Simultaneous antiandrogen withdrawal and treatment with ketoconazole and hydrocortisone in patients with advanced prostate carcinoma

Treatment options in hormone-refractory prostate cancer: current and future approaches

Prostate cancer is the second leading cause of cancer mortality among men in Western countries. The initial treatment of advanced prostate cancer is suppression of testicular androgen production by medical or surgical castration, but nearly all men with metastases will develop disease progression. Patients with hormone refractory prostate cancer (HRPC) have a median survival of approximately 18 months and no therapy has yet demonstrated a definitive survival advantage. However, in the past several years, a number of promising new treatment strategies have emerged. One of the most important new treatment strategies involves secondary hormonal manipulation after the failure of primary androgen deprivation. This approach is predicated on the recognition that HRPC is a heterogeneous disease and some patients may respond to alternative hormonal interventions despite the presence of castrate levels of testosterone. Until recently, cytotoxic chemotherapy was felt to be relatively ineffective in the treatment of HRPC. Combination regimens incorporating new active agents have demonstrated significant activity in this setting, renewing interest in the use of chemotherapy to treat HRPC. Recent advances in the understanding of prostate cancer biology have led to the development of drugs directed against precise molecular alterations in the prostate tumour cell. Biologic agents now in development include those capable of altering signal transduction, blocking angiogenesis, inhibiting cell cycle progression, and stimulating apoptosis. In addition, many types of immune therapies are showing promise. Evaluating these agents, and incorporating them into existing regimens, are major goals of ongoing clinical research in advanced prostate cancer.

Combination of dexamethasone and a somatostatin analogue in the treatment of advanced prostate cancer

The local microenvironment at the sites of cancer metastases protects tumour cells from anticancer drug-induced apoptosis via mechanisms, such as soluble growth factors and cytokines. The concept of antisurvival factor (ASF) therapy as a component of anticancer treatments aims at neutralising the protective effect conferred upon cancer cells by the survival factor(s) derived by the local microenvironment, in order to enhance the sensitivity and/or reverse the resistance of tumour cells to other anticancer therapeutic strategies. Herein, we review the translation of this concept from ex vivo studies to clinical applications in the setting of prostate cancer refractory to androgen ablation (stage D3). At this stage, which predominantly involves bone metastases, insulin-like growth factor 1 (IGF-1) production (either growth hormone (GH)-dependent or GH-independent) can protect tumour cells from apoptosis, despite the significant suppression of androgens. The application of the ASF therapeutic concept involves the combination of dexamethasone (which suppresses GH-independent IGF-1) and somatostatin analogue (which suppresses endocrine, GH-dependent IGF-1) with the pro-apoptotic effect of the testicular androgen suppression by sustained use of LHRH analogues. In stage D3, patients who had failed anti-androgen withdrawal, chemotherapy and also had several other adverse prognostic features, the ASF-based combination achieved durable objective responses and major symptomatic improvement, paving the way for future applications of this approach. The ASF-based combination therapy illustrates a novel paradigm in cancer treatment: anti-tumour treatment strategies may not only aim at directly inducing cancer cell apoptosis, but can also target the tumour microenvironment and neutralise the protection it confers on metastatic cancer cells. The favourable toxicity profile of this therapeutic approach calls for its testing in a randomised controlled setting in metastatic prostate cancer and, conceivably, in other IGF-1-responsive malignancies.

Secondary hormonal manipulation of prostate cancer

Prostate cancer is the second leading cause of cancer mortality among men in Western countries. The initial treatment of advanced prostate cancer is suppression of testicular androgen production by medical or surgical castration, but nearly all men with metastases develop disease progression. Patients with hormone-resistant prostate cancer (HRPC) have a median survival of approximately 18 months, and no therapy has yet demonstrated a definitive survival advantage. However, in the past several years, a number of promising new treatment strategies have emerged. One of the most important new treatment strategies involves secondary hormonal manipulation after the failure of primary androgen deprivation. This approach is predicated on the recognition that HRPC is a heterogeneous disease, and some patients may respond to alternative hormonal interventions despite the presence of castrate levels of testosterone.

Hormonal treatment for prostate cancer

For nearly six decades the preferred primary treatment for advanced prostate cancer has been continuous suppression of testicular androgen production by medical or surgical castration. While androgen deprivation is effective in inducing tumour regression in the large majority of cases, essentially all patients will develop progressive disease. In addition androgen deprivation may be associated with a variety of side effects. Thus, strategies that minimise the use of these agents could potentially lower the morbidity and cost associated with the treatment of advanced prostate cancer. In the era of prostate-specific antigen (PSA) testing, hormonal therapy is being used earlier in the course of the disease when the only evidence of recurrent disease is an elevated PSA. These men may survive for many years and thus have the potential for long periods of exposure to hormonal therapy and its side effects. It has been hoped that the development of alternative hormonal interventions might lead to both enhanced antitumour efficacy as well as improvements in side effect profile.

Antiandrogen withdrawal syndrome associated with prostate cancer therapies: incidence and clinical significance

The antiandrogen withdrawal syndrome is a well established phenomenon in prostate cancer. It is widely accepted that a subset of patients will benefit from the withdrawal of antiandrogen or steroidal hormone from hormonal therapy, exhibiting decreasing prostate-specific antigen (PSA) values and clinical improvement. The pathophysiology of antiandrogen withdrawal syndrome is not completely understood, although androgen receptor gene mutations seem to be the likely explanation. Currently, it is not possible to identify the subset of patients whose tumours will respond to antiandrogen or steroid withdrawal. Tumours that will respond may be classified as androgen-independent and hormone-sensitive tumours as opposed to androgen-independent and hormone-insensitive tumours that do not respond. Patients who respond to antiandrogen withdrawal experience approximately 6 months with improved quality of life; however, it is unknown if this translates into prolonged survival. At the very least, antiandrogen withdrawal offers a therapeutic modality that is not associated with adverse effects and improves quality of life even if only for a very limited time. Recent reports suggest that adding a secondary hormonal therapy such as amino- glutethimide, ketoconazole or steroidal hormones may enhance the response rate and prolong response time to the antiandrogen withdrawal syndrome. However, unless there is proof that this secondary hormonal manipulation prolongs survival, maintenance of quality of life is mandatory because of the possible adverse effects from these potent drugs. The fact that about 30% of patients will respond to antiandrogen or steroid withdrawal in hormone refractory prostate cancer must be taken into account in clinical trials of new cytotoxic agents which have been and will be conducted. Cessation of flutamide for at least 4 weeks and, in the case of bicalutamide, even 8 weeks, is mandatory before antiandrogen withdrawal syndrome can be excluded as the cause of decreasing PSA values. The antiandrogen withdrawal syndrome offers another piece of the puzzle of prostatic carcinoma, but at the same time it demonstrates how different advanced prostate cancer cells may react to therapeutic strategies and, therefore, hormone refractory prostate cancer remains a difficult challenge which must be solved in the future.

New treatment strategies in advanced prostate cancer

The treatment of advanced prostate cancer has evolved rapidly in the last 5 years. Therapeutic options for patients with advanced disease, once essentially limited to the use of androgen deprivation, have expanded to include a number of interventions, including secondary hormonal manipulations, chemotherapy, and a variety of investigational approaches. Novel therapeutic approaches in prostate cancer patients are likely to be undertaken in patients with disease that is at or below the limits of detection by current imaging technology, so novel methods will be essential to the successful evaluation and use of these agents.

Effects of new 17alpha-hydroxylase/C(17,20)-lyase inhibitors on LNCaP prostate cancer cell growth in vitro and in vivo

Our laboratory has been developing new inhibitors of a key regulatory enzyme of testicular and adrenal androgen synthesis 17alpha-hydroxylase/C(17,20)-lyase (P450c17), with the aim of improving prostate cancer treatment. We designed and evaluated two groups of azolyl steroids: delta5-non-competitive inhibitors (delta5NCIs), VN/63-1, VN/85-1, VN/87-1 and their corresponding delta4 derivatives (delta4NCIs), VN/107-1, VN/108-1 and VN/109-1. The human P450c17 gene was transfected into LNCaP human prostate cancer cells, and the resultant LNCaP-CYP17 cells were utilized to evaluate the inhibitory potency of the new azolyl steroids. VN/85-1 and VN/108-1 had the lowest IC50 values of 1.25 +/- 0.44 nM and 2.96 +/- 0.78 nM respectively, which are much lower than that of the known P450 inhibitor ketoconazole (80.7 +/- 1.8 nM). To determine whether the compounds had direct actions on proliferation of wild-type LNCaP cells, cell growth studies were performed. All of the delta5NCIs and VN/108-1 blocked the growth-stimulating effects of androgens. In steroid-free media, the delta5NCIs decreased the proliferation of LNCaP cells by 35-40%, while all of the delta4NCIs stimulated LNCaP cells growth 1.5- to 2-fold. In androgen receptor (AR) binding studies, carried out to determine the mechanism of this effect, all of the delta4NCIs (5 microM) displaced 77-82% of synthetic androgen R1881 (5 nM) from the LNCaP AR. The anti-androgen flutamide and the delta5NCIs displaced 53% and 32-51% of R1881 bound to AR respectively. These results suggested that the delta5NCIs may also be acting as anti-androgens. We further evaluated our inhibitors in male severe combined immunodeficient mice bearing LNCaP tumour xenografts. In this model VN/85-1 was as effective as finasteride at inhibiting tumor growth (26% and 28% inhibition, respectively) and the inhibitory effect of VN/87-1 was similar to that of castration (33% and 36% inhibition respectively). These results suggest that VN/85-1 and VN/87-1 may be potential candidates for treatment of prostate cancer.

Recent advances in the treatment of prostate cancer

As new evidence for prostate cancer treatment has emerged in the last few years, longstanding controversies in the treatment of prostate cancer have resurfaced. A number of long-held tenets of prostate cancer therapy have been revisited, sometimes with surprising and challenging results. Although neoadjuvant hormonal therapy prior to radical prostatectomy decreases positive surgical margin rates, longer follow-up is needed to support survival improvement of this combined modality therapy. Androgen deprivation combined with radiation therapy appears to improve disease-free survival (and survival in one series) in patients with locally advanced cancer. Another approach to locally advanced prostate cancer using three-dimensional conformal radiation therapy may improve long term outcome. The data are currently insufficient to conclude that interstitial low dose rate brachytherapy is equivalent to conventional treatments: patients with small tumor volumes and low Gleason grade seem to obtain more benefit, whereas for large tumors with higher gleason grades this approach seems inferior to conventional treatments. In advanced prostate cancer recent data suggest that immediate hormonal therapy improves survival. In this group of patients the use of maximum androgen blockade remains controversial but may adversely affect quality of life compared to orchiectomy alone. Intermittent hormonal therapy may improve quality of life, although effect upon survival is unknown. Chemotherapy in combination with androgen deprivation is currently being studied as front-line therapy in advanced prostate cancer. Palliative benefit of chemotherapy for hormone refractory prostate cancer remains an important endpoint; survival advantage has not been seen in any randomized trials. Suramin may delay disease progression in hormone refractory prostate cancer. Many aspects of prostate cancer treatment will remain controversial until results of large, randomized trials with longer follow-up are available.

Advances in prostate cancer

The causes of prostate cancer reflect a complex interaction between environmental and genetic factors. Improvement in screening has reduced the incidence of prostate cancer, and risk assessment schemata have enhanced therapy, both for localized disease and for locally recurrent prostate cancer. The use of hormone therapy has been further evaluated, as primary therapy for locally advanced cancers, for lymph node-positive cancers, and for de novo metastatic cancer. Modest inroads have been made in the treatment and understanding of androgen-independent prostate cancer. Advances have been made in the understanding of the risk factors, genetic and environmental, associated with the development and progression of prostate cancer; in screening; and in optimizing therapy for localized, locally recurrent, and advanced disease. This article reviews the most salient observations reported between November 1, 1997 and October 31, 1998.

Secondary hormonal manipulations in hormone refractory prostate cancer

Hormone refractory prostate cancer is clinically heterogeneous, and many patients retain sensitivity to subsequent hormonal manipulations, even after combined androgen blockage. Antiandrogen withdrawal is a mandatory first step. Subsequent treatment with an alternate antiandrogen, adrenal androgen inhibitor (such as ketoconazole), or glucocorticoid may provide both subjective and objective clinical benefit in up to 65% of patients.

Controversies in the management of advanced prostate cancer

For advanced prostate cancer, the main hormone treatment against which other treatments are assessed is surgical castration. It is simple, safe and effective, however it is not acceptable to all patients. Medical castration by means of luteinizing hormone-releasing hormone (LH-RH) analogues such as goserelin acetate provides an alternative to surgical castration. Diethylstilboestrol, previously the only non-surgical alternative to orchidectomy, is no longer routinely used. Castration reduces serum testosterone by around 90%, but does not affect androgen biosynthesis in the adrenal glands. Addition of an anti-androgen to medical or surgical castration blocks the effect of remaining testosterone on prostate cells and is termed combined androgen blockade (CAB). CAB has now been compared with castration alone (medical and surgical) in numerous clinical trials. Some trials show advantage of CAB over castration, whereas others report no significant difference. The author favours the view that CAB has an advantage over castration. No study has reported that CAB is less effective than castration. Of the anti-androgens which are available for use in CAB, bicalutamide may be associated with a lower incidence of side-effects compared with the other non-steroidal anti-androgens and, in common with nilutamide, has the advantage of once-daily dosing. Only one study has compared anti-androgens within CAB: bicalutamide plus LH-RH analogue and flutamide plus LH-RH analogue. At 160-week follow-up, the groups were equivalent in terms of survival and time to progression. However, bicalutamide caused significantly less diarrhoea than flutamide. Withdrawal and intermittent therapy with anti-androgens extend the range of treatment options.