Enhancement of antiangiogenic effects of human canstatin with a hypoxia-regulated transgene vector in lung cancer model.

Canstatin, a newly identified antiangiogenesis protein, has a potent inhibitory effect on the proliferation and growth of endothelial cells. To enhance the expression and antiangiogenic effects of canstatin in solid tumors, we constructed a eukaryotic expression vector that encodes human canstatin cDNA downstream from nine copies of the hypoxia-response element.

METHODS

Canstatin complementary DNA from adult liver tissues was cloned into the mammalian expression vector pCMV-Script. Nine copies of the hypoxia-response element were ligated upstream from the canstatin gene near the cytomegalovirus promoter. The recombinant vector, pCMV9Cans, was transformed into A549 cells by cationic liposomes. The transformed cells were cultured under oxic and anoxic conditions. We detected canstatin messenger ribonucleic acid and protein expression in transformed cells by TaqMan polymerase chain reaction and Western blot analysis, respectively. Human umbilical vein endothelial cells were cocultured with recombinant vector transformed A549 cells using Transwell plates under oxic and anoxic conditions. The proliferation and apoptosis of the cocultured endothelial cells were evaluated with 3H-thymidine incorporation and terminal deoxynucleotidyl-mediated biotinylated deoxyuridine triphosphate nick end-labeling methods (TUNEL), respectively. A canstatin-encoding vector with no hypoxia-response element, pCMVCans, was used as the positive control, and naked plasmid-transformed and singly cultured parental cells were used as negative controls. The biologic activity of the vector in tumor tissues of lung cancer-bearing nude mice was evaluated by microvessel counts. Canstatin protein expression was assessed by Western blot analysis in tumor tissues. pCMVCans and empty vector were used as controls in the in vivo assays.

RESULTS

Canstatin messenger RNA and protein were detected in both pCMV9Cans- and pCMVCans-transformed A549 clones. Under oxic conditions, canstatin expression was not significantly different in clones stably transformed with pCMV9Cans or pCMVCans. However, under anoxic conditions canstatin expression was significantly higher in pCMV9Cans-transformed cells than in pCMVCans-transformed cells. Moreover, the 3H-thymidine uptake rate of the human umbilical vein endothelial cells was markedly lower than that of the pCMVCans-transformed cells, and many endothelial cells underwent apoptosis when cocultured with pCMV9Cans-transformed A549 cells, especially under anoxic conditions. We detected canstatin expression in tumor tissues; the expression level in pCMV9Cans-transformed tumors was significantly higher than that in pCMVCans-transformed tumors. An in vivo assay showed that tumors transformed with pCMV9Cans remained small, and microvessels in those tumors were much fewer than those in pCMVCans-transformed tumors.

CONCLUSIONS

The hypoxia-regulated vector pCMV9Cans increases the expression of canstatin, thereby enhancing its biological effects. We believe that the hypoxia-inducible canstatin-expressing vector is a promising gene therapy tool for antiangiogenesis research.