Bicalutamide in the treatment of advanced prostatic carcinoma: a phase II multicenter trial

Androgen-targeted therapy in men with prostate cancer: evolving practice and future considerations

Background

Androgen deprivation therapy (ADT) is foundational in the management of advanced prostate cancer (PCa) and has benefitted from a recent explosion in scientific advances. These include approval of new therapies that suppress testosterone (T) levels or inactivate its function, improvements in diagnostic and assay technologies, identification of lower therapeutic targets for T, discovery of the relevance of germline genetic mutations and identification of the benefits of sequential and combination therapies.

Methods

This review discusses the clinical profiles of the most up-to-date options for ADT, best practices for managing patients with advanced PCa and future directions in therapy.

Results and conclusions

Modern assay technologies reveal that bilateral orchiectomy results in a serum T level of approximately 15 ng/dL as compared to the historical definition of castration of T < 50 ng/dL. Evidence shows that lowering T levels to <20 ng/dL improves patient survival and delays disease progression. Routine monitoring of T in addition to prostate-specific antigen throughout treatment is important to ensure continuing efficacy of T suppression. New drugs that inhibit androgen signaling in combination with traditional ADT suppress T activity to near zero and have significantly improved patient survival. When personalizing ADT regimens physicians should consider a number of factors including initiation and duration of ADT, monitoring of T levels and PSA, the possibility of switching monotherapies if a patient does not achieve adequate T suppression, and consideration of intermittent vs. continuous ADT according to patients’ lifestyles, comorbidities, risk factors and tolerance to treatment.

Advances in hormonal therapies for hormone naïve and castration-resistant prostate cancers with or without previous chemotherapy

Hormonal manipulation plays a significant role in the treatment of advanced hormone naïve prostate cancer and castration-resistant prostate cancer (CRPC) with or without previous chemotherapy. Combination of gonadotropin releasing hormone (GnRH) agonists and androgen receptor (AR) antagonists (combined androgen blockade; CAB) is the first line therapy for advanced hormone naïve prostate cancer, but current strategies are developing novel GnRH antagonists to overcome disadvantages associated with GnRH agonist monotherapy and CAB in the clinical setting. Abiraterone acetate and enzalutamide are hormonal agents currently available for patients with CRPC and are both shown to improve overall survival versus placebo. Recently, in clinical trials, testosterone has been administered in cycles with existing surgical and chemical androgen deprivation therapies (ADT) (intermittent therapy) to CRPC patients of different stages (low risk, metastatic) to abate symptoms of testosterone deficiency and reduce cost of treatment from current hormonal therapies for patients with CRPC. This review will provide an overview on the therapeutic roles of hormonal manipulation in advanced hormone naïve and castration-resistant prostate cancers, as well as the development of novel hormonal therapies currently in preclinical and clinical trials.

Hormone therapy of prostate cancer: is there a role for antiandrogen monotherapy?

Androgen suppressive maneuvers still represent the gold standard for prostate cancer patients. However, they are associated with side effects (fatigue, sexual impotence, hot flushes, anemia, anxiety, depression and osteoporosis) all of which have a negative impact on quality of life. Nonsteroidal antiandrogens compete with dihydrotestosterone for the linkage of its own receptors. These compounds are commonly used in combination with suppressive maneuvers. However, there is a growing experience with them as monotherapy, based on the possibility to spare gonadal function and therefore prevent the effects related to its suppression. Many studies have demonstrated the feasibility and safety of this approach, which can represent a valuable alternative to suppressive maneuvers for patients wishing to retain sexual function, especially for those without distant metastases. Unfortunately, none of the comparative studies performed so far had the power to detect the equivalence between monotherapy and castration.

Antiandrogens in prostate cancer

Antiandrogens competitively inhibit ligand binding to the androgen receptor (AR), and are used therapeutically in prostate cancer patients. The AR functions as a ligand dependent transcription factor that transduces androgen binding into increased transcription of androgen dependent genes. AR blockade induces programmed cell death in the vast majority of malignant and benign prostate cancer cells that have not previously been exposed to androgen ablation. The antiandrogens are divided structurally into the steroidal and non steroidal agents. The biological effects of the steroidal versus nonsteroidal agents are distinguished by differences in their effects on serum testosterone levels, and by their activity at receptors other than the androgen receptor. There is extensive clinical experience in the palliative and curative therapy of prostate cancer using antiandrogens as monotherapy or antiandrogens in combination with luteinizing hormone agonists or surgical castration. Prolonged therapy with antiandrogens selects for mutations in the AR that change the AR ligand specificity and permits stimulation by ligands that are usually inhibitory. These mutations give insight into one of the means by which prostate cancer progresses despite antiandrogen therapy, and also helps to explain the antiandrogen withdrawal syndrome. Areas of active research that may affect the future use of antiandrogens include the ongoing evaluation of antiandrogens in combination with 5 alpha reductase inhibitors to achieve AR blockade without inducing castrate testosterone levels. There is also interest in developing selective androgen receptor modulators (SARM) that can achieve AR blockade without causing the increased testosterone levels produced by the nonsteroidal antiandrogens currently in use.

Bicalutamide in advanced prostate cancer. A review

Bicalutamide is a nonsteroidal antiandrogen with a long elimination half-life (t1/2) that permits once-daily administration. When combined with a gonadorelin (gonadotrophin releasing hormone; GnRH) agonist in maximum androgen blockade (MAB) regimens, bicalutamide 50 mg once daily is at least as effective as flutamide 250 mg 3 times daily, as shown in a large randomised trial. Rate of treatment failure, the primary end-point, was significantly lower at 49 weeks with bicalutamide in this study, mainly because of a lower rate of withdrawal due to adverse events. Final results at a median follow-up of 160 weeks revealed longer median times to progression and death with bicalutamide than flutamide, but between-group differences were not significant overall. Although early trials demonstrated clinical benefits with bicalutamide 50 mg/day as monotherapy, the drug in this dosage is less effective than castration. Increasing the dosage to 150 mg/day has improved its efficacy in patients with non-metastatic disease: combined data from 2 trials demonstrate similar survival with bicalutamide in this dosage compared with castration. Accumulating evidence from these and other studies indicates that sexual interest appears to be better preserved with bicalutamide than with castration. The tolerability profile of bicalutamide is characteristic of antiandrogens, with breast pain and gynaecomastia occurring most often. Bicalutamide has not been causally associated with problems such as interstitial pneumonitis and difficulty with light/dark adaptation seen with nilutamide, and in a 50 mg/day dosage causes a lower incidence of diarrhoea than flutamide 750 mg/day. Changes in hepatic function are generally transient and resolve or improve during therapy or after bicalutamide treatment is withdrawn.

CONCLUSIONS

Bicalutamide, with its once-daily regimen and good tolerability, is an attractive option when combined with a GnRH agonist in patients with advanced prostate cancer who are suitable to receive MAB regimens. The role of bicalutamide as monotherapy in the management of this common malignancy is currently being assessed.

How is quality of life in prostate cancer patients influenced by modern treatment? The Wallenberg Symposium

OBJECTIVES

To identify complications of various forms of treatments for prostate cancer and their influence on patients' quality of life with the ultimate goal of suggesting a Quality of Life Questionnaire specific for prostate cancer for further validation.

METHODS

The literature was screened for reports on the more common complications following various forms of therapy for prostate cancer. Frequencies were summarized. The scarce literature reporting on quality of life in prostate cancer was reviewed and conflicting data were discussed and reassessed. Suggested questionnaires used in other studies were critically scrutinized and the various questions recorded.

RESULTS

Following radical surgery, impotence and incontinence were the most common complications reducing patients' quality of life. The literature was not uniform with regard to whether loss of sexual function was regarded as a worse complication than loss of urinary control. Following radiotherapy, intestinal problems and sexual dysfunction were the dominating side effects. Quality of life was best preserved in surveillance-only series. Following endocrine therapy, not only impotence and hot flushes were focused upon, but also mental dysfunction and intestinal dysfunction from nonsteroidal antiandrogens, additionally, the importance of effective palliation was highlighted. A Quality of Life Questionnaire should contain general domains relevant to cancer patients, cancer-specific questions, and prostate-cancer-specific questions. The latter group includes: worry for prostate cancer and its prognosis, bone/pelvic pain, lower urinary tract symptoms, urinary incontinence, urinary diversion, bowel function, sexual function, endocrine effects, and satisfaction with medical care for prostate cancer.

CONCLUSIONS

A modern trial of prostate cancer treatment should be regarded as insufficient without including a validated Quality of Life Questionnaire.

Nilutamide: an antiandrogen for the treatment of prostate cancer

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and adverse effects of nilutamide and to compare this agent with the currently marketed nonsteroidal antiandrogens (i.e., bicalutamide, flutamide) by critically analyzing the published literature.

DATA SOURCES

MEDLINE (1980-1995) and CANCERLIT (1991-1995) were searched for English-language publications using the terms nilutamide, bicalutamide, and flutamide alone, and either nilutamide or androgen antagonists in combination with prostatic neoplasms.

STUDY SELECTION AND DATA EXTRACTION

All articles with subject matter on nilutamide, bicalutamide, and flutamide were considered for inclusion. For studies published in more than one journal, the first publication was used unless a subsequent publication included additional or follow-up data, in which case the latter publication was cited instead.

DATA SYNTHESIS

Nilutamide was effective in combination with orchiectomy in improving responses in patients with advanced prostate cancer. However, patient survival was not improved in these trials, and improvements in bone pain did not usually result in improved performance status in these patients. The few trials of nilutamide monotherapy or nilutamide in combination with a luteinizing hormone-releasing hormone analog are too small to draw meaningful conclusions regarding its efficacy or its role in the treatment of advanced prostate cancer. No comparative trials of nilutamide with other antiandrogens and no analysis of the impact of nilutamide on patient quality of life are currently available. Nilutamide appears to produce a higher frequency of adverse effects than the other currently marketed nonsteroidal antiandrogens, bicalutamide and flutamide.

CONCLUSIONS

Nilutamide does not appear to represent a major advance in the treatment of advanced prostate cancer and appears to be somewhat inferior to both flutamide and bicalutamide with regard to adverse effects. Nilutamide should not be considered the antiandrogen of choice in the treatment of advanced prostate cancer.

Serum prostate-specific antigen elevation in the post-radical prostatectomy patient

The management of postprostatectomy serum prostate-specific antigen elevation is hampered by the inability to determine the location of the recurrence accurately and the lack of data demonstrating a survival advantage from any of the available therapies. Treatment must be individualized for each patient.