Recent progress on semiconducting polymer nanoparticles for molecular imaging and cancer phototherapy

Ingestible roasted barley for contrast-enhanced photoacoustic imaging in animal and human subjects

Photoacoustic computed tomography (PACT) is an emerging imaging modality. While many contrast agents have been developed for PACT, these typically cannot immediately be used in humans due to the lengthy regulatory process. We screened two hundred types of ingestible foodstuff samples for photoacoustic contrast with 1064 nm pulse laser excitation, and identified roasted barley as a promising candidate. Twenty brands of roasted barley were further screened to identify the one with the strongest contrast, presumably based on complex chemical modifications incurred during the roasting process. Individual roasted barley particles could be detected through 3.5 cm of chicken-breast tissue and through the whole hand of healthy human volunteers. With PACT, but not ultrasound imaging, a single grain of roasted barley was detected in a field of hundreds of non-roasted particles. Upon oral administration, roasted barley enabled imaging of the gut and peristalsis in mice. Prepared roasted barley tea could be detected through 2.5 cm chicken breast tissue. When barley tea was administered to humans, photoacoustic imaging visualized swallowing dynamics in healthy volunteers. Thus, roasted barley represents an edible foodstuff that should be considered for photoacoustic contrast imaging of swallowing and gut processes, with immediate potential for clinical translation.

"Dual Lock-and-Key"-Controlled Nanoprobes for Ultrahigh Specific Fluorescence Imaging in the Second Near-Infrared Window

Fluorescence imaging in the second near-infrared window (NIR-II) is a new technique that permits visualization of deep anatomical features with unprecedented spatial resolution. Although attractive, effectively suppressing the interference signal of the background is still an enormous challenge for obtaining target-specific NIR-II imaging in the complex and dynamic physiological environment. Herein, dual-pathological-parameter cooperatively activatable NIR-II fluorescence nanoprobes (HISSNPs) are developed whereby hyaluronic acid chains and disulfide bonds act as the "double locks" to lock the fluorescence-quenched aggregation state of the NIR-II fluorescence dyes for performing ultrahigh specific imaging of tumors in vivo. The fluorescence can be lit up only when the "double locks" are opened by reacting with the "dual smart keys" (overexpressed hyaluronidase and thiols in tumor) simultaneously. In vivo NIR-II imaging shows that they reduce nonspecific activitation and achieve ultralow background fluorescence, which is 10.6-fold lower than single-parameter activatable probes (HINPs) in the liver at 15 h postinjection. Consequently, these "dual lock-and-key"-controlled HISSNPs exhibit fivefold higher tumor-to-normal tissue ratio than "single lock-and-key"-controlled HINPs at 24 h postinjection, attractively realizing ultrahigh specificity of tumor imaging. This is thought to be the first attempt at implementing ultralow background interference with the participation of multiple pathological parameters in NIR-II fluorescence imaging.

The evolution of artificial light actuators in living systems: from planar to nanostructured interfaces

Artificially enhancing light sensitivity in living cells allows control of neuronal paths or vital functions avoiding the wiring associated with the use of stimulation electrodes. Many possible strategies can be adopted for reaching this goal, including the direct photoexcitation of biological matter, the genetic modification of cells or the use of opto-bio interfaces. In this review we describe different light actuators based on both inorganic and organic semiconductors, from planar abiotic/biotic interfaces to nanoparticles, that allow transduction of a light signal into a signal which in turn affects the biological activity of the hosting system. In particular, we will focus on the application of thiophene-based materials which, thanks to their unique chemical-physical properties, geometrical adaptability, great biocompatibility and stability, have allowed the development of a new generation of fully organic light actuators for in vivo applications.

Near-infrared light-activated IR780-loaded liposomes for anti-tumor angiogenesis and Photothermal therapy

Tumor angiogenesis is a key step in the process of tumor development, and antitumor angiogenesis has a profound influence on tumor growth. Herein we report a dual-function drug delivery system comprising a Near-infrared (NIR) dye and an anti-angiogenic drug within liposomes (Lip-IR780-Sunitinib) for enhanced antitumor therapy. The hydrophobic NIR dye IR780 was loaded into the liposome phospholipid bilayer, and the bilayer would be disrupted by laser irradiation so that anti-angiogenic drug sunitinib release would be activated remotely at the tumor site. The released hydrophilic sunitinib could potentially target multiple VEGF receptors on the tumor endothelial cell surface to inhibit angiogenesis. Meanwhile, IR780-loaded liposomes kill the cancer cells by photothermal therapy. Lip-IR780-Sunitinib exhibited enhanced anti-tumor and anti-angiogenic effects in vitro and in vivo. This system facilitates easy and controlled release of cargos to achieve anti-tumor angiogenesis and photothermal therapy.

Multiscale Imaging of Brown Adipose Tissue in Living Mice/Rats with Fluorescent Polymer Dots

Brown adipose tissue (BAT) has been identified as a promising target for the treatment of obesity, diabetes, and relevant metabolism disorders because of the adaptive thermogenesis ability of this tissue. Visualizing BAT may provide an essential tool for pathology study, drug screening, and efficacy evaluation. Owing to limitations of current nuclear and magnetic resonance imaging approaches for BAT detection, fluorescence imaging has advantages in large-scale preclinical research on small animals. Here, fast BAT imaging in mice is conducted based on polymer dots as fluorescent probes. As early as 5 min after the intravenous injection of polymer dots, extensive fluorescence is detected in the interscapular BAT and axillar BAT. In addition, axillar and inguinal white adipose tissues (WAT) are recognized. The real-time in vivo behavior of polymer dots in rodents is monitored using the probe-based confocal laser endomicroscopy imaging, and the preferred accumulation in BAT over WAT is confirmed by histological assays. Moreover, the whole study is conducted without a low temperature or pharmaceutical stimulation. The imaging efficacy is verified at the cellular, histological, and whole-body levels, and the present results indicate that fluorescent polymer dots may be a promising tool for the visualization of BAT in living subjects.

N-(2-hydroxypropyl)methacrylamide polymer conjugated pyropheophorbide-a, a promising tumor-targeted theranostic probe for photodynamic therapy and imaging

Tumor-targeted photodynamic therapy (PDT) using polymeric photosensitizers is a promising therapeutic strategy for cancer treatment. In this study, we synthesized a pHPMA conjugated pyropheophorbide-a (P-PyF) as a cancer theranostic agent for PDT and photodynamic diagnostics (PDD). Pyropheophorbide-a has one carboxyl group which was conjugated to pHPMA via amide bond yielding the intended product with high purity. In aqueous solutions, P-PyF showed a mean particle size of ∼200 nm as it forms micelle which exhibited fluorescence quenching and thus very little singlet oxygen (¹O₂) production. In contrast, upon disruption of micelle strong fluorescence and ¹O₂ production were observed. In vitro study clearly showed the PDT effect of P-PyF. More potent ¹O₂ production and PDT effect were observed during irradiation at ∼420 nm, the maximal absorbance of pyropheophorbide-a, than irradiation at longer wavelength (i.e., ∼680 nm), suggesting selection of proper absorption light is essential for successful PDT. In vivo study showed high tumor accumulation of P-PyF compared with most of normal tissues due to the enhanced permeability and retention (EPR) effect, which resulting in superior antitumor effect under irradiation using normal xenon light source of endoscope, and clear tumor imaging profiles even in the metastatic lung cancer at 28 days after administration of P-PyF. On the contrary irradiation using long wavelength (i.e., ∼680 nm), the lowest Q-Band, exhibited remarkable tumor imaging effect with little autofluorescence of background. These findings strongly suggested P-PyF may be a potential candidate-drug for PDT/PDD, particularly using two different wavelength for treatment and detection/imaging, respectively.

Influence of the Surfactant Structure on Photoluminescent π-Conjugated Polymer Nanoparticles: Interfacial Properties and Protein Binding

π-Conjugated polymer nanoparticles (CPNs) are under investigation as photoluminescent agents for diagnostics and bioimaging. To determine whether the choice of surfactant can improve CPN properties and prevent protein adsorption, five nonionic polyethylene glycol alkyl ether surfactants were used to produce CPNs from three representative π-conjugated polymers. The surfactant structure did not influence size or yield, which was dependent on the nature of the conjugated polymer. Hydrophobic interaction chromatography, contact angle, quartz crystal microbalance, and neutron reflectivity studies were used to assess the affinity of the surfactant to the conjugated polymer surface and indicated that all surfactants were displaced by the addition of a model serum protein. In summary, CPN preparation methods which rely on surface coating of a conjugated polymer core with amphiphilic surfactants may produce systems with good yields and colloidal stability in vitro, but may be susceptible to significant surface alterations in physiological fluids.

Recent advances in near-infrared II fluorophores for multifunctional biomedical imaging

In recent years, owing to unsatisfactory clinical imaging clarity and depths in the living body for early diagnosis and prognosis, novel imaging modalities with high bioimaging performance have been actively explored. The remarkable headway made in the second near-infrared region (NIR-II, 1000-1700 nm) has promoted the development of biomedical imaging significantly. NIR-II fluorescence imaging possesses a number of merits which prevail over the traditional and NIR-I (400-900 nm) imaging modalities in fundamental research, such as reduced photon scattering, as well as auto-fluorescence and improved penetration depth. Functional probes for instant and precise feedback of in vivo information are at the core of this modality for superb imaging. Herein, we review the recently developed fluorophores including carbon nanotubes, organic small molecules, quantum dots, conjugated polymers and rare-earth-doped materials to present superior and multifunctionality of biomedical imaging in the NIR-II regions (1000-1700 nm).

Size-Modulable Nanoprobe for High-Performance Ultrasound Imaging and Drug Delivery against Cancer

Among medical imaging modalities available in the clinic, ultrasonography is the most convenient, inexpensive, ionizing-radiation-free, and most common. Micrometer-size perfluorocarbon bubbles have been used as efficient contrast for intravascular ultrasonography, but they are too big for tumor penetration. Nanodroplets (250-1000 nm) encapsulating both perfluorocarbon and drug have been used as an ultrasound-triggered release drug delivery platform against cancer, but they are generally not useful as a tumor imaging agent. The present study aims to develop a type of pH-sensitive, polymersome-based, perfluorocarbon encapsulated ultrasonographic nanoprobe, capable of maintaining at 178 nm during circulation and increasing to 437 nm at the acidic tumor microenvironment. Its small size allowed efficient tumor uptake. At the tumor site, the nanoparticle swells, resulting in lowering of the vaporization threshold for the perfluorocarbon, efficient conversion of nanoprobes to echogenic nano/microbubbles for ultrasonic imaging, and eventual release of doxorubicin from the theranostic nanoprobe for deep tissue chemotherapy, triggered by irradiation with low-frequency ultrasound.

PEGylated TiO2 nanoparticles mediated inhibition of cell migration via integrin beta 1

Nanoparticles (NPs) elicit various physiological responses in cellular environment, and the effect of NPs on cell migration is of high interest. In this work, the effects of NPs on cell migration and their possible mechanisms were studied. Here, we showed that after exposure to pegylated titanium dioxide nanoparticles (TiO₂-PEG NPs, where PEG stands for the polyethylene glycol), NCI-H292 cells exhibited slower migration than control cells. Furthermore, larger NPs inhibited cell migration much stronger than smaller NPs. Following NP exposure, the cells showed decreased expression of integrin beta 1 and phosphorylated focal adhesion kinase (pFAK), and disrupted F-actin structures. We demonstrated that a possible mechanism involved NP-mediated promotion of the lysosomal degradation of integrin beta 1, thus leading to reduced expression of pFAK and cytoskeletal disruption and inhibited cell migration. Therefore, our results showed that inhibition of NCI-H292 cell migration by NPs is mediated through integrin beta 1, which provides useful information for the application of NPs in cancer therapy and related fields.

Oxygenic Hybrid Semiconducting Nanoparticles for Enhanced Photodynamic Therapy

Photodynamic nanotheranostics has shown great promise for cancer therapy; however, its therapeutic efficacy is limited due to the hypoxia of tumor microenvironment and the unfavorable bioavailability of existing photodynamic agents. We herein develop hybrid core-shell semiconducting nanoparticles (SPN-Ms) that can undergo O₂ evolution in hypoxic solid tumor to promote photodynamic process. Such oxygenic nanoparticles are synthesized through a one-pot surface growth reaction and have a unique multilayer structure cored and coated with semiconducting polymer nanoparticles (SPNs) and manganese dioxide (MnO₂) nanosheets, respectively. The SPN core serves as both NIR fluorescence imaging and photodynamic agent, while the MnO₂ nanosheets act as a sacrificing component to convert H₂O₂ to O₂ under hypoxic and acidic tumor microenvironment. As compared with the uncoated SPN (SPN-0), the oxygenic nanoparticles (SPN-M1) generate 2.68-fold more ¹O₂ at hypoxic and acidic conditions under NIR laser irradiation at 808 nm. Because of such an oxygen-evolution property, SPN-M1 can effectively eradicate cancer cells both in vitro and in vivo. Our study thus not only reports an in situ synthetic method to coat organic nanoparticles but also develops a tumor-microenvironment-sensitive theranostic nanoagent to overcome hypoxia for amplified therapy.

Theranostic nanocomposite from upconversion luminescent nanoparticles and black phosphorus nanosheets

An anti-cancer campaign might not be easily achieved through a single therapeutic modality. Collaboration of multimodal therapies and diagnosis could be vital to win the battle against cancer. In this context, we synthesized a multifunctional theranostic nanocomposite (UCNP–BPNS) from upconversion nanoparticles (UCNP) and black phosphorus nanosheets (BPNS) for synergistic photothermal/photodynamic therapies in vitro and dual modal imaging. Core–shell UCNP (NaYF₄:Yb,Er@NaGdF₄) and BPNS were synthesized using solvo-thermal and liquid exfoliation methods, respectively, and then covalently conjugated after UCNP was modified with polyacrylic acid and BPNS with methoxypolyethylene glycol amine. The experimental results validate that the nanocomposite exhibited a good photothermal therapy (PTT) effect under 808 nm laser irradiation, endorsing the apparent heat conversion effect of BPNS. Besides, a very good photodynamic therapy (PDT) effect was achieved under 980 nm laser irradiation of the nanocomposite due to Förster resonance energy transfer from UCNP to BPNS that generated singlet oxygen (¹O₂). The synergistic PTT/PDT therapeutic effect provided by UCNP–BPNS under simultaneous 808 and 980 nm laser irradiation was significantly higher than either PTT or PDT alone. Furthermore, due to the merit of the outer shell coated on the surface of the core of UCNP, the nanocomposite exhibited good potential for magnetic resonance and upconversion luminescence imaging. These results demonstrated that our multifunctional nanocomposite has promising theranostic efficacy under near infrared laser irradiation.

We successfully synthesized a multifunctional theranostic nanocomposite from upconversion nanoparticles and black phosphorus nanosheets for synergistic photothermal/photodynamic therapies in vitro and dual modal imaging.

In vivo theranostics with near-infrared-emitting carbon dots-highly efficient photothermal therapy based on passive targeting after intravenous administration

Carbon dots that exhibit near-infrared fluorescence (NIR CDs) are considered emerging nanomaterials for advanced biomedical applications with low toxicity and superior photostability and targeting compared to currently used photoluminescence agents. Despite progress in the synthesis of NIR CDs, there remains a key obstacle to using them as an in vivo theranostic agent. This work demonstrates that the newly developed sulfur and nitrogen codoped NIR CDs are highly efficient in photothermal therapy (PTT) in mouse models (conversion efficiency of 59%) and can be readily visualized by photoluminescence and photoacoustic imaging. The real theranostic potential of NIR CDs is enhanced by their unique biodistribution and targeting. Contrary to all other nanomaterials that have been tested in biomedicine, they are excreted through the body's renal filtration system. Moreover, after intravenous injection, NIR CDs are accumulated in tumor tissue via passive targeting, without any active species such as antibodies. Due to their accumulation in tumor tissue without the need for intratumor injection, high photothermal conversion, excellent optical and photoacoustic imaging performance, and renal excretion, the developed CDs are suitable for transfer to clinical biomedical practice.

Highly Sensitive MoS2-Indocyanine Green Hybrid for Photoacoustic Imaging of Orthotopic Brain Glioma at Deep Site

Photoacoustic technology in combination with molecular imaging is a highly effective method for accurately diagnosing brain glioma. For glioma detection at a deeper site, contrast agents with higher photoacoustic imaging sensitivity are needed. Herein, we report a MoS₂-ICG hybrid with indocyanine green (ICG) conjugated to the surface of MoS₂ nanosheets. The hybrid significantly enhanced photoacoustic imaging sensitivity compared to MoS₂ nanosheets. This conjugation results in remarkably high optical absorbance across a broad near-infrared spectrum, redshifting of the ICG absorption peak and photothermal/photoacoustic conversion efficiency enhancement of ICG. A tumor mass of 3.5 mm beneath the mouse scalp was clearly visualized by using MoS₂-ICG as a contrast agent for the in vivo photoacoustic imaging of orthotopic glioma, which is nearly twofold deeper than the tumors imaged in our previous report using MoS₂ nanosheet. Thus, combined with its good stability and high biocompatibility, the MoS₂-ICG hybrid developed in this study has a great potential for high-efficiency tumor molecular imaging in translational medicine.

BSA-modified poly(pyrrole-3-carboxylic acid) nanoparticles as carriers for combined chemo-photothermal therapy

Homogenous poly(pyrrole-3-carboxylic acid) nanoparticles with high near-infrared absorption and abundant functional groups were fabricated using a facile reverse microemulsion method.