Targeting of tumor radioiodine therapy by expression of the sodium iodide symporter under control of the survivin promoter

Abstract

To test the feasibility of using the survivin promoter to induce specific expression of sodium/iodide symporter (NIS) in cancer cell lines and tumors for targeted use of radionuclide therapy, a recombinant adenovirus, Ad-SUR-NIS, that expressed the NIS gene under control of the survivin promoter was constructed. Ad-SUR-NIS mediating iodide uptake and cytotoxicity was performed in vitro. Scintigraphic, biodistribution and radioiodine therapy studies were performed in vivo. PC-3 (prostate); HepG2 (hepatoma) and A375 (melanoma) cancer cells all exhibited perchlorate-sensitive iodide uptake after infection with Ad-SUR-NIS, approximately 50 times higher than that of negative control Ad-CMV-GFP-infected cells. No significant iodide uptake was observed in normal human dental pulp fibroblast (DPF) cells after infection with Ad-SUR-NIS. Clonogenic assays demonstrated that Ad-SUR-NIS-infected cancer cells were selectively killed by exposure to (131)I. Ad-SUR-NIS-infected tumors show significant radioiodine accumulation (13.3 ± 2.85% ID per g at 2 h post-injection), and the effective half-life was 3.1 h. Moreover, infection with Ad-SUR-NIS in combination with (131)I suppressed tumor growth. These results indicate that expression of NIS under control of the survivin promoter can likely be used to achieve cancer-specific expression of NIS in many types of cancers. In combination with radioiodine therapy, this strategy is a possible method of cancer gene therapy.

Figure 1

Structures of plasmids used in this study. (a) Diagram represents the structure of the luciferase reporter plasmid. The survivin promoter (−222 to 39 bp) was cloned upstream of the luciferase gene using the restriction sites indicated. (b) Diagram represents the structure of the adenovirus shuttle plasmid pS-SUR-NIS. The plasmid was constructed by inserting a DNA fragment into the E1-deleted region using the KpnI/SalI restriction sites. This DNA fragment contained the survivin promoter, the full length NIS cDNA, and the Simian Virus 40 polyadenylation signal.

Figure 2

In vitro analyses of transgene expression of the survivin and SV40 promoters by transient transfection. The transcriptional activity of the survivin and SV40 promoters was measured in various cancer and normal cells. The data shown are the means±s.d. of at least three independent experiments.

Figure 3

In vitro radioiodine and ^99mTc pertechnetate uptake. PC-3, HepG2 and A375 cancer cell lines and the control DPF cell line were infected with Ad-SUR-NIS, Ad-CMV-NIS or Ad-CMV-GFP viruses and subjected to either ¹²⁵I or ^99mTc pertechnetate uptake. Ad-SUR-NIS-infected PC-3, HepG2 and A375 cancer cell lines all show significant ¹²⁵I and ^99mTc pertechnetate uptake ability compared with Ad-CMV-GFP-infected controls. No significant uptake was observed in Ad-SUR-NIS-infected DPF cells. Ad-CMV-NIS infection resulted in increased ¹²⁵I uptake in all cell lines. Cotreatment with NaClO₄ completely inhibited ¹²⁵I uptake in Ad-SUR-NIS-infected cancer cells.

Figure 4

^99mTc pertechnetate scintigraphic images of PC-3 xenografts infected with either Ad-CMV-GFP or Ad-SUR-NIS. Mice harboring PC-3 xenograft tumors infected with either Ad-CMV-GFP (a) or Ad-SUR-NIS (b) were imaged with a pinhole collimator 2 h after injection of 18.5 MBq ^99mTc pertechnetate. (a) The Ad-CMV-GFP-infected tumor is not visible using ^99mTc pertechnetate imaging. (b) The Ad-SUR-NIS-infected tumor is clearly visible, with an intensity comparable to that of the thyroid or the bladder.

Figure 5

Therapeutic effects of Ad-SUR-NIS infection in combination with ¹³¹I treatment in PC-3 xenografts. Tumor size was assayed after ¹³¹I treatment in nude mice bearing tumors infected with either Ad-SUR-NIS or Ad-CMV-GFP. Growth of Ad-SUR-NIS-infected PC-3 tumors was significantly retarded (^*,**,***P<0.05) at days 20, 25 and 30 after injection of 111 MBq ¹³¹I.

Figure 6

Representative immunostaining of NIS in tumors from nude mice. Note the distinct cell membrane staining of NIS in the PC-3 tumor infected with Ad-SUR-NIS (a). In contrast, the non-infected PC-3 tumor is negative for NIS immunoreactivity (b). Original magnification for each panel was × 400.