Molecular Imaging of Gene Expression and Efficacy following Adenoviral-Mediated Brain Tumor Gene Therapy

Abstract

Cancer gene therapy is an active area of research relying upon the transfer and subsequent expression of a therapeutic transgene into tumor cells in order to provide for therapeutic selectivity. Noninvasive assessment of therapeutic response and correlation of the location, magnitude, and duration of transgene expression in vivo would be particularly useful in the development of cancer gene therapy protocols by facilitating optimization of gene transfer protocols, vector development, and prodrug dosing schedules. In this study, we developed an adenoviral vector containing both the therapeutic transgene yeast cytosine deaminase (yCD) along with an optical reporter gene (luciferase). Following intratumoral injection of the vector into orthotopic 9 L gliomas, anatomical and diffusion-weighted MR images were obtained over time in order to provide for quantitative assessment of overall therapeutic efficacy and spatial heterogeneity of cell kill, respectively. In addition, bioluminescence images were acquired to assess the duration and magnitude of gene expression. MR images revealed significant reduction in tumor growth rates associated with yCD/5-fluorocytosine (5FC) gene therapy. Significant increases in mean tumor diffusion values were also observed during treatment with 5FC. Moreover, spatial heterogeneity in tumor diffusion changes were also observed revealing that diffusion magnetic resonance imaging could detect regional therapeutic effects due to the nonuniform delivery and/or expression of the therapeutic yCD transgene within the tumor mass. In addition, in vivo bioluminescence imaging detected luciferase gene expression, which was found to decrease over time during administration of the prodrug providing a noninvasive surrogate marker for monitoring gene expression. These results demonstrate the efficacy of the yCD/5FC strategy for the treatment of brain tumors and reveal the feasibility of using multimodality molecular and functional imaging for assessment of gene expression and therapeutic efficacy.

Bioluminescence imaging of Smad signaling in living mice shows correlation with excitotoxic neurodegeneration

“…Bioluminescence imaging has been used recently for the study of gene expression in transgenic mice that express luciferase reporter genes under control of various promoters or transcription factor binding sites (35)(36)(37)(38). In the brain, bioluminescence has been used mainly to track and quantify luciferase-tagged tumor cells (39)(40)(41)(42) or to trace migration of neural progenitor cells (43,44). One study used glial fibrillary acidic protein (GFAP)-luciferase transgenic mice to demonstrate activation of the reporter after injury, but no correlation with neuronal injury or degeneration was demonstrated (38).…”

It's not just about anatomy: In vivo bioluminescence imaging as an eyepiece into biology

“…In the study by Rehemtulla et al (2), BLI was used to assess the delivery of a therapeutic transgene for a cancer gene therapy strategy in combination with noninvasive measurements of therapeutic efficacy using MRI. In this study, the efficacy of treating gliomas using an adenoviral vector containing a gene encoding the prodrug converting enzyme, yeast cytosine deaminase (CD), was evaluated.…”

“…At the interface of these fields are applications that employ a variety of imaging modalities, including magnetic resonance imaging (MRI) (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16), the use of radionuclide tracers in positron emission tomography (PET) and single photon emission tomography (SPECT) (16 -25), x-ray computed tomography (CT) (26,27), and optical methods (2,5,28 -40). This nascent area of investigation is rapidly gaining acceptance in diverse fields, such as cancer biology, immunology, gene therapy, and microbiology.…”

Molecular imaging of gene therapy for cancer

“…A recombinant adenovirus coexpressing cytosine deaminase (CD) and firefly luciferase (Fluc) injected directly into the gliomas in mice showed significant expression of luciferase. 79 Further treatment of animals with 5-FC lead to a decrease in this imaging signal, presumably due to cell death. In parallel, diffusion-weighted MRI was used as a surrogate marker of tumor cell death.…”