title: A rapid in vitro method for the evaluation of potential antitumor drugs requiring metabolic activation by hepatic S9 enzymes.
abstract: Metabolic activation is a prerequisite for the antitumor activity of certain drugs such as cyclophosphamide. In vitro assays require systems for metabolic activation to reveal the toxicity of such compounds for tumor cells. Although a number of methods utilizing systems for the in vitro metabolic activation of drugs have been published, practical assays applicable to large scale screening for such agents have been lacking. We, therefore, now report that incorporation of a liver subcellular fraction (S9) into a recently established cell growth inhibition assay (microculture tetrazolium assay) significantly increased the cytotoxicity of cyclophosphamide. Under optimal conditions, the 50% growth inhibitory concentration was decreased in the presence of S9 from more than 600 micrograms/ml to less than 4 micrograms/ml, depending upon the cell line. The method also proved suitable for studies investigating metabolic detoxification (enzymatically or non-enzymatically) by conjugation reactions. For example, glutathione (5 mM) markedly reduced the cytotoxicity of activated cyclophosphamide. In contrast, the addition of UDP glucuronate (10 mM) in the presence of the UDP-glucuronosyltransferase activator UDP-N-acetylglucosamine (10 mM) had little effect on cyclophosphamide toxicity.
authors.affiliation: Dr Karl Thomae Gmbh, Biberach, West Germany.
authors.forename: J
authors.initials: J
authors.lastname: Lebsanft
authors.forename: J B
authors.initials: JB
authors.lastname: McMahon
authors.forename: G G
authors.initials: GG
authors.lastname: Steinmann
authors.forename: R H
authors.initials: RH
authors.lastname: Shoemaker
mesh_terms: D000818:Animals; D001711:Biotransformation; D003520:Cyclophosphamide / Q000493:pharmacokinetics* / Q000633:toxicity; D004354:Drug Screening Assays, Antitumor / Q000379:methods*; D006131:Growth Inhibitors / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors
chemical_list: D006131:Growth Inhibitors; D003520:Cyclophosphamide