Role of aldehyde dehydrogenase activity in cyclophosphamide metabolism in rat hepatoma cell lines

Detoxification of cyclophosphamide by human aldehyde dehydrogenase isozymes

In in vitro studies, no turnover of aldophosphamide and mafosfamide was observed with the tumor-specific aldehyde dehydrogenase 3 isozyme (ALDH3) isolated from human stomach mucosa as well as from lung (A549) and pharynx (UMSCC2) carcinoma cell lines. Only the human liver cytosolic ALDH preparation (ALDH1) showed any significant oxidation of aldophosphamide and mafosfamide.

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 exhibited by a human breast adenocarcinoma subline growing in monolayer culture, viz. MCF-7/OAP, was the overexpression (> 100-fold as compared with 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 (pI values ca. 6.0) present in the cytosol that is heat labile, is insensitive to inhibition by disulfiram (25 microM), much prefers benzaldehyde to acetaldehyde as a substrate and, at concentrations of 4 mM, prefers NADP to NAD as a cofactor. No other aldehyde dehydrogenases were found in these cells. As compared with those of the prototypical class 3 human ALDH-3, viz. constitutive human stomach mucosa ALDH-3, the physical and catalytic properties of the MCF-7/OAP enzyme differed somewhat with regard to pI values, native M(r), subunit M(r), recognition of the subunit by anti-stomach ALDH-3 IgY, pH stability, cofactor influence on catalytic activity, and the ability to catalyze, albeit poorly, the oxidation of an oxazaphosphorine, viz. aldophosphamide. Hence, the MCF-7/OAP ALDH-3 was judged to be a novel class 3 aldehyde dehydrogenase. Small amounts of a seemingly identical enzyme are also present in normal pre- and post-menopausal breast tissue. None could be detected in human liver, kidney or placenta, suggesting that it may be a tissue-specific enzyme.

Aldehyde dehydrogenases and their role in carcinogenesis

Aldehydes are highly reactive molecules that may have a variety of effects on biological systems. They can be generated from a virtually limitless number of endogenous and exogenous sources. Although some aldehyde-mediated effects such as vision are beneficial, many effects are deleterious, including cytotoxicity, mutagenicity, and carcinogenicity. A variety of enzymes have evolved to metabolize aldehydes to less reactive forms. Among the most effective pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs). ALDHs are a family of NADP-dependent enzymes with common structural and functional features that catalyze the oxidation of a broad spectrum of aliphatic and aromatic aldehydes. Based on primary sequence analysis, three major classes of mammalian ALDHs--1, 2, and 3--have been identified. Classes 1 and 3 contain both constitutively expressed and inducible cytosolic forms. Class 2 consists of constitutive mitochondrial enzymes. Each class appears to oxidize a variety of substrates that may be derived either from endogenous sources such as amino acid, biogenic amine, or lipid metabolism or from exogenous sources, including aldehydes derived from xenobiotic metabolism. Changes in ALDH activity have been observed during experimental liver and urinary bladder carcinogenesis and in a number of human tumors, including some liver, colon, and mammary cancers. Changes in ALDH define at least one population of preneoplastic cells having a high probability of progressing to overt neoplasms. The most common change is the appearance of class 3 ALDH dehydrogenase activity in tumors arising in tissues that normally do not express this form. The changes in enzyme activity occur early in tumorigenesis and are the result of permanent changes in ALDH gene expression. This review discusses several aspects of ALDH expression during carcinogenesis. A brief introduction examines the variety of sources of aldehydes. This is followed by a discussion of the mammalian ALDHs. Because the ALDHs are a relatively understudied family of enzymes, this section presents what is currently known about the general structural and functional properties of the enzymes and the interrelationships of the various forms. The remainder of the review discusses various aspects of the ALDHs in relation to tumorigenesis. The expression of ALDH during experimental carcinogenesis and what is known about the molecular mechanisms underlying those changes are discussed. This is followed by an extended discussion of the potential roles for ALDH in tumorigenesis. The role of ALDH in the metabolism of cyclophosphamidelike chemotherapeutic agents is described. This work suggests that modulation of ALDH activity may an important determinant of the effectiveness of certain chemotherapeutic agents.(ABSTRACT TRUNCATED AT 400 WORDS)