Visualization of hypoxia-inducible factor-1 transcriptional activation in C6 glioma using luciferase and sodium iodide symporter genes.
Hypoxia-inducible factor-1 (HIF-1) is a transcription factor of hypoxic response in cancer cells and is associated with tumor progression, angiogenesis, metastasis, and resistance to therapy. We assessed whether the human sodium iodide symporter (NIS) reporter systems can be used to visualize transcriptional activation of HIF-1 in C6 glioma.


METHODS
Two types of plasmid-expressing human NIS or luciferase (Luc) genes, controlled by 5 copies of hypoxia response element (5HRE), were constructed: p5HRE-NIS or p5HRE-Luc. C6 glioma cells were stably transfected with p5HRE-NIS or p5HRE-Luc plasmids (C6-5HRE-NIS or C6-5HRE-Luc). Hypoxic conditions were modeled by exposing culture medium to desferrioxamine (DFO) or a low oxygen atmosphere (<1% O(2)) in a hypoxic chamber. HIF-1 transcription activity was assessed by measuring cellular (125)I uptake and luminescent intensities. Reverse-transcription polymerase chain reaction and Western blotting were performed to observe the messenger RNA and protein levels of reporter and target genes under hypoxic or normoxic conditions. C6, C6-cytomegalovirus (CMV)-NIS, or C6-CMV-Luc and C6-5HRE-NIS or C6-5HRE-Luc cells were injected subcutaneously into nude mice (the NIS and Luc groups, respectively). Two weeks after tumor challenge, bioluminescence and (99m)Tc scintigraphic images were acquired before and after intraperitoneal DFO administration. Natural hypoxia in tumors was induced by growing tumors for 3 wk. Ex vivo studies, such as biodistribution, immunohistochemistry, and (99m)Tc autoradiography, were performed.


RESULTS
Time- and concentration-dependent increases of (125)I uptake and bioluminescence were observed in hypoxically stressed reporter cells. Also, messenger RNA and protein levels of reporter and target genes increased under hypoxic conditions. (99m)Tc uptake and bioluminescence signals from C6-5HRE-NIS and C6-5HRE-Luc tumors increased during hypoxia. In the biodistribution study, a larger amount of (99m)Tc accumulated in C6-5HRE-NIS tumors than in the other tumors not containing 5HRE (P<0.005). In the Luc group, immunostaining showed similar distribution patterns for luciferase and pimonidazole, and in the NIS group, autoradiography of C6-5HRE-NIS tumors showed a distribution similar to that observed for pimonidazole immunostaining.


CONCLUSIONS
The transcriptional activation of HIF-1 induced by hypoxia or DFO was visualized by both bioluminescence and scintigraphic reporter gene systems.
Yeom
Chan Joo
CJ
Department of Nuclear Medicine, Tumor Immunity Medical Research Center, Laboratory of Molecular Imaging and Therapy of Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
Chung
June-Key
JK
Kang
Joo Hyun
JH
Jeon
Yong Hyun
YH
Kim
Kwang Il
KI
Jin
Yong Nan
YN
Lee
You Mie
YM
Jeong
Jae Min
JM
Lee
Dong Soo
DS
D000818:Animals; D045744:Cell Line, Tumor; D005910:Glioma / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D007457:Iodine Radioisotopes; D008156:Luciferases; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D051381:Rats; D027981:Symporters; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D000099209:Sodium-Iodide Symporters
D007457:Iodine Radioisotopes; D008156:Luciferases; D019275:Radiopharmaceuticals; D027981:Symporters; D014157:Transcription Factors; D000099209:Sodium-Iodide Symporters; C485502:HIF-2 protein, mouse