TY - JOUR T1 - Establishment of an Isogenic Human Colon Tumor Model for<em>NQO1</em> Gene Expression: Application to Investigate the Role of DT-Diaphorase in Bioreductive Drug Activation In Vitro and In Vivo JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1146 LP - 1155 DO - 10.1124/mol.58.5.1146 VL - 58 IS - 5 AU - Swee Y. Sharp AU - Lloyd R. Kelland AU - Melanie R. Valenti AU - Lisa A. Brunton AU - Steve Hobbs AU - Paul Workman Y1 - 2000/11/01 UR - http://molpharm.aspetjournals.org/content/58/5/1146.abstract N2 - Many tumors overexpress the NQO1 gene, which encodes DT-diaphorase (NADPH:quinone oxidoreductase; EC 1.6.99.2). This obligate two-electron reductase deactivates toxins and activates bioreductive anticancer drugs. We describe the establishment of an isogenic human tumor cell model for DT-diaphorase expression. An expression vector was used in which the human elongation factor 1α promoter produces a bicistronic message containing the genes for humanNQO1 and puromycin resistance. This was transfected into the human colon BE tumor line, which has a disabling point mutation inNQO1. Two clones, BE2 and BE5, were selected that were shown by immunoblotting and enzyme activity to stably express high levels of DT-diaphorase. Drug response was determined using 96-h exposures compared with the BE vector control. Functional validation of the isogenic model was provided by the much greater sensitivity of theNQO1-transfected cells to the known DT-diaphorase substrates and bioreductive agents streptonigrin (113- to 132-fold) and indoloquinone EO9 (17- to 25-fold) and the inhibition of this potentiation by the DT-diaphorase inhibitor dicoumarol. A lower degree of potentiation was seen with the clinically used agent mitomycin C (6- to 7-fold) and the EO9 analogs, EO7 and EO2, that are poorer substrates for DT-diaphorase (5- to 8-fold and 2- to 3-fold potentiation, respectively), and there was no potentiation or protection with menadione and tirapazamine. Exposure time-dependent potentiation was seen with the diaziquone analogs methyl-diaziquone and RH1 [2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone], the latter being an agent in preclinical development. In contrast to the in vitro potentiation, there was no difference in the response to mitomycin C when BE2 and BE vector control were treated as tumor xenografts in vivo. This isogenic model should be valuable for mechanistic studies and bioreductive drug development. ER -