Activation of tamoxifen and its metabolite alpha-hydroxytamoxifen to DNA-binding products: comparisons between human, rat and mouse hepatocytes.
The metabolic activation of tamoxifen and its metabolite alpha-hydroxytamoxifen in primary cultures of rat, mouse and human hepatocytes has been compared. The extent of formation of DNA adducts in these cells was measured by 32P-postlabelling, using either nuclease P1 digestion or sorbent extraction of DNA digests to enhance the sensitivity of the assay. DNA adducts were readily detected in rat hepatocytes treated with 1 or 10 microM tamoxifen (mean levels 18.2 and 89.8 adducts/10(8) nucleotides respectively). Similar levels of adducts were formed by mouse hepatocytes (15.0 +/- 1.8 adducts/10(8) nucleotides, 10 microM tamoxifen). However DNA adducts were not detected in tamoxifen-treated human hepatocytes with a detection limit for the assay of 4 adducts/10(10) nucleotides. Treatment of rat cells with alpha-hydroxytamoxifen resulted in 15- to 63-fold higher levels of adducts than with comparable concentrations of tamoxifen. A similar level of adducts was also seen in mouse hepatocytes treated with alpha-hydroxytamoxifen at the 1 microM concentration (173.9 +/- 4.1 adducts/10(8) nucleotides). Treatment of human cells with alpha-hydroxytamoxifen resulted in DNA adduct formation at levels (1.94 +/- 0.89 and 18.9 +/- 17.9 adducts/10(8) nucleotides at 1 and 10 microM respectively) approximately 300-fold lower than those in rat hepatocytes. The presence of alpha-hydroxytamoxifen in the culture medium from experiments where cells were incubated with tamoxifen was monitored by mass spectrometry. Concentrations were found to be approximately 50-fold lower in the medium from human hepatocytes than from rat and mouse hepatocytes.
Phillips
D H
DH
Section of Molecular Carcinogenesis, Haddow Laboratories, Sutton, UK.
Carmichael
P L
PL
Hewer
A
A
Cole
K J
KJ
Hardcastle
I R
IR
Poon
G K
GK
Keogh
A
A
Strain
A J
AJ
D000293:Adolescent; D000328:Adult; D000818:Animals; D001711:Biotransformation; D002648:Child; D018736:DNA Adducts / Q000378:metabolism*; D004965:Estrogen Antagonists / Q000378:metabolism*; D005260:Female; D006801:Humans; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D008875:Middle Aged; D051381:Rats; D011916:Rats, Inbred F344; D013045:Species Specificity; D013629:Tamoxifen / Q000378:metabolism*
D018736:DNA Adducts; D004965:Estrogen Antagonists; D013629:Tamoxifen