Imaging of Gene Expression in Live Pancreatic Islet Cell Lines Using Dual-Isotope SPECT

Abstract

We are combining nuclear medicine with molecular biology to establish a sensitive, quantitative, and tomographic method with which to detect gene expression in pancreatic islet cells in vivo. Dual-isotope SPECT can be used to image multiple molecular events simultaneously, and coregistration of SPECT and CT images enables visualization of reporter gene expression in the correct anatomic context. We have engineered pancreatic islet cell lines for imaging with SPECT/CT after transplantation under the kidney capsule. Methods: INS-1 832/13 and aTC1-6 cells were stably transfected with a herpes simplex virus type 12thymidine kinase2green fluoresecent protein (HSV1-thymidine kinase-GFP) fusion construct (tkgfp). After clonal selection, radiolabel uptake was determined by incubation with 5-131 I-iodo-1-(2-deoxy-2-fluoro-b-D-arabinofuranosyl)uracil ( 131 I-FIAU) (aTC1-6 cells) or 123 I-FIAU (INS-1 832/13 cells). For the first set of in vivo experiments, SPECT was conducted after aTC1-6/tkgfp cells had been labeled with either 131 I-FIAU or 111 In-tropolone and transplanted under the left kidney capsule of CD1 mice. Reconstructed SPECT images were coregistered to CT. In a second study using simultaneous acquisition dual-isotope SPECT, INS-1 832/13 clone 9 cells were labeled with 111 In-tropolone before transplantation. Mice were then systemically administered 123 I-FIAU and data for both 131 I and 111 In were acquired simultaneously. Results: aTC1-6/tkgfp cells showed a 15-fold greater uptake of 131 I-FIAU, and INS-1/tkgfp cells showed a 12-fold greater uptake of 123 I-FIAU, compared with that of wild-type cells. After transplantation under the kidney capsule, both reporter gene expression and location of cells could be visualized in vivo with dual-isotope SPECT. Immunohistochemistry confirmed the presence of glucagon-and insulin-positive cells at the site of transplantation. Conclusion: Dual-isotope SPECT is a promising method to detect gene expression in and location of transplanted pancreatic cells in vivo.

Towards PET Imaging of Intact Pancreatic Beta Cell Mass: A Transgenic Strategy

“…We have previously used the HSV1-tk reporter gene to image transplanted pancreatic islet cells in vivo [2]. A number of studies have now shown that islet transplants can be monitored over time using islets transfected with adenoviral or lentiviral sr39tk constructs and [ 18 F]FHBG as a PET probe [3][4][5].…”

PET and SPECT Reporter Gene Imaging

“…43,50,55,70,[78][79][80][83][84][99][100][101][171][172][173][174][175][176][177][178][179] To image cell location, survival and proliferation and determine the cell's quantity at a certain site, cells are first genetically engineered in culture to express RGs under the control of a strong constitutive promoter (i.e., ubiquitin). Then, after the genetically modified cells are adoptively transferred, the recipient is scanned with the imaging modality instrumentation needed to image the expression of the RG that is inserted into the cells (Fig.…”

“…[13][14][16][17][18][19][20][22][23][24][25][26][27][32][33][34][35][36][37][38][39] These probes take advantage of the fact that HSV1-TK and its mutants, especially HSV1-sr39TK, have a much higher affinity for them than the cytoplasmic mammalian TKs. Amongst acycloguanosine probes, 9-(4- 18 [4][5]11,27,[34][35][36]72,[85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100][101] Regardless of sensitivity, the use of each probe has its advantages and disadvantages. For example, [ 18 F]FEAU is predominantly cleared through the renal pathways, hence its low gastrointestinal signal make it a better probe for imaging in the lower abdomen.…”

High-Resolution CT for Small-Animal Imaging Research

“…It is typically advantageous to combine such a micro-SPECT system with micro-CT, in order to provide highresolution coregistered images of anatomy (Ritman, 2002;Tai et al, 2008). Figure 15 illustrates the capability to perform coregistered cardiac imaging with micro-SPECT and micro-CT in a mouse with the U-SPECT-II/CT system (MILabs, Utrecht, the Netherlands).…”