Systemic administration of a conditionally replicating adenovirus, targeted to angiogenesis, reduced lung metastases burden in cotton rats

Purpose: Angiogenesis is an essential process for solid tumor development. To interfere with angiogenesis, AdPPE3x-E1, an adenovirus that is transcriptionally targeted to replicate in angiogenic endothelial cells, was constructed, by replacing the E1 promoter with the modified preproendothelin-1 promoter, PPE-1-3x, previously shown to induce specific transcription in angiogenic endothelial cells. Experimental Design: The specificity of AdPPE3x-E1 to endothelial cells was shown by quantitative PCR and immunostaining, and its antiangiogenic effect was evaluated in Matrigel models. The in vivo efficacy of AdPPE3x-E1 was also tested in a cotton rat lung metastases model. Results: The replication rate ofAdPPE3x-E1 in endothelial cells was similar to that of AdCMV-E1, a nonselective replicating adenovector, but the replication rate was reduced up to 60-fold in nonendothelial cells. Moreover, AdPPE3x-E1 reduced endothelial cell viability by 90% whereas nonendothelial cells were not affected. In in vitro and in vivo Matrigel models, endothelial cells infected with AdPPE3x-E1 did not develop capillary-like structures. The systemic administration ofAdPPE3x-E1 reduced the lung metastases burden in a cotton rat model by 55%, compared with saline-treated rats, without significant evidence of toxicity. Quantitative PCR analysis showed that the viral copy number ofAdPPE3x-E1 was increased 3-fold in the lung metastases but not in the liver, compared with a nonreplicating adenovector control. Conclusions: We have shown here for the first time an antimetastatic effect induced by an angiogenesis-transcriptionally targeted adenovirus following systemic administration. Because adenovirus replication is more efficient in humans than in cotton rats, we assume a significant effect forAdPPE3x-E1 treatment in fighting human solid tumors and metastases.