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Background: Estramustine phosphate is a mustard-oestradiol conjugate, and has hormonal and non-hormonal effects. In phase II trials of patients with cancer, response to microtubule inhibitors increases when these drugs are combined with estramustine. We aimed to assess whether combining estramustine with chemotherapy increases survival in patients with castration-refractory prostate cancer., Methods: We systematically searched for randomised clinical trials that compared chemotherapy regimens with and without estramustine in patients with histologically-proven prostate cancer and were published between 1966 and 2004. Data from these studies were verified centrally and updated individual patient data were analysed. The primary endpoint was overall survival. Secondary endpoints were prostate-specific antigen (PSA) response, time to PSA progression, and toxicity. A Cox regression model that was stratified by trial and adjusted for covariates at baseline was used., Findings: The initial search identified seven eligible trials that included 742 patients, from which data from five trials including 605 patients had been collected. Individual patient data from two trials (137 patients) were no longer available. The 605 patients had been accrued between Jan 1, 1993 and Dec 1, 2003 and randomly assigned to chemotherapy plus estramustine or to chemotherapy without estramustine. Chemotherapy (with or without estramustine) consisted of docetaxel, paclitaxel, ixabepilone, and vinblastine. Median follow-up was 2.8 years (range 0.0-3.4), and 510 deaths had occurred by the end of follow-up. Cox regression analysis stratified by trial showed that concentrations of serum haemoglobin (p<0.0001), use of chemotherapy plus estramustine (p=0.008), performance status (p=0.002), and serum PSA concentrations (p=0.04) were associated independently with overall survival. Overall survival was significantly better in patients assigned chemotherapy plus estramustine (adjusted hazard ratio [HR] 0.77 [95% CI 0.63-0.93], p=0.008). Estimated absolute increase in overall survival when estramustine was added to chemotherapy was 9.5% (SE 4.0) at 1 year after randomisation. We did not note a significant association between treatment effect on overall survival and age, concentration of serum haemoglobin, performance status, or serum PSA concentration. Patients who received chemotherapy plus estramustine had a better PSA response than those who received chemotherapy without estramustine (RR 0.53 [0.38-0.72], p<0.0001). Time to PSA progression was significantly longer in patients assigned chemotherapy plus estramustine than in those assigned chemotherapy without estramustine (HR 0.74 [0.58-0.94], p=0.01). Patients assigned chemotherapy and estramustine had more grade 3 or grade 4 thromboembolic events compared with those assigned chemotherapy without estramustine (12 of 271 vs 1 of 275)., Interpretation: In patients with castration-refractory prostate cancer, addition of estramustine to chemotherapy increases time to PSA progression and overall survival compared with chemotherapy without estramustine. However, this benefit should be balanced with the risk of increased thromboembolic events in patients who receive estramustine and chemotherapy in combination compared with chemotherapy without estramustine.

Purpose: To determine the dose-limiting toxicities, maximum-tolerated dose, and pharmacokinetics of intravenous estramustine phosphate (IV EMP)., Patients and Methods: A total of 31 patients with hormone-refractory prostate cancer received IV EMP as a 30- to 90-minute infusion weekly (n = 28) or for 3 consecutive days followed by a single weekly dose (n = 3). IV EMP dose was escalated from 500 to 3,000 mg/m(2). Pharmacokinetics of EMP and the metabolites estramustine (EaM), estromustine (EoM), estradiol, and estrone were assessed after weeks 1 and 4 of treatment., Results: The initial IV EMP infusion caused perineal discomfort that was ameliorated by lengthening the infusion time. Other common toxicities were grade 1 to 2 hepatotoxicity, nausea or vomiting, and fatigue or malaise. Lower-extremity thrombosis occurred in one patient, and two others developed upper-extremity thrombosis associated with venous infusion catheters. Dose-limiting fatigue and hypotension occurred at 3,000 mg/m(2), and cumulative fatigue developed after multiple cycles at 2,500 mg/m(2). Mean EMP clearance, estimated steady-state volume of distribution, and elimination half-life were 3.7 L/h, 10.6 L, and 3.7 hours, respectively. Variability of EMP clearance was 21%, and variation in area under the curve per dose for the metabolites was 28% to 36%. Elimination half-lives of EoM and EaM were 110 hours and 64 hours, and peak plasma concentrations of these active metabolites exceeded 10 micromol/L after IV EMP doses greater-than-or-equal 2,000 mg/m(2)., Conclusion: High-dose IV EMP can be administered safely as a weekly short infusion to patients with HRPC. High peak concentrations of active metabolites after IV EMP may provide an advantage over oral EMP in antimicrotubule drug combinations.

Objectives: To exploit the favorable dose intensity and safety profile of weekly paclitaxel, we conducted a Phase I trial of paclitaxel by 3-hour infusion in combination with estramustine phosphate (EM) in men with hormone-refractory prostate cancer (HRPC). The antimicrotubule drug combination of paclitaxel by 96-hour infusion plus EM is active in HRPC., Methods: Twenty-four patients with metastatic HRPC and progressive tumor after antiandrogen withdrawal were enrolled in this study. Oral EM was taken at a dose of 600 mg/m(2) daily for the initial 21 patients and on a reduced schedule of 280 mg twice daily for the final 3 patients. Paclitaxel was escalated from 60 to 118 mg/m(2)., Results: The major toxicities were gastrointestinal and thromboembolic complications related to daily oral dosing of EM. Of the first 21 patients, one third (n = 7) discontinued therapy within 4 weeks because of protracted nausea and/or thrombotic complications. Dose-limiting toxicities at 118 mg/m(2) paclitaxel were fatigue and hepatotoxicity. Of 13 patients with measurable soft-tissue lesions, 6 had objective partial regressions, and 9 (37.5%) of 24 patients (95% confidence interval 19.1% to 59.1%) with elevated prostate-specific antigen levels had a 50% or greater decline of at least 4 weeks' duration., Conclusions: Weekly paclitaxel at doses of 60 to 107 mg/m(2) were feasible in combination with oral EM, but daily oral EM produced unacceptable toxicity. On the basis of these results, a Phase II trial of weekly paclitaxel with the reduced dose and schedule of EM was initiated by the Eastern Cooperative Oncology Group to assess further the benefits and risks of this treatment in men with metastatic HRPC.

Purpose: To compare vinblastine versus the combination of vinblastine plus estramustine as treatment for patients with hormone-refractory prostate cancer (HRPC)., Patients and Methods: A total of 201 patients with metastatic prostate cancer, progressive after hormonal therapy and antiandrogen withdrawal (if prior antiandrogen treatment), were randomized to receive vinblastine (V) 4 mg/m(2) by intravenous bolus weekly for 6 weeks followed by 2 weeks off, either alone or together with estramustine phosphate (EM-V) 600 mg/m(2) PO days 1 through 42, repeated every 8 weeks. Of 193 eligible patients, 98 received V, and 95 received EM-V., Results: Overall survival trended in favor of EM-V but was not significantly different as determined by Kaplan-Meier analysis (P =.08). Median survival was 11.9 months for EM-V and 9.2 months for V. EM-V was superior to V for secondary end points of time to progression (P <. 001, stratified log rank test; median 3.7 v 2.2 months, respectively) and for proportion of patients with >/= 50% prostate-specific antigen (PSA) decline sustained for at least 3 monthly measurements (25.2% v 3.2%, respectively; P <.0001). Granulocytopenia was significantly less for EM-V compared with V (grade 2, 3, and 4 = 7%, 7%, and 1% v 27%, 18% and 9%, respectively; P <.0001); however, grade 2 or worse nausea (26% v 7%, respectively; P =.0002) and extremity edema (22% v 8%, respectively; P =.005) were more frequent for EM-V., Conclusion: Although overall survival was not significantly greater for the combination, EM-V was superior to V for time to progression and PSA improvement. These results encourage further study of estramustine-based antimicrotubule drug combinations in HRPC.

Antimicrotubule drugs are used as chemotherapeutic agents due to their effects on essential cellular functions such as mitosis, organelle transport and maintenance of cell shape. When used in combination, paclitaxel with estramustine or vinblastine has demonstrated activity against hormone refractory prostate cancer. To understand the mechanism of resistance that develops in patients as a result of antimicrotubule drug therapy, we exposed human prostate carcinoma cells to IC20 and IC40 doses of estramustine, paclitaxel or vinblastine for 48 h and examined the beta-tubulin (the cellular target) isotype composition. The results revealed an increase in the betaIII-tubulin isotype as a result of drug treatment both at protein and message levels. In addition, examination of human brain cell lines with different intrinsic levels of betaIII showed that cell lines with higher betaIII levels were more resistant to paclitaxel. These results are in agreement with our previous findings in human prostate carcinoma cell lines that were made resistant to estramustine or paclitaxel and suggest an important function for betaIII in antimicrotubule drug resistance. Also, the complete coding sequence of human betaIII tubulin reported here will provide molecular tools for future investigations.

Long misclassified as an alkylating agent, estramustine phosphate is a stable conjugate of estradiol and nornitrogen mustard with antimitotic properties. Binding of the drug to microtubule-associated proteins, tubulin, and proteins of the nuclear matrix are presently considered to be the most likely mechanisms underlying the cytotoxicity of estramustine in androgen-independent prostatic carcinoma. Identification of these mechanisms of action has led to clinical reevaluation of estramustine phosphate (EMP) in several rationally designed drug combinations. Combination of EMP with either vinblastine, paclitaxel or etoposide has produced antitumor responses in 30% to 60% of patients with metastatic hormone-refractory prostate carcinoma as determined by reduction in bidimensionally measurable soft tissue disease, pain, and serum prostate-specific antigen. Whereas the antitumor activity of the combinations has been greater than additive for the single agents, the toxicities of treatment have not been greater than predicted for the individual drugs. The promising results of EMP-based chemotherapy encourage additional laboratory and clinical investigations to develop more effective therapy for hormone-refractory disease and for selected patients with earlier stages of prostate cancer.

Estramustine (EM), an antimicrotubule agent, is effective against hormone-refractory prostate cancer when used in combination with vinblastine or paclitaxel. To understand the effect of EM on beta-tubulin, a cellular target for this class of drugs, human prostate carcinoma cells (DU-145) were made resistant to EM, and two cell lines were selected at 12- (EM-12) and 15-microMolar (EM-15) concentrations of the drug. These cell lines exhibited 8- to 9-fold resistance to EM and 2- to 4-fold cross-resistance to paclitaxel. Immunofluorescent staining of the cells with beta-tubulin isotype-specific antibodies showed an approximately 6-fold increase in the beta(III)-tubulin levels and moderate increase in overall beta-tubulin levels in EM-resistant cells when compared to DU-145 cells. This increase of beta(III) isotype was confirmed by Western analysis. A reverse transcriptase-PCR assay was also employed using beta-tubulin isotype-specific primers to quantify beta-tubulin isotype RNA. A 4-fold increase in beta(III) and a 3-fold increase in beta(IV alpha) transcript were seen in both EM-resistant cell lines. These results indicate that overexpression of specific beta-tubulin isotypes may play a role in the cellular defense against EM and other antimicrotubule agents.

Background: Estramustine previously has been shown to interact with P-glycoprotein and to restore intracellular accumulation of vinblastine and paclitaxel in cells overexpressing this drug transporter. However, the ability of estramustine to potentiate the cytotoxicities of several drugs was less than that expected. To resolve this apparent discordance, the authors examined the effects of serum on the actions of estramustine., Methods: The cytotoxicities of anticancer drugs with or without estramustine or verapamil toward MCF-7 breast carcinoma cells and a P-glycoprotein-overexpressing subline MCF-7/ADR were determined using the sulforhodamine-binding assay. The extent of intracellular accumulation of [3H]vinblastine and [3H]paclitaxel was determined for each using standard methods, and the binding of radiolabeled drugs to plasma proteins was characterized by equilibrium dialysis., Results: Without serum, the sensitivities of MCF-7/ADR cells to several P-glycoprotein-transported drugs were increased by estramustine and verapamil. Conversely, when the cells were treated with a 10% serum, the cytotoxicities of these drugs were increased by verapamil, but not by estramustine. Without serum, intracellular accumulation of [3H]vinblastine and [3H]paclitaxel by MCF-7/ADR cells was increased markedly by verapamil and estramustine; however, serum suppressed the effects of estramustine much more strongly than those of verapamil. Equilibrium dialysis experiments demonstrated that [3H]estramustine binds to plasma proteins, predominantly albumin, whereas [3H]paclitaxel binds to albumin and alpha 1-acid-glycoprotein, and [3H]vinblastine binds predominantly to alpha 1-acid-glycoprotein., Conclusion: Although estramustine can bind to P-glycoprotein, its effectiveness as a reversing agent in vivo likely is limited by binding to plasma proteins.

Background: Previous preclinical studies of combinations of estramustine and vinblastine or paclitaxel (Taxol) have shown that it is possible to achieve a greater than additive cytotoxicity with these antimicrotubule drug combinations. Phase II studies in hormone-refractory prostate cancer have demonstrated clinical antitumor activity of sufficient magnitude to stimulate further laboratory and clinical studies of these drugs combinations., Purpose: Our purpose was to characterize the interactions of estramustine with P-glycoprotein and to determine its effects., Methods: Standard laboratory techniques were used to study the effects of estramustine on intracellular drug concentrations, cytotoxicity, and induction of messenger RNA (mRNA) for the MDR1 (also known as PGY1) gene. Using a photoaffinity analogue of estramustine 17-0-[[2-[3-(4-azido-3-[125I]-iodophenyl) propionamido]ethyl]-carbamyl]estradiol-3-N-bis(2-chloroethyl)ca rba mate ([125I]AIPP-estramustine), binding to the membrane proteins of human ovarian (SKOV3) and their multidrug-resistant counterpart SKVLB1 cells was studied. Southern-blot analysis was performed on DNA extracted from human prostate carcinoma wild-type DU145, estramustine-resistant cell line (E4), and SKVLB1 cells., Results: Membrane fractions from SKOV3 and SKVLB1 cells were analyzed for proteins that could be photoaffinity labeled with [125I]AIPP-estramustine. Competitive inhibition of this binding was achieved with excess concentrations of (in order of efficacy) estramustine, vinblastine, verapamil, progesterone, and to a lesser degree, by paclitaxel but not with estramustine phosphate, estradiol, and estriol. SKVLB1 cells accumulated much less [3H]vinblastine and [3H]paclitaxel than did SKOV3 cells. Estramustine caused a concentration-dependent enhancement of drug accumulation in the SKVLB1 cells to a maximum of approximately 12-fold. No effect of estramustine was apparent for the wild-type SKOV3 cells. In comparison with verapamil, estramustine was less effective as a modulator; however estramustine demonstrated good chemosensitizing activity in combination with actinomycin D and vinblastine. Neither short-term, low-dose no longer-term, higher concentration were found to produce measurable transcript (mRNA for the MDR1 gene levels. Such data suggest that, at least levels. Such data suggest that, at least for two distinct human cell line (SKOV3 and DU145), estramustine does not induce the overexpression of the MDR1 gene., Conclusion: It is apparent from the P-glycoprotein data that estramustine interacts with this efflux pump, altering intracellular drug accumulation. Overall, the nonempiric basis for including estramustine in clinical protocols that contain other multidrug-resistant drugs is strengthened by the present data.

A variety of cell biological, pharmacological, crystallographic and clinical approaches have indicated that the antimitotic drug estramustine has interesting and unusual properties. Although designed as an alkylating agent, the marked stability of the carbamate linkage to the steroid carrier molecule prevents the formation of alkylating intermediates. The affinity of the parent molecule for microtubule associated proteins and the concomitant antimicrotubule activity have cytotoxic consequences in tumor cells. Both preclinical and clinical studies of estramustine in combination with other antimicrotubule agents have shown that this approach has great potential to achieve therapeutic advantage, especially in disease states such as hormone refractory prostate cancer.