Baculovirus vector-mediated transfer of sodium iodide symporter and plasminogen kringle 5 genes for tumor radioiodide therapy

Objectives We investigated the feasibility of combining radioiodide and antiangiogenic therapies after baculovirus vector-mediated transfer of genes encoding the sodium iodide symporter (NIS) and plasminogen kringle 5 (K5) domain.

Methods A recombinant baculovirus dual expression vector, containing the NIS gene under control of the human telomerase reverse transcriptase (hTERT) promoter and the K5 gene driven by the early growth response 1 (Egr1) promoter (Bac-hTERT-NIS-Egr1-K5), was developed. NIS and K5 gene expression levels were examined. Functional NIS activity in baculovirus-infected Hela cells was confirmed by the uptake of 125I and cytotoxicity of 131I. The apoptotic effect of 131I-induced K5 on baculovirus-infected human umbilical vein endothelial cells (HUVECs) was analyzed by a flow cytometry-based assay. In vivo, NIS reporter gene imaging and therapeutic experiments with 131I were performed. Finally, the microvessel density (MVD) in tumors after treatment was determined by CD31 immunostaining.

Results NIS gene expression driven by the hTERT promoter was markedly up-regulated in HeLa cells, but not in MRC5 cells. The Hela cells showed a significant increase of 125I uptake, which was inhibited by NaClO4, and a notably decreased cell survival rate by 131I treatment. Expression of the K5 gene induced by 131I was elevated in a dose- and time-dependent manner and resulted in the apoptosis of HUVECs. Furthermore, 131I single photon emission computed tomography (SPECT) imaging clearly showed cervical tumor xenografts infected with recombinant baculovirus. Following therapy, tumor growth was significantly retarded in Bac-hTERT-NIS-Egr1-K5-infected tumors. CD31 immunostaining further confirmed a significant decrease of MVD.

Conclusions The recombinant baculovirus dual expression vector developed in this study supports a promising strategy of NIS-based raidoiodide therapy combined with K5-based antiangiogenic therapy by targeting both the tumor and its supporting vessels.