Tumor Cell Apoptosis Induced after Treatment with Adenovirally Expressed TRAIL in Vivo.

Tumor necrosis factor -related apoptosis-inducing ligand (TRAIL) is a naturally occurring death inducing ligand that induces apoptosis preferentially in malignant cells as normal cells are protected by expression of decoy receptors. Activation of TRAIL-R1 and R2 leads to the recruitment of procaspase-8 to the receptor, through an adaptor protein FADD, leading to formation of the death inducing complex (DISC), which leads to activation of caspase 8 followed by caspase 3 activation resulting in apoptosis. Our previous in vitro studies indicated that TRAIL induces apoptosis in tumor cells but not in normal cells. In order to improve the delivery of TRAIL to tumor cells, we constructed a recombinant adenovirus pAd5CMV-NpA- TRAIL vector, the TRAIL transgene was placed under the control of the CMV promoter. Ad-CMV-EGFP was constructed and used as control. They were amplified in HEK 293 cells and the titer of both was 1–1.5x10¹⁰pfu/ml.

C57 mice were injected with the adenoviral vectors (200ul) in the tail vein. We examined the expression of EGFP in mice tissues from animals administered adenoviral pAd5CMV-NpA-EGFP vector, and the presence of the EGFP gene was examined in the heart, lung, liver, and kidney of the animals. The results showed that EGFP was detectable in these tissues. Positive signals were obtained 1 and 2 weeks after injection of adenoviral- EGFP construct, the highest tissue levels of EGFP were obtained 1 week after EGFP gene transfer. Western blots revealed strong EGFP expression in the tissues 5 days after Ad-CMVEGFP injection.

In a model for metastatic cancer, tail vein infusion of pAd5CMV-NpA- TRAIL (200ul) resulted in elimination of preestablished liver metastases. Intravenous injection of this vector caused increased TRAIL expressions in tissues in tumor-bearing melanoma C57 mice, which we attributed to factors released from apoptotic tumor cells. Liver histology analyzed at day 7–14 after virus injection did not show signs of hepatocellular damage. This new oncolytic vector represents a potentially efficient means for gene therapy of metastatic cancer. We found that TRAIL can systemically inhibit tumor growth and reduce the size of tumors. In addtion, we also investigated whether pretreatment of TRAIL can prevent the tumor formation in mice treated with B16 melanoma. Normal C57 mice that received 5 days of treatment of TRAIL prior to implanting tumors resulted in the inhibitoty effect on tumor growth when compared to control mice.