Haubner R, Avril N, Hantzopoulos P A, Gansbacher B, Schwaiger M
Department of Nuclear Medicine, Technische Universität München, Munich, Germany.
Eur J Nucl Med. 2000 Mar;27(3):283-91. doi: 10.1007/s002590050035.
Previous studies have shown that the herpes simplex virus type 1 thymidine kinase gene (HSV1-tk), in combination with appropriate radiolabelled substrates (e.g. [I*]-2'-fluoro-2'-deoxy-5-iodo-1-beta-D-arabinofuranosyluracil, I*-FIAU, where the asterisk indicates that any of the various radioactive iodine isotopes can be used), can be used as a reporter gene for in vivo monitoring of gene transfer and expression. The aim of our study was to examine the early kinetics of I*-FIAU and the possibility of utilising iodine-123-labelled FIAU for imaging of gene expression. CMS-5 fibrosarcoma cells were transduced in vitro with the retroviral vector STK containing the HSV1-tk gene. BALB/c mice were inoculated subcutaneously with HSV1-tk(+) and tk(-) cells into both flanks. FAU (2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyluracil was radioiodinated (123I, 125I) using the iodogen method. High-performance liquid chromatography purification resulted in high specific activity and radiochemical purity for both tracers ([123I]FIAU and [125I]FIAU). Biodistribution studies and gamma camera imaging were performed at 0.5, 1, 2 and 4 h p.i. In addition, the genomic DNA of the tumours was isolated for measurement of the activity accumulation resulting from the [125I]FIAU incorporation. Biodistribution studies 0.5 h p.i. showed tumour/blood and tumour/muscle ratios of 3.8 and 7.2, respectively, for the HSV1-tk(+) tumours, and 0.6 and 1.2, respectively, for negative control tumours. Fast renal elimination of the tracer from the body resulted in rapidly increasing tumour/blood and tumour/muscle ratios which reached values of 32 and 88 at 4 h p.i., respectively. Tracer clearance from blood was bi-exponential, with an initial half-life of 0.6 h followed by a half-life of 4.6 h. The tracer half-life in herpes simplex viral thymidine kinase-expressing tumours was 35.7 h. The highest activity accumulation (20.3%+/-5.7% ID/g) in HSV1-tk(+) tumours was observed 1 h p.i. At that time, about 46% of the total activity found in HSV1-tk(+) tumours was incorporated into genomic DNA. Planar gamma camera imaging showed a distinct tracer accumulation as early as 0.5 h p.i., with an increase in contrast over time. These results suggest that sufficient tumour/background ratios for in vivo imaging of HSV1-tk expression with [123I]FIAU are reached as early as 1 h p.i.
先前的研究表明，单纯疱疹病毒1型胸苷激酶基因（HSV1-tk）与合适的放射性标记底物（如[I*]-2'-氟-2'-脱氧-5-碘-1-β-D-阿拉伯呋喃糖基尿嘧啶，I*-FIAU，其中星号表示可使用各种放射性碘同位素中的任何一种）结合，可作为报告基因用于体内监测基因转移和表达。我们研究的目的是检测I*-FIAU的早期动力学以及利用碘-123标记的FIAU进行基因表达成像的可能性。CMS-5纤维肉瘤细胞在体外被含有HSV1-tk基因的逆转录病毒载体STK转导。将HSV1-tk(+)和tk(-)细胞皮下接种到BALB/c小鼠的双侧胁腹。使用碘珠法对FAU（2'-氟-2'-脱氧-1-β-D-阿拉伯呋喃糖基尿嘧啶）进行放射性碘化（123I、125I）。高效液相色谱纯化使两种示踪剂（[123I]FIAU和[125I]FIAU）都具有高比活度和放射化学纯度。在接种后0.5、1、2和4小时进行生物分布研究和γ相机成像。此外，分离肿瘤的基因组DNA以测量[125I]FIAU掺入导致的活性积累。接种后0.5小时的生物分布研究显示，HSV1-tk(+)肿瘤的肿瘤/血液和肿瘤/肌肉比值分别为3.8和7.2，阴性对照肿瘤的该比值分别为0.6和1.2。示踪剂从体内快速经肾清除导致肿瘤/血液和肿瘤/肌肉比值迅速增加，在接种后4小时分别达到32和88。示踪剂从血液中的清除呈双指数形式，初始半衰期为0.6小时，随后半衰期为4.6小时。在表达单纯疱疹病毒胸苷激酶的肿瘤中示踪剂半衰期为35.7小时。接种后1小时在HSV1-tk(+)肿瘤中观察到最高活性积累（20.3%±5.7% ID/g）。此时，在HSV1-tk(+)肿瘤中发现的总活性约46%掺入基因组DNA。平面γ相机成像显示早在接种后0.5小时就有明显的示踪剂积累，且对比度随时间增加。这些结果表明，早在接种后1小时就可达到用[123I]FIAU对HSV1-tk表达进行体内成像的足够肿瘤/背景比值。
