MRI tracking of macrophages labeled with glucan particles entrapping a water insoluble paramagnetic Gd-based agent

Visualizing stem cells in vivo using magnetic resonance imaging

Stem cell (SC) therapies displayed encouraging efficacy and clinical outcome in various disorders. Despite this huge hype, clinical translation of SC therapy has been disheartening due to contradictory results from clinical trials. The ability to monitor migration and engraftment of cells in vivo represents an ideal strategy in cell therapy. Therefore, suitable imaging approach to track MSCs would allow understanding of migratory and homing efficiency, optimal route of delivery and engraftment of cells at targeted location. Hence, longitudinal tracking of SCs is crucial for the optimization of treatment parameters, leading to improved clinical outcome and translation. Magnetic resonance imaging (MRI) represents a suitable imaging modality to observe cells non-invasively and repeatedly. Tracking is achieved when cells are incubated prior to implantation with appropriate contrast agents (CA) or tracers which can then be detected in an MRI scan. This review explores and emphasizes the importance of monitoring the distribution and fate of SCs post-implantation using current contrast agents, such as positive CAs including paramagnetic metals (gadolinium), negative contrast agents such as superparamagnetic iron oxides and ¹⁹ F containing tracers, specifically for the in vivo tracking of MSCs using MRI. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Iron Oxide Nanoparticles as Theranostic Agents in Cancer Immunotherapy

Starting from the mid-1990s, several iron oxide nanoparticles (NPs) were developed as MRI contrast agents. Since their sizes fall in the tenths of a nanometer range, after i.v. injection these NPs are preferentially captured by the reticuloendothelial system of the liver. They have therefore been proposed as liver-specific contrast agents. Even though their unfavorable cost/benefit ratio has led to their withdrawal from the market, innovative applications have recently prompted a renewal of interest in these NPs. One important and innovative application is as diagnostic agents in cancer immunotherapy, thanks to their ability to track tumor-associated macrophages (TAMs) in vivo. It is worth noting that iron oxide NPs may also have a therapeutic role, given their ability to alter macrophage polarization. This review is devoted to the most recent advances in applications of iron oxide NPs in tumor diagnosis and therapy. The intrinsic therapeutic effect of these NPs on tumor growth, their capability to alter macrophage polarization and their diagnostic potential are examined. Innovative strategies for NP-based drug delivery in tumors (e.g., magnetic resonance targeting) will also be described. Finally, the review looks at their role as tracers for innovative, and very promising, imaging techniques (magnetic particle imaging-MPI).

Binding and Release of FeIII Complexes from Glucan Particles for the Delivery of T1 MRI Contrast Agents

Yeast-derived β-glucan particles (GPs) are a class of microcarriers under development for the delivery of drugs and imaging agents to immune-system cells for theranostic approaches. However, the encapsulation of hydrophilic imaging agents in the porous GPs is challenging. Here, we show that the unique coordination chemistry of FeIII -based macrocyclic T1 MRI contrast agents permits facile encapsulation in GPs. Remarkably, GPs labeled with the simple FeIII complexes are stable under physiologically relevant conditions, despite the absence of amphiphilic groups. In contrast to the free FeIII coordination complex, the labeled FeIII -GPs have lowered T1 relaxivity and act as a silenced form of the contrast agent. Addition of a fluorescent tag to the FeIII complex produces a bimodal agent to further enable tracking of the nanoparticles and to monitor release. Treatment of the iron-labeled GPs with a maltol chelator or with mildly acidic conditions releases the intact iron complex and restores enhanced T1 relaxation of the water protons.

Prognostic significance of peritumoral fibrosis after resection of pancreatic head cancer

Prognostic value of peritumoral fibrosis (PF) in pancreatic head cancer after resection was evaluated. A total of 143 pancreatic cancer patients who underwent tumor resection were enrolled. All patients underwent routine preoperative examination, including contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI). Patients receiving preoperative chemoradiation were excluded because it affects the proportion of fibrosis and cancer cells. Histopathological confirmation and classification of pancreatic head cancer (PHC) was made according to the standards of World Health Organization and the American Joint Committee on Cancer (AJCC). The presence of fibrosis was assessed histologically, and correlated with the clinicopathological characteristics and overall survival using univariate Kaplan-Meier analysis and a stepwise multivariable Cox regression model. Vein resection, resection margin, grading, nodal status, preoperative CA19-9 levels and PF were significantly associated with overall survival. Multivariate analysis showed that all the aforementioned were independent predictive factors of survival. In addition, the survival of patients with PF was significantly worse compared to those without (HR 1.392; P=0.027). Tumor necrosis is a valuable prognostic tool that can be included in the routine post-resection histopathological evaluation of pancreatic head cancer patients.

An Efficient T 1 Contrast Agent for Labeling and Tracking Human Embryonic Stem Cells on MRI

Noninvasive cell tracking in vivo has the potential to advance stem cell-based therapies into the clinic. Magnetic resonance imaging (MRI) provides an excellent image-guidance platform; however, existing MR cell labeling agents are fraught with limited specificity. To address this unmet need, we developed a highly efficient manganese porphyrin contrast agent, MnEtP, using a two-step synthesis. In vitro MRI at 3 Tesla on human embryonic stem cells (hESCs) demonstrated high labeling efficiency at a very low dose of 10 µM MnEtP, resulting in a four-fold lower T₁ relaxation time. This extraordinarily low dose is ideal for labeling large cell numbers required for large animals and humans. Cell viability and differentiation capacity were unaffected. Cellular manganese quantification corroborated MRI findings, and the agent localized primarily on the cell membrane. In vivo MRI of transplanted hESCs in a rat demonstrated excellent sensitivity and specificity of MnEtP for noninvasive stem cell tracking.

In vitro anti-Leishmania activity of T6 synthetic compound encapsulated in yeast-derived β-(1,3)-d-glucan particles

The objective of this study was to encapsulate a synthetic compound, the 4-[(2E)-N'-(2,2'-bithienyl-5-methylene)hydra-zinecarbonyl]-6,7-dihydro-1-phenyl-1H-pyrazolo[3,4-d]pyridazin-7-one (T6) in glucan-rich particles mainly composed by the cell wall of Saccharomyces cerevisiae (GPs) and to study their individual and combined activity on Leishmania infantum. The possible mechanism of action of T6 was also investigated. Our results showed the activity of T6 compound in both promastigote (IC₅₀ = 2.5 μg/mL) and intracellular amastigote (IC₅₀ = 1.23 μg/mL) forms. We also found activity against intracellular amastigote forms (IC₅₀ = 8.20 μg/mL) when the T6 compound was encapsulated in GPs. Another interesting finding was the fact that T6 encapsulated in GPs showed a significant decrease in J774A1 macrophage toxicity (CC₅₀ ≥ 18.53 μg/mL) compared to the T6 compound alone (IC₅₀ = 2.27 μg/mL). Through electron microscopy and biochemical methodologies, we verified that the activity of T6 in promastigote forms of L. infantum was characterized by events of cell death by apoptosis like increased ROS production, cell shrinkage, phosphatidylserine exposure and DNA fragmentation. We conclude that T6 can be considered a promising anti-Leishmania compound, and that the use of GPs for drug encapsulation is an interesting approach to the development of new effective and less toxic formulations.

Prognostic Significance of Tumor Necrosis in Hilar Cholangiocarcinoma

BACKGROUND

Tumor necrosis and peritumoral fibrosis have both been suggested to have a prognostic value in selected solid tumors. However, little is known regarding their influence on tumor progression and prognosis in hilar cholangiocarcinoma (HC).

METHODS

Surgically resected tumor specimens of HC (n = 47) were analyzed for formation of necrosis and extent of peritumoral fibrosis. Tumor necrosis and grade of fibrosis were assessed histologically and correlated with clinicopathological characteristics, tumor recurrence, and patients' survival. Univariate Kaplan-Meier analysis and a stepwise multivariable Cox regression model were applied.

RESULTS

Mild peritumoral fibrosis was evident in 12 tumor samples, moderate peritumoral fibrosis in 20, and high-grade fibrosis in 15. Necrosis was evident in 19 of 47 tumor samples. Patients with tumors characterized by necrosis showed a significantly decreased 5-year recurrence-free survival (37.9 vs. 25.7 %; p < .05) and a significantly decreased 5-year overall survival (42.6 vs. 12.4 %; p < .05), when compared with patients with tumors showing no necrosis. R status, tumor recurrence, and tumor necrosis were of prognostic value in the univariate analysis (all p < .05). Multivariate survival analysis confirmed tumor necrosis (p = .038) as the only independent prognostic variable.

CONCLUSIONS

The assessment of tumor necrosis appears as a valuable additional prognostic tool in routine histopathological evaluation of HC. These observations might have implications for monitoring and more individualized multimodal therapeutic strategies.

Monitoring the Growth of an Orthotopic Tumour Xenograft Model: Multi-Modal Imaging Assessment with Benchtop MRI (1T), High-Field MRI (9.4T), Ultrasound and Bioluminescence

BACKGROUND

Research using orthotopic and transgenic models of cancer requires imaging methods to non-invasively quantify tumour burden. As the choice of appropriate imaging modality is wide-ranging, this study aimed to compare low-field (1T) magnetic resonance imaging (MRI), a novel and relatively low-cost system, against established preclinical techniques: bioluminescence imaging (BLI), ultrasound imaging (US), and high-field (9.4T) MRI.

METHODS

A model of colorectal metastasis to the liver was established in eight mice, which were imaged with each modality over four weeks post-implantation. Tumour burden was assessed from manually segmented regions.

RESULTS

All four imaging systems provided sufficient contrast to detect tumours in all of the mice after two weeks. No significant difference was detected between tumour doubling times estimated by low-field MRI, ultrasound imaging or high-field MRI. A strong correlation was measured between high-field MRI estimates of tumour burden and all the other modalities (p < 0.001, Pearson).

CONCLUSION

These results suggest that both low-field MRI and ultrasound imaging are accurate modalities for characterising the growth of preclinical tumour models.

In Vivo Tracking of Phagocytic Immune Cells Using a Dual Imaging Probe with Gadolinium-Enhanced MRI and Near-Infrared Fluorescence

A novel dual imaging probe for in vivo magnetic resonance imaging (MRI) and optical imaging was developed by combining gadolinium (Gd)-chelating MR probe and a near-infrared (NIR) fluorophore, aza-BODIPY (AB; BODIPY = boron-dipyrromethene). This aza-BODIPY-based bimodal contrast agent (AB-BCA) showed a significant fluorescence emission around the NIR range and an enhanced longitudinal relaxivity in MR modality. The probe was easily delivered to phagocytic cells of the innate immune system, together with macrophages and dendritic cells (DCs), and presented high-performance fluorescence and MR imaging without obvious cytotoxicity. For in vivo visualization of AB-BCA using MRI and optical imaging, bone marrow-derived DCs were labeled and injected into the footpad of mice, and labeled DCs were tracked in vivo. We observed the migration of AB-BCA-labeled DCs into the lymph nodes via lymphatic vessels using NIR fluorescence and T1-weighted MR images. This dual-modality imaging probe was used for noninvasive monitoring of DC migration into lymph nodes and could be useful for investigating advanced cellular immunotherapy.

An enzyme-activatable and cell-permeable MnIII-porphyrin as a highly efficient T1 MRI contrast agent for cell labeling

MnAMP, a cell-trappable pro-contrast agent gets enzymatically activated and accumulated intracellularly to provide a strong MRI signal for cell labeling.

Magnetic resonance imaging (MRI) is a preferred technique for noninvasively monitoring the fate of implanted cells, such as stem cells and immune cells in vivo. Cellular MRI requires contrast agents (CAs) to label the cells of interest. Despite promising progress made in this emerging field, highly sensitive, stable and biocompatible T₁ CAs with high cell permeability and specificity remains an unmet challenge. To address this need, a novel Mn^III-porphyrin, MnAMP was designed and synthesized based on the modification of Mn^IIItetra(carboxy-porphyrin) (MnTCP), a small and highly stable non-Gd extracellular CA with good biocompatibility and high T₁ relaxivity (r₁ = 7.9 mM^–1 s^–1) at clinical field of 3 Tesla (T). Cell permeability was achieved by masking the polar carboxylates of MnTCP with acetoxymethyl-ester (AM) groups, which are susceptible to hydrolysis by intracellular esterases. The enzymatic cleavage of AM groups led to disaggregation of the hydrophobic MnAMP, releasing activated MnTCP with significant increase in T₁ relaxivity. Cell uptake of MnAMP is highly efficient as tested on two non-phagocytic human cell lines with no side effects observed on cell viability. MRI of labeled cells exhibited significant contrast enhancement with a short T₁ of 161 ms at 3 T, even though a relatively low concentration of MnAMP and short incubation time was applied for cell labeling. Overall, MnAMP is among the most efficient T₁ cell labeling agents developed for cellular MRI.

Prognostic significance of macrophage invasion in hilar cholangiocarcinoma

Background

Tumor-associated macrophages (TAMs) promote tumor progression and have an effect on survival in human cancer. However, little is known regarding their influence on tumor progression and prognosis in human hilar cholangiocarcinoma.

Methods

We analyzed surgically resected tumor specimens of hilar cholangiocarcinoma (n = 47) for distribution and localization of TAMs, as defined by expression of CD68. Abundance of TAMs was correlated with clinicopathologic characteristics, tumor recurrence and patients’ survival. Statistical analysis was performed using SPSS software.

Results

Patients with high density of TAMs in tumor invasive front (TIF) showed significantly higher local and overall tumor recurrence (both ρ < 0.05). Furthermore, high density of TAMs was associated with decreased overall (one-year 83.6 % vs. 75.1 %; three-year 61.3 % vs. 42.4 %; both ρ < 0.05) and recurrence-free survival (one-year 93.9 % vs. 57.4 %; three-year 59.8 % vs. 26.2 %; both ρ < 0.05). TAMs in TIF and tumor recurrence, were confirmed as the only independent prognostic variables in the multivariate survival analysis (all ρ < 0.05).

Conclusions

Overall survival and recurrence free survival of patients with hilar cholangiocarcinoma significantly improved in patients with low levels of TAMs in the area of TIF, when compared to those with a high density of TAMs. These observations suggest their utilization as valuable prognostic markers in routine histopathologic evaluation, and might indicate future therapeutic approaches by targeting TAMs.

Nanoparticles and clinically applicable cell tracking

In vivo cell tracking has emerged as a much sought after tool for design and monitoring of cell-based treatment strategies. Various techniques are available for pre-clinical animal studies, from which much has been learned and still can be learned. However, there is also a need for clinically translatable techniques. Central to in vivo cell imaging is labelling of cells with agents that can give rise to signals in vivo, that can be detected and measured non-invasively. The current imaging technology of choice for clinical translation is MRI in combination with labelling of cells with magnetic agents. The main challenge encountered during the cell labelling procedure is to efficiently incorporate the label into the cell, such that the labelled cells can be imaged at high sensitivity for prolonged periods of time, without the labelling process affecting the functionality of the cells. In this respect, nanoparticles offer attractive features since their structure and chemical properties can be modified to facilitate cellular incorporation and because they can carry a high payload of the relevant label into cells. While these technologies have already been applied in clinical trials and have increased the understanding of cell-based therapy mechanism, many challenges are still faced.

Glucan particles loaded with a NIRF agent for imaging monocytes/macrophages recruitment in a mouse model of rheumatoid arthritis

We report here thein vivorecruitment of immune cells in inflamed sites on a mouse model of rheumatoid arthritis (CIA) by NIRF imaging of fluorescent glucan microspheres (GPs).

High-resolution cellular MRI: gadolinium and iron oxide nanoparticles for in-depth dual-cell imaging of engineered tissue constructs

Recent advances in cell therapy and tissue engineering opened new windows for regenerative medicine, but still necessitate innovative noninvasive imaging technologies. We demonstrate that high-resolution magnetic resonance imaging (MRI) allows combining cellular-scale resolution with the ability to detect two cell types simultaneously at any tissue depth. Two contrast agents, based on iron oxide and gadolinium oxide rigid nanoplatforms, were used to "tattoo" endothelial cells and stem cells, respectively, with no impact on cell functions, including their capacity for differentiation. The labeled cells' contrast properties were optimized for simultaneous MRI detection: endothelial cells and stem cells seeded together in a polysaccharide-based scaffold material for tissue engineering appeared respectively in black and white and could be tracked, at the cellular level, both in vitro and in vivo. In addition, endothelial cells labeled with iron oxide nanoparticles could be remotely manipulated by applying a magnetic field, allowing the creation of vessel substitutes with in-depth detection of individual cellular components.