Megestrol acetate in the treatment of hormone refractory prostate cancer

Next Generation of Androgen Deprivation Therapy Combined With Radiotherapy for N0 M0 Prostate Cancer

Androgen deprivation therapy in combination with definitive radiation therapy is a standard of care for both intermediate-/high-risk localized prostate, locally advanced prostate cancer. Newer hormonal therapies have shown promising results in patients with castration-resistant disease and are now being investigated in early stages, in combination with radiation therapy. In this section, we review the body of evidence elucidating the mechanism of synergy and immune modulation effect of androgen deprivation therapy and radiation therapy, summarize the pivotal studies supporting its use in the nonmetastatic setting, and present the ongoing studies who will likely shape the management of locally advanced disease, in the upcoming years.

Non-metastatic CRPC and asymptomatic metastatic CRPC: which treatment for which patient?

The introduction of early PSa-based diagnosis has profoundly impacted the epidemiology of castration-resistant prostate cancer (CRPC). Many patients enter the disease at an early stage when the only sign of resistance to androgen deprivation therapy (ADT) is a progressive elevation of prostate-specific antigen (PSA). This created a very heterogeneous population of non-metastatic (M0) CRPC. PSa kinetics is the most powerful indicator of aggressiveness in that population and can be used to trigger imaging investigation and enrollment in clinical trials. Several registered and near to come treatments have not been tested in that population but in men with more advanced metastatic and often symptomatic disease. Several agents have been investigated to delay the onset of the first bone metastasis but only one, denosumab, has reached its end-point. Because CRPC remains largely driven by the androgen receptor (AR), physicians have relied on second-line hormonal manipulations to delay the progression of the disease, including first generation antiandrogens, adrenal synthesis inhibitors, steroids and estrogens. The data however are mostly limited to phase II trials.

Phase 2 trial of weekly intravenous 1,25 dihydroxy cholecalciferol (calcitriol) in combination with dexamethasone for castration-resistant prostate cancer

BACKGROUND

Preclinical data indicate that there is substantial antitumor activity and synergy between calcitriol and dexamethasone. On the basis of these data, the authors conducted a phase 2 trial of intravenous (iv) calcitriol at a dose of 74 microg weekly (based on a recent phase 1 trial) and dexamethasone in patients with castration-resistant prostate cancer (CRPC).

METHODS

A 2-stage Kepner-Chang design was used. Oral dexamethasone at a dose of 4 mg was given weekly on Days 1 and 2, and iv calcitriol (74 microg over 1 hour) was administered weekly on Day 2 from 4 to 8 hours after the dexamethasone dose in patients with CRPC. Laboratory data were monitored weekly, and renal sonograms, computed tomography scans, and bone scans were obtained every 3 months. Disease response was assessed by using the Response Evaluation Criteria in Solid Tumors (RECIST) and standard criteria for prostate-specific antigen (PSA) response. The calcitriol dose was delineated by from the authors' recent phase 1 trial.

RESULTS

Of 18 evaluable patients, 15 patients were Caucasian (83%). No patients had a complete or partial response by either RECIST or PSA response criteria. Fourteen patients had progressive disease, 2 patients refused to continue treatment (after 64 days and 266 days), and 2 patients remain on the trial (for 306 days and 412 days).The median time to disease progression was 106 days (95% confidence interval, 80-182 days). Fourteen episodes of grade 3 or 4 toxicity were noted in 7 patients (hyperglycemia, hypocalemia, chest pain, dyspnea, hypercalcemia, hypophosphatemia, cardiac arrhythmia, and pain). Only 1 episode of grade 3/ 4 toxicity was related definitely to calcitriol (hypercalcemia). No treatment-related deaths were noted.

CONCLUSIONS

High-dose, iv calcitriol at a dose of 74 microg weekly in combination with dexamethasone was well tolerated but failed to produce a clinical or PSA response in men with CRPC.

The case for secondary hormonal therapies in the chemotherapy age

PURPOSE

Virtually all patients with high risk localized and metastatic prostate cancer who are treated with androgen deprivation therapy eventually have progressive clinical or biochemical disease despite this therapy. Despite this fact numerous therapies are available that target the interaction of androgen and androgen receptor in the castrate testosterone milieu and many clinical investigations are under way in this area.

MATERIALS AND METHODS

This literature review focuses on the current clinical literature in support of secondary hormonal therapy.

RESULTS

Despite low androgen levels the androgen receptor remains active through the amplification, mutation or alteration of coactivator function. These observations suggest that secondary hormonal therapies remain a reasonable clinical approach. Such approaches can be receptor or ligand directed. Receptor directed approaches to secondary hormonal therapy are antiandrogen withdrawal, sequential use of antiandrogens and estrogenic compounds. Ligand directed therapies are adrenal cortex inhibitors, such as ketoconazole and others in clinical development. Furthermore, in the context of androgen independent tumor growth in patients with metastatic disease clinicians are now faced with the choice of using chemotherapy or secondary hormonal manipulations. Appropriate patient selection is a critical component to the effective use of these agents.

CONCLUSIONS

The modest activity of these secondary therapies challenges the notion that advancing prostate cancer uniformly becomes hormone refractory. It offers an alternative to the early use of chemotherapy in patients with androgen independent disease.

[Hormone-refractory prostate cancer. Modifications of the therapeutic strategies since chemotherapy proved its usefulness]

Back in the 90's it was difficult to have access to the conclusions of publications on HRPC. Homogeneity was very scarce regarding issues as significant as the definition of HRPC itself, patient selection, or evaluation of the responses to therapy. Consensus has currently been reached on such matters, and it is described in this text. Two works were published in late 2004 showing that docetaxel-based chemotherapy improved metastatic HRPC survival. Until then, the different treatments used could only provide symptomatic relief. But probably not all of the HRPC patients are eligible for primary docetaxel chemotherapy. The current debate focuses on determinating to which patients should chemotherapy be administered and at which time should it start, in order to exclude those patients at risk of experiencing its adverse effects without benefitting from its clinical advantages. Non-metastatic HRPC patients may be candidates to receiving secondary hormone manoeuvres before starting with chemotherapy. We will analyse in this review the changes occurred in the therapeutic strategies ever since chemotherapy showed its value, and we shall also disclose our attitude regarding treatment of these patients in daily practice.

Role of secondary hormonal therapy in the management of recurrent prostate cancer

Androgen ablation remains the cornerstone of the systemic management of prostate cancer. After initial androgen deprivation, clinical outcomes vary considerably. For the patient with progressive disease after androgen deprivation, multiple therapeutic options are available and include antiandrogen withdrawal, chemotherapy, and secondary hormonal agents. Multiple secondary hormonal agents have clinical activity and the sequential use of these agents may lead to prolonged periods of clinical response. In addition to the use of oral antiandrogens, active secondary hormonal therapies include adrenolytic agents such as ketoconazole and aminoglutethimide, corticosteroids and estrogenic compounds. This article reviews the clinical trial data for these various agents and discusses their role in the management of patients with advanced prostate cancer.

Chemotherapy of prostate cancer: present and future

The role of chemotherapy in prostate cancer continues to evolve. In men with symptomatic androgen-independent prostate cancer, significant reduction in pain and analgesic requirements are achievable with mitoxantrone and glucocorticoid combinations compared with glucocorticoids alone. However, survival rates are not improved. Taxane-based combinations with estramustine phosphate or other new agents show promise. Prostate-specific antigen response rates with these combinations appear to be 1.5 to 2 times more frequent than with mitoxantrone-based combinations. Randomized trials of taxane versus mitoxantrone-based therapies are underway. New agents and applications of current agents in adjuvant settings should be explored if survival in men with prostate cancer is to be improved.

Nilutamide as second line hormone therapy for prostate cancer after androgen ablation fails

PURPOSE

We investigate the prostate specific antigen (PSA) response rate with nilutamide as a second line hormonal agent in patients with advanced prostate cancer in whom androgen ablation failed.

MATERIALS AND METHODS

From 1998 to 2001, 28 patients with hormone resistant prostate cancer were treated with nilutamide as second line hormonal therapy. Average patient age +/- SD was 72.9 +/- 9.1 years. Median time from diagnosis of cancer to hormone failure was 48 months (range 2 to 120). Median followup from initiation of nilutamide therapy was 26 months (range 15 to 44). All patients had previously received at least 1 antiandrogen (flutamide or bicalutamide) in addition to medical or surgical castration, which failed.

RESULTS

Upon initiation of nilutamide therapy 18 of the 28 patients (64%) had an initial reduction in PSA and 8 (29%) sustained a PSA response (greater than 50% decrease) beyond 3 months (range 3 to 21). PSA response to nilutamide in patients with a previous antiandrogen withdrawal response versus nonresponse was 100% and 18%, respectively. In 10 of the 28 patients, (36%) PSA continued to increase. Interstitial pneumonitis developed, in 1 patient and 5 had nonspecific complaints (headaches, nausea, dizziness). During followup 6 of the 28 patients died 1 of whom was a nilutamide responder. No patient died while on nilutamide.

CONCLUSIONS

Nilutamide can achieve a significant sustained PSA response with a favorable toxicity profile. Patients with a previous antiandrogen withdrawal response have a significantly greater chance of responding to nilutamide.

SWOG-9510: evaluation of topotecan in hormone refractory prostate cancer: a Southwest Oncology Group study

BACKGROUND

Prostate cancer is the most common malignancy in American men, and as many as 70% of those initially treated for localized disease will ultimately progress and be considered candidates to receive therapy for metastatic cancer [Fuks et al.: Int J Radiat Oncol Bio Phys 21:537-547, 1991; Chodak et al.: N Engl J Med 330:246-248, 1994]. Although most will respond initially to hormone manipulation, essentially all will fail and require additional therapy. No standard chemotherapy approach has been shown to prolong survival significantly, and new agents are desperately needed. Topotecan is a new topoisomerase-1 inhibitor whose early investigation suggested possible activity in hormone-refractory prostate cancer.

METHODS

In this phase II trial, patients having failed one or two prior androgen ablative therapies were treated with 21-day continuous intravenous infusions of topotecan at a dose of 0.5 mg/m(2) per day every 28 days.

RESULTS

Twenty-six eligible patients were entered on the study. There were no confirmed tumor responses. Median survival was 9 months. The most common toxicities were hematologic, with 8 of 24 assessable patients experiencing grade 4 toxicity.

CONCLUSION

Topotecan infusions at this dose are ineffective in the management of hormone-refractory prostate cancer.

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.

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.

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.

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.

Anti-androgens and other hormonal therapies for prostate cancer

Many men who show evidence of a progression of prostate cancer by rising prostate-specific antigen (PSA) or other symptoms are treated with anti-androgens. Anti-androgen withdrawal represents the first line of treatment after failure of hormonal manipulation. Flutamide is an approved anti-androgen that has been incorporated in many of the combined androgen blockade studies. Bicalutamide is also a nonsteroidal anti-androgen that offers the advantages of reduced dosage amounts and reduction in side effects. Additionally, there are a variety of therapeutic agents that can suppress adrenal secretion of androgens. The most promising of these agents include aminoglutethamide, ketoconazole, and corticosteroids, with an expected response rate of 10% to 15%. Studies have shown that some patients may respond to an anti-estrogen such as tamoxifen. There are a variety of therapeutic treatment options available for patients with hormone refractory prostate cancer. However, quality-of-life issues are becoming increasingly important and should be incorporated into clinical trial endpoints.

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.