Assessing gene and cell therapies applied in striated skeletal and cardiac muscle: is there a role for nuclear magnetic resonance?

MR imaging to assess immediate response to irreversible electroporation for targeted ablation of liver tissues: preclinical feasibility studies in a rodent model

PURPOSE

To test the hypothesis that magnetic resonance (MR) imaging measurements can be used to immediately detect treated tissue regions after irreversible electroporation (IRE) ablation procedures in rodent liver tissues.

MATERIALS AND METHODS

All experiments received institutional animal care and use committee approval. In four rats for preliminary studies and 18 rats for formal assessment, MR imaging-compatible electrodes were inserted into the liver and MR imaging-monitored IRE procedures were performed at one of three electrode voltages (1000, 1500, or 2500 V), with T1- and T2-weighted images acquired before and immediately after application of the IRE pulses. MR imaging measurements were compared with both finite element modeling (FEM)-anticipated ablation zones and histologically confirmed ablation zones at necropsy. Intraclass and Spearman correlation coefficients were calculated for statistical comparisons.

RESULTS

MR imaging measurements permitted immediate depiction of IRE ablation zones that were hypointense on T1-weighted images and hyperintense on T2-weighted images. MR imaging-based measurements demonstrated excellent consistency with FEM-anticipated ablation zones (r > 0.90 and P < .001 for both T1- and T2-weighted images). MR imaging measurements were also highly correlated with histologically confirmed ablation zone measurements (rho > 0.90 and P < .001 for both T1- and T2-weighted images).

CONCLUSION

MR imaging permits immediate depiction of ablated tissue zones for monitoring of IRE ablation procedures. These measurements could potentially be used during treatment to elicit repeat application of IRE pulses or adjustments to electrode positions to ensure complete treatment of targeted lesions.

Magnetic resonance imaging-monitored plasmid DNA delivery in primate limb muscle

The purpose of this work is to investigate the use of magnetic resonance imaging (MRI) to monitor the effects of high-pressure naked plasmid DNA (pDNA) intravascular injections in primate limbs, studying both the distribution of the injected solution in the muscle space, as well as the effects on the vascular system. The distal portion of the four limbs of each of six rhesus monkeys were hydrodynamically injected with naked pDNA, which expressed the luciferase reporter gene. Three-dimensional (3D) T1-weighted gradient echo and 2D multislice T2-weighted fast spin echo (FSE) series were acquired before and immediately after the injection to confirm the volume of solution injected into the limb, and to study the distribution of the injected solution in the individual muscle groups. Time-resolved contrast-enhanced 3D magnetic resonance angiography (MRA) was performed several days before, immediately after, and in a follow-up examination after the pDNA injection to study the effects of the procedure on the primate peripheral vascular system. T1-weighted gradient echo imaging confirmed the delivery of the majority of the solution after successful pDNA injections. T2-weighted FSE imaging demonstrated the distribution of the saline solution in individual muscles in the target limbs, with enhancement showing a weak but significant correlation with the level of gene expression. Time-resolved contrast-enhanced MRA demonstrated effects of the injection procedure on the arterial and venous vascular systems, and the intramuscular compartments; and these effects largely returned to normal on short-term follow-up.

Molecular imaging of novel cell- and viral-based therapies

Drugs, surgery, and radiation are the traditional modalities of therapy in medicine. To these are being added new therapies based on cells and viruses or their derivatives. In these novel therapies, a cell or viral vector acts as a drug in its own right, altering the host or a disease process to bring about healing. Most of these advances originate from the significant recent advances in molecular medicine, but some have been around for some time. Blood transfusions and cowpox vaccinations are part of the history of medicine...but nevertheless are examples of cell- and viral-based therapies. This article focuses on the modern molecular incarnations of these therapies, and specifically on how imaging is used to track and guide these novel agents. We survey the literature dealing with imaging these new cell and viral particle therapies and provide a framework for understanding publications in this area. Leading technology of gene modifications are the fundamental modifications applied to make these new therapies amenable to imaging.

Cellular MR Imaging

Cellular MR imaging is a young field that aims to visualize targeted cells in living organisms. In order to provide a different signal intensity of the targeted cell, they are either labeled with MR contrast agents in vivo or prelabeled in vitro. Either (ultrasmall) superparamagnetic iron oxide [(U)SPIO] particles or (polymeric) paramagnetic chelates can be used for this purpose. For in vivo cellular labeling, Gd3+- and Mn2+- chelates have mainly been used for targeted hepatobiliary imaging, and (U)SPIO-based cellular imaging has been focused on imaging of macrophage activity. Several of these magneto-pharmaceuticals have been FDA-approved or are in late-phase clinical trials. As for prelabeling of cells in vitro, a challenge has been to induce a sufficient uptake of contrast agents into nonphagocytic cells, without affecting normal cellular function. It appears that this issue has now largely been resolved, leading to an active research on monitoring the cellular biodistribution in vivo following transplantation or transfusion of these cells, including cell migration and trafficking. New applications of cellular MR imaging will be directed, for instance, towards our understanding of hematopoietic (immune) cell trafficking and of novel guided (stem) cell-based therapies aimed to be translated to the clinic in the future.