A phase II study Nolvadex: tamoxifen citrate in the treatment of advanced prostatic adenocarcinoma

Androgen receptor and estrogen receptor variants in prostate and breast cancers

The androgen receptor (AR) and estrogen receptor alpha (ERα) are steroid receptor transcription factors with critical roles in the development and progression of prostate and breast cancers. Advances in the understanding of mechanisms underlying the ligand-dependent activation of these transcription factors have contributed to the development of small molecule inhibitors that block AR and ERα actions. These inhibitors include competitive antagonists and degraders that directly bind the ligand binding domains of these receptors, luteinizing hormone releasing hormone (LHRH) analogs that suppress gonadal synthesis of testosterone or estrogen, and drugs that block specific enzymes required for biosynthesis of testosterone or estrogen. However, resistance to these therapies is frequent, and is often driven by selection for tumor cells with alterations in the AR or ESR1 genes and/or alternatively spliced AR or ESR1 mRNAs that encode variant forms AR or ERα. While most investigations involving AR have been within the context of prostate cancer, and the majority of investigations involving ERα have been within the context of breast cancer, important roles for AR have been elucidated in breast cancer, and important roles for ERα have been elucidated in prostate cancer. Here, we will discuss the roles of AR and ERα in breast and prostate cancers, outline the effects of gene- and mRNA-level alterations in AR and ESR1 on progression of these diseases, and identify strategies that are being developed to target these alterations therapeutically.

Expression of estrogen and progesterone receptors across human malignancies: new therapeutic opportunities

Estrogen and progesterone receptors (ERs and PRs) are known for their prognostic as well as treatment predictive value in breast cancer. Although these receptors are differentially expressed in some other malignancies, and likely participate in the biology of those cancer types, the relevance to outcome and therapy is not well established. The use of ER as a highly effective therapeutic target in oncology was pioneered in breast cancer, and the lessons learned from its success could potentially benefit patients with several other malignancies in which hormone receptors are highly expressed. Indeed, there are several potent drugs available that target hormone receptors. These agents show incontrovertible evidence of benefit in patients with hormone receptor-positive breast cancer. It is conceivable that these drugs may have salutary effects in a variety of cancers other than those originating in the breast, based on the overexpression of hormone receptors in some patients, and the preclinical and clinical reports showing responses to these drugs in diverse cancers, albeit in small series or anecdotally. We therefore undertook a literature review in order to summarize the current data regarding the biologic and clinical implications of expression of estrogen and progesterone receptors in various malignancies and the possibilities for deployment of hormone manipulation beyond breast cancer.

Importance of Estrogenic Signaling and Its Mediated Receptors in Prostate Cancer

Prostate cancer (PCa) treatment was first established by Huggins and Hodges in 1941, primarily described as androgen deprivation via interference of testicular androgen production. The disease remains incurable with relapse of hormone-refractory cancer after treatments. Epidemiological and clinical studies disclosed the importance of estrogens in PCa. Discovery of estrogen receptor ERβ prompted direct estrogenic actions, in conjunction with ERα, on PCa cells. Mechanistically, ERs upon ligand binding transactivate target genes at consensus genomic sites via interactions with various transcriptional co-regulators to mold estrogenic signaling. With animal models, Noble revealed estrogen dependencies of PCa, providing insight into potential uses of antiestrogens in the treatment. Subsequently, various clinical trials were conducted and molecular and functional consequences of antiestrogen treatment in PCa were delineated. Besides, estrogens can also trigger rapid non-genomic signaling responses initiated at the plasma membrane, at least partially via an orphan G-protein-coupled receptor GPR30. Activation of GPR30 significantly inhibited in vitro and in vivo PCa cell growth and the underlying mechanism was elucidated. Currently, molecular networks of estrogenic and antiestrogenic signaling via ERα, ERβ and GPR30 in PCa have not been fully deciphered. This crucial information could be beneficial to further developments of effective estrogen- and antiestrogen-based therapy for PCa patients.

Selective aromatase inhibition for patients with androgen-independent prostate carcinoma

BACKGROUND

First and second-generation aromatase inhibitors have shown activity in patients with androgen-independent prostate carcinoma. These early-generation aromatase inhibitors are nonselective, however, and inhibition of other steroidogenic enzymes may contribute to their reported clinical activity. The authors conducted a Phase II clinical study of letrozole to determine the safety and efficacy of a potent and selective third-generation aromatase inhibitor in men with androgen-independent prostate carcinoma.

METHODS

Forty-three men with androgen-independent prostate carcinoma were treated with oral letrozole (2.5 mg daily). Treatment was continued until progressive disease or Grade 3 toxicity developed. Response and progressive disease were defined according to recommendations of the Prostate Specific Antigen Working Group.

RESULTS

In total, 380 weeks of treatment were administered to the 43 study patients. The median duration of treatment was 8 weeks. Forty men discontinued treatment due to progressive disease. Only one patient responded to treatment with a sustained decrease > 50% in serum prostate specific antigen (PSA) levels. Three other patients experienced transient minor decreases (< 50%) in serum PSA levels. There were no serious treatment-related adverse events.

CONCLUSIONS

Selective aromatase inhibition with letrozole is not active in men with androgen-independent prostate carcinoma.

CGA gene (coding for the alpha subunit of glycoprotein hormones) overexpression in ER alpha-positive prostate tumors

OBJECTIVE

The precise role of estrogen, estrogen receptor (ER) and ER-responsive genes in prostate carcinogenesis is unclear. Paradoxically, estrogens and antiestrogens are used in the treatment of advanced metastatic prostate cancers. Recently, we identified CGA gene coding for the alpha subunit of glycoprotein hormones as a new ER alpha-responsive gene in human breast cancer cells. The aim of this study was to explore the role of CGA in the second major hormone-related cancer, i.e. prostate cancer.

PATIENTS AND METHODS

We quantified CGA mRNA in nine cases of benign prostatic hyperplasia (BPH) and 23 sporadic prostate tumors (TP) by using a real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay.

RESULTS

CGA overexpression (> 10 S.D. above the mean in normal prostate tissues (NP)) was observed in 39% of the TP (ranging from 4.4 to 174.5 times the level in NP) and in none of the BPH samples. CGA overexpression was not accompanied by overexpression of the CGB, LHB, TSHB or FSHB genes to produce ectopic glycoprotein hormones. CGA gene overexpression correlated with ER alpha normal expression (P = 0.016), but not with ER beta or androgen receptor (AR) expression status.

CONCLUSION

These results point to CGA gene as a member of a novel dysregulated pathway in prostate cancer. CGA should therefore be considered for investigation as possible novel molecular marker in clinical applications and as possible new potential therapeutic target.

Raloxifene (LY156758) produces antimetastatic responses and extends survival in the PAIII rat prostatic adenocarcinoma model

The benzothiophene antiestrogen, raloxifene (LY156758), has selective estrogen pharmacological antagonist activity in rats. The PAIII rat prostatic adenocarcinoma model was used to evaluate the effects of this agent on the lymphatic and pulmonary metastasis and survival in tumor-bearing male Lobund-Wistar (LW) rats. Raloxifene was inactive against colony formation of PAIII cells in vitro. Similarly, following subcutaneous (s.c.) implantation of 10(6) PAIII cells in the tail, s.c. administration of raloxifene (2.0, 10.0, or 20.0 mg/kg/day) for 30 days failed to demonstrate cytoreductive activity against primary tumor growth in the tail. However, in these same animals, raloxifene administration produced significant (P < 0.05) inhibition of PAIII metastasis from the primary tumor in the tail to the gluteal and iliac lymph nodes (maximal responses = 89% and 81% from control values, respectively). PAIII metastasis to the lungs was significantly inhibited by raloxifene treatment. Numbers of pulmonary foci in PAIII-bearing rats were significantly (P < 0.05) reduced by raloxifene administration in a dose-related manner (maximal reduction = 97% from control values). In these animals, maximal regression of 20% for ventral prostate and 21% for seminal vesicle were also seen after raloxifene administration (P < 0.05 for both). Coadministration of E2B and raloxifene had no consistent antagonistic effect upon the antitumor responses produced by raloxifene. Raloxifene (40.0 mg/kg/day for 28 days) produced marked decreases in PAIII metastasis in the lymphatic and pulmonary components. Continued administration of the compound produced significant (P < 0.05) extension of survival of PAIII-bearing rats. Further studies are needed to define the maximal antitumor efficacy and the mechanism of action of raloxifene in urogenital solid tumor animal models. These data support the contention that raloxifene represents a class of active antimetastatic agents with potential efficacy in the treatment of hormone-insensitive human prostatic cancer.

The role of endocrine therapy in prostatic cancer

When judged by randomized clinical trial, current endocrine therapies offer symptomatic relief to prostatic cancer patients for an average period of 1-2 years following initiation of therapy. Medical castration with LHRH analogues is a safe and effective way of achieving 'castrate' levels of circulating androgens without the undesirable aspects of surgery. While there is some evidence for the value of combined therapies using these agents in combination with anti-androgens for 'total androgen blockade' in some patients, overall this approach has not been shown to offer advantages over castration, either surgical or medical, alone in controlled trials. Secondary endocrine therapy does not offer convincing objective response rates, suggesting that disease progression is independent of androgens.

Tamoxifen. A reappraisal of its pharmacodynamic and pharmacokinetic properties, and therapeutic use

Tamoxifen, a non-steroidal antioestrogen, represents a significant advance in treatment of female breast cancer. In trials of tamoxifen as postsurgical adjuvant treatment of early breast cancer, disease-free survival is consistently prolonged, representing an enhanced quality of life in association with tamoxifen's favourable adverse effect profile. Moreover, overview analysis indicates a survival benefit of approximately 20% at 5 years for all women, most clearly evident in women over 50 years, while a survival benefit independent of menopausal, nodal or oestrogen receptor status has been demonstrated in some individual trials. Thus, for postmenopausal women, tamoxifen is clearly optimal adjuvant treatment, although the relative benefit of adjuvant chemotherapy in node-negative patients requires clarification. A survival benefit for women under 50 has not been clearly demonstrated in overview analysis, but is not precluded by these rather limited data, and adjuvant treatment of premenopausal women with tamoxifen may also warrant serious consideration. Response rates to tamoxifen in advanced breast cancer are around 30 to 35%, increasing with patient selection for oestrogen receptor positivity. Tamoxifen must be regarded as first-line endocrine treatment in postmenopausal women, and may represent an alternative to first-line ovarian ablation in premenopausal women. An emergent role in primary therapy of elderly and frail patients with operable disease is apparent. Tamoxifen is also of benefit following surgery in male breast cancer, and may have a role as first-line endocrine treatment. Tamoxifen also has a potential role in other hormone-sensitive malignancies such as pancreatic carcinoma, and in treatment of benign breast disease. Finally, tamoxifen has a place in treatment of male and female infertility. because of adverse effects is rarely necessary. The most frequent adverse effects are related to the drug's anti-oestrogenic activity, and include hot flushes, nausea and/or vomiting, vaginal bleeding or discharge, and menstrual disturbances in premenopausal patients. Thus, tamoxifen continues to play a major role in management of female breast cancer in both early and advanced stages of disease, with a place also in treatment of male breast cancer and of infertility.

Effects of long-term administration of tamoxifen on steroid metabolism in prostatic carcinoma patients

Six patients with advanced prostatic carcinoma were treated with tamoxifen (2 X 20 mg daily) for up to 3 months before orchiectomy. Blood samples for gonadotropin, sex steroid, and prostate-specific acid phosphatase (PAP) determinations were taken before tamoxifen treatment, daily for 1 week, and at monthly intervals. Steroid concentrations in the testis tissue and spermatic vein blood were assayed from samples taken at orchiectomy. No consistent changes were observed during tamoxifen treatment, although there was a transient drop in the mean concentrations of LH on days 3 and 4 of treatment. The circulating concentrations of estradiol tended to be increased at 1, 2, and 3 months of treatment. The spermatic vein concentrations of testosterone and its precursors tended to be higher than those in nontreated prostatic carcinoma patients previously reported from this laboratory, indicating slight stimulation of testicular steroidogenesis. There were no changes in circulating levels of PAP and no improvement in clinical condition, indicating that long-term tamoxifen administration is not effective in the treatment of prostate carcinoma.

Tamoxifen in advanced prostatic carcinoma. A dose escalation study

Patients with advanced prostatic carcinoma who had received minimal or no prior therapy were treated with tamoxifen citrate in escalating doses from 10 to 50 mg orally twice a day. Twenty-nine courses were evaluated in 17 patients. Entry was limited to patients with measurable sites of disease. There were no objective responses at any dose level in these measurable sites. Acid and alkaline phosphatase were reduced in 0% and 18% of courses, respectively. Serum testosterone increased by an average of 119 ng/ml. Most increases were transient; no tumor flares were observed. Transperineal prostate biopsies in selected patients after completion of treatment showed no evidence of tumor necrosis or alteration in histologic grade of the tumors. Tamoxifen citrate, over the range of doses evaluated, has no activity in metastatic prostatic carcinoma.

The patient, disease status, and treatment options for prostate cancer: stages D1 and D2

The treatment of choice for disseminated prostate cancer remains endocrine manipulation, either bilateral orchiectomy or exogenous estrogens. The recommended dose of diethylstilbestrol is 1 mg tid. Unanswered questions include: When should endocrine manipulation be instituted for the patient with advanced prostatic cancer? At the time of diagnosis, when clinical symptoms occur, or not at all? With few exceptions those patients relapsing after initial endocrine manipulation do not respond to successive attempts at further endocrine therapy. Much of the confusion in this regard relates to the variable response criteria used, more often subjective than objective. Since the polyclonal theory of prostatic cancer is attractive, its logical extension is the evaluation of combinations of treatments including both endocrine manipulation and cytotoxic agents. Because the currently available antiandrogens and luteinizing hormone-releasing hormone agonists have mechanisms of action different from conventional estrogens or bilateral orchiectomy, they too may have a role in the multimodal treatment of advanced prostatic cancer. Therapy for stage D1 prostatic cancer implies that information is available either from pelvic lymphadenectomy or from fine-needle aspiration cytology related to abnormal findings on CT scanning, lymphangiography, or excretory urography. Some evidence exists supporting the case of potential cure by radical prostatectomy when pelvic nodal involvement is minimal. Other options include standard external beam irradiation therapy, endocrine therapy with transurethral prostatic resection, and finally, observation until distant metastases occur. Because of the increased risk of distant metastases in patients with stage D1 prostatic cancer, adjuvant chemotherapy programs are rational with clinical trials now in progress.