Labeling Stem Cells with a Near-Infrared Fluorescent Heptamethine Dye for Noninvasive Optical Tracking

Near-infrared-II fluorescence/magnetic resonance double modal imaging of transplanted stem cells using lanthanide co-doped gadolinium oxide nanoparticles

To ensure maximum therapeutic safety and efficacy of stem cell transplantation, it is essential to observe the kinetics of behavior, accumulation, and engraftment of transplanted stem cells in vivo. However, it is difficult to detect transplanted stem cells with high sensitivity by conventional in vivo imaging technologies. To diagnose the kinetics of transplanted stem cells, we prepared multifunctional nanoparticles, Gd2O3 co-doped with Er3+ and Yb3+ (Gd2O3: Er, Yb-NPs), and developed an in vivo double modal imaging technique with near-infrared-II (NIR-II) fluorescence imaging and magnetic resonance imaging (MRI) of stem cells using Gd2O3: Er, Yb-NPs. Gd2O3: Er, Yb-NPs were transduced into adipose tissue-derived stem cells (ASCs) through a simple incubation process without cytotoxicity under certain concentrations of Gd2O3: Er, Yb-NPs and were found not to affect the morphology of ASCs. ASCs labeled with Gd2O3: Er, Yb-NPs were transplanted subcutaneously onto the backs of mice, and successfully imaged with good contrast using an in vivo NIR-II fluorescence imaging and MRI system. These data suggest that Gd2O3: Er, Yb-NPs may be useful for in vivo double modal imaging with NIR-II fluorescence imaging and MRI of transplanted stem cells.

Fluorescence-Based Mono- and Multimodal Imaging for In Vivo Tracking of Mesenchymal Stem Cells

The advancement of stem cell therapy has offered transformative therapeutic outcomes for a wide array of diseases over the past decades. Consequently, stem cell tracking has become significant in revealing the mechanisms of action and ensuring safe and effective treatments. Fluorescence stands out as a promising choice for stem cell tracking due to its myriad advantages, including high resolution, real-time monitoring, and multi-fluorescence detection. Furthermore, combining fluorescence with other tracking modalities-such as bioluminescence imaging (BLI), positron emission tomography (PET), photoacoustic (PA), computed tomography (CT), and magnetic resonance (MR)-can address the limitations of single fluorescence detection. This review initially introduces stem cell tracking using fluorescence imaging, detailing various labeling strategies such as green fluorescence protein (GFP) tagging, fluorescence dye labeling, and nanoparticle uptake. Subsequently, we present several combinations of strategies for efficient and precise detection.

FITC characterization of a cathepsin B-responsive nanoprobe for report of differentiation of HL60 cells into macrophages

A cathepsin B (Cat B)-responsive optical nanoprobe is designed and prepared for report of HL60 differentiation into macrophage. A peptide sequence FRFK is linked to fluorescein (FITC) via the distant amino group of its lysine and N-terminated with acrylic acid (AA) to yield a molecular fluorescent probe AA-FRFK (FITC). The molecular probe is further embedded in poly(lactic-co-glycolic acid) (PLGA) to form a fluorescent nanoprobe AA-FRFK (FITC)@PLGA. The resultant optical nanoprobe is degradable by lysosomal Cat B, which is expressed in macrophages with a level of 5-10 times of that in HL60 cells. As a result, a significant decrease in fluorescence intensity is associated with the differentiation process of HL60 to macrophage and can be used as an indication of the differentiation process. The findings may pave a way toward the development of a universal in vitro labeling strategy of exogenous stem cells for report of in vivo cell differentiation by a dual-mode imaging modality involving optical imaging and magnetic resonance imaging.

Non-invasive in vivo monitoring of transplanted stem cells in 3D-bioprinted constructs using near-infrared fluorescent imaging

Cell-based tissue engineering strategies have been widely established. However, the contributions of the transplanted cells within the tissue-engineered scaffolds to the process of tissue regeneration remain poorly understood. Near-infrared (NIR) fluorescence imaging systems have great potential to non-invasively monitor the transplanted cell-based tissue constructs. In this study, labeling mesenchymal stem cells (MSCs) using a lipophilic pentamethine indocyanine (CTNF127, emission at 700 nm) as a NIR fluorophore was optimized, and the CTNF127-labeled MSCs (NIR-MSCs) were printed embedding in gelatin methacryloyl bioink. The NIR-MSCs-loaded bioink showed excellent printability. In addition, NIR-MSCs in the 3D constructs showed high cell viability and signal stability for an extended period in vitro. Finally, we were able to non-invasively monitor the NIR-MSCs in constructs after implantation in a rat calvarial bone defect model, and the transplanted cells contributed to tissue formation without specific staining. This NIR-based imaging system for non-invasive cell monitoring in vivo could play an active role in validating the cell fate in cell-based tissue engineering applications.

Sandwich-Type Near-Infrared Conjugated Polymer Nanoparticles for Revealing the Fate of Transplanted Human Umbilical Cord Mesenchymal Stem Cells

Near-infrared conjugated polymer nanoparticles (NIR-CPNs) have been widely used in in vivo imaging fields. However, most of them face the aggregation-induced fluorescence quenching (ACQ) dilemma and serious dye leakage behavior, which impedes the long-term monitoring of transplanted cells in vivo. In the present work, a novel strategy of sandwich-type encapsulation of the conjugated polymer interlayer in the crystalline SiO2 core + shell (SSiO2@SPFTBT@CSiO2) is developed, which works well to avoid the ACQ problem by homogeneously dispersing poly((9,9-dioctylfluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5',5″-diyl) (PFTBT) and suppressing intermolecular π-π stacking. Furthermore, the unparalleled nanostructure efficiently stabilizes nanoparticles and successfully achieves long-term biocompatibility without interfering the biological characteristics of stem cells, indicating the potential of SSiO2@SPFTBT@CSiO2 in cell labeling. In addition, the fate of human umbilical cord mesenchymal stem cells (hucMSCs) in a mouse model with acute liver injury was disclosed. We found that the hucMSCs mainly migrated from the lungs to the injured liver and most transplanted hucMSCs were cleared up by the liver at 8 days post-injection. Revelation of the shuttle process and period will benefit in improving the clinical efficacy of hucMSCs, and the sandwich-type encapsulation strategy could also open a new avenue to obtain bright and robust NIR-CPNs for long-term fluorescence imaging.

Immune cells as tumor drug delivery vehicles

This review article describes the use of immune cells as potential candidates to deliver anti-cancer drugs deep within the tumor microenvironment. First, the rationale of using drug carriers to target tumors and potentially decrease drug-related side effects is discussed. We further explain some of the current limitations when using nanoparticles for this purpose. Next, a comprehensive step-by-step description of the migration cascade of immune cells is provided as well as arguments on why immune cells can be used to address some of the limitations associated with nanoparticle-mediated drug delivery. We then describe the benefits and drawbacks of using red blood cells, platelets, granulocytes, monocytes, macrophages, myeloid-derived suppressor cells, T cells and NK cells for tumor-targeted drug delivery. An additional section discusses the versatility of nanoparticles to load anti-cancer drugs into immune cells. Lastly, we propose increasing the circulatory half-life and development of conditional release strategies as the two main future pillars to improve the efficacy of immune cell-mediated drug delivery to tumors.

Role of Albumin in Accumulation and Persistence of Tumor-Seeking Cyanine Dyes

Some heptamethine cyanine dyes accumulate in solid tumors in vivo and persist there for several days. The reasons why they accumulate and persist in tumors were incompletely defined, but explanations based on uptake into cancer cells via organic anion transporting polypeptides (OATPs) have been widely discussed. All cyanine-based "tumor-seeking dyes" have a chloride centrally placed on the heptamethine bridge (a "meso-chloride"). We were intrigued and perplexed by the correlation between this particular functional group and tumor uptake, so the following study was designed. It features four dyes (1-Cl, 1-Ph, 5-Cl, and 5-Ph) with complementary properties. Dye 1-Cl is otherwise known as MHI-148, and 1-Ph is a close analog wherein the meso-chloride has been replaced by a phenyl group. Data presented here shows that both 1-Cl and 1-Ph form noncovalent adducts with albumin, but only 1-Cl can form a covalent one. Both dyes 5-Cl and 5-Ph have a methylene (CH₂) unit replaced by a dimethylammonium functionality (N⁺Me₂). Data presented here shows that both these dyes 5 do not form tight noncovalent adducts with albumin, and only 5-Cl can form a covalent one (though much more slowly than 1-Cl). In tissue culture experiments, uptake of dyes 1 is more impacted by the albumin in the media than by the pan-OATP uptake inhibitor (BSP) that has been used to connect uptake of tumor-seeking dyes in vivo with the OATPs. Uptake of 1-Cl in media containing fluorescein-labeled albumin gave a high degree of colocalization of intracellular fluorescence. No evidence was found for the involvement of OATPs in uptake of the dyes into cells in media containing albumin. In an in vivo tumor model, only the two dyes that can form albumin adducts (1-Cl and 5-Cl) gave intratumor fluorescence that persisted long enough to be clearly discerned over the background (∼4 h); this fluorescence was still observed at 48 h. Tumors could be imaged with a higher contrast if 5-Cl is used instead of 1-Cl, because 5-Cl is cleared more rapidly from healthy tissues. Overall, the evidence is consistent with in vitro and in vivo results and indicates that the two dyes in the test series that accumulate in tumors and persist there (1-Cl and 5-Cl, true tumor-seeking dyes) do so as covalent albumin adducts trapped in tumor tissue via uptake by some cancer cells and via the enhanced permeability and retention (EPR) effect.

Lipophilic Near-Infrared Dyes for In Vivo Fluorescent Cell Tracking

Cells can be easily and noninvasively tracked in the body by labeling them with a lipophilic, near-infrared dye and using a live fluorescence imaging system to image the position of the dye in the body. Near-infrared dyes provide several advantages, primarily that tissue is mostly highly transparent to near-infrared light, resulting in clearer and more accurate images. Briefly, cells are labeled with a near-infrared dye such as DiR and injected into a disease model. The model is then imaged using the live fluorescence imaging system on an hourly and/or daily basis to track cell migration and final location. The relative number of cells that migrate to the desired location can be measured by measuring the fluorescent intensity at the location versus elsewhere in the body. This paper describes a method for using DiR dye to label and track C17.2 neural progenitor cells to a murine model of mammary carcinoma.

Noninvasive Tracking and Regenerative Capabilities of Transplanted Human Umbilical Cord-Derived Mesenchymal Stem Cells Labeled with I-III-IV Semiconducting Nanocrystals in Liver-Injured Living Mice

Acute liver injury is a critical syndrome ascribed to prevalent death of hepatocytes and imperatively requires liver transplantation. Such a methodology is certainly hampered due to the deficit of healthy donors. In this regard, stem cell-based regenerative therapies are attractive in repairing injured tissues and organs for medical applications. However, it is crucial to understand the migration, engraftment, and regeneration capabilities of transplanted stem cells in the living animal models. For the first time, we demonstrate rapid labeling of umbilical cord-derived mesenchymal stem cells (MSCs) with near-infrared (NIR)-fluorescent CuInS₂-ZnS nanocrystals (CIZS-NCs) to develop innovative nanobioconjugates (MSCs-CIZS-NBCs) that exhibit 98% labeling efficiency. Before nanobioconjugate synthesis, the pristine CIZS-NCs were prepared via a two-step, hot-injection, rapid and low-cost domestic-microwave-refluxing (MW-R) method within 6 min. The as-synthesized CIZS-NCs display high photoluminescence quantum yield (∼88%) and long-lived lifetime (23.4 μs). In contrast to unlabeled MSCs, the MSCs-CIZS nanobioconjugates show excellent biocompatibility without affecting the stemness, as confirmed by cell viability, immunophenotyping (CD44⁺, CD105⁺, CD90⁺), multi-lineage-specific gene expressions, and differentiation into adipocytes, osteocytes, and chondrocytes. The in vivo fluorescence tracking analyses revealed that the MSCs-CIZS-NBCs after tail-vein injection were initially trapped in the lungs and gradually engrafted in the injured liver within 2 h. The regeneration potential of MSCs-CIZS-NBCs was confirmed via renewal of the portal tract composed of portal veins, bile ducts, and hepatic arteries around the hepatocytes. Consequently, no apparent inflammations, necrosis, or apoptosis was observed in the acetaminophen (APAP)-induced liver-injured BALB/c mice model over 3 days after transplantation, as corroborated using laser-scanning confocal microscopy and histopathological and hematological analyses. Hence, our innovative NIR-fluorescent MSCs-CIZS-NBCs offer an off-the-self technology for noninvasive tracking of transplanted MSCs in an acute-liver-injured animal model for future image-guided cell-therapies.

Recent Advances in Tracking the Transplanted Stem Cells Using Near-Infrared Fluorescent Nanoprobes: Turning from the First to the Second Near-Infrared Window

Stem cell-based regenerative medicine has attracted tremendous attention for its great potential to treat numerous incurable diseases. Tracking and understanding the fate and regenerative capabilities of transplanted stem cells is vital for improving the safety and therapeutic efficacy of stem cell-based therapy, therefore accelerating the clinical application of stem cells. Fluorescent nanoparticles (NPs) have been widely used for in vivo tracking of the transplanted stem cells. Among these fluorescent NPs, near-infrared (NIR) NPs have greatly improved the sensitivity, tissue penetration depth, spatial and temporal resolutions of the fluorescence imaging-based stem cell tracking technologies due to the reduced absorption, scattering, and autofluorescence of NIR fluorescence in tissues. Here, this review summarizes the recent studies regarding the tracking of transplanted stem cells using NIR NPs and emphasizes the recent advances of fluorescence imaging in the second NIR window (NIR-II, 1000-1700 nm). Furthermore, the challenges and future prospects of the NIR NP-based technologies are also discussed.

A mitochondria-selective near-infrared-emitting fluorescent dye for cellular imaging studies

This communication details the synthesis, evaluation of photophysical properties, and cellular imaging studies of cyanine chromophore based fluorescent dye 1 as a selective imaging agent for mitochondria.

Cell Surface Nano-modulation for Non-invasive in vivo Near-IR Stem Cell Monitoring

A stem cell tracking system is in high demand for the determination of cell destinations and for the validation of cell therapeutic efficacy in regenerative transplantation. To date, near-infrared (NIR) imaging technology has received considerable attention in cell behavior monitoring, owing to its patient compatibility, easy accessibility and cost effectiveness. Conventionally, in vivo cell tracking has been visualized by direct in-cell staining with NIR, where it may be achieved by complicated genetic engineering. Such genetic amendment techniques have suffered from serious challenges, which can destroy a cell's metabolism and can accidentally incur unexpected carcinoma. Herein we demonstrate a novel cell nano-modulation method for noninvasive stem cell monitoring. It is simply achieved by conjugating stem cells with lipid-supported, NIR-tagged, polymeric nanoparticles. These engineered cells, which are designated as NIR-labeled light-emitting stem cells (LESCs), maintain their biochemical functionality (i.e., differentiation, quantum efficacy, etc.) even after conjugation. LESCs were used for in situ stem cell monitoring at inoculation sites. It is speculated that the LESC technique could provide a new preparative methodology for in vivo cell tracking in advanced diagnostic medicine, where cell behavior is a critical issue.

Non-cultured dermal-derived mesenchymal cells attenuate sepsis induced by cecal ligation and puncture in mice

Sepsis remains a threat to critically ill patients and carries a high morbidity and mortality. Cell-based therapies have risen in prominence in recent years. Dermal-derived mesenchymal cells (DMCs) are attractive as one of the abundant sources from which to isolate mesenchymal cells for therapeutic applications and can be easily accessed with minimal harm to the donor. In this study, we described for the first time the use of non-cultured DMCs for treating sepsis in a cecal ligation and puncture (CLP) mouse model and investigated their immunomodulatory effects. We found that non-cultured DMCs administration provides a beneficial effect to improve survival in CLP-induced sepsis. This effect is partly mediated by the ability of DMCs to home to sites of injury, to reduce the inflammatory response, to inhibit apoptosis, and to stimulate macrophage migration and phagocytosis. Our further findings suggest that DMCs treatment modulates the beneficial cytoprotective effects exhibited during sepsis, at least in part, by altering miRNA expression. These discoveries provide important evidence that non-cultured DMCs therapy has a specific anti-inflammatory effect on sepsis, and provide the basis for the development of a new therapeutic strategy for managing clinical sepsis.

Magnetic Nanoparticles Labeled Mesenchymal Stem Cells: A Pragmatic Solution toward Targeted Cancer Theranostics

Mesenchymal stem cells (MSCs) have gained much interest to be used as targeting vehicle in cancer therapy due to the intrinsic tumor-homing behavior associated with them. In this scenario, superparamagnetic nanoparticles are emerging as an ideal probe for noninvasive cell tracking for different stem cell applications. In the study, it is demonstrated that the formulated aqueous dispersible glyceryl monooleate coated magnetic nanoparticles (MNPs) can act as a better labeling and efficient tracking agent without affecting the inherent properties of MSCs. The MNPs-MSCs facilitate the stem cell tracking by magnetic resonance imaging at a very low cell number having high T₂ relaxivity and potentiates the use of MNPs-MSCs as a prospective diagnostic tool. Most importantly, the homing of MNPs-MSCs toward inflammation site, subcutaneous prostate tumor (small as well as large tumor), and in orthotopic prostate tumor suggests the clinical relevance of the system. In addition, intraperitoneal delivery of MNPs-MSCs shows enhanced tumor accumulation and less sequestration in liver as revealed by in vivo imaging and histological studies. The results here demonstrate that MNPs-MSCs may prove as a better targeted delivery agent for early diagnosis of tumors even of smaller size.

IR-780 dye for near-infrared fluorescence imaging in prostate cancer

Background

The aim of this study was to investigate near-infrared fluorescence (NIRF) imaging as a novel imaging modality that allows for early detection of cancer and real-time monitoring to acquire related information. IR-780 iodide, a lipophilic dye, accumulates selectively in breast cancer cells and drug-resistant human lung cancer cells, with a peak emission at 780 nm that can be easily detected by the NIRF imaging system. The application of IR-780 for prostate cancer imaging was thoroughly investigated to further expand its clinical value.

Material/Methods

The impact of IR-780 on the survival of prostate cancer cells PC-3 and LNCaP as well as normal prostate epithelial cells RWPE-1 was determined. Duration of IR-780 dye staining was optimized in PC-3 cells. The involvement of specific OATP1B3 inhibitor in the selective accumulation of IR-780 was investigated. IR-780 for prostate cancer imaging was carried out in athymic nude mouse models and, acute toxicity of IR-780 was evaluated.

Results

IR-780 incubation resulted in a dose-dependent inhibition to cell proliferation. Mean fluorescence intensity of prostate cancer cells peaked at 20-min IR-780 incubation. Specific uptake of IR-780 dye in prostate cancer cells was mainly through the function of OATP1B3. We also demonstrated that NIRF dye effectively identified the subcutaneous prostate cancer xenografts, subsequently confirmed by histological examination. There was no significant impact on the physical activity, weight, and tissue histology of BABL/C mice with 10-fold imaging dose of 1-month IR-780 dye administration.

Conclusions

NIRF imaging using IR-780 dye is a feasible and practicable method for prostate cancer detection, with potential tumor-killing ability, although more investigations are needed before clinical translation.

Non-invasive monitoring of transplanted endothelial progenitor cells in diabetic ischemic stroke models

Endogenous endothelial progenitor cells (EPCs) are functionally impaired in hyperglycemia through the p38 MAPK signaling pathway. However, the number and function of transplanted exogenous EPCs in diabetic animals remains unclear. The objectives of this study were to establish a non-invasive imaging strategy to monitor the homing of transplanted EPCs in diabetic stroke mice and to assess the effect of RWJ 67657, an inhibitor of p38 MAPK, on the homing ability of exogenous EPCs. Bone marrow-derived EPCs were labeled in vitro with a multi-functional nanoprobe modified with paramagnetic chelators and fluorophores before being infused into stroke mice. The signal of the nanoprobe reached its peak on day 5 in both magnetic resonance imaging and near-infrared fluorescence imaging after EPC transplantation in wild-type stroke models. The signal enhancement of diabetic stroke models was significantly lower than that of wild-type controls. However, the signal intensity of diabetic stroke models significantly increased after oral administration of RWJ 67657, indicating that more transplanted EPCs migrated to the ischemic brain. Furthermore, the increased exogenous EPCs induced remarkably greater angiogenesis after stroke. These results suggest that this dual-modal imaging strategy is feasible for non-invasively monitoring transplanted cells in vivo.

Multimodality molecular imaging of stem cells therapy for stroke

Stem cells have been proposed as a promising therapy for treating stroke. While several studies have demonstrated the therapeutic benefits of stem cells, the exact mechanism remains elusive. Molecular imaging provides the possibility of the visual representation of biological processes at the cellular and molecular level. In order to facilitate research efforts to understand the stem cells therapeutic mechanisms, we need to further develop means of monitoring these cells noninvasively, longitudinally and repeatedly. Because of tissue depth and the blood-brain barrier (BBB), in vivo imaging of stem cells therapy for stroke has unique challenges. In this review, we describe existing methods of tracking transplanted stem cells in vivo, including magnetic resonance imaging (MRI), nuclear medicine imaging, and optical imaging (OI). Each of the imaging techniques has advantages and drawbacks. Finally, we describe multimodality imaging strategies as a more comprehensive and potential method to monitor transplanted stem cells for stroke.