Growth Suppression of Human Lung Cancer Cells and Implanted Tumors by Adenovirus-mediated Transfer of the PTEN Gene

This study examined the effects of a recombinant adenovirus Ad-PTEN-EGFP on the proliferation of A549 cells, a human lung carcinoma cell line, in vitro and on the growth of the implanted tumors in the nude mice in vivo, explored the underlying mechanisms and evaluated the in vitro transfection efficiency of Ad-PTEN-EGFP into A549 cells. The expression of Ad-PTEN-EGFP in the A549 cells was determined. The proliferation and the apoptosis rates of the A549 cells with Ad-PTEN-EGFP transfection or not was detected by MTT and flow cytometry. Ad-PTEN-EGFP at different doses was injected intratumorally to the tumor-bearing mice induced by the A549 cells. Tumor sizes were measured on an alternate day. After all the mice were sacrificed, the implanted tumors were removed for routine histological examination, weight test, HE staining and immunohistochemical staining. The expressions of Bax, P16 and P53 in the tumor tissues and those of caspase-3, CD34 and VEGF in the mouse sera were detected. Tumor cell apoptosis was measured by TUNEL method. The results showed that the vitality of the A549 cells after transfection with Ad-PTEN-EGFP declined. The expression of green fluorescent protein was observed under fluorescent microscope. The transfection rate was in excess of 50%. The mRNA and protein expression of PTEN in the transfected cells was confirmed. The proliferation rate of the transfected cells was significantly decreased when compared with that of the non-transfected cells (P<0.05). The number of the apoptosis cells was increased in the transfected cells (P<0.05). The models of implanted tumors were successfully established by injection of the A549 cells in the flank of Balb/c nude mice. Administration of Ad-PTEN-EGFP to the tumor-bearing nude mice resulted in a suppression of tumor growth. There were statistically significant differences in the tumor weight and tumor volume between the Ad-PTEN-EGFP-treated group and the control groups (P<0.05). In contrast to those in the control groups, tumor tissues in the Ad-PTEN-EGFP-treated group were shown to have typical extensive vacuolar degeneration and massive hemorrhagic necrosis. Apoptotic bodies were also observed in the tumor cells. The expressions of Bax, caspase-3 and P16 were increased (P<0.05) while those of CD34, VEGF and P53 decreased (P<0.05) in the Ad-PTEN-EGFP-treated group. It is concluded that Ad-PTEN-EGFP could induce the apoptosis of the A549 cells and inhibit their proliferation. And it could also substantially suppress the tumor growth in the tumor-bearing nude mice and induce apoptosis of the tumor cells as well. These findings carry significant implications for adenovirus vector-based PTEN gene therapies for lung cancers.