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M Dowsett

Publications and source records attributed to M Dowsett.

At least 91 records · Page 5Linked to original sources
PubMed1998

Theoretical considerations for the ideal aromatase inhibitor.

A definition of the theoretical components of an ideal aromatase inhibitor is developed, one aspect of which is completeness of enzyme inhibition. The three triazole inhibitors, letrozole, vorozole and anastrozole all inhibit whole body aromatisation by > 96% at their clinically used doses and vorozole and letrozole were more effective in Phase III clinical trials than aminoglutethimide (250 mg bd) which achieves < 90% inhibition. The possibility is considered that the apparent small differences between the triazoles may be associated with differences in clinical effectiveness. These new compounds merit consideration for studies of breast cancer prevention.

Aminoglutethimide↗
PubMed1998

Comparison of in situ methods to assess DNA cleavage in apoptotic cells in patients with breast cancer.

BACKGROUND: Apoptosis has a role in many cellular processes including development, normal tissue homeostasis, and malignancy. This aspect of research is relatively new with distinct methods of analysing disparate biochemical and genetic events to measure apoptotic cells. The use of biotinylated nucleotides to identify DNA strand breaks is a commonly reported method of estimating cells numbers undergoing apoptosis; however, investigators report inconsistent results for a variety of reasons. AIMS AND METHOD: To compare two in situ techniques of measuring apoptosis: in situ nick translation (ISNT) and TdT mediated dUTP-biotin nick end labelling (TUNEL); and to assess DNA cleavage in 20 paired paraffin wax embedded breast cancer tissues from patients; one group who had received no prior treatment and one group who had received chemohormonal treatment. RESULTS AND CONCLUSIONS: Apoptotic scores obtained from paraffin wax embedded human breast cancer after using ISNT and TUNEL methods were not significantly different (p = 0.11). A strong correlation between scores obtained from the two techniques was found (r = 0.758, p < 0.0001). Optimisation of both techniques is crucial to ensure maximal assay performance in breast cancer tissue.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1998

In vivo inhibition of aromatization by exemestane, a novel irreversible aromatase inhibitor, in postmenopausal breast cancer patients.

The effect of exemestane (6-methylenandrosta-1,4-diene-3,17-dione) 25 mg p.o. once daily on in vivo aromatization was studied in 10 postmenopausal women with advanced breast cancer. Aromatization was determined before treatment and after 6-8 weeks on therapy by administering a bolus injection of [3H]androstenedione (500 microCi) and [14C]estrone (5 microCi) followed by measurement of the isotope ratio of urinary estrogens after high-performance liquid chromatography purification. In addition, plasma endogenous estrogens were measured with highly sensitive radioimmunoassays after separation with high-performance liquid chromatography. Treatment with exemestane suppressed whole body aromatization from a mean pretreatment value of 2.059% to 0.042% (mean suppression of 97.9%). Plasma levels of estrone, estradiol, and estrone sulfate were found to be suppressed by 94.5%, 92.2%, and 93.2%, respectively. This is the first study revealing near total aromatase inhibition in vivo with the use of a steroidal aromatase inhibitor. The observation that exemestane is a highly potent aromatase inhibitor, together with the fact that the drug is administered p.o. and causes limited side effects, suggests that exemestane is a promising new drug for the treatment of hormone sensitive breast cancer.

Administration, Oral↗
PubMed1997

Comparison of estrogen receptor DNA binding in untreated and acquired antiestrogen-resistant human breast tumors.

Preliminary studies have suggested that measuring the ability of immunoreactive 67-kDa estrogen receptor (ER) to bind DNA and form in vitro complexes with its cognate estrogen response element (ERE) might serve to identify breast tumors most likely to respond to antiestrogens like tamoxifen. Data from two different surveys of untreated primary breast tumors confirmed that only 67% (74 of 111) of ER-positive tumors express a receptor capable of forming ER-ERE complexes by gel-shift assay, with tumors of lower ER content having significantly reduced ER DNA-binding frequency (56%) relative to those of higher ER content (82%; P = 0.007). In contrast to these untreated tumors, a panel of 41 receptor-positive breast tumors excised after acquiring clinical resistance to tamoxifen during either primary (n = 26) or adjuvant therapy (n = 15) showed a significantly greater ER DNA-binding frequency, with nearly 90% capable of forming ER-ERE complexes (P < 0.02). To assess experimentally whether ER DNA-binding function is altered during the development of antiestrogen resistance, nude mouse MCF-7 tumor xenografts were analyzed before and after the acquisition of in vivo resistance to either tamoxifen or a pure steroidal antiestrogen, ICI 182,780. Tamoxifen-resistant MCF-7 tumors retained full expression of 67-kDa DNA-binding ER, and despite a markedly reduced ER content in the ICI 182,780-treated tumors, the expressed ER in these antiestrogen-resistant tumors exhibited full ability to form ER-ERE complexes. These findings indicate that breast tumors with acquired antiestrogen resistance continue to express ER of normal size and DNA-binding ability and suggest that the failure of antiestrogens to arrest tumor growth during emergence of clinical resistance results from an altered gene-regulatory mechanism(s) other than ER-ERE complex formation.

Animals↗
PubMed1997

Identification of an exon 3 deletion splice variant androgen receptor mRNA in human breast cancer.

Androgens and androgen receptor (AR) are involved in many regulatory processes in the growth of female breast cells. Mutations in the AR gene and/or alterations of the AR protein sequence may be related to the development and progression of breast cancer. Using reverse transcription-polymerase chain reaction we have examined 31 female breast-cancer samples, 5 normal female breast tissues and 6 breast-cancer cell lines for the presence of splice variants of AR mRNA and have identified an exon 3 deletion splice variant (delta3AR). The higher expression of the variant relative to the wild-type AR (WT AR) was found in 7 breast-cancer samples (delta3/WT > 15%) and relatively lower levels of the variant were observed in 3 breast-cancer cell lines (delta3/WT < 5%). However, in normal breast tissues, expression of the variant was undetectable by Southern blot analysis. In vitro translation of the delta3AR mRNA resulted in a variant AR protein of about 105 kDa, smaller than the WT AR by about 5 kDa. We thus report an exon deletion splice variant of AR mRNA in breast cancer. The variant protein is predicted to lack the second zinc finger within the DNA-binding domain and is expected to be unable or to have reduced ability to bind to androgen-response elements and to activate transcription. The relatively high expression of this AR variant in some breast-cancer tissues may indicate its role in regulating the growth of these cancers.

Alternative Splicing↗
PubMed1997

Induction of apoptosis by tamoxifen and ICI 182780 in primary breast cancer.

Hormonal breast cancer therapies have traditionally been considered cytostatic, but recent pre-clinical data suggest that anti-oestrogens can induce apoptosis. The aim of this study was to assess whether tamoxifen (TAM) and ICI 182780 (ICI) could induce apoptosis in human breast cancer, and whether this was related to oestrogen receptor status. We measured apoptosis in primary breast cancer patients before and after pre-surgical treatment with 20 mg/day TAM (study 1) or 6 or 18 mg/day ICI (study 2). In each study there was a randomised non-treatment (NT) control group. TAM significantly increased apoptotic index (AI) in ER+ but not in ER- tumours. There was a significant increase in AI following treatment with ICI. Insufficient pairs of samples were available to determine whether this change was confined to ER+ tumours, but in a cross-sectional analysis AI was significantly higher in excision biopsies for ICI-treated than NT patients for ER+ but not ER- tumours. Our results provide clinical evidence that apoptosis may be induced in ER+ primary breast cancer by both non-steroidal and steroidal anti-oestrogens.

Adult↗
PubMed1997

Screening for ESR mutations in breast and ovarian cancer patients.

In the present study, leukocyte DNA from 143 patients with familial clustering of breast and/or ovarian cancer and tumour DNA from 96 breast carcinomas were screened for base mutations in the estrogen receptor gene (ESR). Three patients with a family history of cancer were carrying a Gly160Cys germline substitution. This alteration was also detected in eight (four females and four males) of 729 controls (366 female, 363 males), indicating that the substitution probably represents a polymorphism. However, in the 229 female controls in whom family history of cancer was known, one of two who had a sister with breast cancer was carrying the variant allele. Hence, a possible clinical significance of the glycine into cysteine cannot be completely ruled out and should be further investigated. Somatic mutations were not detected in any of the tumours studied, and the present data do not provide support for somatic ESR base mutations as an important mechanism for hormonal therapy resistance in estrogen receptor-positive breast carcinomas.

Adult↗
PubMed1997

Oestrogen receptor mutants and variants in breast cancer.

Oestrogen receptor (ER) status is the only biochemical predictive factor which is routinely measured in breast carcinomas. ER gene mutations can profoundly change the biochemical activity of the protein. If these occurred in vivo, they could be expected to affect breast cancer risk or phenotype, such as endocrine responsiveness. However, no mutations of significance have been described in breast carcinomas. In contrast, numerous variant forms of ER have been reported at the mRNA level. Most of these appear to be due to aberrant exon splicing which results in predicted protein products whose activities range from dominant positive to dominant negative. In some instances, these mRNA variants have also been demonstrated in normal tissue (breast and others). Their biological and clinical significance might be profound, but remain to be established because of a lack of evidence for their existence at the protein level. On the currently available data, routine analysis for ER mutants and variants is not justified.

Biomarkers, Tumor↗
PubMed1997

Biochemistry and pharmacokinetics of potent non-steroidal cytochrome P450(17alpha) inhibitors.

Two potent non-steroidal inhibitors (CB7645 and CB7661) of human cytochrome P450(17alpha) were tested for in vivo activity in WHT mice. There were no signs of toxicity, but there was no effect on the androgen-dependent organs. The pharmacokinetics and biochemistry of the compounds in mice were investigated. Following i.p. administration of 0.5 mmol/kg of CB7645 and CB7661, peak plasma levels of 13.4 and 3.4 microM, respectively, occurred after 2-4 h, both compounds were cleared rapidly (terminal half-lives 2.7 and 3.3 h, respectively) and neither was detectable at 24 h. CB7645 produced some decrease in plasma testosterone at 4 h, but this was not sustained. When tested in vitro against the WHT testicular enzyme, the CB7645 and CB7661 were competitive inhibitors with K(i) values of 10 and 13 nM, respectively. However, the K(m) for the substrate progesterone was lower at 4.3 nM. These data indicate that, for effective and continuous inhibition of the murine cytochrome P450(17alpha) enzyme, higher peak levels of the compounds would be required, and these levels would need to be maintained throughout the treatment period.

Adamantane↗
PubMed1997

A novel estrogen receptor variant mRNA lacking exons 4 to 6 in breast carcinoma.

A novel estrogen receptor mRNA splice variant which lacks the entire exon 5 and part of exon 4 and 6 was identified using reverse transcription PCR in human breast carcinomas. The variant was translated in vitro and produced a protein of approximately Mr 31000 which lacked the ligand binding domain. The binding of the variant estrogen receptor (ER) to a synthetic estrogen-responsive element (ERE) was compared with that of the wild-type ER (wtER). The variant ER bound weakly to the synthetic ERE, both in the presence and absence of estradiol, whilst the wtER bound strongly in the absence and the presence of estradiol. When wtER and variant ER were simultaneously translated in vitro, no heterodimerization was observed using band shift assay. Addition of increasing amounts of variant ER protein to the wtER in the ERE binding reaction showed that the variant protein competed with the binding of the wtER to the synthetic ERE. Furthermore, variant ER are not transcriptionally active. The variant was also expressed in 96% of the 102 breast tumours analysed, of which 62 were tamoxifen-resistant tumours. The expression of this variant was significantly higher (relative to ER) in untreated ER-positive breast tumours which were both progesterone receptor (PgR) negative and pS2 negative phenotype.

Amino Acid Sequence↗
PubMed1997

Cytological evaluation of biological prognostic markers from primary breast carcinomas.

This study was undertaken to evaluate our ability to detect multiple molecular markers of prognosis and response to treatment in fine needle aspirates (FNA) from patients with primary breast carcinomas. 147 patients with operable primary breast carcinomas who had been recruited to a randomized trial of primary medical therapy (PMT) versus adjuvant chemoendocrine therapy were analysed. FNAs were taken prior to therapy and from this multiple slides were produced using cytospin cytocentrifugation and stored at -80 degrees C for subsequent immunocytochemical analysis (ICA). ICA was performed for oestrogen receptor (ER), progesterone receptor (PgR), p53, Ki67, and Bcl-2. Part of the aspirate was snap frozen and used for flow cytometric analysis of ploidy and S-phase fraction (SPF). In a subgroup of 50 patients who had surgery prior to systemic therapy, as well as FNAs, sections were also taken from paraffin-embedded blocks and stained by ICA for ER, PgR and p53 for validation. In these patients ER was additionally measured by enzyme immunoassay (EIA) from frozen tissue taken at surgery. ER, PgR, p53, Bcl-2, and Ki67 were successfully detected by ICA while ploidy and SPF were successfully measured by flow cytometry from FNA material. The percentage positive values obtained were reasonable and as follows: 74% for ER, 70% for PgR, 36% for p53, 80% for Bcl-2,68% of tumours were aneuploid and 32% diploid. Significant relationships between these measurements were observed in accordance with expectations. The concordance for ER, PgR, and p53 from FNA when compared to ICA of matching histological sections was 91.5%, 75.5%, and 75% respectively. For ER the concordance between measurement by ICA of cytological and histological samples and by EIA of frozen tissue was 82.5% and 84% respectively. These results indicate that multiple molecular markers can be adequately tested on cytological preparations from primary breast tumours. These markers can be used to determine prognosis and predict response to PMT.

Adult↗
PubMed1997

The novel anti-oestrogen idoxifene inhibits the growth of human MCF-7 breast cancer xenografts and reduces the frequency of acquired anti-oestrogen resistance.

The effect of idoxifene, a novel anti-oestrogen with less agonist activity than tamoxifen, was compared with that of tamoxifen on the growth of hormone-dependent MCF-7 breast cancer xenografts. Forty tumours were established with oestradiol support in ovariectomized athymic mice, allowed to grow to a median volume of 420 mm3 and then continued with oestradiol, no support, tamoxifen or idoxifene delivered by 1.5-cm silastic capsule. Tumour regression occurred with both anti-oestrogens, although maximum regression was observed following oestradiol withdrawal alone. While prolonged anti-oestrogen therapy was associated with static growth, tumour volumes were significantly lower with idoxifene (P=0.01). After 6 months, 0/10 idoxifene-treated tumours developed acquired resistance compared with 3/10 tumours treated with tamoxifen. In separate experiments, 94 animals were treated initially with oestradiol, tamoxifen, idoxifene or placebo following implantation with 1-mm3 pieces of either wild-type (WT) or tamoxifen-resistant (TR) MCF-7 tumour. After 4 months, only 1/11 WT tumours became established with idoxifene compared with 4/11 with tamoxifen, 8/12 with oestradiol and 0/12 with placebo. Likewise, fewer TR tumours were supported by idoxifene (3/12) than by tamoxifen (8/12) or oestrogen (11/12). These data indicate that, compared with tamoxifen, idoxifene shows reduced growth support of MCF-7 xenografts and may share only partial cross-resistance. Furthermore, the development of acquired anti-oestrogen resistance may be reduced during long-term idoxifene therapy. The drug's reduced agonist activity may, in part, explain these observations and indicate a preferable biochemical profile for breast cancer treatment.

Animals↗
PubMed1997

A prospective study of endogenous serum hormone concentrations and breast cancer risk in premenopausal women on the island of Guernsey.

The associations between serum concentrations of oestradiol, progesterone, testosterone and sex hormone-binding globulin (SHBG) and risk of breast cancer in premenopausal women were investigated in a prospective study of breast cancer on the island of Guernsey. Sixty-two women diagnosed with breast cancer an average of 8 years subsequent to blood collection were matched for day of menstrual cycle, age and year of blood collection with 182 control subjects. Cases had a 12% higher mean oestradiol concentration over the whole menstrual cycle (P = 0.17) with a large difference at mid-cycle (75% higher, P = 0.04). Differences between cases and control subjects in progesterone (luteal phase), testosterone and SHBG were small and not statistically significant: luteal phase progesterone 9% lower in cases, P = 0.64; testosterone 4% higher, P = 0.57; SHBG 8% higher, P = 0.24. The small difference in oestradiol concentration could be aetiologically important, but larger prospective studies are needed.

Breast Neoplasms↗