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

Cabazitaxel for the treatment of castration-resistant prostate cancer

Treatment with docetaxel-based chemotherapy results in improved survival in patients with metastatic castration-resistant prostate cancer. However, all patients eventually develop progressive disease associated with poor outcomes. In this article, we discuss the available second-line therapeutic options following docetaxel, with a special focus on cabazitaxel, which is the first agent to yield extended survival as second-line therapy following docetaxel. Cabazitaxel, a novel semi-synthetic taxane, is effective even in docetaxel-resistant model systems. Recently, results of the Phase III TROPIC trial demonstrated improved survival with cabazitaxel plus prednisone compared with mitoxantrone and prednisone in patients with progressive metastatic castration-resistant prostate cancer, following prior docetaxel, which led to approval by the US FDA.

Synthesis and biological evaluations of putative metabolically stable analogs of VN/124-1 (TOK-001): head to head anti-tumor efficacy evaluation of VN/124-1 (TOK-001) and abiraterone in LAPC-4 human prostate cancer xenograft model

In a continuing study of our clinical candidate 5 VN/124-1 (TOK-001) and analogs as potential agents for prostate cancer therapy, putative metabolites (10, 15 and 18) of compound 5 were rationally designed and synthesized. However, none of these agents were as efficacious as 5 in several in vitro studies. Using western blot analysis, we have generated a preliminary structure-activity relationship (SAR) of 5 and related analogs as androgen receptor ablative agents (ARAAs). In vivo using the androgen-dependent LAPC-4 prostate cancer xenograft model, we demonstrated for the first time that 5 is more efficacious than the 17-lyase inhibitor 3 (abiraterone)/4 (abiraterone acetate) that is currently in phase III clinical trials. In our desire to optimize the potency of 5, compounds 6 (3ξ-fluoro-) and 9 (3β-sulfamate-) designed to increase the stability and oral bioavailability of 5, respectively were evaluated in vivo. We showed, that on equimolar basis, compound 6 was ∼2-fold more efficacious versus LAPC-4 xenografts than 5, but the toxicity observed with 6 is of concern. These studies further demonstrate the efficacy of 5 in a clinically relevant prostate cancer model and justify its current clinical development as a potential treatment of prostate cancer.

Castration-resistant prostate cancer: many treatments, many options, many challenges ahead

Although the long natural history of prostate cancer presents challenges in the development of novel therapeutics, major contributions have been observed recently. A better understanding of the long-term complications of androgen deprivation has changed the initial approach to most patients with advanced disease. Specifically, recognition of the limitations of prostate-specific antigen has driven the pursuit of new tools capable of becoming true surrogates for disease outcome. Understanding the molecular biology of castration-resistant prostate cancer (CRPC) has led to a dramatic paradigm shift in the treatment of patients with metastatic disease where the androgen receptor becomes a central therapeutic target. Specific adrenal inhibitors and engineered super androgen receptor inhibitors have become the most promising agents in the disease. Novel immune therapies have been shown to improve survival in selected patients with castration-resistant disease despite the inability to impact traditional markers of response. Similarly, agents such as cabazitaxel and abiraterone acetate have demonstrated clinical benefit are now a standard of care in docetaxel-refractory metastatic CRPC patients. All these changes have occurred in a relatively short period and are likely to change the prostate cancer treatment paradigm. This review summarizes the current management of CRPC and discusses potential future directions.

Translating scientific advancement into clinical benefit for castration-resistant prostate cancer patients

In the past 12 months, three novel therapeutics-sipuleucel-T, cabazitaxel, and abiraterone acetate-were granted Food and Drug Administration regulatory approval for the treatment of metastatic castration-resistant prostate cancer (CRPC) patients based on phase III studies that showed a survival advantage. Other agents, including the novel antiandrogen MDV3100, are at an advanced stage of clinical phase III evaluation. The treatment paradigm for CRPC has now changed significantly, and this has introduced new challenges for physicians, including selecting patients for specific therapies, developing the best sequencing and combination regimens for the several new effective agents that have recently been approved or are in development, and dissecting mechanisms of resistance that will inform the development of a new generation of therapeutics. This Focus issue reviews the results obtained with immunotherapies, taxane cytotoxics, and androgen receptor targeting therapeutics for CRPC, as well as the postulated mechanisms of resistance to these protocols and proposed strategies for improvement. The use of biomarkers for patient selection, monitoring of treatment activity, and acceleration of drug approval will be critical for achieving further improvements in the treatment for CRPC, and is also discussed in detail.

New insights into the androgen-targeted therapies and epigenetic therapies in prostate cancer

Prostate cancer is the most common cancer in men in the United States, and it is the second leading cause of cancer-related death in American men. The androgen receptor (AR), a receptor of nuclear family and a transcription factor, is the most important target in this disease. While most efforts in the clinic are currently directed at lowering levels of androgens that activate AR, resistance to androgen deprivation eventually develops. Most prostate cancer deaths are attributable to this castration-resistant form of prostate cancer (CRPC). Recent work has shed light on the importance of epigenetic events including facilitation of AR signaling by histone-modifying enzymes, posttranslational modifications of AR such as sumoylation. Herein, we provide an overview of the structure of human AR and its key structural domains that can be used as targets to develop novel antiandrogens. We also summarize recent findings about the antiandrogens and the epigenetic factors that modulate the action of AR.

Plasma and tissue insulin-like growth factor-I receptor (IGF-IR) as a prognostic marker for prostate cancer and anti-IGF-IR agents as novel therapeutic strategy for refractory cases: a review

Cancer database analysis indicates that prostate cancer is one of the most seen cancers in men meanwhile composing the leading cause of morbidity and mortality among developed countries. Current available therapies are surgery, radiotherapy and androgene ablation for prostate carcinoma. The response rate is as high nearly 90% however, most of these recur or become refractory and androgene independent (AI). Therefore recent studies intensified on molecular factors playing role on development of prostate carcinoma and novel treatment strategies targetting these factors and their receptors. Insulin-like growth factor-I (IGF-I) and its primary receptor insulin-like growth factor receptor-I (IGF-IR) are among these factors. Biologic functions and role in malign progression are primarily achieved via IGF-IR which is a type 2 tyrosine kinase receptor. IGF-IR plays an important role in mitogenesis, angiogenesis, transformation, apoptosis and cell motility. It also generates intensive proliferative signals leading to carcinogenesis in prostate tissue. So IGF-IR and its associated signalling system have provoked considerable interest over recent years as a novel therapeutic target in cancer. In this paper it is aimed to sum up the lately published literature searching the relation of IGF-IR and prostate cancer in terms of incidence, pathologic features, and prognosis. This is followed by a discussion of the different possible targets within the IGF-1R system, and drugs developed to interact at each target. A systems-based approach is then used to review the in vitro and in vivo data in the published literature of the following compounds targeting IGF-1R components using specific examples: growth hormone releasing hormone antagonists (e.g. JV-1-38), growth hormone receptor antagonists (e.g. pegvisomant), IGF-1R antibodies (e.g. CP-751,871, AVE1642/EM164, IMC-A12, SCH-717454, BIIB022, AMG 479, MK-0646/h7C10), and IGF-1R tyrosine kinase inhibitors (e.g. BMS-536942, BMS-554417, NVP-AEW541, NVP-ADW742, AG1024, potent quinolinyl-derived imidazo (1,5-a)pyrazine PQIP, picropodophyllin PPP, nordihydroguaiaretic acid Insm-18/NDGA). And the other end point is to yield an overview on the recent progress about usage of this receptor as a novel anticancer agent of targeted therapies in treatment of prostate carcinoma.

Potential prostate cancer drug target: bioactivation of androstanediol by conversion to dihydrotestosterone

High-affinity binding of dihydrotestosterone (DHT) to the androgen receptor (AR) initiates androgen-dependent gene activation, required for normal male sex development in utero, and contributes to prostate cancer development and progression in men. Under normal physiologic conditions, DHT is synthesized predominantly by 5α-reduction of testosterone, the major circulating androgen produced by the testis. During androgen deprivation therapy, intratumoral androgen production is sufficient for AR activation and prostate cancer growth, even though circulating testicular androgen levels are low. Recent studies indicate that the metabolism of 5α-androstane-3α, 17β-diol by 17β-hydroxysteroid dehydrogenase 6 in benign prostate and prostate cancer cells is a major biosynthetic pathway for intratumoral synthesis of DHT, which binds AR and initiates transactivation to promote prostate cancer growth during androgen deprivation therapy. Drugs that target the so-called backdoor pathway of DHT synthesis provide an opportunity to enhance clinical response to luteinizing-hormone-releasing hormone (LHRH) agonists or antagonists, AR antagonists, and inhibitors of 5α-reductase enzymes (finasteride or dutasteride), and other steroid metabolism enzyme inhibitors (ketoconazole or the recently available abiraterone acetate).

Current paradigms and evolving concepts in metastatic castration-resistant prostate cancer

Until recently, docetaxel-based therapy represented the only therapy shown to prolong survival in patients with metastatic castration-resistant prostate cancer (mCRPC). The past year and a half has been marked by unprecedented progress in treatments for this disease. Three positive phase III clinical trials have emerged, each evaluating agents (sipuleucel-T, cabazitaxel and abiraterone) with distinct mechanisms of action. Herein, the three pivotal trials are described alongside both past and current large phase III studies conducted in this mCRPC. The overall survival for patients with mCRPC treated in current clinical trials is considerably longer than noted in the past. We note that more recent trials with older agents have also shown improved survival and discuss potential non-therapeutic biases that influence this critical measure of outcome. The necessity for utilizing randomized trials when evaluating new therapeutics is emphasized given the changing prognosis in this mCRPC.

Evolving standards in the treatment of docetaxel-refractory castration-resistant prostate cancer

The management of men with metastatic castration-resistant prostate cancer (CRPC) has taken several leaps forward in the past year, with the demonstration of improved overall survival with three novel agents (sipuleucel-T, cabazitaxel with prednisone and abiraterone acetate with prednisone), and a significant delay in skeletal-related events observed with denosumab. The pipeline of systemic therapies in prostate cancer remains strong, as multiple agents with a diverse array of mechanisms of action are showing preliminary signs of clinical benefit, leading to more definitive phase III confirmatory trials. In this review, which represents part 1 of a two-part series on metastatic CRPC, we will summarize the mechanisms of resistance to hormonal and chemotherapies and discuss the evolving landscape of treatment options for men with CRPC, with a particular focus on currently approved and emerging treatment options following docetaxel administration, as well as prognostic factors in this post-docetaxel state. As docetaxel remains the standard initial systemic therapy for men with metastatic CRPC for both palliative and life-prolonging purposes, knowledge of these evolving standards will help to optimize delivery of care and long-term outcomes.

Androgen receptor rediscovered: the new biology and targeting the androgen receptor therapeutically

Discoveries over the past decade suggest that castration-resistant prostate cancer (CRPC) is sensitive, but not resistant to, further manipulation of the androgen-androgen receptor (AR) axis. Several new therapies that target this axis have demonstrated clinical activity. In this article, preclinical and clinical findings occurring in the field of AR-targeted therapies are reviewed. Reviews of scientific and clinical development are divided into those occurring prereceptor (androgen production and conversion) and at the level of the receptor (AR aberrations and therapies targeting AR directly). Intracrine androgen production and AR amplification, among others, are among the principal aberrancies driving CRPC growth. Phase III data with abiraterone acetate and phase II data with MDV-3100, along with other similar therapies, confirm for the clinician that the scientific findings related to persistent AR signaling in a castrate milieu can be harnessed to produce significant clinical benefit for patients with the disease. Studies aimed at optimizing the timing of their use and exploring the mechanisms of resistance to these therapies are under way. The clinical success of therapies that directly target androgen synthesis as well as the most common aberrancies of the AR confirm that prostate cancer retains dependence on AR signaling, even in the castrate state.

The changing therapeutic landscape of castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) has a poor prognosis and remains a significant therapeutic challenge. Before 2010, only docetaxel-based chemotherapy improved survival in patients with CRPC compared with mitoxantrone. Our improved understanding of the underlying biology of CRPC has heralded a new era in molecular anticancer drug development, with a myriad of novel anticancer drugs for CRPC entering the clinic. These include the novel taxane cabazitaxel, the vaccine sipuleucel-T, the CYP17 inhibitor abiraterone, the novel androgen-receptor antagonist MDV-3100 and the radioisotope alpharadin. With these developments, the management of patients with CRPC is changing. In this Review, we discuss these promising therapies along with other novel agents that are demonstrating early signs of activity in CRPC. We propose a treatment pathway for patients with CRPC and consider strategies to optimize the use of these agents, including the incorporation of predictive and intermediate end point biomarkers, such as circulating tumor cells.

A phase II study of sorafenib in combination with bicalutamide in patients with chemotherapy-naive castration resistant prostate cancer

PURPOSE

The objective of this trial was to evaluate the clinical effects of sorafenib, a multi-targeted kinase inhibitor, in combination with androgen receptor blockade in patients with castration-resistant prostate cancer.

METHODS

This was a multicenter, two-stage, phase 2 trial. Eligible patients had rising PSA, minimal symptoms and were chemotherapy-naïve. Sorafenib 400 mg twice daily was administered with bicalutamide 50 mg once daily on a 28-day cycle. The primary endpoint was PSA response (≥ 50% decline) or stable disease ≥ 6 months.

RESULTS

39 patients were enrolled including eight without clinical evidence of metastases. Eighteen (47%) patients have had either a PSA response or stable disease ≥ 6 months. PSA declines of ≥ 50% occurred in 12 (32%) of 38 assessable patients, including seven of 27 patients (26%) with prior anti-androgen use. Median time to treatment failure was 5.5 months (95%CI = 4.8.1-8.3). Grade ≥ 3 adverse events included fatigue, skin rash, and hand-foot syndrome.

CONCLUSIONS

PSA declines and stable disease were observed with a combination of sorafenib and bicalutamide including in patients previously progressing on bicalutamide. Strategies to combine multi-targeted kinase inhibitors with hormonal therapies warrant further study in patients with CRPC.

Contemporary management of metastatic castration-resistant prostate cancer

PURPOSE OF REVIEW

This review will describe the contemporary management of castration-resistant prostate cancer in the context of multiple recent advances.

RECENT FINDINGS

Two novel agents have been added to the therapeutic armamentarium including cabazitaxel and sipuleucel-T. Cabazitaxel, a novel taxane extended survival in men with progressive metastatic CRPC following conventional docetaxel-based chemotherapy. Sipuleucel-T, an autologous dendritic cell based vaccine extended survival in men with relatively asymptomatic metastatic CRPC without visceral metastasis. A third agent, abiraterone acetate, an orally administered CYP17 inhibitor, which suppresses androgen synthesis has been preliminarily reported to significantly prolong survival following prior docetaxel and approval by regulatory agencies is anticipated. Baseline and early changes in circulating tumor cells appear useful as a prognostic factor. Additionally, data demonstrated the superiority of denosumab, a RANK-ligand antagonist, compared to zoledronic acid in the prevention of skeletal related events in men with bone metastases.

SUMMARY

Cabazitaxel, sipuleucel-T and denosumab were approved in 2010 by regulatory agencies in the USA for men with metastatic CRPC, and approval of abiraterone acetate is anticipated based on the results of a phase III trial. The evaluation of circulating tumor cells assists in determining prognosis, although its utility for clinical decision-making entails validation.

Emerging novel therapies in the treatment of castrate-resistant prostate cancer

The treatment options for patients with castration-resistant prostate cancer (CRPC), until very recently, only included docetaxel. In the past 10 months, newly Federal Drug Administration (FDA) approved agents in the United States have shown survival benefit for patients with CRPC. This review takes a closer look at these newer agents: sipuleucel-T (immune therapy) and cabazi-taxel (cytotoxic therapy). We also review the evidence supporting the FDA's approval of denosumab (bone-targeted therapy) as a treatment option for men with CRPC and bony metastases. Newer agents currently being investigated in phase III clinical trials for their potential role in metastatic CRPC are also reviewed. These agents include abiraterone (hormonal therapy), TAK-700 (hormonal therapy), MDV3100 (hormonal therapy), ipilimumab (immune therapy), zibotentan (endothelin-A receptor antagonist) and dasatinib (tyrosine kinase inhibitor). As ongoing studies using all the aforementioned agents continue to evolve, our understanding of how and where these agents fit into the treatment paradigm for patients with CRPC will become clearer.

Sipuleucel-T for therapy of asymptomatic or minimally symptomatic, castrate-refractory prostate cancer: an update and perspective among other treatments

Sipuleucel-T is an autologous cell immunotherapy for castrate-refractory prostate cancer, with US Food and Drug Administration (FDA) approval in asymptomatic or minimally symptomatic prostate cancer. In this review we address the background of prostate cancer incidence and other available therapy onto which sipuleucel-T treatment has been added, with discussion of hormone-therapy, chemotherapy, and other investigational immunotherapies. The sipuleucel-T manufacturing process, toxicity and clinical benefit are reviewed, along with an examination of the issue of clinical benefit to survival, independent of apparent changes of prostate-specific antigen (PSA) levels. Sipuleucel-T therapy is appraised from clinician, patient and immunotherapeutic perspectives, with reference to the clinical data from the pivotal trial, the mechanism of action, and the treatment process.

Current management of castrate-resistant prostate cancer

Prostate cancer (PCa) is the most frequently diagnosed cancer in North America. Castrate-resistant PCa presents a spectrum of disease ranging from rising PSA levels in the absence of metastases or symptoms and despite androgen-deprivation therapy, to metastases and significant debilitation from cancer symptoms. Castrate-resistant PCa is usually suspected in patients with new symptoms on androgen deprivation therapy, with a rising PSA, or with new evidence of disease on bone scans or computed tomography scans. Institution of treatment and the choice of systemic or local therapy depend on a number of factors. This review discusses the various currently available treatments for patients with castrate-resistant PCa, from secondary hormonal manipulations to options for post-docetaxel systemic therapy.

Targeting continued androgen receptor signaling in prostate cancer

Prostate cancer is the most common cancer and the second leading cause of death from cancer in males in most Western countries. Prostate cancer has an exquisite sensitivity to androgen deprivation therapy and is the most endocrine-sensitive solid neoplasm, although advanced disease eventually progresses to castration-resistant prostate cancer (CRPC). Recent evidence has shown that cancer progression at the CRPC stage is often mediated by androgen receptor signaling, so that subsequent androgen receptor targeting may further contribute to disease control and, eventually, survival improvement. Abiraterone acetate, an androgen biosynthesis inhibitor, was tested in patients with CRPC pretreated with docetaxel in a phase III trial with demonstration of an overall survival benefit, confirming that CRPC remains hormone driven, even in advanced stages of the disease. Several novel agents also targeting androgen receptor signaling are currently being evaluated, including MDV3100 and orteronel (TAK-700). With the availability of newer endocrine treatments and also nonendocrine treatments (e.g., chemotherapy, immunotherapy, and bone-targeting agents), data supporting a more rational use of therapeutic agents are urgently required in patients with CRPC. It is likely that molecular characterization of prostate cancer will lead to the identification of different subsets of prostate cancer disease with a different natural history, sensitivity, and resistance to treatment; efforts to develop, validate, and implement predictive biomarkers in clinical trials and eventually in routine care should now be strongly supported.

Management of metastatic castration-resistant prostate cancer after first-line docetaxel

Although chemotherapy, based on docetaxel, is now established in the management of metastatic castration-resistant prostate cancer (mCRPC), until recently, there has been no treatment licensed for use in the second line in men whose disease progresses during or after docetaxel therapy. This article reviews the classes of agents that have shown potential in this setting, notably chemotherapy drugs, hormonal therapies, immunotherapies, anti-angiogenic drugs, and clusterin-targeted therapy.

Phase II study of abiraterone acetate in chemotherapy-naive metastatic castration-resistant prostate cancer displaying bone flare discordant with serologic response

PURPOSE

Abiraterone is an oral inhibitor of CYP17, which is essential for androgen biosynthesis. This multicenter study assessed its efficacy in patients with castration-resistant prostate cancer (CRPC), without prior chemotherapy or CYP17-targeted therapy, and frequency of bone scans discordant with prostate-specific antigen (PSA) and clinical response.

EXPERIMENTAL DESIGN

Thirty-three patients received abiraterone acetate 1,000 mg daily with prednisone 5 mg twice daily in continuous 28-day cycles. Patients were evaluated monthly for efficacy and safety. Bone scan flare was defined as the combination, after 3 months of therapy, of an interpreting radiologist's report indicating "disease progression" in context of a 50% or more decline in PSA level, with scan improvement or stability 3 months later.

RESULTS

A 50% or more decline in PSA level at week 12 was confirmed in 22 of 33 (67%) patients. Declines in PSA level of 50% or more were seen in 26 of 33 (79%) patients. Undetectable PSA levels (≤0.1 ng/mL) occurred in 2 patients. Median time on therapy and time to PSA progression were 63 weeks and 16.3 months, respectively. Twenty-three patients were evaluable for bone scan flare. Progression was indicated in radiologist's report in 12 of 23 (52%), and 11 of 12 subsequently showed improvement or stability. As prospectively defined, bone scan flare was observed in 11 of 23 (48%) evaluable patients or 11 of 33 (33%) enrolled patients. Adverse events were typically grade 1/2 and consistent with prior published abiraterone reports.

CONCLUSION

Clinical responses to abiraterone plus prednisone were frequent and durable in men with metastatic CRPC. Further investigation is needed to clarify the confounding effect of bone scan flare on patient management and interpretation of results. Clin Cancer Res; 17(14); 4854-61. ©2011 AACR.

Targeting 5α-reductase for prostate cancer prevention and treatment

Testosterone is the most abundant circulating androgen, and can be converted to dihydrotestosterone (DHT), a more potent androgen, by the 5α-reductase enzymes in target tissues. Current treatments for prostate cancer consist of reducing androgen levels by chemical or surgical castration or pure antiandrogen therapy that directly targets the androgen receptor (AR). Although these therapies reduce tumor burden and AR activity, the cancer inevitably recurs within 18-30 months. An approach targeting the androgen-AR axis at different levels could, therefore, improve the efficacy of prostate cancer therapy. Inhibition of 5α-reductase is one such approach; however, the two largest trials to investigate the use of the 5α-reductase inhibitors (5ARIs) finasteride and dutasteride in patients with prostate cancer have shown that, although the incidence of cancer was reduced by 5ARI treatment, those cancers that were detected were more aggressive than in patients treated with placebo. Thus, the best practice for using these drugs to prevent and treat prostate cancer remains unclear.

CYP17 inhibitors for prostate cancer therapy

Prostate cancer (PC) is now the second most prevalent cause of death in men in the USA and Europe. At present, the major treatment options include surgical or medical castration. These strategies cause ablation of the production of testosterone (T), dihydrotestosterone (DHT) and related androgens by the testes. However, because these procedures do not affect adrenal, prostate and other tissues' androgen production, they are often combined with androgen receptor antagonists to block their action. Indeed, recent studies have unequivocally established that in castration-resistant prostate cancer (CRPC) many androgen-regulated genes become re-expressed and tissue androgen levels increase despite low serum levels. Clearly, inhibition of the key enzyme which catalyzes the biosynthesis of androgens from pregnane precursors, 17α-hydroxy/17,20-lyase (hereafter referred to as CYP17) could prevent androgen production from all sources. Thus, total ablation of androgen production by potent CYP17 inhibitors may provide effective treatment of prostate cancer patients. This review highlights the role of androgen biosynthesis in the progression of prostate cancer and the impact of CYP17 inhibitors, such as ketoconazole, abiraterone acetate, VN/124-1 (TOK-001) and TAK-700 in the clinic and in clinical development. Article from the special issue on Targeted Inhibitors.

The role of abiraterone acetate in the management of prostate cancer: a critical analysis of the literature

CONTEXT

The development of agents targeting androgen signalling holds promise for men with castration-resistant prostate cancer (CRPC).

OBJECTIVE

The emerging role of abiraterone acetate (AA), a novel, orally administered androgen synthesis inhibitor, is critically analysed.

EVIDENCE ACQUISITION

Data were acquired from critically important original research published in peer-reviewed literature or presented at conferences conducted by the American Society of Clinical Oncology and the European Society of Medical Oncology.

EVIDENCE SYNTHESIS

The major findings are addressed in an evidence-based, objective, and balanced fashion.

CONCLUSIONS

AA specifically inhibits CYP17 and substantially reduces serum androgen levels without inducing significant adrenal insufficiency. A phase 3 trial reported a significant extension of survival in metastatic CRPC with AA plus prednisone compared to prednisone alone following docetaxel. The primary toxicity of mineralocorticoid excess is manageable. The addition of low-dose corticosteroids to AA may be necessary for controlling symptoms of mineralocorticoid excess.

New strategies in metastatic prostate cancer: targeting the androgen receptor signaling pathway

Recent data report that abiraterone acetate, a specific inhibitor of CYP17 that is key to androgen and estrogen synthesis, improves survival in metastatic castration-resistant prostate cancer (CRPC), confirming the continued dependency of CRPC on the androgen receptor (AR) signaling pathway. MDV3100 is a novel antagonist of AR that is also in phase III clinical trials. In addition, several other agents targeting the AR axis are undergoing evaluation in early clinical studies. CRPC patients progress on these therapies with an increasing prostate specific antigen (PSA), suggesting that repeated therapeutic interventions targeting the AR signaling axis could induce secondary responses and achieve prolonged clinical benefit for a subgroup of patients. These exciting results are good news for patients but introduce a number of treatment paradigm dilemmas for physicians. Clinical studies evaluating the ideal sequence of administration of these new agents, best timing for initiation, combination strategies, discontinuation beyond progression and after commencement of subsequent therapies, and coordination with other treatments have not been done. Predictive biomarkers could allow patient selection for a specific treatment, but in their absence, most physicians will rely on a trial of treatment with a preferred agent and substitute for an alternative therapy on objective progression. Current data suggest that the response rate to drugs targeting the AR ligand-binding domain decreases with each treatment, but we hypothesize that a significant proportion of CRPC remains dependent on the AR axis and, therefore, novel strategies for disrupting AR signaling merit evaluation.

Current treatment strategies for castration-resistant prostate cancer

Prostate cancer is the most common cancer in men in United States and the fifth most common cancer in men in Korea. Although the majority of patients with metastatic prostate cancer initially respond to androgen deprivation therapy, almost all patients will eventually progress to develop castration-resistant prostate cancer (CRPC). Treatment options for CRPC remain limited. Prostate cancer was considered unresponsive to chemotherapy until the mid-1990s, when mitoxantrone combined with prednisone was shown to play a role in the palliative treatment of patients with CRPC. In 2004, two large randomized clinical trials demonstrated for the first time a small but significant survival advantage of docetaxel-based chemotherapy compared with mitoxantrone in patients with metastatic CRPC. Recently, cabazitaxel was shown to improve survival in patients with metastatic CRPC who progressed after docetaxel-based chemotherapy. Sipuleucel-T was also demonstrated to improve overall survival in patients with asymptomatic or minimally symptomatic metastatic CRPC. Along with mitoxantrone and docetaxel, cabazitaxel and sipuleucel-T are now approved for use in metastatic CRPC by the US Food and Drug Administration. There have been multiple early-phase clinical trials of various agents for the treatment of CRPC, and some are in phase III development. This review focuses on the key clinical trials of various treatment options of CRPC currently in use and under investigation.

Saudi Oncology Society clinical management guidelines for prostate cancer

In this report, guidelines for the evaluation, medical and surgical management of testicular germ cell tumors is presented. It is categorized according to the stage of the disease using the tumor node metastasis staging system, 7th edition. The recommendations are presented with supporting level of evidence.

Castration-resistant prostate cancer: targeted therapies and individualized treatment

Various molecular mechanisms have been implicated in the progression from hormone-sensitive to castration-resistant prostate cancer (CRPC). Novel targeted agents to treat CRPC have been developed that inhibit either androgen receptor (AR)-mediated signaling (AR antagonists and inhibitors of androgen synthesis) or non-AR-mediated signaling (inhibitors of Src, mammalian target of rapamycin, chaperone proteins, insulin-like growth factor-1 receptor, vascular endothelial growth factor, and endothelin-A receptor) pathways. However, variable efficacy has been observed in clinical trials, most likely because of the biologic heterogeneity of CRPC. To account for potential differences in disease biology, a more individualized approach to treatment, based on genomic and/or proteomic analyses of individual tumors, is being investigated. By identifying tumors with a characteristic molecular subtype and assigning treatment accordingly, it is hoped that a higher proportion of patients will benefit from targeted therapy. Additionally, lessons learned through the application of these technologies to prostate cancer may subsequently influence therapeutic development in other solid tumors.

Second-line chemotherapy in metastatic docetaxel-resistant prostate cancer: a review

The results of cytotoxic therapy in the second-line setting of metastatic castration-resistant prostate cancer have demonstrated that disease is poorly controlled after taxane resistance with a time to progression of 3 months or less. Many trials of second-line chemotherapy have been disappointing. However, most of patients with docetaxel-pretreated castration-resistant disease receive a second-line chemotherapy. Molecular mechanism of castration resistance and docetaxel resistance is resumed, and clinical trials of second-line chemotherapy after docetaxel progression are reviewed. Reintroduction of docetaxel after a drug-free interval is an active treatment in docetaxel-pretreated patients, and only recently a prospective study documented a survival benefit of 2.4 months after second-line taxane-based chemotherapy of metastatic docetaxel-resistant prostate cancer. Although a second-line chemotherapy with a taxane could improve overall survival, a change of biology of castration-resistant prostate cancer after docetaxel is suggested, as inferred by the renewed hormonal sensitivity, whose role on survival remains unknown, and from the activity of antiangiogenic drugs.

Effect of castration monotherapy on the levels of adrenal androgens in cancerous prostatic tissues

The mechanism accounting for the development of castration-resistant prostate cancer (CRPC) remains unclear. Studies in CRPC tissues suggest that, after androgen deprivation therapy (ADT), the adrenal androgens may be an important source of testosterone (T) and 5-alpha dihydrotestosterone (DHT) in CRPC tissues. To clarify the role of adrenal androgens in the prostatic tissues (prostatic tissue adrenal androgens) during ADT, we developed a high sensitive and specific quantification method for the levels of androgens in prostatic tissue using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Human prostatic tissues were purified using mixed-mode reversed-phase, strong anion exchange Oasis cartridges (Oasis MAX). Analysis of steroids was performed using LC-MS/MS after picolinic acid derivatization. The validation tests showed that our method of quantitative analysis was precise and sensitive enough for the quantification of dehydroepiandrosterone (DHEA), androstenedione, androstenediol, T, and DHT in the prostatic tissue. The levels of adrenal androgens in prostate cancer tissues after ADT were similar to those in untreated PCa. Especially, DHEA was the most existing androgen precursor in PCa tissues after ADT. The levels of DHEA were high in PCa tissues, irrespective of ADT. We assumed that DHEA played a significant role in the synthesis of T and DHT in PCa tissues after ADT.

Novel therapeutic strategies for castration resistant prostate cancer: inhibition of persistent androgen production and androgen receptor mediated signaling

PURPOSE

Androgen receptor signaling remains essential for many prostate cancers that have progressed despite androgen deprivation therapy. After medical or surgical castration persistent though not insignificant low levels of androgens are produced from nongonadal sources, such as the adrenal glands. Some castration resistant prostate cancers acquire the ability to convert adrenal steroids to androgens, maintaining levels sufficient to activate androgen receptor. Inhibition of persistent androgen production and androgen receptor mediated signaling are relevant therapeutic strategies for castration resistant prostate cancer.

MATERIALS AND METHODS

The scientific foundation of and clinical experience with secondary hormonal therapy as well as the development of new investigational agents for castration resistant prostate cancer, specifically selective cytochrome p450 17 inhibitors and second generation antiandrogens, are discussed.

RESULTS

Selective inhibition of cytochrome p450 17 has emerged as an important therapeutic pathway for castration resistant prostate cancer. The selective cytochrome p450 17 inhibitor abiraterone acetate showed promising activity and tolerability in phase I-II trials. Phase III studies are underway in men with chemotherapy naïve castration resistant prostate cancer as well as those with progression after docetaxel based chemotherapy. TAK-700 and TOK-001 (formerly VN124-1) are novel selective cytochrome p450 17 inhibitors that recently entered phase I/II evaluation. MDV3100 is a second generation antiandrogen that blocks androgen receptor signaling by inhibiting nuclear translocation of the ligand-receptor complex. Clinical data on MDV3100 are encouraging and support continued phase III study.

CONCLUSIONS

Novel therapies for castration resistant prostate cancer that target persistent androgen production and androgen receptor mediated signaling have demonstrated promising activity in many men with castration resistant prostate cancer and may redefine the clinical management of these patients.

Comparison of Ketoconazole and Estramustine for Treating Patients with Castration-Resistant Prostate Cancer

Purpose

We investigated the efficacy of ketoconazole and estramustine before chemotherapy for treating patients with progressive castration-resistant prostate cancer (CRPC) after anti-androgen withdrawal syndrome.

Materials and Methods

Eighty-four patients who were diagnosed with CRPC and were treated between 2005 and 2009 were included. Thirty-nine patients were treated with 600 mg of ketoconazole and 10 mg of prednisolone per day (group I), and 45 patients were treated with 560 mg of estramustine per day (group II). The prostate-specific antigen (PSA) response, progression-free survival, and side effects were compared.

Results

The median age of the patients, PSA level, and follow-up period were 72 years, 48.5 ng/ml, and 4 months (range, 1 to 29 months), respectively. The overall PSA response rate was 35.7%, and the PSA response rates were 33.3% for group I and 37.8% for group II (p=0.672). The median progression-free survival times were 8 months (95% confidence interval [CI] 5.9-10.1) overall, 5 months (95% CI 1.6-8.3) in group I, and 8 months (95% CI 5.9-10.0) in group II (p=0.282). The most common complications in groups I and II were nausea and vomiting (51.3%) and anemia (77.8%), respectively. Nausea and vomiting and hepatotoxicity were observed more often in group I, and gynecomastia, neutropenia, and anemia were observed more often in group II. The toxicities of each adverse effect were ≤grade 2.

Conclusions

With a resultant PSA decline and mild adverse effects, both ketoconazole and estramustine are worth consideration as treatment options for progressive CRPC patients after primary hormonal therapy.

Abiraterone acetate for castration resistant prostate cancer

IMPORTANCE OF THE FIELD

Androgen deprivation therapy has been the standard of care in advanced prostate cancer for > 50 years. Although castration is initially effective, most patients eventually develop progressive disease despite low levels of testosterone (termed castration resistant prostate cancer, CRPC). Intratumor and extra-gonadal androgens (specifically adrenal androgens) represent a means for continued androgen receptor-mediated growth in CRPC and have thus become therapeutic targets. One novel therapeutic is abiraterone acetate (AA): an inhibitor of CYP17, an enzyme that catalyzes two key serial reactions in androgen and estrogen biosynthesis. Data from Phase I and II trials suggest that clinically important antitumor activity is seen in up to 70% of castrate patients with advanced prostate cancer resistant to currently available endocrine therapies. The toxicity profile has also been found to be acceptable. Two large Phase III clinical trials are currently open to accrual and will hopefully validate the impressive Phase II data.

AREAS COVERED IN THE REVIEW

The chemistry, pharmacodynamics, pharmacokinetics, clinical efficacy and safety/tolerability of AA.

WHAT THE READER WILL GAIN

Readers will understand the function of non-gonadal androgens, the importance of continued androgen deprivation in advanced prostate cancer and the role/clinical efficacy of AA.

TAKE HOME MESSAGE

The recent realization that non-gonadal sources of androgens (adrenal and intracrine de novo synthesis) may be a major mediator of disease progression forms the biological rationale behind the development of abiraterone acetate and related drugs. Abiraterone acetate is an orally administered, specific inhibitor of CYP17A1, a rate-limiting enzyme in androgen biosynthesis. Preliminary data from Phase I and II trials suggest that prostate specific antigen declines occur in a large proportion of patients and that the toxicity profile is acceptable. Two large Phase III clinical trials are currently open to accrual and, if proven to be efficacious, will result in widespread use of a drug specifically developed to suppress adrenal androgens.

Retrospective analysis of the consequences of acid suppressive therapy on ketoconazole efficacy in advanced castration-resistant prostate cancer

BACKGROUND

The area under the curve of a single ketoconazole dose has been shown to decrease significantly when administered with acid suppressive therapy. No published studies have examined the clinical impact of concurrent ketoconazole and acid suppressive therapy in patients with castration-resistant prostate cancer (CRPC).

OBJECTIVE

To evaluate the effect of acid suppressive therapy on prostate-specific antigen (PSA) response rate in CRPC patients receiving ketoconazole.

METHODS

This retrospective study evaluated CRPC patients treated with ketoconazole 3 times daily between January 1, 1999, and September 30, 2009. Patients included in the analysis had failed androgen deprivation therapy, and were subsequently initiated on ketoconazole. Response (PSA decline ≥50% maintained ≥4 weeks) was evaluated in patients receiving ketoconazole with (group 1 [G1]) or without (group 2 [G2]) concurrent acid suppressive therapy.

RESULTS

Thirty patients (G1: 11 patients; G2: 19 patients) were included in the analysis. Mean age in G1 and G2 was 71.8 and 69.6 years, respectively. Most patients had received prior therapy with an antiandrogen (90.9% G1; 100% G2) and fewer patients received antiandrogen withdrawal therapy (27.3% G1; 21.1% G2). Median baseline PSA was 109.4 (G1) and 86.9 ng/mL (G2) (p = 0.55). Median duration of ketoconazole was 7.2 months in G1 and 5.8 months in G2 (p = 0.09). Ketoconazole adherence was 82% (G1) and 100% (G2). Median duration of concurrent acid suppressive therapy was 3.8 months (range 2.0-20.4) in G1. PSA response (72.7% and 47.4%; p = 0.26) and time to PSA response (1.2 vs 0.9 mo; p = 0.53) were statistically similar between G1 and G2, respectively. Median progression free survival was higher in G1 (11.5 vs 6.9 months in G2; p = 0.047).

CONCLUSIONS

Use of concurrent acid suppressive therapy and ketoconazole in CRPC patients did not decrease PSA response rate, and progression free survival was unexpectedly higher compared with the non-acid suppressive therapy group. Larger studies are needed to verify the clinical impact of acid suppressive therapy in combination with ketoconazole.

Influence of sex hormones on cancer progression

To review the influence of sex hormones on the progression of breast, prostate, gynecologic, and colorectal cancer. The literature was reviewed in an informal manner utilizing the authors' prior knowledge to collate the current evidence for the involvement of sex hormones, particularly estrogens and androgens in the progression of a range of hormonally responsive cancers. In particular, the effect of treatment involving hormone withdrawal treatment was considered strong evidence for involvement. The impact of basal levels of endogenous steroids was considered. Data from clinical trials indicate the efficacy of therapeutic interventions that result in ablation or antagonism of host steroids for a range of cancers. Demonstration of the correlation of the completeness of withdrawal with clinical outcome together with direct evidence of progression from studies looking at the influence of tissue and circulating levels of sex hormones more recently in conjunction with gene expression profiles all provide compelling evidence for the involvement of steroids in the progression of disease. The involvement of steroids in the progression of cancer in hormone-sensitive tissues is well established and an important target for therapy.

Abiraterone acetate: a promising drug for the treatment of castration-resistant prostate cancer

Abiraterone acetate (CB7630), a pregnenolone analog, is an orally administered small molecule that irreversibly inhibits a rate-limiting enzyme in androgen biosynthesis, CYP17, and blocks the synthesis of androgens in the testes, adrenal glands and prostate without causing adrenal insufficiency. In clinical studies, abiraterone acetate is well tolerated and shows promising clinical activity in castration-resistant prostate cancer. The recommended Phase II dose of abiraterone acetate is 1000 mg orally daily in combination with prednisone 5 mg twice daily. Side effects are minimal and mostly associated with secondary mineralocorticoid excess, owing to a compensatory increase in upstream steroids, such as deoxycorticosterone and corticosterone. These include hypertension, hypokalemia and edema and are easily manageable with a selective mineralocorticoid antagonist, such as eplerenone, or low-dose corticosteroids. Currently, abiraterone acetate is being tested in a Phase III trial for men with progressive castration-resistant prostate cancer who are chemotherapy naive. A Phase III trial for patients following prior chemotherapy has been completed and is awaiting analysis.

Castration-resistant prostate cancer: current and emerging treatment strategies

Until very recently, docetaxel was the only approved agent in castration-resistant prostate cancer (CRPC) and other effective therapeutic options are urgently needed. In recent years, several new agents with promising activity and a favourable toxicity profile have been developed and clinically investigated in the fields of hormonal, cytotoxic, targeted and immune therapy. In particular, recent results from two large phase III trials of sipuleucel-T and cabazitaxel show that these two agents significantly prolong overall survival in CRPC. Indeed, sipuleucel-T has recently been approved by the US FDA for the treatment of CRPC. Many other pharmaceuticals, which are presented in this review, have been investigated recently or are being investigated in phase III trials and might prove to be effective in the future. Reviewed articles are discussed in light of the innovations in study design brought by the Prostate Cancer Clinical Trials Working Group (PCWG2), which updated the Prostate-Specific Antigen Working Group (PCWG1) guidelines, in order to allow better identification of potentially active drugs in clinical trials.

Overcoming persistent dependency on androgen signaling after progression to castration-resistant prostate cancer

Prostate cancer is the most common form of cancer in males in the United States, and the second leading cause of cancer death. Initially, most cases of prostate cancer respond well to hormone therapy; however, resistance often develops rapidly, leading to castration-resistant prostate cancer (CRPC). Several mechanisms for castration resistance have been proposed, of which the most significant seems to be the "intracrine" production of androgens from adrenal androgen or intratumorally via the de novo route. This mechanism stimulates disease progression through reactivation of androgen receptor signaling in patients who have previously undergone castration therapy. 17,20-lyase is essential for androgen synthesis in both the adrenal glands and CRPC tissue, and some 17,20-lyase inhibitors and second-generation anti-androgens that were developed to treat CRPC are currently under clinical investigation, with encouraging preliminary data reported so far. However, resistance to some of these therapies has already been noted. The study of circulating tumor cells will likely be important not only to identify patients likely to receive benefit from this therapeutic approach, but also to further understand the molecular mechanisms of resistance.

The antiparasitic agent ivermectin induces chloride-dependent membrane hyperpolarization and cell death in leukemia cells

To identify known drugs with previously unrecognized anticancer activity, we compiled and screened a library of such compounds to identify agents cytotoxic to leukemia cells. From these screens, we identified ivermectin, a derivative of avermectin B1 that is licensed for the treatment of the parasitic infections, strongyloidiasis and onchocerciasis, but is also effective against other worm infestations. As a potential antileukemic agent, ivermectin induced cell death at low micromolar concentrations in acute myeloid leukemia cell lines and primary patient samples preferentially over normal hematopoietic cells. Ivermectin also delayed tumor growth in 3 independent mouse models of leukemia at concentrations that appear pharmacologically achievable. As an antiparasitic, ivermectin binds and activates chloride ion channels in nematodes, so we tested the effects of ivermectin on chloride flux in leukemia cells. Ivermectin increased intracellular chloride ion concentrations and cell size in leukemia cells. Chloride influx was accompanied by plasma membrane hyperpolarization, but did not change mitochondrial membrane potential. Ivermectin also increased reactive oxygen species generation that was functionally important for ivermectin-induced cell death. Finally, ivermectin synergized with cytarabine and daunorubicin that also increase reactive oxygen species production. Thus, given its known toxicology and pharmacology, ivermectin could be rapidly advanced into clinical trial for leukemia.

Novel Androgen Deprivation Therapy (ADT) in the Treatment of Advanced Prostate Cancer

Androgen deprivation therapy has been the mainstay of treatment for advanced and metastatic prostate cancer. The use of novel agents targeting the androgen receptor and its signaling pathways offers a promising approach that is both safe and effective. We describe the rationale behind the use of these compounds in clinical development and the existing challenges as to how best to incorporate these new and emerging therapies in the changing treatment paradigm of metastatic prostate cancer.

A water-soluble parthenolide analogue suppresses in vivo prostate cancer growth by targeting NFkappaB and generating reactive oxygen species

BACKGROUND

To characterize the molecular changes associated with DMAPT-induced prostate cancer cell death and its in vivo activity.

METHODS

CWR22Rv1 and PC-3 were subjected to flow cytometry, electrophoretic mobility shift assays, and Western blot studies to measure DMAPT's ability to generate reactive oxygen species (ROS), inhibit NFkappaB DNA binding, and cause changes in anti-apoptotic proteins. N-acetyl cysteine (NAC) and short hairpin RNA (shRNA) were used to determine the contribution of ROS and JNK2 activation, respectively. The BrdU incorporation assay was used to measure proliferation and trypan blue studies assessed cell viability after DMAPT treatment. The in vivo activity of DMAPT as a single agent and in combination with bicalutamide or docetaxel was assessed in a subcutaneous xenograft model with athymic nude female mice.

RESULTS

DMAPT generated ROS with subsequent JNK activation and inhibited NFkappaB DNA binding and expression of NFkappaB-regulated anti-apoptotic proteins. DMAPT increased necrotic and apoptotic cell death in a cell-type-dependent manner and both types of cell death were blocked by NAC. Additionally, shRNA JNK2 partially blocked the anti-proliferative activity of DMAPT. DMAPT inhibited CWR22Rv1 and PC-3 cellular proliferation by 100% with 10 and 20 microM respectively and in vivo, DMAPT was more effective at inhibiting growth than biclutamide (CWR22v1) and docetaxel (PC-3).

CONCLUSIONS

DMAPT promotes cell death by both generating ROS and inhibition of NFkappaB. Its in vivo activity supports the conduct of clinical trials in patients with castrate-resistant disease.