The presence of hypoxic cells in human brain tumors is an important factor
leading to resistance to radiation therapy. However, this physiological dif
ference between normal tissues and tumors also provides the potential for d
esigning cancer-specific gene therapy. We compared the increase of gene exp
ression under anoxia (<0.01% oxygen) produced by 3, 6, and 9 copies of hypo
xia-responsive elements (HRE) from the erythropoietin gene (Epo), which are
activated through the transcriptional complex hypoxia-inducible factor 1 (
HIF-1). Under anoxic conditions, nine copies of HIRE (9XHRE) yielded 27- to
37-fold of increased gene expression in U-251 MG and U-87 MG human brain t
umor cell lines. Under the less hypoxic conditions of 0.3% and 1% oxygen, g
ene activation by 9XHRE increased expression 11- to 18-fold in these cell l
ines. To generate a recombinant adeno-associated virus (rAAV) in which the
transgene can be regulated by hypoxia, we inserted the DNA fragment contain
ing 9XHRE and the LacZ reporter gene into an AAV vector. Under anoxic condi
tions, this vector produced 79- to 110-fold increase in gene expression. We
believe this hypoxia-regulated rAAV vector will provide a useful delivery
vehicle for cancer-specific gene therapy.