Radio-deoxynucleoside Analogs used for Imaging tk Expression in a Transgenic Mouse Model of Induced Hepatocellular Carcinoma

A Human-derived Dual MRI/PET Reporter Gene System with High Translational Potential for Cell Tracking

PURPOSE

Reporter gene imaging has been extensively used to longitudinally report on whole-body distribution and viability of transplanted engineered cells. Multi-modal cell tracking can provide complementary information on cell fate. Typical multi-modal reporter gene systems often combine clinical and preclinical modalities. A multi-modal reporter gene system for magnetic resonance imaging (MRI) and positron emission tomography (PET), two clinical modalities, would be advantageous by combining the sensitivity of PET with the high-resolution morphology and non-ionizing nature of MRI.

PROCEDURES

We developed and evaluated a dual MRI/PET reporter gene system composed of two human-derived reporter genes that utilize clinical reporter probes for engineered cell detection. As a proof-of-concept, breast cancer cells were engineered to co-express the human organic anion transporter polypeptide 1B3 (OATP1B3) that uptakes the clinical MRI contrast agent gadolinium ethoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA), and the human sodium iodide symporter (NIS) which uptakes the PET tracer, [18F] tetrafluoroborate ([18F] TFB).

RESULTS

T1-weighted MRI results in mice exhibited significantly higher MRI signals in reporter-gene-engineered mammary fat pad tumors versus contralateral naïve tumors (p < 0.05). No differences in contrast enhancement were observed at 5 h after Gd-EOB-DTPA administration using either intravenous or intraperitoneal injection. We also found significantly higher standard uptake values (SUV) in engineered tumors in comparison to the naïve tumors in [18F]TFB PET images (p < 0.001). Intratumoral heterogeneity in signal enhancement was more conspicuous in relatively higher resolution MR images compared to PET images.

CONCLUSIONS

Our study demonstrates the ability to noninvasively track cells engineered with our human-derived dual MRI/PET reporter system, enabling a more comprehensive evaluation of transplanted cells. Future work is focused on applying this tool to track therapeutic cells, which may one day enable the broader application of cell tracking within the healthcare system.

Non-invasive Bioluminescence Monitoring of Hepatocellular Carcinoma Therapy in an HCR Mouse Model

Animal models play crucial roles in the development of anticancer therapeutics. The ability to quickly assess the localized primary hepatocellular carcinoma (HCC) status in a non-invasive manner would significantly improve the effectiveness of anti-HCC therapeutic studies. However, to date, animal models with this advantage are extremely scarce. In this study, we developed a novel animal model for the fast assessment of drug efficacy against primary HCC in vivo. HCC was induced in immunocompetent hepatocarcinogenesis reporter (HCR) mice by diethylnitrosamine (DEN) injection and confirmed by histopathological staining. Using the bioluminescence imaging (BLI) technique, HCC progression was longitudinally visualized and monitored in a non-invasive way. Tests of two clinical drugs showed that both sorafenib and oxaliplatin significantly inhibited the BLI signal in mouse liver in a dose-dependent manner. The in vivo intensity of BLI signals was highly consistent with the final tumor burden status in mouse liver after drug treatment. The inhibitory effect of anti-HCC drugs was accurately evaluated through in vivo BLI intensity detection. Our study successfully established a bioluminescence mouse model for non-invasive real-time monitoring of HCC therapy, and this HCR mouse model would be a useful tool for potential anti-HCC drug screening and new therapeutic strategy development.

Alpha-Herpesvirus Thymidine Kinase Genes Mediate Viral Virulence and Are Potential Therapeutic Targets

Alpha-herpesvirus thymidine kinase (TK) genes are virulence-related genes and are nonessential for viral replication; they are often preferred target genes for the construction of gene-deleted attenuated vaccines and genetically engineered vectors for inserting and expressing foreign genes. The enzymes encoded by TK genes are key kinases in the nucleoside salvage pathway and have significant substrate diversity, especially the herpes simplex virus 1 (HSV-1) TK enzyme, which phosphorylates four nucleosides and various nucleoside analogues. Hence, the HSV-1 TK gene is exploited for the treatment of viral infections, as a suicide gene in antitumor therapy, and even for the regulation of stem cell transplantation and treatment of parasitic infection. This review introduces the effects of α-herpesvirus TK genes on viral virulence and infection in the host and classifies and summarizes the current main application domains and potential uses of these genes. In particular, mechanisms of action, clinical limitations, and antiviral and antitumor therapy development strategies are discussed.

Multimodality reporter gene imaging: Construction strategies and application

Molecular imaging has played an important role in the noninvasive exploration of multiple biological processes. Reporter gene imaging is a key part of molecular imaging. By combining with a reporter probe, a reporter protein can induce the accumulation of specific signals that are detectable by an imaging device to provide indirect information of reporter gene expression in living subjects. There are many types of reporter genes and each corresponding imaging technique has its own advantages and drawbacks. Fused reporter genes or single reporter genes with products detectable by multiple imaging modalities can compensate for the disadvantages and potentiate the advantages of each modality. Reporter gene multimodality imaging could be applied to trace implanted cells, monitor gene therapy, assess endogenous molecular events, screen drugs, etc. Although several types of multimodality imaging apparatus and multimodality reporter genes are available, more sophisticated detectors and multimodality reporter gene systems are needed.

PET imaging of oncolytic VSV expressing the mutant HSV-1 thymidine kinase transgene in a preclinical HCC rat model

Hepatocellular carcinoma (HCC) is the most predominant form of liver cancer and the third leading cause of cancer-related death worldwide. Due to the relative ineffectiveness of conventional HCC therapies, oncolytic viruses have emerged as novel alternative treatment agents. Our previous studies have demonstrated significant prolongation of survival in advanced HCC in rats after oncolytic vesicular stomatitis virus (VSV) treatment. In this study, we aimed to establish a reporter system to reliably and sensitively image VSV in a clinically relevant model of HCC for clinical translation. To this end, an orthotopic, unifocal HCC model in immune-competent Buffalo rats was employed to test a recombinant VSV vector encoding for an enhanced version of the herpes simplex virus 1 (HSV-1) thymidine kinase (sr39tk) reporter, which would allow the indirect detection of VSV via positron emission tomography (PET). The resulting data revealed specific tracer uptake in VSV-HSV1-sr39tk-treated tumors. Further characterization of the VSV-HSV1-sr39tk vector demonstrated its optimal detection time-point after application and its detection limit via PET. In conclusion, oncolytic VSV expressing the HSV1-sr39tk reporter gene allows for highly sensitive in vivo imaging via PET. Therefore, this imaging system may be directly translatable and beneficial in further clinical applications.