfK)]₂ staining was also performed in surgical biospecimens from patients with HCC. IR820-E[c(RGDfK)]₂ has a simple synthetic method at gram scale, high affinity, and specificity for integrin α_vβ₃, excellent pharmacokinetic and safety profile can effectively differentiate tumor from normal liver tissues in animal models and surgical biospecimens from HCC patients. Preoperative tumor localization, intraoperative tumor boundaries delineation, and tumor excision, and postoperative negative margin assessment were successfully achieved during irregular hepatectomy. This initial attempt allows one to preoperatively detect tumor lesions, intraoperatively delineate tumor boundaries and guide tumor resection, and postoperatively evaluate tumor margin status during irregular hepatectomy. IR820-E[c(RGDfK)]₂ has the potential to be an investigational new drug for clinical use in multispectral photoacoustic imaging-guided irregular hepatectomy.

Near-infrared-IIb probe affords ultrahigh contrast inflammation imaging

Deep tissue imaging in the near-infrared II (NIR-II) window with significantly reduced tissue autofluorescence and scattering provides an important modality to visualize various biological events. Current commercially used contrast agents in the near-infrared spectrum suffer from severe photobleaching, high tissue scattering, and background signals, hampering high-quality in vivo bioimaging, particularly in small animals. Here, we applied a NIR-IIb quantum dot (QD) probe with greatly suppressed photon scattering and zero autofluorescence to map inflammatory processes. Two-layer surface modification by a combination of amphiphilic polymer and mixed linear and multi-armed polyethylene glycol chains prolonged probe circulation in vivo and improved its accumulation in the inflammation sites. Compared to indocyanine green, a widely applied dye in the clinic, our QD probe showed greater photostability and capacity for deeper tissue imaging with superior contrast. The longer circulation of QDs also improved vessel imaging, which is vital for better understanding of biological mechanisms of the inflammation microenvironment. Our proposed NIR-IIb in vivo imaging modality proved effective for the visualization of inflammation in small animals, and its use may be extended in future to studies of immunity and cancer.

Structural and process controls of AIEgens for NIR-II theranostics

Aggregation-induced emission (AIE) is a cutting-edge fluorescence technology, giving highly-efficient solid-state photoluminescence. Particularly, AIE luminogens (AIEgens) with emission in the range of second near-infrared window (NIR-II, 1000-1700 nm) have displayed salient advantages for biomedical imaging and therapy. However, the molecular design strategy and underlying mechanism for regulating the balance between fluorescence (radiative pathway) and photothermal effect (non-radiative pathway) in these narrow bandgap materials remain obscure. In this review, we outline the latest achievements in the molecular guidelines and photophysical process control for developing highly efficient NIR-II emitters or photothermal agents with aggregation-induced emission (AIE) attributes. We provide insights to optimize fluorescence efficiency by regulating multi-hierarchical structures from single molecules (flexibilization) to molecular aggregates (rigidification). We also discuss the crucial role of intramolecular motions in molecular aggregates for balancing the functions of fluorescence imaging and photothermal therapy. The superiority of the NIR-II region is demonstrated by fluorescence/photoacoustic imaging of blood vessels and the brain as well as photothermal ablation of the tumor. Finally, a summary of the challenges and perspectives of NIR-II AIEgens for in vivo theranostics is given.

Depth-resolved NIR-II fluorescence mesoscope

NIR-II fluorescence imaging is a promising method for visualizing biological structures in deep tissue, owing to the advantages of significantly suppressed optical scattering and diminished autofluorescence in biological tissues. However, few NIR-II fluorescence imaging approaches can simultaneously achieve a large field of view, high resolution and superior penetration depth, while exhibiting optical sectioning capability. In this paper, we present a novel NIR-II fluorescence mesoscopy system based on the f-θ scanning scheme and confocal detection to overcome these limitations. When used with NIR-II fluorescent dyes, our setup performs NIR-II fluorescence imaging on samples as large as 7.5×7.5 mm2 with a lateral resolution of 6.3 µm. In addition, our system provides a depth-resolved imaging ability and zooming function. We successfully demonstrate in vivo cerebrovascular imaging of a mouse with local ischemia. Thus, our system provides new opportunities to explore the mechanism of cerebrovascular disease.

miR-211-5p alleviates focal cerebral ischemia-reperfusion injury in rats by down-regulating the expression of COX2

The present study was to investigate the role of microRNA (miR)-211-5p on cerebral ischemia-reperfusion injury (CIRI) and clarify its underlying mechanisms. Middle cerebral artery occlusion/reperfusion (MCAO/R) was operated on male Sprague Dawley (SD) rats, oxygen-glucose deprivation/reperfusion (OGD/R) was conducted on pheochromocytoma-12 (PC12) cells. Here, we found that miR-211-5p and Cyclooxygenase (COX2) expressions were altered in the plasma, cortex and hippocampus of MCAO/R-treated rats, as well as in the OGD/R-treaded PC12 cells. In vivo, overexpression of miR-211-5p resulted in decrease of infarct volumes, neurological deficit scores and histopathological damage. In vitro, miR-211-5p overexpression significantly decreased cell apoptosis and Lactate dehydrogenase (LDH) release rate, increased cell viability. Furthermore, our data showed that miR-211-5p overexpression markedly reduced the expressions of COX2 mRNA and protein, and the contents of Prostaglandin D2 (PGD2), PGE2, tumor necrosis factor-α (TNF-α) and Interleukin-1β (IL-1β). In addition, inhibition of COX2 significantly rescued the effects of miR-211-5p inhibitor. At last, dual luciferase experimental data showed that miR-211-5p regulated the mRNA stability of COX2 by directly binding to the 3'-untranslated region (3'-UTR) of COX2. In conclusion, our data suggested the neuroprotective effects of miR-211-5p on CIRI by targeting COX2.

NIR-II fluorescence microscopic imaging of cortical vasculature in non-human primates

Vasculature architecture of the brain can provide revealing information about mental and neurological function and disease. Fluorescence imaging in the second near-infrared (NIR-II) regime with less light scattering is a more promising method for detecting cortical vessels than traditional visible and NIR-I modes. Methods: Clinically approved dye indocyanine green (ICG) was used for NIR-II fluorescence imaging. Here, for the first time, we developed two NIR-II fluorescence microscopy systems for brain vasculature imaging in macaque monkeys. The first is a wide-field microscope with high temporal resolution for measuring blood flow velocity and cardiac impulse period, while the second is a high spatial resolution confocal microscope producing three-dimensional maps of the cortical microvascular network. Both were designed with flexibility to image various cortical locations on the head. Results: Here, ICG was proved to have high brightness in NIR-II region and an 8-fold QY increase in serum than in water. We achieved cerebrovascular functional imaging of monkey with high temporal resolution (25 frames/second) with wide-field microscope. The blood flow velocity of capillaries can be precisely calculated and the cardiac impulse period can be monitored as well. In vivo structural imaging of cerebrovasculature was accomplished with both high spatial lateral resolution (~8 µm) and high signal to background ratio (SBR). Vivid 3D reconstructed NIR-II fluorescence confocal microscopic images up to depth of 470 μm were also realized. Conclusion: This work comprises an important advance towards studies of neurovascular coupling, stroke, and other diseases relevant to neurovascular health in humans.

Molecular Antenna-Sensitized Upconversion Nanoparticle for Temperature Monitored Precision Photothermal Therapy

Background

Photothermal therapy with accurate and real-time temperature detection is desired in clinic. Upconversion nanocrystals (UCNs) are candidate materials for simultaneous temperature detection and photothermal agents carrying. However, the weak luminescence and multiple laser excitations of UCNs limit their application in thermal therapy.

Materials and Methods

NaYF₄:Yb³⁺,Er³⁺,Nd³⁺, PL-PEG-NH₂, IR-806 and folic acid are selected as structural components. A nanoprobe (NP) integrated with efficient photothermal conversion and sensitive temperature detection capabilities is synthesized for precise photothermal therapy. The probes are based on near-infrared upconversion nanocrystals doped with Yb, Er and Nd ions, which can be excited by 808 nm light. IR-806 dye molecules are modified on the surface as molecular antennas to strongly absorb near-infrared photons for energy transfer and conversion.

Results

The results show that under an 808 nm laser irradiation upconversion luminescence of the nanocrystals is enhanced based on both the Nd ion absorption and the FRET energy transfer of IR-806. The luminescence ratio at 520 and 545 nm is calculated to accurately monitor the temperature of the nanoparticles. The temperature of the nanoprobes increases significantly through energy conversion of the molecular antennas. The nanoparticles are found successfully distributed to tumor cells and tumor tissue due to the modification of the biocompatible molecules on the surface. Tumor cells can be killed efficiently based on the photothermal effect of the NPs. Under the laser irradiation, temperature at mouse tumor site increases significantly, tissue necrosis and tumor cell death can be observed.

Conclusion

Precision photothermal therapy can thus be achieved by highly efficient near-infrared light absorption and accurate temperature monitoring, making it promising for tumor treatment, as well as the biological microzone temperature detection.

Multiplexed NIR-II Probes for Lymph Node-Invaded Cancer Detection and Imaging-Guided Surgery

Tumor-lymph node (LN) metastasis is the dominant prognostic factor for tumor staging and therapeutic decision-making. However, concurrently visualizing metastasis and performing imaging-guided lymph node surgery is challenging. Here, a multiplexed-near-infrared-II (NIR-II) in vivo imaging system using nonoverlapping NIR-II probes with markedly suppressed photon scattering and zero-autofluorescence is reported, which enables visualization of the metastatic tumor and the tumor metastatic proximal LNs resection. A bright and tumor-seeking donor-acceptor-donor (D-A-D) dye, IR-FD, is screened for primary/metastatic tumor imaging in the NIR-IIa (1100-1300 nm) window. This optimized D-A-D dye exhibits greatly improved quantum yield of organic D-A-D fluorophores in aqueous solutions (≈6.0%) and good in vivo performance. Ultrabright PbS/CdS core/shell quantum dots (QDs) with dense polymer coating are used to visualize cancer-invaded sentinel LNs in the NIR-IIb (>1500 nm) window. Compared to clinically used indocyanine green, the QDs show superior brightness and photostability (no obvious bleaching even after continuous laser irradiation for 5 h); thus, only a picomolar dose is required for sentinel LNs detection. This combination of dual-NIR-II image-guided surgery can be performed under bright light, adding to its convenience and appeal in clinical use.

Extrahepatic cholangiography in near-infrared II window with the clinically approved fluorescence agent indocyanine green: a promising imaging technology for intraoperative diagnosis

Rationale: Biliary tract injury remains the most dreaded complication during laparoscopic cholecystectomy. New intraoperative guidance technologies, including near-infrared (NIR) fluorescence cholangiography with indocyanine green (ICG), are under comprehensive evaluation. Previous studies had shown the limitations of traditional NIR light (NIR-I, 700-900 nm) in visualizing the biliary tract structures in specific clinical situations. The aim of this study was to evaluate the feasibility of performing the extrahepatic cholangiography in the second NIR window (NIR-II, 900-1700 nm) and compare it to the conventional NIR-I imaging. Methods: The absorption and emission spectra, as well as fluorescence intensity and photostability of ICG-bile solution in the NIR-II window were recorded and measured. In vitro intralipid® phantom imaging was performed to evaluate tissue penetrating depth in NIR-I and NIR-II window. Different clinical scenarios were modeled by broadening the penetration distance or generating bile duct injuries, and bile duct visualization and lesion site diagnosis in the NIR-II window were evaluated and compared with NIR-I imaging. Results: The fluorescence spectrum of ICG-bile solution extends well into the NIR-II region, exhibiting intense emission value and excellent photostability sufficient for NIR-II biliary tract imaging. Extrahepatic cholangiography using ICG in the NIR-II window obviously reduced background signal and enhanced penetration depth, providing more structural information and improved visualization of the bile duct or lesion location in simulated clinical scenarios, outperforming the NIR-I window imaging. Conclusions: The conventional clinically approved agent ICG is an excellent fluorophore for NIR-II bile duct imaging. Fluorescence cholangiography with ICG in the NIR-II window could provide adequate visualization of the biliary tract structures with increased resolution and penetration depth and might be a valid option to increase the safety of cholecystectomy in difficult cases.

Deciphering of cerebrovasculatures via ICG-assisted NIR-II fluorescence microscopy

Benefiting from high spatial resolution and large penetration depth, NIR-II (second near-infrared spectral region, 900-1700 nm) fluorescence imaging based on US Food and Drug Administration (FDA)-approved indocyanine green (ICG) is expected to be a good approach for clinical applications. As of now, nearly all reported works on ICG-assisted NIR-II fluorescence imaging are macro-imaging while micro-angiography is also a significant imaging modality, especially during the diagnosis and treatment of cerebrovascular diseases. Herein, based on NIR-II fluorescence wide-field microscopy, the high-resolution observation of cerebral vasculature was performed at deep brain tissues in mice via intramuscular (IM) injection of ICG. Altered cerebral vessels in mice after brain embolism were further noticed by means of noninvasive through-skull NIR-II fluorescence microscopy. Moreover, ICG-assisted NIR-II fluorescence confocal microscopy was executed to observe cerebral vasculature, presenting optical sectioning capability and higher spatial resolution.