Pharmacogenomic-pharmacokinetic study of selective estrogen-receptor modulators with intra-patient dose escalation in breast cancer.

BACKGROUND: An association between CYP2D6 polymorphisms and tamoxifen (TAM) efficacy has not been confirmed, partly due to unreliable prediction of active metabolite exposure solely by CYP2D6 activity. The efficacy of TAM dose escalation appears limited in poor TAM metabolizers. Since the chlorine atom on the side chain of toremifene (TOR) prevents 4-hydroxylation by CYP2D6, its contribution to active conversion of TOR is minor. We examined the role of TOR and its dose escalation among poor TAM metabolizers. METHODS: The pharmacokinetics (PK) and pharmacogenomics (PGx) of TAM and TOR were studied. Correlation between PK and CYP2D6 inhibitor use, smoking status, and PGx were examined by regression analysis. For patients showing low endoxifen levels, an intra-patient dose escalation of TOR was conducted, and TOR was increased from 40 to 120 mg for ≥ 24 weeks with PK sampling. Total activity was calculated as the sum of the concentration of each active metabolite adjusted by their respective in vitro activities. RESULTS: Fifty and 11 of the 273 participating patients had endoxifen levels < 15 and < 7.5 ng/mL, respectively. The CYP2D6 genotype was the major determinant for TAM activity (p < 0.01). Smoking status (p = 0.07) and the CYP2C19 phenotype (p = 0.07), but not the CYP2D6 genotype (p = 0.61), showed marginally significant effects on TOR activity. TOR activity increased significantly with dose escalation, even among poor TAM metabolizers, and was maintained for ≥ 24 weeks. CONCLUSION: TOR might be a valid alternative to TAM in patients predicted to be poor TAM metabolizers.

Drug-drug interaction and doping, part 1: an in vitro study on the effect of non-prohibited drugs on the phase I metabolic profile of toremifene.

The present study was designed to provide preliminary information on the potential impact of metabolic drug-drug interaction on the effectiveness of doping control strategies currently followed by the anti-doping laboratories to detect the intake of banned agents. In vitro assays based on the use of human liver microsomes and recombinant CYP isoforms were designed and performed to characterize the phase I metabolic profile of the prohibited agent toremifene, selected as a prototype drug of the class of selective oestrogen receptor modulators, both in the absence and in the presence of medicaments (fluconazole, ketoconazole, itraconazole, miconazole, cimetidine, ranitidine, fluoxetine, paroxetine, nefazodone) not included in the World Anti-Doping Agency list of prohibited substances and methods and frequently administered to athletes. The results show that the in vitro model developed in this study was adequate to simulate the in vivo metabolism of toremifene, confirming the results obtained in previous studies. Furthermore, our data also show that ketoconazole, itraconazole, miconazole and nefazodone cause a marked modification in the production of the metabolic products (i.e. hydroxylated and carboxylated metabolites) normally selected by the anti-doping laboratories as target analytes to detect toremifene intake; moderate variations were registered in the presence of fluconazole, paroxetine and fluoxetine; while no significant modifications were measured in the presence of ranitidine and cimetidine. This evidence imposes that the potential effect of drug-drug interactions is duly taken into account in anti-doping analysis, also for a broader significance of the analytical results.

Characterization of the biotransformation pathways of clomiphene, tamoxifen and toremifene as assessed by LC-MS/(MS) following in vitro and excretion studies.

The use of selective oestrogen receptor modulators has been prohibited since 2005 by the World Anti-Doping Agency regulations. As they are extensively cleared by hepatic and intestinal metabolism via oxidative and conjugating enzymes, a complete investigation of their biotransformation pathways and kinetics of excretion is essential for the anti-doping laboratories to select the right marker(s) of misuse. This work was designed to characterize the chemical reactions and the metabolizing enzymes involved in the metabolic routes of clomiphene, tamoxifen and toremifene. To determine the biotransformation pathways of the substrates under investigation, urine samples were collected from six subjects (three females and three males) after oral administration of 50 mg of clomiphene citrate or 40 mg of tamoxifen or 60 mg of toremifene, whereas the metabolizing enzymes were characterized in vitro, using expressed cytochrome P450s and uridine diphosphoglucuronosyltransferases. The separation, identification and determination of the compounds formed in the in vivo and in vitro experiments were carried out by liquid chromatography coupled with mass spectrometry techniques using different acquisition modes. Clomiphene, tamoxifen and toremifene were biotransformed to 22, 23 and 18 metabolites respectively, these phase I reactions being catalyzed mainly by CYP3A4 and CYP2D6 isoforms and, to a lesser degree, by CYP3A5, CYP2B6, CYP2C9, CYP2C19 isoforms. The phase I metabolic reactions include hydroxylation in different positions, N-oxidation, dehalogenation, carboxylation, hydrogenation, methoxylation, N-dealkylation and combinations of them. In turn, most of the phase I metabolites underwent conjugation reaction to form the corresponding glucuro-conjugated mainly by UGT1A1, UGT1A3, UGT1A4, UGT2B7, UGT2B15 and UGT2B17 isoenzymes.

Pharmacokinetic evaluation of toremifene and its clinical implications for the treatment of osteoporosis.

INTRODUCTION: Toremifene is a triphenylethylene selective estrogen receptor modulator (SERM) that differs from tamoxifen in a single chloride ion addition on a side chain, resulting in a potentially more favorable toxicity profile. AREAS COVERED: This article reviews the pharmacokinetics of toremifene and its potential use for the treatment of osteoporosis. This article was based on articles found through a literature search containing the terms 'toremifene' and 'SERMs.' EXPERT OPINION: Toremifene can be administered orally with an excellent bioavailability. The overall pharmacokinetic profile is remarkably similar to tamoxifen. Toremifene is highly metabolized in the liver and is eliminated primarily in the feces following enterohepatic circulation. Some of its metabolites retain biological activity. This SERM was approved by the FDA for the treatment of estrogen receptor-positive metastatic breast cancer and is under investigation for its potential skeletal benefits in men on androgen deprivation therapy. Despite the positive preclinical and clinical evidences for the prevention of bone loss and fractures, the chemopreventive effect on prostate cancer remains to be confirmed and an increased risk of venous thromboembolism was evidenced in a large Phase III trial. Thus, additional data are required to establish the full clinical profile of this compound and its potential advantages over antiresorptive agents commonly in use for the treatment of osteoporosis.

Mass spectrometric characterization of toremifene metabolites in human urine by liquid chromatography-tandem mass spectrometry with different scan modes.

The metabolism and excretion of toremifene were investigated in one healthy male volunteer after a single oral administration of 120 mg toremifene citrate. Different liquid chromatographic/tandem mass spectrometric (LC/MS/MS) scanning techniques were carried out for the characterization of the metabolites in human urine for doping control purposes. The potential characteristic fragmentation pathways of toremifene and its major metabolites were presented. An approach for the metabolism study of toremifene and its analogs by liquid chromatography-tandem mass spectrometry was established. Five different LC/MS/MS scanning methods based on precursor ion scan (precursor ion scan of m/z 72.2, 58.2, 44.2, 45.2, 88.2 relative to five metabolic pathways) in positive ion mode were assessed to recognize the metabolites. Based on product ion scan and precursor ion scan techniques, the metabolites were proposed to be identified as 4-hydroxy-toremifene (m/z 422.4), 4'-hydroxy-toremifene (m/z 422.4), α-hydroxy-toremifene (m/z 422.4), 3,4-dihydroxy-toremifene (m/z 404.2), toremifene acid (m/z 402.2), 3-hydroxy-4-methoxy-toremifene (m/z 456.2), dihydroxy-dehydro-toremifene (m/z 440.2), 3,4-dihydroxy-toremifene (m/z 438.2), N-demethyl-4-hydroxy-toremifene (m/z 408.3), N-demethyl-3-hydroxy-4-methoxy-toremifene (m/z 438.3). In addition, a new metabolite with a protonated molecule at m/z 390.3 was detected in all urine samples. The compound was identified by LC/MS/MS as N-demethyl-4,4'-dihydroxy-tamoxifene. The results indicated that 3,4-dihydroxy-toremifene (m/z 404.2), toremifene acid (m/z 402.2) and N-demethyl-4,4'-dihydroxy-tamoxifene (m/z 390.3) were major metabolites in human urine.

Synthesis of a novel antiestrogen radioligand (99mTc-TOR-DTPA).

This study was aimed at developing a hydrophilic radioligand as an antiestrogen drug derivative to be used for imaging breast tumors. Toremifene [TOR; 4-chloro-1,2-diphenyl-1-(4-(2-(N,N-di-methylamino)ethoxy)phenyl)-1-butene, as citrate salt] was selected as the starting material to be derived, since it has been used extensively as an antiestrogen drug for treatment and prevention of human breast cancer. An antiestrogen drug derivative, TOR attached to diethylenetriamine pentaacetic acid (DTPA), was synthesized by two experimental treatments, including a purification and a reaction step. We described the synthesis of this TOR derivative, (3Z)-4-{4-[2-(dimethylamino) ethoxy] phenyl}-3,4-diphenylbut-3-en-1-ylN,N-bis[2-(2,6-dioxomorpholin-4-yl)ethyl]glycinate (TOR-DTPA), in detail. Mass spectroscopy confirmed the expected structures. TOR-DTPA was labeled with technetium-99m ((99m)Tc), using stannous chloride (SnCl(2)) as the reducing agent. Biodistribution studies were performed on female Albino Wistar rats. Quality controls, radiochemical yield, and stability studies were done utilizing high-performance liquid chromatography, radioelectrophoresis, thin-layer chromatography, and thin-layer radiochromatography methods. The synthesized compound was found to be hydrophilic and anionic, with high stability for the duration of the testing period in vitro. The results indicated that the radiolabeled compound has estrogen-receptor specificity, especially for the breast tissue. It is highly possible that this compound could be used for imaging breast tumors as a novel technetium-labeled hydrophilic estrogen derivative radioligand.

DNA adduct formation in the livers of female Sprague-Dawley rats treated with toremifene or alpha-hydroxytoremifene.

Toremifene, an analogue of tamoxifen in which the ethyl side chain has been replaced with a 2-chloroethyl substituent, is used as a chemotherapeutic agent in postmenopausal women with advanced breast cancer. Toremifene is metabolized in a manner similar to that of tamoxifen, with alpha-hydroxytoremifene being a predominant metabolite in incubations in vitro. DNA adducts have been detected previously in liver DNA upon the administration of toremifene to rats; however, the identity of these adducts is unknown. In the present study, we have characterized the DNA adducts produced by alpha-hydroxytoremifene and have compared the extent of hepatic DNA adduct formation in rats administered toremifene, alpha-hydroxytoremifene, or tamoxifen. alpha-Hydroxytoremifene was synthesized, further activated by sulfation, and then reacted with salmon testis DNA. After enzymatic hydrolysis to deoxynucleosides, HPLC analysis indicated the formation of two major DNA adducts, which were characterized as (E)- and (Z)-alpha-(deoxyguanosin-N2-yl)toremifene on the basis of 1H NMR and mass spectral analyses. To assess the formation of toremifene DNA adducts in vivo, female Sprague-Dawley rats were treated intraperitoneally with toremifene, alpha-hydroxytoremifene, or tamoxifen. 32P-Postlabeling analyses of hepatic DNA from the tamoxifen-treated rats indicated three DNA adducts at a total level of 2,200 +/- 270 adducts/108 nucleotides. DNA adducts were not detected (<5 adducts/108 nucleotides) in the livers of rats treated with toremifene. Two DNA adducts, of which the major one coeluted with the 3',5'-bis-phosphate of (E)-alpha-(deoxyguanosin-N2-yl)toremifene, were present at a level of 57 +/- 12 adducts/108 nucleotides in hepatic DNA from rats administered alpha-hydroxytoremifene. The low level of hepatic DNA adduct formation observed with both toremifene and alpha-hydroxytoremifene, as compared to that with tamoxifen, may be due to the limited esterification of alpha-hydroxytoremifene and/or the poor reactivity of alpha-sulfoxytoremifene.

[Assessment of post-administration body distribution of toremifene and tamoxifen, and their administration regimens].

Toremifene is an anti-estrogenic drug like tamoxifen. We assessed the body distributions after administration of toremifene and tamoxifen in order to evaluate their treatment regimens by measuring the concentrations in tissues. It is known that, after toremifene (TOR) or tamoxifen (TAM) is consecutively administered to breast cancer patients, TOR or TAM and their main active N-desmethyl-metabolites (TOR-1 or TAM-1) are detected in sera, tumor tissues, and lymph nodes. Accordingly, after we administered toremifene or tamoxifen to primary breast cancer patients previous to surgery, we measured the concentrations of TOR, TOR-1, TAM, TAM-1 in sera, tumor tissues, and lymph nodes. We found that the concentrations of TOR and TOR-1 in sera, tumors, and lymph nodes reached a peak about 2 weeks after administration of toremifene 40 mg. Likewise, the concentrations of TAM and TAM-1 in sera, tumors, and lymph nodes reached a peak about 2 weeks after administration of tamoxifen, although the peak levels were lower than those of TOR or TOR-1. The concentrations of TAM-1 in lymph nodes were significantly and positively correlated to the duration of administration of TAM, and it was predicted that the concentration of TAM-1 in lymph nodes would reach a steady state at more than 4 weeks after administration of tamoxifen. The concentrations of TOR and TOR-1 were higher in tumors and lymph nodes than in sera. Furthermore, the concentrations of TOR and TOR-1 were significantly higher than those of TAM and TAM-1 in sera and tumors, respectively. Moreover, the concentration in tissue increased in a dose-dependent manner with administration of toremifene 120 mg. There were no significant differences between breast cancers positive and negative for estrogen receptors, with regard to the concentrations of TOR and TOR-1 in either sera, tumors, or lymph nodes. In conclusion, it would be expected that treatment with toremifene might be more effective for breast cancer than that with tamoxifen.

Clinical pharmacokinetics of toremifene.

Toremifene is a chlorinated triphenylethylene derivative of tamoxifen approved for use in the treatment of patients with metastatic breast cancer. Toremifene is well tolerated in patients, and common adverse effects of this drug include vasomotor symptoms such as hot flashes and vaginal discharge. This compound is administered to patients orally at a dose of 60 mg/day, although alternative methods of administration have been investigated. Oral bioavailability is estimated to be approximately 100%. At steady state, toremifene and its metabolites are highly protein bound (>95%). Toremifene is metabolised in the liver by cytochrome P450 enzymes, and it is eliminated primarily in the faeces following enterohepatic circulation. The half-life of toremifene is approximately 5 days, and steady state is reached by 6 weeks depending on the dose given. The pharmacokinetics of toremifene have been shown to be altered by certain liver conditions, but age and kidney function do not appear to be as significant.

In vitro evaluation of sol-gel processed spray dried silica gel microspheres as carrier in controlled drug delivery.

The objective of this study was to evaluate sol-gel-derived spray dried silica gel microspheres as carrier material for dexmedetomidine HCl and toremifene citrate. The drug was dissolved in sol-gel processed silica sol before spray drying with Büchi laboratory scale equipment. Microspheres with a low specific surface area were spherical by shape with a smooth surface without pores on the external surface. The particle size distribution was quite narrow. The in vitro release of toremifene citrate and dexmedetomidine HCl showed a dose-dependent burst followed by a slower release phase, that was proportional to the drug concentration in the concentration range between 3.9 and 15.4 wt.%. The release period for toremifene citrate was approximately 10 days and for dexmedetomidine HCl between 7 and 50 days depending on drug concentration. Spray drying is a promising way to produce spherical silica gel particles with a narrow particle size range for controlled delivery of toremifene citrate and dexmedetomidine HCl.

Genotoxic effects of the novel mixed antiestrogen FC-1271a in comparison to tamoxifen and toremifene.

Tamoxifen has been used for the treatment of breast cancer since the 1970s, but is considered a carcinogen because it has been linked to liver cancer in rats and an increased risk of endometrial cancer in patients. In rats, DNA adducts appear to be responsible for carcinogenesis, but their contribution to carcinogenesis in humans is not clear. FC-1271a and toremifene are mixed antiestrogens similar to tamoxifen. In order to compare the genotoxicity of these different triphenylethylenes, we treated mice for 28 days with 50 mg/kg of either tamoxifen, toremifene, FC- 1271 a or vehicle control. DNA from liver and uterus was assayed by standard 32P-postlabeling and thin layer chromatography for the presence of DNA adducts. Two methods of drug administration (oral and subcutaneous) and two strains of mice were compared and the plasma and tissue concentrations of the drugs and three metabolites of tamoxifen and toremifene were determined. Regardless of the conditions, only tamoxifen-treated mice showed DNA adducts in the liver. Adduct levels did not correlate with drug or metabolite levels and adducts were present even when drug was not detectable. Mice were also treated orally with either 50, 100, or 200 mg/kg of drug for 7 days. Again, adducts were found only in liver tissue of mice treated with tamoxifen, and adduct levels were dose-dependent. In conclusion, the chlorinated triphenylethylene FC-1271a did not cause DNA adducts under various conditions in mice, suggesting a low carcinogenic potential.

Silica xerogel carrier material for controlled release of toremifene citrate.

Sol-gel processed silica xerogel was used as a carrier material for toremifene citrate in order to develop an implantable controlled release formulation which could be localised to a desired site providing targeted and long-lasting disease control and resulting in a reduced amount of drug needed. Toremifene citrate, an anti-estrogenic compound, was incorporated into silica xerogel matrixes during polycondensation of organic silicate, tetraethyl ortho silicate (TEOS). The effects of drug amount, drying temperature and polyethylene glycol (PEG) on the release rate of toremifene citrate and degradation of the silica xerogel matrixes were investigated. Addition of PEG (M(w) 4600/10000) decreased the specific surface area of the matrix and lowered the release rate of the drug. Reducing the amount of drug in the matrix also decreased the release rate of toremifene citrate. However, drying temperature did not affect the release rate of silica or toremifene citrate. The release profiles of toremifene citrate were according to zero order kinetics, suggesting that drug release was controlled by erosion of the silica xerogel matrix. These results suggest that the toremifene citrate release rate can be controlled to some extent by adding (PEG) or by varying the amount of drug in the silica xerogel matrix.

Silica xerogel as an implantable carrier for controlled drug delivery--evaluation of drug distribution and tissue effects after implantation.

The purpose of the present study was to examine controlled delivery of toremifene citrate from subcutaneously implanted silica xerogel carrier and to evaluate silica xerogel related tissue effects after implantation. Toremifene citrate was incorporated into hydrolyzed silica sol in a room temperature process. Toremifene citrate treated silica xerogel implants were tested both in vitro and in vivo using healthy mice. Silica xerogel with tritium-labelled toremifene was implanted subcutaneously in mice for 42 d. To determine the amount of tritiated toremifene remaining in the silica discs at the implantation site, the discs were excised periodically and radioactivity measured. The amount of tritiated toremifene in the implant after 42 d was still about 16% and the amount of silica xerogel about 25%. In a histopathological study silica xerogel did not show any tissue irritation at the site of the implantation. A fibrotic capsule was formed around the implant. No silica xerogel related histological changes in liver, kidney, lymph nodes and uterus were observed during the implantation period. The silica xerogel discs showed a sustained release of toremifene citrate over 42 d. Histologically, toremifene-related changes in the uterus were also detectable at all studied time points. These findings suggest that silica xerogel is a promising carrier material for implantable controlled drug delivery system.

4-Hydroxylated metabolites of the antiestrogens tamoxifen and toremifene are metabolized to unusually stable quinone methides.

Tamoxifen is widely prescribed for the treatment of hormone-dependent breast cancer, and it has recently been approved by the Food and Drug Administration for the chemoprevention of this disease. However, long-term usage of tamoxifen has been linked to increased risk of developing endometrial cancer in women. One of the suggested pathways leading to the potential toxicity of tamoxifen involves its oxidative metabolism to 4-hydroxytamoxifen, which may be further oxidized to an electrophilic quinone methide. The resulting quinone methide has the potential to alkylate DNA and may initiate the carcinogenic process. To further probe the chemical reactivity and toxicity of such an electrophilic species, we have prepared the 4-hydroxytamoxifen quinone methide chemically and enzymatically, examined its reactivity under physiological conditions, and quantified its reactivity with GSH. Interestingly, this quinone methide is unusually stable; its half-life under physiological conditions is approximately 3 h, and its half-life in the presence of GSH is approximately 4 min. The reaction between 4-hydroxytamoxifen quinone methide and GSH appears to be a reversible process because the quinone methide GSH conjugates slowly decompose over time, regenerating the quinone methide as indicated by LC/MS/MS data. The tamoxifen GSH conjugates were detected in microsomal incubations with 4-hydroxytamoxifen; however, none were observed in breast cancer cell lines (MCF-7) perhaps because very little quinone methides is formed. Toremifene, which is a chlorinated analogue of tamoxifen, undergoes similar oxidative metabolism to give 4-hydroxytoremifene, which is further oxidized to the corresponding quinone methide. The toremifene quinone methide has a half-life of approximately 1 h under physiological conditions, and its rate of reaction in the presence of excess GSH is approximately 6 min. More detailed analyses have indicated that the 4-hydroxytoremifene quinone methide reacts with two molecules of GSH and loses chlorine to give the corresponding di-GSH conjugates. The reaction mechanism likely involves an episulfonium ion intermediate which may contribute to the potential cytotoxic effects of toremifene. Similar to what was observed with 4-hydroxytamoxifen, 4-hydroxytoremifene was metabolized to di-GSH conjugates in microsomal incubations at about 3 times the rate of 4-hydroxytamoxifen, although no conjugates were detected with MCF-7 cells. Finally, these data suggest that quinone methide formation may not make a significant contribution to the cytotoxic and genotoxic effects of tamoxifen and toremifene.

Sol-gel-processed sintered silica xerogel as a carrier in controlled drug delivery.

Sol-gel-processed sintered silica xerogel was studied as a controllable, dissolvable, implantable material. The erosion of the matrix and the release of the preadsorbed drug toremifene citrate was investigated both in vitro and in vivo using mice. In an in vitro dissolution study, 50 to 60% of the drug was released after 24 h, according to the square root of time kinetics, and the weight loss of the silica was 24 wt %. Silica xerogel with tritium-labeled toremifene was implanted subcutaneously in mice for 56 days. To determine the amount of tritiated drug remaining in the silica disks at the implantation site, the disks were excised periodically and the radioactivity measured. About 40% of the radioactivity was released during the first 4 days and all of it within 28 days. Radioactivity also was measured in the liver, lungs, kidneys, uterus, and blood. The radioactivity reached a maximum level after 4 days in the liver, kidneys, and lungs and slowly decreased until all of the drug had been released from the matrix after 28 days. After release of the drug (28 days) the amount of remaining silica xerogel implant was 45 wt %, and at the end of the study (56 days) it was 24 wt %. In the histopathological study, sintered silica xerogel did not show any tissue toxicity at the site of the implantation, in the liver, or in the kidneys. It was concluded that sintered silica xerogel is a biocompatible and controllably resorbable material and therefore is a promising matrix for use in the sustained delivery of drugs.

Intratumoral toremifene therapy and tissue distribution in the baboon.

The purpose of the present study was to evaluate the tissue distribution of toremifene (TOR) in baboons following intra-tissue injections and to examine the effectiveness of intratumoral TOR therapy of baboons with various spontaneous neoplasms. Five healthy baboons (Papio sp.) were used to examine the distribution of TOR following intra-tissue injections. Twenty-three different tissue specimens were collected for HPLC analysis. In addition, four baboons with various spontaneous neoplasms (myxoma, squamous cell carcinoma, lymphosarcoma and adenocarcinoma) were treated with intratumoral TOR and their responses were evaluated. Tissue TOR distribution was also examined in these animals. In the tissue distribution study, target tissue/serum TOR concentration ratios ranged from 138 to 8873 and the target tissue/other tissue ratios ranged from 1.2 to 2428. The distribution of TOR was very favorable, with the highest concentrations outside the injection sites noted in adjacent organs. A marked response was observed in the myxoma and partial responses were observed in the other three cases. Drug level analysis data from these four animals revealed tissue concentrations similar to those seen in the TOR tissue distribution study. Intratumoral administration of TOR can achieve effective local tumor and tissue concentrations, while systemic distribution via circulation to other organs is limited.

Toremifene in postmenopausal breast cancer. Efficacy, safety and cost.

Toremifene is a chlorinated tamoxifen analogue that is indicated for the treatment of postmenopausal hormone-dependent breast cancer. It competes with estradiol for estrogen receptors and has growth-inhibitory effects on MCF-7 breast cancer cells. At concentrations < 10(-6) mol/L, this growth inhibition can be reversed by estradiol, but at higher concentrations toremifene is cytotoxic. In dimethylbenzanthracene (DMBA)-induced mammary cancer in rats, toremifene has been shown to decrease the number of new tumours and to inhibit the growth of existing tumours. Toremifene causes growth inhibition by suppressing mitosis and inducing apoptosis. The mechanism by which these events occur may involve the induction of transforming growth factor-beta 1 and inhibition of insulin-like growth factor-1 (mecasermin). Toremifene is primarily an antiestrogen, but it has some estrogen agonist properties in postmenopausal women. The latter are reflected by the fall in luteinising hormone and follicle-stimulating hormone levels and the rise in sex hormone-binding globulin levels that are associated with its use in most women. After estrogen priming, toremifene 68mg administered orally has been found to exert a similar antiestrogenic effect on the vaginal epithelium in postmenopausal women as tamoxifen 60mg. The half-life of toremifene in plasma is 5 days, and the drug is > 99% bound to plasma proteins. The main metabolites of toremifene are N-demethyl-toremifene and deaminohydroxy-toremifene. Altered liver, but not kidney, function affects the pharmacokinetics of toremifene. Toremifene 60mg daily is as effective as tamoxifen 20mg daily in the treatment of postmenopausal hormone-dependent breast cancer, producing a response in about 50% of patients. Soft tissue and visceral metastases respond better to toremifene than bone metastases. Most of the adverse effects of toremifene are related to its activity at estrogen receptors and include hot flashes, vaginal discharge and nausea. Although toremifene decreases antithrombin III levels slightly, the incidence of thromboembolic complications is low. Thus far, no carcinogenic effects have been noted in humans, and preclinical data are mostly reassuring. Toremifene has favourable effects on serum lipids, and thus has potential in preventing coronary heart disease. Although toremifene is somewhat more expensive to use than tamoxifen, toremifene is an effective and well tolerated alternative to tamoxifen in the treatment of postmenopausal women with hormone-dependent breast cancer. No formal pharmacoeconomic comparisons of toremifene and tamoxifen have yet been published. Toremifene is potentially safer than tamoxifen in relation to carcinogenic effects and effects on serum lipids.

Toremifene. A review of its pharmacological properties and clinical efficacy in the management of advanced breast cancer.

The triphenylethylene antiestrogen toremifene is a chlorinated derivative of the antiestrogen tamoxifen, an agent which has been widely and successfully used in the treatment of breast cancer. Clinical trials investigating the efficacy of toremifene as first-line endocrine therapy in postmenopausal women with advanced breast cancer (estrogen receptor status positive or unknown) have shown this drug to have similar antitumour activity to that of tamoxifen. In multicentre comparative trials, objective responses (complete and partial) occurred in 20 to 29% of patients treated with toremifene (60 to 240 mg/day) and in 19 to 37.5% of tamoxifen (20 or 40 mg/day) recipients. The duration of response, time to disease progression and median overall survival time were generally similar in both treatment groups. Toremifene is well tolerated. Most drug-related adverse effects are mild or moderate in severity and rarely necessitate discontinuation of therapy. The tolerability profile of toremifene is similar to that reported for tamoxifen, the most common adverse effects being hot flushes, sweating, nausea and/or vomiting, dizziness, oedema, and vaginal discharge and/or bleeding. Thus, toremifene provides an equally effective and well tolerated alternative to tamoxifen for the first-line endocrine therapy of postmenopausal advanced breast cancer. Preclinical studies showing toremifene to have a lower carcinogenic potential than tamoxifen indicate that toremifene may be a preferable agent for long term treatment regimens; however, these findings require confirmation in the clinical setting.

Influence of age on toremifene pharmacokinetics.

Toremifene pharmacokinetics were compared in ten healthy young men (< 33 years) and elderly women (< 65 years). A single oral 120-mg dose of toremifene was given after an overnight fast and blood samples were collected over 28 days. Serum levels of the parent drug and the metabolites were determined; appropriate pharmacokinetic parameters were calculated and statistically evaluated. Toremifene peak concentrations (average 640 ng/ml) were achieved at 3.5 h. The area under the curve (AUC) and the apparent oral clearance were comparable in the young and elderly subjects. The half-life was prolonged (4.2 versus 7.2 days) and the apparent volume of distribution was increased (457 versus 627 1) in the elderly. The peak concentration of the main metabolite N-demethyltoremifene was lower (159 versus 233 ng/ml) and the half-life was prolonged (8.3 versus 19.1 days) in the elderly subjects, but the AUC values were comparable. The results suggest that toremifene is distributed more widely in the elderly but that its clearance is unaffected by age. It is concluded that the dosage requirement of the drug is unlikely to differ between young and elderly subjects.