IDENTIFICATION AND CHARACTERIZATION OF A NOVEL CLASS-3 ALDEHYDE DEHYDROGENASE OVEREXPRESSED IN A HUMAN BREAST ADENOCARCINOMA CELL-LINE EXHIBITING OXAZAPHOSPHORINE-SPECIFIC ACQUIRED-RESISTANCE

Associated with the oxazaphosphorine-specific acquired resistance exhi bited by a human breast adenocarcinoma subline growing in monolayer cu lture, viz. MCF-7/OAP, was the overexpression (>100-fold as compared w ith the very small amount expressed in the oxazaphosphorine-sensitive parent line) of a class 3 aldehyde dehydrogenase, viz. ALDH-3, judged to be so because it is a polymorphic enzyme (pl values ca. 6.0) presen t in the cytosol that is heat labile, is insensitive to inhibition,by disulfiram (25 muM), much prefers benzaldehyde to acetaldehyde as a su bstrate and, at concentrations of 4 mM, prefers NADP to NAD as a cofac tor. No other aldehyde dehydrogenases were found in these cells. As co mpared with those of the prototypical class 3 human ALDH-3, viz. const itutive human stomach mucosa ALDH-3, the physical and catalytic proper ties of the MCF-7/OAP enzyme differed somewhat with regard to pl value s, native M(r), subunit M(r), recognition of the subunit by anti-stoma ch ALDH-3 IgY, pH stability, cofactor influence on catalytic activity, and the ability to catalyze, albeit poorly, the oxidation of an oxaza phosphorine, viz. aldophosphamide. Hence, the MCF-7/OAP ALDH-3 was jud ged to be a novel class 3 aldehyde dehydrogenase. Small amounts of a s eemingly identical enzyme are also present in normal pre- and post-men opausal breast tissue. None could be detected in human liver, kidney o r placenta, suggesting that it may be a tissue-specific enzyme.