XXII. BIOCHEMICKÝ ZJAZD - Jesseniova lekárska fakulta

Posters
114.
THE STUDY ON CYTOCHROME B 5
–MEDIATED STIMULATION
OF ELLIPTICINE OXIDATION BY CYTOCHROME P450 3A4 TO ITS
PHarMACOLOGICALLY MORE EffICIENT METABOLITES
Barbora Mrázová 1 , Eva Martínková 1 , Radek Indra 1 , Eva Frei 2 and Marie Stiborová 1
1
Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030,
128 43 Prague 2, Czech Republic
2
German Cancer Research Center, 69 120 Heidelberg, Germany
Ellipticine alkaloid exhibiting significant antineoplastic activities. CYP3A4 was found to be
the major enzyme responsible for oxidation of ellipticine to 13-hydroxy- and 12-hydroxyellipticine,
two metabolites generating DNA adducts. Many CYP3A4-dependent reactions have
been shown to be stimulated by another microsomal protein, cytochrome b 5
(b 5
). Beside
12-hydroxy- and 13-hydroxyellipticine, other three ellipticine metabolites are generated
by CYP3A4. Human b 5
, purified rabbit hepatic b 5
and apo-b 5
reconstituted with heme were
capable of stimulating oxidation of ellipticine by CYP3A4. The patterns and amounts of
ellipticine metabolites vary significantly when b 5
is present in the incubations. Whereas,
the formation of detoxication product of ellipticine oxidation (9-hydroxyellipticine) is
practically not influenced by b 5
, generation of 13-hydroxy- and 12-hydroxyellipticine is
increased significantly by these b 5
proteins. The enhanced generation of ellipticine-DNA
adducts in the presence of b 5
in the system was confirmed by 32 P postlabeling. Other
proteins with or without heme in their molecules are without such effects on ellipticine
oxidation. The hyperbolic kinetics of ellipticine oxidation by CYP3A4 with or without b 5
indicates no cooperativity. The results indicate that the presence of heme in b 5
seems to
be required for the stimulation of CYP3A4-mediated oxidation of ellipticine.
Acknowledgments: Supported by GACR (P303/10/0356, 203/09/0812), the Czech Ministry
of Education (MSM0021620808, 1M0505) and GAUK (1272080).
XXII. Biochemistry Congress, Martin
239