In vitro metabolism by mouse and human liver preparations of halomon, an antitumor halogenated monoterpene.
OBJECTIVE
To characterize the enzymes responsible for and metabolites produced from the metabolism of halomon, a halogenated monoterpene that is isolated from the red algae Portieria hornemanii and has in vitro activity in the NCI screen against brain, renal, and colon cancer cell lines.


METHODS
Mouse and human liver fractions, prepared by homogenization and differential centrifugation, were incubated with halomon, extracted with toluene, and analyzed by gas chromatography.


RESULTS
In the presence of NADPH, mouse-liver 9,000-g supernatant (S9) fractions metabolized halomon, but boiled S9 fractions did not. NADH could not substitute for NADPH. Further separation of murine hepatic S9 fractions produced a microsomal fraction that contained all of the halomon-metabolizing activity; cytosol had none. Carbon monoxide reduced murine hepatic microsomal metabolism of halomon, whereas an anaerobic, N2 environment greatly accelerated the disappearance of halomon. Human hepatic microsomes metabolized halomon and required NADPH to do so. Carbon monoxide completely inhibited human hepatic microsomal metabolism of halomon. Unlike murine hepatic microsomal metabolism of halomon, anaerobic conditions did not enhance the metabolism of halomon by human hepatic microsomes. Neither 100 microM diethyldithiocarbamate, 1 microM quinidine, 100 microM ciprofloxacin, 3 microM ketoconazole, nor 100 microM sulfinpyrazone inhibited the metabolism of halomon by human hepatic microsomes. Both murine and human hepatic microsomes produced a metabolite of halomon. The mass spectrum of this metabolite indicated the loss of one chlorine atom and one bromine atom.


CONCLUSIONS
Halomon is metabolized by mouse and human hepatic cytochrome P-450 enzymes, the identities of which remain unknown. Hepatic metabolism of halomon is very consistent with the concentrations of halomon measured in mouse tissues and urine after i.v. administration of the drug.
Egorin
M J
MJ
Division of Developmental Therapeutics, University of Maryland Cancer Center, Baltimore 21201, USA.
Rosen
D M
DM
Benjamin
S E
SE
Callery
P S
PS
Sentz
D L
DL
Eiseman
J L
JL
D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D006846:Hydrocarbons, Halogenated / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D000461:Rhodophyta / Q000737:chemistry; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D006846:Hydrocarbons, Halogenated; C076123:6-bromo-3-(bromomethyl)-7-methyl-2,3,7-trichloro-1-octene; D003577:Cytochrome P-450 Enzyme System