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 9L 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.

In vivo monitoring of antiangiogenic therapy by magnetic resonance and bioluminescence imaging in an M21 tumor model through activation of an hsp70 promoter–luciferase reporter construct

“…Rehemtulla also found a good correlation between MRI data and bioluminescence data (52). In his study, BLI was used to assess the delivery of a therapeutic transgene for cancer gene therapy, along with noninvasive measurements of therapeutic efficacy using MRI.…”

Diffusion imaging for evaluation of tumor therapies in preclinical animal models

“…For the last ten years diffusion MRI has been under active investigation as a possible surrogate marker of anti-tumor therapeutic efficacy [8][9][10][11][12][13][14][15][16][17][18][19]. As depicted in Fig.…”

The status of gene therapy for brain tumors

“…The teams of Schellingerhout [71] and Rehemtulla [114] have employed molecular imaging in experimental glioma models in which vectors radiolabelled with 111 In-Oxine or engineered with an Escherichia coli LacZ gene were delivered. Both groups quantified a precise mass distribution of the vector [71,114].…”

“…Both groups quantified a precise mass distribution of the vector [71,114]. Another group also used an OV adenovirus engineered with the E. coli LacZ gene to quantify and compare intratumoral replication and persistence of the OV in the presence and absence of the immunomodulator cyclophosphamide, thus demonstrating the possibility of non-invasive in vivo imaging of the efficiency of gene therapy applied in combination with other chemotherapeutic agents [81].…”