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A E Wakeling

Publications and source records attributed to A E Wakeling.

72 records · Page 4Linked to original sources
PubMed1984

Non-steroidal antioestrogens--receptor binding and biological response in rat uterus, rat mammary carcinoma and human breast cancer cells.

The non-steroidal antioestrogens tamoxifen, 4-hydroxytamoxifen, trioxifene, LY 117018 and LY 139481 have widely divergent affinities for oestrogen receptors from rat mammary tumours. The latter two compounds have much reduced partial agonist activity in rat uterus, compared to tamoxifen, but were less effective antitumour agents than tamoxifen. No direct correlation was established between receptor affinity and biological response in rat uterus or rat mammary carcinoma. However, in in vitro studies of growth inhibition of human breast cancer cells (MCF7), the order of potency was the same as the order of relative binding affinity. Differences in in vivo activity of these antioestrogens may be related to biological "half-life" which is dependent on the dose, route of administration and metabolic stability of the antioestrogens. Growth inhibition in MCF 7 cells did not correlate with affinity for tamoxifen-specific binding sites, nor was there any evidence for differences between antioestrogens in their mechanism of action on the rat uterus. It is concluded that the primary effects of antioestrogens are mediated by binding to oestrogen receptors.

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PubMed1983

Identification and biological activity of tamoxifen metabolites in human serum.

During the examination of serum samples from patients on chronic 'Nolvadex' therapy three major metabolites (X, Y and Z) were detected in addition to the parent drug. Two of these metabolites have been positively identified as N-desmethyltamoxifen (X) and a side-chain primary alcohol (Y). The third metabolite (Z) has been tentatively identified as N-desdimethyltamoxifen. Quantitative analysis of these metabolites in sera from patients undergoing chronic Nolvadex therapy (20 mg approximately b.d.) has shown that the mean N-desmethyltamoxifen concentration was 481 ng/ml, the mean metabolite Y concentration was 49 ng/ml and that desdimethyltamoxifen concentrations were in the range 20-40 ng/ml. The corresponding mean unchanged drug level in these patients was 310 ng/ml. 4-Hydroxytamoxifen could not be detected in these samples. Measurements of the relative binding affinities of tamoxifen and its metabolites for rat uterus oestrogen receptors have shown that 4-hydroxytamoxifen had a relative binding affinity similar to oestradiol while tamoxifen and its side-chain metabolites had lower affinities. It has been shown that all the metabolites examined are antioestrogenic, as demonstrated by their ability to prevent implantation in pregnant rats and inhibit oestradiol-induced uterine weight gain. It is therefore possible that the metabolites of tamoxifen collectively contribute to the therapeutic activity of the drug.

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PubMed1983

A rationalization of the effects of anti-oestrogens and oestrogens on uterine RNA synthesis in the immature rat.

A series of oestrogens and anti-oestrogens have been compared with respect to their effects on RNA synthesis in the uterus of immature rats. The normal transcriptional response to oestrogen is a biphasic stimulation of transcription. The first phase is a sharp stimulation of RNA synthesis, 2-4 h after hormone administration which peaks at 7-11-fold unstimulated controls but which rapidly falls to near control levels by 8 h after injection. The second phase is a broad peak of RNA synthesis, typically lasting from 12-32 h after hormone administration and accompanied to a much greater extent than the first phase by increases in precursor pool sizes. Oestradiol-17 beta does not show the second phase of this response. This is presumably due to rapid metabolism as derivatives with a longer tissue half life induce the complete response. The first phase of the response is not induced by tamoxifen but is by monohydroxy tamoxifen.

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PubMed1983

Tamoxifen-induced changes in the polyribosomes and associated mRNA of rat uterus.

We have analysed the effect of tamoxifen on the accumulation of polysomes and their associated mRNA populations in the uterus of the immature rat. Tamoxifen caused the aggregation of ribosomes into polysomes but, when compared with the effects of oestrogen, the accumulation was delayed, of smaller magnitude and resulted in smaller polysomes. Tamoxifen did not inhibit oestrogen-induced polysome aggregation. Tamoxifen and monohydroxytamoxifen caused oestrogen-like changes in the polyadenylated mRNA population of uterine polysomes, but some quantitative and qualitative as well as kinetic differences were found in the response to the inhibitors when compared with the hormone. The reasons for these differences are discussed.

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PubMed1983

Comparison of the biological effects of tamoxifen and a new antioestrogen (LY 117018) on the immature rat uterus.

The uterotrophic and antiuterotrophic activities of tamoxifen and 6-hydroxy-2-(p-hydroxyphenyl)-benzo(b)thien-3-yl p- less than 2-(1-pyrrolidinyl) ethoxyphenyl ketone (LY 117018) in the immature rat uterus have been evaluated. The antioestrogens were administered alone, concurrently or sequentially with or without oestradiol. LY 117018 administered alone was less uterotrophic (oestrogenic) than tamoxifen. At high doses, when administered concurrently with oestradiol, LY 117018 was more antiuterotrophic (antioestrogenic) than tamoxifen. When uterine growth was maximally stimulated by prior treatment with oestradiol, tamoxifen and LY 117018 were equally effective in reducing uterine weight. However, when uterine growth was induced with a dose of oestradiol producing an oestrogenic effect equivalent to that of tamoxifen (but less that produced by LY 117018) LY 117018 was more effective than tamoxifen in reversing the uterotrophic effect of oestradiol. In animals pretreated with LY 117018 a further increase in uterine weight occurred on treatment with tamoxifen. The increase in uterine weight after tamoxifen was progressively reversed by increasing doses of LY 117018. The hypothesis that tamoxifen and LY 117018 may act by different mechanisms, based on the apparent failure of LY 117018 to antagonize the uterotrophic action of tamoxifen, is not supported by these studies.

Animals↗
PubMed1983

Antioestrogenic and antitumour activities of a series of non-steroidal antioestrogens.

The relative oestrogenic and antioestrogenic activities in the immature rat uterus of the antioestrogens tamoxifen, trioxifene, 6-hydroxy-2-(p-hydroxyphenyl)-benzo(b)thien-3-yl p- less than 2-(1-pyrrolidinyl) ethoxyphenyl ketone (LY 117018) and 6-hydroxy-2-(p-hydroxyphenyl)-benzo(b)thien-3-yl p- less than 2-(1-piperidinyl) ethoxyphenyl ketone (LY 139481) were compared. The efficacy of these compounds in inhibiting the growth of 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary carcinomas was also measured. Tamoxifen and trioxifene were equipotent antioestrogens (ED50 = dose required to produce 50% reduction in oestradiol-stimulated uterine growth = 0.1 mg/kg); both compounds also demonstrated a maximal partial agonist (uterotrophic) effect of 40% that of oestradiol. LY 117018 and LY 139481 were less potent antioestrogens (ED50 = 0.7 and 0.25 mg/kg respectively) than tamoxifen but both compounds were also less oestrogenic (partial agonist activities 20 and 10% respectively compared with oestradiol). The differences in partial agonist activity were reflected by differences in maximum antioestrogenic effects. High doses of tamoxifen or trioxifene produced 60% inhibition of oestradiol-induced uterine growth whereas LY 117018 (80% inhibition) and LY 139481 (90% inhibition) were both more antioestrogenic because of their reduced partial agonist activity. In rats bearing DMBA-induced mammary tumours tamoxifen was the most effective inhibitor of tumour growth. In tamoxifen-treated animals only 7% (8/111) of hormone-dependent tumours showed progressive growth, compared to 60% in controls. The other antioestrogens were less effective; in trioxifene-treated animals 42% (18/43) of tumours continued to grow during treatment. Similarly, for LY 117018, 39% (14/36) and for LY 139481, 26% (10/38) of tumours showed progression. High doses of trioxifene and LY 117018 were markedly less efficacious than low doses. The increased separation between oestrogenic and antioestrogenic activity in the rat uterus, exemplified by LY 117018 and LY 139481 compared to tamoxifen and trioxifene, did not lead to increased antitumour efficacy.

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PubMedDate not supplied

Estrogen-receptor binding and biologic activity of tamoxifen and its metabolites.

In female patients treated with tamoxifen (T), the major metabolite of T in serum is N-desmethyltamoxifen (N-d-Me T). The serum concentration of d-Me T may equal or exceed that of T, and 4-hydroxytamoxifen (4-OH T) is present in much lower concentration (< 10% that of T). The biologic properties and estrogen-receptor binding affinity of T and its desmethyl and 4-hydroxy metabolites have been compared. In competition studies with the rat uterus estrogen receptor at 0 degrees C and 25 degrees C, the relative affinities of T and d-Me T were similar, and their apparent affinity decreased when the incubation temperature was increased (38.2, 21.0 and 1.8, 1.1, respectively at 0 degrees C and 25 degrees C; 17 beta-estradiol = 100). In contrast, 4-OH T was a more potent inhibitor of estradiol binding (110 and 188 at 0 degrees C and 25 degrees C and its apparent affinity increased, rather than decreased, when the incubation temperature was raised from 0 degrees C to 25 degrees C. These differences in receptor binding were not reflected in biologic activity; all three compounds were potent antiestrogens of approximately equal activity in the rat. In patients, the pharmacologic effect of T may be due, in part, to d-Me T, but it is unlikely that 4-OH T plays a major role because of its relatively low serum concentration. The antiestrogenic potencies of T, d-Me T, and 4-OH T are similar, so the extent of metabolism in individual patients is unlikely to influence clinical response to tamoxifen therapy.

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