Preclinical imaging methods for assessing the safety and efficacy of regenerative medicine therapies

CT-Visible Microspheres Enable Whole-Body In Vivo Tracking of Injectable Tissue Engineering Scaffolds

Targeted delivery and retention are essential requirements for implantable tissue-engineered products. Non-invasive imaging methods that can confirm location, retention, and biodistribution of transplanted cells attached to implanted tissue engineering scaffolds will be invaluable for the optimization and enhancement of regenerative therapies. To address this need, an injectable tissue engineering scaffold consisting of highly porous microspheres compatible with transplantation of cells is modified to contain the computed tomography (CT) contrast agent barium sulphate (BaSO4). The trackable microspheres show high x-ray absorption, with contrast permitting whole-body tracking. The microspheres are cellularized with GFP+ Luciferase+ mesenchymal stem cells and show in vitro biocompatibility. In vivo, cellularized BaSO4-loaded microspheres are delivered into the hindlimb of mice where they remain viable for 14 days. Co-registration of 3D-bioluminescent imaging and µCT reconstructions enable the assessment of scaffold material and cell co-localization. The trackable microspheres are also compatible with minimally-invasive delivery by ultrasound-guided transthoracic intramyocardial injections in rats. These findings suggest that BaSO4-loaded microspheres can be used as a novel tool for optimizing delivery techniques and tracking persistence and distribution of implanted scaffold materials. Additionally, the microspheres can be cellularized and have the potential to be developed into an injectable tissue-engineered combination product for cardiac regeneration.

Harmonic Imaging of Stem Cells in Whole Blood at GHz Pixel Rate

The pre-clinical validation of cell therapies requires monitoring the biodistribution of transplanted cells in tissues of host organisms. Real-time detection of these cells in the circulatory system and identification of their aggregation state is a crucial piece of information, but necessitates deep penetration and fast imaging with high selectivity, subcellular resolution, and high throughput. In this study, multiphoton-based in-flow detection of human stem cells in whole, unfiltered blood is demonstrated in a microfluidic channel. The approach relies on a multiphoton microscope with diffractive scanning in the direction perpendicular to the flow via a rapidly wavelength-swept laser. Stem cells are labeled with metal oxide harmonic nanoparticles. Thanks to their strong and quasi-instantaneous second harmonic generation (SHG), an imaging rate in excess of 10 000 frames per second is achieved with pixel dwell times of 1 ns, a duration shorter than typical fluorescence lifetimes yet compatible with SHG. Through automated cell identification and segmentation, morphological features of each individual detected event are extracted and cell aggregates are distinguished from isolated cells. This combination of high-speed multiphoton microscopy and high-sensitivity SHG nanoparticle labeling in turbid media promises the detection of rare cells in the bloodstream for assessing novel cell-based therapies.

Multimodal Imaging-Guided Stem Cell Ocular Treatment

Stem cell therapies are gaining traction as promising treatments for a variety of degenerative conditions. Both clinical and preclinical studies of regenerative medicine are hampered by the lack of technologies that can evaluate the migration and behavior of stem cells post-transplantation. This study proposes an innovative method to longitudinally image in vivo human-induced pluripotent stem cells differentiated to retinal pigment epithelium (hiPSC-RPE) cells by multimodal photoacoustic microscopy, optical coherence tomography, and fluorescence imaging powered by ultraminiature chain-like gold nanoparticle cluster (GNC) nanosensors. The GNC exhibits an optical absorption peak in the near-infrared regime, and the 7-8 nm size in diameter after disassembly enables renal excretion and improved safety as well as biocompatibility. In a clinically relevant rabbit model, GNC-labeled hiPSC-RPE cells migrated to RPE degeneration areas and regenerated damaged tissues. The hiPSC-RPE cells' distribution and migration were noninvasively, longitudinally monitored for 6 months with exceptional sensitivity and spatial resolution. This advanced platform for cellular imaging has the potential to enhance regenerative cell-based therapies.

Enabling Non-invasive Tracking of Vascular Endothelial Cells Derived from Induced Pluripotent Stem Cells Using Nuclear Imaging

PURPOSE

The absence of clinically applicable imaging techniques for continuous monitoring of transplanted cells poses a significant obstacle to the clinical translation of stem cell-based therapies for vascular regeneration. This study aims to optimize a clinically applicable, non-invasive imaging technique to longitudinally monitor vascular endothelial cells (ECs) for vascular regeneration in peripheral artery disease (PAD).

METHODS

Human induced pluripotent stem cells (HiPSCs) were employed to generate ECs (HiPSC-ECs). Lentiviral vectors encoding human sodium iodide symporter (hNIS) and enhanced green fluorescent protein (eGFP) genes were introduced to HiPSCs and HiPSC-ECs at varying multiplicities of infection (MOI). Through a combination of fluorescence microscopy and flow cytometry, an optimized transduction technique for introducing hNIS-eGFP into HiPSC-ECs was established. Subsequently, single-photon emission computed tomography (SPECT) was utilized for imaging of the transduced cells in vitro and in vivo after transplantation into the gastrocnemius muscle of nude mice.

RESULTS

Lentiviral transduction resulted in sustained co-expression of hNIS and eGFP in HiPSC-ECs when transduced post-endothelial differentiation. An optimal MOI of five yielded over 90% hNIS-eGFP expression efficiency without compromising cell viability. hNIS-eGFP+ HiPSC-ECs exhibited 99mTc uptake and were detectable through SPECT in vitro. Additionally, intramuscular injection of hNIS-eGFP+ HiPSC-ECs with MatrigelTM into the hindlimbs of nude mice enabled real-time SPECT/CT tracking, from which a reduction in signal exceeding 80% was observed within 7 days.

CONCLUSIONS

This study establishes an optimized cell modification and imaging protocol for tracking transplanted cells. Future efforts will focus on enhancing cell survival and integration via improved delivery systems, thereby advancing the potential of cell-based therapies for PAD.

X-Ray Visible Protein Scaffolds by Bulk Iodination

Protein-based biomaterial use is expanding within medicine, together with the demand to visualize their placement and behavior in vivo. However, current medical imaging techniques struggle to differentiate between protein-based implants and surrounding tissue. Here a fast, simple, and translational solution for tracking transplanted protein-based scaffolds is presented using X-ray CT-facilitating long-term, non-invasive, and high-resolution imaging. X-ray visible scaffolds are engineered by selectively iodinating tyrosine residues under mild conditions using readily available reagents. To illustrate translatability, a clinically approved hernia repair mesh (based on decellularized porcine dermis) is labeled, preserving morphological and mechanical properties. In a mouse model of mesh implantation, implants retain marked X-ray contrast up to 3 months, together with an unchanged degradation rate and inflammatory response. The technique's compatibility is demonstrated with a range of therapeutically relevant protein formats including bovine, porcine, and jellyfish collagen, as well as silk sutures, enabling a wide range of surgical and regenerative medicine uses. This solution tackles the challenge of visualizing implanted protein-based biomaterials, which conventional imaging methods fail to differentiate from endogenous tissue. This will address previously unanswered questions regarding the accuracy of implantation, degradation rate, migration, and structural integrity, thereby accelerating optimization and safe translation of therapeutic biomaterials.

Current views on in vivo models for breast cancer research and related drug development

INTRODUCTION

Animal models play a crucial role in breast cancer research, in particular mice and rats, who develop mammary tumors that closely resemble their human counterparts. These models allow the study of mechanisms behind breast carcinogenesis, as well as the efficacy and safety of new, and potentially more effective and advantageous therapeutic approaches. Understanding the advantages and disadvantages of each model is crucial to select the most appropriate one for the research purpose.

AREA COVERED

This review provides a concise overview of the animal models available for breast cancer research, discussing the advantages and disadvantages of each one for searching new and more effective approaches to treatments for this type of cancer.

EXPERT OPINION

Rodent models provide valuable information on the genetic alterations of the disease, the tumor microenvironment, and allow the evaluation of the efficacy of chemotherapeutic agents. However, in vivo models have limitations, and one of them is the fact that they do not fully mimic human diseases. Choosing the most suitable model for the study purpose is crucial for the development of new therapeutic agents that provide better care for breast cancer patients.

Future Nanotechnology-Based Strategies for Improved Management of Helicobacter pylori Infection

Helicobacter pylori (H. pylori) is a recalcitrant pathogen, which can cause gastric disorders. During the past decades, polypharmacy-based regimens, such as triple and quadruple therapies have been widely used against H. pylori. However, polyantibiotic therapies can disturb the host gastric/gut microbiota and lead to antibiotic resistance. Thus, simpler but more effective approaches should be developed. Here, some recent advances in nanostructured drug delivery systems to treat H. pylori infection are summarized. Also, for the first time, a drug release paradigm is proposed to prevent H. pylori antibiotic resistance along with an IVIVC model in order to connect the drug release profile with a reduction in bacterial colony counts. Then, local delivery systems including mucoadhesive, mucopenetrating, and cytoadhesive nanobiomaterials are discussed in the battle against H. pylori infection. Afterward, engineered delivery platforms including polymer-coated nanoemulsions and polymer-coated nanoliposomes are poposed. These bioinspired platforms can contain an antimicrobial agent enclosed within smart multifunctional nanoformulations. These bioplatforms can prevent the development of antibiotic resistance, as well as specifically killing H. pylori with no or only slight negative effects on the host gastrointestinal microbiota. Finally, the essential checkpoints that should be passed to confirm the potential effectiveness of anti-H. pylori nanosystems are discussed.

Near infrared conjugated polymer nanoparticles (CPN™) for tracking cells using fluorescence and optoacoustic imaging

Tracking the biodistribution of cell therapies is crucial for understanding their safety and efficacy. Optical imaging techniques are particularly useful for tracking cells due to their clinical translatability and potential for intra-operative use to validate cell delivery. However, there is a lack of appropriate optical probes for cell tracking. The only FDA-approved material for clinical use is indocyanine green (ICG). ICG can be used for both fluorescence and photoacoustic imaging, but is prone to photodegradation, and at higher concentrations, undergoes quenching and can adversely affect cell health. We have developed novel near-infrared imaging probes comprising conjugated polymer nanoparticles (CPNs™) that can be fine-tuned to absorb and emit light at specific wavelengths. To compare the performance of the CPNs™ with ICG for in vivo cell tracking, labelled mesenchymal stromal cells (MSCs) were injected subcutaneously in mice and detected using fluorescence imaging (FI) and a form of photoacoustic imaging called multispectral optoacoustic tomography (MSOT). MSCs labelled with either ICG or CPN™ 770 could be detected with FI, but only CPN™ 770-labelled MSCs could be detected with MSOT. These results show that CPNs™ show great promise for tracking cells in vivo using optical imaging techniques, and for some applications, out-perform ICG.

Community Survey Results Show that Standardisation of Preclinical Imaging Techniques Remains a Challenge

PURPOSE

To support acquisition of accurate, reproducible and high-quality preclinical imaging data, various standardisation resources have been developed over the years. However, it is unclear the impact of those efforts in current preclinical imaging practices. To better understand the status quo in the field of preclinical imaging standardisation, the STANDARD group of the European Society of Molecular Imaging (ESMI) put together a community survey and a forum for discussion at the European Molecular Imaging Meeting (EMIM) 2022. This paper reports on the results from the STANDARD survey and the forum discussions that took place at EMIM2022.

PROCEDURES

The survey was delivered to the community by the ESMI office and was promoted through the Society channels, email lists and webpages. The survey contained seven sections organised as generic questions and imaging modality-specific questions. The generic questions focused on issues regarding data acquisition, data processing, data storage, publishing and community awareness of international guidelines for animal research. Specific questions on practices in optical imaging, PET, CT, SPECT, MRI and ultrasound were further included.

RESULTS

Data from the STANDARD survey showed that 47% of survey participants do not have or do not know if they have QC/QA guidelines at their institutes. Additionally, a large variability exists in the ways data are acquired, processed and reported regarding general aspects as well as modality-specific aspects. Moreover, there is limited awareness of the existence of international guidelines on preclinical (imaging) research practices.

CONCLUSIONS

Standardisation of preclinical imaging techniques remains a challenge and hinders the transformative potential of preclinical imaging to augment biomedical research pipelines by serving as an easy vehicle for translation of research findings to the clinic. Data collected in this project show that there is a need to promote and disseminate already available tools to standardise preclinical imaging practices.

The evolving role of investigative toxicology in the pharmaceutical industry

For decades, preclinical toxicology was essentially a descriptive discipline in which treatment-related effects were carefully reported and used as a basis to calculate safety margins for drug candidates. In recent years, however, technological advances have increasingly enabled researchers to gain insights into toxicity mechanisms, supporting greater understanding of species relevance and translatability to humans, prediction of safety events, mitigation of side effects and development of safety biomarkers. Consequently, investigative (or mechanistic) toxicology has been gaining momentum and is now a key capability in the pharmaceutical industry. Here, we provide an overview of the current status of the field using case studies and discuss the potential impact of ongoing technological developments, based on a survey of investigative toxicologists from 14 European-based medium-sized to large pharmaceutical companies.

Cell-Based HIF1α Gene Therapy Reduces Myocardial Scar and Enhances Angiopoietic Proteome, Transcriptomic and miRNA Expression in Experimental Chronic Left Ventricular Dysfunction

Recent preclinical investigations and clinical trials with stem cells mostly studied bone-marrow-derived mononuclear cells (BM-MNCs), which so far failed to meet clinically significant functional study endpoints. BM-MNCs containing small proportions of stem cells provide little regenerative potential, while mesenchymal stem cells (MSCs) promise effective therapy via paracrine impact. Genetic engineering for rationally enhancing paracrine effects of implanted stem cells is an attractive option for further development of therapeutic cardiac repair strategies. Non-viral, efficient transfection methods promise improved clinical translation, longevity and a high level of gene delivery. Hypoxia-induced factor 1α is responsible for pro-angiogenic, anti-apoptotic and anti-remodeling mechanisms. Here we aimed to apply a cellular gene therapy model in chronic ischemic heart failure in pigs. A non-viral circular minicircle DNA vector (MiCi) was used for in vitro transfection of porcine MSCs (pMSC) with HIF1α (pMSC-MiCi-HIF-1α). pMSCs-MiCi-HIF-1α were injected endomyocardially into the border zone of an anterior myocardial infarction one month post-reperfused-infarct. Cell injection was guided via 3D-guided NOGA electro-magnetic catheter delivery system. pMSC-MiCi-HIF-1α delivery improved cardiac output and reduced myocardial scar size. Abundances of pro-angiogenic proteins were analyzed 12, 24 h and 1 month after the delivery of the regenerative substances. In a protein array, the significantly increased angiogenesis proteins were Activin A, Angiopoietin, Artemin, Endothelin-1, MCP-1; and remodeling factors ADAMTS1, FGFs, TGFb1, MMPs, and Serpins. In a qPCR analysis, increased levels of angiopeptin, CXCL12, HIF-1α and miR-132 were found 24 h after cell-based gene delivery, compared to those in untreated animals with infarction and in control animals. Expression of angiopeptin increased already 12 h after treatment, and miR-1 expression was reduced at that time point. In total, pMSC overexpressing HIF-1α showed beneficial effects for treatment of ischemic injury, mediated by stimulation of angiogenesis.

Click-Ready Perfluorocarbon Nanoemulsion for 19F MRI and Multimodal Cellular Detection

We describe an in vivo imaging probe platform that is readily modifiable to accommodate binding of different molecular targeting moieties and payloads for multimodal image generation. In this work, we demonstrate the utility of perfluorocarbon (PFC) nanoemulsions incorporating dibenzocyclooctyne (DBCO) by enabling postemulsification functionalization via a click reaction with azide-containing ligands. The addition of DBCO-lipid to the surfactant in PFC nanoemulsions did not affect nanoemulsion size or nanoemulsion stability. As proof-of-concept, fluorescent dye-azides were conjugated to PFC nanoemulsions, demonstrating the feasibility of functionalization the by click reaction. Uptake of the fluorescent PFC by macrophages was demonstrated both in vitro in cultured macrophages and in situ in an acute inflammation mouse model, where fluorescence imaging and ¹H/¹⁹F magnetic resonance imaging (MRI) were used for in vivo detection. Overall, these data demonstrate the potential of PFC nanoemulsions incorporating DBCO as a versatile platform for generating functionalized probes.

Biodistribution studies for cell therapy products: Current status and issues

Information on the biodistribution (BD) of cell therapy products (CTPs) is essential for prediction and assessment of their efficacy and toxicity profiles in non-clinical and clinical studies. To conduct BD studies, it is necessary to understand regulatory requirements, implementation status, and analytical methods. This review aimed at surveying international and Japanese trends concerning the BD study for CTPs and the following subjects were investigated, which were considered particularly important: 1) comparison of guidelines to understand the regulatory status of BD studies in a global setting; 2) case studies of the BD study using databases to understand its current status in cell therapy; 3) case studies on quantitative polymerase chain reaction (qPCR) used primarily in non-clinical BD studies for CTPs; and 4) survey of imaging methods used for non-clinical and clinical BD studies. The results in this review will be a useful resource for implementing BD studies.

Interventional Strategies for Parkinson Disease: Can Neural Precursor Cells Forge a Path Ahead?

Neural precursor cells (NPCs), derived from pluripotent stem cells (PSCs), with their unique ability to generate multiple neuronal and glial cell types are extremely useful for understanding biological mechanisms in normal and diseased states. However, generation of specific neuronal subtypes (mature) from NPCs in large numbers adequate for cell therapy is challenging due to lack of a thorough understanding of the cues that govern their differentiation. Interestingly, neural stem cells (NSCs) themselves are in consideration for therapy given their potency to form different neural cell types, release of trophic factors, and immunomodulatory effects that confer neuroprotection. With the recent COVID-19 outbreak and its accompanying neurological indications, the immunomodulatory role of NSCs may gain additional significance in the prevention of disease progression in vulnerable populations. In this regard, small-molecule mediated NPC generation from PSCs via NSC formation has become an important strategy that ensures consistency and robustness of the process. The development of the mammalian brain occurs along the rostro-caudal axis, and the establishment of anterior identity is an early event. Wnt signaling, along with fibroblast growth factor and retinoic acid, acts as a caudalization signal. Further, the increasing amount of epigenetic data available from human fetal brain development has enhanced both our understanding of and ability to experimentally manipulate these developmental regulatory programs in vitro. However, the impact on homing and engraftment after transplantation and subsequently on therapeutic efficacy of NPCs based on their derivation strategy is not yet clear. Another formidable challenge in cell replacement therapy for neurodegenerative disorders is the mode of delivery. In this Perspective, we discuss these core ideas with insights from our preliminary studies exploring the role of PSC-derived NPCs in rat models of MPTP-induced Parkinson's disease following intranasal injections.

Perspective: Why and How Ubiquitously Distributed, Vascular-Associated, Pluripotent Stem Cells in the Adult Body (vaPS Cells) Are the Next Generation of Medicine

A certain cell type can be isolated from different organs in the adult body that can differentiate into ectoderm, mesoderm, and endoderm, providing significant support for the existence of a certain type of small, vascular-associated, pluripotent stem cell ubiquitously distributed in all organs in the adult body (vaPS cells). These vaPS cells fundamentally differ from embryonic stem cells and induced pluripotent stem cells in that the latter possess the necessary genetic guidance that makes them intrinsically pluripotent. In contrast, vaPS cells do not have this intrinsic genetic guidance, but are able to differentiate into somatic cells of all three lineages under guidance of the microenvironment they are located in, independent from the original tissue or organ where they had resided. These vaPS cells are of high relevance for clinical application because they are contained in unmodified, autologous, adipose-derived regenerative cells (UA-ADRCs). The latter can be obtained from and re-applied to the same patient at the point of care, without the need for further processing, manipulation, and culturing. These findings as well as various clinical examples presented in this paper demonstrate the potential of UA-ADRCs for enabling an entirely new generation of medicine for the benefit of patients and healthcare systems.

Long-Term, Noninvasive In Vivo Tracking of Progenitor Cells Using Multimodality Photoacoustic, Optical Coherence Tomography, and Fluorescence Imaging

Stem cell regenerative medicine therapies have emerged as promising treatments for currently incurable diseases. A remaining challenge for cell therapies is the ability to track the migration and distribution of the transplanted cells in a long-term, noninvasive manner in vivo to assess their efficacy. This study develops a noninvasive, and high spatial resolution photoacoustic microscopy (PAM) and optical coherence tomography (OCT) imaging system for in vivo tracking of subretinally injected progenitor human retinal pigment epithelium cells (ARPE-19) labeled with chainlike gold nanoparticle (CGNP) clusters in RPE damage. CGNP provided significant PAM, OCT, and fluorescence signals to selectively track the migration of ARPE-19 cells in living rabbit eyes for 3 months. PAM and OCT imaging allow accurate anatomical information to determine the exact retinal layer in which the transplanted ARPE-19 cells are located which was confirmed by histology. This presents an efficient and advanced technology to visualize fundamental biological processes of cell therapies in complex in vivo environments in real time.

In Vivo Subretinal ARPE-19 Cell Tracking Using Indocyanine Green Contrast-Enhanced Multimodality Photoacoustic Microscopy, Optical Coherence Tomography, and Fluorescence Imaging for Regenerative Medicine

Purpose

Cell-based regenerative therapies are being investigated as a novel treatment method to treat currently incurable eye diseases, such as geographic atrophy in macular degeneration. Photoacoustic imaging is a promising technology which can visualize transplanted stem cells in vivo longitudinally over time in the retina. In this study, a US Food and Drug Administration (FDA)-approved indocyanine green (ICG) contrast agent is used for labeling and tracking cell distribution and viability using multimodal photoacoustic microscopy (PAM), optical coherence tomography (OCT), and fluorescence imaging.

Methods

Twelve rabbits (2.4–3.4 kg weight, 2–4 months old) were used in the study. Human retinal pigment epithelial cells (ARPE-19) were labeled with ICG dye and transplanted in the subretinal space in the rabbits. Longitudinal PAM, OCT, and fluorescence imaging was performed for up to 28 days following subretinal administration of ARPE-19 cells.

Results

Cell migration location, viability, and cell layer thickness were clearly recognized and determined from the fluorescence, OCT, and PAM signal. The in vivo results demonstrated that fluorescence signal increased 37-fold and PAM signal enhanced 20-fold post transplantation.

Conclusions

This study demonstrates that ICG-assisted PAM, OCT, and fluorescence imaging can provide a unique platform for tracking ARPE-19 cells longitudinally with high resolution and high image contrast.

Translational Relevance

Multimodal PAM, OCT, and fluorescence in vivo imaging with ICG can improve our understanding of the fate, distribution, and function of regenerative cell therapies over time nondestructively.

Biodistribution of Intramuscularly-Transplanted Human Dental Pulp Stem Cells in Immunocompetent Healthy Rats through NIR Imaging

Owing to their neural crest origin, dental pulp stem cells (DPSCs) are increasingly gaining prominence in treating nervous system disease conditions. However, as per the regulatory bodies [European-Medicines Agency (EMA), Indian-Council of Medical-Research (ICMR)], their biodistribution after transplantation needs to be evaluated for them to be considered for cell-based therapy for clinical trials. There are yet no studies describing the dynamic distribution of human origin DPSCs (hDPSCs) after transplantation in an immunocompetent, physiologically healthy animal model. Here, using near-infrared (NIR)-based whole animal and ex vivo tissue imaging, we assessed the biodistribution of intramuscularly transplanted hDPSCs in immunocompetent healthy Wistar rats. Further validation was done by quantifying gene expression of the human Alu gene in rat tissues. After 24 h of transplantation, an increase in signal intensity and area of signal was observed in the muscle of administration compared to 30 min and 6 h. At hour 24, neither increase in human Alu nor human Ki67 gene expression was seen in the rat muscle, thus confirming that the increase in signal area and intensity at hour 24 was not due to proliferation of the transplanted cells. Rather at hour 24, the NIR-signal intensity in bone marrow increased, suggesting that the NIR-tagged DPSCs have started entering into the blood vessels adjacent to the muscle, and the blood vessels being placed just beneath the subcutaneous layer might be responsible for an increase in signal intensity. Signal intensity increased distinctly in all organs at this timepoint, confirming that the cells entered the bloodstream by hour 24. Lung entrapment of DPSCs was not observed, since signal intensity was least in lungs as compared to the site of injection. Cells were retained for up to 28 days at the site of injection. These findings lay the basis to design the dosage for intramuscular delivery of hDPSCs for degenerative disease models and for future clinical trials.

Intrinsic Heart Regeneration in Adult Vertebrates May be Strictly Limited to Low-Metabolic Ectotherms

The heart has a high-metabolic rate, and its "around-the-clock" vital role to sustain life sets it apart in a regenerative setting from other organs and appendages. The landscape of vertebrate species known to perform intrinsic heart regeneration is strongly biased toward ectotherms-for example, fish, salamanders, and embryonic/neonatal ectothermic mammals. It is hypothesized that intrinsic heart regeneration is exclusively limited to the low-metabolic hearts of ectotherms. The biomedical field of regenerative medicine seeks to devise biologically inspired regenerative therapies to diseased human hearts. Falsification of the ectothermy dependency for heart regeneration hypothesis may be a crucial prerequisite to meaningfully seek inspiration in established ectothermic regenerative animal models. Otherwise, engineering approaches to construct artificial heart components may constitute a more viable path toward regenerative therapies. A more strict definition of regenerative phenomena is generated and several testable sub-hypotheses and experimental avenues are put forward to elucidate the link between heart regeneration and metabolism. Also see the video abstract here https://youtu.be/fZcanaOT5z8.

Multi-modal imaging probe for assessing the efficiency of stem cell delivery to orthotopic breast tumours

Stem cells have been utilised as anti-cancer agents due to their ability to home to and integrate within tumours. Methods to augment stem cell homing to tumours are being investigated with the goal of enhancing treatment efficacy. However, it is currently not possible to evaluate both cell localisation and cell viability after engraftment, hindering optimisation of therapy. In this study, luciferase-expressing human adipocyte-derived stem cells (ADSCs) were incubated with Indium-111 radiolabelled iron oxide nanoparticles to produce cells with tri-modal imaging capabilities. ADSCs were administered intravenously (IV) or intracardially (IC) to mice bearing orthotopic breast tumours. Cell fate was monitored using bioluminescence imaging (BLI) as a measure of cell viability, magnetic resonance imaging (MRI) for cell localisation and single photon emission computer tomography (SPECT) for cell quantification. Serial monitoring with multi-modal imaging showed the presence of viable ADSCs within tumours as early as 1-hour post IC injection and the percentage of ADSCs within tumours to be 2-fold higher after IC than IV. Finally, histological analysis was used to validate engraftment of ADSC within tumour tissue. These findings demonstrate that multi-modal imaging can be used to evaluate the efficiency of stem cell delivery to tumours and that IC cell administration is more effective for tumour targeting.

Multimodal Imaging Techniques Show Differences in Homing Capacity Between Mesenchymal Stromal Cells and Macrophages in Mouse Renal Injury Models

PURPOSE

The question of whether mesenchymal stromal cells (MSCs) home to injured kidneys remains a contested issue. To try and understand the basis for contradictory findings reported in the literature, our purpose here was to investigate whether MSC homing capacity is influenced by administration route, the type of injury model used, and/or the presence of exogenous macrophages.

PROCEDURES

To assess the viability, whole-body biodistribution, and intra-renal biodistribution of MSCs, we used a multimodal imaging strategy comprising bioluminescence and magnetic resonance imaging. The effect of administration route (venous or arterial) on the ability of MSCs to home to injured renal tissue, and persist there, was assessed in a glomerular injury model (induced by the nephrotoxicant, Adriamycin) and a tubular injury model induced by ischaemia-reperfusion injury (IRI). Exogenous macrophages were used as a positive control because these cells are known to home to injured mouse kidneys. To assess whether the homing capacity of MSCs can be influenced by the presence of exogenous macrophages, we used a dual-bioluminescence strategy that allowed the whole-body biodistribution of the two cell types to be monitored simultaneously in individual animals.

RESULTS

Following intravenous administration, no MSCs were detected in the kidneys, irrespective of whether the mice had been subjected to renal injury. After arterial administration via the left cardiac ventricle, MSCs transiently populated the kidneys, but no preferential homing or persistence was observed in injured renal tissue after unilateral IRI. An exception was when MSCs were co-administered with exogenous macrophages; here, we observed some homing of MSCs to the injured kidney.

CONCLUSIONS

Our findings strongly suggest that MSCs do not home to injured kidneys.

Lung delivery of MSCs expressing anti-cancer protein TRAIL visualised with 89Zr-oxine PET-CT

BACKGROUND

MSCTRAIL is a cell-based therapy consisting of human allogeneic umbilical cord-derived MSCs genetically modified to express the anti-cancer protein TRAIL. Though cell-based therapies are typically designed with a target tissue in mind, delivery is rarely assessed due to a lack of translatable non-invasive imaging approaches. In this preclinical study, we demonstrate 89Zr-oxine labelling and PET-CT imaging as a potential clinical solution for non-invasively tracking MSCTRAIL biodistribution. Future implementation of this technique should improve our understanding of MSCTRAIL during its evaluation as a therapy for metastatic lung adenocarcinoma.

METHODS

MSCTRAIL were radiolabelled with 89Zr-oxine and assayed for viability, phenotype, and therapeutic efficacy post-labelling. PET-CT imaging of 89Zr-oxine-labelled MSCTRAIL was performed in a mouse model of lung cancer following intravenous injection, and biodistribution was confirmed ex vivo.

RESULTS

MSCTRAIL retained the therapeutic efficacy and MSC phenotype in vitro at labelling amounts up to and above those required for clinical imaging. The effect of 89Zr-oxine labelling on cell proliferation rate was amount- and time-dependent. PET-CT imaging showed delivery of MSCTRAIL to the lungs in a mouse model of lung cancer up to 1 week post-injection, validated by in vivo bioluminescence imaging, autoradiography, and fluorescence imaging on tissue sections.

CONCLUSIONS

89Zr-oxine labelling and PET-CT imaging present a potential method of evaluating the biodistribution of new cell therapies in patients, including MSCTRAIL. This offers to improve understanding of cell therapies, including mechanism of action, migration dynamics, and inter-patient variability.

Perylene Diimide Nanoprobes for In Vivo Tracking of Mesenchymal Stromal Cells Using Photoacoustic Imaging

Noninvasive bioimaging techniques are critical for assessing the biodistribution of cellular therapies longitudinally. Among them, photoacoustic imaging (PAI) can generate high-resolution images with a tissue penetration depth of ∼4 cm. However, it is essential and still highly challenging to develop stable and efficient near-infrared (NIR) probes with low toxicity for PAI. We report here the preparation and use of perylene diimide derivative (PDI) with NIR absorbance (around 700 nm) as nanoprobes for tracking mesenchymal stromal cells (MSCs) in mice. Employing an in-house synthesized star hyperbranched polymer as a stabilizer is the key to the formation of stable PDI nanoparticles with low toxicity and high uptake by the MSCs. The PDI nanoparticles remain within the MSCs as demonstrated by in vitro and in vivo assessments. The PDI-labeled MSCs injected subcutaneously on the flanks of the mice are clearly visualized with PAI up to 11 days postadministration. Furthermore, bioluminescence imaging of PDI-labeled luciferase-expressing MSCs confirms that the administered cells remain viable for the duration of the experiment. These PDI nanoprobes thus have good potential for tracking administered cells in vivo using PAI.

Stem cell delivery to kidney via minimally invasive ultrasound-guided renal artery injection in mice

Cell-based therapies are promising treatments for various kidney diseases. However, the major hurdle in initiating therapeutic responses is the inefficiency of injection routes to deliver cells to the kidney parenchyma. Systemic injection, such as intravenous injection only delivers a small proportion of cells to the kidney. Whereas direct delivery, such as renal artery injection requires surgical procedures. A minimally invasive renal artery injection was therefore developed to enhance cell delivery to kidney. In this study, luciferase expressing human adipocyte derived stem cells (ADSC) were labelled with gold nanorods (GNR) and injected into the renal artery using ultrasound guidance. The ADSCs were tracked using bioluminescence and photoacoustic imaging serially over 7 days. Imaging confirmed that the majority of signal was within the kidney, indicative of successful injection and that the cells remained viable for 3 days. Histology showed co-localization of GNRs with ADSC staining throughout the kidney with no indication of injury caused by injection. These findings demonstrate that ultrasound-guided renal artery injection is feasible in mice and can successfully deliver a large proportion of cells which are retained within the kidney for 3 days. Therefore, the techniques developed here will be useful for optimising cell therapy in kidney diseases.

Triple-marker cardiac MRI detects sequential tissue changes of healing myocardium after a hydrogel-based therapy

Regenerative therapies based on injectable biomaterials, hold an unparalleled potential for treating myocardial ischemia. Yet, noninvasive evaluation of their efficacy has been lagging behind. Here, we report the development and longitudinal application of multiparametric cardiac magnetic resonance imaging (MRI) to evaluate a hydrogel-based cardiac regenerative therapy. A pH-switchable hydrogel was loaded with slow releasing insulin growth factor 1 and vascular endothelial growth factor, followed by intramyocardial injection in a mouse model of ischemia reperfusion injury. Longitudinal cardiac MRI assessed three hallmarks of cardiac regeneration: angiogenesis, resolution of fibrosis and (re)muscularization after infarction. The multiparametric approach contained dynamic contrast enhanced MRI that measured improved vessel features by assessing fractional blood volume and permeability*surface area product, T₁-mapping that displayed reduced fibrosis, and tagging MRI that showed improved regional myocardial strain in hydrogel treated infarcts. Finally, standard volumetric MRI demonstrated improved left ventricular functioning in hydrogel treated mice followed over time. Histology confirmed MR-based vessel features and fibrotic measurements. Our novel triple-marker strategy enabled detection of ameliorated regeneration in hydrogel treated hearts highlighting the translational potential of these longitudinal MRI approaches.

Cell tracking of chromium-labeled mesenchymal stem cells using laser ablation inductively coupled plasma imaging mass spectrometry

RATIONALE

Mesenchymal stem cells (MSCs) are widely used in regenerative medicine research. Evaluating the biodistribution of MSCs is important for determining whether the cells have reached the target tissue, and the time that the stem cells reside in each area is required to estimate the duration of efficacy.

METHODS

A laser ablation inductively coupled plasma imaging mass spectrometry (LAICP-IMS) method was developed for highly sensitive and quantitative surface analysis of metal elements for solid samples. We evaluated the usefulness of a cell-tracking system with LAICP-IMS to investigate the biodistribution of mouse mesenchymal stem cells (mMSCs) labeled with the natural composition of chromium (Cr) in mice. To prepare the dosing solution, mMSCs were incubated with both Na₂ CrO₄ and fluorescent labeling solutions. The concentration of the cells was adjusted by vehicle solution at 2.0 to 2.5 × 10⁷ cells/mL, and the dosing suspension of mMSCs was administered by intramuscular or intravenous injection to the mice.

RESULTS

Thigh muscle sections after intramuscular injection of chromium- and fluorescence-labeled mMSCs were analyzed by LAICP-IMS and fluorescence microscopy, respectively. ⁵² Cr mass spectrometry and fluorescence signals were detected in the same thigh muscle sections after administration of mMSCs. A half-body section was also analyzed by LAICP-IMS. ⁵² Cr signals were mainly detected in the lungs.

CONCLUSIONS

The ⁵² Cr signals were observed in sections through the thigh muscle and half body after intramuscular and intravenous administration, respectively, of Cr-labeled mMSCs to mice. Our results suggest that LAICP-IMS is a sensitive and useful technique to evaluate biodistribution in cell therapy research.

Optical fluorescence imaging with shortwave infrared light emitter nanomaterials for in vivo cell tracking in regenerative medicine

In vivo tracking and monitoring of adoptive cell transfer has a distinct importance in cell‐based therapy. There are many imaging modalities for in vivo monitoring of biodistribution, viability and effectiveness of transferred cells. Some of these procedures are not applicable in the human body because of low sensitivity and high possibility of tissue damages. Shortwave infrared region (SWIR) imaging is a relatively new technique by which deep biological tissues can be potentially visualized with high resolution at cellular level. Indeed, scanning of the electromagnetic spectrum (beyond 1000 nm) of SWIR has a great potential to increase sensitivity and resolution of in vivo imaging for various human tissues. In this review, molecular imaging modalities used for monitoring of biodistribution and fate of administered cells with focusing on the application of non‐invasive optical imaging at shortwave infrared region are discussed in detail.

Vulnerable Plaque, Characteristics, Detection, and Potential Therapies

Plaque development and rupture are hallmarks of atherosclerotic vascular disease. Despite current therapeutic developments, there is an unmet necessity in the prevention of atherosclerotic vascular disease. It remains a challenge to determine at an early stage if atherosclerotic plaque will become unstable and vulnerable. The arrival of molecular imaging is receiving more attention, considering it allows for a better understanding of the biology of human plaque and vulnerabilities. Various plaque therapies with common goals have been tested in high-risk patients with cardiovascular disease. In this work, the process of plaque instability, along with current technologies for sensing and predicting high-risk plaques, is debated. Updates on potential novel therapeutic approaches are also summarized.

Magnetic Particle Imaging: Current Applications in Biomedical Research

Magnetic particle imaging (MPI) is a new imaging modality with the potential for high-resolution imaging while retaining the noninvasive nature of other current modalities such as magnetic resonance imaging (MRI) and positron emission tomography (PET). It is able to track location and quantities of special superparamagnetic iron oxide nanoparticles without tracing any background signal. MPI utilizes the unique, intrinsic aspects of the nanoparticles: how they react in the presence of the magnetic field, and the subsequent turning off of the field. The current group of nanoparticles that are used in MPI are usually commercially available for MRI. Special MPI tracers are in development by many groups that utilize an iron-oxide core encompassed by various coatings. These tracers would solve the current obstacles by altering the size and material of the nanoparticles to what is required by MPI. In this review, the theory behind and the development of these tracers are discussed. In addition, applications such as cell tracking, oncology imaging, neuroimaging, and vascular imaging, among others, stemming from the implementation of MPI into the standard are discussed. Level of Evidence: 5 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:1659-1668.

In vivo fate of free and encapsulated iron oxide nanoparticles after injection of labelled stem cells

Nanoparticle contrast agents are useful tools to label stem cells and monitor the in vivo bio-distribution of labeled cells in pre-clinical models of disease. In this context, understanding the in vivo fate of the particles after injection of labelled cells is important for their eventual clinical use as well as for the interpretation of imaging results. We examined how the formulation of superparamagnetic iron oxide nanoparticles (SPIONs) impacts the labelling efficiency, magnetic characteristics and fate of the particles by comparing individual SPIONs with polyelectrolyte multilayer capsules containing SPIONs. At low labelling concentration, encapsulated SPIONs served as an efficient labelling agent for stem cells. The bio-distribution after intra-cardiac injection of labelled cells was monitored longitudinally by MRI and as an endpoint by inductively coupled plasma-optical emission spectrometry. The results suggest that, after being released from labelled cells after cell death, both formulations of particles are initially stored in liver and spleen and are not completely cleared from these organs 2 weeks post-injection.

Multicolour In Vivo Bioluminescence Imaging Using a NanoLuc-Based BRET Reporter in Combination with Firefly Luciferase

The ability to track the biodistribution and fate of multiple cell populations administered to rodents has the potential to facilitate the understanding of biological processes in a range of fields including regenerative medicine, oncology, and host/pathogen interactions. Bioluminescence imaging is an important tool for achieving this goal, but current protocols rely on systems that have poor sensitivity or require spectral decomposition. Here, we show that a bioluminescence resonance energy transfer reporter (BRET) based on NanoLuc and LSSmOrange in combination with firefly luciferase enables the unambiguous discrimination of two cell populations in vivo with high sensitivity. We insert each of these reporter genes into cells using lentiviral vectors and demonstrate the ability to monitor the cells' biodistribution under a wide range of administration conditions, including the venous or arterial route, and in different tissues including the brain, liver, kidneys, and tumours. Our protocol allows for the imaging of two cell populations in the same imaging session, facilitating the overlay of the signals and the identification of anatomical positions where they colocalise. Finally, we provide a method for postmortem confirmation of the presence of each cell population in excised organs.

Science-based assessment of source materials for cell-based medicines: report of a stakeholders workshop

Human pluripotent stem cells (hPSCs) have the potential to transform medicine. However, hurdles remain to ensure safety for such cellular products. Science-based understanding of the requirements for source materials is required as are appropriate materials. Leaders in hPSC biology, clinical translation, biomanufacturing and regulatory issues were brought together to define requirements for source materials for the production of hPSC-derived therapies and to identify other key issues for the safety of cell therapy products. While the focus of this meeting was on hPSC-derived cell therapies, many of the issues are generic to all cell-based medicines. The intent of this report is to summarize the key issues discussed and record the consensus reached on each of these by the expert delegates.

Non-invasive imaging reveals conditions that impact distribution and persistence of cells after in vivo administration

Background

Cell-based regenerative medicine therapies are now frequently tested in clinical trials. In many conditions, cell therapies are administered systemically, but there is little understanding of their fate, and adverse events are often under-reported. Currently, it is only possible to assess safety and fate of cell therapies in preclinical studies, specifically by monitoring animals longitudinally using multi-modal imaging approaches. Here, using a suite of in vivo imaging modalities to explore the fate of a range of human and murine cells, we investigate how route of administration, cell type and host immune status affect the fate of administered cells.

Methods

We applied a unique imaging platform combining bioluminescence, optoacoustic and magnetic resonance imaging modalities to assess the safety of different human and murine cell types by following their biodistribution and persistence in mice following administration into the venous or arterial system.

Results

Longitudinal imaging analyses (i) suggested that the intra-arterial route may be more hazardous than intravenous administration for certain cell types, (ii) revealed that the potential of a mouse mesenchymal stem/stromal cell (MSC) line to form tumours depended on administration route and mouse strain and (iii) indicated that clinically tested human umbilical cord (hUC)-derived MSCs can transiently and unexpectedly proliferate when administered intravenously to mice.

Conclusions

In order to perform an adequate safety assessment of potential cell-based therapies, a thorough understanding of cell biodistribution and fate post administration is required. The non-invasive imaging platform used here can expose not only the general organ distribution of these therapies, but also a detailed view of their presence within different organs and, importantly, tumourigenic potential. Our observation that the hUC-MSCs but not the human bone marrow (hBM)-derived MSCs persisted for a period in some animals suggests that therapies with these cells should proceed with caution.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1076-x) contains supplementary material, which is available to authorized users.

Evaluation of different routes of administration and biodistribution of human amnion epithelial cells in mice

Placenta is a non-controversial and promising source of cells for the treatment of several liver diseases. We previously reported that transplanted human amnion epithelial cells (hAECs) differentiate into hepatocyte-like cells, resulting in correction of mouse models of metabolic liver disease or acute hepatic failure. As part of preclinical safety studies, we investigated the distribution of hAECs using two routes of administration to efficiently deliver hAECs to the liver. Optical imaging is commonly used because it can provide fast, high-throughput, whole-body imaging, thus DiR-labeled hAECs were injected into immunodeficient mice, via the spleen or the tail vein. The cell distribution was monitored using an in vivo imaging system over the next 24 h. After splenic injection, the DiR signal was detected in liver and spleen at 1, 3 and 24 h post-transplant. The distribution was confirmed by analysis of human DNA content at 24 h post-transplant and human-specific cytokeratin 8/18 staining. Tail vein infusion resulted in cell engraftment mainly in the lungs, with minimal detection in the liver. Delivery of cells to the portal vein, via the spleen, resulted in efficient delivery of hAECs to the liver, with minimal, off-target distribution to lungs or other organs.