Evaluation of the major metabolites of raloxifene as modulators of tissue selectivity

Dodge, Jeffrey A.; Lugar, Charles W.; Cho, Stephen; Short, Lorri L.; Sato, Masahiko; Yang, Na; Spangle, Larry A.; Martin, Michael; Phillips, Donald A.; Glasebrook, Andrew L.; Osborne, John; Frolik, Charles A.; Bryant, Henry U.

doi:10.1016/s0960-0760(97)00008-3

Cited by 50 publications

(38 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Metabolites of raloxifene are not known to be significantly active relative to the parent compound (43). In contrast, tamoxifen can be converted by liver enzymes to N-desmethyltamoxifen and the more potent form, 4OH, among other species (44 -46).…”

Section: Discussionmentioning

confidence: 99%

The Selective Estrogen Receptor Modulators, Tamoxifen and Raloxifene, Impair Dendritic Cell Differentiation and Activation

Nalbandian

Paharkova-Vatchkova

Mao

et al. 2005

The Journal of Immunology

104

View full text Add to dashboard Cite

Most immune cells, including myeloid progenitors and terminally differentiated dendritic cells (DC), express estrogen receptors (ER) making these cells sensitive to estrogens. Our laboratory recently demonstrated that 17-β-estradiol (E2) promotes the GM-CSF-mediated development of CD11c+CD11bint DC from murine bone marrow precursors. We tested whether the therapeutic selective estrogen receptor modulators (SERM), raloxifene and tamoxifen, can perturb DC development and activation. SERM, used in treatment of breast cancer and osteoporosis, bind to ER and mediate tissue-specific agonistic or antagonistic effects. Raloxifene and tamoxifen inhibited the differentiation of estrogen-dependent DC from bone marrow precursors ex vivo in competition experiments with physiological levels of E2. DC differentiated in the presence of SERM were assessed for their capacity to internalize fluoresceinated Ags as well as respond to inflammatory stimuli by increasing surface expression of molecules important for APC function. Although SERM-exposed DC exhibited increased ability to internalize Ags, they were hyporesponsive to bacterial LPS: relative to control DC, they less efficiently up-regulated the expression of MHC class II, CD86, and to a lesser extent, CD80 and CD40. This phenotype indicates that these SERM act to maintain DC in an immature state by inhibiting DC responsiveness to inflammatory stimuli. Thus, raloxifene and tamoxifen impair E2-promoted DC differentiation and reduce the immunostimulatory capacity of DC. These observations suggest that SERM may depress immunity when given to healthy individuals for the prevention of osteoporosis and breast cancer and may interfere with immunotherapeutic strategies to improve antitumor immunity in breast cancer patients.

show abstract

Section: Discussionmentioning

confidence: 99%

The Selective Estrogen Receptor Modulators, Tamoxifen and Raloxifene, Impair Dendritic Cell Differentiation and Activation

Nalbandian

Paharkova-Vatchkova

Mao

et al. 2005

The Journal of Immunology

104

View full text Add to dashboard Cite

show abstract

“…The structure of the raloxifene metabolites was established by comparison with the NMR data (Table 1) of unreacted raloxifene and that of synthetic raloxifene glucuronides previously characterized (Dodge et al, 1997). Specifically, the glucuronide at rt 12 min was identified to be R-6-G based on an exact match with the literature values for proton chemical shifts, proton integral ratios, and coupling patterns.…”

Section: Raloxifene Glucuronidation In Vitromentioning

confidence: 99%

Characterization of Raloxifene Glucuronidation in Vitro: Contribution of Intestinal Metabolism to Presystemic Clearance

Kemp¹,

Fan²,

Stevens³

2002

Drug Metab Dispos

177

150

View full text Add to dashboard Cite

This article is available online at http://dmd.aspetjournals.org ABSTRACT:Raloxifene, a selective estrogen receptor modulator used for the treatment of osteoporosis, undergoes extensive conjugation to the 6-␤-and 4-␤-glucuronides in vivo. This paper investigated raloxifene glucuronidation by human liver and intestinal microsomes and identified the responsible UDP-glucuronosyltransferases (UGTs). UGT1A1 and 1A8 were found to catalyze the formation of both the 6-␤-and 4-␤-glucuronides, whereas UGT1A10 formed only the 4-␤-glucuronide. Expressed UGT1A8 catalyzed 6-␤-glucuronidation with an apparent K m of 7.9 M and a V max of 0.61 nmol/min/mg of protein and 4-␤-glucuronidation with an apparent K m of 59 M and a V max of 2.0 nmol/min/mg. Kinetic parameters for raloxifene glucuronidation by expressed UGT1A1 could not be determined due to limited substrate solubility. Based on rates of raloxifene glucuronidation and known extrahepatic expression, UGT1A8 and 1A10 appear to be primary contributors to raloxifene glucuronidation in human jejunum microsomes. For human liver microsomes, the variability of 6-␤-and 4-␤-glucuronide formation was 3-and 4-fold, respectively. Correlation analyses revealed that UGT1A1 was responsible for 6-␤-but not 4-␤-glucuronidation in liver. Treatment of expressed UGTs with alamethicin resulted in minor increases in enzyme activity, whereas in human intestinal microsomes, maximal increases of 8-fold for the 6-glucuronide and 9-fold for the 4-glucuronide were observed. Intrinsic clearance values in intestinal microsomes were 17 l/min/mg for the 6-glucuronide and 95 l/min/mg for the 4-isomer. The corresponding values for liver microsomes were significantly lower, indicating that intestinal glucuronidation may be a significant contributor to the presystemic clearance of raloxifene in vivo.

show abstract

“…Although raloxifene conjugates do not bind with estrogen receptors with affinity high enough to evoke a pharmacological response they are considered as carriers of active raloxifene [9,10]. Their blood serum concentration is more than hundred times higher than raloxifene serum concentration (Table 5) and they can be cleaved back to parent raloxifene in many tissues and organs [7,10].…”

Section: Discussionmentioning

confidence: 99%

“…The rest represents raloxifene conjugated by UDP-glucuronosyltransferases (UGTs) to raloxifene-4'-β-glucuronide (M2), raloxifene-6-β-glucuronide (M1) [7,8] and raloxifene-6,4'-diglucuronide (M3) [7,9]. Although the glucuronides show little affinity for the estrogen receptors and for bone tissue, they are important because they can be readily reconverted back into active raloxifene in various organs by β-glucuronidases residing in the liver, lung, spleen, kidney, bone and uterus [10]. Raloxifene and its metabolites are primarily excreted in feces and less than 0.2% and 6% of raloxifene and its metabolites, respectively, are recovered in urine [7].…”

Section: Discussionmentioning

confidence: 99%

“…Their blood serum concentration is more than hundred times higher than raloxifene serum concentration (Table 5) and they can be cleaved back to parent raloxifene in many tissues and organs [7,10]. Therefore, in order to elucidate the complex raloxifene disposition it is vital to understand raloxifene glucuronide membrane transport and its effect on both raloxifene pharmacokinetics and pharmacodynamics.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Influence of hepatic and intestinal efflux transporters and their genetic variants on the pharmacokinetics and pharmacodynamics of raloxifene in osteoporosis treatment

Lušin

Mrhar

Stieger

et al. 2012

Translational Research

View full text Add to dashboard Cite

Raloxifene exhibits a large and unexplained interindividual variability in its pharmacokinetics and pharmacodynamics. The aim of our study was to identify transporters involved in the efflux of raloxifene and its glucuronide metabolites by various in vitro models and by an in vivo study to explore the possible involvement of P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP)1, MRP2, MRP3, and breast cancer resistance protein in the observed high interindividual variability. Experiments with the parallel artificial membrane permeability assay showed the highest passive permeability for raloxifene, followed by raloxifene-6--glucuronide (M1), raloxifene-4'--glucuronide (M2), and raloxifene-6,4'-diglucuronide (M3). Caco-2 cell monolayer experiments indicated an interaction of raloxifene with Pgp. The ATPase assay confirmed the raloxifene interaction with Pgp and indicated interactions of all raloxifene species with MRP1, MRP2, MRP3, and breast cancer resistance protein, except for M1, which did not show any interactions with MRP2. Furthermore, the vesicular experiments confirmed the interaction of M2 and M3 with MRP2. Although the in vivo study on osteoporotic postmenopausal women on raloxifene could not confirm a significant influence of ABCB1 and ABCC2 genetic polymorphisms on its pharmacokinetics, a clear trend toward higher total raloxifene concentrations was observed in carriers of at least 1 ABCB1 c.3435T allele. Moreover, the same polymorphism effect was also observed as a significant increase in total hip bone mineral density after 1 year of treatment. The results of our study support the involvement of efflux transporters in disposition of raloxifene and its metabolites and may partially explain the observed raloxifene variability by the influence of the ABCB1 c.3435C>T polymorphism. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 AbstractRaloxifene exhibits quite a large and unexplained interindividual variability in its pharmacokinetics and pharmacodynamics. The aim of our study was to identify transporters involved in the efflux of raloxifene and its glucuronide metabolites by various in vitro models and by an in vivo study to explore the possible involvement of Pgp, MRP1, MRP2, MRP3, and BCRP in the observed high interindividual variability. Experiments with PAMPA (Parallel Artificial Membrane Permeability Assay) showed the highest passive permeability for raloxifene, followed by raloxifene-6-β-glucuronide (M1), raloxifene-4'-β-glucuronide (M2) and raloxifene-6,4'-diglucuronide (M3). Caco-2 cell monolayer experiments indicated an inte...

show abstract

Evaluation of the major metabolites of raloxifene as modulators of tissue selectivity

Cited by 50 publications

References 18 publications

The Selective Estrogen Receptor Modulators, Tamoxifen and Raloxifene, Impair Dendritic Cell Differentiation and Activation

The Selective Estrogen Receptor Modulators, Tamoxifen and Raloxifene, Impair Dendritic Cell Differentiation and Activation

Characterization of Raloxifene Glucuronidation in Vitro: Contribution of Intestinal Metabolism to Presystemic Clearance

Influence of hepatic and intestinal efflux transporters and their genetic variants on the pharmacokinetics and pharmacodynamics of raloxifene in osteoporosis treatment

Contact Info

Product

Resources

About