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Biomedical subjects

V C Jordan

Publications and source records attributed to V C Jordan.

At least 109 records · Page 6Linked to original sources
PubMed1997

Pure antiestrogens as a new therapy for breast cancer.

Tamoxifen is the endocrine therapy of choice for all stages of breast cancer. However, the drug cannot be considered to be a cure as drug resistance will eventually develop. The resistance can take two forms: either the loss of estrogen receptor or the selection of estrogen receptor positive disease that is tamoxifen stimulated for growth. Laboratory studies have demonstrated that tamoxifen-stimulated MCF-7 breast tumors can develop in athymic mice. A number of pure (nonestrogenic) antiestrogens have been discovered that can either be administered by injection (e.g., ICI 182,780) or orally (e.g., EM-800). In preliminary clinical studies, the compound ICI 182,780 (Faslodex) has been shown to be an effective second-line therapy after tamoxifen failure. The goal of future clinical studies is to evaluate the therapeutic efficacy and patient acceptability of aromatase inhibitors (postmenopausal estrogen withdrawal), and injectable or oral pure antiestrogens after the failure of long-term tamoxifen therapy. Clearly, the primary purpose for the treatment of advanced breast cancer is to control disease growth; nevertheless, an evaluation of the effect of new agents on bones and lipids is required before pure antiestrogens could be considered for adjuvant therapy.

Animals↗
PubMed1997

A phase I study of high-dose tamoxifen for the treatment of refractory malignant gliomas of childhood.

Recent studies have indicated that the proliferation of malignant gliomas is in part dependent on excessive activation of protein kinase C (PKC)-mediated pathways. Conversely, inhibiting PKC may provide a novel approach for blocking glioma growth. The antiestrogen tamoxifen, a moderately potent PKC inhibitor, has been shown in vitro to block the proliferation of malignant glioma cell lines at concentrations several-fold higher than those typically attained during the treatment of breast cancer; such serum concentrations may be achieved with doses > 40 mg/m2 b.i.d. The safety and efficacy of these high doses for producing disease control in patients with malignant gliomas has recently been noted anecdotally, although a rigorous study of this agent has been lacking. To address this issue, we examined the safety and efficacy of high-dose tamoxifen in a series of children with malignant gliomas that had progressed after conventional therapy. An initial group was treated with 60 mg/m2 p.o. b.i.d. and a second group with 100 mg/m2 b.i.d. Steady-state serum tamoxifen and metabolite levels were measured in most patients. Toxicity with the regimen was minimal; two patients treated at the higher dose required reduction to the lower dose because of asymptomatic prolongation of the QT interval on an electrocardiogram. Although none of the patients exhibited clear-cut tumor regression, 4 of 14 patients had stabilization of previously progressive disease for at least 3 months; the longest survivor lived for 17 months after beginning tamoxifen. The moderate efficacy of this agent in otherwise end-stage disease coupled with its low toxicity and the relative ease of oral administration provides a rationale for proceeding with larger studies of this agent in patients with malignant gliomas, possibly as a means for potentiating the effects of conventional chemotherapeutic agents, which to date have shown limited efficacy in the treatment of these tumors.

Administration, Oral↗
PubMed1996

Phase II enzyme expression in rat liver in response to the antiestrogen tamoxifen.

The genotoxicity and carcinogenicity of tamoxifen have been attributed to metabolic activation of tamoxifen to an electrophile. Phase II enzymes are known to be involved in the metabolism of the drug and possibly in the formation or elimination of the active metabolite. To determine the effects of tamoxifen on phase II enzyme expression, the drug was administered to F344 rats, and hepatic glutathione S-transferase (GST), UDP-glucuronosyltransferase (UGT), and sulfotransferase (ST) expression was evaluated. Some of the tamoxifen-induced effects, including dramatic suppression of selected GST enzymes and activity, were observed at a dose in rats that is directly equivalent, on a mg/kg b.w. basis, to the doses used for breast cancer treatment. Most of the observed responses are not consistent with the previously described phenobarbital-like properties of tamoxifen and could be the result of the partial agonist activity of tamoxifen at the estrogen receptor. Northern blot analysis was performed with isozyme-specific oligonucleotide probes for rat GST, ST, and UGT. In addition, GST subunit protein levels were assayed by high-performance liquid chromatography. In females, tamoxifen treatment resulted in a 60% suppression of GST Ya1 mRNA and protein levels and a 40% suppression of GST Ya2 levels. In males, tamoxifen treatment suppressed GST Ya1 expression approximately 60%, and GST Ya2 expression was suppressed at low doses but induced above control at high doses. Male GST Yc1 was induced approximately 80% over control. The expression of all other major forms of rat hepatic GST subunit protein, including GST Yb1, Yb2, Yb3, Yp, and Yl, was unaffected by tamoxifen treatment. GST conjugation activity toward delta 5-androstene-3,17-dione, a GST Ya1- and Ya2-specific substrate, was suppressed approximately 40% in both sexes, consistent with our protein and mRNA data. Total GST activity, as measured by the rate of chlorodinitrobenzene conjugation, was not changed. Tamoxifen also produced a dose-dependent increase in UGT2B1 mRNA, a phenobarbital-inducible enzyme; mRNA levels reached 210 and 420% of control in females and males, respectively. In addition, mRNA levels for ST2A2, a female-specific ST gene, were suppressed 50% in females and induced 120% over control in males. mRNA expression for all other forms of rat liver UGT and ST isozymes that were tested was not significantly affected by tamoxifen treatment. Overall, these results demonstrate that tamoxifen has significant effects on hepatic phase II enzyme expression that may have implications for the carcinogenicity and/or therapeutic activity of the drug.

Animals↗
PubMed1996

Models of estrogen receptor regulation by estrogens and antiestrogens in breast cancer cell lines.

The expression and stability of the estrogen receptor (ER) is the result of a complex process that is modulated by estrogens and antiestrogens. Regulation of the steady-state ER mRNA and protein levels in breast cancer cells appears to be the result of either of two distinct regulatory mechanisms. Estrogen exposure causes a rapid down-regulation of the steady-state level of ER mRNA and protein in model I regulation, as exemplified by the MCF-7:WS8 cell line. Conversely, in model II regulation, as observed in the T47D:A18 cell line, estrogen exposure causes an increase in the steady-state ER mRNA level and a maintenance of the ER protein level. In both these cell lines, the nonsteroidal antiestrogen 4-hydroxytamoxifen has little effect on the mRNA level but causes a net accumulation of the ER protein over time. In contrast, the pure antiestrogen ICI 182,780 causes a dramatic reduction of the ER protein in both the MCF-7:WS8 and T47D:A18 cell lines. This loss has little effect upon the ER mRNA level in the MCF-7:WS8 cells but leads to a decline in the ER mRNA in the T47D:Al8 cells. The estrogen-independent MCF-7:2A cell line, which has adapted to growth in estrogen free media, expresses two forms of the ER, a wild-type Mr66,000 ER and a mutant Mr77,000 ER (ER77). ER77 is the product of a genomic rearrangement resulting in a tandem duplication of exons 6 and 7 (J. J. Pink et al, Nucleic Acids Res., 24:962-969,1996). This exon duplication has abolished ligand binding by this protein. Here we demonstrate that the loss of ligand binding has eliminated the effects of 4-OHT and ICI 182,780 on the steady-state ER77 protein level. However, in the MCF-7:2A cells, antiestrogens affect the wild-type ER protein in the same manner as observed in the MCF-7:WS8 and T47D:A18 cells. Estrogen regulates the ER mRNA and wild-type ER and ER77 proteins in the MCF-7:2A cells in the same manner as observed in the MCF-7:WS8 cells. Interestingly, treatment of the MCF-7:2A cells with ICI 182,780 causes a slight increase in ER mRNA, which is reflected in a net increase in the ER77 protein but a dramatic decrease in the wild-type ER. The models presented here describe the response of two human breast cancer cell lines in short-term studies. These distinct regulation pathways are predictive of the response of these cell lines to long-term estrogen deprivation. This study illustrates two alternative regulation pathways that are present in ER-positive, estrogen-dependent breast cancer cells. This variable response highlights the diversity of responses potentially present in the heterogeneous cell populations of clinically observed breast cancer.

Adenocarcinoma↗
PubMed1996

A novel 80 kDa human estrogen receptor containing a duplication of exons 6 and 7.

Alterations in the amino acid sequence of the estrogen receptor (ER) have been shown to have dramatic effects on its function. Recently, mutant ERs have been isolated from both clinical samples and established breast cancer cell lines, primarily through the use of the polymerase chain reaction (PCR). All previously reported mutations have given rise to either alterations or truncations of the ER protein. We determined the structure of a novel 80 kDa ER which is expressed in an estrogen independent subclone of the MCF-7 human breast cancer cell line (MCF-7:2A). This 80 kDa ER was initially detected by Western blot analysis using a variety of ER specific antibodies. PCR mapping and partial PCR mediated subcloning of the ER cDNA were used to demonstrate that this protein was an ER containing an in-frame duplication of exons 6 and 7. This type of duplication has not been previously described for any members of the steroid receptor superfamily. Karyotype analysis coupled with fluorescence in situ hybridization (FISH) demonstrated that MCF-7:2A cells contained 4-5 copies of the ER gene in contrast to 2 copies in MCF-7:WS8 cells. The ER gene was localized by FISH analyses in both the MCF-7:WS8 and MCF-7:2A cells on chromosome 6, which is the source of the ER in normal human cells. The relative expression level of 2:1 is consistent with DNA gene dosage analysis. Genomic PCR was then used to demonstrate that the 80 kDa ER mRNA was not derived from the trans-splicing of two ER mRNAs but was the result of a genomic rearrangement in which exons 6 and 7 were duplicated in an in-frame fashion. This variant ER may prove to be useful in elucidating the mechanism of estrogen action in breast cancer cells.

Base Sequence↗
PubMed1996

Mutations of the estrogen receptor in endometrial carcinoma: evidence of an association with high tumor grade.

The majority (60-70%) of endometrial cancers express estrogen receptor. Typically, estrogen-receptor-positive endometrial tumors are associated with a more favorable outcome. Despite this, there is often a discrepancy between estrogen receptor expression and clinical outcome of the disease. Although little is known about the exact role of the estrogen receptor in endometrial malignancies, in breast cancer, where such information is abundant, a number of mutations of the estrogen receptor have been identified. To investigate whether mutations of the estrogen receptor gene occur in endometrial cancers we performed single-stranded conformational polymorphism analysis (SSCP) on 35 human endometrial tumors. We detected four point mutations in three different patients. Interestingly, all the mutations were detected in patients who had aggressive endometrial tumors (grade 3). Although we found the incidence of mutations of the estrogen receptor to be low (8.5%) and thus unlikely to be associated with the majority of endometrial cancers, further investigation is needed to elucidate the role of aberrant estrogen receptor expression in the progression of endometrial malignancies.

DNA Mutational Analysis↗
PubMed1996

A realistic clinical perspective of tamoxifen and endometrial carcinogenesis.

Tamoxifen has been the endocrine treatment of choice for all stages of breast cancer for nearly a decade. Millions of women are currently receiving tamoxifen worldwide, while large-scale randomised trials have been launched aiming to investigate the drug's merit as a preventive agent. However, there are now concerns about tamoxifen's potential carcinogenicity. The goal of this review is to address these concerns, re-evaluate the available data from laboratory biological models and those from clinical reports and put the whole issue into perspective. Our focus is the association between tamoxifen and the increased frequency of endometrial tumours, while key issues, such as the role of duration of tamoxifen therapy, are also addressed. Finally, we discuss the various monitoring strategies for early detection of endometrial lesions and pertinent problems most likely to be encountered by clinicians taking care of patients who are receiving tamoxifen.

Animals↗
PubMed1996

An analysis of tamoxifen-stimulated human carcinomas for mutations in the AF-2 region of the estrogen receptor.

The estrogen receptor (ER) contains two transcriptional activation domains: AF-1 and AF-2. AF-2 is dependent on a highly species-conserved region of the ER. It has been shown that site-directed point mutations of conserved hydrophobic amino acids within this region reduce estrogen-dependent transcriptional activation. In addition, when these mutated ERs are transfected into HeLa cells, both tamoxifen and ICI 164,384 become strong agonists. The implication is that mutations in this region could account for the tamoxifen-stimulated tumors seen clinically. We performed single stranded conformational polymorphism (SSCP) analysis spanning the entire ER along with DNA sequencing of the AF-2 region of the ER isolated from two different tamoxifen-stimulated breast cancers, MCF-7/TAM and MCF-7/MT2, and a tamoxifen-stimulated endometrial cancer, EnCa 101. In addition, a tamoxifen-stimulated endometrial carcinoma cell line, the Ishikawa cell line, was also studied. There were no mutations found by SSCP analysis and sequencing of all four AF-2 regions also revealed no mutations. Mutations within the AF-2 region of the human ER do not appear to account for the growth of human breast and endometrial carcinomas that are used as reproducible laboratory models of tamoxifen-stimulated growth observed clinically.

Carcinoma↗
PubMed1996

Targeted anti-estrogens to treat and prevent diseases in women.

The estrogen receptor has been successfully targeted with the anti-estrogen tamoxifen to treat all stages of breast cancer. Because tamoxifen is a partial agonist, it exhibits target-site specificity: it acts as an anti-estrogen in the breast to inhibit tumor growth, while exhibiting estrogenic effects on bones and lipid metabolism. Therefore, tamoxifen has the added benefit of maintaining bone density and reducing the risk of myocardial infarction in postmenopausal women. However, undesirable side effects of tamoxifen preclude its use as a hormone replacement therapy for otherwise healthy women. New anti-estrogens are currently being developed that may prevent osteoporosis, breast and endometrial cancer, and reduce the risk of myocardial infarction.

Animals↗
PubMed1996

Irreversible loss of the oestrogen receptor in T47D breast cancer cells following prolonged oestrogen deprivation.

The development of antioestrogen resistance is a major clinical obstacle encountered in the treatment of breast cancer. By long-term growth in oestrogen-free medium, we have derived an oestrogen-independent, anti-oestrogen resistant cell line from the oestrogen receptor (ER)-positive, oestrogen-dependent T47D human breast cancer cell line. This cell line grows maximally in oestrogen-free medium and is resistant to all tested antioestrogens. This cell line does not express any measurable amounts of ER mRNA or protein and, in short-term studies, these cells show no response to either oestrogens or antioestrogens. However, return of these cells to oestrogen-containing medium for more than 8 weeks resulted in the re-expression of ER mRNA and protein. Subsequent limiting dilution subcloning of the T47D:C4 line revealed two phenotypically distinct clones, one which did not express measurable ER after long-term growth in oestrogen-containing medium and one which expressed ER mRNA and protein after a number of weeks in oestrogen-containing medium. In the absence of oestrogen, both types of cells are ER-negative as determined by Northern and Western blotting and lack of any oestrogen-dependent responses. The clone which re-expresses the ER (T47D:C4:5W) now responds to E2 with a 50% increase in growth and a 30-fold induction of an ER-responsive luciferase reporter construct. Long-term growth of the stably ER-negative clone (T47D:C4:2W) causes no measurable oestrogen-mediated responses, as assessed by ER expression, growth stimulation or luciferase induction. Interestingly, ER mRNA can be detected in both cell types by using reverse transcriptase-polymerase chain reaction (RT-PCR). This suggests that the ER mRNA present in the T47D:C4:2W clone is either inefficiently translated or is present at such a low level as to be functionally irrelevant. These novel clonal cell lines will prove to be invaluable in the study of the regulation of ER expression and regulatory pathways leading to oestrogen-independent growth.

Blotting, Southern↗
PubMed1996

The effect of tamoxifen and two of its non-isomerizable fixed-ring analogs on multistage rat hepatocarcinogenesis.

Long-term treatment of breast cancer patients with tamoxifen has prompted concern over potential toxicity of this drug with chronic administration. Since tamoxifen has estrogenic action in the rat liver and estrogenic agents can increase hepatoma incidence in rats, tamoxifen and two non-isomerizable, fixed-ring analogs (FRT1 and FRT2) were evaluated as promoting agents in a two-stage model of hepatocarcinogenesis in female Fischer F344 rats. The rats were subjected to 70% partial hepatectomy and half of the animals were administered the initiating agent, diethylnitrosamine (DEN; 10 mg/kg body wt), while the other half were not initiated. Groups of initiated and uninitiated animals were allowed to recover for 2 weeks and were then administered tamoxifen or one of the fixed-ring analogs admixed into AIN-76A diet at 25, 100 or 250 mg/kg diet. After 6 months of anti-estrogen administration the rats were sacrificed and uterine weights, blood levels of anti-estrogen, and liver histopathology were assessed. Uterine weights were decreased 2- to 3-fold by each of the agents, consistent with an anti-estrogenic action in the rat. The serum levels in rats administered 250 mg anti-estrogen/kg diet for 6 months were 320+/-20 ng/ml for tamoxifen, 320+/-10 for FRT1 and 350+/-20 for FRT2. The liver levels after a 6 month administration of 250 mg anti-estrogen/kg diet were 13 870+/-860 ng/g for tamoxifen, 13 300 +/-860 for FRT1 and 26 900+/-1900 for FRT2. A dose-dependent increase in serum and liver level of each compound was noted when measured at the 6 month time period. The number and percentage of the liver occupied by altered hepatic foci (AHF) were determined by quantitative stereology. A dose-dependent increase above initiated controls was observed in the initiated, tamoxifen-treated rats. Both fixed-ring analogs also increased the number and size of AHF compared with initiated controls, but were less potent than tamoxifen, suggesting that tamoxifen has an intrinsic promoting action in the liver that is independent of its ability to isomerize to more potent estrogenic compounds. In addition, the fixed-ring analogs have a weaker promoting activity in the rat liver than does tamoxifen. This may be due to pharmacokinetic differences at the lower two doses, but it is independent of achieved serum level at the highest dose and hence may reflect differences in intrinsic activity of these compounds. Thus tamoxifen and the two fixed-ring analogs promote the development of rat hepatocarcinogenesis.

Animals↗
PubMed1996

Induction of hepatic aneuploidy in vivo by tamoxifen, toremifene and idoxifene in female Sprague-Dawley rats.

Since tamoxifen is efficacious for the prevention of second primary breast neoplasms in humans and has a low reported incidence of acute side effects, several structurally related compounds have been developed for the treatment of breast cancer including toremifene and idoxifene. We have compared the karyotypic alterations that occur after a single per os administration of 35 mg/kg of tamoxifen, toremifene or idoxifene to female Sprague-Dawley rats. One day following treatment, the rats were sacrificed and the hepatocytes isolated and cultured. After 47 h in culture, colcemid was added for 3 h prior to harvest of the hepatocytes for karyotypic evaluation. At least 100 metaphase spreads were examined for each of five rats per treatment. Toremifene resulted in aneuploidy in 50 +/- 7% of the cells examined and idoxifene induced a 57 +/- 4% aneuploidy compared with the 85 +/- 7% level induced by tamoxifen. Since the level of aneuploidy in solvent-treated rats was 3 +/- 3 %, the induction of aneuploidy in at least 50% of the cells from rats treated with tamoxifen, toremifene or idoxifene was highly significant. Analysis of electron micrographs of cultures treated with these antiestrogens demonstrated a range of phenotypes including multipolar spindles in toremifene-treated rats and condensed chromosomes in the presence of an intact nuclear envelope in occasional idoxifene-treated rat hepatocytes. The exclusion of chromosomes from the spindle apparatus and the lagging of some chromosomes on the metaphase plate correlate with the high rate of induction of aneuploidy in the rat liver as determined by karyotypic analysis of hepatocytes from rats treated with these triphenylethylenes.

Aneuploidy↗