Affinity of estradiol mustard for estrogen receptors and its enzymatic degradation in uterine and breast cancer cytosols

Endocrine effects of Trilostane: in vitro and in vivo studies

Trilostane (4-alpha-5-epoxy-17 beta-hydroxy-3-oxo-5-alpha-androstan-2-carbonitrile) is a modified steroidal molecule. In vitro and in vivo studies in rats have shown that it inhibits adrenal, ovarian and placental steroid synthesis. It seems to act by exerting a selective blockade on 3 beta-hydroxysteroid dehydrogenase. In this study, we investigated whether this molecule interacts with hormone receptors for estrogen, androgen or progesterone. We also tried to demonstrate the effect which Trilostane may have on cellular cultures of human mammary carcinoma (MCF-7 Evsa-T). We also studied hormonal modifications in a series of 12 patients treated with different doses of Trilostane, since this drug is supposed to inhibit the production by the adrenal glands of mineralocorticoids, of glucocorticoids and of the precursors of estrogens. Our results indicate that Trilostane does not react with any of the main hormonal sex steroid receptors, nor does it interfere with cultures of human mammary cancer cells either containing estrogen receptors and therefore allegedly hormone-dependent (MCF-7 line), or estrogen receptor-negative cells, presumably independent of hormonal manipulations (Evsa-T cell line). Finally, endocrine studies on postmenopausal women with advanced breast cancer show that Trilostane significantly reduces the plasma levels of estrone and of its major androgen precursor (androstenedione). However, the latter inhibition is no different from that exerted by hydrocortisone acetate administered alone at a dose of 40 mg/day. The results of clinical trials comparing hydrocortisone alone with hydrocortisone plus Trilostane are awaited.

Metabolism of tamoxifen by isolated rat hepatocytes. Identification of 1-[4-(2-hydroxyethoxy)phenyl]-1-(4-hydroxyphenyl)-2-phenyl-1-butene and the dependence of N-oxidation on oxygen availability

Metabolism of tamoxifen by rat hepatocytes and hydrolysis of the resulting polar metabolites corresponding to conjugates with beta-glucuronidase gave a major component which was identified as 1-[4-(2-hydroxyethoxy)phenyl]-1-(4-hydroxyphenyl)-2-phenyl-1-butene by comparison of mass spectral properties with those of synthetic material. This compound, which was not observed as a phase I metabolite, is believed to have been found previously in rat bile and in human faeces (metabolite F) but its structure had been incorrectly assigned. Its binding affinity for the estrogen receptor was greater than that of tamoxifen but less than that of 4-hydroxytamoxifen, and it possessed a corresponding degree of antitumour activity against the MCF-7 breast cancer cell line. By carrying out the hepatocyte incubation separately under oxygen and air, it has been shown that the N-oxidation of tamoxifen is favoured by a high concentration of oxygen during in vitro metabolism but that the rate of 4-hydroxylation is not dependent on oxygen availability.

Cytotoxic esters of 1,1-bis-(4-hydroxyphenyl)-2-phenyl-but-1-ene with selective antitumor activity against estrogen receptor-containing mammary tumors

Both hydroxy groups of 1,1-bis-(4-hydroxyphenyl)-2-phenyl-but-1-ene (1) were esterified with the beta-chloropropionate (2), beta-bromopropionate (3) and acrylate functions (4). Linkage of these cytotoxic moieties reduced the estrogen receptor affinities of these compounds, especially in the case of the beta-haloesters only slightly compared with the affinity of the unsubstituted carrier molecule 1. The estrogenic potencies of the derivatives 2-4 and of 1 were nearly identical. The alkylating activities increased in the order 2, 3, and 4. Because of their alkylating activities, all cytotoxic esters showed an irreversible mode of binding to the estrogen receptor. In vitro, 3 in particular, exerted better growth inhibition of the hormone-dependent MCF-7 cell line than of the hormone-independent MDA cell line. In vivo, all cytotoxic derivatives caused almost complete inhibition of the growth of the hormone-dependent MXT M3.2 mouse mammary tumor, whereas growth of the hormone-independent MXT-Ovex tumor was much less inhibited. In all tumor models, the antitumor effect of the cytotoxic esters was better than that of the unsubstituted carrier. Therefore, the antitumor activity of these esters could be due not only to their improved pharmacokinetic properties compared to 1, but also to a selective estrogen receptor-mediated cytotoxic action.

Competitive binding assay for estrogen receptor in monolayer culture: measure of receptor activation potency

MCF-7 cells were incubated with [3H]estradiol, unlabeled estradiol and various estrogens or antiestrogens to measure their relative binding affinity (whole-cell assay). Comparison of the values with those previously established on uterine cytosol with a DCC assay revealed a good parallelism for both steroid and diphenolic diethylstilbestrol based estrogens. On the contrary, in the whole-cell assay, antiestrogens and weak estrogens of the triphenyl- and gem-diphenylethylene categories always displayed low values which were in the order of magnitude found with weak steroid estrogens. This property was not due to a reduction of binding capacity, nor to the presence in some compounds of an ethoxyaminoalkyl side-chain (source of antiestrogenicity). In view of all these data, it was concluded that the present test would provide an estimate of the ability of a given compound to transform the receptor in a form which interacts with genomic sites involved in the regulation of "estrogenic-induced products" ("activation").

In vitro synergism between estrogens and cytotoxic agents

Two lines of research intending to achieve synergism between cytotoxic agents and estrogens for breast cancer treatment are pursued in our laboratory. According to a screening procedure we select cytotoxic-linked estrogens which bind to estrogen receptors and thereby would be specifically concentrated into the tumor cells. A mesylate derivative of estrone has emerged from our investigations. This compound displays a very strong binding affinity for the receptors and inhibits the growth of the receptor-positive MCF-7 breast cancer cell line. The lack of growth inhibition in the receptor-negative line Evsa-T indicates that it is devoid of major non-specific cytotoxicity. We attempt to enhance the vulnerability of the tumor cells by producing an estrogen-induced modification of their chromatin. The in vitro exposure of isolated uterine nuclei to uterine cytosol preincubated with estradiol increases their ability to bind [3H]actinomycin D. Identical results are obtained with MXT mouse mammary tumors. Experiments are in progress to settle whether these changes are associated with enhanced cell killing.

Synthesis and evaluation of novel N-substituted N'-(3-hydroxy-17-oxoestra-1,3,5(10)-trien-2- and -4-yl)thiourea derivatives for binding to the estrogen receptor and cytotoxic activity on MCF-7 cells

A novel series of estrone derivatives having a free 3-phenolic group with the 2- or 4-position substituted with a thiourea function was synthesized. None of the products showed significant binding to the estrogen receptor, and the cytotoxic activity on MCF-7 cells for VII and X was weak.