XXII. BIOCHEMICKÝ ZJAZD - Jesseniova lekárska fakulta

Posters
104.
CYTOCHrOME b 5
POTENTIaTES aCTIvITIES of CYTOCHrOMES
P450 1A1 aND 1A2 TO OXIDIZE aNTICaNCEr drUG ELLIPTICINE TO
PHarmaCOLOGICaLLY effICIENT METaBOLITES
Věra Kotrbová 1 , Barbora Mrázová 1 , Eva Frei 2 and Marie Stiborová 1
1
Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030,
128 40 Prague 2, Czech Republic; 2 Department of Molecular Toxicology,
German Cancer Research Center, 69 120 Heidelberg, Germany
Ellipticine is an alkaloid exhibiting significant antineoplastic activities. Its mode of action
is based mainly on cytochrome P450 (CYP)-mediated formation of covalent DNA
adducts. Many CYP-dependent reactions have been shown to be stimulated by another
microsomal protein, cytochrome b 5
(b 5
). Five ellipticine metabolites, 9-OH-, 12-OH-,
13-OH-, 7-OH-ellipticine and the ellipticine N 2 -oxide, are generated by CYP1A1/2. The
patterns and amounts of ellipticine metabolites vary significantly when b 5
is present
in the incubations. The formation of detoxication products of its oxidation (7-OH- and
9-OH-ellipticine) is decreased, while generation of 13-OH- and 12-OH-ellipticine, the
metabolites responsible for formation of DNA adducts, is increased considerably. The
enhanced generation of ellipticine-DNA adducts in the presence of b 5
in the system was
confirmed by 32 P postlabeling. The treatment of rats with ellipticine resulted in elevated
expression of b 5
. Other proteins with or without heme in their molecules are without
such effects on ellipticine oxidation. Cytochrome b 5
affects also the kinetics of ellipticine
oxidation by CYP1A1/2. In the case of the CYP1A1, the presence of b 5
changes the kinetics
of ellipticine oxidation to 12-OH- and 13-OH-ellipticine from hyperbolic to sigmoidal,
whereas no cooperativity was observed with CYP1A2.
Acknowledgements: Supported by GACR (203/09/0812, P301/10/0356), the Czech Ministry
of Education (MSM0021620808, 1M0505) and GAUK (127208).
XXII. Biochemistry Congress, Martin
229