1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) modulates rat liver microsomal cyclophosphamide and ifosphamide activation by suppressing cytochrome P450 2C11 messenger RNA levels.
The alkylating anticancer drug 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU; lomustine) is frequently administered to cancer patients as part of a combination chemotherapy regimen. Previous studies have indicated that CCNU treatment of adult male rats leads to prolonged decreases in liver cytochrome P450 (CYP)-mediated enzyme activities. Because the alkylating agent prodrugs cyclophosphamide and ifosphamide are known to be activated by liver cytochrome P450 enzymes, the potential for interaction between CCNU and these oxazaphosphorines was examined. Treatment of adult male rats with a single dose of CCNU (30 mg/kg i.p.) resulted in a progressive loss of liver microsomal cyclophosphamide and ifosphamide hydroxylation activities in vitro (30-60% decrease after 7-27 days). The individual liver P450 forms modulated by CCNU were then identified using P450 form-specific microsomal testosterone hydroxylase assays. CCNU treatment was found to decrease substantially CYP2C11-dependent testosterone 2 alpha-hydroxylase activity (80-90% decrease after 14 or 27 days), but it did not affect CYP3A2-dependent testosterone 6 beta-hydroxylase activity. It only modestly decreased CYP2A2-mediated testosterone 15 alpha-hydroxylase activity. The reduction in CYP2C11 activity was not associated with a decline in liver microsomal NADPH-cytochrome P450 reductase activity, but rather was caused by a complete suppression of CYP2C11 mRNA levels. In contrast to other alkylating agents, such as cisplatin, which is known to feminize the overall expression profile of gender-specific liver enzymes, CCNU did not increase levels of the female-predominant liver enzymes steroid 5 alpha-reductase and CYP2C7, nor did it deplete circulating testosterone levels.(ABSTRACT TRUNCATED AT 250 WORDS)
Chang
T K
TK
Department of Biology, Boston University, MA 02215.
Chen
H
H
Waxman
D J
DJ
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001711:Biotransformation / Q000187:drug effects; D015152:Blotting, Northern; D003520:Cyclophosphamide / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D000072467:Cytochrome P450 Family 2; D003864:Depression, Chemical; D004789:Enzyme Activation / Q000187:drug effects; D006900:Hydroxylation; D007069:Ifosfamide / Q000378:metabolism*; D066298:In Vitro Techniques; D008130:Lomustine / Q000494:pharmacology*; D008297:Male; D008565:Membrane Proteins; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D015345:Oligonucleotide Probes; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D011916:Rats, Inbred F344; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D013739:Testosterone / Q000097:blood
D065607:Cytochrome P-450 Enzyme Inhibitors; D008565:Membrane Proteins; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D013739:Testosterone; D008130:Lomustine; D003520:Cyclophosphamide; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; C465260:Cyp3a2 protein, rat; D051544:Cytochrome P-450 CYP3A; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; D009251:NADPH-Ferrihemoprotein Reductase; D007069:Ifosfamide