Baculovirus vector-mediated transfer of NIS gene into colon tumor cells for radionuclide therapy

Abstract

Aim: To investigate the feasibility of radionuclide therapy of colon tumor cells by baculovirus vector-mediated transfer of the sodium/iodide symporter (NIS) gene.

Methods: A recombinant baculovirus plasmid carrying the NIS gene was constructed, and the viruses (Bac-NIS) were prepared using the Bac-to-Bac system. The infection efficiency in the colon cancer cell line SW1116 of a green fluorescent protein (GFP) expressing baculovirus (Bac-GFP) at different multiplicities of infection (MOI) with various concentrations of sodium butyrate was determined by flow cytometry. An in vitro cytotoxicity assay was also conducted after infection of SW1116 cells with Bac-NIS. Iodine uptake of Bac-NIS infected SW1116 cells and inhibition of this uptake by sodium perchlorate was examined, and the effect of Bac-NIS-mediated (131)I in killing tumor cells was evaluated by cell colony formation tests.

Results: Infection and transgene expression in SW1116 with Bac-GFP were significantly enhanced by sodium butyrate, as up to 72% of SW1116 cells were infected with the virus at MOI of 400 and sodium butyrate at 0.5 mmol/L. No obvious cytotoxicity was observed under these conditions. Infection of SW1116 with Bac-NIS allowed uptake of (131)I in these tumor cells, which could be inhibited by sodium perchlorate. The viability of SW1116 cells infected with Bac-NIS was significantly lower than with Bac-GFP, suggesting that NIS gene-mediated (131)I uptake could specifically kill tumor cells.

Conclusion: Baculovirus vector-mediated NIS gene therapy is a potential approach for treatment of colon cancer.

Figure 1

Effects of sodium butyrate on infection efficiency of SW1116 cells. The transduction efficiency (A) and fluorescence intensity (B) of recombinant green fluorescent protein gene baculovirus (Bac-GFP) infection of SW1116 cells at multiplicities of infection (MOI) of 400 in the presence of sodium butyrate at the indicated concentrations. Error bars represent standard deviations.

Figure 2

Recombinant green fluorescent protein gene baculovirus infection efficiency in SW1116 cells with or without sodium butyrate. The transduction efficiency (A) and fluorescence intensity (B) of recombinant green fluorescent protein gene baculovirus (Bac-GFP) infection of SW1116 cells at different multiplicities of infections (MOIs) as indicated with or without 0.5 mmol/L sodium butyrate. The infection efficiency (%) and the fluorescence intensity of GFP were determined by flow cytometry. Error bars represent standard deviations.

Figure 3

Cytotoxic effects of baculovirus infection and sodium butyrate in SW1116 cells. A: The cytotoxic effects in SW1116 infected with recombinant green fluorescent protein gene baculovirus (Bac-GFP) at different multiplicities of infection (MOI); B: The cytotoxic effects of sodium butyrate at various concentrations in SW1116 cells infected with Bac-GFP at MOI of 400.

Figure 4

Iodine uptake of SW1116 cells after infection by recombinant sodium/iodide symporter gene baculovirus in the absence or presence of sodium butyrate. ¹²⁵I iodine uptake (counts per minute) was determined in SW1116 cells infected with recombinant sodium/iodide symporter gene baculovirus at indicated multiplicities of infection (MOI) with or without 0.5 mmol/L sodium butyrate 30 min after exposure to ¹²⁵I. Error bars represents standard deviations.

Figure 5

Dynamic changes of iodine uptake in recombinant sodium/iodide symporter gene baculovirus infected SW1116 cells. SW1116 cells were infected with recombinant sodium/iodide symporter gene baculovirus (Bac-NIS) at 400 multiplicities of infection, and iodine uptake (counts per minute) was determined over time when incubated with Na¹²⁵I and NaI. Error bars represent standard deviations.

Figure 6

Inhibition rate of NaClO₄ in radioiodine uptake in tumor cells after infection. Radioiodine uptake was inhibited by pre-treatment of the SW1116 tumor cells with sodium perchlorate at various concentrations for 30 min. Error bars represent standard deviations.

Figure 7

Survival rates (%) of SW1116 cells treated with Na¹³¹I. Cell viability of infected SW1116 cells was determined after treatment with Na¹³¹I, SW1116 cells were treated with bHBSS, recombinant green fluorescent protein gene baculovirus (Bac-GFP) with 0.5 mmol/L sodium butyrate, and recombinant sodium/iodide symporter gene baculovirus (Bac-NIS) with 0.5 mmol/L sodium butyrate.