BACKGROUNDThe sodium-iodide symporter (NIS) protein can mediate the active radioiodine uptake. The human telomerase reverse transcriptase (hTERT) promoter is known to be selectively reactivated in majority of tumors and hence could be used for tumor targeting. We constructed a recombinant adenovirus containing the human sodium iodide symporter (hNIS) gene directed by the hTERT promoter, characterized the ability of infected cells in uptaking iodide, and explored the therapeutic efficacy of (131)I in a lung cancer cell line in vitro.

METHODSThe hTERT promoter was amplified by PCR from DNA isolated from log-phase HepG2 cells, subcloned into lineralized FL*-hNIS/pcDNA3, and then the hTERT-hNIS sequence was subcloned into the shuttle plasmid pAdTrack. The recombinant adenovirus Ad-hTERT-hNIS was constructed by AdEasy system. A positive control adenovirus Ad-CMV-hNIS and a negative control adenovirus Ad-CMV were created similarly. A549 cells were transduced with recombinant adenoviruses. (125)I uptake studies and sodium perchlorate suppression studies were used to confirm hNIS expression and function. Toxic effects of (131)I on tumor cells were studied by in vitro clonogenic assay.

RESULTSWe first successfully constructed an adenovirus mediated transgene expression system of the hNIS under the control of hTERT promoter. When infected with recombinant adenovirus constructs expressing hNIS directed by hTERT- and CMV-promoters (Ad-hTERT-hNIS and Ad-CMV-hNIS, respectively), the lung cancer cell line A549 had increased ability to uptake radioiodide up to 23- and 30-fold compared to the control parental cells, respectively. The radioiodide uptake ability of both the Ad-CMV-hNIS and Ad-hTERT-hNIS transduced cell lines were repressed 11-fold by sodium perchlorate (NaClO4). The subsequent in vitro clonogenic assay of the infected A549 cell line was further repressed to 23% (Ad-CMV-hNIS) and 30% (Ad-hTERT-hNIS) of the control group after receiving radioiodide for 7 hours (P < 0.001).

CONCLUSIONOur preliminary study indicates that an adenovirus mediated transgene expression system of the hNIS under the control of hTERT promoter has the potential to become an effective wide-spectrum yet highly specific anti-cancer strategy.