Proteolytic cleavage of high-molecular-weight microtubule-associated proteins by the prostatic estramustine-binding protein

Phase II trial of oral estramustine, oral etoposide, and intravenous paclitaxel in hormone-refractory prostate cancer

PURPOSE

To evaluate the combination of intravenous (IV) paclitaxel, oral estramustine, and oral etoposide in patients with advanced hormone-refractory prostate cancer.

PATIENTS AND METHODS

Forty patients with carcinoma of the prostate that was progressing despite hormonal therapy and who had undergone antiandrogen withdrawal (if previously treated with an antiandrogen) were enrolled onto this phase II trial. Patients were treated with oral estramustine 280 mg tid and oral etoposide 100 mg/d for 7 days, with paclitaxel 135 mg/m(2) IV over 1 hour on day 2 of each 21-day treatment cycle. Patients received a maximum of six cycles of therapy.

RESULTS

Thirty-seven patients were assessable for response. Twenty-two had measurable disease at baseline; response was not assessable in six of these patients. Overall response was 45% (10 of 22 patients; 95% confidence interval [CI], 24% to 68%), and response was 63% (10 of 16) in assessable patients. Twenty-six patients had a > or = 50% decrease from their baseline prostate-specific antigen levels during therapy, for a response rate of 65% (95% CI, 48% to 79%) by this criterion. Median duration of response was 3.2 months, with an estimated median survival of 12.8 months. Major toxicities of therapy were leukopenia (eight patients had > or = grade 4 leukopenia) and anemia. Hematologic toxicity seemed to be associated with liver metastases. Serial measurements in 24 patients using the Functional Assessment of Cancer Therapy-Prostate (FACT-P) showed no significant change in quality of life (QOL) as a result of therapy.

CONCLUSION

The combination of IV paclitaxel, oral estramustine, and oral etoposide is active in patients with advanced prostate cancer. The regimen is tolerable and does not have a significant impact on QOL as measured by the FACT-P in a limited sample of patients.

Phase II study of estramustine and vinorelbine in hormone-refractory prostate carcinoma patients

The purpose of this study was to evaluate the antitumor activity of vinorelbine and oral estramustine phosphate in patients with metastatic, hormone-refractory prostate cancer. We evaluated the activity of this association using the following schedule: estramustine phosphate 600 mg/m2/day orally days 1-42 and vinorelbine 25 mg/m1 days 1, 8, 22, 29 cycles repeated every 56 days. Twenty-five patients were included in the study, 24 being evaluable for response and 25 for toxicity. Out of 5 patients with measurable disease, none had an objective response. Of the 24 assessable patients with bone metastases, 9 patients had a > or = 65% decline in pretreatment prostate-specific antigen (PSA) level, stable disease was observed in 10 and 5 patients progressed. Toxicities were minimal. Anemia was observed in 5 patients, alopecia in 4 and nausea and vomiting was observed in 6 patients. Anorexia and weight loss of more than 10% were observed in 2 patients. This combination is active and well tolerated in hormone-resistant prostate cancer. These results support the therapeutic strategy of combining agents that impair microtubule function.

Radioiodinated estramustine phosphate and estramustine binding protein antibody accumulate in the prostate of a mouse

BACKGROUND

The purpose of this study was to determine the distribution of radioiodinated estramustine (RI-EMP) and a radioiodinated antibody against estramustine binding protein (RI-EMBP-AB) in mice.

METHODS

RI-EMP and RI-EMBP-AB were injected in male mice intravenously, and the activities of tissue samples were measured 1-31 hr from the injection. Pure iodine-125 (RI) was used as a control.

RESULTS

RI-EMP accumulated in the prostate, which contained 2.6% of injected activity (ID) per gram tissue at 7 hr. The liver had an activity of 21.4% ID/g at 1 hr, which decreased as RI-EMP was secreted in bile. The lung contained 2.3% ID/g at 7 hr, and it retained the activity longer than the prostate. RI-EMBP-AB accumulated in the prostate: The activity was 2.9% ID/g at 7 hr. The gallbladder contained 6.5% ID/g at 7 hr.

CONCLUSIONS

Due to its cytotoxic and radiosensitizing properties, RI-EMP can possibly be used for treating prostate cancer and other tumors.

Effect of castration on metalloprotease activities in the lateral, dorsal, and anterior lobes of the rat prostate

Several proteolytic enzymes are involved in mediating the regression of the prostate gland following castration. A previous study showed that plasminogen activator activities are elevated only in the ventral lobe by castration in the rat. Since matrix metalloproteases represent a different class of protease that degrade extracellular matrix, this study examined their activities in the lateral, dorsal, and anterior lobes of the rat in response to androgen deprivation. The results indicate that, in contrast to plasminogen activators, metalloprotease activities are increased in the lateral, dorsal, and anterior lobes following orchiectomy. This suggests that differences in regulation of certain proteases by androgens may occur in individual prostatic lobes.

Purification of estramustine-binding protein and production of monoclonal antibodies to its different components

Estramustine-binding protein (EMBP) is a heterodimeric 46-kDa glycoprotein that is secreted from the prostate. Upon reductive cleavage it decomposes into two closely related components, C1 and C2, and the shared glycosylated peptide C3. EMBP binds estramustine and estromustine, the active metabolites of estramustine phosphate (Estracyt), which is a drug with antimitotic properties used in the treatment of prostatic carcinoma. In the present study, a two-step procedure (i.e., anion-exchange and Con A-Sepharose chromatography) is described for the isolation of EMBP in high yield from rat prostate tissue. Mouse monoclonal antibodies (mAbs) were produced using the major DEAE-Sepharose fraction of EMBP as an immunogen. Eleven mAbs were selected by screening in a solid-phase ELISA. One displayed high-affinity binding with soluble EMBP (Ka approximately 3 x 10(10) M-1) and crossreacted with a human prostate tumor extract in a radioimmunoassay. The epitopes defined by these mAbs were analyzed by Western immunoblotting. All constituents of EMBP, except component C1, were identified by at least one antibody. Nine visualized either one or both of the two EMBP subunits under denaturing conditions, two of which retained their reactivity after reduction of disulfide bridges. One epitope was exposed to its mAb only when the antigen was in its reduced state. The immunoreactivity was eliminated by protease treatment, whereas deglycosylation with glycopeptidase F had a minimal effect. EMBP has been detected in tissues other than the prostate as well as in prostate neoplastic specimens and in several other human malignancies. Hence, these mAbs will be a useful tool in the characterization of EMBP in different tissues and in evaluating existing and in defining new indications for Estracyt therapy.

Inhibition of prostate cancer growth by estramustine and etoposide: evidence for interaction at the nuclear matrix

Metastatic prostate cancer which is refractory to hormone therapy remains an incurable disease for which there is no effective therapy. We have begun to investigate the nuclear matrix, the RNA-protein network of the nucleus that plays an important role in DNA replication and gene expression, as a target for cancer chemotherapy. It was postulated that estramustine phosphate (EMP), an estradiol-nitrogen mustard conjugate that binds to the nuclear matrix, might enhance the cytotoxicity of etoposide (VP-16), a topoisomerase II inhibitor that acts at the level of the nuclear matrix. In a nascent DNA synthesis assay, EMP and etoposide interact to selectively inhibit new DNA synthesis on the nuclear matrix. In vitro, EMP and etoposide appeared to act synergistically to inhibit the growth of the metastatic Dunning rat prostate adenocarcinoma cell line Mat-LyLu as well as the metastatic human prostate adenocarcinoma cell line PC-3. In vivo, EMP and etoposide inhibited prostate adenocarcinoma growth in the Dunning Copenhagen rat model. These data have formed the basis of a Phase I/II clinical trial to examine the effect of EMP and etoposide in patients with stage D hormone-refractory prostate cancer.