Antiandrogen withdrawal alone or in combination with ketoconazole in androgen-independent prostate cancer patients: a phase III trial (CALGB 9583)

Management of castration-resistant prostate cancer: a global approach

Treatment options for castration-resistant prostate cancer (crpc) have evolved since the start of the 2000s, with most of the new effective therapies appearing since 2010. In 2004, docetaxel was the first chemotherapeutic agent to improve survival in crpc, but little else was available once patients recurred. Since 2010, four new options have been shown to improve survival in patients with refractory or recurring disease after docetaxel. In the management of bone metastases, two bone-targeted therapies have been shown to reduce the risk of bone complications, and they are part of the overall management strategy in crpc patients. Therapeutic options before chemotherapy have shown promising results and may soon become available in Canada. The present article reviews the treatment options that have shown to be effective in crpc and also some of the ongoing work in the field.

Repurposing itraconazole as a treatment for advanced prostate cancer: a noncomparative randomized phase II trial in men with metastatic castration-resistant prostate cancer

BACKGROUND

The antifungal drug itraconazole inhibits angiogenesis and Hedgehog signaling and delays tumor growth in murine prostate cancer xenograft models. We conducted a noncomparative, randomized, phase II study evaluating the antitumor efficacy of two doses of oral itraconazole in men with metastatic prostate cancer.

PATIENTS AND METHODS

We randomly assigned 46 men with chemotherapy-naïve metastatic castration-resistant prostate cancer (CRPC) to receive low-dose (200 mg/day) or high-dose (600 mg/day) itraconazole until disease progression or unacceptable toxicity. The primary endpoint was the prostate-specific antigen (PSA) progression-free survival (PPFS) rate at 24 weeks; a 45% success rate in either arm was prespecified as constituting clinical significance. Secondary endpoints included the progression-free survival (PFS) rate and PSA response rate (Prostate Cancer Working Group criteria). Exploratory outcomes included circulating tumor cell (CTC) enumeration, serum androgen measurements, as well as pharmacokinetic and pharmacodynamic analyses.

RESULTS

The high-dose arm enrolled to completion (n = 29), but the low-dose arm closed early (n = 17) because of a prespecified futility rule. The PPFS rates at 24 weeks were 11.8% in the low-dose arm and 48.0% in the high-dose arm. The median PFS times were 11.9 weeks and 35.9 weeks, respectively. PSA response rates were 0% and 14.3%, respectively. In addition, itraconazole had favorable effects on CTC counts, and it suppressed Hedgehog signaling in skin biopsy samples. Itraconazole did not reduce serum testosterone or dehydroepiandrostenedione sulfate levels. Common toxicities included fatigue, nausea, anorexia, rash, and a syndrome of hypokalemia, hypertension, and edema.

CONCLUSION

High-dose itraconazole (600 mg/day) has modest antitumor activity in men with metastatic CRPC that is not mediated by testosterone suppression.

Current management of prostate cancer: dilemmas and trials

The past decade has witnessed significant advances in our understanding of the biology of prostate cancer. Androgen ablation/androgen receptor inhibition remains as the mainstay of treatment for advanced prostate cancer. Our understanding of the biology of prostate cancer has increased exponentially owing to advances in molecular biology. With this knowledge many intriguing issues have come to light, which clinicians and scientists alike strive to answer. These include why prostate cancer is so common, what drives the development of prostate cancer at a molecular level, why prostate cancer appears refractory to many families of cytotoxic chemotherapeutics, and why prostate cancer preferentially metastasizes to bone. Two clinical forms of prostate cancer have been identified: indolent organ confined disease, which elderly men often die of, and aggressive metastatic disease. A method of distinguishing between these two forms of the disease at an organ-confined stage remains elusive. Understanding the mechanisms of castrate resistance is a further issue of clinical importance. New trials of treatments, including molecular agents that target prostate cancer from a range of angles, have been instituted over the past 10-15 years. We can look at these trials not only as a chance to investigate the effectiveness of new treatments but also as an opportunity to further understand the complex biology of this disease.

Cabazitaxel

Prostate cancer is the most common cancer in men in the United States excluding skin cancer. Androgen deprivation therapy is initially effective for most patients with metastatic prostate cancer; however, castration-resistant prostate cancer (CRPC) usually develops when disease progresses despite conventional hormone therapies. There are few treatment options for progressive CRPC. Until recently, only one treatment, docetaxel, had been shown to prolong survival, and no agents had been shown to improve survival in docetaxel-refractory disease. This changed in June 2010 with the U.S. Food and Drug Administration approval of cabazitaxel. Cabazitaxel is a new option for patients with CRPC whose disease progresses during or after docetaxel treatment (docetaxel refractory). Cabazitaxel is a novel taxane that has been shown to have poor affinity for the p-glycoprotein drug efflux pump, a major mechanism of resistance to docetaxel. In combination with prednisone, cabazitaxel was shown to significantly prolong overall survival by 2.4 months when compared with mitoxantrone in a large randomized phase III trial in metastatic CRPC patients previously treated with first-line docetaxel. The most common toxicities with cabazitaxel are neutropenia (88%), anemia (81%), thrombocytopenia (43%), fatigue (27%), nausea (23%), and diarrhea (11%). This review will examine the clinical development, efficacy, adverse effects, and suggested monitoring for this new agent. The combination of cabazitaxel and prednisone is an important new treatment option for men with docetaxel-refractory metastatic CRPC. However, this agent should be administered with close, appropriate monitoring, especially in men at high risk of neutropenia or diarrhea. Future research directions for this new agent will include exploring its role in combination with other agents and comparing with docetaxel for the first-line treatment of metastatic CRPC.

Targeting the androgen receptor

Androgen receptor (AR)-mediated signaling is critical to the growth and survival of prostate cancer. Although medical castration and antiandrogen therapy can decrease AR activity and lower PSA, castration resistance eventually develops. Recent work exploring the molecular structure and evolution of AR in response to hormonal therapies has revealed novel mechanisms of progression of castration-resistant prostate cancer and yielded new targets for drug development. This review focuses on understanding the mechanisms of persistent AR signaling in the castrate environment, and highlights new therapies either currently available or in clinical trials, including androgen synthesis inhibitors and novel direct AR inhibitors.

The unfolding treatment landscape for men with castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) is a fatal disease in virtually all patients. Docetaxel chemotherapy became the standard front-line agent based on the results of the TAX327 trial in 2004, with a survival advantage of 3 months achieved over mitoxantrone. Over the past few years, an improved understanding of the molecular biology of castration-resistance has resulted in expansion of the treatment armamentarium for advanced prostate cancer with the emergence of novel androgen receptor-directed therapies, cytotoxic chemotherapies, as well as immunotherapies. Four different agents have very recently gained approval by the U.S. Food and Drug Administration for the treatment of CRPC and this review will summarize the development, mechanism of action, and safety and efficacy of these agents as demonstrated in preclinical as well as clinical studies.

Management of docetaxel failures in metastatic castrate-resistant prostate cancer

The treatment of metastatic castration-resistant prostate cancer has evolved since the approval of docetaxel-based therapy. Since docetaxel approval, three new agents have gained approval for this indication: sipuleucel-T, cabazitaxel, and abiraterone. Recent Phase III trials have also demonstrated survival benefits for MDV-3100 and radium-223 though regulatory approval ispending. Practicing physicians face the challenge of determining the optimal sequencing of these new agents. This dilemma is particularly relevant to the post-docetaxel setting, in which the indication for several of these agents overlaps. This article details the efficacy and safety of these agents to provide a framework for their clinical use.

[Recomendations on the management of controversies in advanced castrate-resistant prostate cancer]

CONTEXT

Controversies and uncertainties among integral management of advanced castration resistant prostate cancer continue to exist despite the number of evidence based clinical practice guidelines published with high international consensus.

OBJECTIVE

To develop a document that reviews the management of controversies in advanced castration resistant prostate cancer, with recommendations from the definition, to the management in hormonal maneuvers, first-line treatment and second-line with new treatments as cabazitaxel or abirarerone and the multidisciplinary approach of the pathology with the goal of finding the most efficient, best time to act and safety.

EVIDENCE ACQUISITION

Two meetings of a multidisciplinary group of experts involved in the management of this disease (Oncologist and Urologist) where pooled analysis of original literature and reached consensus document of recommendations on castration resistant prostate cancer, reviewing and attempting to address the current controversies of the disease.

EVIDENCE SYNTHESIS

This document is endorsed by the corresponding Scientific Associations and Working Groups involved in the current management of Genitourinary Tumours: the Spanish Association of Urology (AEU) with the Uro-Oncoloy Group (GUO) and the Spanish Oncology of Genitourinary Group (SOGUG).

CONCLUSIONS

With the adaptation and implementation of this Document of Recommendations for clinical practice are available for the first time, a real road map for quality, efficiency and safety in the management of patients with CRPC.

Management of metastatic castration-resistant prostate cancer: recent advances

Metastatic prostate cancer remains a considerable therapeutic challenge; however, advances in clinical research have resulted in five new treatments in the last 2 years. The immunotherapy sipuleucel-T, the cytotoxic cabazitaxel, the androgen biosynthesis inhibitor abiraterone acetate, the radioisotope alpharadin and the anti-androgen MDV3100 have all been shown to improve overall survival in randomized phase III studies for patients with metastatic castration-resistant prostate cancer. The therapeutic strategies of targeting androgen-receptor signalling and other key intracellular pathways involved in tumour progression and treatment resistance are yielding promising results. Agents such as the dual vascular endothelial growth factor receptor/MET inhibitor cabozantinib, the clusterin inhibitor custirsen and the Src inhibitor dasatinib have shown encouraging results in phase II studies. Novel immunotherapeutics such as prostate-specific membrane antigen-directed therapy and the anti-cytotoxic T lymphocyte-associated receptor 4 (CTLA4) antibody ipilimumab are also under investigation. Optimal methods of treatment selection, combination and sequencing have yet to be determined.

Pretreatment neutrophil-to-lymphocyte ratio in metastatic castration-resistant prostate cancer patients treated with ketoconazole: association with outcome and predictive nomogram

BACKGROUND

The neutrophil-to-lymphocyte ratio (NLR), an inflammation marker, is prognostic in several cancers. We assessed the association between the pretreatment NLR and outcome of patients with metastatic castration-resistant prostate cancer (mCRPC) treated with the CYP17 inhibitor ketoconazole.

METHODS

This was an international, retrospective study of 156 mCRPC patients treated with ketoconazole. The independent effect of the pretreatment NLR and factors associated with treatment outcome were determined by multivariate analysis.

RESULTS

Seventy-eight patients (50%) had a ≥50% decline in prostate-specific antigen (PSA). The median progression-free survival (PFS) time was 8 months. Excluded from the analysis were 23 patients without available data on their NLR and those with a recent health event or treatment associated with a blood count change. Sixty-two patients (47%) had a pretreatment NLR >3. Risk factors associated with the PFS outcome were a pretreatment NLR >3 and PSA doubling time (PSADT) <3 months and a prior response to a gonadotropin-releasing hormone agonist of <24 months or to an antiandrogen of <6 months. The number of risk factors was used to form a predictive nomogram by patient categorization into favorable (zero or one factor), intermediate (two factors), and poor (three or four factors) risk groups.

CONCLUSIONS

In mCRPC patients treated with ketoconazole, the pretreatment NLR and PSADT, and prior response to androgen-deprivation therapy, may be associated with the PFS time and used to form a risk stratification predictive nomogram.

Putting the brakes on continued androgen receptor signaling in castration-resistant prostate cancer

Patients with advanced prostate cancer initially respond very well to medical or surgical castration. Despite a good initial response, the disease progresses to a castration-resistant state. Castration-resistant prostate cancer (CRPC) remains addicted to androgen receptor signaling. The addition of conventional anti-androgen agents, such as bicalutamide, only provides a transient benefit. This has led to a search for further drug targets. Cytochrome P450 17 (CYP17) is an enzyme that is vital for the adrenal biosynthesis of androgens. The CYP17 inhibitor abiraterone acetate has a proven benefit in a phase III randomized trial and other CYP17 inhibitors are currently being evaluated. The novel antiandrogen MDV3100 is a small molecule androgen receptor antagonist with promising activity. Heat shock proteins (HSPs) bind to the androgen receptor and modify its activity. Several HSP inhibitors are under evaluation in clinical trials. This review explores the role of CYP17 inhibitors, MDV3100, and HSP inhibitors.

The role of enzalutamide in the treatment of castration-resistant prostate cancer

Prostate cancer is the most common solid organ cancer affecting the male population. Men with metastatic prostate cancer treated with androgen ablation therapy often respond rapidly, with improvement in bone pain and decreases in serum prostate-specific antigen. However, almost all patients progress to the castration-resistant state and abiraterone acetate was the last treatment available with proven survival benefit. Enzalutamide (formerly MDV3100) is an androgen receptor signaling inhibitor that has been shown to improve survival in men with metastatic castration-resistant prostate cancer previously treated with chemotherapy. In this article we discuss the characteristics of enzalutamide and provide a review of its clinical development.

The prognostic factors of effective ketoconazole treatment for metastatic castration-resistant prostate cancer: who can benefit from ketoconazole therapy?

We investigated the prognostic value of some variables of effective ketoconazole treatment for metastatic castration-resistant prostate cancer (mCRPC). In total, 163 patients with mCRPC were eligible, receiving ketoconazole 200-400 mg three times daily with replacement doses of prednisone. Progression-free survival (PFS) was calculated from the beginning of the ketoconazole therapy to the onset of disease progression. The prognostic value of different variables for PFS was assessed by Cox regression analysis. The median PFS was 2.6 months (0.5-8.6 months) for these patients. The serum testosterone level changed during therapy, which decreased when the prostate-specific antigen (PSA) declined; the serum testosterone level increased as the levels of PSA relapsed. The median PFS values for patients associated with different factors were the following: 1.4 and 3.5 months for a nadir PSA of ≥ 0.2 and <0.2 ng ml(-1), respectively (hazard rate (HR)=4.767, P<0.001); 3.1 and 1.6 months for a baseline testosterone of ≥ 0.1 and <0.1 ng ml(-1), respectively (HR=2.865, P=0.012); 2.8 and 1.9 months for a baseline haemoglobin of ≥ 120 and <120 g l(-1), respectively (HR=1.605, P<0.001); and 3.0 and 1.9 months for a PSA doubling time (PSADT) of ≥ 2.0 and <2.0 months, respectively (HR=1.454, P=0.017). A risk model was constructed according to the four factors that divided patients into three subgroups of low risk (0-1 factors), moderate risk (2 factors) and high risk (3-4 factors) with PFS values of 3.6, 3.0 and 1.4 months, respectively (HR=1.619, P<0.001). A nadir PSA of ≥ 0.2 ng ml(-1), a baseline testosterone of <0.1 ng ml(-1), a baseline haemoglobin of <120 g l(-1) and a PSADT of <2 months were associated with a poor PFS. This risk model could provide evidence to predict the survival benefit of ketoconazole therapy.

New developments in castrate-resistant prostate cancer

Castrate-resistant prostate cancer (CRPC) occurs when disease progresses in the presence of castrate levels of androgens and remains sensitive to further hormonal manipulation. For many years the treatment of CRPC was limited to the use of docetaxel for metastatic disease. However, this has recently changed with the approval of several new agents. Sipuleucel-T, an immunotherapeutic vaccine, is now available in the US for patients with non-metastatic CRPC and abiraterone, an oral enzyme inhibitor of androgen biosynthesis, as well as cabazitaxel, a cytotoxic chemotherapeutic, have been approved for the treatment of metastatic CRPC. Also, denosumab, a subcutaneous antibody, is now an option for the treatment of patients with CRPC with bone metastases, in addition to zoledronic acid, an intravenous bisphosphonate. Further treatment advances for metastatic CRPC therapeutics are in late stage phase III development. These include therapies affecting the androgen receptor (MDV3100) as well as additional immune-based therapeutics, PROSTVAC and ipilimumab. A broad range of agents is also emerging under the term targeted therapies. The endothelin-A receptor antagonist zibotentan, the tyrosine kinase inhibitors dasatinib, sorafenib and cabozantinib, the anti-angiogenic agent aflibercept, and the clusterin inhibitor custirsen, are all currently being tested for efficacy in metastatic CRPC. The mechanism of action of these and other promising agents are discussed alongside current therapeutic options and their potential place in the treatment landscape for CRPC is considered.

Abiraterone and other novel androgen-directed strategies for the treatment of prostate cancer: a new era of hormonal therapies is born

The number of life-prolonging therapies proven effective in the treatment of metastatic castrate-resistant prostate cancer (CRPC) has been limited until recently. In the past 2 years several such therapies have come to market. In 2010, the autologous immunotherapy sipuleucel-T and the next-generation taxane cabazitaxel were approved in this setting. However, abundant evidence has shown that CRPC growth continues to be driven through androgen-dependent signaling. Both of these drugs fail to take advantage of this targetable oncogenic pathway. Potent specific inhibitors of cytochrome P450-17 have been engineered with the aim of suppressing androgen synthesis beyond that seen with the luteinizing hormone-releasing hormone agonists/antagonists. Abiraterone acetate was developed by rational design based on a pregnenolone parent structure. Its approval by the US Food and Drug Administration (FDA) was granted in 2011 based on phase III data demonstrating an overall survival advantage compared with placebo. More recently, other drugs that act along the androgen signaling pathway, such as orteronel (TAK-700), galeterone (TOK-001), enzalutamide (MDV3100) and ARN-509, have shown promise in clinical trials. Some of these are expected to gain FDA approval in the near future. Here, we review abiraterone and other novel androgen-directed therapeutic strategies for the management of advanced prostate cancer.

Novel agents for the management of castration-resistant prostate cancer

PURPOSE OF REVIEW

Over the past 2 years, four new treatments have entered the treatment armamentarium for patients with castration-resistant prostate cancer (CRPC). Although these novel agents differ in their mechanism of action, they all face the same challenges: patient selection, timing of therapy and the cost/benefit of their use. In this review, we will discuss their development and implications when selecting treatment options for CRPC patients.

RECENT FINDINGS

Over the past few years, a better understanding of the biology of CRPC has allowed us to develop rational therapies that have resulted in an improvement in the outcome of prostate cancer patients. Immunotherapy has entered the field and despite its limitations and challenges is here to stay. A better understanding of the long-term complications of androgen deprivation has changed the initial approach to most patients with advanced disease, and bone health has become a major focus in their management. Understanding the importance of the androgen receptor and other ligands has led to a dramatic paradigm shift in the treatment of patients with metastatic disease in which the androgen receptor becomes a central therapeutic target in the disease. Specific adrenal inhibitors and engineered super androgen receptor inhibitors have become the most promising agents in the disease. Similarly, chemotherapy has demonstrated clinical benefit and is now a standard of care in docetaxel-refractory patients.

SUMMARY

The management of CRPC patients continues to evolve. Novel treatments recently approved by the US Food and Drug Administration have significantly impacted the outcome of CRPC. With the economic impact of their use, selecting the right patient, defining the appropriate timing and sequence of therapy have become critical facts that need to be followed when defining the contemporary treatment options for men with CRPC.

Overcoming castration resistance in prostate cancer

PURPOSE OF REVIEW

Recent advances in our understanding of the androgen axis signaling pathway have led to the development of therapeutic strategies to overcome the state of 'castration resistance' in prostate cancer. In this review, we examine the mechanisms of castration resistance, as well as recently reported and ongoing clinical studies, which will further identify therapeutic opportunities for novel therapeutics targeting the androgen-signaling axis in advanced prostate cancer.

RECENT FINDINGS

As evidenced by recently reported positive phase III clinical trials, secondary hormonal agents such as abiraterone and MDV3100 may still be very effective in the treatment of castration-resistant prostate cancer, even after the use of docetaxel chemotherapy.

SUMMARY

Novel agents targeting this pathway have demonstrated a proof of principle that overcoming castration resistance is possible, leading to significant changes in the landscape of treatment in this disease. The optimal combination, sequence, and pattern of use in these novel therapies will be the focus of clinical research in the near future.

[Therapy of castration-resistant prostate cancer]

Within the last two years the therapy of castration resistant prostate cancer (CRPC) has made major advances. Both the COU-AA-301 phase III trial and the TROPIC trial showed a survival benefit for patients after docetaxel failure treated with abiraterone or cabazitaxel, respectively. With rising interest for chemotherapeutic options and novel drugs, our goal was to review within the context of a multidisciplinary team the available evidence and explore the standards for medical treatment of prostate cancer outside of clinical trials. From this background, we are carefully evaluating the current treatment recommendations, based on the available evidence, and highlight potential future treatment options but also discuss important clinical topics like treatment until progression versus the advantage of chemo holidays and definition of particular patient subgroups. Additionally, we focus on novel molecular entities, which will most likely be available in the near future, such as MDV3100 and Sipuleucel T. The role and importance of palliation with radiotherapy and proactive medical management of pain is also discussed, as well as new options for bone directed therapy. The multitude of treatment options for patients with advanced prostate cancer clearly asks for a close collaboration between urologists, medical oncologists and radiation therapists.

Abiraterone acetate: a guide to its use in metastatic castration-resistant prostate cancer

Oral abiraterone acetate (Zytiga®), a selective cytochrome P450 17A1 enzyme inhibitor, is used in combination with prednisone or prednisolone to treat patients with metastatic castration-resistant prostate cancer (CRPC) who have previously received docetaxel-containing chemotherapy. In a clinical trial in patients with CRPC, abiraterone acetate plus prednisone significantly prolonged overall survival, the time to prostate-specific antigen progression and progression-free survival compared with placebo plus prednisone.

Challenges to improved therapeutics for metastatic castrate resistant prostate cancer: from recent successes and failures

Men with metastatic castration-resistant prostate cancer (mCRPC) carry poor prognosis despite the use of docetaxel-based regimens which has modest survival benefit shown by randomized clinical trials. Significant progress in the discovery of novel therapeutic agents has been made in the past few years. While sipuleucel-T, cabazitaxel, and abiraterone gained regulatory approval in 2010 and 2011, several highly promising candidates/regimens have failed in large scale clinical trials. Challenges remain to optimize the design and interpretation of clinical trial results and develop more effective strategies for mCRPC. In this review, we examined the positive and negative clinical trials in mCRPC in the past and discussed the various aspects of clinical trial design including selection of targets and appropriate outcome measures, biomarker development and implementation, and strategies for combination therapy.

The evolving paradigm of second-line hormonal therapy options for castration-resistant prostate cancer

PURPOSE OF REVIEW

The review examines recent advances in second-line hormonal therapy for the treatment of castrate-resistant prostate cancer (CRPC).

RECENT FINDINGS

Recent data highlight the continued importance of androgen signaling in CRPC. These findings have spurred the development of novel inhibitors of adrenal and intra-tumoral androgen synthesis and novel androgen signaling inhibitors with activity in CRPC. In the past year abiraterone acetate, a CYP17 (17α-hydroxylase/17, 20 lyase) inhibitor, received US FDA approval for use in the treatment of metastatic CRPC in patients previously treated with docetaxel. Additionally, the novel androgen signaling inhibitor MDV3100 has been reported to confer a survival advantage compared to placebo in the same patient population. Here we review the scientific rationale for targeting androgen signaling in CRPC and the recent pivotal trials that support the use of novel second-line hormonal therapies. Additionally, we summarize ongoing preclinical and clinical efforts to ascertain and overcome mechanisms of resistance.

SUMMARY

Novel inhibitors of extra-gonadal androgen synthesis and androgen receptor function demonstrate the continued importance of androgen signaling in CRPC. These agents have improved clinical outcomes for patients with metastatic CRPC.

[Castration-resistant prostate cancer: where are we going?]

CONTEXT

Hormonal therapy allows effective control of cancer-related symptoms in advanced stages. However, the disease will progress in almost all these metastatic prostate cancer patient until becoming resistant to androgen suppression. The emergence of new drugs will most probably have open up new expectations regarding the treatment of this cancer.

OBJECTIVE

The aim of the present review has been to provide an overview of the current status of castration-resistant prostate cancer and to share the high expectations created with the new treatments.

EVIDENCE ACQUISITION

Evidence was obtained from multidisciplinary meetings with the participation of urologists and oncologists, where they pooled the analysis of original articles in the literature and defined the content of the article.

EVIDENCE SYNTHESIS

Chemotherapy with docetaxel was a turning point in castration-resistant prostate cancer after the failure of hormonal therapy failure. For the first time, it achieved increased survival time in comparison with mitoxantrone and prednisone. Combination therapy with docetaxel and prednisone is the first-line choice treatment. Once the cancer has progressed, there is no clear alternative, although some novel agents have created expectations for the treatment of this type of cancer.

CONCLUSIONS

The range of therapeutic options for castration-resistant prostate cancer has increased dramatically with the arrival of new drugs. At present, cabazitaxel, and in the near future, abiraterone, have been found to be effective drugs in second-line treatment after progression to docetaxel, increasing survival by 2-4 months and reducing risk of death by 30-35%.

Efficacy of docetaxel-based chemotherapy following ketoconazole in metastatic castration-resistant prostate cancer: implications for prior therapy in clinical trials

OBJECTIVES

Abiraterone acetate (AA) is a CYP17 inhibitor of androgen synthesis approved for use following docetaxel for metastatic castration-resistant prostate cancer (mCRPC); evaluation in the pre-docetaxel setting is ongoing. Given that the reported efficacy of AA is lower following docetaxel vs. pre-docetaxel, the potential exists for cross resistance given docetaxel's partly androgen receptor targeting activity. The efficacy of docetaxel following ketoconazole (KC), a weaker and nonspecific inhibitor of CYP17, may provide some insights into this potential interaction. We retrospectively evaluated the efficacy of every 3-week docetaxel with prednisone (DP) in mCRPC previously exposed to KC compared to KC-naive patients.

MATERIALS AND METHODS

A randomized phase II trial of men with mCRPC treated with DP + AT-101 (bcl-2 inhibitor) vs. DP plus placebo was analyzed. Both arms were combined for analysis as no significant differences were seen. Overall survival (OS), progression-free survival (PFS), objective response (ORR), pain, and prostate-specific antigen (PSA) response rates were estimated with and without prior KC. Cox proportional hazards regression models were used to estimate the effect of covariates on OS.

RESULTS

Of 220 evaluable men, 40 (18.2%) received prior KC. The median OS with DP-based therapy of KC-naive patients (18.3 months, 95% CI: 15.0, 24.5) and post-KC patients (17.0 months, 95% CI: 9.9, 20.4) was not statistically different (P = 0.20). After controlling for prognostic classifications, analyses demonstrated consistent trends for worsening of OS after KC, with (hazard ratios (HRs) 1.33-1.46. Similar unfavorable trends were observed for ORR, PSA declines, and PFS.

CONCLUSIONS

In this hypothesis-generating analysis, patients treated with docetaxel-based chemotherapy following prior KC had numerically and consistently worse outcomes than patients not exposed to prior KC. Although the estimated differences did not attain statistical significance, evaluation of outcomes with docetaxel in particular, and all classes of novel and emerging agents following AA, is of clinical importance, given its more potent androgen synthesis inhibition compared with KC. Drug development should take into account the potential impact of previous therapy.

[Strategy in advanced castration-resistant prostate cancer]

If androgen deprivation, chemical with LH-RH analogs or surgical with bilateral orchiectomy, still remains the stone edge of treatment of prostate cancer, in the metastatic setting, this hormonosensitivity, most of the time long, finally move on in hormonal-failure. If rare changes in the therapeutic strategy have been achieved in this setting since 2004 and the arrival of docetaxel, it is the global perception of the disease that has been modified and the definition of one specific entity: the castrate-resistant prostate cancer. This new definition and the changes of design and end-points of clinical trials testing new agents with strong recruitment during the past years have conducted to a real revolution in the management of castrate-refractory prostate cancer. The place of secondary hormonal manipulations, such as withdrawal of the anti-androgen, oestrogen or ketoconazole, still exists for a selected group of patients. In case of aggressive disease and symptoms, chemotherapy should be selected, docetaxel, in a three weeks schedule, and may be combined with Estracyt. It is time to consider the revolution of the post-chemotherapy setting with the arrival of two new drugs ; a cytotoxic one, the cabazitaxel and hormonal for the second one, the abiraterone acetate. The place of the immunotherapy with the sipuleucel-T may be more difficult to precise, especially in Europe, even if it has been finally indicated in the United States in the metastatic setting. Concerning bone metastasis, zoledronic acid was during a long time the only bone-targeted agent, effective in reducing the incidence of skeletal related events, and was recently exceeded by the denosumab, an anti-RANK ligand. Finally, let us hope that other changes will be achieved in the near future, with the cabazitaxel-docetaxel confrontation in the first-line setting, and the introduction of the abiraterone acetate before chemotherapy with docetaxel, already tested in ongoing trials.

Open-label, phase I, pharmacokinetic studies of abiraterone acetate in healthy men

Purpose

To evaluate pharmacokinetics, safety, and tolerability of abiraterone acetate (AA) in healthy men.

Methods

Two phase I studies (dose-escalation study and dose-proportionality study) were conducted in healthy men aged 18–55 years. All subjects received 4 consecutive single doses of AA (250, 500, 750 and 1,000 mg). The dose-escalation study subjects (N = 33) received AA doses in a sequential manner, starting with the lowest dose. The dose-proportionality study subjects (N = 32) were randomly allocated (1:1:1:1) to receive each of the 4 doses in a four-way crossover design.

Results

A dose-related increase in abiraterone exposure was observed in both studies. Over the evaluated dose range, the mean abiraterone maximum plasma concentrations increased from 26 to 112 ng/mL in dose-escalation study and from 40 to 125 ng/mL in dose-proportionality study; the mean area under the plasma concentration–time curve from 0 to the last measurable plasma concentration increased from 155 to 610 ng.h/mL in dose-escalation study, and from 195 to 607 ng.h/mL in dose-proportionality study. In the dose-proportionality study, abiraterone exposure was dose proportional between 1,000 and 750 mg doses; however, the exposure was slightly greater than dose proportional when exposures at 500 and 250 mg doses were compared with the exposure at 1,000 mg. Single doses of AA were well tolerated in healthy men, and safety profile was consistent with its known toxicities in CRPC patients.

Conclusion

Systemic exposure to abiraterone increased with increasing doses of AA (250–1,000 mg) in healthy men; AA was well tolerated in this population.

The role of abiraterone in the management of metastatic castration-resistant prostate cancer

Prostate cancer is the most common solid-organ cancer affecting the male population. Men with metastatic prostate cancer treated with androgen ablation therapy often respond rapidly, with improvement in bone pain and decreases in serum prostate-specific antigen. However, almost all patients progress to the castrate-resistant state and until recently chemotherapy was the only treatment available with proven survival benefit. Abiraterone is a new class of anti-androgen with proven survival benefit post-chemotherapy. In this review we discuss the characteristics of abiraterone and the clinical trials that led to its approval for the treatment of patients with prostate cancer.

[Androgen deprivation therapy in prostate cancer. Indication and systemic consequences]

Androgen deprivation therapy (ADT) is effective in prolonging the progression free survival of patients with symptomatic/metastatic prostate cancer (PC). The reduction of clinical symptoms of tumour disease and the reduction of tumour growth and metastatic dissemination is accompanied by systemic consequences of testosterone deficiency. These are hot flushes, fatigue due to reduction of muscular strength and muscle mass as well as anaemia. Moreover, patients develop cognitive impairment und depressive mood. Weight gain with insulin resistance, disturbances of lipid metabolism and gynecomastia are other effects of androgen deficiency. A decrease in bone mineral density may lead to an increased susceptibility to bone fractures. There are several options to reduce these side effects of ADT, e.g. physical activity, dietary supplementation, tailored pharmacological therapy and psychotherapy. The knowledge of these adjuvant treatment options, despite their palliative character, is relevant to optimize the quality of life of these patients.

Abiraterone in prostate cancer: a new angle to an old problem

Abiraterone acetate is an orally administered potent inhibitor of cytochrome P450, family 17, subfamily A, polypeptide 1 (CYP17), which is essential for synthesis of testosterone from cholesterol. Although decreasing serum testosterone through inhibition of testicular function is the first line of treatment for men with metastatic prostate cancer, residual androgens may still be detected in patients treated with luteinizing hormone-releasing hormone agonists or antagonists. Treatment with abiraterone results in rapid, and complete, inhibition of androgen synthesis in the adrenal glands and potentially within the tumor itself. An overall survival benefit of maximal androgen suppression was recently shown in a randomized placebo-controlled phase III clinical trial of abiraterone with prednisone versus prednisone in men with metastatic castrate-resistant prostate cancer previously treated with docetaxel chemotherapy. Abiraterone's efficacy shows the importance of androgen signaling in patients with castrate-resistant metastatic disease, with additional confirmation from recent studies of other novel agents such as MDV3100, an androgen receptor signaling inhibitor. These promising results now pose a new angle to an old problem about hormonal therapy and raise new questions about how resistance develops, how to best sequence therapy, and how to optimize combinations with other emerging novel agents.

Orteronel (TAK-700), a novel non-steroidal 17,20-lyase inhibitor: effects on steroid synthesis in human and monkey adrenal cells and serum steroid levels in cynomolgus monkeys

Surgical or pharmacologic methods to control gonadal androgen biosynthesis are effective approaches in the treatment of a variety of non-neoplastic and neoplastic diseases. For example, androgen ablation and its consequent reduction in circulating levels of testosterone is an effective therapy for advanced prostate cancers. Unfortunately, the therapeutic effectiveness of this approach is often temporary because of disease progression to the 'castration resistant' (CRPC) state, a situation for which there are limited treatment options. One mechanism thought to be responsible for the development of CRPC is extra-gonadal androgen synthesis and the resulting impact of these residual extra-gonadal androgens on prostate tumor cell proliferation. An important enzyme responsible for the synthesis of extra-gonadal androgens is CYP17A1 which possesses both 17,20-lyase and 17-hydroxylase catalytic activities with the 17,20-lyase activity being key in the androgen biosynthetic process. Orteronel (TAK-700), a novel, selective, and potent inhibitor of 17,20-lyase is under development as a drug to inhibit androgen synthesis. In this study, we quantified the inhibitory activity and specificity of orteronel for testicular and adrenal androgen production by evaluating its effects on CYP17A1 enzymatic activity, steroid production in monkey adrenal cells and human adrenal tumor cells, and serum levels of dehydroepiandrosterone (DHEA), cortisol, and testosterone after oral dosing in castrated and intact male cynomolgus monkeys. We report that orteronel potently suppresses androgen production in monkey adrenal cells but only weakly suppresses corticosterone and aldosterone production; the IC(50) value of orteronel for cortisol was ~3-fold higher than that for DHEA. After single oral dosing, serum levels of DHEA, cortisol, and testosterone were rapidly suppressed in intact cynomolgus monkeys. In castrated monkeys treated twice daily with orteronel, suppression of DHEA and testosterone persisted throughout the treatment period. In both in vivo models and in agreement with our in vitro data, suppression of serum cortisol levels following oral dosing was less than that seen for DHEA. In terms of human CYP17A1 and human adrenal tumor cells, orteronel inhibited 17,20-lyase activity 5.4 times more potently than 17-hydroxylase activity in cell-free enzyme assays and DHEA production 27 times more potently than cortisol production in human adrenal tumor cells, suggesting greater specificity of inhibition between 17,20-lyase and 17-hydroxylase activities in humans vs monkeys. In summary, orteronel potently inhibited the 17,20-lyase activity of monkey and human CYP17A1 and reduced serum androgen levels in vivo in monkeys. These findings suggest that orteronel may be an effective therapeutic option for diseases where androgen suppression is critical, such as androgen sensitive and CRPC.

Castration-resistant prostate cancer: mechanisms, targets, and treatment

Patients with castration-resistant prostate cancer (CRPC), who progress after docetaxel therapy, had until very recently, only a few therapeutic options. Recent advances in this field brought about new perspectives in the treatment of this disease. Molecular, basic, and translational research has given us a better understanding on the mechanisms of CRPC. This great investment has turned into a more rational approach to the development of new drugs. Some of the new treatments are already available to our patients outside clinical trials and may include inhibitors of androgen biosynthesis; new chemotherapy agents; bone-targeted therapy; and immunotherapy. This paper aims to review the mechanisms of prostate cancer resistance, possible therapeutic targets, as well as new options to treat CRPC.

Contemporary experience with ketoconazole in patients with metastatic castration-resistant prostate cancer: clinical factors associated with PSA response and disease progression

BACKGROUND

Adrenal/intratumoral androgen biosynthesis contributes to ligand-dependent androgen receptor activation in metastatic castration-resistant prostate cancer (mCRCP). Compounds targeting CYP-17 hydroxylase and lyase, as ketoconazole and abiraterone, block adrenal/intratumoral androgen biosynthesis, and are used as sequential endocrine approaches in mCRCP. We aimed to describe contemporary experience and association of clinical factors with Prostate specific antigen (PSA) response and disease progression, in mCRPC progressing on GnRH-agonist, antiandrogen, antiandrogen withdrawal, and treated with ketoconazole.

METHODS

Data were retrospectively analyzed in all mCRPC patients treated with ketoconazole. Patients continued GnRH-agonist, and treated with ketoconazole 200-400 mg 3× a day until dose-limiting toxicity or disease progression. A multivariate cox regression model was used to identify clinical factors associated with PSA response and disease progression.

RESULTS

From 1999 to 2010, 114 mCRPC patients were treated with ketoconazole. With a median follow-up time of 31 months (range 5-129), 25 patients (22%) had grade 3/4 toxicity, most commonly fatigue, abdominal discomfort, nausea, and dizziness. Sixty-one patients (54%) had ≥50% PSA decline. Median time to progression was 8 months (range 1-129). Factors associated with PSA response and disease progression were response to prior antiandrogen (≥6 vs. <6 months), pre-treatment PSADT (≥3 vs. <3 months) and extent of disease (limited-axial skeleton and/or nodal vs. extensive-appendicular skeleton and/or visceral).

CONCLUSIONS

Ketoconazole is effective and safe in mCRPC. Prior response to antiandrogen, pre-treatment PSADT, and disease extent are associated with PSA response and disease progression, and further supports a therapeutic role in suppressing adrenal androgens in mCRPC.

A new era for castrate resistant prostate cancer: a treatment review and update

PURPOSE

The purpose of this review article is to present the current treatment options for castrate resistant prostate cancer in addition to the recently approved agents and their role in treatment.

SUMMARY

The biology of prostate cancer and the data supporting the use of traditional chemotherapeutic options in castrate resistant prostate cancer are reviewed. The newly approved agents, sipuleucel-T, cabazitaxel, and abiraterone, are presented as well. The studies that led to the approval of these three agents are discussed in this article as well as their current and potential roles in the treatment of castrate resistant prostate cancer.

CONCLUSION

New mechanisms, drugs, and clinically relevant molecular targets show survival advantage and are new options available for patients after traditional chemotherapy. The roles of these new agents have yet to be further clarified in future studies.

Recommendations from the Spanish Oncology Genitourinary Group for the treatment of patients with metastatic castration-resistant prostate cancer

Prostate cancer is the most prevalent urogenital malignancy. However, despite initial disease control using androgen deprivation, most of patients eventually develop progressive disease that is resistant to further hormone manipulation. For these patients with castration-resistant prostate cancer (CRPC), and particularly patients with metastatic disease, options have been limited, and prognosis is grim. However, as newer regimens and agents become available, higher rates of objective and biochemical response are being achieved, providing renewed hope for the management of these patients. With the aim of facilitating the treatment of these patients, the Spanish Oncology Genitourinary Group (SOGUG) has issued a series of the recommendations which have been collected in this review. Each recommendation is accompanied by the appropriate level of evidence and grade of recommendation on the basis of the characteristics of the data available.

[Inhibitors of androgen and estrogen biosynthesis in castration-resistant prostate cancer]

Advanced prostate cancer remains dependent on androgens and signaling through the androgen receptor despite castrate levels of testosterone defined as testosterone levels <1.7 nmol/l. Ketoconazole, a nonspecific inhibitor of androgen synthesis, has been tested in clinical trials and showed clinical activity; however, high doses are needed which are associated with significant sides effects, mainly neurotoxicity, gastrointestinal intolerance, and liver toxicity. Abiraterone acetate is an irreversible inhibitor of two key enzymes of androgen synthesis, 17a-hydroxylase and 17,20-lyase, and has been tested in a randomized phase III study in patients with castration-resistant prostate cancer who progressed after chemotherapy. Abiraterone plus prednisone resulted in a significant overall survival benefit of 4.6 months compared to prednisone alone. Abiraterone was well tolerated, with mostly mild or moderate side effects consistent with secondary mineralocorticoid excess, namely fluid retention, hypokalemia, and hypertension. Abiraterone plus prednisone is considered a new standard therapy option for patients with castration-resistant prostate cancer who progressed after chemotherapy.

Abiraterone acetate: oral androgen biosynthesis inhibitor for treatment of castration-resistant prostate cancer

Prostate cancer is the second leading cause of cancer death in men in the US and Europe. The treatment of advanced-stage prostate cancer has been androgen deprivation. Medical castration leads to decreased production of testosterone and dihydrotestosterone by the testes, but adrenal glands and even prostate cancer tissue continue to produce androgens, which eventually leads to continued prostate cancer growth despite castrate level of androgens. This stage is known as castrate-resistant prostate cancer (CRPC), which continues to be a challenge to treat. Addition of androgen antagonists to hormonal deprivation has been successful in lowering the prostate-specific antigen levels further, but has not actually translated into life-prolonging options. The results of several contemporary studies have continued to demonstrate activation of the androgen receptor as being the key factor in the continued growth of prostate cancer. Blockade of androgen production by nongonadal sources has led to clinical benefit in this setting. One such agent is abiraterone acetate, which significantly reduces androgen production by blocking the enzyme, cytochrome P450 17 alpha-hydroxylase (CYP17). This has provided physicians with another treatment option for patients with CRPC. The landscape for prostate cancer treatment has changed with the approval of cabazitaxel, sipuleucel-T and abiraterone. Here we provide an overview of abiraterone acetate, its mechanism of action, and its potential place for therapy in CRPC.

Abiraterone acetate: in metastatic castration-resistant prostate cancer

Oral abiraterone acetate, in combination with prednisone/prednisolone, is used to treat patients with metastatic castration-resistant prostate cancer (CRPC) who have previously received docetaxel-containing chemotherapy. Abiraterone acetate was developed to specifically inhibit cytochrome P450 (CYP)17A1, which is an essential enzyme in the biosynthesis of testosterone. In a pivotal phase III trial in patients with metastatic CRPC who have previously received docetaxel-containing chemotherapy, abiraterone acetate 1000 mg once daily plus prednisone 5 mg twice daily significantly prolonged overall survival compared with placebo plus prednisone. In this trial, abiraterone acetate plus prednisone was significantly more effective than placebo plus prednisone in prolonging the time to prostate-specific antigen (PSA) progression and in prolonging progression-free survival. Significantly more abiraterone acetate plus prednisone recipients than placebo plus prednisone recipients were considered to be responders, when assessed by PSA levels or radiographic imaging. Treatment with abiraterone acetate plus prednisone in the phase III trial was associated with an acceptable tolerability profile, which was generally similar to that of the placebo plus prednisone group. However, adverse events of special interest (e.g. cardiac disorders and liver-function test abnormalities and adverse events resulting from elevated mineralocorticoid levels because of CYP17A1 inhibition [i.e. fluid retention and oedema, hypokalaemia, hypertension]) occurred in significantly more abiraterone acetate plus prednisone than in placebo plus prednisone recipients.

Use of androgen deprivation therapy in prostate cancer: indications and prevalence

Androgens play a prominent role in the development, maintenance and progression of prostate cancer. The introduction of androgen deprivation therapies into the treatment paradigm for prostate cancer patients has resulted in a wide variety of benefits ranging from a survival advantage for those with clinically localized or locally advanced disease, to improvements in symptom control for patients with advanced disease. Controversies remain, however, surrounding the optimal timing, duration and schedule of these hormonal approaches. Newer hormonal manipulations such as abiraterone acetate have also been investigated and will broaden treatment options for men with prostate cancer. This review highlights the various androgen-directed treatment options available to men with prostate cancer, their specific indications and the evidence supporting each approach, as well as patterns of use of hormonal therapies.

Castration-resistant prostate cancer: systemic therapy in 2012

Prostate cancer is the most common non-cutaneous neoplasm in the male population worldwide. It is typically diagnosed in its early stages, and the disease exhibits a relatively indolent course in most patients. Despite the curability of localized disease with prostatectomy and radiation therapy, some patients develop metastatic disease and die. Although androgen deprivation is present in the majority of patients with metastatic prostate cancer, a state of androgen resistance eventually develops. Castration-resistant prostate cancer, defined when there is progression of disease despite low levels of testosterone, requires specialized care, and improved communication between medical and urologic oncologists has been identified as a key component in delivering effective therapy. Despite being considered a chemoresistant tumor in the past, the use of a prostate-specific antigen has paved the way for a new generation of trials for castration-resistant prostate cancer. Docetaxel is a life-prolonging chemotherapy that has been established as the standard first-line agent in two phase III clinical trials. Cabazitaxel, a novel taxane with activity in cancer models resistant to paclitaxel and docetaxel, is the only agent that has been compared to a chemotherapy control in a phase III clinical trial as a second-line therapy; it was found to prolong the overall survival of patients with castration-resistant prostate cancer previously treated with docetaxel when compared to mitoxantrone. Other agents used in this setting include abiraterone and sipuleucel-T, and novel therapies are continually being investigated in an attempt to improve the outcome for patients with castration-resistant prostate cancer.

Efficacy of peripheral androgen blockade in prostate cancer patients with biochemical failure after definitive local therapy: results of Cancer and Leukemia Group B (CALGB) 9782

BACKGROUND

The treatment for prostate cancer patients with biochemical failure after local therapy remains controversial. Peripheral androgen blockade using a combination of a 5-alpha reductase inhibitor and an antiandrogen may allow control of the prostate-specific antigen (PSA). Because testosterone levels are not suppressed, this approach may be associated with less morbidity than conventional gonadal androgen suppression.

METHODS

All patients had undergone previous definitive local therapy and had evidence of a rising PSA >1ng/mL, with no evidence of recurrent disease. Patients received both finasteride, 5 mg orally per day, and flutamide, 250 mg orally 3× a day. Patients were followed for a PSA response and quality of life assessment.

RESULTS

Ninety-nine of 101 accrued patients were eligible. A ≥80% PSA decline was seen in 96 (96%) patients. The median time to PSA progression was 85 months. With a median follow-up of 10 years, the median survival time had not been reached, and the 5-year overall survival rate was 87%. Toxicity was mild, with 18 patients stopping for toxicity; 15 had diarrhea, 4 had gynecomastia, and 3 had transaminase elevation. Baseline Functional Assessment of Cancer Therapy Prostate Module and Treatment Outcome Index scores decreased by 5 points each at 6 months after enrollment.

CONCLUSIONS

The use of the finasteride/flutamide combination is feasible, and results in PSA declines of ≥80% in 96% of patients with serologic progression after definitive local therapy. There were no unexpected toxicities, and the change in quality of life was mild. Further evaluation of this or a similar regimen in a controlled clinical trial is warranted.

Development and clinical utility of abiraterone acetate as an androgen synthesis inhibitor

In April 2011, abiraterone acetate (AA) was approved by the US Food and Drug Administration (FDA) for the treatment of metastatic castration-resistant prostate cancer (CRPC) after chemotherapy. The development of AA is the direct result of our increased understanding of the intricacies of the androgen receptor (AR) pathway and its natural evolution in prostate cancer cells over the course of treatment. In this paper we review the biology of the AR and how it led to the rational design of AA. We also examine the clinical development of AA, its current use, and questions to be addressed for future development.

[Second line therapy for castration-resistant prostate cancer (CRPC)]

Every year in Germany approximately 12,000 men die of castration-resistant prostate cancer even though early detection using PSA-based diagnostics allows more patients to be diagnosed with a curable cancer. An established first line therapy at this stadium is docetaxel chemotherapy, given in a 3-week regimen, providing an overall survival advantage of 2 months. In 6-9 months, the patients treated primarily with docetaxel will progress to a docetaxel-insensitive phase which requires a secondary systemic therapy. Increasing understanding of molecular signal transduction has permitted a growing variety of promising modern drugs, including cabazitaxel, sipuleucel-T and abiraterone. More prospective clinical data will provide a large variety of different therapy combinations, sequence therapies or other therapy regimens particularly for selected subgroups of patients with castration-resistant prostate cancer.