Abstract
To assess the effects of external beam radiotherapy (EBRT) on adenoviral-mediated transgene expression in vitro and in vivo and to define an optimal strategy for combining sodium iodide symporter (NIS)-mediated (131)I therapy with EBRT. Expression of reporter genes [NIS, green fluorescent protein (GFP), beta-galactosidase (lacZ), and luciferase (Luc)] from replication-deficient adenoviruses was assessed in tumor cell lines under basal conditions and following irradiation. The effects of viral multiplicity of infection (MOI) and EBRT dose on the magnitude and duration of gene expression were determined. In vivo studies were done with Ad-CMV-GFP and Ad-RSV-Luc. EBRT increased NIS, GFP, and beta-galactosidase expression in colorectal, head and neck, and lung cancer cells. Radiation dose and MOI were important determinants of response to EBRT, with greatest effects at higher EBRT doses and lower MOIs. Radiation exerted both transductional (through increased coxsackie-adenoviral receptor and integrin alpha(v)) and nontransductional effects, irrespective of promoter sequence (CMV, RSV, hTR, or hTERT). Analysis of the schedule of EBRT followed by viral infection revealed maximal transduction at 24 hours. Radiation maintained increasing radioiodide uptake from Ad-hTR-NIS over 6 days, in direct contrast to reducing levels in unirradiated cells. The effects of EBRT in increasing and maintaining adenovirus-mediated transgene expression were also seen in vivo using GFP- and luciferase-expressing adenoviral vectors. Radiation increased the magnitude and duration of NIS gene expression from replication-deficient adenoviruses. The transductional effect is maximal at 24 hours, but radioiodide uptake is maintained at an elevated level over 6 days after infection.
Highlights
To assess the effects of external beam radiotherapy (EBRT) on adenoviral-mediated transgene expression in vitro and in vivo and to define an optimal strategy for combining sodium iodide symporter (NIS) ^ mediated 131I therapy with EBRT
In vivo NIS gene transfer has been shown by noninvasive imaging of xenografts by g-camera scintigraphy after 125I or 99mTc injection, suggesting that NIS may serve both as a therapeutic and reporter gene in clinical trials [7]
Four tumor cell lines [HCT116, SIHN-5B, HN5, and H1299] were infected with adenoviral vectors expressing NIS regulated by the constitutive (CMV) or telomerase promoters, and NIS expression was quantitated by performing radioiodide uptake assays at various time points after infection
Summary
To assess the effects of external beam radiotherapy (EBRT) on adenoviral-mediated transgene expression in vitro and in vivo and to define an optimal strategy for combining sodium iodide symporter (NIS) ^ mediated 131I therapy with EBRT. In vivo studies were done with Ad-CMV-GFP and Ad-RSV-Luc. Results: EBRT increased NIS, GFP, and h-galactosidase expression in colorectal, head and neck, and lung cancer cells. NIS mediates Na+/K+ ATPase – dependent active transport of iodide across the basolateral membrane of thyroid follicular cells. Iodide is subsequently transported into the follicular lumen and undergoes thyroperoxidase-mediated organification This reaction is not observed in NIS-expressing extrathyroidal tissues, such as salivary glands, gastric mucosa, and lactating mammary gland Several investigators have confirmed the efficacy of in vivo NIS-mediated 131I therapy in nonthyroid (glioma, prostate, and head and neck cancer) malignancies, allaying initial doubts that the lack of iodide organification in nonthyroid tissues would jeopardize therapeutic efficacy (4 – 6, 8 – 10). In vivo NIS gene transfer has been shown by noninvasive imaging of xenografts by g-camera scintigraphy after 125I or 99mTc injection, suggesting that NIS may serve both as a therapeutic and reporter gene in clinical trials [7]
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