Purified recombinant mouse endostatin protein has been reported to regress established murine solid tumors by inhibiting the proliferation of endothelial cells. To develop a clinical gene therapy strategy with endostatin, we cloned the cDNA of human endostatin by RT-PCR from human placenta. A 150-bp sequence encoding the IgG leader peptide was fused in frame to the 5' end of the endostatin cDNA and recombinant adenoviruses, AdENDO-YFP and AdENDO, carrying endostatin gene expression cassettes were rescued. AdENDO-YFP infects cultured mammalian cells at high efficiency and expresses a biologically active human endostatin in secreted form at high levels both in vitro and in vivo. When delivered in vivo, a strain-specific expression pattern was observed, with the highest and longest endostatin expression in 129/J mice. After systemic delivery of 2 x 10(9) PFU of AdENDO-YFP into 129/J mice, human endostatin expression was achieved at a mean value of 1.34 +/- 0.42 microg/ml of serum (n = 6) and inhibition of lung metastasis was observed in an EOMA tumor model. However, high dose intravenous delivery of AdENDO-YFP and AdENDO was associated with severe acute toxicity in recipient mice that included loss of weight, bleeding, and death of animals. These events were not observed with the injection of identical doses of a control adenovirus that did not contain the endostatin gene. Because the endostatin adenovirus-associated acute toxicity was also observed in immunodeficient NCRNU-M nude mice, the toxicity does not appear to be the result of the immunogenicity against human endostatin or the EYFP protein.