Combination therapy in A549 cells☆

Abstract 

Background and aim

We investigated the anti-tumor effect induced by the combination of the radiotherapeutic agent ¹³¹I-RC-160 and the prodrug 5-FC in human non-small cell lung cancer (NSCLC) A549 cells that were co-expressing the human somatostatin receptor 2 gene (hSSTR2) and E. coli cytosine deaminase gene (CD).

Methods

We cloned both hSSTR2 and CD into a bicistronic mammalian expression plasmid and stably transfected it into A549 cells (pCIS-A549 cells). After antibiotic selection, SSTR expression in stable clones was determined by reverse transcription and polymerase chain reaction (RT-PCR), Western blot, flow cytometry and immunofluorescence analyses. To assess the in vivo targeting efficiency of the “engineered” A549 cells, the cells were subcutaneously injected into nude mice and the biodistribution of ^99mTc-RC-160 was assessed at different time points. The tumor inhibitory effects of ¹³¹I-RC-160 and/or 5-FC were evaluated by measurement of tumor growth and immunohistochemical analysis.

Results

Multiple analyses demonstrated the successful expression of hSSTR2 in A549 cells. In vivo radioimaging revealed specific targeting of RC-160 to the tumors derived from pCIS-A549 cells when compared to those from control A549 cells. The tumor inhibitory rate of pCIS-A549 tumors in the ¹³¹I-RC-160 plus 5-FC-treated group was significantly higher than that in the single agent-treated group, control group and control tumors.

Conclusion

Co-expression of the hSSTR2 and CD genes in tumor cells can selectively sensitize these cells to the infra-additive effects of radioisotope-labeled RC-160 and 5-FC in vivo. This approach offers a potential therapeutic strategy for the treatment of lung cancer.

Keywords: Lung cancer, Somatostatin receptor, Cytosine deaminase, A549, Receptor-mediated radionuclide imaging, Suicide gene