Toremifene metabolism in rat, mouse and human liver microsomes: Identification of α‐hydroxytoremifene by LC‐MS

Abstract

The in vitro metabolism of toremifene has been studied in liver microsomal preparations from rat, mouse and human sources using high-performance liquid chromatography-electrospray ionisation mass spectrometry (HPLC-ESIMS). The metabolites detected were N-desmethyltoremifene (m/z 392), 4-hydroxytoremifene (m/z 422), 4'-hydroxytoremifene (m/z 422) and toremifene N-oxide m/z 422). In addition, a new polar metabolite with a protonated molecule at m/z 422 has been detected in all three species. The compound was identified by tandem MS-MS as alpha-hydroxytoremifene, an analogue of alpha-hydroxytamoxifen. The results showed that alpha-hydroxylation is a common feature of tamoxifen and toremifene metabolism and that alpha-hydroxytamoxifen is unlikely to be the reactive metabolite responsible for the hepatocarcinogenesis in rat, as widely believed.

Mass spectrometric characterization of urinary toremifene metabolites for doping control analyses

“…4). These results are in agreement with those previously reported [17,26,29] where the first eluting monohydroxylated metabolite was described as ␣-hydroxytoremifene and can correspond to M3a.…”

“…Metabolic pathways studied were based on those metabolites reported in previous studies for toremifene [3,13,14,20,21,24,26,[28][29][30] and other related compounds, such as tamoxifen and clomifene [3,4,17,[31][32][33][34][35][36][37][38][39][40][41]. All previously reported metabolic pathways and their combination were included in SRM method, with the main exception of those proposed after metabolic removal of the amine function because of no ionization in positive ion mode was expected for these compounds [13][14][15][18][19][20][21][22][23][24][25]27,42] ( Table 1).…”

“…Few analytical methods for the urinary detection of toremifene administration have been developed [3,14,[26][27][28][29]. Different metabolic pathways have been described as the most characteristic for toremifene and related compounds such as tamoxifen and clomifene including, hydroxylation, N-desmethylation, N,Ndidesmethylation, deaminohydroxylation, deaminocarboxylation, N-oxide formation, among others [3,4,17,[30][31][32][33][34][35][36][37][38][39][40][41][42].…”

OXIDATION OF TAMOXIFEN BY HUMAN FLAVIN-CONTAINING MONOOXYGENASE (FMO) 1 AND FMO3 TO TAMOXIFEN-N-OXIDE AND ITS NOVEL REDUCTION BACK TO TAMOXIFEN BY HUMAN CYTOCHROMES P450 AND HEMOGLOBIN

“…These findings and the observations that TNO forms far less DNA and protein adducts than does TAM (Dehal and Kupfer, 1999;Umemoto et al, 2000) suggest that TNO could be an attractive candidate for a prodrug of TAM. Other tamoxifen analogs undergoing clinical trials for antibreast cancer treatment (e.g., iodoxifene, toremifene, and droloxifene) have also been shown to form the corresponding N-oxides (McCague et al, 1990;John et al, 2002;Jones and Lim, 2002). Given the structural similarities between these TPE compounds and TAM, it seems reasonable that the N-oxides of these selective estrogen receptor modulator analogs and of related TPEs could also be reduced to their respective tertiary amines.…”

Applicability of bioanalysis of multiple analytes in drug discovery and development: review of select case studies including assay development considerations

“…Using a similar analogy to torimefene moiety, it was thought that the α-hydroxylation pathway is unlikely to happen in torimefene because of the chloro substituent in the ethyl group, and it has not been reported to occur in torimefene metabolism (Potter et al, 1994). However, Jones and Lim (2002) described for the first time the occurrence of α-hydroxy torimefene metabolite in the liver microsomal preparations using a liquid chromatography and tandem mass spectrometry. Because of this important finding, the authors postulated that it is highly unlikely that α-hydroxytamoxifen is very reactive and contributes to genotoxicity.…”