Effects of water content on physical and chemical stability of tablets containing an anticancer drug TAT-59

(E)-4-[1-[4-[2-(Dimethylamino)ethoxy]phenyl]-2-(4-isopropyl) phenyl]-1-butenyl]phenyl monophosphate (TAT-59) is a new drug for the treatment of breast cancer. Physical and chemical stability of a tablet consisting of TAT-59 powder and a few excipients (Formulated tablet), a tablet consisting of only TAT-59 powder (TAT-59 tablet) and TAT-59 powder itself was evaluated based on water content, tensile strength, porosity, the amount of TAT-59 and its hydrolysis product, DP-TAT-59. The water content of Formulated tablet increased with relative humidity (RH), whereas that of TAT-59 tablet and TAT-59 powder scarcely changed. The equilibrium water content of Formulated tablet was much greater than that of the TAT-59 tablet or TAT-59 powder due to adsorbed moisture by the excipients. The tensile strength and porosity of Formulated tablet decreased and increased linearly, respectively, with increasing water content. The degradation rate of TAT-59 decreased in the following order: Formulated tablet > TAT-59 tablet > TAT-59 powder. The relationship between equilibrium water content and degradation rate of the Formulated tablet was determined by the Carstensen equation, in which the interaction order between the drug and water content was 1.9, and the degradation of TAT-59 in Formulated tablet was related to water content. Thus, it was found that the degradation of TAT-59 was accelerated by compression and addition of excipients.

Point mutation of estrogen receptor (ER) in the ligand-binding domain changes the pharmacology of antiestrogens in ER-negative breast cancer cells stably expressing complementary DNAs for ER

The antiestrogen tamoxifen is used in the treatment of hormone-responsive breast cancer. However, therapeutic failure has frequently been observed in both patients and animal models after long term treatment. We have studied the effect of a point mutation that leads to the substitution of Val for Gly at codon 400 in the ligand-binding domain of the estrogen receptor (ER) on estrogenic and antiestrogenic activities of 4-hydroxytamoxifen (4-OHT) and its derivatives. Stable ER transfectants derived from MDA-MB-231 CL10A, an ER-negative breast cancer cell line, have been used in these studies. 4-OHT and its fixed ring derivatives showed more estrogen-like activity in ER transfectants than in MCF-7, an ER-positive breast cancer cell line. In this study, 4-OHT was a partial agonist of cell growth in the transfectant S30 cells, which express the wild-type ER. However, it was a full agonist in the mutant ER transfectant ML alpha 2H, which expressed ER with Val at codon 400. The increased estrogenic activity of 4-OHT in ML alpha 2H cells was not due to the preferential isomerization of trans 4-OHT to cis 4-OHT, since the nonisomerizable fixed ring trans 4-OHT was a partial agonist for cell growth in S30 cells and was a full agonist in ML alpha 2H cells. Transient transfection using a reporter plasmid containing an estrogen response element demonstrated that fixed ring trans 4-OHT had estrogenic activity in ML alpha 2H cells.(ABSTRACT TRUNCATED AT 250 WORDS)

A note on the conformational flexibility of the antiestrogenic drug tamoxifen: preferred conformations in the free state and bound to the protein calmodulin

The conformational properties of the antiestrogenic drug tamoxifen, a triphenylbut-1-ene derivative, have been studied using molecular mechanics. Four distinct conformers have been identified, and the energy barriers between them have been established. The orientation of the ethyl group substituent has been examined in particular, since the lowest-energy conformers have this group orientated 180 degrees away from its position in the crystal structures of tamoxifen and its derivatives. These differences have implications for the interactions of tamoxifen with the calcium-binding protein calmodulin; relevant results from a molecular-modelling study of this protein-drug complex are presented.

Structure of 1,1-dichloro-2-(4-methoxyphenyl)-2,3-diphenylcyclopropane

C22H18Cl2O, M(r) = 369.3, monoclinic, P2(1)/a, a = 16.585(1), b = 17.328(1), c = 13.192(3) A, beta = 107.443(8) degrees, V = 3616.8 A3, Z = 8, Dx = 1.356 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 3.2 cm-1, F(000) = 1536, T = 138 K, R = 0.039 for 5450 observed reflections. The structural features of the two independent molecules are quite similar except in the orientation of the methoxy group. The cyclopropane ring shows the expected bond-length asymmetry with C(2)-C(3) as the longest bond. The two cis-arranged phenyl rings adopt similar conformations as observed in diaryl-cyclopropanes, with one ring in the bisecting position and the other near the perpendicular position. The conformation of the third aryl ring is also near the perpendicular position. The overall conformation of the three aryl rings is different from the helical propeller conformation consistently observed in tamoxifen and all other known tri(tetra)aryl-vinyl systems.

The structural mimicry of membrane sterols by tamoxifen: evidence from cholesterol coefficients and molecular-modelling for its action as a membrane anti-oxidant and an anti-cancer agent

The anti-cancer drug tamoxifen is a potent inhibitor of lipid peroxidation induced by Fe(III)-ascorbate in ox-brain phospholipid liposomes. Similar anti-oxidant effects, but with varying potencies, are also shown by 4-hydroxy-tamoxifen, cholesterol, ergosterol and 17-beta-oestradiol. We now describe a computer-graphic fitting technique that demonstrates a structural similarity between the five compounds. In addition, we have quantified the differences (relative to cholesterol) between the anti-oxidant activities of the compounds in terms of a novel expression referred to here as the cholesterol coefficient (Cc) Finally, we discuss how the inhibitory effect of tamoxifen on lipid peroxidation may result from a membrane stabilization that is associated with a decrease in membrane fluidity. This action may be related to the anti-proliferative effect exerted by tamoxifen on cancer and fungal cells.

A three-dimensional molecular template for substrates of human cytochrome P450 involved in debrisoquine 4-hydroxylation

A three-dimensional molecular template has been generated for substrates of human debrisoquine 4-hydroxylase cytochrome P450 (CYP2D6). This template defines the stereochemical requirements for CYP2D6 substrates in terms of the volume occupied and positions of key atoms. The modelling was based on the X-ray crystallographic coordinates of the location of the attacked C5 atom of camphor in relation to the haem in cytochrome P450 cam. Interactive molecular graphics combined with energy calculations were used to identify allowed conformers to superpose known CYP2D6 substrates to yield a molecular template. This model takes into account the site of attack of the known substrates and the requirement for a protonated nitrogen atom to interact with an anion site of the protein. A nitrogen-anion distance of between 2.5 and 4.5 A was allowed for the interaction. The substrates modelled were cardiovascular drugs (debrisoquine, sparteine, guanoxan and perhexiline), beta-adrenergic blocking agents (bufuralol and propranolol), tricyclic anti-depressants (desipramine, amitriptyline and nortriptyline) and other miscellaneous compounds (phenformin, methoxy-amphetamine, codeine and dextromethorphan). The template generated in this manner was then used to determine the likelihood that certain other compounds were substrates for CYP2D6. A carcinogenic protein pyrolysate product, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), did not fit the template and is therefore unlikely to be activated by this enzyme. A potent carcinogen in tobacco smoke, 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), fitted the template but could not be modelled to form a favourable nitrogen-anion interaction. Experimental substrate competition studies also showed that NNK is unlikely to be a CYP2D6 substrate. It was also shown that the widely used drug for treatment of breast cancer, trans-1-(4-beta-dimethylaminoethoxyphenyl)-,2-diphenyl-1-ene (tamoxifen), did not fit the molecular template and is unlikely to be metabolized by CYP2D6. Coordinates of the template are available.

Studies on the activation of the oestrogen receptor bound to the anti-oestrogens 4-hydroxytamoxifen and ICI 164,384 by using three monoclonal antibodies

Three monoclonal antibodies, H222, H226 and D547, which provided evidence of the structural transformation and change in exposure of the functional domains of the oestrogen receptor from fetal guinea-pig uterus upon activation, were used to study the receptor bound to the anti-oestrogens 4-hydroxytamoxifen and ICI 164,384. No differences in the structure of non-activated 4-hydroxytamoxifen- and ICI 164,384-receptor complexes, as compared with the oestradiol-receptor complex, were detected by the three monoclonal antibodies. When heated at 28 degrees C, both anti-oestrogen-receptor complexes became capable of binding the D547 antibody, which reacts selectively with the activated receptor; however, this binding was lower than that of the oestradiol-receptor complex. The interaction with the H226 antibody showed that anti-oestrogens can induce receptor dimerization, but to a lesser extent than oestradiol. In addition, both anti-oestrogen-receptor complexes can bind to DNA-cellulose and are retained in nuclei from intact cells at 28 degrees C, but less efficiently than the oestradiol-receptor complex. On the other hand, the nuclear receptor seems to have a similar dimeric structure when bound to either anti-oestrogens or oestradiol, as detected by the three monoclonal antibodies. The data suggest that 4-hydroxytamoxifen and ICI 164,384 induce and impaired activation of the oestrogen receptor; this difference, although quantitative rather than qualitative, might be related to the partial agonistic action of these anti-oestrogens in the fetal guinea-pig uterus.

Structure-activity relationships of nonisomerizable derivatives of tamoxifen: importance of hydroxyl group and side chain positioning for biological activity

The antiestrogen tamoxifen [(Z)-1(p-beta-dimethylaminoethoxy-phenyl)-1,2-diphenylbut-1-ene] is an effective anticancer agent against estrogen receptor (ER)-positive breast cancer. The alkylaminoethane side chain is essential for antiestrogenic activity, but the potency of the antiestrogen can be increased by para hydroxylation of the phenyl ring on carbon 1 of but-1-ene. This compound, 4-hydroxytamoxifen, is a metabolite of tamoxifen and has a very high binding affinity for ER [J. Endocrinol. 75:305-316 (1977)] because the hydroxyl is located in the equivalent position as the 3-phenolic hydroxyl of 17 beta-estradiol. In this study, we have examined the relationship between the relative positions of the hydroxyl and the alkyl-aminoethane side chain and the pharmacological activity of the ligand. A fixed seven-membered ring derivative of the triphenylethylene was used to prevent isomerization. All compounds were tested, with and without 17 beta-estradiol, for their effects on the growth of estrogen-responsive T47D and MCF-7 human breast cancer cells in vitro. The growth of MDA-MB-231 ER-negative breast cancer cells was not affected by any of the compounds tested, at a concentration (1 microM) that had a profound estrogenic or antiestrogenic action in ER-positive cell lines. The relative binding affinity of the compounds was determined using rat uterine ER and was found to be consistent with the observed potencies in vitro. The compounds found to be antiestrogens in vitro were antiestrogenic against estradiol (0.08 micrograms daily) in the 3-day immature rat uterine weight test. All compounds were partial agonists in vivo. In general, the estrogenic and antiestrogenic results obtained in vivo were consistent with the potency estimates obtained with the breast cancer cells in vitro. The results of this extensive structure-activity relationship study demonstrate that the substitution for 4-hydroxytamoxifen appears to be optimal to produce a potent antiestrogen; all other substitutions produced either estrogenic compounds or less potent antiestrogens. The hydroxyl group appears to be critical to locate the alkyl aminoethoxy side chain in the correct position in the steroid-binding site to block estrogen action. Novel antiestrogens were identified that could have been predicted based upon earlier drug-receptor models for the ER.

Activity of various amphiphilic agents in reversing multidrug resistance of L 1210 cells

Several compounds (bamipine, chlorphenoxamine, estracyt, hycanthone, quinidine, quinine, tamoxifen, trifluoperazine and verapamil) have a common basic structure with the following features: lipophilic aromatic ring system; linked chain hydrophilic N-alkyl group. They are used medically for varying diseases. Their activity in reversing multidrug-resistance (MDR) with other compounds (diethylstilbestrol, beta-estradiol, methylbiguanide, methylpiperazine, testosterone) lacking one of these chemical features is compared. The in vitro test system we used was the nucleoside incorporation assay using parental L 1210 ascites tumor cells and a doxorubicin resistant subline, which expresses the MDR phenotype. The substances lacking one of these features were not effective in reversing the MDR whereas all other tested substances demonstrated modulating potential in the MDR resistant L 1210 cells.

Metabolism of the 4-iodo derivative of tamoxifen by isolated rat hepatocytes. Demonstration that the iodine atom reduces metabolic conversion and identification of four metabolites

The 4-iodo derivative of tamoxifen, which has been reported to possess improved oestrogen receptor affinity and effectiveness as an inhibitor of breast tumour cell growth in vitro, was metabolized by hepatocytes isolated from rats pretreated with phenobarbital four times more slowly than tamoxifen and there was very little formation of glucuronide conjugates. Four principal metabolites were isolated. Examination of mass spectra revealed desmethyl-4-iodotamoxifen, 4-iodotamoxifen N-oxide, and alpha-hydroxydesmethyl-4-iodotamoxifen (4-[4-[2-(methylamino)ethoxy]phenyl]-4-(4-iodophenyl)-3-phenyl-but-3- (Z)-en-2-ol). Their identification was confirmed by comparison with synthesized samples. The structure of the fourth metabolite, 4'-hydroxy-4-iodotamoxifen was revealed by 1H NMR spectroscopy. The iodophenyl moiety is thus retained in all the metabolites. The iodine atom not only blocks metabolism in its vicinity but also reduced the rate of side-chain demethylation and N-oxidation by three-fold. It can be predicted from this study that the presence of the iodine atom should give the compound a greater duration of action in vivo.

Structure-function relationships of hydroxylated metabolites of tamoxifen that control the proliferation of estrogen-responsive T47D breast cancer cells in vitro

Several hydroxylated derivatives of tamoxifen were tested for their effects on the growth of T47D human breast cancer cells in vitro. Compounds containing a fused seven-membered ring were used to prevent isomerization of the triphenyl-ethylenes at the double bond. This stable structure permitted the determination of the activity of the cis and trans forms of tamoxifen and the true activity of two of its metabolites, 4-hydroxytamoxifen and metabolite E. Estradiol stimulates the growth of T47D cells 3-4-fold over control after 6 days of treatment (EC50 = congruent to 3 x 10(-12) to 3 x 10(-11) M, depending upon the particular experiment). The fixed ring form of the trans isomer of tamoxifen is an antiestrogen, whereas the cis isomer is estrogenic. Fixed ring-trans-4-hydroxytamoxifen is a potent antiestrogen, and its cis isomer is a weak antiestrogen (IC50 congruent to 4 x 10(-8) to 2 x 10(-7) M). The fixed ring form of trans-metabolite E (tamoxifen without the dimethylaminoethane side chain) is only a weak partial estrogen agonist, whereas the fixed ring derivative of its cis isomer is a potent estrogen agonist (EC50 congruent to 4 x 10(-12) to 1 x 10(-11) M). These studies have determined the true biological activities of the hydroxylated derivatives of tamoxifen. This information will be valuable for the development of drug receptor models and will be particularly useful when the three-dimensional structure of the receptor complex is determined.

Specific high-performance liquid chromatographic analysis of tamoxifen and its major metabolites by "on-line" extraction and post-column photochemical reaction

A new and simplified high-performance liquid chromatographic (HPLC) method for the determination of the antiestrogenic drug tamoxifen (TAM) and its desmethylated and hydroxylated metabolites in human plasma is described. Specific and sensitive fluorescence detection is achieved by "on-line" photochemical conversion of the TAM structure to a highly fluorescent phenanthrene product using a newly developed post-column photoreactor included in the HPLC system. A highly selective chromatographic separation was established by using unmodified silica with aqueous mobile phase for separation, with the sample preparation step on a small CN-propyl pre-column, included in the HPLC system. Due to the high specificity of the separation and detection system, even small volumes of deproteinized plasma sample can be injected directly without prior sample extraction. The described method permits a very fast and reproducible determination of TAM and its two major metabolites in plasma on a routine basis, down to 100 pg ml-1 concentration.