Estramustine Phosphate: Metabolic Aspects Related to Its Action in Prostatic Cancer

A randomized comparative study of endocrine monotherapy and a combination of estramustine phosphate with the endocrine therapy in patients with untreated stage D prostate cancer

BACKGROUND

We investigated the clinical efficacy and the prolongation of survival with combination therapy of estramustine phosphate (EMP) and endocrine therapy in untreated patients with progressive prostate cancer.

METHODS

We randomly divided 57 patients with untreated stage D prostate cancer into two groups, an endocrine monotherapy group and a group receiving combination treatment, consisting of endocrine therapy plus EMP. Treatment was continued until deterioration.

RESULTS

There were no significant differences in the improvement rating for subjective/objective symptoms or in progression-free survival between the two groups. However, overall survival was significantly prolonged in the combination therapy group (log-rank test, P = 0.0394; generalized Wilcoxon's test, P = 0.0145). In particular, overall survival was significantly prolonged, compared to that in the endocrine monotherapy group, in patients in the combination therapy group who were less than 74 years old, those with a performance status (PS) of 1 to 3, a pretreatment prostate-specific antigen (PSA) level of more than 20 ng/ml, moderately or poorly differentiated carcinoma, or a partial response (PR) based on the PSA level 12 weeks after the start of treatment. There was no significant difference in the incidence of side effects between the combination therapy and the endocrine monotherapy groups.

CONCLUSION

A combination of EMP with endocrine therapy may be useful for initial treatment in younger patients (aged 73 or younger) and in patients at high risk of progressive prostate cancer.

Therapy for hormone-resistant prostate cancer: no longer a myth

In conclusion, there have been impressive efforts to identify new cellular targets for the treatment of hormone-refractory disease. It appears that in some cases, survival may be extended; however, further prospective trials are necessary to confirm these observations.

Uptake of estramustine phosphate (estracyt) metabolites in prostatic cancer

Plasma and tumour concentrations of estramustine, estromustine, estradiol and estrone, the major metabolites of estramustine phosphate (estracyt), were determined in patients with prostatic carcinoma treated between one and nine years with repeated oral doses of estracyt (560 to 840 mg./day). The last dose was given 12 to 16 hours before sampling. The binding of radioactive estramustine and estromustine was determined in the tumour tissue to examine the possible role of estramustine-binding protein for the accumulation of these metabolites into the tumour. Comparison was made with benign prostate hyperplastic tissue from untreated patients. Estromustine was the main metabolite in plasma as well as in the tumour (range 235 to 450 and 205 to 485 ng./gm., respectively), whereas estramustine (20 to 45; 95 to 370), estrone (62 to 140; 63 to 160) and estradiol (8 to 15; 7 to 36) were found in lower concentrations. Interestingly the concentration of estramustine was as an average six times higher in the tumour than in plasma contrasting with the other metabolites which were present in equal amounts of the two localities. Binding of 3H-estramustine and 3H-estromustine was two to three times higher in the tumour than in benign hyperplastic tissue and negligible in plasma samples. The present study is the first where substantial amounts of cytotoxically active estramustine and estromustine are demonstrated in tumour tissue from estracyt treated patients. Our findings suggest a mechanism for selective uptake of these metabolites in prostatic cancer (estramustine-binding protein). The uptake and binding of estramustine and estromustine in the tumour may account for the clinical effects of estracyt in prostatic carcinoma.

Estramustine affects bone mineral metabolism in metastatic prostate cancer

A patient with metastatic prostate cancer is described where treatment with Adriamycin (doxorubicin) and estramustine produced severe hypophosphatemia (serum phosphate level, 1.2 mg/dl), which was reversible when treatment was discontinued. Previous studies have shown no effect of Adriamycin on serum phosphate levels. A retrospective study of serial serum chemistry values was done in 15 patients treated with estramustine. A significant fall in the serum phosphate level (mean, 0.8 +/- 0.3 mg/dl) was observed during the first 6 weeks of treatment. When compared with similar patients treated with bilateral orchiectomy, estramustine-treated patients had lower levels of serum calcium, fractional excretion of calcium, serum phosphate, and renal tubular threshold for phosphate reabsorption (TmPO4/GFR). Qualitatively similar but quantitatively smaller effects were also seen in a group of patients treated with diethylstilbestrol (DES) in a dose of 1 to 3 mg daily. Estramustine appears to have significant effects on bone mineral metabolism, particularly on renal phosphate handling resulting in significant hypophosphatemia. This is probably due to an estrogenic effect.

Estramustine phosphate sodium

Estramustine phosphate is approved by the Food and Drug Administration for oral use in the palliative treatment of patients with metastatic and/or progressive carcinoma of the prostate. Estramustine is a conjugate of 17 beta-estradiol and the carbamate of nitrogen mustard. Although its therapeutic efficacy has been demonstrated, it is not clear to what extent each constituent contributes to estramustine's effectiveness. Estramustine phosphate therapy achieves objective response rates of 60-90 percent in advanced stage D prostatic cancer patients with no prior hormonal therapy. These results are consistent with those obtained with conventional hormonal therapy in similar patient populations. Therapeutic efficacy does not appear to increase when estramustine is used concurrently with other cytotoxic chemotherapeutic agents. An objective response rate of 20-30 percent can be anticipated in patients refractory to conventional hormonal therapy. It is in this group, the estrogen-resistant patients, that estramustine shows the most promise. Adverse effects of estramustine are similar to those of diethylstilbestrol. Gastrointestinal and cardiovascular side effects appear to be the most important and may be severe enough to require discontinuation of therapy.

The hydrolysis of estramustine phosphate; in vitro studies

The hydrolysis of estramustine phosphate by enzymes of blood, liver, intestines and prostate of man, dog and rat was studied by using specific analytical methods for the parent compound and some of its metabolites. Estramustine phosphate was stable in blood and plasma of different species but rapidly dephosphorylated to estramustine by liver, intestinal and prostatic enzymes. The prostate was the most active tissue. The ester bond by which nornitrogen mustard is linked to estradiol-17-phosphate was slowly cleaved by enzymes from the liver and prostate of the rat, dog and man. The dog tissues were more effective than those of the rat and man. Intestinal enzymes also exhibited the ability to hydrolyze the carbamic ester, but to a greater extent in the rat than in the dog. It is concluded that, with regard to the metabolism of estramustine, the rat is more similar to man than is the dog. Possible clinical implications of the biotransformation of estramustine phosphate are discussed.

Change in white cell count during treatment of advanced cancer of the prostate with estramustine phosphate and with stilboestrol

Patients with locally advanced (category T3-4 of the TNM system) and metastatic prostatic cancer, not previously treated, seen by one of the authors (P.H.S.) have been entered into EORTC Protocol 30762 which has compared the therapeutic effects of estramustine phosphate (Estracyt) and of diethyl-stilboestrol (DES) as primary treatment. A gradual and as yet unexplained rise in the total leucocyte count was seen in patients treated with estramustine phosphate. This was always apparent within 2 months of starting treatment and did not change significantly thereafter unless treatment was stopped, when the raised values soon returned to normal. In four patients in whom the white cell count rose to levels above the normal range a neutrophil leucocytosis was always reported. The cause of this is not yet understood.

Metabolism of estramustine phosphate (Estracyt) in patients with prostatic carcinoma

Plasma samples from patients with prostatic cancer under oral treatment with estramustine phosphate (Estracyt) were quantitatively analyzed for the presence of the parent drug and some of its possible metabolites. Specific methods based on radioimmunoassay and gas chromatography-mass fragmentography were used. Dephosphorylation and oxidation at the 17-position of estradiol were shown to be the major metabolic routes. The estrone analogue of estramustine was found to be the main metabolite in plasma. Elevated levels of estradiol and estrone showed that hydrolysis of the carbamic ester also occurred in these patients. Their estrogen levels were compared with those of another group of prostatic cancer patients receiving conventional hormonal therapy, polyestradiol phosphate (Estradurin). Similar concentrations of estradiol were found in the two groups but the concentrations of estrone were higher in patients given estramustine phosphate.

Hormonal effects of different doses of estramustine phosphate (Estracyt) in patients with prostatic carcinoma

Ten patients with previously untreated prostatic carcinoma were studied to evaluate the hormonal effects of different doses of estramustine phosphate (Estracyt). The drug was given by mouth in increasing doses; during the first month 70 mg daily, during the second 140 mg, during the third 280 mg and during the fourth and following months 560 mg. The following hormonal parameters were studied before the treatment and then once weekly during a period of four months: testosterone, dihydrotestosterone, androstenedione, cortisol, FSH and LH. The levels of the steroids were also re-assessed one to two years later. The patients were also followed clinically at regular intervals. Initial testosterone levels of approximately 20 nmol/l plasma were reduced to approximately 0.6 nmol/l already by the lowest Estracyt dose of 70 mg/day. No further decrease was obtained by a stepwise increase of doses up to 560 mg/day. The plasma levels of dihydrotestosterone, androstenedione, FSH and LH were also reduced significantly following the administration of the lowest daily Estracyt dose and then remained at that low level. Cortisol levels increased steadily during the four months of the study. After longterm treatment the hormonal indices were by and large the same as during the last initial treatment period. Initially, the clinical effect of the treatment was excellent. In 4 patients, however, the therapy had to be discontinued after some time, because of complicating oedema (2 patients) or refractoriness to therapy (2 patients). Three years after initiating the therapy 6 patients still were on Estracyt treatment. All of them were doing well subjectively. In 5 patients the prostatic cancer was in remission or at least stable. In one patient, however, skeletal metastases were progressing. In conclusion, Estracyt was found to possess a maximal hormonal (oestrogenic) effect already in doses far below those usually recommended.

Plasma concentrations of estramustine phosphate and its major metabolites in patients with prostatic carcinoma treated with different doses of estramustine phosphate (Estracyt)

Plasma concentrations of estramustine phosphate and its major metabolites were measured in patients with prostatic carcinoma treated with increasing oral doses, 70-650 mg/day, of estramustine phosphate (Estracyt). Parent drug and estradiol were measured by radioimmunoassay, and estramustine and its estrone analogue (Leo 271) utilizing gas chromatography. The concentrations of estramustine phosphate and estramustine were below or close to the limits of the methods. A linear correlation was found between the daily dose of estramustine phosphate, and plasma concentrations of Leo 271-the main metabolite-and estradiol, which suggests that no capacity limiting processes are involved in the pharmacokinetics of estramustine phosphate in man. Plasma was also analyzed during prolonged treatment with 560 mg/day. The metabolite pattern was not changed by two to three years of estramustine phosphate treatment.

Estramustine phosphate in the treatment of advanced prostatic cancer

Thirty patients with advanced carcinoma of the prostate were treated with estramustine phosphate. All patients were followed up for a minimum of 9 months. Of 15 not previously treated with oestrogens 9 responded objectively and 11 subjectively. Of 15 patients whose tumours had failed to respond to at least 2 oestrogens, 3 responded objectively and 5 subjectively. Adverse effects consisted of cardiovascular complications, gynaecomastia and impotence. Gastrointestinal side effects were minimal and no hepatic, renal or marrow toxicity was seen. The criteria of assessment of response are discussed.