Biocompatible and Water-Soluble Shortwave-Infrared (SWIR)-Emitting Cyanine-Based Fluorescent Probes for In Vivo Multiplexed Molecular Imaging.

Extending molecular imaging into the shortwave-infrared (SWIR, 900-1400 nm) region provides deep tissue visualization of biomolecules in the living system resulting from the low tissue autofluorescence and scattering. Looking at the Food and Drug Administration-approved and clinical trial near-infrared (NIR) probes, only indocyanine green (ICG) and its analogues have been approved for biomedical applications. Excitation wavelength less than 800 nm limits these probes from deep tissue penetration and noninvasive fluorescence imaging. Herein, we present the synthesis of ICG-based π-conjugation-extended cyanine dyes, ICG-C9 and ICG-C11 as biocompatible, and water-soluble SWIR-emitting probes with emission wavelengths of 922 and 1010 nm in water, respectively. Also, ICG-, ICG-C9-, and ICG-C11-based fluorescent labeling agents have been synthesized for the development of SWIR molecular imaging probes. Using the fluorescence of ICG, ICG-C9, and ICG-C11, we demonstrate three-color SWIR fluorescence imaging of breast tumors by visualizing surface receptors (EGFR and HER2) and tumor vasculature in living mice. Furthermore, we demonstrate two-color SWIR fluorescence imaging of breast tumor apoptosis using an ICG-conjugated anticancer drug, Kadcyla and ICG-C9 or ICG-C11-conjugated annexin V. Finally, we show long-term (38 days) SWIR fluorescence imaging of breast tumor shrinkage induced by Kadcyla. This study provides a general strategy for multiplexed fluorescence molecular imaging with biocompatible and water-soluble SWIR-emitting cyanine probes.

A near-infrared fluorescent long-chain fatty acid toward optical imaging of cardiac metabolism in living mice.

Non-invasive fatty acid (FA) metabolic imaging is crucial for the evaluation of cardiac function in the heart. Currently, single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are widely employed for cardiac metabolic imaging both in pre-clinical and clinical studies. Although SPECT and PET enable highly sensitive cardiac metabolic imaging, there are several disadvantages such as the high cost of instruments and radioactive tracer synthesis. In contrast, near-infrared (NIR) optical imaging using fluorescent FAs provides a simple and useful platform for in vivo imaging of cardiac metabolism. In this work, we synthesized a NIR fluorescence labelled long-chain fatty acid (LCFA) for real-time imaging of cardiac metabolism in vivo. A NIR fluorescence labelled LCFA was designed as an analogue of ß-methyl [123I] iodophenyl-pentanedecanoic acid (123I-BMIPP), which is widely used for the diagnosis of heart diseases in clinical practice. As a NIR fluorescent label, we used an Alexa 680 fluorophore that emits over 700 nm. By conjugation of Alexa 680 to Amino-BMPP (15-(4-(3-aminopropyl)phenyl)-3-methylpentadecanoic acid), we prepared a NIR fluorescent BMIPP analogue, Alexa680-BMPP. NIR fluorescence imaging showed that Alexa680-BMPP is taken up by the mouse heart tissue after intravenous injection, showing that Alexa680-BMPP can act as a fluorescent LCFA analogue. Among Alexa680 conjugated FA analogues including short and middle chain NIR fluorescent FAs, Alexa680-BMPP was most efficiently taken up by heart tissues. For fasted and fed mice, the difference in the degree of the uptake of Alexa680-BMPP in their heart tissues was clearly observed by in vivo and ex vivo NIR fluorescence imaging. Herein, we present the synthesis of a NIR fluorescent LCFA, Alexa680-BMPP, and its capability for real-time optical imaging of cardiac metabolism in living mice.

Shortwave-infrared (SWIR) emitting annexin V for high-contrast fluorescence molecular imaging of tumor apoptosis in living mice.

Recently, shortwave infrared (SWIR) fluorescence imaging over 1000 nm has attracted much attention for in vivo optical imaging because of the higher signal to background ratios in the SWIR region. For the application of SWIR fluorescence imaging to biomedical fields, the development of SWIR fluorescent molecular probes with high biocompatibility is crucial. Although many researchers have designed a variety of SWIR emitting probes based on organic dyes, the synthesis of biocompatible SWIR fluorescent molecular imaging probes is still challenging. In this work we synthesized indocyanine green (ICG) and π-conjugation extended ICG (ICG-C11) labelled annexin V as SWIR fluorescent probes for tumor apoptosis. Annexin V is an endogenous protein with binding ability to phosphatidylserine (PS) which appears on the outer monolayer of apoptotic cell membranes. Although there are many types of visible and NIR fluorescent annexin V, there are no SWIR emitting fluorescent probes that can be used for high contrast fluorescence imaging of apoptosis in vivo. Herein, we report the synthesis and application of ICG and ICG-C11 conjugated annexin V for SWIR fluorescence imaging of tumor apoptosis. The presented fluorescent annexin V is the first SWIR emitting probe for in vivo optical imaging of tumor apoptosis. We demonstrate that SWIR emitting ICG- and ICG-C11 conjugated annexin V enable high-contrast fluorescence imaging of tumor apoptosis in living mice. We further demonstrate that ICG-C11-annexin V can be used for long-term (ca. two weeks) SWIR fluorescence imaging of tumor apoptosis. The SWIR fluorescent annexin V will greatly contribute not only to the study of tumor-apoptosis induced by anti-cancer drugs, but also to the study of apoptosis-related diseases in a living system.

BRET-Based Dual-Color (Visible/Near-Infrared) Molecular Imaging Using a Quantum Dot/EGFP-Luciferase Conjugate.

By virtue of its high sensitivity, bioluminescence imaging (BLI) is an important tool for biosensing and bioimaging in life sciences. Compared to fluorescence imaging (FLI), BLI has a superior advantage that the background signals resulting from autofluorescence are almost zero due to the unnecessity of external excitation. In addition, BLI can permit a long-term observation of living cells because BL results in very low photocytotoxicity toward the host cells. Although BLI has such superior properties over FLI, the available wavelengths in BLI are mostly limited to the visible region. Here we present bioluminescence resonance energy transfer (BRET)-based visible and near-infrared dual-color molecular imaging using a quantum dot (QD) and luciferase-protein conjugate.

In Vitro and In Vivo Fluorescence Imaging of Antibody-Drug Conjugate-Induced Tumor Apoptosis Using Annexin V-EGFP Conjugated Quantum Dots.

Antibody-drug conjugates (ADCs) are conjugates of a monoclonal antibody and a cytotoxic drug that induce tumor apoptosis. The evaluation of ADC-induced tumor apoptosis is crucial for the development of ADCs for cancer therapy. To evaluate the efficacy of ADCs, we present in vitro and in vivo fluorescence imaging techniques for ADC-induced tumor apoptosis using annexin V-EGFP (EGFP: enhanced green fluorescent protein) conjugated quantum dots (annexin V-EGFP-QDs). This probe emits visible (VIS) and near-infrared (NIR) dual fluorescence at 515 nm (EGFP emission) and 850 nm (QD emission), which can be used for the detection of tumor apoptosis at the cellular and whole-body levels. By using annexin V-EGFP-QDs, we achieved VIS and NIR fluorescence imaging of human epidermal growth factor receptor 2-positive breast tumor apoptosis induced by an ADC, Kadcyla (trastuzumab emtansine). The results show that the in vitro and in vivo fluorescence imaging of ADC-induced tumor apoptosis using annexin V-EGFP-QDs is a useful tool to evaluate the efficacy of ADCs for cancer therapy.

Shortwave-Infrared Fluorescent Molecular Imaging Probes Based on π-Conjugation Extended Indocyanine Green.

Recently, shortwave-infrared (SWIR) fluorescence imaging for the optical diagnostics of diseases has attracted much attention as a new noninvasive imaging modality. For this application, the development of SWIR molecular imaging probes with high biocompatibility is crucial. Although many types of biocompatible SWIR fluorescent probes based on organic dyes have been reported, there are no SWIR-emitting molecular imaging probes that can be used for the detection of specific biomolecules in vivo. To apply SWIR-emitting molecular imaging probes to biomedical fields, we developed a biocompatible SWIR fluorescent dye based on π-conjugation extended indocyanine green (ICG), where ICG is the only approved near-infrared dye by the US Food and Drug Administration (FDA) for use in the clinic. Using the π-conjugation extended ICG, we prepared SWIR molecular imaging probes that can be used for in vivo tumor imaging. Herein, we demonstrate noninvasive SWIR fluorescence imaging of human epidermal growth factor receptor 2 (HER2)-positive and epidermal growth factor receptor (EGFR)-positive breast tumors using π-conjugation extended ICG and monoclonal antibody conjugates. The presented π-conjugation extended ICG analog probes will be a breakthrough to apply SWIR fluorescence imaging in biomedical fields.

Dual-colour (near-infrared/visible) emitting annexin V for fluorescence imaging of tumour cell apoptosis in vitro and in vivo.

Indocyanine green (ICG) labelled recombinant annexin V proteins (ICG-EGFP-Annexin V and ICG-mPlum-Annexin V) were synthesized for dual-colour fluorescence imaging of tumour cell apoptosis in vitro and in vivo. The ICG-labelled fluorescent annexin V proteins showed dual (near-infrared and visible) fluorescence emissions with binding ability to phosphatidylserines on the plasma membranes of apoptotic cells. Although several types of fluorescence labelled annexin V (e.g. FITC-annexin V, Cy3- and Cy5-annexin V) have been reported, there are no dual-colour (near-infrared/visible) emitting apoptosis-detection probes which can be used in vitro and in vivo. In this paper, the utilities of the dual-colour fluorescent annexin V are demonstrated for in vitro and in vivo fluorescence imaging of the apoptosis of human breast tumour cells induced by an antibody-drug conjugate, Kadcyla. The results suggest that the present annexin V probes will be useful to visualize the action of anti-cancer drugs against tumours both at the cellular and whole-body level.

Shortwave-infrared (SWIR) fluorescence molecular imaging using indocyanine green-antibody conjugates for the optical diagnostics of cancerous tumours.

Recently, shortwave-infrared (SWIR, 1000-1400 nm) fluorescence imaging has attracted much attention due to the higher contrast and sensitivity with deeper penetration depths compared to conventional visible and near-infrared (NIR) fluorescence imaging. For the SWIR fluorescence imaging, the development of fluorescent probes emitting over 1000 nm is necessary. So far, a variety of SWIR fluorescent probes based on single-walled carbon nanotubes, quantum dots, rare-metal doped nanomaterials, and organic dyes have been developed. However, there are a very limited number of biocompatible SWIR fluorescent probes, which can be used to biomedical applications. Among NIR and SWIR fluorescent probes, indocyanine green (ICG) is the only fluorescent dye approved by US Food and Drug Administration (FDA) for clinical use. Although ICG has a fluorescence maximum at a NIR region (ca. 830 nm), ICG emits in the SWIR region over 1000 nm. Here, we present ICG-based SWIR fluorescence molecular imaging for the highly-sensitive optical detection of breast and skin tumours in mice. As SWIR fluorescent molecular-imaging probes, we synthesized ICG-antibody conjugates, which prepared from anti-HER2 antibody (Herceptin), anti-EGFR antibody (Erbitux), anti-VEGFR-2 antibody (Cyramza), and anti-PD-L1 antibody (anti-PD-L1 ab). The present SWIR molecular imaging probes specifically accumulated to the breast and skin tumours, and their SWIR fluorescence images (>1000 nm) showed 1.5-2.0 times higher contrast than NIR tumour images taken at 830 nm. We show that the SWIR fluorescence imaging using ICG-antibody conjugates can be used for the elucidation of expression level of cancer-specific membrane proteins, HER2, EGFR, VEGFR-2, and PD-L1 in vivo. We also show that the SWIR fluorescence imaging enables quantitative analysis of the change in the size of tumour treated with an anti-cancer drug, Kadcyla. Our findings suggest that the SWIR fluorescence molecular imaging using ICG-antibody conjugates has potential to use for the optical diagnostics of cancerous tumors in medical and clinical fields.

Bioluminescence Resonance Energy Transfer (BRET) Coupled Near-Infrared Imaging of Apoptotic Cells.

Detection of apoptotic cells is crucial for understanding the mechanism of diseases and for therapy development. So far, visible-emitting fluorescent probes such as FITC-labeled Annexin V has been widely used for the detection of apoptotic cells. However, such probes cannot be applied to noninvasive imaging in the near-infrared (NIR) region. Compared with visible light, NIR light is highly permeable in turbid biological samples and tissues. In addition, NIR optical imaging has several advantages such as lower autofluorescence and scattering from biological samples, leading to clearer images with high signal to background ratios. Here, we describe the synthesis and application of bioluminescence resonance energy transfer (BRET)-coupled quantum dots (QDs) for the NIR optical imaging of apoptotic cells.

Fluorescent, Recombinant-Protein-Conjugated, Near-Infrared-Emitting Quantum Dots for in Vitro and in Vivo Dual-Color Molecular Imaging.

Near-infrared (NIR)-emitting fluorescent probes are widely used for molecular imaging at the whole-body level. However, NIR-emitting fluorescent probes emitting over λ=700 nm are not suitable for molecular imaging at the cellular level, because most of the conventional fluorescence microscopes have very low optical sensitivity in the NIR region. Thus, to achieve fluorescence imaging at the cellular and whole-body levels by using single probes, visible and NIR-emitting dual-color fluorescent probes are desirable. For dual-color fluorescence molecular imaging, we synthesized fluorescent, recombinant-protein-conjugated, NIR-emitting quantum dots (QDs), in which the recombinant protein consists of enhanced green fluorescent protein (EGFP) and the immunoglobulin binding domain (B1) of protein G. This dual-color fluorescent QD probe binds the Fc region of immunoglobulin G (IgG) through its B1 domain at the QD surface and acts as a molecular-imaging probe at both the cellular and whole-body levels. In this paper, we present the synthesis of fluorescent, recombinant protein (HisEGFP-GB1)-conjugated, NIR-emitting QDs and their application to the dual-color molecular imaging of breast cancer cells in vitro and in vivo.

BRET based dual-colour (visible/near-infrared) molecular imaging using a quantum dot/EGFP-luciferase conjugate.

Owing to its high sensitivity, bioluminescence imaging is an important tool for biosensing and bioimaging in life sciences. Compared to fluorescence imaging, bioluminescence imaging has a superior advantage that the background signals resulting from autofluorescence are almost zero. In addition, bioluminescence imaging can permit long-term observation of living cells because external excitation is not needed, leading to no photobleaching and photocytotoxicity. Although bioluminescence imaging has such superior properties over fluorescence imaging, observation wavelengths in bioluminescence imaging are mostly limited to the visible region. Here we present bioluminescence resonance energy transfer (BRET) based dual-colour (visible/near-infrared) molecular imaging using a quantum dot (QD) and luciferase protein conjugate. This bioluminescent probe is designed to emit green and near-infrared luminescence from enhanced green fluorescent protein (EGFP) and CdSeTe/CdS (core/shell) QDs, where EGFP-Renilla luciferase (RLuc) fused proteins are conjugated to the QDs. Since the EGFP-RLuc fused protein contains an immunoglobulin binding domain (GB1) of protein G, it is possible to prepare a variety of molecular imaging probes functionalized with antibodies (IgG). We show that the BRET-based QD probe can be used for highly sensitive dual-colour (visible/near-infrared) bioluminescence molecular imaging of membrane receptors in cancer cells.

Recombinant Protein (Luciferase-IgG Binding Domain) Conjugated Quantum Dots for BRET-Coupled Near-Infrared Imaging of Epidermal Growth Factor Receptors.

For the highly sensitive near-infrared (NIR) optical detection of epidermal growth factor receptors (EGFRs) expressed on cancer cells, bioluminescence resonance energy transfer (BRET) coupled NIR quantum dots (QDs) are prepared by direct conjugation of his-tagged Renilla luciferase (RLuc) recombinant protein (HisRLuc·GB1) to glutathione-coated CdSeTe/CdS QDs (GSH-QDs). The recombinant protein has two functional groups consisting of a luciferase enzyme and an immunoglobulin binding domain (GB1) of protein G. Recombinant protein (HisRLuc·GB1) conjugated QDs (GB1·RLuc-QDs) show BRET-coupled NIR emission, which results from energy transfer from luciferin to QDs with a high BRET efficiency of ca. 50%. Since the GB1·RLuc-QDs have the GB1 domain at their surface, the QDs have an ability to bind the Fc moiety of immunoglobulin G (IgG). The resulting IgG bound QDs can be used as a molecular imaging probe with NIR fluorescence and BRET-coupled NIR emission. For NIR optical detection of EGFRs on cancer cells, we conjugated anti-EGFR monoclonal antibody to the GB1·RLuc-QDs. Herein, we show that the detection sensitivity of EGFRs by BRET-coupled NIR emission of GB1·RLuc-QDs is at least three times higher than that of the NIR fluorescence of the QDs. The conjugates between anti-EGFR antibody and GB1·RLuc-QDs make it possible to perform BRET-based highly sensitive NIR imaging of EGFRs in living cells.

Bioluminescence Resonance Energy Transfer (BRET)-coupled Annexin†V-functionalized Quantum Dots for Near-Infrared Optical Detection of Apoptotic Cells.

Deregulation in apoptosis induces numerous diseases such as cancer, cardiovascular, and neurodegenerative diseases. Detection of apoptotic cells is crucial for understanding the mechanism of these diseases and for therapy development. Although optical imaging using visible-emitting fluorescent probes, such as FITC-labeled annexin V, is widely used for the detection of apoptotic cells, there are very limited probes that can be used in the near-infrared region (NIR) over 700 nm. Compared with visible light, NIR light is highly permeable in turbid biological samples and tissues. In addition, optical imaging in the NIR region shows low autofluorescence from biological samples, leading to clearer images with high signal to background ratios. Here, we report the synthesis of bioluminescence resonance energy transfer (BRET)-coupled annexin V-functionalized quantum dots (QDs) and their application to NIR optical detection of apoptotic cells.

Immunoglobulin binding (B1) domain mediated antibody conjugation to quantum dots for in vitro and in vivo molecular imaging.

A facile method for the preparation of antibody-quantum dot (QD) conjugates using the immunoglobulin binding (B1) domain of protein G is presented. The utility of antibody-QD conjugates using the B1 domain is demonstrated for fluorescence imaging of breast tumor cells in vitro and in vivo.

Near-Infrared Emitting PbS Quantum Dots for in Vivo Fluorescence Imaging of the Thrombotic State in Septic Mouse Brain.

Near-infrared (NIR) fluorescent imaging is a powerful tool for the non-invasive visualization of the inner structure of living organisms. Recently, NIR fluorescence imaging at 1000-1400 nm (second optical window) has been shown to offer better spatial resolution compared with conventional NIR fluorescence imaging at 700-900 nm (first optical window). Here we report lead sulfide (PbS) quantum dots (QDs) and their use for in vivo NIR fluorescence imaging of cerebral venous thrombosis in septic mice. Highly fluorescent PbS QDs with a 1100 nm emission peak (QD1100) were prepared from lead acetate and hexamethyldisilathiane, and the surface of QD1100 was coated with mercaptoundecanoic acid so as to be soluble in water. NIR fluorescence imaging of the cerebral vessels of living mice was performed after intravascular injection (200-300 µL) of QD1100 (3 µM) from a caudal vein. By detecting the NIR fluorescence of QD1100, we achieved non-invasive NIR fluorescence imaging of cerebral blood vessels through the scalp and skull. We also achieved NIR fluorescence imaging of cerebral venous thrombosis in septic mice induced by the administration of lipopolysaccharide (LPS). From the NIR fluorescence imaging, we found that the number of thrombi in septic mice was significantly increased by the administration of LPS. The formation of thrombi in cerebral blood vessels in septic mice was confirmed by enzyme-linked immunosorbent assay (ELISA). We also found that the number of thrombi significantly decreased after the administration of heparin, an inhibitor of blood coagulation. These results show that NIR fluorescence imaging with QD1100 is useful for the evaluation of the pathological state of cerebral blood vessels in septic mice.

Compact and stable SNAP ligand-conjugated quantum dots as a fluorescent probe for single-molecule imaging of dynein motor protein.

Compact SNAP ligand-conjugated quantum dots (<10 nm) with high colloidal stability over a wide range of pH (5-9) have been synthesized as fluorescent probe for the single-molecule imaging of dynein motor protein.