Crystalline Form Information from Multiwell Plate Salt Screening by Use of Raman Microscopy

PURPOSE

The purpose of this study was to establish a useful methodology, possibly providing information on the stoichiometry of pharmaceutical drug salts obtained from salt screening by using a multiwell plate and a Raman microscope.

METHODS

Tamoxifen salt screening was conducted with monobasic and polybasic acids on 96-well quartz plates with a Raman microscope. Appearance and crystalline forms of salts prepared on 96-well plates were observed by polarizing light microscope and Raman microscope, respectively. Based on the results of the salt screening, tamoxifen citrate and fumarate salts were prepared on a large scale. The salts prepared were characterized by powder X-ray diffractometry (PXRD) and ion chromatography.

RESULTS

The results of the multiwell salt screening indicated that tamoxifen has a tendency toward the formation of mono salt as opposed to hemi salt with polybasic acid, and that most of tamoxifen salts gave several potential polymorphic forms. PXRD patterns of scaled-up tamoxifen citrate and fumarate salts suggested that the same crystalline form was obtained from the binary mixture regardless of molar ratios of 2:1 or 1:1 (tamoxifen/acid). The crystalline forms obtained were tamoxifen monocitrate and monofumarate salts as measured by ion chromatography.

CONCLUSIONS

Salt screening on multiwell plates with a Raman microscope provided novel insight into the characteristics prediction of the stoichiometrical salts in addition to potential polymorph information. Based on the stoichiometrical information of salts, the amount of compound and time required for crystalline form selection of drug candidates would be significantly reduced.

New self-assembled nanogels based on host–guest interactions: Characterization and drug loading

We show here, for the first time, that two neutral polymers may completely associate together in water to spontaneously form supramolecular nanoassemblies (nanogels) of spherical shape. The cohesion of these stable structures of about 200 nm is based upon a "lock and key" mechanism: inclusion complexes are formed between the hydrophobic alkyl chains grafted on a polysaccharide (dextran) and the molecular cavities contained in a poly-cyclodextrin polymer. Production yields reached 95%. It was established that all the alkyl chains were included within the cyclodextrins' cavities in these nanoassemblies. The multivalent character of the interactions between the two polymers ensures the stability of the nanoassemblies. Moreover, empty cyclodextrin units remained accessible for the inclusion of compounds of interest such as benzophenon or tamoxifen.

Functional inhibition of intestinal and uterine muscles by non-permeant triphenylethylene derivatives

We have previously shown that the triphenylethylene antiestrogen tamoxifen reversibly inhibited spontaneous contractile activity in isolated duodenal muscle. Now, we have synthesized different quaternary ammonium salts of tamoxifen by changing the substituents on the nitrogen of the alkylaminoethoxy side-chain, to obtain plasma membrane impermeable compounds. Synthesized molecules were N-desmethyl-tamoxifen-hydrochloride, ethylbromide-tamoxifen and butylbromide-tamoxifen, which differed in the size of their ionic side-chain. All compounds rapidly and reversibly inhibited spontaneous and CaCl(2)-induced contractions in mouse duodenum and uterus. Dose-response analyses revealed a structure-activity relationship where the larger the side-chain the higher the inhibitory potency. Fourier analyses on triphenylethylene-relaxed duodenal tissues showed that harmonic components of contractile activity were readily recovered upon exposure to the L-type calcium channel agonist 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-pyridine-3-carboxilic acid methyl ester (BAY-K644). Likewise, BAY-K644 completely reversed triphenylethylene-induced effects on uterine tonic tension. Our experiments suggest that impermeant tamoxifen derivatives relax visceral smooth muscle through a membrane-mediated non-genomic mechanism that involves inhibition of L-type calcium channels.

Sterile, injectable cyclodextrin nanoparticles: effects of gamma irradiation and autoclaving

Sterility is required as stated by compendial requirements and registration authorities worldwide for an injectable drug carrier system. In this study, injectable nanospheres and nanocapsules prepared from amphiphilic beta-cyclodextrin, beta-CDC6, were assessed for their in vitro properties such as particle size distribution, zeta potential, nanoparticle yield (%), drug entrapment efficiency and in vitro drug release profiles. Different sterilization techniques such as gamma irradiation and autoclaving were evaluated for their feasibility regarding the maintenance of the above mentioned nanoparticle properties after sterilization. It was found that amount these techniques, sterilization with gamma irradiation seemed to be the most appropriate technique with no effect on particle size, drug loading and drug release properties. Gamma irradiation causes some chemical changes on beta-CDC6 observed as changes in zeta potential but this does not lead to any significant changes for nanoparticle properties. Autoclaving caused massive aggregation for the nanoparticles followed by precipitation, which led to the conclusion that excessive heat disrupted nanoparticle integrity. Sterile filtration was not feasible since nanoparticle sizes were larger than the filter pore size and the yield after sterilization was very low. Thus, it can be concluded that blank and drug loaded beta-CDC6 nanospheres and nanocapsules are capable of being sterilized by gamma irradiation.

Induction and inhibition of oocyte maturation by EDCs in zebrafish

BACKGROUND

Oocyte maturation in lower vertebrates is triggered by maturation-inducing hormone (MIH), which acts on unidentified receptors on the oocyte surface and induces the activation of maturation-promoting factor (MPF) in the oocyte cytoplasm. We previously described the induction of oocyte maturation in fish by an endocrine-disrupting chemical (EDC), diethylstilbestrol (DES), a nonsteroidal estrogen.

METHODS

In this study, stimulatory and inhibitory effects of EDCs and natural steroids on oocyte maturation were examined in zebrafish. For effective agents, some details about the mechanism in induction or inhibition of maturation were examined. Possible groups of DES interacting with the MIH receptor are discussed based on relative potency of steroids to induce maturation.

RESULTS

Among agents tested, tamoxifen (TAM) and its metabolite 4-hydroxytamoxifen (4-OHT) showed stimulatory activity similar to DES. The time courses of the change in germinal vesicle breakdown and an intracellular molecular event (the synthesis of cyclin B) induced by TAM were indistinguishable from those induced by MIH. In contrast, pentachlorophenol (PCP) had a potent inhibitory effect on MIH-induced oocyte maturation. PCP inhibited not only MIH-induced maturation but also DES- and TAM-induced maturation. Methoxychlor also inhibited maturation when oocytes were pre-treated with this agent.

CONCLUSION

These results suggest that EDCs act as agonists or antagonists in the induction of oocyte maturation in fish.

Light activated recombination

Many genes elicit their actions through their expression in precise spatial patterns in tissues. Photoregulated expression systems offer a means to remotely pattern gene expression in tissues. Using currently available photopatterning methods, gene expression is only transient. Herein is described a general method to permanently alter a cell's genome under the control of light. The photocaged estrogen receptor (ER) antagonists, nitroveratryl-hydroxytamoxifen (Nv-HTam) and nitroveratryl-hydroxytamoxifen aziridine (Nv-HTaz), mediate exposure-dependent recombination in cells expressing the Cre-ER, a fusion of the site-specific recombinase Cre and ER. Both Nv-HTam and Nv-HTaz only activate recombination by Cre-ER after exposure to light. When released only intracellularly, the covalent-modifying Taz can mediate significant amounts of recombination in an exposure-dependent manner. Nv-HTaz and Cre-ER represent perhaps the first compound that can be used to photopattern gene expression through recombination.

Ospemifene inhibits the growth of dimethylbenzanthracene-induced mammary tumors in Sencar mice

Ospemifene is a new selective estrogen receptor modulator (SERM) that is being developed for the treatment of urogenital atrophy and osteoporosis. Similarly to other SERMs, ospemifene exhibits antiestrogenic effects in breast tissue, which led to the hypothesis that it may be a potential breast cancer chemopreventive agent. We first assessed the ability of ospemifene, compared to tamoxifen and raloxifene, to prevent dimethylbenzanthracene (DMBA)-induced mammary tumors in female Sencar mice. Ospemifene (N = 18), tamoxifen (N = 20) and raloxifene (N = 17), each dosed at 50 mg/kg, were administered daily by oral gavage, in combination with 20 microg DMBA for the first 6 weeks. Control mice (N = 21) received vehicle plus DMBA only for the first 6 weeks. Daily treatment then continued for 37 weeks. As hypothesized, ospemifene greatly reduced the incidence of mammary carcinomas compared to control mice (p = 0.003), similar to tamoxifen (p = 0.0004); however, in the raloxifene group, no significant effect was seen in mammary tumor prevention (p = 0.20). A follow-up study comparing ospemifene (N = 20) to tamoxifen (N = 20) in the same model was then performed to confirm the results of the first study. The results of the follow-up study, which extended the treatment to 52 weeks, confirmed the results of our previous study, with ospemifene (p = 0.01) and tamoxifen (p = 0.004) significantly decreasing mammary carcinomas compared to controls. The results of these two studies suggest that women taking ospemifene for osteoporosis and/or urogenital atrophy may further benefit from ospemifene's breast cancer chemopreventive effects.

Structural insights into drug processing by human carboxylesterase 1: tamoxifen, mevastatin, and inhibition by benzil

Human carboxylesterase 1 (hCE1) exhibits broad substrate specificity and is involved in xenobiotic processing and endobiotic metabolism. We present and analyze crystal structures of hCE1 in complexes with the cholesterol-lowering drug mevastatin, the breast cancer drug tamoxifen, the fatty acyl ethyl ester (FAEE) analogue ethyl acetate, and the novel hCE1 inhibitor benzil. We find that mevastatin does not appear to be a substrate for hCE1, and instead acts as a partially non-competitive inhibitor of the enzyme. Similarly, we show that tamoxifen is a low micromolar, partially non-competitive inhibitor of hCE1. Further, we describe the structural basis for the inhibition of hCE1 by the nanomolar-affinity dione benzil, which acts by forming both covalent and non-covalent complexes with the enzyme. Our results provide detailed insights into the catalytic and non-catalytic processing of small molecules by hCE1, and suggest that the efficacy of clinical drugs may be modulated by targeted hCE1 inhibitors.

Preferential π–π complexation between tamoxifen and borage oil/γ linolenic acid: Transcutaneous delivery and NMR spectral modulation

The effect of different proportions of borage oil on the in vitro transcutaneous delivery of tamoxifen were studied, with the aim of developing a gel capable of the simultaneous delivery of tamoxifen and gamma linolenic acid across (breast) skin. Supplementary work probed 1H NMR spectral data for tamoxifen in the presence of different proportions of polyunsaturated or unsaturated fatty acids. Typical, non-aqueous gels were modified to contain 1% tamoxifen and three levels of borage oil ( approximately 25% gamma linolenic acid) and the transcutaneous delivery of both tamoxifen and GLA across full thickness skin determined in vitro. Both tamoxifen and gamma linolenic acid permeated the skin with the ratio of moles being consistent at approximately 4:1. This was irrespective of time, amount of borage oil contained in the formulation (above a minimum) and the presence of other (unsaturated) excipients: mineral oil, Miglyiol 810N, white soft paraffin, PEG400 and Cabosil M5. Dose-dependent downfield shifts of tamoxifen aromatic protons were observed in the presence of borage oil and linolenic acid (gamma and alpha), but not saturated triacyl glycerol. The permeation data suggested vehicular complexation between tamoxifen and polyunsaturated constituents of borage oil and that such complexes permeated the skin intact. The 1H NMR data supported the hypothesis that such complexation was a consequence of preferential pi-pi orbital interactions between the phenyl groups of tamoxifen and the multiple double bonds of GLA. The mechanism for the permeation of intact complexes across skin remains to be elucidated.

Formation of tamoxifen-DNA adducts via O-sulfonation, not O-acetylation, of alpha-hydroxytamoxifen in rat and human livers

Tamoxifen (TAM) is used as the standard endocrine therapy for breast cancer patients and as a chemopreventive agent for women at high risk for this disease. Unfortunately, treatment of TAM increases the incidence of endometrial cancer; this may be due to the genotoxic damage induced by TAM metabolites. Formation of TAM-DNA adducts in rat liver correlates with the development of hepatocarcinoma. TAM-DNA adducts are proposed to be formed through O-sulfonation and/or O-acetylation of alpha-hydroxylated TAM and its metabolites. However, the role of O-sulfonation and O-acetylation in the formation of TAM-DNA adducts has not been extensively investigated. Rat or human hydroxysteroid sulfotransferases (HST), acetyltransferases, and liver cytosol were incubated with calf thymus DNA, alpha-OHTAM, and either 3'-phosphoadenosine 5'-phosphosulfate (PAPS) or acetyl coenzyme A (acetyl-CoA) as a cofactor and analyzed for TAM-DNA adduct formation, using 32P postlableling/polyacrylamide gel electrophoresis analysis. TAM-DNA adduct was formed when PAPS, not acetyl-CoA, was used. No TAM-DNA adducts were produced using human N-acetyltransferase I and II. HST antibody inhibited approximately 90% of TAM-DNA adduct formation generated by the cytosol or HST, suggesting that HST is primarily involved in the formation of TAM-DNA adducts. The formation of TAM-DNA adducts with rat liver cytosol and HST was much higher than that of human liver cytosol and HST. Our results indicate that TAM-DNA adducts are formed via O-sulfonation, not O-acetylation, of alpha-hydroxylated TAM and its metabolites.

Determination of tamoxifen--DNA adducts in leukocytes from breast cancer patients treated with tamoxifen

Tamoxifen (TAM), a widely used antiestrogen for breast cancer therapy and chemoprevention, increases the incidence of endometrial cancer in women. The formation of DNA adducts induced by tamoxifen may initiate endometrial cancer. To evaluate the genotoxic risk of TAM, the formation of DNA adducts in leukocytes was examined. Blood samples were collected from 47 breast cancer patients (61.7 +/- 12.5 years) taking TAM (20 mg/day; average duration until sampling, approximately 37 months) and 20 untreated patients (58.2 +/- 12.3 years), and their leukocyte DNA was analyzed by 32P-postlabeling/HPLC analysis. This assay resolves synthetic standards, trans- and cis-diastereoisomers of alpha-(N2-deoxyguanosinyl)tamoxifen 3'-monophosphate (dG3'P-N2-TAM), alpha-(N2-deoxyguanosinyl)-N-desmethyltamoxifen 3'-monophosphate (dG3'P-N2-N-dMeTAM), and alpha-(N2-deoxyguanosinyl)tamoxifen N-oxide 3'-monophosphate', and is capable of determining TAM adducts quantitatively. The detection limit of this assay is 0.6 adducts/10(9) nucleotides. trans-dG3'P-N2-TAM (fr-2; one of the two trans-isomers) was detected in six of 47 breast cancer patients treated with TAM. Among them, trans-dG(3'P-N2-N-dMeTAM (fr-2) was also detected in two patients. The total amounts of TAM-DNA adducts in the positive patients were 2.6 +/- 3.0 adducts/10(9) nucleotides. No adducts were detected in the controls. The presence of TAM-DNA adducts in the leukocyte DNA samples was confirmed using several 32P-postlabeling/HPLC systems.

Tamoxifen citrate loaded amphiphilic β-cyclodextrin nanoparticles: In vitro characterization and cytotoxicity

Nanospheres and nanocapsules of beta-CDC6, amphiphilic beta-cyclodextrin modified on the secondary face with 6C aliphatic esters, were prepared with nanoprecipitation technique directly from inclusion complexes of tamoxifen citrate and beta-CDC6 (1:1 molar ratio). Blank and loaded nanospheres and nanocapsules were characterized by particle size distribution, zeta potential, drug loading and in vitro drug release. Particle sizes were between 250 and 300 nm for different formulations of nanospheres and nanocapsules. Zeta potential which was around -18 mV for blank particles was reported to be between +12 and +15 mV for tamoxifen-loaded particles. Average entrapped drug quantity was found to be around 150 mug/mL for particles prepared from inclusion complexes and this is double the loading value for conventionally prepared particles. Pre-loaded formulations showed a significantly slower release profile extended up to 6 h while formulations loaded conventionally displayed rapid and complete release within an hour. Cytotoxic efficacy of tamoxifen citrate loaded nanospheres and nanocapsules was determined against MCF-7 cells and tamoxifen citrate incorporated in amphiphilic beta-cyclodextrin nanoparticles was found to be cytotoxic and effective against this cell line.

Cell cycle progression stimulated by tamoxifen-bound estrogen receptor-alpha and promoter-specific effects in breast cancer cells deficient in N-CoR and SMRT

Estrogen receptor alpha (ERalpha) mediates the effects of estrogens in breast cancer development and growth via transcriptional regulation of target genes. Tamoxifen can antagonize ERalpha activity and has been used in breast cancer therapy. Tamoxifen-bound ERalpha associates with nuclear receptor corepressor (N-CoR) and silencing mediator for retinoid and thyroid hormone receptors (SMRT) at certain target genes. Here we show the effects of reducing N-CoR and SMRT levels on the actions of estrogen and tamoxifen in breast cancer cells. Silencing both corepressors led to tamoxifen-stimulated cell cycle progression without activation of the ERalpha target genes c-myc, cyclin D1, or stromal cell-derived factor 1, which play a role in estrogen-induced proliferation. By contrast, expression of X-box binding protein 1 was markedly elevated in tamoxifen-treated cells in which N-CoR and SMRT had been silenced. The gain in cell cycle entry seen with tamoxifen when N-CoR and SMRT were silenced was dependent on ERalpha and not observed upon treatment with estradiol or epidermal growth factor. These results suggest that N-CoR and SMRT play an active role in preventing tamoxifen from stimulating proliferation in breast cancer cells through repression of a subset of target genes involved in ERalpha function and cell proliferation.

Selective Estrogen Receptor Modulators in the Ruthenocene Series. Synthesis and Biological Behavior

A series of ruthenocene derivatives, 1-[4-(O(CH(2))(n)()N(CH(3))(2))phenyl]-1-(4-hydroxyphenyl)-2-ruthenocenylbut-1-ene, with n = 2-5, based on the structure of the breast cancer drug tamoxifen has been prepared. These compounds were obtained, via a McMurry cross-coupling reaction, as a mixture of Z and E isomers that could not be separated by HPLC. The relative binding affinity values for estrogen receptor alpha (ERalpha) for n = 2 and 3 were very high (85 and 53%) and surpassed even that of hydroxytamoxifen (38.5%), the active metabolite of tamoxifen. Ruthenocene derivatives act as anti-estrogens as effective (n = 2) or slightly more effective (n = 3-5) than hydroxytamoxifen on ERalpha-positive breast cancer cell lines but, unlike ferrocifens, do not show antiproliferative effects on ERalpha-negative breast cancer cell lines. Electrochemical studies showed that the ruthenocifen radical cations are unstable, which may account for this behavior. Some of these compounds could be useful as radiopharmaceuticals for ERalpha-positive breast cancer tumors.

Hepatic DNA adduct dosimetry in rats fed tamoxifen: a comparison of methods

Liver homogenates from rats fed tamoxifen (TAM) in the diet were shared among four different laboratories. TAM-DNA adducts were assayed by high pressure liquid chromatography-electrospray tandem mass spectrometry (HPLC-ES-MS/MS), TAM-DNA chemiluminescence immunoassay (TAM-DNA CIA), and (32)P-postlabeling with either thin layer ((32)P-P-TLC) or liquid chromatography ((32)P-P-HPLC) separation. In the first study, rats were fed a diet containing 500 p.p.m. TAM for 2 months, and the values for measurements of the (E)-alpha-(deoxyguanosin-N(2)-yl)-tamoxifen (dG-N(2)-TAM) adduct in replicate rat livers varied by 3.5-fold when quantified using 'in house' TAM-DNA standards, or other approaches where appropriate. In the second study, rats were fed 0, 50, 250 or 500 p.p.m. TAM for 2 months, and TAM-DNA values were quantified using both 'in house' approaches as well as a newly synthesized [N-methyl-(3)H]TAM-DNA standard that was shared among all the participating groups. In the second study, the total TAM-DNA adduct values varied by 2-fold, while values for the dG-N(2)-TAM varied by 2.5-fold. Ratios of dG-N(2)-TAM:(E)-alpha-(deoxyguanosin-N(2)-yl)-N-desmethyltamoxifen (dG-N(2)-N-desmethyl-TAM) in the second study were approximately 1:1 over the range of doses examined. The study demonstrated a remarkably good agreement for TAM-DNA adduct measurements among the diverse methods employed.

Lead identification of a potent benzopyranone selective estrogen receptor modulator

Starting from a phenol screening hit (6), three series of benzopyranone selective estrogen receptor modulators (SERMs) have been designed, synthesized, and analyzed for both estrogen receptor alpha binding affinity and in vitro activity in two cell assays. The lead compound identified, SP500263 (13), was more potent than raloxifene and tamoxifen in a cell-based assay measuring inhibition of interleukin-6 release.

Multiple targeting by the antitumor drug tamoxifen: a structure-activity study

Tamoxifen is a well-known antiestrogen used for the hormonotherapy of estrogen receptor positive breast cancer. In addition to its high affinity binding to the estrogen receptor (ER), tamoxifen binds with comparable affinity to the microsomal antiestrogen binding site (AEBS), and inhibits with a micromolar efficiency, protein kinase C (PKC), calmodulin (CaM)-dependent enzymes and Acyl CoenzymeA: Cholesterol Acyl Transferase (ACAT). Each of these tamoxifen targets might explain the genomic as well as non-genomic effects of tamoxifen. In this review, we will report current knowledge about the structural features of tamoxifen involved in this multiple targeting. These data provide a useful guide for the conception of selective ligands of ERs, AEBS, PKC, CaM or ACAT based on the chemical structure of tamoxifen.

Use of molecule imprinting-chemiluminescence method for the determination of tamoxifen in breast cancer sufferers' urine

The reaction between soluble Mn(IV) and tamoxifen can produce chemiluminescence and formaldehyde can enhance this chemiluminescence reaction. A tamoxifen molecular imprinted polymer (MIP) was synthesized and its adsorption selectivity to tamoxifen in aqueous solution was evaluated. Using a synthesized tamoxifen MIP as the recognition material and a soluble Mn(IV)-formaldehyde-tamoxifen chemiluminesence system as the detection system, a new molecule imprinting-chemiluminesence method of determination of tamoxifen was established. The response range of this method was 1.0 x 10(-7)-6.0 x 10(-6) g/mL, with a linear correlation coefficient of 0.997. The detection limit was 4 x 10(-8) g/mL. The relative standard deviation for 5.0 x 10(-7) g/mL tamoxifen solution was 4.1% (n = 9).

Compounds Structurally Related to Tamoxifen as Openers of Large-Conductance Calcium-Activated K+ Channel

We found that a variety of compounds containing partial structures of tamoxifen showed activity as chemical modulators of large-conductance calcium-activated K+ channels (BK channels).

Characterization of drug interactions with soluble beta-cyclodextrin by high-performance affinity chromatography

This study examined the use of an immobilized human serum albumin (HSA) column to study solution-phase reactions between drugs and beta-cyclodextrin (beta-CD). Chromatographic equations were developed to characterize the binding of chemicals to a soluble ligand (beta-CD) in the presence of an independent immobilized ligand (HSA). Situations considered included the presence of both a homogeneous and heterogeneous immobilized ligand, as well as complex interactions between the chemical of interest and soluble ligand. Three drugs (warfarin, tamoxifen, and phenytoin) were examined by this approach. This method involved injecting a small amount of each drug onto an HSA column in the presence of various concentrations of beta-CD in the mobile phase. By measuring the change in the drug's retention factor as the concentration of beta-CD was varied, it was possible to determine the stability constant between the injected drug and beta-CD. With this approach, warfarin and beta-CD were found to have 1:1 interactions with a stability constant of 5.2 x 10(2) M(-1) at 37 degrees C and pH 7.4, a result in close agreement with previous literature values. Tamoxifen and phenytoin were also found to have 1:1 interactions with beta-CD and had stability constants of 0.9-1.2 x 10(4) and 6-9 x 10(2) M(-1) respectively. With these latter solutes, the effects of secondary binding to the chromatographic support had to be considered. The theory and methods described in this report are not limited to these drugs and beta-CD but can be applied to other analytes and soluble ligands.

Tamoxifen-loaded polymeric micelles: preparation, physico-chemical characterization and in vitro evaluation studies

Several samples of polymeric micelles, formed by amphiphilic derivatives of PHEA, obtained by grafting into polymeric backbone of PEGs and/or hexadecylamine groups (PHEA-PEG-C(16) and PHEA-C(16)) and containing different amount of Tamoxifen, were prepared. All Tamoxifen-loaded polymeric micelles showed to increase drug water solubility. TEM studies provided evidence of the formation of supramolecular core/shell architectures containing drug, in the nanoscopic range and with spherical shape. Samples with different amount of encapsulated Tamoxifen were subjected to in vitro cytotoxic studies in order to evaluate the effect of Tamoxifen micellization on cell growth inhibition. All samples of Tamoxifen-loaded polymeric micelles showed a significantly higher antiproliferative activity in comparison with free drug, probably attributable to fluidification of cellular membranes, caused by amphiphilic copolymers, that allows a higher penetration of the drug into tumoral cells. To gain preliminary information about the potential use of prepared micelles as Tamoxifen drug delivery systems, studies evaluating drug release ability of micelle systems in media mimicking biological fluids (buffer solutions at pH 7.4 and 5.5) and in human plasma were carried out. These studies, performed evaluating the amount of Tamoxifen that remains in solution as a function of time, showed that at pH 7.4, as well as in plasma, PHEA-C(16) polymeric micelles were able to release lower drug amounts than PHEA-PEG(5000)-C(16) ones, while at pH 5.5, the behavior difference between two kind of micelles was less pronounced.

Kinetic studies of the radical-scavenging activity of estrogens and antiestrogens

Quinoids, quinoid radicals and phenoxyl radicals formed from estrogens (estrone; diethylstilbestrol, DES) and antiestrogens (tamoxifen; toremifene) may be responsible for adverse effects such as carcinogenesis. The radical-scavenging activity of estrogens and antiestrogens was determined quantitatively by the induction period method for the polymerization of methyl methacrylate initiated by thermal decomposition of 2,2'-azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) under nearly anaerobic conditions. The inhibition rate constant (k(inh), x10(-3) M(-1)s(-1)) for estrone, DES, tamoxifen, toremifene and 2,6-di-t-butyl-4-methyphenol (BHT) was 1-3, 2-4, 6-12, 6-13 and 1-2, respectively. The k(inh) for antiestrogens was two-fold greater than that for estrogens or BHT. In contrast, the stoichiometric factor (n, number of free radicals trapped by one mole of antioxidant moiety) for estrone, DES, tamoxifen, toremifene and BHT was 1.2-1.5, 1.8-2.4, 0.5-0.9, 0.4- 0.5 and 1.5-1.9, respectively. The fully oxidized n values for estrone, DES and BHT would be 2, whereas that for antiestrogens would be 1. However, the n values for estrone and antiestrogens were markedly less than 2 and 1, respectively, suggesting a complex oxidation process resulting in the formation of quinoids, quinoid radicals and phenoxyl radicals during the induction period.

Identification of tamoxifen-induced coregulator interaction surfaces within the ligand-binding domain of estrogen receptors

Tamoxifen is a selective estrogen receptor (ER) modulator that is clinically used as an antagonist to treat estrogen-dependent breast cancers but displays unwanted agonistic effects in other tissues. Previous studies on ERalpha have delineated a role of the N-terminal activation function AF-1 in mediating the agonistic effects of tamoxifen, while the mechanisms for how ERbeta mediates tamoxifen action remain to be elucidated. As peptides can be used to detect distinct receptor conformations and binding surfaces for coactivators and corepressors, we attempted in this study to identify previously unrecognized peptides that interact specifically with ERs in the presence of tamoxifen. We identified two distinct peptides among others that are highly selective for tamoxifen-bound ERalpha or ERbeta. Domain mapping and mutation analysis suggest that these peptides recognize a novel tamoxifen-induced binding surface within the C-terminal ligand-binding domain that is distinct from the agonist-induced AF-2 surface. Peptide expression specifically inhibited transcriptional ER activity in response to tamoxifen, presumably by preventing the binding of endogenous coactivators. Moreover, tamoxifen-responsive and ER subtype-selective coactivators were engineered by replacing the LXXLL motifs in the coactivator TIF2 with either of the two peptides. Finally, our results indicate that related coactivators may act via the novel tamoxifen-induced binding surface, referred to as AF-T, allowing us to propose a revised model of tamoxifen agonism.

Requirements for transcriptional regulation by the orphan nuclear receptor ERRgamma

Estrogen-related receptor gamma (ERRgamma) is an orphan nuclear receptor lacking identified natural ligands. We have addressed the requirements for ERRgamma-mediated gene regulation. ERRgamma transactivates constitutively reporter genes driven by ERR response elements (ERREs) or estrogen response elements (EREs). The activation depends on an intact DNA-binding domain (DBD) and activation function-2 (AF2). ERRgamma-mediated transactivation is further enhanced by peroxisome proliferator-activated receptor coactivator-1. Interestingly, ligand-binding domain (LBD) mutations predicted to either enlarge or diminish the putative ligand-binding pocket have no effect on the transcriptional activity implying that ERRgamma activity does not depend on any ligands. Antiestrogens 4OH-tamoxifen (4OHT) and 4-hydroxytoremifene (4OHtor) inhibit the ability of ERR to transactivate ERRE and ERE reporters. In contrast, ERRgamma activates transcription at AP-1 sites in the presence of 4OHT and 4OHtor. Thus, the transcriptional activity of ERRgamma seems not to require ligand binding but is modulated by binding of certain small synthetic ligands.

Ospemifene Hormos

Hormos Medical is developing the selective estrogen receptor modulator ospemifene, for the potential treatment of postmenopausal osteoporosis and urogenital atrophy. By November 2003, Hormos had advanced the drug into phase II/III testing for both indications.

Simultaneous permeation of tamoxifen and γ linolenic acid across excised human skin. Further evidence of the permeation of solvated complexes

Tamoxifen is the hormonal treatment of choice in women who have hormone-dependent breast cancer and its efficacy in those women considered to have a high risk of developing breast cancer, has also been established. Gamma linolenic acid (GLA) has been shown to decrease the invasion of breast cancer and recent studies have demonstrated that GLA can enhance the oestrogen receptor down-regulation induced by tamoxifen. However, tamoxifen is associated with serious side-effects due mainly to systemic delivery, and targeted delivery of both tamoxifen and GLA would be highly beneficial. This work was a preliminary study for the development of a transcutaneous system to simultaneously deliver both tamoxifen and GLA directly to the breast. Full thickness human skin was dosed with 500 microl saturated solution of tamoxifen in borage oil (25% GLA) and the simultaneous permeation of the two actives determined. There was rapid flux with minimal lag time, the cumulative permeation at 24 h was 764.3 +/- 94.2 microg cm(-2) for GLA and 5.44 +/- 0.67 microg cm(-2) for tamoxifen: the latter being comparable to the amount of tamoxifen associated with cancerous breast tissue from a 20 mg oral dose. The ratio of GLA/tamoxifen permeated at different timepoints was quite consistent, both in terms of mass (mean 138, S.D. 15.1) and mols (mean 184, S.D. 20.3). It was determined that 2.5 molecules of GLA were associated with each molecule of tamoxifen in the permeation process, equating to a solvation cage of three molecules of triacylglycerol. This study has demonstrated the feasibility of administering simultaneously tamoxifen and GLA using borage oil as vehicle, which warrants further investigation as a novel topical two-component system in relation to or prophylaxis of those perceived at high risk of developing breast cancer. The study also provides further evidence of the permeation of solvated complexes across skin, rather than discrete penetrant molecules.

Design, Synthesis, and Biological Evaluation of Doxorubicin−Formaldehyde Conjugates Targeted to Breast Cancer Cells

The anthracycline antitumor drug doxorubicin (DOX) has been utilized for decades as a broad-spectrum chemotherapeutic. Recent literature evidence documents the role of formaldehyde in the cytotoxic mechanism, and anthracycline-formaldehyde conjugates possess substantially enhanced activity in vitro and in vivo. Targeting a doxorubicin-formaldehyde conjugate specifically to cancer cells may provide a more efficacious chemotherapeutic. The design and 11-step synthesis of doxorubicin-formaldehyde conjugates targeted to the estrogen receptor, which is commonly overexpressed in breast cancer cells, are reported. The formaldehyde is incorporated in a masked form as an N-Mannich linkage between doxorubicin and salicylamide. The salicylamide triggering molecule, previously developed to release the doxorubicin-formaldehyde active metabolite, is tethered via derivatized ethylene glycols to an E and Z mixture of 4-hydroxytamoxifen. The targeting group, E/Z-4-hydroxytamoxifen, was selected for its ability to tightly bind the estrogen receptor and antiestrogen binding sites. The targeted doxorubicin-formaldehyde conjugates' estrogen receptor binding and in vitro growth inhibition were evaluated as a function of tether length. The lead compound, DOX-TEG-TAM, bearing a triethylene glycol tether, binds the estrogen receptor with a binding affinity of 2.5% relative to E/Z-4-hydroxytamoxifen and inhibits the growth of four breast cancer cell lines with 4-fold up to 140-fold enhanced activity relative to doxorubicin.

Acid-Base Cosolvent Method for Determining Aqueous Permeability of Amiodarone, Itraconazole, Tamoxifen, Terfenadine and Other Very Insoluble Molecules

A high-throughput, UV-detection PAMPA (parallel artificial membrane permeability assay) cosolvent procedure is described, based on the use of 20% v/v acetonitrile in aqueous buffer. A training set of 32 drugs (17 bases, 13 acids, 2 ampholytes) was studied both in aqueous buffer and in cosolvent-buffer solutions. A procedure was devised, where intrinsic permeability values, log P(o)(COS), measured in cosolvent solution, are converted to values expected under cosolvent-free conditions, using an in silico model based on Abraham H-bond acidity (alpha) and basicity (beta) descriptors, developed with the Algorithm Builder computer program, to obtain aqueous intrinsic permeability values: log P(o)=0.738+0.885 log P(o)(COS)-1.262alpha+0.436beta, r(2)=0.97, q(2)=0.96, s=0.38, n=32, F=279. Five sparingly-soluble weak bases (solubility <1 microg/ml), which could not be characterized without cosolvent, had their aqueous intrinsic permeability, P(o), estimated: miconazole 0.32 cm/s; itraconazole 3.2 cm/s; amiodarone 13 cm/s; tamoxifen 28 cm/s; terfenadine 162 cm/s.

[Development of sustained release tablet of tamoxifen citrate and its in vitro release profile]

OBJECTIVE

To reduce the frequency of administration of tamoxifen citrate so as to improve its bioavailability and patients' compliance.

METHODS

HPMC(K4M) was employed as major retarded-release controller. The wetting granulation and directly compressing method was used to produce the sustained release tablet. Then the in vitro release profile was applied as main criteria to evaluate six formulations according to the variation of HPMC(K4M) amount. The concentration of tamoxifen citrate was measured by UV spectrometry. Finally the releasing characteristics of sustained release and conventional tablets were compared to clarify the sustained effect of the former.

RESULT

At 278 nm there was no interaction between tamoxifen citrate and the recipients so that it was adopted as the wavelength of determination. The recovery efficiency of this method ranged from 95%-105%. The final formulation could release 86.40% of its loading amount in 12 h and its releasing profile fitted the Zero-order equation well. The percentages of accumulative release in 1 h were 76.81% and 7.08% for sustained release tablet and conventional tablet respectively.

CONCLUSION

The sustained release tablet of tamoxifen citrate could demonstrate a continuous and stable releasing profile and last for over 12 h. It has significant retarded effect in comparison with the conventional one and could be a new choice of regimen in its clinical application.

Novel fluorescence based receptor binding assay method for receptors lacking ligand conjugates with preserved affinity: study on estrogen receptor alpha

In this study a novel general approach is presented that allows for a straightforward design of receptor binding assays. This principle of a receptor binding assay is applied to the estrogen receptor, which is important in the management of breast cancer and for the estimation of the estrogenic potency of chemicals in the environment. The inhibitory concentrations to reduce cell proliferation in 50% of controls for 17-beta-estradiol, 4-hydroxy tamoxifen, and tamoxifen are determined to be 61 nM, 33 nM, and 17 microM, respectively. The measurement time of the nanoparticle based immunoassay format is 3 s. The Z' factor, which is calculated to be 0.89, reflects the excellent assay performance.

Biotransformation of tamoxifen in a human endometrial explant culture model

Although long-term tamoxifen therapy is associated with increased risk of endometrial cancer, little is known about the ability of endometrial tissue to biotransform tamoxifen to potentially reactive intermediates, capable of forming DNA adducts. The present study examined whether explant cultures of human endometrium provide a suitable in vitro model to investigate the tissue-specific biotransformation of tamoxifen. Fresh human endometrial tissue, microscopically uninvolved in disease, was cut into 1 x 2-mm uniform explants and incubated with media containing either 25 or 100 microM tamoxifen in a 24-well plate. Metabolites were analyzed by reversed-phase HPLC using postcolumn, online, photochemical activation and fluorescence detection. Three metabolites, namely, alpha-hydroxytamoxifen, 4-hydroxytamoxifen, and N-desmethyltamoxifen were identified in culture medium and tissue lysates. N-desmethyltamoxifen was found to be the major metabolite in both tissue and media extracts of tamoxifen-exposed explants. Incubations of tamoxifen with recombinant human cytochrome P-450s (CYPs) found that CYP2C9 and CYP2D6 produced all three of the above tamoxifen metabolites, while CYP1A1 and CYP3A4 catalyzed the formation of alpha-hydroxytamoxifen and N-desmethyltamoxifen, and CYP1A2 and CYP1B1 only formed the alpha-hydroxy metabolite. CYP2D6 exhibited the greatest activity for the formation of all three tamoxifen metabolites. Western immunoblots of microsomes from human endometrium detected the presence of CYPs 2C9, 3A, 1A1 and 1B1 in fresh endometrium, while CYPs 2D6 and 1A2 were not detected. Immunohistochemical (IHC) analysis also confirmed the presence of CYPs 2C9, 3A and 1B1 in fresh human endometrium and in viable tissue cultured for 24 h with or without tamoxifen. Together, the results support the use of explant cultures of human endometrium as a suitable in vitro model to investigate the biotransformation of tamoxifen in this target tissue. In addition, the results support the role of CYPs 2C9, 3A, 1A1 and 1B1 in the biotransformation of tamoxifen, including the formation of the DNA reactive alpha-hydroxytamoxifen metabolite, in human endometrium.

Tamoxifen Is a Potent Inhibitor of Cholesterol Esterification and Prevents the Formation of Foam Cells

Tamoxifen is a selective estrogen receptor modulator (SERM) used for the treatment and prevention of breast cancer. Tamoxifen has been reported to protect against the progression of coronary artery diseases in human and different atherosclerosis animal models by blocking the appearance of the atheromatous plaque. However, the molecular mechanism of this effect remains unknown. Acyl-CoA:cholesterol acyl transferase (ACAT) catalyzes the biosynthesis of cholesteryl esters, which are the major lipids found in the atheromatous plaque. In this paper we have tested whether ACAT might be inhibited by tamoxifen. We show, using molecular modeling, that tamoxifen displays three-dimensional structural homology with Sah 58-035 (3-[decyldimethylsilyl]-N-[2-(4-methylphenyl)-1-phenylethyl]-propanamide), a prototypical inhibitor of ACAT. We report that tamoxifen inhibits ACAT in a concentration-dependent manner on rat liver microsomal extract. We show that the presence on estrogen receptor ligands of a backbone isosteric to the diphenyl ethane backbone of Sah 58-035 constitutes a pharmacophore for ACAT inhibition. More importantly, tamoxifen was able to inhibit ACAT on intact macrophages stimulated with acetylated low-density lipoproteins and blocked the formation of foam cells, a step that precedes the formation of the atheromatous plaque. This work constitutes the first evidence that tamoxifen is an inhibitor of ACAT and foam cell formation at therapeutic doses and that this may account for its atheroprotective action.

Synthesis, Biochemical Properties and Molecular Modelling Studies of Organometallic Specific Estrogen Receptor Modulators (SERMs), the Ferrocifens and Hydroxyferrocifens: Evidence for an Antiproliferative Effect of Hydroxyferrocifens on both Hormone-Dependent and Hormone-Independent Breast Cancer Cell Lines

A series of ferrocene derivatives based upon the structure of the antiestrogenic drug tamoxifen or of its active metabolite hydroxytamoxifen has been prepared and named by analogy ferrocifens and hydroxyferrocifens. This series includes 1-[4-(O(CH(2))(n)NMe(2))phenyl]-1-phenyl-2-ferrocenyl-but-1-ene and 1-[4-(-O(CH(2))(n)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene, with n=2, 3, 5 and 8, and 1-[4-(-O(CH(2))(2)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenylethene. Most of these molecules have been synthesised by McMurry cross-coupling of the appropriate ketones, except for the ethene complexes, which were prepared by a four-step reaction sequence starting from the ferrocenylacetic acid. All these compounds were obtained as mixtures of Z and E isomers. The isomers were separated in the cases of the ferrocenyl derivatives of tamoxifen and hydroxytamoxifen (n=2). No isomerisation of the Z and E isomers occurred in DMSO after one day, while a 50:50 mixture of the isomers was obtained within one hour in chloroform. The X-ray structure of (E)-1-[4-(-O(CH(2))(2)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene has been determined. The relative binding affinity (RBA) values of the hydroxyferrocifens for the estrogen receptor alpha (ERalpha) was good to moderate, with values decreasing progressively with the length of the basic chain. The RBA values found for the estrogen receptor beta (ERbeta) are equal to or slightly less than those found for the alpha form. The lipophilicity of the hydroxyferrocifens are superior to the values found for estradiol and increase with lengthening of the chain. The antiproliferative effects of the four hydroxyferrocifens with n=2, 3, 5 and 8 were studied on four breast cancer cell lines (MCF7, MDA-MB231, RTx6 and TD5) possessing different levels of ERalpha. On MCF7 cells containing high levels of ERalpha, hydroxyferrocifens behave as antiestrogens. At a molarity of 1 microM the effect is close to that of hydroxytamoxifen (used for reference) when n=2 or 5, more marked when n=3, and weaker when n=8. Ferrocene alone has no effect. For the MDA-MB231 cells, classed as a hormone-independent breast cancer cell line, on the other hand, the hydroxyferrocifens show remarkable antiproliferative behaviour while the hydroxytamoxifen is completely inactive. Hydroxyferrocifens therefore show the unique property of being active both on hormone-dependent and on hormone-independent breast cancer cell lines. The molecular modelling study provides some clues for understanding of the antagonist effect of these molecules, while an additional cytotoxic effect due to the vectorised ferrocenyl unit is revealed in some occasions.

Mechanisms governing the accumulation of estrogen receptor alpha in MCF-7 breast cancer cells treated with hydroxytamoxifen and related antiestrogens

This study aimed at a better understanding of estrogen receptor alpha (ER) up regulation induced by partial estrogen antagonists. Effect of treatment with hydroxytamoxifen (OH-Tam) on ER level in MCF-7 cells was investigated by an approach combining ER measurement (enzyme immunoassay) and morphological demonstration (immunofluorescence). Furthermore, the influence of drug exposure on the rates of ER synthesis and degradation was assessed by determining [35S]methionine incorporated into the receptor in different experimental conditions (measurement of synthesis or pulse-chase experiments). ER up regulation was already induced by a 1-h pulse treatment with OH-Tam, thus a continuous exposure was not required. This process appeared reversible (i.e. ER accumulation due to OH-Tam rapidly vanished upon subsequent exposure to 17beta-estradiol (E2) or the pure antiestrogen RU 58668). While OH-Tam did not affect the rate of [35S]methionine incorporation into ER, it clearly caused an impairment of ER degradation (pulse-chase experiments) indicating that up regulation results from a stabilization of the receptor associated with the maintenance of its synthesis. Various tamoxifen derivatives, as well as a few related partial antiestrogens, were compared on the basis of binding ability and propensity to induce ER up regulation. A close relationship was found between both properties. Structure-activity analysis revealed that the capacity of these compounds to induce ER up regulation is associated with characteristics of their aminoalkyle side-chain, similar to those required for antiestrogenicity.

Simple and Efficient Production of (Z)-4-Hydroxytamoxifen, a Potent Estrogen Receptor Modulator

A McMurry coupling reaction and selective crystallization were used to develop a simple and efficient two-step synthesis of (Z)-4-hydroxytamoxifen (2a). This compound is an active metabolite of tamoxifen, a selective estrogen receptor (ER) modulator widely used to treat breast cancer. The synthesis employed 1,1-bis(4-hydroxyphenyl)-2-phenylbut-1-ene (1) as a useful building block.

Tamoxifen might influence the affinity of LPL for heparin-sepharose

BACKGROUND

We previously reported that the tamoxifen treatment caused a decrease in lipoprotein lipase (LPL) activity and an increase in LPL mass. We hypothesized that tamoxifen may increase the quantity of inactive LPL.

METHODS

Lipoprotein lipase in post-heparin plasma usually exists in both monomeric and dimeric forms, which may be separated on a heparin-Sepharose column with different salt concentrations. Lipoprotein lipase in post-heparin plasma from postmenopausal patients with hypertriglyceridemia treated with or without tamoxifen was incubated with or without 4-hydroxy-tamoxifen (4-OHT), the monomers and dimers were separated on a heparin-Sepharose column and their masses were measured.

RESULTS

The masses of total LPL and dimeric LPL of tamoxifen-treated patients were significantly higher than those of control subjects. Monomeric LPL of tamoxifen-treated patients passed more slowly through the heparin-Sepharose column compared with that of control subjects. The ratio of monomeric LPL to dimeric LPL of tamoxifen-treated patients was 0.61, significantly lower than that of control subjects, which was 1.45 (p<0.01). In addition, monomeric LPL incubated with 4-OHT passed more slowly through the heparin-Sepharose column compared with that incubated without 4-OHT.

CONCLUSION

Tamoxifen influences the affinity of LPL for heparin.

Synthesis and investigation of alpha-hydroxy-N,N-didesmethyltamoxifen as a proximate carcinogen in the metabolic activation of tamoxifen

Tamoxifen is an adjuvant chemotherapeutic agent for the treatment of breast cancer and a chemoprotective agent for breast cancer prevention. Despite being beneficial in regard to breast cancer, tamoxifen is known to increase the risk of endometrial cancer and thromboembolic events in women; in addition, it induces liver tumors in rats and endometrial tumors in rats and mice. Tamoxifen and its metabolite, N-desmethyltamoxifen, are metabolically activated to DNA binding electrophiles through alpha-hydroxylation, followed by O-esterification, primarily via sulfation. In the present study, we have investigated whether a second desmethylated metabolite of tamoxifen, N,N-didesmethyltamoxifen, is also involved in the metabolic activation of this antiestrogen to a genotoxic species. Alpha-hydroxy-N,N-didesmethyltamoxifen was synthesized, further activated by sulfation, and then reacted with DNA. After enzymatic hydrolysis to deoxynucleosides, HPLC analysis indicated the formation of one major DNA adduct, which was characterized as (E)-alpha-(deoxyguanosin-N(2)-yl)-N,N-didesmethyltamoxifen. Using (32)P-postlabeling, in combination with HPLC, the same adduct was detected in liver DNA from rats treated intraperitoneally with alpha-hydroxy-N,N-didesmethyltamoxifen. In contrast, only a low extent of adduct formation could be found in rats administered N,N-didesmethyltamoxifen. These data indicate that although alpha-hydroxy-N,N-didesmethyltamoxifen can be converted to a genotoxin in rat liver, this pathway is a minor one in the metabolic activation of tamoxifen.

Enzyme-mediated precipitation of parent drugs from their phosphate prodrugs

Many oral phosphate prodrugs have failed to improve the rate or extent of absorption compared to their insoluble parent drugs. Rapid parent drug generation via intestinal alkaline phosphatase can result in supersaturated solutions, leading to parent drug precipitation. The purpose was to (1) investigate whether parent drugs can precipitate from prodrug solutions in presence of alkaline phosphatase; (2) determine whether induction times are influenced by (a) dephosphorylation rate, (b) parent drug supersaturation level, and (c) parent drug solubility. Induction times were determined from increases in optical densities after enzyme addition to prodrug solutions of TAT-59, fosphenytoin and estramustine phosphate. Apparent supersaturation ratios (sigma) were calculated from parent drug solubility at intestinal pH. Precipitation could be generated for all three prodrugs. Induction times decreased with increased enzyme activity and supersaturation level and were within gastrointestinal residence times for TAT-59 concentration>/=21microM (sigma>/=210). Induction times for fosphenytoin were less than the GI residence time (199min) for concentrations of approximately 352 microM (sigma=4.0). At approximately 475 microM (sigma=5.3) the induction times were less than 90min. For estramustine-phosphate, no precipitation was observed within GI residence times. Enzyme-mediated precipitation will depend on apparent supersaturation ratios, parent drug dose, solubility and solubilization by the prodrug.

Antioxidant inhibits tamoxifen-DNA adducts in endometrial explant culture

Fresh human endometrial explants were incubated for 24h at 37 degrees C with either tamoxifen (10-100 micro M) or the vehicle (0.1% ethanol). Three metabolites namely, alpha-hydroxytamoxifen, 4-hydroxytamoxifen, and N-desmethyltamoxifen were identified in the culture media. Tissue size was limited but DNA adducts formed by the alpha-hydroxytamoxifen pathway were detected using authentic alpha-(deoxyguanosyl-N(2)) tamoxifen standards. Relative DNA-adduct levels of 2.45, 1.12, and 0.44 per 10(6) nucleotides were detected following incubations with 100, 25, and 10 micro M tamoxifen, respectively. The concurrent exposure of the explants to 100 micro M tamoxifen with 1mM ascorbic acid reduced the level of alpha-hydroxytamoxifen substantially (68.9%). The formation of tamoxifen-DNA adducts detectable in the explants from the same specimens exposed to 100 micro M tamoxifen with 1mM ascorbic acid were also inhibited. These results support the role of oxidative biotransformation of tamoxifen in the subsequent formation of DNA adducts in this tissue.

Absorption rate limit considerations for oral phosphate prodrugs

PURPOSE

To evaluate the potential of phosphate ester prodrugs to significantly improve the absorptive flux of poorly soluble parent drugs.

METHODS

Absorptive transport studies of parent drugs and their prodrugs were carried out in Caco-2 cells. Prodrugs of parent drugs with variable aqueous solubilities were tested: Hydrocortisone-phosphate/Hydrocortisone, Fosphenytoin/phenytoin, TAT-59/DP-TAT-59, and Entacapone phosphate/Entacapone. Additional absorption studies were carried out in rats.

RESULTS

Absorptive fluxes of DP-TAT-59 and phenytoin increased 9.8 or 3.3-fold after dosing TAT-59 and 500 microM fosphenytoin, respectively. Hydrocortisone's flux did not increase with hydrocortisone-phosphate at 100 microM. Permeability of the highly lipophilic and protein bound compound, DP-TAT-59, was significantly increased with serosal albumin. No permeability increase was observed for the other drugs with albumin. Entacapone phosphate failed to improve the flux of entacapone compared to an entacapone solution, but the prodrug solution did yield higher entacapone plasma levels in rats when compared with an entacapone suspension.

CONCLUSION

Ideal phosphate prodrug candidates are characterized by high permeability and low solubility (BCS Class II drugs). For low dose BCS Class II drug candidates, however, no biopharmaceutical advantage may be gained. Phosphate prodrugs of parent drugs with limited permeability may fail. When screening highly lipophilic parent drugs transport studies should be done with albumin.

Myometrial effects of selective estrogen receptor modulators on estradiol-responsive gene expression are gene and cell-specific

We examined in vivo effects of selective estrogen receptor modulators (SERMs) 4-OH-tamoxifen (Tam), GW 5638 (GW) and EM-800 (EM) on myometrial gene expression. The uteri of ovariectomized ewes were infused with 10(-7)M of one SERM via indwelling catheters for 24h preceding hysterectomy. Half of the ewes in each SERM group received an intramuscular injection of 50 microg 17beta-estradiol (E2) 18 h prior to hysterectomy. Northern blot analysis and in situ hybridization demonstrated that E2 increased estrogen receptor (ER), progesterone receptor (PR) and cyclophilin (CYC) gene expression in the cells of both inner layer of myometrium (IM) and outer layer of myometrium (OM) as well as glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene expression in OM. Tam also increased ER mRNA levels in OM. EM appeared to increase ER gene expression, but antagonized E2's up-regulation of PR and CYC gene expression in both IM and OM. Tam and GW also antagonized E2 up-regulation of PR gene expression in OM but not IM. No SERM affected GAPDH gene expression with or without E2. Immunohistochemistry indicated that E2 increased nuclear ER and PR protein levels in both IM and OM. EM was unique in up-regulating ER protein levels, opposite to its effects in endometrial cells. All SERMs tested antagonized this increase in PR immunostaining preferentially in OM compared to the IM layer. These results illustrate gene and cell layer-specific effects of SERMs in sheep myometrium.

Endometrial effects of selective estrogen receptor modulators (SERMs) on estradiol-responsive gene expression are gene and cell-specific

Three selective estrogen receptor modulator (SERM) drugs which included 4-OH-tamoxifen (Tam), EM-800 (EM) and GW 5638 (GW) were investigated to determine their ability to inhibit estradiol-responsive gene expression in sheep endometrium. The uteri of ovariectomized ewes (10 ewes per SERM group) were infused with 10(-7)M SERMs for 24h prior to hysterectomy. Five ewes from each group received 50 microg 17beta-estradiol (E2) and the remaining five ewes received vehicle 18 h prior to hysterectomy. Northern blot analyses and in situ hybridization demonstrated that E2 treatment increased estrogen receptor (ER), progesterone receptor (PR), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and cyclophilin (CYC) mRNA levels in most endometrial cells examined. Tam and GW exhibited characteristics similar to E2 by increasing ER gene expression, but they antagonized the E2-induced increases in PR and CYC mRNA levels. EM acted as an E2-agonist of GAPDH gene expression, but antagonized the E2 up-regulation of ER, PR and CYC gene expression in most endometrial cells. Immunohistochemistry determined that EM decreased ER protein levels in the glandular epithelium, and the SERMs investigated antagonized increases in PR protein levels in endometrium. In conclusion, GW and EM exhibit fewer agonist effects than Tam on endometrial gene expression. EM demonstrated the greatest antagonism of E2-enhanced levels of ER, PR and CYC, likely due to the inhibition of ER gene expression at both mRNA and protein levels.

Quantification of tamoxifen DNA adducts using on-line sample preparation and HPLC-electrospray ionization tandem mass spectrometry

The nonsteroidal antiestrogen tamoxifen is used as an adjuvant chemotherapeutic agent for the treatment of all stages of hormone-dependent breast cancer and more recently as a chemopreventive agent in women with elevated risk of developing the disease. While clearly beneficial for the treatment of breast cancer, tamoxifen has been reported to increase the risk of endometrial cancer in women. Furthermore, it has been shown to be hepatocarcinogenic in rats. Tamoxifen is clearly genotoxic in rat liver, as indicated by the formation of DNA adducts; the occurrence of tamoxifen DNA adducts in human endometrial tissue is more controversial. The detection and quantitation of tamoxifen DNA adducts have relied primarily upon (32)P-postlabeling, with other techniques, such as immunoassays and accelerator mass spectrometry, being used to a much lesser extent. To expand the range of available analytical methodologies for quantifying tamoxifen DNA adducts, we have developed an assay using on-line sample preparation, coupled with HPLC and electrospray ionization tandem mass spectrometry (ES-MS/MS). alpha-Acetoxytamoxifen was reacted with salmon testis DNA at ratios between 0.1 ng and 1 mg alpha-acetoxytamoxifen per mg DNA. After enzymatic hydrolysis to nucleosides, the most highly modified DNA samples were analyzed by HPLC-UV, which indicated the presence of two adduct peaks in approximately a 1:4 ratio. The major adduct was isolated, rigorously characterized as (E)-alpha-(deoxyguanosin-N(2)-yl)tamoxifen, and quantified on the basis of its molar extinction coefficient. A similar reaction was conducted with [N(CD(3))(2)]-alpha-acetoxytamoxifen to prepare a deuterated adduct that could serve as an internal standard for ES-MS/MS. The limit of detection for the HPLC-ES-MS/MS method was approximately 5 adducts/10(9) nucleotides, with an intra- and interassay precision of 3% relative standard deviation. The method was validated over the range of 8-1 520,000 adducts/10(8) nucleotides using 100 microg samples of DNA modified in vitro. Analysis of liver DNA from female Sprague-Dawley rats treated by gavage with seven daily doses of 20 mg tamoxifen/kg body weight gave a value of 496 +/- 16 adducts/10(8) nucleotides for (E)-alpha-(deoxyguanosin-N(2)-yl)tamoxifen and 626 +/- 18 adducts/10(8) nucleotides for (E)-alpha-(deoxyguanosin-N(2)-yl)-N-desmethyltamoxifen. These data indicate that the HPLC-ES-MS/MS methodology has sufficient sensitivity and precision to be useful in the analysis of tamoxifen DNA adducts formed in vivo in experimental models and may be able to detect tamoxifen DNA adduct formation in human tissue samples.

Product ion spectral simplification using time-delayed fragment ion capture with tandem linear ion traps

A new technique to generate product ion spectra as the internal energy of a collisionally activated precursor ion evolves is described. The precursor ion is activated by acceleration into a mass-selective linear ion trap under conditions whereby some of the fragment ions formed are unstable within the trap. After a time delay the stability parameters of the ion trap are changed to allow capture of fragments that that were previously unstable. The result is a product ion spectrum that originates from precursor ions with a modified internal energy distribution. It is possible to follow the evolution of the precursor internal energy distribution for many milliseconds after admittance of the precursor ions into the linear ion trap. Time-delayed fragmentation product ion spectra typically display reduced sequential fragmentation products leading to spectra that are more easily interpreted. Several important experimental parameters important to time-delayed fragmentation have been identified and are discussed. The technique has applications for both small precursor ions and multiply charged peptides.

Synthesis and estrogen receptor affinity of a 4-hydroxytamoxifen-labeled ligand for diagnostic imaging

A 10-step synthesis of a novel 4-hydroxytamoxifen-DTPA ligand (HOTam-DTPA) is reported. Tamoxifen and its primary metabolite 4-hydroxytamoxifen are common estrogen receptor ligands. Consequently, tamoxifen has found utility as the targeting component of various diagnostic agents for selective imaging of estrogen receptor-rich tissue, specifically breast cancer. An L-aspartic acid-derived DTPA analogue was attached to the ethyl side chain of 4-hydroxy-tamoxifen using N,N'-dimethylethylenediamine as a hydrophilic linker. A competitve estrogen receptor binding assay using [3H]-17beta-estradiol was performed to determine the effect of the ethyl side chain modification on estrogen receptor affinity. The results show that while the relative affinity of HOTam-DTPA for the estrogen receptor is approximately 10-fold lower than that of tamoxifen, it still remains a potent ligand at relatively low concentrations.

Evidence for and role of the dimethylamino group in tamoxifen DNA intercalation in intact Chinese hamster V79 cells

The in vitro and in vivo genotoxicity of tamoxifen is well documented but the underlying mechanism of this genotoxicity is only poorly understood. Tamoxifen is known to form adducts with DNA and it has been suggested that DNA intercalation may facilitate this covalent interaction. However, the low aqueous solubility of tamoxifen has made it difficult to demonstrate DNA intercalation by standard physico-chemical methods. In the present paper, we have employed the Chinese hamster V79 cell-based assay for the detection of DNA intercalation and report that tamoxifen, indeed, appears to have DNA intercalative properties. A partial structure activity relationship evaluation suggests that the N-dimethyl group of tamoxifen enhances intercalation.

Metabolism of tamoxifen by recombinant human cytochrome P450 enzymes: formation of the 4-hydroxy, 4'-hydroxy and N-desmethyl metabolites and isomerization of trans-4-hydroxytamoxifen

The cytochrome P450 (P450)-mediated biotransformation of tamoxifen is important in determining both the clearance of the drug and its conversion to the active metabolite, trans-4-hydroxytamoxifen. Biotransformation by P450 forms expressed extrahepatically, such as in the breast and endometrium, may be particularly important in determining tissue-specific effects of tamoxifen. Moreover, tamoxifen may serve as a useful probe drug to examine the regioselectivity of different forms. Tamoxifen metabolism was investigated in vitro using recombinant human P450s. Forms CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7 were coexpressed in Escherichia coli with recombinant human NADPH-cytochrome P450 reductase. Bacterial membranes were harvested and incubated with tamoxifen or trans-4-hydroxytamoxifen under conditions supporting P450-mediated catalysis. CYP2D6 was the major catalyst of 4-hydroxylation at low tamoxifen concentrations (170 +/- 20 pmol/40 min/0.2 nmol P450 using 18 microM tamoxifen), but CYP2B6 showed significant activity at high substrate concentrations (28.1 +/- 0.8 and 3.1 +/- 0.5 nmol/120 min/0.2 nmol P450 for CYP2D6 and CYP2B6, respectively, using 250 microM tamoxifen). These two forms also catalyzed 4'-hydroxylation (13.0 +/- 1.9 and 1.4 +/- 0.1 nmol/120 min/0.2 nmol P450, respectively, for CYP2B6 and CYP2D6 at 250 microM tamoxifen; 0.51 +/- 0.08 pmol/40 min/0.2 nmol P450 for CYP2B6 at 18 microM tamoxifen). Tamoxifen N-demethylation was mediated by CYP2D6, 1A1, 1A2, and 3A4, at low substrate concentrations, with contributions by CYP1B1, 2C9, 2C19 and 3A5 at high concentrations. CYP1B1 was the principal catalyst of 4-hydroxytamoxifen trans-cis isomerization but CYP2B6 and CYP2C19 also contributed.