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Targeting of lacZ reporter gene expression with radioiodine-labelled phenylethyl-β-d-thiogalactopyranoside

  • Molecular Imaging
  • Published:
European Journal of Nuclear Medicine and Molecular Imaging Aims and scope Submit manuscript

Abstract

There has recently been increasing interest in the development of radioprobes that specifically target proteins transcribed from expression of reporter genes of interest. The purpose of this study was to develop a radioprobe that targets one of the most widely used reporter genes, the bacterial lacZ gene. We synthesised and purified radioiodine-labelled phenylethyl-β-d-thiogalactopyranoside (PETG), a competitive inhibitor specific against Escherichia coli β-galactosidase. We showed that [125I]iodo-PETG specifically binds to β-galactosidase as verified by column chromatography and polyacrylamide gel electrophoresis after incubation of radiotracer with the protein. We also showed through enzyme kinetic studies that iodo-PETG retains inhibitory action against β-galactosidase activity. COS-7 cells infected with a recombinant adenovirus expressing the lacZ gene had viral titre-dependent enhancements in [125I]iodo-PETG uptake (r 2=0.897; P=0.001), which reached up to 642.5%±16.7% of control levels (P<0.00001). Moreover, the level of uptake was highly correlated to luminescent measurements of β-galactosidase activity (r 2=0.878; P<0.0001). These results confirm that radioiodine-labelled PETG specifically targets β-galactosidase and that its uptake rates faithfully reflect levels of expression of the lacZ reporter gene. Further investigations were performed in nude mice bearing human neuroblastoma tumours transferred with the lacZ gene. Compared with control tumours, lacZ-expressing tumours were slightly better visualised on [123I]iodo-PETG images and had a modest increase in tumour to muscle count ratio (2.6±0.2 vs 1.9±0.1, P<0.05). The present results provide proof-of-principle for the potential of radiolabelled inhibitors as promising radiotracers to monitor lacZ gene expression levels. Future modifications to improve cell permeability should enhance in vivo contrast levels and may allow the use of radiolabelled β-galactosidase inhibitors for non-invasive monitoring of lacZ gene expression.

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Acknowledgements

The authors thank Hye-Kyoung Kim for technical assistance. This work was supported in part by the National Mid- and Long-term Nuclear R&D Program Grant # M20333010001-03A0726-00114 of the Korean Ministry of Science and Technology.

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Authors and Affiliations

  1. Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwondong, Kangnamgu, Seoul, Korea

    Kyung-Han Lee, Sang Sung Byun, Joon Hun Choi, Jin-Young Paik, Yearn Seong Choe & Byung-Tae Kim

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  1. Kyung-Han Lee
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  2. Sang Sung Byun
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  3. Joon Hun Choi
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Correspondence to Byung-Tae Kim.

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This work was presented in part at the 49th Annual Meeting of the Society of Nuclear Medicine, LA, USA, June 15–19, 2002.

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Lee, KH., Byun, S.S., Choi, J.H. et al. Targeting of lacZ reporter gene expression with radioiodine-labelled phenylethyl-β-d-thiogalactopyranoside. Eur J Nucl Med Mol Imaging 31, 433–438 (2004). https://doi.org/10.1007/s00259-003-1395-7

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