Verapamil regulates activity and mRNA-expression of human beta-glucuronidase in HepG2 cells.
A promising development in tumor therapy is the application of non-toxic prodrugs from which the active cytostatic is released by endogenous enzymes such as beta-glucuronidase (beta-gluc). Regulation of beta-gluc expression is one crucial factor modulating bioactivation of prodrugs. Recent experiments in rats indicate regulation of beta-gluc activity by the calcium channel blocker verapamil. To further explore this phenomenon, we investigated the effect of verapamil on beta-gluc enzyme activity, protein (western blot) and mRNA expression (RT-PCR) as well as the underlying mechanisms (effects of verapamil metabolites; promoter activity) in the human hepatoma cell line HepG2. Treatment of HepG2 cells with verapamil revealed down-regulation of beta-gluc activity, protein, and mRNA level down to 50% of the control with EC(50) values of 25 microM. Effects were similar for both enantiomers. Moreover, it was demonstrated that reduced promoter activity contributes to the observed effects. In summary, our data demonstrate regulation of human beta-glucuronidase expression by verapamil. Based on our findings we hypothesize that coadministration of verapamil may effect cleavage of glucuronides by beta-glucuronidase.
Grube
M
M
Department of Pharmacology, Peter Holtz Research Center of Pharmacology and Experimental Therapeutics, Friedrich Loefflerstrasse 23d, 17487 Greifswald, Germany.
Kunert-Keil
C
C
Sperker
B
B
Kroemer
H K
HK
D015153:Blotting, Western; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000235:genetics; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D017930:Genes, Reporter; D005966:Glucuronidase / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000096:biosynthesis; D006801:Humans; D006923:Hymecromone / Q000031:analogs & derivatives* / Q000378:metabolism; D008113:Liver Neoplasms / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis*; D013237:Stereoisomerism; D013997:Time Factors; D014162:Transfection; D014700:Verapamil / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D012333:RNA, Messenger; D006923:Hymecromone; C034888:4-methylumbelliferyl glucuronide; D014700:Verapamil; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D005966:Glucuronidase