Xumeng Wu

In Vivo and in Situ Tracking Cancer Chemotherapy by Highly Photostable NIR Fluorescent Theranostic Prodrug

In vivo monitoring of the biodistribution and activation of prodrugs is urgently required. Near infrared (NIR) fluorescence-active fluorophores with excellent photostability are preferable for tracking drug release in vivo. Herein, we describe a NIR prodrug DCM-S-CPT and its polyethylene glycol-polylactic acid (PEG-PLA) loaded nanoparticles as a potent cancer therapy. We have conjugated a dicyanomethylene-4H-pyran derivative as the NIR fluorophore with camptothecin (CPT) as the anticancer drug using a disulfide linker. In vitro experiments verify that the high intracellular glutathione (GSH) concentrations in tumor cells cause cleavage of the disulfide linker, resulting in concomitantly the active drug CPT release and significant NIR fluorescence turn-on with large Stokes shift (200 nm). The NIR fluorescence of DCM-S-CPT at 665 nm with fast response to GSH can act as a direct off-on signal reporter for the GSH-activatable prodrug. Particularly, DCM-S-CPT possesses much better photostability than ICG, which is highly desirable for in situ fluorescence-tracking of cancer chemotherapy. DCM-S-CPT has been successfully utilized for in vivo and in situ tracking of drug release and cancer therapeutic efficacy in living animals by NIR fluorescence. DCM-S-CPT exhibits excellent tumor-activatable performance when intravenously injected into tumor-bearing nude mice, as well as specific cancer therapy with few side effects. DCM-S-CPT loaded in PEG-PLA nanoparticles shows even higher antitumor activity than free CPT, and is also retained longer in the plasma. The tumor-targeting ability and the specific drug release in tumors make DCM-S-CPT as a promising prodrug, providing significant advances toward deeper understanding and exploration of theranostic drug-delivery systems.

Near-Infrared Cell-Permeable Hg2+-Selective Ratiometric Fluorescent Chemodosimeters and Fast Indicator Paper for MeHg+ Based on Tricarbocyanines

Three tricarbocyanine dyes (IR-897, IR-877, and IR-925) with different thiourea substituents that function as dosimeter units through specific Hg(2+)-induced desulfurization have been demonstrated in a fast indicator paper for Hg(2+) and MeHg(+) ions. In comparison with available Hg(2+)-selective chemodosimeters, IR-897 and IR-877 show several advantages, such as convenient synthesis, very long wavelengths falling in the near-infrared (NIR) region (650-900 nm) with high molar extinction coefficients, a ratiometric response, and quite low disturbance with Ag(+) and Cu(2+) ions. They exhibit large redshifts, which result in a clear color change from deep blue to pea green that can be easily monitored by the naked eye for a convenient indicator paper. In emission spectra, they display a characteristic turn-off mode at 780 nm and turn-on mode at 830 nm with titration of Hg(2+) ions. Remarkably, the signal/noise (S/N) ratio with other thiophilic metal ions (Ag(+) and Cu(2+)) is greatly enhanced with ratiometric measurement of two channels: excitation spectra mode (I(810 nm)/I(670 nm), monitored at 830 nm) and emission spectra mode (I(830 nm)/I(780 nm), isosbestic absorption point at 730 nm as excitation). The distinct response is dependent upon the electron-donating effect of the thiourea substituents; that is, the stronger the electron-donating capability of the thiourea substituents, the faster the Hg(2+)-promoted cyclization. Additionally, experiments with living SW1116 cells show that these three tricarbocyanine dyes with low toxicity can exhibit special characteristics that are favorable for visualizing intracellular Hg(2+) and MeHg(+) ions in biological systems, including excellent membrane permeability, minimal interfering absorption and fluorescence from biological samples, low scattering, and deep penetration into tissues.

A near-infrared colorimetric fluorescent chemodosimeter for the detection of glutathione in living cells

A novel near-infrared (NIR) and colorimetric fluorescent molecular probe based on a dicyanomethylene-4H-pyran chromophore for the selective detection of glutathione in living cells has been developed. The fluorescence OFF-ON switch is triggered by cleavage of the 2,4-dinitrobenzensulfonyl (DNBS) unit by the interaction with GSH.

Constructing NIR silica–cyanine hybrid nanocomposite for bioimaging in vivo: a breakthrough in photo-stability and bright fluorescence with large Stokes shift

Optical near-infrared (NIR) nanomaterials provide a unique opportunity for applications in bioimaging and medical diagnosis. A kind of hydrophilic NIR fluorescent core–shell structured silica nanoparticle containing NIR cyanine chromophore, named as CyN-12@NHs, for in vivo bioimaging is developed through a facile one-pot strategy. The hydrophobic CyN-12 molecules can be successfully encapsulated into the core via the self-assembly of the amphiphilic block copolymer PS-b-PAA and subsequent shell cross-linking of silane. The as-prepared CyN-12@NHs exhibits typically spherical core–shell structure, which has a uniform size of 35 nm with a narrow size distribution, and excellent dispersity in aqueous solution. Moreover, NIR absorption (690 nm) and bright fluorescence (800 nm) of CyN-12@NHs with a large Stokes shift (110 nm) in aqueous system make it an amenable high quality bioimaging contrast agent. The core–shell nanostructure significantly enhances the chemical and photo-stability of CyN-12 via the encapsulation, which possesses a 50-times longer half-life period than free CyN-12, along with a better resistance to reactive oxygen species (ROS). Furthermore, in living cell imaging, CyN-12@NHs shows nearly no cytotoxicity and is able to outline the HepG2 cells. The in vivo imaging on a tumor-bearing mouse model indicates that CyN-12@NHs selectively accumulates in the liver after intravenous injection, and has a long retention in tumor after intra-tumor injection without decrease in fluorescence activity. Overall, the excellent photo-properties of CyN-12@NHs could meet the intricate requirements for tumor imaging, such as high sensitivity, sufficient tissue penetration, and high spatial resolution. The strategy of the silica–cyanine hybrid nanoparticles paves a desirable and efficient route to fabricate highly hydrophilic NIR fluorescent contrast agents for tumor imaging and therapy, especially with a breakthrough in photo-stability, bright fluorescence as well as large Stokes shift.

Near-Infrared Colorimetric and Fluorescent Cu2+ Sensors Based on Indoline–Benzothiadiazole Derivatives via Formation of Radical Cations

The donor-acceptor system of indoline-benzothiadiazole is established as the novel and reactive platform for generating amine radical cations with the interaction of Cu(2+), which has been successfully exploited as the building block to be highly sensitive and selective near infrared (NIR) colorimetric and fluorescent Cu(2+) sensors. Upon the addition of Cu(2+), an instantaneous red shift of absorption spectra as well as the quenched NIR fluorescence of the substrates is observed. The feasibility and validity of the radical cation generation are confirmed by cyclic voltammetry and electron paramagnetic resonance spectra. Moreover, the introduction of an aldehyde group extends the electron spin density and changes the charge distribution. Our system demonstrates the large scope and diversity in terms of activation mechanism, response time, and property control in the design of Cu(2+) sensors.

A novel colorimetric and ratiometric NIR fluorescent sensor for glutathione based on dicyanomethylene-4 H -pyran in living cells

Glutathione (GSH) plays a critical role in maintaining oxidation-reduction homeostasis in biological systems. Considering the detection of GSH by fluorescence sensors is limited by either the short wavelength emission or the poor photostability, a highly stable colorimetric and ratiometric NIR fluorescent sensor (DCM-S) for GSH detection has been constructed on the basis of dicyanomethylene-4H-pyran (DCM) chromophore. The specific disulfide bond is incorporated via a carbamate linker as the GSH responsive group, which simultaneously blue-shifts and quenches the fluorescence. Upon addition of GSH, DCM-S exhibits outstanding colorimetric (from yellow to red) and ratiometric fluorescent response with the 6-fold enhancement of NIR fluorescence at 665 nm in quantum yield. More importantly, the GSH-treated DCM-S (DCM-NH2 actually) possesses 20-fold longer fluorescence half-life period as well as much better photostability than the FDA-approved ICG. Finally, the ratiometric detection of GSH is also successfully operated in the living cell imaging, exhibiting NIR fluorescence and large Stokes shift (215 nm) with nearly no background fluorescence interference. As a consequence, DCM-S can be utilized as colorimetric and ratiometric NIR fluorescent sensor for GSH, with a great potential in the development of GSH-induced drug delivery system.

A Hydrophobic Dye-Encapsulated Nano-Hybrid as an Efficient Fluorescent Probe for Living Cell Imaging

Water-soluble hydrophobic-dye@nano-hybrids (DPN@NHs) with extraordinarily enhanced fluorescent performance were fabricated by encapsulating the hydrophobic dye molecules into the core of the hybrid nanospheres based on the self-assembly of amphiphilic block copolymers followed by shell cross-linking using 3-mercaptopropyltrimethoxy-silane. The DPN@NHs are 50 nm in size, are monodispersed in aqueous solution and have a quantum yield enhanced by 30 times.

CHAPTER 5:Bioimaging Nanomaterials Based on Near Infrared Organic Dyes

Organic fluorescent dyes active in the near infrared (NIR) region have attracted ongoing attention because of their diverse applications in biomedicine, materials, and related fields. The advantages include minimal interfering absorption and fluorescence from biological samples, inexpensive laser diode excitation, reduced scattering, and enhanced tissue penetration depth. Great efforts have been made in the design, synthesis, and application of organic NIR fluorophores. So far, several classes of NIR dyes, including bay-substituted perylene or naphthalene bisimides, cyanine dyes, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives, 1,4-diketo-3,6-diphenylpyrrole[3,4-c]pyrrole (DPP) derivatives, and porphyrin analogues, have been developed and intensively researched. However, most organic NIR fluorophores, which commonly have a large conjugation system, suffer from low stability. Although structural modification of existing fluorophores could enhance stability to some extent, attention has increasingly been focused on the fabrication of NIR dye-based nanomaterials with better stability and performance than free dyes. Various kinds of nanoparticles based on different substrates that encapsulate or dope NIR dyes (and therapeutic agents), some of which are surface modified by functional groups, have been derived for biological application. Moreover, fluorophores with very bright fluorescence in the aggregated form, also known as aggregation-induced emission (AIE) derivatives, have recently become a brand new research field. AIE derivatives with NIR fluorescence have exhibited excellent performance in in vivo bioimaging. This chapter focuses on recent progress in this area, including major NIR organic chromophores, luminescent principles, and construction methods, as well as applications in biomedicine and challenges.