Feasibility of poly(ethylene glycol) derivatives as diagnostic drug carriers for tumor imaging

Sequential Diagnosis and Treatment for Colon Cancer via Derived Iridium and Indocyanine Green Hybrid Nanomicelles

Indocyanine green (ICG) has been widely explored for the theranostics of tumors. However, ICG mainly accumulates in the liver, spleen, or kidney in addition to in tumors, causing inaccurate diagnoses and impaired therapeutic effects under NIR irradiation. Herein, a hybrid nanomicelle was constructed by integrating hypoxia-sensitive iridium(III) and ICG for precise tumor localization and photothermal therapy in sequence. In this nanomicelle, the amphiphilic iridium(III) complex (BTPH)₂Ir(SA-PEG) was synthesized through the coordination substitution of hydrophobic (BTPH)₂IrCl₂ and hydrophilic PEGlyated succinylacetone (SA-PEG). Meanwhile, PEGlyated ICG (ICG-PEG) as a derivative of the photosensitizer ICG was also synthesized. (BTPH)₂Ir(SA-PEG) and ICG-PEG were coassembled by dialysis to form the hybrid nanomicelle M-Ir-ICG. Hypoxia-sensitive fluorescence, ROS generation, and the photothermal effect of M-Ir-ICG were investigated in vitro and in vivo. The experimental results indicated that M-Ir-ICG nanomicelles could locate at the tumor site first and then perform photothermal therapy with 83.90% TIR, demonstrating great potential for clinical applications.

Influence of Elasticity of Hydrogel Nanoparticles on Their Tumor Delivery

Polymeric nanocarriers have a broad range of clinical applications in recent years, but an inefficient delivery of polymeric nanocarriers to target tissues has always been a challenge. These results show that tuning the elasticity of hydrogel nanoparticles (HNPs) improves their delivery efficiency to tumors. Herein, a microfluidic system is constructed to evaluate cellular uptake of HNPs of different elasticity under flow conditions. It is found that soft HNPs are more efficiently taken up by cells than hard HNPs under flow conditions, owing to the greater adhesion between soft HNPs and cells. Furthermore, in vivo imaging reveals that soft HNPs have a more efficient tumor delivery than hard HNPs, and the greater targeting potential of soft HNPs is associated with both prolonged blood circulation and a high extent of cellular adhesion.

A Bright, Renal-Clearable NIR-II Brush Macromolecular Probe with Long Blood Circulation Time for Kidney Disease Bioimaging

Early detection of kidney disease is of vital importance due to its current prevalence worldwide. Fluorescence imaging, especially in the second near-infrared window (NIR-II) has been regarded as a promising technique for the early diagnosis of kidney disease due to the superior resolution and sensitivity. However, the reported NIR-II organic renal-clearable probes are hampered by their low brightness (ϵ_max Φ_f>1000 nm <10 M^-1  cm^-1 ) and limited blood circulation time (t_1/2 <2 h), which impede the targeted imaging performance. Herein, we develop the aza-boron-dipyrromethene (aza-BODIPY) brush macromolecular probes (Fudan BDIPY Probes (FBP 912)) with high brightness (ϵ_max Φ_f>1000 nm ≈60 M^-1  cm^-1 ), which is about 10-fold higher than that of previously reported NIR-II renal-clearable organic probes. FBP 912 exhibits an average diameter of ≈4 nm and high renal clearance efficiency (≈65 % excretion through the kidney within 12 h), showing superior performance for non-invasively diagnosis of renal ischemia-reperfusion injury (RIR) earlier than clinical serum-based protocols. Additionally, the high molecular weight polymer brush enables FBP 912 with prolonged circulation time (t_1/2 ≈6.1 h) and higher brightness than traditional PEGylated renal-clearable control fluorophores (t_1/2 <2 h), facilitating for 4T1 tumor passive targeted imaging and renal cell carcinoma active targeted imaging with higher signal-to-noise ratio and extended retention time.

Enhanced Delivery of Thermoresponsive Polymer-Based Medicine into Tumors by Using Heat Produced from Gold Nanorods Irradiated with Near-Infrared Light

Simple Summary

To establish a therapy targeting scattered tumors throughout the body, we propose a novel drug delivery system using a thermoresponsive polyoxazoline (POZ) as a drug carrier in combination with gold nanorods (GNR), which produce heat when irradiated with near-infrared (NIR) light. After the tumor was irradiated with NIR light, where GNR was accumulated in advance, the radiolabeled POZ was intravenously injected. As a result, a marked tumor uptake was achieved via self-aggregation of POZ by sensing heat yielded from the GNR. Because the POZ would be chemically modified with various anti-tumor drugs including therapeutic radionuclides, remarkable anti-tumor effects can be expected by enhancing delivery of POZ-based medicine into scattered tumors throughout the body.

Abstract

The aim of this study was to establish a drug delivery system (DDS) for marked therapy of tumors using a thermoresponsive polymer, polyoxazoline (POZ). The effectiveness of the following was investigated: (i) the delivery of gold nanorods (GNRs) to tumor tissues, (ii) heat production of GNR upon irradiation with near-infrared (NIR) light, and (iii) high accumulation of an intravenously injected radiolabeled POZ as a drug carrier in tumors by sensing heat produced by GNRs. When the GNR solution was irradiated with NIR light (808 nm), the solution temperature was increased both in a GNR-concentration-dependent manner and in a light-dose-dependent manner. POZ, with a lower critical solution temperature of 38 °C, was aggregated depending on the heat produced by the GNR irradiated by NIR light. When it was intratumorally pre-injected into colon26-tumor-bearing mice, followed by NIR light irradiation (GNR+/Light+ group), the tumor surface temperature increased to approximately 42 °C within 5 min. Fifteen minutes after irradiation with NIR light, indium-111 (¹¹¹In)-labeled POZ was intravenously injected into tumor-bearing mice, and the radioactivity distribution was evaluated. The accumulation of POZ in the tumor was significantly (approximately 4-fold) higher than that in the control groups (GNR+/without NIR light irradiation (Light–), without injection of GNR (GNR–)/Light+, and GNR–/Light– groups). Furthermore, an in vivo confocal fluorescence microscopy study, using fluorescence-labeled POZ, revealed that uptake of POZ by the tumor could be attributed to the heat produced by GNR. In conclusion, we successfully established a novel DDS in which POZ could be efficiently delivered into tumors by using the heat produced by GNR irradiated with NIR light.

Development of Gold Nanorods Conjugated with Radiolabeled Anti-human Epidermal Growth Factor Receptor 2 (HER2) Monoclonal Antibody as Single-Photon Emission Computed Tomography/Photoacoustic Dual-Imaging Probes Targeting HER2-Positive Tumors

Surgery remains one of the main treatments of cancer and both precise pre- and intraoperative diagnoses are crucial in order to guide the operation. We consider that using an identical probe for both pre- and intra-operative diagnoses would bridge the gap between surgical planning and image-guided resection. Therefore, in this study, we developed gold nanorods (AuNRs) conjugated with radiolabeled anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody, and investigated their feasibility as novel HER2-targeted dual-imaging probes for both single photon emission computed tomography (SPECT) (preoperative diagnosis) and photoacoustic (PA) imaging (intraoperative diagnosis). To achieve the purpose, AuNRs conjugated with different amount of trastuzumab (Tra) were prepared, and Tra-AuNRs were labeled with indium-111. After the evaluation of binding affinity to HER2, cell binding assay and biodistribution studies were carried out for optimization. AuNRs with moderate trastuzumab conjugation (Tra2-AuNRs) were proposed as the novel probe and demonstrated significantly higher accumulation in NCI-N87 (HER2 high-expression) tumors than in SUIT2 (low-expression) tumors 96 h post-injection along with good affinity towards HER2. Thereafter, in vitro PA imaging and in vivo SPECT imaging studies were performed. In in vitro PA imaging, Tra2-AuNRs-treated N87 cells exhibited significant PA signal increase than SUIT2 cells. In in vivo SPECT, signal increase in N87 tumors was more notable than that in SUIT2 tumors. Herein, we report that the Tra2-AuNRs enabled HER2-specific imaging, suggesting the potential as a robust HER2-targeted SPECT and PA dual-imaging probe.

Near-Infrared Heptamethine Cyanine Dyes for Nanoparticle-Based Photoacoustic Imaging and Photothermal Therapy

We have synthesized and characterized a library of near-infrared (NIR) heptamethine cyanine dyes for biomedical application as photoacoustic imaging and photothermal agents. These hydrophobic dyes were incorporated into a polymer-based nanoparticle system to provide aqueous solubility and protection of the photophysical properties of each dye scaffold. Among those heptamethine cyanine dyes analyzed, 13 compounds within the nontoxic polymeric nanoparticles have been selected to exemplify structural relationships in terms of photostability, photoacoustic imaging, and photothermal behavior within the NIR (∼650-850 nm) spectral region. The most contributing structural features observed in our dye design include hydrophobicity, rotatable bonds, heavy atom effects, and stability of the central cyclohexene ring within the dye core. The NIR agents developed within this project serve to elicit a structure-function relationship with emphasis on their photoacoustic and photothermal characteristics aiming at producing customizable NIR photoacoustic and photothermal tools for clinical use.

Photoacoustic in vivo 3D imaging of tumor using a highly tumor-targeting probe under high-threshold conditions

Three-dimensional (3D) representation of a tumor with respect to its size, shape, location, and boundaries is still a challenge in photoacoustic (PA) imaging using artificial contrast agents as probes. We carried out PA imaging of tumors in mice using 800RS-PMPC, which was obtained by coupling of 800RS, a near-infrared cyanine dye, with PMPC, a highly selective tumor-targeting methacrylate polymer having phosphorylcholine side chains, as a probe. The conjugate 800RS-PMPC forms compact nanoparticles (dDLS = 14.3 nm), retains the biocompatibility of the parent polymer (PMPC) and exhibits unprecedented PA performance. When applied to mice bearing a 6 × 3 × 3 mm3 tumor buried 6 mm beneath the skin, the probe 800RS-PMPC selectively accumulates in the tumor and emits PA signals that are strong enough to be unambiguously distinguished from noise signals of endogenous blood/hemoglobin. The PA image thus obtained under high-threshold conditions allows 3D characterization of the tumor in terms of its size, shape, location, and boundaries.

Tailoring Kidney Transport of Organic Dyes with Low-Molecular-Weight PEGylation

Subtle changes in size can induce distinct responses of the body to hard nanomaterials; however, it is largely unknown whether just a few ethylene oxide unit differences in soft poly(ethylene glycol) (PEG) molecules could significantly alter the renal clearance of small molecules. By systematically investigating in vivo transport of the representative renal clearable organic dyes, IRDye800CW after being conjugated with a series of PEG molecules with molecular weight (MW) below 10 kDa, we found a MW-dependent scaling law: PEG45 (MW = 2100 Da) is an optimized MW to generate the most efficient renal clearance for IRDye800CW by expediting the glomerular filtration of organic dyes and reducing their nonspecific interactions with background tissue. Moreover, the uniqueness of PEG45 can be generalized to other organic dyes such as ZW800-1 and fluorescein. This finding highlights the importance of low-MW PEGylation in tailoring in vivo transport of organic fluorophores, which would broaden their biomedical applications.

Molecular Photoacoustic Contrast Agents: Design Principles & Applications

Photoacoustic imaging (PAI) is a rapidly growing field which offers high spatial resolution and high contrast for deep-tissue imaging in vivo. PAI is nonionizing and noninvasive and combines the optical resolution of fluorescence imaging with the spatial resolution of ultrasound imaging. In particular, the development of exogenous PA contrast agents has gained significant momentum of late with a vastly expanding complexity of dye materials under investigation ranging from small molecules to macromolecular proteins, polymeric and inorganic nanoparticles. The goal of this review is to survey the current state of the art in molecular photoacoustic contrast agents (MPACs) for applications in biomedical imaging. The fundamental design principles of MPACs are presented and a review of prior reports spanning from early-to-current literature is put forth.

Near-infrared light-activatable siRNA delivery by microcapsules for combined tumour therapy

A polyelectrolyte microcapsule-based layer-by-layer (LbL) technique has been widely used as a multifunctional vehicle for combined tumor therapy. Meanwhile, with the rapid development of combined tumour therapy, the challenge for designing multifunctional drug delivery system has attracted much more attention. Herein, we developed a new type of microcapsule (MC) system called MPA@siRNA@DOX@MC, which conjugated with siRNA and DOX as well as ICG-Der-02 (MPA) by electrostatic absorption. MPA as indocyanine green (ICG) fluorescence dye, exhibiting high fluorescence emission and photothermal conversion ability under NIR laser irradiation, was uploaded onto this drug system for realizing the controllable drug release and cancer theranostics. In addition, the results revealed that MPA@siRNA@DOX@MC possessed several ideal properties including high drug-loading capacity, excellent siRNA transfection efficiency, siRNA sequence protection and remarkably improved tumour-targeting capacity. Moreover, the combined therapy based on this drug system displayed improved therapeutic efficacy and negligible side effects both in vivo and in vitro experiment. Ultimately, MPA@siRNA@DOX@MC drug delivery system successfully combined the photothermal therapy and chemotherapy with controlled siRNA sequence silencing may have a promising potential in combined tumor therapy.

Homing of ICG-loaded liposome inlaid with tumor cellular membrane to the homologous xenografts glioma eradicates the primary focus and prevents lung metastases through phototherapy

Liposomes inlaid with tumor cellular membranes may serve as an excellent nanoplatform for homologous-targeting phototherapy using ICG.

Nanotechnologies for early diagnosis, in situ disease monitoring, and prevention

Nanotechnology is an enabling technology with great potential for applications in stem cell research and regenerative medicine. Fluorescent nanodiamond (FND), an inherently biocompatible and nontoxic nanoparticle, is well suited for such applications. We had developed a prospective isolation method using CD157, CD45, and CD54 to obtain lung stem cells. Labeling of CD45⁻CD54⁺CD157⁺ cells with FNDs did not eliminate their abilities for self-renewal and differentiation. The FND labeling in combination with cell sorting, fluorescence lifetime imaging microscopy, and immunostaining identified transplanted stem cells allowed tracking of their engraftment and regenerative capabilities with single-cell resolution. Time-gated fluorescence (TGF) imaging in mouse tissue sections indicated that they reside preferentially at the bronchoalveolar junctions of lungs, especially in naphthalene-injured mice. Our results presented in Subchapter 1.1 demonstrate not only the remarkable homing capacity and regenerative potential of the isolated stem cells, but also the ability of finding rare lung stem cells in vivo using FNDs.

The topical use of antiretroviral-based microbicides, namely of a dapivirine ring, has been recently shown to partially prevent transmission of HIV through the vaginal route. Among different formulation approaches, nanotechnology tools and principles have been used for the development of tentative vaginal and rectal microbicide products. Subchapter 1.2 provides an overview of antiretroviral drug nanocarriers as novel microbicide candidates and discusses recent and relevant research on the topic. Furthermore, advances in developing vaginal delivery platforms for the administration of promising antiretroviral drug nanocarriers are reviewed. Although mostly dedicated to the discussion of nanosystems for vaginal use, the development of rectal nanomicrobicides is also addressed.

Infectious diseases are currently responsible for over 8 million deaths per year. Efficient treatments require accurate recognition of pathogens at low concentrations, which in the case of blood infection (septicemia) can go as low as 1 mL^–1. Detecting and quantifying bacteria at such low concentrations is challenging and typically demands cultures of large samples of blood (∼1 mL) extending over 24–72 h. This delay seriously compromises the health of patients and is largely responsible for the death toll of bacterial infections. Recent advances in nanoscience, spectroscopy, plasmonics, and microfluidics allow for the development of optical devices capable of monitoring minute amounts of analytes in liquid samples. In Subchapter 1.3 we critically discuss these recent developments that will, in the future, enable the multiplex identification and quantification of microorganisms directly on their biological matrix with unprecedented speed, low cost, and sensitivity.

Radiolabeled nanoparticles (NPs) are finding an increasing interest in a broad range of biomedical applications. They may be used to detect and characterize diseases, to deliver relevant therapeutics, and to study the pharmacokinetic/pharmacodynamic parameters of nanomaterials. The use of radiotracer techniques in the research of novel NPs offers many advantages, but there are still some limitations. The binding of radionuclides to NPs has to be irreversible to prevent their escape to other tissues or organs. Due to the short half-lives of radionuclides, the manufacturing process is time limited and difficult, and there is also a risk of contamination. Subchapter 1.4 presents the main selection criteria for radionuclides and applicable radiolabeling procedures used for the radiolabeling of various NPs. Also, an overview of different types of NPs that have so far been labeled with radionuclides is presented.

Development of a high quantum yield dye for tumour imaging

A fluorescent dye, FEB, with high fluorescence quantum yield for tumour imaging is reported. FEB dyes can be efficiently synthesized in three steps and then easily modified with either PEG or PEG-iRGD to yield FEB-2000 or FEB-2000-iRGD, respectively. Both modified dyes showed negligible toxicity and were thus able to be adopted for in vivo tumour imaging. PEG modification endowed the dye FEB-2000 with both long circulating times and good tumour targeting properties in a MDA-MB-231 xenograft model. Further conjugation with iRGD to generate FEB-2000-iRGD showed minimal targeting enhancement. These results provide a template for the efficient preparation of FEB dyes for use in tumour imaging, thus providing a foundation for future modifications.

Development of Molecular Probes Based on Iron Oxide Nanoparticles for in Vivo Magnetic Resonance/Photoacoustic Dual Imaging of Target Molecules in Tumors

Molecular imaging probes that enable seamless diagnoses of tumors in the preoperative and intraoperative stages could lead to surgical resection of tumors based on highly accurate diagnoses. Because iron oxide nanoparticles (IONPs) have high proton relaxivity and high molar extinction coefficients suitable for magnetic resonance imaging (MRI) and photoacoustic imaging, respectively, we planned to develop molecular imaging probes applicable to the pre- (MRI) and intraoperative (photoacoustic imaging) stages. Human epidermal growth factor receptor 2 (EGFR2; HER2) was selected as a target molecule, and we designed IONPs (20, 50, and 100 nm) conjugated with anti-HER2 moieties [whole IgG (trastuzumab), single-chain fragment variable (scFv), and peptide] for HER2-targeted tumor imaging. Among the probes tested, scFv-conjugated IONPs (scFv-IONPs) (20 nm) exhibited the highest binding affinity to HER2 (K_d=0.01 nM). An in vivo biodistribution study using ¹¹¹In-labeled probes demonstrated that more scFv-IONPs (20 nm) accumulated in HER2-positive than in HER2-negative tumors, suggesting that the uptake of scFv-IONPs is HER2 specific. The scFv-IONPs (20 nm) showed high proton relaxivity and a probe concentration-dependent photoacoustic signal. In vivo MR/photoacoustic imaging studies using scFv-IONPs (20 nm) facilitated HER2-specific visualization of tumors. Furthermore, an iron-staining study demonstrated that the uptake of scFv-IONPs was notable only in HER2-positive tumors. These results suggest that scFv-IONPs (20 nm) may be useful for MR/photoacoustic dual imaging, which could achieve seamless diagnoses in the preoperative and intraoperative stages.

Polyoxazoline multivalently conjugated with indocyanine green for sensitive in vivo photoacoustic imaging of tumors

Photoacoustic imaging, which enables high-resolution imaging in deep tissues, has lately attracted considerable attention. For tumor imaging, photoacoustic probes have been proposed to enhance the photoacoustic effect to improve detection sensitivity. Here, we evaluated the feasibility of using a biocompatible hydrophilic polymer, polyoxazoline, conjugated with indocyanine green (ICG) as a tumor-targeted photoacoustic probe via enhanced permeability and retention effect. ICG molecules were multivalently conjugated to partially hydrolyzed polyoxazoline, thereby serving as highly sensitive photoacoustic probes. Interestingly, loading multiple ICG molecules to polyoxazoline significantly enhanced photoacoustic signal intensity under the same ICG concentration. In vivo biodistribution studies using tumor bearing mice demonstrated that 5% hydrolyzed polyoxazoline (50 kDa) conjugated with ICG (ICG/polyoxazoline = 7.8), P14-ICG7.8, showed relatively high tumor accumulation (9.4%ID/g), resulting in delivery of the highest dose of ICG among the probes tested. P14-ICG7.8 enabled clear visualization of the tumor regions by photoacoustic imaging 24 h after administration; the photoacoustic signal increased in proportion with the injected dose. In addition, the signal intensity in blood vessels in the photoacoustic images did not show much change, which was attributed to the high tumor-to-blood ratios of P14-ICG7.8. These results suggest that polyoxazoline-ICG would serve as a robust probe for sensitive photoacoustic tumor imaging.

Development of a bone-targeted pH-sensitive liposomal formulation containing doxorubicin: physicochemical characterization, cytotoxicity, and biodistribution evaluation in a mouse model of bone metastasis

Background

Despite recent advances in cancer therapy, the treatment of bone tumors remains a major challenge. A possible underlying hypothesis, limitation, and unmet need may be the inability of therapeutics to penetrate into dense bone mineral, which can lead to poor efficacy and high toxicity, due to drug uptake in healthy organs. The development of nanostructured formulations with high affinity for bone could be an interesting approach to overcome these challenges.

Purpose

To develop a liposomal formulation with high affinity for hydroxyapatite and the ability to release doxorubicin (DOX) in an acidic environment for future application as a tool for treatment of bone metastases.

Materials and methods

Liposomes were prepared by thin-film lipid hydration, followed by extrusion and the sulfate gradient-encapsulation method. Liposomes were characterized by average diameter, ζ-potential, encapsulation percentage, X-ray diffraction, and differential scanning calorimetry. Release studies in buffer (pH 7.4 or 5), plasma, and serum, as well as hydroxyapatite-affinity in vitro analysis were performed. Cytotoxicity was evaluated by MTT assay against the MDA-MB-231 cell line, and biodistribution was assessed in bone metastasis-bearing animals.

Results

Liposomes presented suitable diameter (~170 nm), DOX encapsulation (~2 mg/mL), controlled release, and good plasma and serum stability. The existence of interactions between DOX and the lipid bilayer was proved through differential scanning calorimetry and small-angle X-ray scattering. DOX release was faster when the pH was in the range of a tumor than at physiological pH. The bone-targeted formulation showed a strong affinity for hydroxyapatite. The encapsulation of DOX did not interfere in its intrinsic cytotoxicity against the MDA-MB-231 cell line. Biodistribution studies demonstrated high affinity of this formulation for tumors and reduction of uptake in the heart.

Conclusion

These results suggest that bone-targeted pH-sensitive liposomes containing DOX can be an interesting strategy for selectively delivering this drug into bone-tumor sites, increasing its activity, and reducing DOX-related toxicity.

Theranostic unimolecular micelles of highly fluorescent conjugated polymer bottlebrushes for far red/near infrared bioimaging and efficient anticancer drug delivery

Theranostic unimolecular micelles of highly fluorescent amphiphilic conjugated bottlebrushes loaded with anticancer drugs are efficient for cancer imaging and therapy.