Cardiovascular MRI for stem cell therapy

Rationale and Design of Sodium Tanshinone IIA Sulfonate in Left Ventricular Remodeling Secondary to Acute Myocardial Infarction (STAMP-REMODELING) Trial: A Randomized Controlled Study

BACKGROUND

Left ventricular (LV) remodeling in ischemic cardiomyopathy is the leading cause of heart failure and is an established prognostic factor for adverse cardiovascular events. Experimental studies suggest that sodium tanshinone IIA sulfonate attenuates cardiac remodeling in animal models of acute myocardial infarction (AMI). However, the effects of this drug in the clinical setting remain unclear. Therefore, the STAMP-REMODELING trial is set up to investigate whether treatment with sodium tanshinone IIA sulfonate would prevent the maladaptive progression to adverse LV remodeling in patients following ST-segment elevation myocardial infarction (STEMI).

METHODS

Approximately 80 patients with STEMI successfully treated with primary percutaneous coronary intervention (PCI) will be enrolled and randomized to receive sodium tanshinone IIA sulfonate (80 mg q.d. for 7 days) in addition to standard therapy or the same volume of hydration per day. The primary endpoint is the variation in LV end-diastolic volume index (LVEDVi) assessed with cardiac magnetic resonance imaging (CMR) at baseline and 6 months.

CONCLUSION

This study will provide important clinical evidence on the efficacy of sodium tanshinone IIA sulfonate treatment in patients with STEMI when used in combination with current therapies that may significantly reduce adverse LV remodeling and potentially improve clinical outcomes.

TRIAL REGISTRATION

Clinical Trials.gov: NCT02524964.

In vivo molecular MRI of cell survival and teratoma formation following embryonic stem cell transplantation into the injured murine myocardium

Embryonic stem cells (ESCs) have shown the potential to restore cardiac function after myocardial injury. Superparamagnetic iron oxide nanoparticles (SPIO) have been widely employed to label ESCs for cellular MRI. However, nonspecific intracellular accumulation of SPIO limits long-term in vivo assessment of the transplanted cells. To overcome this limitation, a novel reporter gene (RG) has been developed to express antigens on the ESC surface. By employing SPIO-conjugated monoclonal antibody against these antigens (SPIO-MAb), the viability of transplanted ESCs can be detected in vivo. This study aims to develop a new molecular MRI method to assess in vivo ESC viability, proliferation, and teratoma formation. The RG is designed to express 2 antigens (hemagglutinin A and myc) and luciferase on the ESC surface. The two antigens serve as the molecular targets for SPIO-MAb. The human and mouse ESCs were transduced with the RG (ESC-RGs) and transplanted into the peri-infarct area using the murine myocardial injury model. In vivo MRI was performed following serial intravenous administration of SPIO-MAb. Significant hypointense signal was generated from the viable and proliferating ESCs and subsequent teratoma. This novel molecular MRI technique enabled in vivo detection of early ESC-derived teratoma formation in the injured murine myocardium.

Multiwall carbon nanotubes as MRI contrast agents for tracking stem cells

In this study we investigate the potential of multiwall carbon nanotubes (MWCNTs) with low metal impurities (2.57% iron) as magnetic resonance imaging (MRI) contrast agents. Taking into account probable aggregation at high MWCNTs concentration analysis shows that the r(2) relaxivity of MWCNTs in 1% agarose gels at 19 °C is 564 ± 41 s(-1) mM(-1); this is attributed to both the presence of iron oxide impurities and also to the carbon MWCNT structure itself. Stem cells were labelled with MWCNTs to demonstrate the effectiveness of MWCNTs as MRI contrast agents for cellular MRI. The MWCNTs did not impair cell viability or proliferation. These results suggest that the MRI contrast agent properties of the MWCNTs could be used in vivo for stem cell tracking/imaging and during MWCNT-mediated targeted electro-chemotherapy of tumours.

Dual-modal nanoprobes for imaging of mesenchymal stem cell transplant by MRI and fluorescence imaging

Objective

To determine the feasibility of labeling human mesenchymal stem cells (hMSCs) with bifunctional nanoparticles and assessing their potential as imaging probes in the monitoring of hMSC transplantation.

Materials and Methods

The T1 and T2 relaxivities of the nanoparticles (MNP@SiO₂[RITC]-PEG) were measured at 1.5T and 3T magnetic resonance scanner. Using hMSCs and the nanoparticles, labeling efficiency, toxicity, and proliferation were assessed. Confocal laser scanning microscopy and transmission electron microscopy were used to specify the intracellular localization of the endocytosed iron nanoparticles. We also observed in vitro and in vivo visualization of the labeled hMSCs with a 3T MR scanner and optical imaging.

Results

MNP@SiO₂(RITC)-PEG showed both superparamagnetic and fluorescent properties. The r₁ and r₂ relaxivity values of the MNP@SiO₂(RITC)-PEG were 0.33 and 398 mM^-1 s^-1 at 1.5T, respectively, and 0.29 and 453 mM^-1 s^-1 at 3T, respectively. The effective internalization of MNP@SiO₂(RITC)-PEG into hMSCs was observed by confocal laser scanning fluorescence microscopy. The transmission electron microscopy images showed that MNP@SiO₂(RITC)-PEG was internalized into the cells and mainly resided in the cytoplasm. The viability and proliferation of MNP@SiO₂(RITC)-PEG-labeled hMSCs were not significantly different from the control cells. MNP@SiO₂(RITC)-PEG-labeled hMSCs were observed in vitro and in vivo with optical and MR imaging.

Conclusion

MNP@SiO₂(RITC)-PEG can be a useful contrast agent for stem cell imaging, which is suitable for a bimodal detection by MRI and optical imaging.

Molecular imaging in clinical trials

Imaging of biological processes using specific molecular probes allows exploration of the mechanism of action and efficacy for new therapies. This molecular imaging has made use of modalities including single photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI), and optical techniques. Molecular imaging can be used to explore many of the hallmarks of cancer biology, including angiogenesis, proliferation, tissue invasion, evasion of apoptosis, and self-sufficiency in growth signals. Since many of these aspects of cancer biology are in turn the targets of novel therapies in development, molecular imaging techniques have great potential to inform trials of these new agents. The high cost of clinical drug development mandates the optimisation of early phase trial design to maximise the collection of evidence for efficacy and proof of mechanism, endpoints which have, in a number of examples, already been provided by molecular imaging. The variety provided by novel chemistry, and the availability of isotopes with varying physical properties, particularly suits PET imaging as a functional modality for application in clinical trials.

Comparison of reporter gene and iron particle labeling for tracking fate of human embryonic stem cells and differentiated endothelial cells in living subjects

Human embryonic stem (hES) cells are pluripotent stem cells capable of self-renewal and differentiation into virtually all cell types. Thus, they hold tremendous potential as cell sources for regenerative therapies. The concurrent development of accurate, sensitive, and noninvasive technologies capable of monitoring hES cells engraftment in vivo can greatly expedite basic research prior to future clinical translation. In this study, hES cells were stably transduced with a lentiviral vector carrying a novel double-fusion reporter gene that consists of firefly luciferase and enhanced green fluorescence protein. Reporter gene expression had no adverse effects on cell viability, proliferation, or differentiation to endothelial cells (human embryonic stem cell-derived endothelial cells [hESC-ECs]). To compare the two popular imaging modalities, hES cells and hESC-ECs were then colabeled with superparamagnetic iron oxide particles before transplantation into murine hind limbs. Longitudinal magnetic resonance (MR) imaging showed persistent MR signals in both cell populations that lasted up to 4 weeks. By contrast, bioluminescence imaging indicated divergent signal patterns for hES cells and hESC-ECs. In particular, hESC-ECs showed significant bioluminescence signals at day 2, which decreased progressively over the following 4 weeks, whereas bioluminescence signals from undifferentiated hES cells increased dramatically during the same period. Post-mortem histology and immunohistochemistry confirmed teratoma formation after injection of undifferentiated hES cells but not hESC-ECs. From these data taken together, we concluded that reporter gene is a better marker for monitoring cell viability, whereas iron particle labeling is a better marker for high-resolution detection of cell location by MR. Furthermore, transplantation of predifferentiated rather than undifferentiated hES cells would be more suited for avoiding teratoma formation.