CYP2C subfamily, primarily CYP2C9, catalyses the enantioselective demethylation of the endocrine disruptor pesticide methoxychlor in human liver microsomes: use of inhibitory monoclonal antibodies in P450 identification

Xenobiotica. 2004 Feb;34(2):117-32. doi: 10.1080/00498250310001644535.


1. The endocrine disruptor pesticide methoxychlor undergoes O-demethylation by mammalian liver microsomes forming chiral mono-phenolic (1,1,1-trichloro-2-(4-hydroxyphenyl)-2-(4-methoxyphenyl)ethane, i.e. mono-OH-M) and achiral bis-phenolic oestrogenic metabolites. Human liver microsomes (HLM) generated primarily the S-mono-OH-M. 2. Inhibitory monoclonal antibodies (MAb) identified those P450s catalysing the enantioselective O-demethylation of methoxychlor. In HLM, O-demethylation was inhibited by MAb anti-2C9 (30-40%), diminishing the per cent of S-mono-OH-M from about 80 to 55-60%. MAb anti-CYP1A2, 2A6, 2B6, 2C8, 2C19, 2D6 and 3A4 did not affect the demethylation rate in HLM. Nevertheless, MAb anti-CYP1A2 decreased the formation of R-mono-OH-M from 21-23 to 10-17%, indicating that CYP1A2 exhibits a role in generating the R-enantiomer. 3. Among cDNA-expressed human P450s (supersomes), CYP2C19 was the most active in demethylation, but in HLM, CYP2C19 appeared inactive (no inhibition by MAb anti-CYP2C19). There was a substantial difference in the per cent inhibition of demethylation by MAb anti-CYP2C9 and anti-rat CYP2C (MAb inhibiting all human CYP2C forms) and in altering the enantioselectivity, suggesting that demethylation by combined CYP2C8, 2C18 and 2C19 was significant (20-30%). 4. Polymorphism of methoxychlor demethylation was examined with supersomes and HLM-expressing CYP2C9 allelic variants. CYP2C9*1 and 2C9*2 were highly active; however, CYP2C9*3 appeared inactive.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alleles
  • Antibodies, Blocking / pharmacology*
  • Antibodies, Monoclonal / pharmacology*
  • Aryl Hydrocarbon Hydroxylases / antagonists & inhibitors*
  • Aryl Hydrocarbon Hydroxylases / genetics
  • Aryl Hydrocarbon Hydroxylases / metabolism*
  • Biotransformation
  • Catalysis
  • Cytochrome P-450 CYP1A2 / metabolism
  • Cytochrome P-450 CYP1A2 Inhibitors
  • Cytochrome P-450 CYP2C9
  • DNA, Complementary / biosynthesis
  • DNA, Complementary / genetics
  • Dealkylation
  • Endocrine Glands / drug effects
  • Humans
  • In Vitro Techniques
  • Insecticides / metabolism*
  • Insecticides / toxicity
  • Methoxychlor / metabolism*
  • Methoxychlor / toxicity
  • Microsomes, Liver / drug effects
  • Microsomes, Liver / enzymology*
  • Stereoisomerism


  • Antibodies, Blocking
  • Antibodies, Monoclonal
  • Cytochrome P-450 CYP1A2 Inhibitors
  • DNA, Complementary
  • Insecticides
  • CYP2C9 protein, human
  • Cytochrome P-450 CYP2C9
  • Aryl Hydrocarbon Hydroxylases
  • Cytochrome P-450 CYP1A2
  • Methoxychlor