Human NIS gene radiotherapy targeting for HIF-1 activated cancer cells

Abstract

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Objectives: It is well known that hypoxic cancer cells are resistant to chemotherapy and radiotherapy and create dilemma for cancer therapy. Therefore, new therapeutic models targeting for HIF-1 activated cancer cells should be developed. Our purpose was to develop the human sodium iodide symporter (hNIS) gene radiotherapy system targeting for HIF-1 highly activated cancer cells.

Methods: We constructed a HIF-1-dependent therapeutic reporter gene, p5HRE-NR, in which the hNIS-DsRed2 fusion protein (provided by Kim KI, KIRAMS) is expressed under the 5 copies of HRE promoter. SK-Hep1 human hepatoma cells were stably transfected with p5HRE-NR and selected with treatment of geneticin for 2 weeks. Hypoxic conditions were induced by treatment with various concentrations (0 to 400 μM) of desferrioxamine (DFO) or by a hypoxic chamber (< 1% O2) for 4 to 24 hours. Established cells were exposed to hypoxic conditions and the cell population expressing HIF-1-inducible DsRed at high levels was selected using fluorescence-activated cell sorter (FACS) (SK-5HRE-NR). HIF-1-inducible hNIS activity was assessed using I-125 uptake assay. In vitro clonogenic assay of SK-Hep1 or SK-5HRE-NR cells was performed after incubation with or without I-131 37 MBq under normoxic or hypoxic conditions.

Results: In FACS analysis, ten-fold induction of DsRed fluorescence was observed in the SK-5HRE-NR cells under hypoxic conditions. Time and concentration dependent increases of I-125 uptake were observed in SK-5HRE-NR cells (~5-fold) under normoxic or hypoxic conditions. In clonogenic assay after I-131 treatment, the survival rate of hypoxically stressed SK-5HRE-NR cells was significantly lower than SK-Hep1 cells.

Conclusions: These results imply that our therapeutic system can be useful for HIF-1 specific hNIS gene radiotherapy of SK-Hep1 cells.