Hexokinase type II: A novel tumor-specific promoter for gene-targeted therapy differentially expressed and regulated in human cancer cells

The use of tissue- or tumor-selective promoters in targeted gene therapy fo r cancer depends on strong and selective activity. Hexokinase type II (HK I I) catalyzes the first committed step of glycolysis and is overexpressed in tumors, where it is no longer responsive to normal physiological inhibitor s, e.g., glucagon. We show, in a reporter gene assay, activation of HK II i n non-small cell lung carcinomas NCI-H661 and NCI-H460 at 61 and 40%, respe ctively, relative to the activation observed with a constitutive promoter, while it was only 0.9% in different preparations of primary normal human br onchial epithelial cells (NHBECs). Similar results were observed in a varie ty of normal and tumor cells. Moreover, treatment of the transfectants with glucagon did not inhibit promoter activation in the transformed H661 cells , while endogenous HK II in NHBECs is suppressed by glucagon. H460 and H661 cells infected with a recombinant adenovirus carrying an HK II/LacZ expres sion cassette, AdHexLacZ, demonstrated beta-galactosidase activity that cor related with the level of HK II promoter activation in these cells. Under s imilar conditions, no enzyme activity was observed in NHBECs. Cells were th en infected with AdHexTk and treated with GCV. Our results demonstrate sele ctivity in toxicity, with a 10- to 100-fold increase in IC50 between lung c ancer cell lines H661 and H460, respectively, and NHBECs. There was also a 100-fold increase in IC50 in NHMECs relative to breast carcinoma cell line MCF-7. In HepG2 cells, an IC50 of 1 mu g/ml was observed, comparable to tha t of other tumor cell lines. This represents a novel use of the hexokinase type II as a selective promoter in cancer gene therapy.