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Endocrinology |
Lilly Research Laboratories, A Division of Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana 46285
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ABSTRACT |
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 Top ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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(ER) and antagonistic activity against ER-mediated gene expression. The PAIII rat prostatic adenocarcinoma (PCa) is an androgen receptor-negative, ER- and ERß-positive, spontaneously metastatic rodent tumor cell line. After s.c. implantation of 106 PAIII cells in the tail, s.c. administration of trioxifene (2.0, 4.0, 20.0, or 40.0 mg/kg-day) for 30 days produced significant (P < 0.05) inhibition of PAIII metastasis from the primary tumor in the tail to the gluteal and iliac lymph nodes (maximum nodal weight decreases, 86% and 88% from control values, respectively). PAIII metastasis to the lungs was significantly inhibited by trioxifene treatment. Numbers of pulmonary foci in PAIII-bearing rats were significantly (P < 0.05) reduced by trioxifene administration in a dose-related manner (maximal reduction, 98% from control values). Continual administration of the compound significantly (P < 0.05) extended survival of PAIII-bearing rats. Trioxifene inhibited the proliferation of PAIII cells at micromolar levels in vitro but did not slow growth of the primary tumor growth in the tail. Trioxifene administration also produced regression of male accessory sex organs. In PAIII-tumor-bearing animals, trioxifene administration produced a maximal regression of 76% for ventral prostate and 64% for seminal vesicle (P < 0.05 for both). SERMs may be preferable to estrogens given their efficacy in experimental PCa models and relative lack of side effects observed in clinical trials. Our data support the contention that trioxifene represents a SERM with potential antimetastatic efficacy for the treatment of androgen-independent, metastatic PCa. |
INTRODUCTION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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in human prostatic malignancies may not be entirely attributable to decreased circulating androgens. Doses of synthetic estrogens that are efficacious in treating human PCa do not consistently reduce circulating testosterone to castrate levels (2, 3, 4)
. Indeed, estrogens may exert direct cytoreductive effects through ER (5)
in PCa cells that contribute to the observed clinical antitumor activity (6)
. Although estrogens such as diethylstilbestrol are effective in treating progressive, metastatic PCa, this utility is complicated by the risk of cardiovascular side effects. Consequently, the use of estrogens in treating advanced PCa has been superseded by luteinizing hormone-releasing hormone agonist analogues that produce androgen ablation but do not induce hypercoagulation or increase the incidence of cerebrovascular accidents.
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has been widely used to treat and prevent breast cancer and osteoporosis, but clinical experience in treating male disorders is limited. Second, a novel ER gene product, ERß (also known as ERß1), was cloned from a rat prostatic cDNA library and is expressed in murine and human prostate (8, 9, 10)
. ERß has been proposed to act as a ligand-activated tumor suppressor (11)
. The more recently characterized ER has been designated ERß, whereas the classical ER characterized in female accessory sex organs is designated ER.
Trioxifene (LY133314; [3,4-dihydro-2-(4-methoxyphenyl)-1-naphthalenyl][4-]2-(L-pyrrolidinyl)ethoxyphenylmethanone, methansulfonic acid salt; Fig. 1c
) is a SERM with activity in rat uterine bioassays (12)
. In these estrogen-supplemented female rats, the antagonist activity of trioxifene was comparable to that of tamoxifen. The inherent estrogenicity of trioxifene in immature female rats was approximately one-third less than that of tamoxifen (12)
. Trioxifene has demonstrated activity in dimethylbenzanthracene-induced mammary carcinoma in rats (13)
and human breast cancer patients (14)
. Our laboratory first demonstrated that SERMs such as LY117018 (Fig. 1d
; Ref. 15
) and raloxifene (Fig. 1e)
produce significant antiprostatic (16)
and antitumor responses in male LW rats that had received s.c. injections of PAIII cells in the tail (17)
. The antitumor activity of SERMs in rat models have recently been extended to cells and tumors of murine (18)
and human origin (19)
. Given the ability to surgically reduce primary tumor bulk and the lack of curative chemotherapy, antimetastatic agents may be useful to treat disseminated, androgen-independent human PCa after hormonal ablation (20)
. The PAIII adenocarcinoma in LW rats is a spontaneously metastatic tumor that is useful to evaluate agents to treat disseminated PCa. When PAIII cells are injected s.c. into the tails of male LW rats, a reproducible, time-dependent, sequential spread of the tumor through the gluteal and iliac lymph nodes to the lungs is observed (21)
. The morphology of the PAIII tumor resembles anaplastic lesions in humans, supporting its utility in evaluating cytotoxic and antimetastatic agents in advanced disease (22, 23, 24)
. This report characterizes the expression of ER and ERß protein in PAIII rat PCa cells as well as the ER/ERß selectivity of binding and agonist activity of trioxifene in vitro. Our data show that trioxifene administration dramatically suppresses PAIII metastasis to the lymph nodes and lungs, extends survival, produces involution of male accessory sex organs, and provides additional rationale for the use of SERMs to treat human PCa.
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MATERIALS AND METHODS |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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and ERß Binding Assay. and ERß followed modification of previously published procedures developed for cell and tissue lysates (25)
. The assays were run in buffer containing 50 mM HEPES (pH 7.5), 1.5 mM EDTA, 150 mM NaCl, 10% glycerol, 1 mg/ml ovalbumin, 5 mM DTT, 0.025 µCi/well of [3 H]-E2 (118 Ci/mmol, 1 mCi/ml; NEN Life Sciences, Boston, MA), and 10 ng/well of human recombinant ER or ERß protein (PanVera, Madison, WI). Trioxifene and LY117018 (Fig. 1)
were synthesized at the Lilly Research Laboratories (Indianapolis, IN) and added at 10 concentrations ranging from 0.3 to 10,000 nM. Nonspecific binding was determined in the presence of 1.0 µM E2 (Sigma, St. Louis, MO). The binding reaction (140 µl) was incubated 4 h at room temperature and terminated with 70 µl of cold dextran-coated charcoal buffer. Dextran-coated charcoal buffer was prepared by adding 0.75g of charcoal (Sigma) and 0.25g of dextran (Amersham Pharmacia Biotech, Piscataway, NJ) per 50 ml of assay buffer. The incubation plates were mixed 8 min on an orbital shaker at 4°C and then centrifuged at 3000 rpm for 10 min at 4°C. A 120-µl aliquot of the mixture was transferred to a 96-well, white, flat-bottomed plate (Costar, Acton, MA), and 175 µl of Wallac Optiphase Hisafe-3 (Boston, MA) scintillation fluid was added to each well. The plates were sealed and shaken vigorously on an orbital shaker. Radioactivity was counted in a Microbeta counter (Wallac, Turku, Finland) after an incubation of 2.5 h. The IC50, inhibition at 10 µM, and Kd values for [3 H]-E2 were determined by saturation binding to ER and ERß. The IC50 values for compounds were converted to Ki values by use of the Cheng-Prusoff equation and the Kd values determined by saturation binding assay (A-base software; IDBusiness Solution, Ltd., Guildford, United Kingdom).
PAIII ER-ERE and ERß-ERE Cotransfection Assay.
PAIII cells were cultured as described above, plated in 6-well plates (25,000 cells/well) and transfected using 6 µl/well Fugene-6 (Roche, Indianapolis, IN). Human ER or ERß cDNA was added to the cells with the human estrogen response element ERE-luc (11)
at concentrations of 0.5 µg/well each. Luciferase activity from PAIII cells exposed to trioxifene (0–10 µM in 0.1% DMSO) during the final 24 h of the 72-h transfection was normalized to renilla activity expressed by cotransfected pRLSV40 plasmid. Chemiluminescent activity was measured according to the manufacturer’s protocol (Dual-Luciferase Reporter 1000 Assay System kit; Promega, Madison, WI) and expressed as relative light units compared with that of vehicle (0.1% DMSO) control.
Western Blot Assays.
Protein extracts were taken from PAIII cells and analyzed by previously described Western blotting techniques (26)
. Protein lysates from PAIII, LNCaP, and LNCaP-derived LNAI T1.16 cells (27)
were previously prepared with use of radioimmune precipitation cell lysis buffer (New England Biolabs, Cambridge, MA). For Western blots, 30–40 µg of protein extract/lane was electrophoresed, transferred to polyvinylidene membranes (Hybond-P; Amersham Pharmacia Biotech) using the XCell II Mini-Cell apparatus (Novex, San Diego, CA), and immunoblotted. The antibodies used in these studies were as follows: ER (1:250 dilution; Chemicon International, Inc., Temecula, CA), ERß (1:200 dilution; Upstate Biotechnology, Inc., Lake Placid, NY), AR (1:500 dilution; Santa Cruz Biotechnology, Inc., Santa Cruz Biotechnology, CA), and ß-actin (1:2000; Sigma). Anti-mouse IgG, anti-rabbit IgG (Santa Cruz Biotechnology), and anti-sheep IgG (Upstate Biotechnology) secondary antibodies were used at a 1:2000 dilution. All Western blots were detected by chemiluminescence (Pierce, Rockford, IL) captured with the Lumi-imager and quantitated using the Lumi-Analyst software (Roche Molecular Biochemicals, Indianapolis, IN).
PI Cell Proliferation Assay.
PI (Sigma) for the proliferation assays was stored at a stock concentration of 1.0 mg/ml of H2O (-4°C). Five hundred PAIII cells per well (passage 113–115) in 100 µl of growth medium (DMEM with 10% fetal bovine serum) were plated in each well of a 96-well plate. An additional 100 µl of growth medium containing either trioxifene or LY117018 was added to each well at 24 h after plating to give a final incubation volume of 200 µl. Fresh medium containing drug or DMSO control was added every 2–3 days for a total of 7 days. Replacement of the growth medium with 200 µl of PBS and 10-min centrifugation of the plates (2000 rpm) completed the preparation. A working solution of PI was prepared at a final concentration of 50 µg/ml in distilled H2O. Twenty-five µl of working solution was added to each well. Cells were lysed by placing the plates in a -80°C freezer overnight and thawing to room temperature in a 37°C incubator. Foil-covered 96-well plates were placed on a rotator for 30 min and analyzed using the Victor2
fluorescent plate reader (Wallac). The plates were read from the bottom with excitation at 500 nm and emission at 615 nm for 1 s. Raw data were obtained as light units and reported as percentage of control (JMP; SAS Institute, Cary, NC).
PAIII Cell Culture and LW Rats.
Dr. Morris Pollard (University of Notre Dame, South Bend, IN) supplied a stock culture of PAIII rat PCa cells at passage 107. This original stock culture was expanded through two passages and stored in liquid nitrogen with 10% DMSO as a cryoprotectant. The cells were kept in liquid nitrogen as 1.0-ml aliquots at a minimum concentration of 1.0 x 106 cells/ml. PAIII cells were grown in antibiotic-free MEM with Earle’s salts (Life Technologies, Grand Island, NY) supplemented with 10% FCS (Hyclone Laboratories, Logan, UT). The cells were grown to confluency and harvested with use of 0.06 units/cm2 trypsin (2x recrystallized grade; Worthington Biochemical Corp., Freehold, NJ).
The breeding stock of LW rats was a gift from Dr. Morris Pollard. LW rats were maintained as a closed colony at Harlan Industries (Cumberland, IN). Male rats weighing 110–125 g were used. Two or three rats were housed in screen-bottomed cages in a light-controlled environment (lights on: 6:00 a.m., lights off: 8:00 p.m.). Water and powdered Rodent Laboratory Chow 5001 (Ralston-Purina, St. Louis, MO) were supplied ad libitum. These investigations were conducted under practices outlined for the care and use of laboratory animals set forth by the NIH and the American Association for Laboratory Animal Care.
On day 0, animals were randomized into five or six groups (10 rats/group). All except one of these groups received injections of PAIII cells. Injections of tumor cells and surgical procedures were done under light Metofane (Pittman-Moore, Washington Crossing, NJ) anesthesia. For each injection, 106 PAIII cells in a volume of 50 µl were injected s.c. into the dorsal surface halfway between the base and tip of the tail with a 25-gauge needle. Control animals received saline injections. Rats not receiving injections of PAIII cells were designated the non-PAIII-bearing (NO PAIII) control group. These studies were conducted for 28–29 days. In the dose-response studies, PAIII-bearing experimental groups were administered trioxifene (2.0, 4.0, 20.0, and 40.0 mg/kg) as 0.2-ml single daily s.c. injections. Daily injections were given in the morning (8:00 to 9:00 a.m.). Control groups received equivolumetric vehicle injections.
Trioxifene administered to PAIII-bearing rats was dissolved in ethanol and diluted to a final ethanol:peanut oil ratio of 1:10. The compound was stored in lightproof containers at -20°C before formulation and in lightproof bottles at room temperature during compound administration. Trioxifene for injection was formulated for 2-week treatment intervals on a body-weight basis. Initial dose formulations were calculated based on previously observed 2-week body weight gains in untreated rats. After 2 weeks of trioxifene treatment, doses in each group were adjusted relative to changes in group body weight mean values.
One-half of the rats in each treatment group were sacrificed on day 28. The remaining animals were sacrificed the following day. Rats were sacrificed by CO2 asphyxiation, body weights was recorded, and tails were amputated 1 inch from the base and weighed. The gluteal and iliac lymph nodes were also excised and weighed. The lungs were removed and inflated through the trachea with 
5.0 ml of Bouin’s fixative. The lungs were placed in Bouin’s fixative for 24 h and stored in 70% ethanol. Pleural lesions on the lung surface were counted under a dissecting microscope by methods published previously (21)
.
Effects of Trioxifene on Survival.
The effects of trioxifene on PAIII-bearing LW rat survival were subsequently evaluated in studies using a 40.0 mg/kg-day dose of the compound. Rats were divided into six experimental groups. Five groups received injections of PAIII cells as described above, and one experimental group received injections of 50 µl of isotonic saline in the tail. Three of the PAIII-bearing experimental groups were administered trioxifene (40.0 mg/kg-day) as described above. After 28 days, the PAIII- and non-PAIII-bearing control groups and one of the three trioxifene-treated groups were sacrificed as described above. At this time, compound administration was discontinued in one group of trioxifene-treated PAIII-bearing rats. These animals were administered vehicle until death. The remaining trioxifene-treated group continued to receive the compound (40.0 mg/kg-day) until death. The rats were checked each morning, and moribund animals were sacrificed if their condition indicated that they would not live through the day. These animals were necropsied, and tissues were processed as described above.
Statistical Analysis.
Numerical data from the cell proliferation studies were expressed as mean percentage of control ± SE from triplicate observations during three separate experiments. Differences in the mean values among different treatment groups were compared using Dunnett’s test (JMP; SAS Institute). Differences with P values <0.05 were considered statistically significant. The data from the in vivo experiments were analyzed using Dunnett’s multiple comparison procedure. Dunnett’s test assumes equal group variances. Analyses with Bartlett’s test determined that there were significant (P < 0.001) differences among the group variances for the tail, gluteal and iliac lymph nodal, and pulmonary focal variables; therefore, Dunnett’s test was performed on the rank-transformed data, providing a nonparametric analysis (27)
.
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RESULTS |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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and rhERß Protein and Inhibits ER-mediated Luciferase Activity. and rhERß binding are depicted in panels a and b of Fig. 2
, respectively. Trioxifene competed with [3 H]-E2 binding to rhER with an IC50 of 203.49 nM and a Ki of 20.84 nM. The compound was less potent at displacing [3 H]-E2 binding to rhERß, with an IC50 of 1506.04 nM and a Ki of 144.85 nM.
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- and ERß-ERE-driven luciferase reporter assay was used to assess the estrogenic activity of trioxifene in PAIII cells. E2 administration induced ER- and ERß-ERE-mediated luciferase transcription in cultured PAIII cells at concentrations >10 nM and >100 nM, respectively. Trioxifene was a weak antagonist for ER-mediated luciferase transcription in PAIII cells, inhibiting reporter activity at concentrations >100 nM (Fig. 3)
. Trioxifene had no activity against ERß-ERE-mediated luciferase transcription in PAIII cells at any of the concentrations studied.
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and ERß but Not AR. (Fig. 4)
. PAIII cells expressed lower levels of ER than their human PCa cell line comparators. ERß expression was detected in PAIII cells, albeit at lower levels than in the parental LNCaP cells. AR protein immunoreactivity was observed in LNCaP but not detected in PAIII rat PCa cells.
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). In vivo administration of trioxifene failed to produce cytoreductive effects against primary PAIII tumor growth in the tail (Table 1)
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. Maximum inhibition of PAIII lymphatic metastasis to the gluteal and iliac lymph nodes was 86 and 88%, respectively. In addition to suppressing lymph nodal metastases, trioxifene inhibited metastasis to the lungs. Lung colony numbers were significantly reduced (P < 0.05) by trioxifene administration. Maximum inhibition of pulmonary metastasis was 98% with a daily trioxifene dose of 40.0 mg/kg-day (Fig. 7)
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and pulmonary foci counts (-87%; Fig. 9
). Trioxifene failed to reduce the primary tumor weights in the tail (data not shown).
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). Administration of trioxifene to PAIII-bearing rats from the day after PAIII cell injection until death significantly (P < 0.05) extended survival (mean survival, 64.44 ± 2.99 days) beyond the vehicle control and trioxifene (28 days) plus vehicle treatment groups.
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. Trioxifene also produced decreases in normalized seminal vesicular weights with maximum inhibition of 64% at a daily dose of 40.0 mg/kg-day. Trioxifene administration to PAIII-bearing rats produced significant (P < 0.05) increases in normalized (per 100 g of body weight) testicular weights (Table 1)
over PAIII control levels. In these animals, the absolute testicular wet weights were not significantly changed from control values. Trioxifene administration to PAIII-bearing rats produced significant (P < 0.05) dose-related decreases in final-to-initial body weight ratios (Table 1)
. Maximum inhibition of body weight gain was 31% from nontreated controls at a daily trioxifene dose of 40.0 mg/kg-day. |
DISCUSSION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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-selective SERM trioxifene inhibits the in vitro cellular proliferation and in vivo metastasis of the androgen-independent PAIII metastatic PCa cell line in rats. PAIII cells express measurable levels of both the and ß isoforms of ER and are AR negative. Unlike most human prostatic malignancies, PAIII and other rat metastatic PCa cells are AR negative (28
, 29)
. Despite this phenotypic difference, the PAIII model has utility for evaluating the potential role of ER and ERß in mediating tumor progression and metastasis. Our results with trioxifene confirm previously published findings of antimetastatic activity with LY117018 (15)
and raloxifene (17)
in this rat PCa preclinical model. In dimethylbenzanthracene-treated female rats, trioxifene administered in the dose range used in our PAIII studies was less effective than tamoxifen in preventing the development of mammary tumors (13)
. The antimetastatic activity of tamoxifen in the PAIII model is inferior to trioxifene.3
In contrast, the highest trioxifene dose tested in the PAIII model (40.0 mg/kg-day, or 240.0 mg/m2) was comparable to an active dose of the drug (200.0 mg/m2) evaluated in human breast cancer patients (30)
. Our data add to a growing body of evidence that suggests potential therapeutic utility of SERMs such as trioxifene in PCa patients with androgen-independent metastatic disease. A recent publication demonstrated the AR-independent activation of caspase-9-related apoptotic activity of a related SERM, raloxifene, in LNCaP cells. These data have provided part of the preclinical rationale for ongoing human clinical trials with raloxifene in PCa patients (19)
.
Trioxifene is an active competitor for human ER, binding with approximately 20-fold selectivity over the ERß isoform. The compound is antagonistic for ER-mediated luciferase activity in PAIII cells at concentrations exceeding 100 nM. Trioxifene did not markedly alter ERß-mediated luciferase activity at any concentration tested in these same cells. Given these in vitro responses, trioxifene can be considered a SERM with selective ER-antagonistic properties in a malignant prostatic epithelial cellular environment. PAIII rat prostatic adenocarcinoma cells express both ER and ERß but are AR negative, as evidenced by the Western blot immunoreactivity described here and the lack of in vivo responsiveness to castration of the tumor-bearing host (15)
. Our data from PAIII cell lysates correlate with the findings of Lau et al. (31)
, who demonstrated variable expression of ERß and ER in the AR-negative human PCa cell lines DU-145 and PC-3.
We have demonstrated an approximate 50-fold difference in trioxifene concentrations needed to compete for ER binding and ER-mediated luciferase gene activation as well as the antiproliferative effects of the compound in PAIII cell cultures. This differential potency between the biochemical and PAIII cellular responses may reflect the cellular trafficking of trioxifene or the potential for this agent and other SERMs to impinge on off-target-mediated cellular pathways at concentrations in excess of levels relevant to their binding to the two ER gene products. ER-independent high-affinity binding sites for SERM binding have been demonstrated in a variety of models (32
, 33)
; however, the role of these binding proteins in mediating estrogenic and SERM cellular responses is poorly understood.
Trioxifene treatment significantly inhibited PAIII metastasis through lymphatic channels and reduced the spread of the tumor to the lungs. One mechanism for the antimetastatic action of trioxifene, like LY117018 and raloxifene in PAIII tumors, may be mediated by the ER antagonistic properties of these SERMs. In a limited series of human androgen-independent and metastatic PCa specimens, Bonkhoff et al. (34)
demonstrated an association between increased levels of endogenous ER and expression of the androgen-independent metastatic PCa phenotype. The antiproliferative effects seen with trioxifene in cell culture conditions were not extended in vivo to a reduction of primary PAIII tumor in the tail. The observed antimetastatic effects of trioxifene may result from the action of ER as an antagonist to processes involved with tumor metastasis (34)
rather than as an inhibitor of growth of the metastatic lesions.
Although these studies lacked sufficient numbers of PAIII-bearing rats to demonstrate a statistical response based on Kaplan-Meier analysis,3 trioxifene-induced decreases in metastatic tumor burden were sufficient to significantly extend the life span of PAIII-bearing rats. Survival is the key preclinical end point for the assessment of a potential antimetastatic agent for human trials (35) . These data support the contention that trioxifene treatment reduces lymphatic and pulmonary tumor burden and extends life span, producing significant statistical and meaningful clinical responses in tumor-bearing animals. Despite the variability in untreated control absolute PAIII tumor burdens, trioxifene produced consistent antimetastatic responses in multiple in vivo studies. It should be noted that trioxifene-treated PAIII-bearing rats were not free of metastatic disease. Total lymphatic and pulmonary tumor burden was markedly reduced but not eliminated by 28 days of trioxifene treatment, and residual lesions persisted that were apparently resistant to the antimetastatic effects of the compound. On the basis of these studies and the findings of others, a potential therapeutic strategy for PCa may involve the adjunctive use of trioxifene or other SERMs in combination with hormonal ablation or cytoreductive therapy (19) .
Given the ER-selective pharmacological activity of trioxifene, the caveat imparted by the evidence is that there were no significant patient responses to the early-generation SERMs, toremifene and tamoxifen, when they were used to treat advanced androgen-independent PCa (36, 37, 38, 39, 40, 41, 42, 43, 44)
. In these trials, the early-generation SERMs were administered to patients whose disease may have progressed to the point where the tumors were refractory to therapy. In our studies, trioxifene was administered to PAIII-bearing LW rats beginning the day after tumor cell inoculation. The antimetastatic activity of other SERMs in the PAIII model is diminished when therapy is delayed.3
Early intervention with toremifene has been shown to prevent carcinogenesis in TRAMP mice (18)
and is presently being evaluated as a chemopreventive agent in presurgical patients with the diagnosis of high-grade prostatic intraepithelial neoplasia, a presumed PCa precursor lesion. Unlike toremifene, which increased rodent ventral prostatic weights, trioxifene produced regression of the ventral prostate and seminal vesicles consistent with its SERM activity in the male accessory sex organs (16)
. The degree of trioxifene-induced accessory sex organ regression was similar to the effects of comparable tamoxifen doses in rats.3
Trioxifene-induced reductions in rodent accessory sex organ weights raise the possibility that this agent might be useful in treating androgen-sensitive benign and malignant neoplasms in addition to androgen-independent metastatic PCa. Apparent increases in normalized testicular weights in trioxifene-treated rats were largely attributable to slight, nonsignificant organ weight decreases in the presence of diminished body weight gains. Dose-related reductions in final-to-initial body weight ratios observed in these pubescent rats treated with trioxifene, although being statistically significant and substantial (-31%), were not the result of systemic compound toxicity. Estrogen agonists and SERMs produce significant, albeit nontoxic body weight reductions in rodents through their hypothalamic-mediated inhibition of feeding behavior (45
, 46)
.
Although trioxifene appeared to exert its antitumor activity in the PAIII model through ER, modulation of the related gene product, ERß, may provide an additional approach to the treatment of PCa and other malignancies. Using human PCa xenograft models, Corey et al. (47)
have proposed that the antitumor activity of estrogenic agents in PCa xenograft models is mediated exclusively through the ERß isoform. These issues will be resolved as ER- and ERß-selective modulators become available for study in PCa cell and tumor models. The data presented here support the contention that trioxifene and related compounds could be useful in the treatment of androgen-independent metastatic PCa. Trioxifene was well tolerated and showed activity in human breast cancer studies (14)
. To the extent that the metastatic processes in the rat PAIII model may be similar in human PCa, trioxifene deserves consideration for clinical evaluation in humans for this indication. In addition, understanding the antimetastatic mechanism(s) of trioxifene action in PCa may provide new approaches to the treatment of androgen-independent metastatic disease.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 To whom requests for reprints should be addressed, at Cancer Research, Lilly Research Laboratories Drop Code 0546, Lilly Corporate Center, Indianapolis, IN 46285. Phone: (317) 276-5675; Fax: (317) 277-3652; E-mail: neubauer_blake_l{at}lilly.com 
2 The abbreviations used are: PCa, prostatic cancer; ER, estrogen receptor; SERM, selective estrogen receptor modulator; LW, Lobund Wistar; E2, 17ß-estradiol; ERE, estrogen response element; AR, androgen receptor; PI, propidium iodide; rh, recombinant human.
3 B. L. Neubauer, unpublished observations.
Received 11/ 6/02. Revised 6/16/03. Accepted 7/21/03.
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REFERENCES |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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and ß. Endocrinology, 138: 863-870, 1997. (ER-) and ß (ER-ß) mRNA in the rat pituitary, gonad, and reproductive tract. Steroids, 63: 498-504, 1998.[Medline]
(ER) and estrogen receptor-ß (ERß) messenger ribonucleic acid in the wild-type and ER-knockout mouse. Endocrinology, 138: 4613-4621, 1997. and ER-ß in normal and malignant prostatic epithelial cells: regulation by methylation and involvement in growth regulation. Cancer Res., 60: 3175-3182, 2000.This article has been cited by other articles:
|
|
 |
|
  O. Wada-Hiraike, O. Imamov, H. Hiraike, K. Hultenby, T. Schwend, Y. Omoto, M. Warner, and J.-A. Gustafsson Role of estrogen receptor beta in colonic epithelium PNAS, February 21, 2006; 103(8): 2959 - 2964. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Mimeault and S. K. Batra Recent advances on multiple tumorigenic cascades involved in prostatic cancer progression and targeting therapies Carcinogenesis, January 1, 2006; 27(1): 1 - 22. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 O. Imamov, G.-J. Shim, M. Warner, and J.-A. Gustafsson Estrogen Receptor beta in Health and Disease Biol Reprod, November 1, 2005; 73(5): 866 - 871. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Pollard and M. A. Suckow Hormone-Refractory Prostate Cancer in the Lobund-Wistar Rat Exp Biol Med, September 1, 2005; 230(8): 520 - 526. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. Guerini, D. Sau, E. Scaccianoce, P. Rusmini, P. Ciana, A. Maggi, P. G.V. Martini, B. S. Katzenellenbogen, L. Martini, M. Motta, et al. The Androgen Derivative 5{alpha}-Androstane-3{beta},17{beta}-Diol Inhibits Prostate Cancer Cell Migration Through Activation of the Estrogen Receptor {beta} Subtype Cancer Res., June 15, 2005; 65(12): 5445 - 5453. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. F. Koehler, L. A. Helguero, L.-A. Haldosen, M. Warner, and J.-A. Gustafsson Reflections on the Discovery and Significance of Estrogen Receptor {beta} Endocr. Rev., May 1, 2005; 26(3): 465 - 478. [Abstract] [Full Text] [PDF]
|
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 |
|
 C. P. Cheung, S. Yu, K. B. Wong, L. W. Chan, F. M. M. Lai, X. Wang, M. Suetsugi, S. Chen, and F. L. Chan Expression and Functional Study of Estrogen Receptor-Related Receptors in Human Prostatic Cells and Tissues J. Clin. Endocrinol. Metab., March 1, 2005; 90(3): 1830 - 1844. [Abstract] [Full Text] [PDF]
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 X. Zhu, I. Leav, Y.-k. Leung, M. Wu, Q. Liu, Y. Gao, J. E. McNeal, and S.-M. Ho Dynamic Regulation of Estrogen Receptor-{beta} Expression by DNA Methylation During Prostate Cancer Development and Metastasis Am. J. Pathol., June 1, 2004; 164(6): 2003 - 2012. [Abstract] [Full Text] [PDF]
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