Challenges in the sequencing of therapies for the management of metastatic castration-resistant prostate cancer

Prior to 2010, docetaxel was the standard option for chemotherapy in men with metastatic castration-resistant prostate cancer (mCRPC). Today, the picture is vastly different: several additional therapies have each demonstrated a survival benefit such that we now have chemotherapy (cabazitaxel), androgen suppressive agents (abiraterone acetate and enzalutamide), a cellular vaccine (sipuleucel-T) and radium-233 (for symptomatic bone metastases). With several other agents in the pipeline for late-stage disease, the future looks promising for mCRPC. As the available data are not able to inform as to the optimum sequencing of therapy, this remains a challenge. This paper draws on insights from published and ongoing clinical studies to provide a practical patient-focused approach to maximize the benefits of the current therapeutic armamentarium. Preliminary sequencing suggestions are made based on clinical trial criteria. But until more data become available, clinical gestalt, experience, cost and individual patient preferences will continue to drive choices.

Sequential use of novel therapeutics in advanced prostate cancer following docetaxel chemotherapy

In the last three years, five novel treatments have been shown to improve survival in metastatic castration-resistant prostate cancer (CRPC). These novel treatments have distinct mechanisms of action: tubulin-binding chemotherapy (cabazitaxel); immunotherapy (sipuleucel-T); CYP-17 inhibition (abiraterone); androgen receptor (AR) blockade (enzalutamide); and radioisotope therapy (radium-223). For a number of years, docetaxel was the only treatment with a proven survival benefit for patients with CRPC. Therefore, somewhat artificially, three treatment spaces for drug development in CRPC have emerged: pre-docetaxel; docetaxel combinations; and post-docetaxel. For patients progressing after docetaxel-based chemotherapy, treatment options available outside of clinical trials now include abiraterone, cabazitaxel and enzalutamide. Prospective data on how to best use these novel agents sequentially are not available. Clinicians face the difficult task of choosing between treatment options for individual patients to maximize patient benefit. Treatment evaluation in patients with CRPC remains challenging due to the predominance of bone metastatic disease and the lack of validated surrogate markers for survival. This review summarizes the data available with regards to sequencing of the novel treatments for CRPC.

Beyond abiraterone: new hormonal therapies for metastatic castration-resistant prostate cancer

Prostate cancer is a heterogeneous disease where the previous concept of "hormone resistance" has been changed by a new generation of hormonal therapies that have proven efficacy in the castration-resistant setting. The fact is that androgens play a crucial role in the whole clinical course of prostate cancer, even when a patient meets castration-resistance criteria. The development of abiraterone showed how important and clinically meaningful can be to achieve the lowest possible levels of testosterone, and androgen receptor overexpression, mutation, or enhanced crosstalk with other pathways, which can also be targeted with new agents tested in the last few years. New androgen biosynthesis inhibitors have been developed, such as orteronel (TAK-700), but also new antiandrogens (enzalutamide, ARN-509, ODM-201) or even agents with a dual mechanism of action (galeterone). In this review the development of new hormonal therapies following the arrival of abiraterone for the treatment of prostate cancer will be summarized.

Novel therapies for the treatment of advanced prostate cancer

In recent years, great success has been achieved on many fronts in the treatment of men with metastatic castration-resistant prostate cancer (CRPC), including novel chemotherapeutics, immunotherapies, bone microenvironment-targeted agents, and hormonal therapies. Numerous agents are currently in early-phase clinical trial development for the treatment of advanced prostate cancer. These novel therapies target several areas of prostate tumor biology, including the upregulation of androgen signaling and biosynthesis, critical oncogenic intracellular pathways, epigenetic alterations, and cancer immunology. Importantly, the characterization of the prostate cancer genome offers the potential to exploit conserved genetic alterations, which may increase the efficacy of these targeted therapies. Predictive and prognostic biomarkers are urgently needed to maximize therapeutic efficacy and safety of these promising new treatments options in prostate cancer.

Emerging therapeutics targeting castration-resistant prostate cancer: the AR-mageddon of tumor epithelial-mesenchymal transition

Advanced prostate cancer will claim nearly 30,000 lives among men in the USA in the year 2013. Most of these will be castration-resistant prostate cancers that are not responsive to traditional therapeutic modalities, and there is no available regimen that fully eradicates metastatic disease. This poses a significant clinical challenge for practitioners and has stimulated the development of novel agents that target these castration-resistant tumor cells. Development of metastatic prostate cancer is orchestrated by multiple signaling pathways that regulate cell survival, apoptosis, anoikis, epithelial-mesenchymal transition (EMT), invasion, the androgen signaling axis and angiogenesis. Disruption of the mechanisms underlying these processes is critical for development of agents that can target otherwise resistant tumor cells. Insights into the mechanisms by which rounds of EMT/mesenchymal-epithelial transition conversions facilitate the progression of localized prostate carcinomas to advanced metastatic and castration-resistant disease emerge as attractive targets for drug development. In this review, the authors discuss the current understanding of therapeutic resistance in castration-resistant prostate cancer with focus on the androgen receptor signaling axis and EMT. Novel therapeutic approaches targeting critical players of both pathways as well as the results from ongoing clinical trials will be discussed in this review.

Phase III, randomized, placebo-controlled study of docetaxel in combination with zibotentan in patients with metastatic castration-resistant prostate cancer

PURPOSE As part of the ENTHUSE (Endothelin A Use) program, the efficacy and safety of zibotentan (ZD4054), an oral specific endothelin A receptor antagonist, has been investigated in combination with docetaxel in patients with metastatic castration-resistant prostate cancer (CRPC). PATIENTS AND METHODS In this randomized, double-blind, placebo-controlled, phase III study, patients received intravenous docetaxel 75 mg/m(2) on day 1 of 21-day cycles plus oral zibotentan 10 mg or placebo once daily. The primary end point was overall survival (OS). Secondary end points included time to pain and prostate-specific antigen (PSA) progression, pain and PSA response, progression-free survival, health-related quality of life, and safety. Results A total of 1,052 patients received study treatment (docetaxel-zibotentan, n = 524; docetaxel-placebo, n = 528). At the time of data cutoff, there had been 277 and 280 deaths, respectively. There was no difference in OS for patients receiving docetaxel-zibotentan compared with those receiving docetaxel-placebo (hazard ratio, 1.00; 95% CI, 0.84 to 1.18; P = .963). No significant differences were observed on secondary end points, including time to pain progression (median 9.3 v 10.0 months, respectively) or pain response (odds ratio, 0.84; 95% CI, 0.61 to 1.16; P = .283). The median time to death was 20.0 and 19.2 months for the zibotentan and placebo groups, respectively. The most commonly reported adverse events in zibotentan-treated patients were peripheral edema (52.7%), diarrhea (35.4%), alopecia (33.9%), and nausea (33.3%). CONCLUSION Docetaxel plus zibotentan 10 mg/d did not result in a significant improvement in OS compared with docetaxel plus placebo in patients with metastatic CRPC.

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.