Multimodality Imaging of Gene Transfer with a Receptor-Based Reporter Gene

Abstract

Gene therapy trials have traditionally used tumor and tissue biopsies for assessing the efficacy of gene transfer. Noninvasive imaging techniques offer a distinct advantage over tissue biopsies in that the magnitude and duration of gene transfer can be monitored repeatedly. Human somatostatin receptor subtype 2 (SSTR2) has been used for the nuclear imaging of gene transfer. To extend this concept, we have developed a somatostatin receptor-enhanced green fluorescent protein fusion construct (SSTR2-EGFP) for nuclear and fluorescent multimodality imaging. Methods: An adenovirus containing SSTR2-EGFP (AdSSTR2-EGFP) was constructed and evaluated in vitro and in vivo. SCC-9 human squamous cell carcinoma cells were infected with AdEGFP, AdSSTR2, or AdSSTR2-EGFP for in vitro evaluation by saturation binding, internalization, and fluorescence spectroscopy assays. In vivo biodistribution and nano-SPECT imaging studies were conducted with mice bearing SCC-9 tumor xenografts directly injected with AdSSTR2-EGFP or AdSSTR2 to determine the tumor localization of 111 In-diethylenetriaminepentaacetic acid (DTPA)-Tyr3-octreotate. Fluorescence imaging was conducted in vivo with mice receiving intratumoral injections of AdSSTR2, AdSSTR2-EGFP, or AdEGFP as well as ex vivo with tissues extracted from mice. Results: The similarity between AdSSTR2-EGFP and wild-type AdSSTR2 was demonstrated in vitro by the saturation binding and internalization assays, and the fluorescence emission spectra of cells infected with AdSSTR2-EGFP was almost identical to the spectra of cells infected with wildtype AdEGFP. Biodistribution studies demonstrated that the tumor uptake of 111 In-DTPA-Tyr3-octreotate was not significantly different (P . 0.05) when tumors (n 5 5) were injected with AdSSTR2 or AdSSTR2-EGFP but was significantly greater than the uptake in control tumors. Fluorescence was observed in tumors injected with AdSSTR2-EGFP and AdEGFP in vivo and ex vivo but not in tumors injected with AdSSTR2. Although fluorescence was observed, there were discrepancies between in vivo imaging and ex vivo imaging as well as between nuclear imaging and fluorescent imaging. Conclusion: These studies showed that the SSTR2-EGFP fusion construct can be used for in vivo nuclear and optical imaging of gene transfer.

Noninvasive Assessment of Gene Transfer and Expression by In Vivo Functional and Morphologic Imaging in a Rabbit Tumor Model

“…In comparison, Chen et al . [39] delivered Ad-SSTR2-EGFP IT in a mouse model and detected expression by in vivo nuclear and optical imaging; however, in vivo quantification was not evaluated. For the first time, we were able to directly compare IA and IT gene transfer in vivo within a large animal model and quantify gene expression.…”

Classification and evaluation strategies of auto-segmentation approaches for PET: Report of AAPM task group No. 211

“…Multimodality imaging is of increasing importance for cancer detection, staging, and monitoring of treatment response …”

“…Multimodality imaging is of increasing importance for cancer detection, staging, and monitoring of treatment response. [117][118][119][120][121] In radiotherapy treatment planning, significant variability can occur when multiple observers contour the target volume. 122 This inter-observer variability has been shown to be reduced by combining information from multimodality imaging and performing single delineations on fused images, such as CT and PET, or MRI and PET.…”

Sequential SPECT and Optical Imaging of Experimental Models of Prostate Cancer with a Dual Modality Inhibitor of the Prostate‐Specific Membrane Antigen

“…[8][9][10] For staging and preoperative assessment of tumor burden the radionuclide component could initially be used to map disseminated lesions or lesions within the prostate at sub-centimeter resolution. The optical mode could aid in image-guided surgery to delineate tumor margins precisely during and following resection, using a minimally invasive laparoscopic instrument equipped with a NIRF detection system.…”