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cAMP‐dependent phosphorylation of CYP2B1 as a functional switch for cyclophosphamide activation and its hormonal control in vitro and in vivo
Author(s) -
OeschBartlomowicz Barbara,
Richter Bernd,
Becker Roger,
Vogel Stephan,
Padma Palghat R.,
Hengstler JanGeorg,
Oesch Franz
Publication year - 2001
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.1517
Subject(s) - phosphorylation , in vivo , hydroxylation , serine , biology , microbiology and biotechnology , in vitro , cytochrome p450 , biochemistry , chemistry , cancer research , enzyme , genetics
An important feature of cytochrome P450 (CYP) 2B1 is its high ability to convert the prodrug cyclophosphamide (CPA) to therapeutically cytotoxic metabolites, resulting in interstrand DNA‐cross‐linking and cell death. We have examined whether and how the phosphorylation of CYP2B1 influences CPA metabolic activation in vitro and in vivo . We found first that only part of the total CYP2B1 pool undergoes phosphorylation. This part is fully inactivated. Second, phosphorylation of CYP2B1 in intact hepatocytes reduced by up to 75% toxification of CPA to mutagenic metabolites (totally dependent on the same preferentially CYP2B‐catalyzed 4‐hydroxylation of CPA as is the generation of highly cytotoxic species). Third, the phosphoacceptor‐serine 128 of CYP2B1 in the consensus sequence for interaction with the protein kinase A represents an on/off switch for the activation of CPA depending on the phosphorylation conditions in the cell. Fourth, evidence is presented that the above‐described events also occur in vivo . In conclusion, a successful therapy with CPA, helped by forced expression of CYP2B1 in tumor cells (as recently proposed) will, in addition, be profoundly modified by its phosphorylation status. © 2001 Wiley‐Liss, Inc.