Estrogen receptors interaction with Estracyt and degradation products, a biochemical study on a potential agent in the treatment of breast cancer

Chlorocarbamate-mustard-linked 1,1,2-triphenylbut-1-enes with a selective antitumor activity on mammary tumors containing estrogen receptors

A 1,1,2-triphenylbut-1-ene with a 4-OH group at one C-1 phenyl ring and a chlorocarbamate mustard moiety at the second C-1 ring (compound 3) was synthesized in order to obtain a "cytotoxic estrogen" with a specific antitumor effect on estrogen-receptor-containing tumors. This compound was tested in comparison to the carrier (compound 1) and a compound (2) having a carbamate mustard group on both C-1 phenyl rings. The estrogen receptor affinity of compound 3 was only about one-quarter lower than that of compound 1, but much higher than that of compound 2. Compounds 2 and 3 showed only partially irreversible binding to the receptor owing to their relatively low alkylating properties. The growth inhibition of the receptor-positive MCF-7 breast cancer cell line by compound 3, but not by compound 1 or 2, was more pronounced than the inhibition of the receptor-negative line MDA. In vivo the hormone-dependent, transplantable mammary tumor MXT M3.2 of the mouse was much better inhibited by compound 3 than its hormone-resistent line MXT OVEX. Compounds 1-3 had no antiestrogenic properties in the mouse, but estrogenic activity was in the order 1 greater than 3 greater than 2. From these results and because the antitumor activity of compound 3 was superior to that of compounds 1 and 2 in the hormone-dependent tumor models, a selective, receptor-mediated cytotoxic effect of compound 3 on estrogen-receptor-positive tumors in obvious.

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.

The oestrogenic effects of ethinyl oestradiol/polyoestradiol phosphate and estramustine phosphate in patients with prostatic carcinoma. A comparative study of oestrogen sensitive liver proteins, gonadotrophins and prolactin

Thirty previously untreated patients with carcinoma of the prostate were prospectively randomised to one of the following treatments: ethinyl oestradiol (Etivex) combined with polyoestradiol phosphate (Estradurin); estramustine phosphate (Estracyt); bilateral orchiectomy. Oestrogenic effects were measured by blood levels of pregnancy zone protein, sex hormone binding globulin, LH, FSH and prolactin. During a follow-up period of 6 months, estramustine phosphate and ethinyl oestradiol/polyoestradiol phosphate induced comparable changes in these proteins, suggesting comparable oestrogenic effects of these two forms of treatment in patients with prostatic carcinoma.

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.

Chemotherapy principles in the treatment of prostatic cancer

The efficacy of chemotherapy for prostatic cancer is difficult to evaluate owing to the low incidence of measurable indicator lesions and the resulting need for indirect response criteria. Although complete regressions remain exceptional, a number of agents, eg, doxorubicin and cisplatin have been shown to be effective in the treatment of this disease. So far, combinations of effective agents with or without concomitant hormone therapy have not proven to be more effective than single agents. Androgen priming has considerable theoretical appeal and deserves further consideration. A higher effectiveness of chemotherapeutic agents might be obtained by linkage to various carriers. Estramustine phosphate is an example of such a complex that has a cytotoxic effect in test systems in which estrogen has no effect and in patients with hormone-refractory prostatic cancer. The use of hormonal and other carriers that could increase the specificity of chemotherapeutic agents deserves extensive exploration.

Estracyt in advanced carcinoma of the breast: a phase II study

Estracyt, a conjugate of an alkylating agent with an oestrogenic sterol, was given in a dose of 420 mg daily to a group of 44 postmenopausal patients with very advanced breast carcinoma. Thirty-eight of these were in relapse following chemotherapy and 32 had evidence of distant metastases. Seventeen patients had an objective response and marked or complete alleviation of symptoms, four others had a useful symptomatic response but no beneficial effect was observed in the remainder. Three who had shown no response to previous oestrogen therapy also failed to respond to Estracyt as did all nine patients with hepatic metastases. Oestrogen receptor status and age within the postmenopausal group seemed to have no bearing on the result. Side-effects were minimal with nausea in 18 patients but in only two did this necessitate withdrawal of the drug. Bone marrow depression did not occur. Changes in acute-phase reactant proteins suggested that part of the Estracyt was de-esterified in the liver liberating oestrone but the low incidence of vaginal haemorrhage and the recalcification of bony metastases suggested that on the whole Estracyt behaves as an anti-oestrogen as well as an antimitotic.

Estramustine phosphate: a specific chemotherapeutic agent?

Estramustine phosphate is a nitrogen mustard derivative of estradiol that has been advocated for the treatment of prostatic cancer. The compound was designed with the hope that the estrogen moiety would direct the alkylating moiety to estrogen-dependent malignancies, where the alkylating moiety would be released specifically. Preclinical and clinical data are reviewed to determine to what extent that challenging concept is fulfilled. In addition, we have examined critically the efficacy of this drug for the treatment of prostatic cancer. From available data it appears that there is no evidence that the alkylating moiety of estramustine phosphate is specifically freed in estrogen-dependent tissues. Estramustine phosphate appears to be an active compound with acceptable toxicity in prostatic cancer. However, further clinical trials must be undertaken to clarify the future role of estramustine phosphate in the treatment of prostatic cancer.

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

Estradiol mustard (EM) is the 3,17beta-diester of estradiol-17beta (E2) with the nitrogen mustard derivative chlorphenacyl. The ability of EM to bind to cytoplasmic estrogen receptors was tested by inhibition of the binding of 3H-E2 to rat uterine cytosol at 18 degrees C and 30 degrees C. At both temperatures an inhibition curve was observed in the presence of a large excess of drug, suggesting that the latter has a very weak binding affinity (100,000 times lower than E2). Incubation of uterine cytosol with increasing amounts of 3H-E2 in the presence and absence of an excess of EM indicated that the drug interacted with the receptors at the same sites as E2 (competitive inhibition). Preincubation of uterine cytosol at 18 degrees C with EM induced a progressive reduction of 3H-E2 binding capacity. This reduction also occurred, although to a lesser extent, when long-term incubation of the cytosol with EM was performed in the presence of labelled E2 from the start. The process was faster at 18 degrees C than at 4 degrees C and did not occur with EM preincubated in homogenization buffer. Exchange assays by 3H-E2 of uterine receptors preincubated with labelled E2 and excess EM indicated that the drug-induced inhibition of binding capacity was reversible and produced no apparent alteration of the receptors. Furthermore, the rate of exchange was similar to that observed with receptors previously filled with unlabelled E2. In 9 "receptor-positive" cytosols from human breast cancers, time-course study of the binding of 3H-E2 in the presence of excess of EM yielded similar results as those obtained with rat uterine cytosol. These results show that EM has a very low binding affinity for the extrogen receptors and that it is metabolized into one or several compounds of higher binding affinity. They suggest that EM is probably not significantly concentrated by the estrogen target tissues such as mammary cancers. Therefore, the drug is unlikely to be very valuable in the treatment of breast cancer through a specific mechanism involving concentration by the estrogen receptors.