Overall survival analysis of a phase II randomized controlled trial of a Poxviral-based PSA-targeted immunotherapy in metastatic castration-resistant prostate cancer

Prostate cancer immunotherapy

The interaction between the immune system and prostate cancer has been an area of research interest for several decades. The recent U.S. Food and Drug Administration approval of 2 first-in-class proof-of-concept immunotherapies (sipuleucel-T and ipilimumab) has stimulated broader interest in manipulating immunity to fight cancer. In the context of prostate cancer, the immunotherapy strategies that have garnered the most interest are the therapeutic vaccination strategies, exemplified by sipuleucel-T and PROSTVAC-VF, and immune checkpoint blockade of CTLA-4 and PD-1. Improved understanding of the immune responses generated by these strategies and development of predictive biomarkers for patient selection will guide rational combinations of these treatments and provide building blocks for future immunotherapies.

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.

Cancer immunology--analysis of host and tumor factors for personalized medicine

Immune cells in the tumor microenvironment have an important role in regulating tumor progression. Therefore, stimulating immune reactions to tumors can be an attractive therapeutic and prevention strategy. Cancer cells and host cells constantly interact with each other in the tumor microenvironment; thus, cancer immunology is an interdisciplinary area where integrated analysis of both host and tumor factors is needed. Cancer represents a heterogeneous group of diseases with different genetic and epigenetic alterations; therefore, molecular classification of cancer (for example lung, prostate and breast cancers) is an important component in clinical decision making. However, most studies on antitumor immunity and clinical outcome lack analysis of tumor molecular biomarkers. In this Review, we discuss colorectal cancer as a prototypical example of cancer. Common molecular classifiers of colon cancer include KRAS, BRAF and PIK3CA mutations, microsatellite instability, LINE-1 methylation, and CpG island methylator phenotype. Since tumor molecular features and immune reactions are inter-related, a comprehensive assessment of these factors is critical. Examining the effects of tumor-host interactions on clinical outcome and prognosis represents an evolving interdisciplinary field of molecular pathological epidemiology. Pathological immunity evaluation may provide information on prognosis and help identify patients who are more likely to benefit from immunotherapy.

Immunotherapy for prostate cancer: biology and therapeutic approaches

Although prostate cancer was not historically considered to be a particularly immune-responsive cancer, recent clinical trials have demonstrated that immunotherapy for prostate cancer can lead to improvements in overall survival (OS). These studies include randomized controlled trials with sipuleucel-T and another with PROSTVAC-VF, both of which rely on stimulating the immune system to target prostate proteins. This review discusses the most promising developments over the past year in immune-based therapy for prostate cancer and the opportunities that lie ahead. Recent randomized immunotherapy trials in prostate cancer have demonstrated improvements in OS but without the concomitant improvements in progression-free survival. This uncoupling of survival from clinical response poses challenges to clinical management, because conventional measures of objective response cannot be used to identify patients benefiting from treatment. There is a significant need to identify immunologic or clinical surrogates for survival so that clinical benefit can be assessed in a timely manner. Immunotherapy is now an established treatment approach for prostate cancer, with multiple clinical trials demonstrating improvements in OS. Significant challenges to this modality remain, including determining best clinical setting for immunotherapy, identifying patients who benefit, and defining relevant clinical and immunologic end points. Nevertheless, the broader availability of novel immunotherapies will provide opportunities not only to target different components of the immune system but also to combine immunotherapies with other treatments for improved clinical efficacy.

Immunotherapy of prostate cancer: should we be targeting stem cells and EMT?

Cancer stem cells have been implicated in a number of solid malignancies including prostate cancer. In the case of localised prostate cancer, patients are often treated with surgery (radical prostatectomy) and/or radiotherapy. However, disease recurrence is an issue in about 30% of patients, who will then go on to receive hormone ablation therapy. Hormone ablation therapy is often palliative in a vast proportion of individuals, and for hormone-refractory patients, there are several immunotherapies targeting a number of prostate tumour antigens which are currently in development. However, clinical responses in this setting are inconsistent, and it is believed that the failure to achieve full and permanent tumour eradication is due to a small, resistant population of cells known as 'cancer stem cells' (CSCs). The stochastic and clonal evolution models are among several models used to describe cancer development. The general consensus is that cancer may arise in any cell as a result of genetic mutations in oncogenes and tumour suppressor genes, which consequently result in uncontrolled cell growth. The cancer stem cell theory, however, challenges previous opinion and proposes that like normal tissues, tumours are hierarchical and only the rare subpopulation of cells at the top of the hierarchy possess the biological properties required to initiate tumourigenesis. Furthermore, where most cancer models infer that every cell within a tumour is equally malignant, i.e. equally capable of reconstituting new tumours, the cancer stem cell theory suggests that only the rare cancer stem cell component possess tumour-initiating capabilities. Hence, according to this model, cancer stem cells are implicated in both tumour initiation and progression. In recent years, the role of epithelial--mesenchymal transition (EMT) in the advancement of prostate cancer has become apparent. Therefore, CSCs and EMT are both likely to play critical roles in prostate cancer tumourigenesis. This review summarises the current immunotherapeutic strategies targeting prostate tumour antigens taking into account the need to consider treatments that target cancer stem cells and cells involved in epithelial--mesenchymal transition.

Vaccine discovery and translation of new vaccine technology

An unprecedented increase in new vaccine development has occurred over the past three decades. This activity has resulted in vaccines that protect against an increased range of vaccine-preventable diseases, vaccines that reduce the number of required injections, and vaccines with improved safety and purity. New methods of discovery, such as reverse vaccinology, structural biology, and systems biology, promise new vaccines for different diseases and efficient development pathways for these vaccines. We expect development of vaccines not only for infectious diseases in children but also for healthy adults, pregnant women, and elderly people, and for new indications such as autoimmune disease and cancer. We have witnessed a concomitant development of new technology for assessment of vaccine safety to rapidly identify potential safety issues. Success of these new approaches will depend on effective implementation of vaccination programmes, creative thinking on the part of manufacturers and regulators as to how best to ensure that safe and effective vaccines are available in a timely manner, and improvement of public awareness about the benefits and risks of new vaccines in a way that encourages confidence in vaccines.

Therapeutic cancer vaccines: are we there yet?

Enthusiasm for therapeutic cancer vaccines has been rejuvenated with the recent completion of several large, randomized phase III clinical trials that in some cases have reported an improvement in progression free or overall survival. However, an honest appraisal of their efficacy reveals modest clinical benefit and a frequent requirement for patients with relatively indolent cancers and minimal or no measurable disease. Experience with adoptive cell transfer-based immunotherapies unequivocally establishes that T cells can mediate durable complete responses, even in the setting of advanced metastatic disease. Further, these findings reveal that the successful vaccines of the future must confront: (i) a corrupted tumor microenvironment containing regulatory T cells and aberrantly matured myeloid cells, (ii) a tumor-specific T-cell repertoire that is prone to immunologic exhaustion and senescence, and (iii) highly mutable tumor targets capable of antigen loss and immune evasion. Future progress may come from innovations in the development of selective preparative regimens that eliminate or neutralize suppressive cellular populations, more effective immunologic adjuvants, and further refinement of agents capable of antagonizing immune check-point blockade pathways.

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.

Therapeutic vaccines in renal cell carcinoma

Metastatic renal cell carcinoma (mRCC) is a lethal disease. The advent of tyrosine kinase inhibitors (TKIs) has changed the disease process, yet the majority of patients will develop treatment-resistant disease. IL-2 based immunotherapy in mRCC is the only US FDA-approved treatment with curative results. Immunotherapeutic vaccine approaches to mRCC have been under investigation for several decades with mixed results. The recent FDA-approval of the first cellular immunotherapy in prostate cancer (Provenge(®)) has reinvigorated the search for similar vaccines approaches in mRCC. This review introduces the concepts and different features required for a successful anticancer vaccine approach.

Randomized trial of autologous cellular immunotherapy with sipuleucel-T in androgen-dependent prostate cancer

PURPOSE

Sipuleucel-T, an autologous cellular immunotherapy, was investigated in a randomized, double-blind, controlled trial to determine its biologic activity in androgen-dependent prostate cancer (ADPC).

EXPERIMENTAL DESIGN

Patients with prostate cancer detectable by serum prostate-specific antigen (PSA) following radical prostatectomy received 3 to 4 months of androgen suppression therapy, and were then randomized (2:1) to receive sipuleucel-T (n = 117) or control (n = 59). The primary endpoint was time to biochemical failure (BF) defined as serum PSA ≥ 3.0 ng/mL. PSA doubling time (PSADT), time to distant failure, immune response, and safety were also evaluated.

RESULTS

Median time to BF was 18.0 months for sipuleucel-T and 15.4 months for control (HR = 0.936, P = 0.737). Sipuleucel-T patients had a 48% increase in PSADT following testosterone recovery (155 vs. 105 days, P = 0.038). With only 16% of patients having developed distant failure, the treatment effect favored sipuleucel-T (HR = 0.728, P = 0.421). The most frequent adverse events in sipuleucel-T patients were fatigue, chills, and pyrexia. Immune responses to the immunizing antigen were greater in sipuleucel-T patients at Weeks 4 and 13 (P < 0.001, all) and were sustained prior to boosting as measured in a subset of patients a median of 22.6 months (range: 14.3-67.3 months) following randomization.

CONCLUSIONS

No significant difference in time to BF could be shown. The finding of increased PSADT in the sipuleucel-T arm is consistent with its biologic activity in ADPC. Long-term follow-up will be necessary to determine if clinically important events, such as distant failure, are affected by therapy. Treatment was generally well tolerated.

Immune parameters affecting the efficacy of chemotherapeutic regimens

The outcome of chemotherapy can be influenced by the host immune system at multiple levels. Chemotherapy can kill cancer cells by causing them to elicit an immune response or alternatively, by increasing their susceptibility to immune attack. In addition, chemotherapy can stimulate anticancer immune effectors either in a direct fashion or by subverting immunosuppressive mechanisms. Beyond cancer-cell-intrinsic factors that determine the cytotoxic or cytostatic response, as well as the potential immunogenicity of tumor cells, the functional state of the host immune system has a major prognostic and predictive impact on the fate of cancer patients treated with conventional or targeted chemotherapies. In this Review, we surmise that immune-relevant biomarkers may guide personalized therapeutic interventions including compensatory measures to restore or improve anticancer immune responses.

Immunotherapy for prostate cancer: recent advances, lessons learned, and areas for further research

A surge of interest in therapeutic cancer vaccines has arisen in the wake of recent clinical trials suggesting that such vaccines can result in statistically significant and clinically meaningful improvements in overall survival-with substantially limited side effects compared with chemotherapy-in patients with metastatic castration-resistant prostate cancer. One of these trials led to the registration of sipuleucel-T, the first therapeutic vaccine to be approved for cancer patients. In this review we highlight emerging patterns from clinical trials that suggest a need for more-appropriate patient populations (i.e., with lower tumor volume and less-aggressive disease) and endpoints (i.e., overall survival) for studies of immunotherapy alone, as well as biologically plausible explanations for these findings. We also explore the rationale for ongoing and planned studies combining therapeutic vaccines with other modalities. Finally, we attempt to put these findings into a practical clinical context and suggest fertile areas for future study. Although our discussion focuses on prostate cancer, the concepts we address most likely have broad applicability to immunotherapy for other cancers as well.

Recent advances in immunotherapy for the treatment of prostate cancer

INTRODUCTION

Prostate cancer vaccines attempt to induce cancer-specific systemic immune responses and represent a new class of targeted therapies, many of which are non-toxic. Several vaccine technologies are in development.

AREAS COVERED

An autologous antigen presenting cell vaccine loaded with prostate acid phosphatase conjugated with GM-CSF, sipuleucel-T confers a survival advantage in men with metastatic castration-resistant prostate cancer (CRPC) and is now FDA approved based on the IMPACT trial. A poxvirus-based vaccine, PROSTVAC-VF TRICOM targeting prostate-specific antigen (PSA), has demonstrated improved survival in a randomized Phase II trial of patients with metastatic CRPC. Novel T lymphocyte checkpoint inhibitors of cytotoxic T lymphocyte antigen 4 and programmed death-1 are also emerging. Recognition of improved survival without an earlier clinical signal of activity by conventional criteria has led to new guidelines to evaluate immunotherapeutic agents. The clinical benefit of combining vaccines with chemotherapy, radiotherapy and other immunotherapeutic and biologic agents is being evaluated in the context of disappointing results of combination GVAX vaccine and docetaxel chemotherapy.

EXPERT OPINION

To build on the success of early phase trials, efforts must be made to optimize vaccine approaches and patient selection.

Exosome targeting of tumor antigens expressed by cancer vaccines can improve antigen immunogenicity and therapeutic efficacy

MVA-BN-PRO (BN ImmunoTherapeutics) is a candidate immunotherapy product for the treatment of prostate cancer. It encodes 2 tumor-associated antigens, prostate-specific antigen (PSA), and prostatic acid phosphatase (PAP), and is derived from the highly attenuated modified vaccinia Ankara (MVA) virus stock known as MVA-BN. Past work has shown that the immunogenicity of antigens can be improved by targeting their localization to exosomes, which are small, 50- to 100-nm diameter vesicles secreted by most cell types. Exosome targeting is achieved by fusing the antigen to the C1C2 domain of the lactadherin protein. To test whether exosome targeting would improve the immunogenicity of PSA and PAP, 2 additional versions of MVA-BN-PRO were produced, targeting either PSA (MVA-BN-PSA-C1C2) or PAP (MVA-BN-PAP-C1C2) to exosomes, while leaving the second transgene untargeted. Treatment of mice with MVA-BN-PAP-C1C2 led to a striking increase in the immune response against PAP. Anti-PAP antibody titers developed more rapidly and reached levels that were 10- to 100-fold higher than those for mice treated with MVA-BN-PRO. Furthermore, treatment with MVA-BN-PAP-C1C2 increased the frequency of PAP-specific T cells 5-fold compared with mice treated with MVA-BN-PRO. These improvements translated into a greater frequency of tumor rejection in a PAP-expressing solid tumor model. Likewise, treatment with MVA-BN-PSA-C1C2 increased the antigenicity of PSA compared with treatment with MVA-BN-PRO and resulted in a trend of improved antitumor efficacy in a PSA-expressing tumor model. These experiments confirm that targeting antigen localization to exosomes is a viable approach for improving the therapeutic potential of MVA-BN-PRO in humans.

State of the art in tumor antigen and biomarker discovery

Our knowledge of tumor immunology has resulted in multiple approaches for the treatment of cancer. However, a gap between research of new tumors markers and development of immunotherapy has been established and very few markers exist that can be used for treatment. The challenge is now to discover new targets for active and passive immunotherapy. This review aims at describing recent advances in biomarkers and tumor antigen discovery in terms of antigen nature and localization, and is highlighting the most recent approaches used for their discovery including “omics” technology.

From clinical trials to clinical practice: therapeutic cancer vaccines for the treatment of prostate cancer

Therapeutic options for patients with metastatic castration-resistant prostate cancer are increasing, spurring an urgent need to better understand which treatments are best for individual patients. The recent approval of a first-in-class agent, sipuleucel-T, has intensified this need. This therapeutic cancer vaccine has demonstrated a survival advantage in two Phase III trials, but does not alter progression in the short term. Therefore, a new therapeutic approach for patients with metastatic castration-resistant prostate cancer is taking shape, based on broader understanding of available therapies. This new clinical approach seeks to maximize patient benefit from treatment, minimize associated toxicities, and may have far-reaching implications for other therapeutic cancer vaccines currently in clinical development.

Vaccine therapy with sipuleucel-T (Provenge) for prostate cancer

As the most common malignancy among North American males, prostate cancer causes more than 30,000 deaths each year. After local and hormonal treatments, a great number of patients ultimately progressed to castrate-resistant prostate cancer (CRPC), in which chemotherapy provides a small survival advantage, but with significant toxicities. In the past decade, prostate cancer has become a target for several immunotherapeutic approaches. Sipuleucel-T (Provenge®, or APC8015) is a novel cancer vaccine developed from autologous dendritic cells (DC) loaded with engineered fusion protein of prostatic acid phosphatase (PAP) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Phase I and Phase II trials show that the vaccine is safe and effective in creating immune responses toward the fusion-protein target antigen, PAP-GM-CSF also call PA2024. Recent Phase III studies also demonstrated sipuleucel-T's efficacy in prolonging median survival in patients with CRPC, despite little or no effect on clinical disease progression or surrogates such as serum PSA kinetics. Subsequently, the United States Food and Drug Administration approved sipuleucel-T for the treatment of asymptomatic or minimally symptomatic CRPC in April 2010. Filings are projected with international regulatory agencies in 2011. While the development of sipuleucel-T provides an option for patients with early CRPC, it also introduces physicians and researchers to new unanswered questions regarding its optimal clinical use and questions about mechanism of action and combination and sequencing with other agents.

A novel candidate HIV vaccine vector based on the replication deficient Capripoxvirus, Lumpy skin disease virus (LSDV)

BACKGROUND

The Capripoxvirus, Lumpy skin disease virus (LSDV) has a restricted host-range and is being investigated as a novel HIV-1 vaccine vector. LSDV does not complete its replication cycle in non-ruminant hosts.

METHODS

The safety of LSDV was tested at doses of 104 and 106 plaque forming units in two strains of immunocompromised mice, namely RAG mice and CD4 T cell knockout mice. LSDV expressing HIV-1 subtype C Gag, reverse transcriptase (RT), Tat and Nef as a polyprotein (Grttn), (rLSDV-grttn), was constructed. The immunogenicity of rLSDV-grttn was tested in homologous prime-boost regimens as well as heterologous prime-boost regimes in combination with a DNA vaccine (pVRC-grttn) or modified vaccinia Ankara vaccine (rMVA-grttn) both expressing Grttn.

RESULTS

Safety was demonstrated in two strains of immunocompromised mice.In the immunogenicity experiments mice developed high magnitudes of HIV-specific cells producing IFN-gamma and IL-2. A comparison of rLSDV-grttn and rMVA-grttn to boost a DNA vaccine (pVRC-grttn) indicated a DNA prime and rLSDV-grttn boost induced a 2 fold (p < 0.01) lower cumulative frequency of Gag- and RT-specific IFN-γ CD8 and CD4 cells than a boost with rMVA-grttn. However, the HIV-specific cells induced by the DNA vaccine prime rLSDV-grttn boost produced greater than 3 fold (p < 0.01) more IFN- gamma than the HIV-specific cells induced by the DNA vaccine prime rMVA-grttn boost. A boost of HIV-specific CD4 cells producing IL-2 was only achieved with the DNA vaccine prime and rLSDV-grttn boost. Heterologous prime-boost combinations of rLSDV-grttn and rMVA-grttn induced similar cumulative frequencies of IFN- gamma producing Gag- and RT-specific CD8 and CD4 cells. A significant difference (p < 0.01) between the regimens was the higher capacity (2.1 fold) of Gag-and RT-specific CD4 cells to produce IFN-γ with a rMVA-grttn prime - rLSDV-grttn boost. This regimen also induced a 1.5 fold higher (p < 0.05) frequency of Gag- and RT-specific CD4 cells producing IL-2.

CONCLUSIONS

LSDV was demonstrated to be non-pathogenic in immunocompromised mice. The rLSDV-grttn vaccine was immunogenic in mice particularly in prime-boost regimens. The data suggests that this novel vaccine may be useful for enhancing, in particular, HIV-specific CD4 IFN- gamma and IL-2 responses induced by a priming vaccine.

Current and emerging treatment modalities for metastatic castration-resistant prostate cancer

Docetaxel-based therapy is established as the standard first-line chemotherapy in patients with metastatic castration-resistant prostate cancer (mCRPC), based on results from two landmark Phase III studies. However, prognosis remains poor, with a median survival of less than 2 years. There is no standard of care for patients who progress during or after docetaxel treatment, which represents a real unmet medical need. Several small retrospective studies suggest that patients with mCRPC who responded to first-line docetaxel-based therapy are sensitive to re-treatment, but a survival benefit in prospective randomized trials has not been demonstrated. Epithelial-stromal interactions in the tumour microenvironment appear to play a central role in prostate cancer progression and response to therapy. Recent insights into the molecular mechanisms that underpin prostate cancer progression have allowed the identification of potential therapeutic targets. New agents, including angiogenesis inhibitors, hormone therapies, chemotherapies, bone targeting agents, vaccines and immunotherapies are currently undergoing clinical development in advanced prostate cancer using docetaxel as a backbone. Several Phase III studies have now been completed. Sipuleucel-T prolonged survival compared with placebo in asymptomatic or minimally symptomatic patients with mCRPC. Cabazitaxel plus prednisone prolonged survival in patients with mCRPC who progressed during or after docetaxel-based therapy compared with the active agent mitoxantrone, plus prednisone. Multidisciplinary management and optimization of the role and timing of new agents in this evolving treatment continuum will be critical to maximizing patient outcomes. Identification of predictive markers and better gene expression profiling will be critical to tailoring therapies to individual patients and disease states, whereas validated surrogate markers of overall survival will help accelerate drug approval.

An update on TroVax for the treatment of progressive castration-resistant prostate cancer

Prostate cancer is a common human malignancy with few effective therapeutic options for treating advanced castration-resistant disease. The potential therapeutic effectiveness of immunotherapy and vaccines, in particular, has gained popularity based on the identification of prostate-associated antigens, potent expression vectors for vaccination, and data from recent clinical trials. A modified vaccinia Ankara (MVA) virus expressing 5T4, a tumor-associated glycoprotein, has shown promise in preclinical studies and clinical trials in patients with colorectal and renal cell carcinoma. This review will discuss the rationale for immunotherapy in prostate cancer and describe preclinical and limited clinical data in prostate cancer for the MVA-5T4 (TroVax^®) vaccine.

New therapies for castration-resistant prostate cancer: efficacy and safety

CONTEXT

Prostate cancer (PCa) is the most common noncutaneous malignancy and the second leading cause of cancer mortality amongst men in the Western world. Up to 40% of men diagnosed with PCa will eventually develop metastatic disease, and although most respond to initial medical or surgical castration, progression to castration resistance is universal. The average survival for patients with castration-resistant prostate cancer (CRPC) is 2-3 yr.

OBJECTIVE

To discuss the biologic rationale and evidence supporting current management of patients with CRPC and to review promising novel agents.

EVIDENCE ACQUISITION

Electronic databases (PubMed, ClinicalTrials.gov), relevant journals, and conference proceedings were searched manually for preclinical studies, clinical trials, and biomarker analyses focused on the treatment of CRPC. Keywords included castrate resistant prostate cancer and: targeted therapy, novel therapy, immunotherapy, androgen therapy, bone therapy, mechanisms, biomarkers, and trial endpoints; no time range was specified. Information pertaining to current studies was discussed with key opinion leaders.

EVIDENCE SYNTHESIS

We focus on the efficacy and safety of approved agents, promising therapies that have proceeded to phase 3 evaluation, and those that have enhanced our understanding of the biology of CRPC. Biomarkers are considered in the context of novel targeted agents and immunotherapy.

CONCLUSIONS

CRPC has many targets. Four new agents with different mechanisms of action have recently been shown to have positive results in large phase 3 randomized trials, and have already been approved in the United States for CRPC: cabazitaxel, sipuleucel-T, denosumab, and abiraterone acetate. With our improved understanding of tumor biology and the incorporation of new prognostic and molecular biomarkers into clinical trials, we are making progress in the management of patients with CRPC.

Sipuleucel-T: immunotherapy for advanced prostate cancer

Prostate cancer continues to be one of the most serious afflictions of men of advanced age, remaining the most commonly diagnosed and second leading cause of cancer-related deaths in American men. The treatment options for patients with incurable metastatic, castrate-resistant disease have long focused on various chemotherapeutic approaches, which provide a slight survival benefit while being associated with potentially significant side effects. However, the recent approval of sipuleucel-T has given patients with advanced disease an additional treatment option that has demonstrated benefit without the side effects associated with chemotherapy. Sipuleucel-T is an antigen-presenting cell-based active immunotherapy that utilizes a patient’s own immune cells, presumably to activate an antigen-specific immune response against tumor cells. This review focuses on the development and implementation of sipuleucel-T as a therapy for prostate cancer. Specifically, we present some of the issues associated with the management of advanced prostate cancer, the research and development that led to the approval of sipuleucel-T, how the approval of sipuleucel-T could change the clinical management of prostate cancer, and current and future areas of investigation that are being pursued with regard to sipuleucel-T and other treatments for advanced prostate cancer.

Progression of metastatic castrate-resistant prostate cancer: impact of therapeutic intervention in the post-docetaxel space

Despite the proven success of hormonal therapy for prostate cancer using chemical or surgical castration, most patients eventually will progress to a phase of the disease that is metastatic and shows resistance to further hormonal manipulation. This has been termed metastatic castrate-resistant prostate cancer (mCRPC). Despite this designation, however, there is evidence that androgen receptor (AR)-mediated signaling and gene expression can persist in mCRPC, even in the face of castrate levels of androgen. This may be due in part to the upregulation of enzymes involved in androgen synthesis, the overexpression of AR, or the emergence of mutant ARs with promiscuous recognition of various steroidal ligands. The therapeutic options were limited and palliative in nature until trials in 2004 demonstrated that docetaxel chemotherapy could significantly improve survival. These results established first-line docetaxel as the standard of care for mCRPC. After resistance to further docetaxel therapy develops, treatment options were once again limited. Recently reported results from phase 3 trials have shown that additional therapy with the novel taxane cabazitaxel (with prednisone), or treatment with the antiandrogen abiraterone (with prednisone) could improve survival for patients with mCRPC following docetaxel therapy. Compared with mitoxantrone/prednisone, cabazitaxel/prednisone significantly improved overall survival, with a 30% reduction in rate of death, in patients with progression of mCRPC after docetaxel therapy in the TROPIC trial. Similarly, abiraterone acetate (an inhibitor of androgen biosynthesis) plus prednisone significantly decreased the rate of death by 35% compared with placebo plus prednisone in mCRPC patients progressing after prior docetaxel therapy in the COU-AA-301 trial. Results of these trials have thus established two additional treatment options for mCRPC patients in the "post-docetaxel space." In view of the continued AR-mediated signaling on mCRPC, results from additional phase 3 studies with novel antiandrogens which are directed at inhibition of the AR (e.g., MDV3100), as well as other agents, are awaited with interest and may further expand the treatment choices for this difficult-to-manage population of patients.

PROVENGE (Sipuleucel-T) in prostate cancer: the first FDA-approved therapeutic cancer vaccine

Sipuleucel-T (PROVENGE; Dendreon) is the first therapeutic cancer vaccine to be approved by the U.S. Food and Drug Administration. In men who have metastatic castration-resistant prostate cancer with no or minimal symptoms, sipuleucel-T prolongs median survival by 4.1 months compared with results in those treated with placebo. At 3 years, the proportion of patients in the vaccine group who were alive was 50% higher than that in the control group (31.7% versus 21.7%, respectively). Sipuleucel-T, which is designed to elicit an immune response to prostatic acid phosphatase, uses the patient's own immune system to recognize and combat his cancer. Currently, no other agents are available that offer a survival benefit for this population of asymptomatic patients who have not been treated with chemotherapy, except for docetaxel (whose inherent toxicities often lead patients and physicians to delay administration until symptoms develop). Straightforward strategies to increase the efficacy of sipuleucel-T are likely to provide even greater benefit. The preclinical and clinical development of sipuleucel-T is reviewed, and approaches to enhance efficacy are considered herein.

Drug development for metastatic castration-resistant prostate cancer: current status and future perspectives

Prostate cancer represents a third of all newly diagnosed cancers in men in the USA with an estimated incidence of 192,280 cases and 27,360 deaths in 2009. It continues to be a major cause of cancer-related morbidity and mortality, and there is an urgent need for new treatments. Historically, systemic therapy options were limited after progression on docetaxel-based chemotherapy. This article reviews current data on the novel therapeutics demonstrating activity in metastatic castration-resistant prostate cancer and their future role in the treatment of this disease with a poor prognosis.

Polyclonal immune responses to antigens associated with cancer signaling pathways and new strategies to enhance cancer vaccines

Aberrant signaling pathways are a hallmark of cancer. A variety of strategies for inhibiting signaling pathways have been developed, but monoclonal antibodies against receptor tyrosine kinases have been among the most successful. A challenge for these therapies is therapeutic unresponsiveness and acquired resistance due to mutations in the receptors, upregulation of alternate growth and survival pathways, or inadequate function of the monoclonal antibodies. Vaccines are able to induce polyclonal responses that can have a multitude of affects against the target molecule. We began to explore therapeutic vaccine development to antigens associated with these signaling pathways. We provide an illustrative example in developing therapeutic cancer vaccines inducing polyclonal adaptive immune responses targeting the ErbB family member HER2. Further, we will discuss new strategies to augment the clinical efficacy of cancer vaccines by enhancing vaccine immunogenicity and reversing the immunosuppressive tumor microenvironment.

Strategies to target molecules that control the acquisition of a mesenchymal-like phenotype by carcinoma cells

The switch of carcinoma cells from an epithelial to a mesenchymal-like phenotype, via a process designated 'epithelial-to-mesenchymal transition (EMT),' has been recognized as a relevant step in the metastasis of solid tumors. Additionally, this phenotypic switch of carcinoma cells has been associated with the acquisition of tumor resistance mechanisms that reduce the antitumor effects of radiation, chemotherapy and some small-molecule-targeted therapies. As multiple signaling pathways and transcriptional regulators that play a role in this phenotypic switch are being identified, novel strategies can be designed to specifically target tumor cells with this metastatic and resistant phenotype. In particular, this review focuses on the potential use of cancer vaccine strategies to target tumor cells that exhibit a mesenchymal-like phenotype, with an emphasis on the characterization of a novel tumor antigen, Brachyury, which we have identified as a critical regulator of EMT in human cancer cells.

Cabazitaxel: a novel second-line treatment for metastatic castration-resistant prostate cancer

Until recently, patients with castration-resistant prostate cancer (CRPC) had limited therapeutic options once they became refractory to docetaxel chemotherapy, and no treatments improved survival. This changed in June 2010 when the Food and Drug Administration (FDA) approved cabazitaxel as a new option for patients with CRPC whose disease progresses during or after docetaxel treatment. For most of these patients, cabazitaxel will now replace mitoxantrone (a drug that was FDA-approved because of its palliative effects) as the treatment of choice for docetaxel-refractory disease. The approval of cabazitaxel was based primarily on the TROPIC trial, a large (n = 755) randomized Phase III study showing an overall median survival benefit of 2.4 months for men with docetaxel-pretreated metastatic CRPC receiving cabazitaxel (with prednisone) compared to mitoxantrone (with prednisone). Cabazitaxel is a novel tubulin-binding taxane that differs from docetaxel because of its poor affinity for P-glycoprotein (P-gp), an ATP-dependent drug efflux pump. Cancer cells that express P-gp become resistant to taxanes, and the effectiveness of docetaxel can be limited by its high substrate affinity for P-gp. Preclinical and early clinical studies show that cabazitaxel retains activity in docetaxel-resistant tumors, and this was confirmed by the TROPIC study. Common adverse events with cabazitaxel include neutropenia (including febrile neutropenia) and diarrhea, while neuropathy was rarely observed. Thus, the combination of cabazitaxel and prednisone is an important new treatment option for men with docetaxel-refractory metastatic CRPC, but this agent should be administered cautiously and with appropriate monitoring (especially in men at high risk of neutropenic complications).

Recent developments in cancer vaccines

The adoptive transfer of cancer Ag-specific effector T cells in patients can result in tumor rejection, thereby illustrating the immune system potential for cancer therapy. Ideally, one would like to directly induce efficient tumor-specific effector and memory T cells through vaccination. Therapeutic vaccines have two objectives: priming Ag-specific T cells and reprogramming memory T cells (i.e., a transformation from one type of immunity to another, for example, regulatory to cytotoxic). Recent successful phase III clinical trials showing benefit to the patients revived cancer vaccines. Dendritic cells (DCs) are essential in generation of immune responses, and as such represent targets and vectors for vaccination. We have learned that different DC subsets elicit different T cells. Similarly, different activation methods result in DCs able to elicit distinct T cells. We contend that a careful manipulation of activated DCs will allow cancer immunotherapists to produce the next generation of highly efficient cancer vaccines.

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.

The genomic complexity of primary human prostate cancer

Prostate cancer is the second most common cause of male cancer deaths in the United States. However, the full range of prostate cancer genomic alterations is incompletely characterized. Here we present the complete sequence of seven primary human prostate cancers and their paired normal counterparts. Several tumours contained complex chains of balanced (that is, 'copy-neutral') rearrangements that occurred within or adjacent to known cancer genes. Rearrangement breakpoints were enriched near open chromatin, androgen receptor and ERG DNA binding sites in the setting of the ETS gene fusion TMPRSS2-ERG, but inversely correlated with these regions in tumours lacking ETS fusions. This observation suggests a link between chromatin or transcriptional regulation and the genesis of genomic aberrations. Three tumours contained rearrangements that disrupted CADM2, and four harboured events disrupting either PTEN (unbalanced events), a prostate tumour suppressor, or MAGI2 (balanced events), a PTEN interacting protein not previously implicated in prostate tumorigenesis. Thus, genomic rearrangements may arise from transcriptional or chromatin aberrancies and engage prostate tumorigenic mechanisms.

CD8+ T cells specific for the androgen receptor are common in patients with prostate cancer and are able to lyse prostate tumor cells

The androgen receptor (AR) is a hormone receptor that plays a critical role in prostate cancer, and depletion of its ligand has long been the cornerstone of treatment for metastatic disease. Here, we evaluate the AR ligand-binding domain (LBD) as an immunological target, seeking to identify HLA-A2-restricted epitopes recognized by T cells in prostate cancer patients. Ten AR LBD-derived, HLA-A2-binding peptides were identified and ranked with respect to HLA-A2 affinity and were used to culture peptide-specific T cells from HLA-A2+ prostate cancer patients. These T-cell cultures identified peptide-specific T cells specific for all ten peptides in at least one patient, and T cells specific for peptides AR805 and AR811 were detected in over half of patients. Peptide-specific CD8+ T-cell clones were then isolated and characterized for prostate cancer cytotoxicity and cytokine expression, identifying that AR805 and AR811 CD8+ T-cell clones could lyse prostate cancer cells in an HLA-A2-restricted fashion, but only AR811 CTL had polyfunctional cytokine expression. Epitopes were confirmed using immunization studies in HLA-A2 transgenic mice, in which the AR LBD is an autologous antigen with an identical protein sequence, which showed that mice immunized with AR811 developed peptide-specific CTL that lyse HLA-A2+ prostate cancer cells. These data show that AR805 and AR811 are HLA-A2-restricted epitopes for which CTL can be commonly detected in prostate cancer patients. Moreover, CTL responses specific for AR811 can be elicited by direct immunization of A2/DR1 mice. These findings suggest that it may be possible to elicit an anti-prostate tumor immune response by augmenting CTL populations using AR LBD-based vaccines.

Are cancer stem cells radioresistant?

Based on findings that cancer cell clonogens exhibit stem cell features, it has been suggested that cancer stem-like cells are relatively radioresistant owing to different intrinsic and extrinsic factors, including quiescence, activated radiation response mechanisms (e.g., enhanced DNA repair, upregulated cell cycle control mechanisms and increased free-radical scavengers) and a surrounding microenvironment that enhances cell survival mechanisms (e.g., hypoxia and interaction with stromal elements). However, these radiosensitivity features are probably dynamic in nature and come into play at different times during the course of chemo/radiotherapy. Therefore, different molecularly targeted radiosensitization strategies may be needed at different stages of therapy. This article describes potential sensitization approaches based on the dynamics and changing properties of cancer stem-like cells during therapy.

Vaccines based on whole recombinant Saccharomyces cerevisiae cells

The ultimate goal of therapeutic vaccines is to activate and exploit the patient's own immune system to vigorously and dynamically seek and eradicate established malignant or virally infected cells. Therapeutic vaccines also offer the potential for preventing disease recurrence. Saccharomyces cerevisiae-based vaccines, where the yeast is engineered to express viral or tumor antigens, represent an ideal therapeutic approach due to their ability to stimulate tumor- or viral-specific CD4(+) and CD8(+) T-cell responses that are capable of reducing disease burden. This review describes preclinical and clinical studies supporting the development of S. cerevisiae-based therapeutic vaccines for the treatment of cancer and viral diseases, as well as multimodal strategies in which therapeutic vaccines are combined with cytotoxic drugs to achieve a greater clinical response.

A phase II study of the cancer vaccine TG4010 alone and in combination with cytokines in patients with metastatic renal clear-cell carcinoma: clinical and immunological findings

MUC1 over-expression in renal clear-cell carcinoma (RCC) is associated with poor prognosis. This phase II study determined the efficacy and tolerability of TG4010, a cancer vaccine based on a modified vaccinia virus expressing MUC1 and interleukin-2, in combination with cytokines, as first-line therapy in metastatic RCC. Thirty-seven patients with progressive, MUC1-positive RCC received TG4010 10(8) pfu/inj weekly for 6 weeks, then every 3 weeks until progression, when TG4010 was continued in combination with interferon-α2a and interleukin-2. Assessments included clinical response (primary endpoint), safety, time to treatment failure (TTF), overall survival (OS), and immune response. No objective clinical responses occurred. Five of the 27 evaluable patients (18%) had stable disease for >6 months with TG4010 alone and six of 20 patients (30%) had stable disease for >6 months with TG4010 plus cytokines. Median TTF was 4.1, 3.6, and 9.3 months for monotherapy, combination therapy, and overall, respectively. Median OS was 19.3 months for all patients and 22.4 months combination therapy recipients. The most frequent TG4010-related adverse events were minor-to-moderate injection-site reactions, fatigue, and flu-like symptoms. Six of 28 patients showed a MUC1 CD4+ T cell proliferative response during therapy. Anti-MUC1 CD8+ T cells were detected before and after therapy in 3 and 4 patients, respectively. MUC1-specific CD8+ T cell responses were associated with longer survival. Therapy with TG4010 plus cytokines appears to be feasible and well tolerated in patients with metastatic RCC. However, these data should be interpreted with caution, as additional prospective studies are necessary to clarify the clinical efficacy of this therapy.

Analysis of circulating regulatory T cells in patients with metastatic prostate cancer pre- versus post-vaccination

We have previously shown that the suppressive function of regulatory T cells (Tregs) from peripheral blood mononuclear cells (PBMCs) is enhanced in patients with prostate cancer when compared with healthy individuals. Two phase II studies using the PSA-TRICOM vaccine in patients with metastatic castration-resistant prostate cancer (mCRPC) showed evidence of patient benefit in terms of enhanced survival. The Halabi nomogram has been used to predict survival (HPS) of patients with mCRPC treated with conventional chemotherapy or second-line hormonal therapy. Tregs from PBMCs of patients (n = 23) with mCRPC were obtained pre- and post-three monthly vaccinations, and analyzed for number, phenotype, and suppressive function. Changes post- versus pre-vaccination in these parameters were compared with 3-year survival and HPS. No differences in Treg numbers were observed post- versus pre-vaccination. Trends (P = 0.029) were observed between overall survival (OS) and a decrease in Treg suppressive function post- versus pre-vaccination. Trends were also observed in analyzing effector:Treg (CD4(+)CD25(+)CD127(-)FoxP3(+)CTLA4(+)) ratio post- versus pre-vaccination with OS versus HPS. These data provide preliminary evidence for a possible association between improved OS and a decrease in Treg function when PBMCs are analyzed after three monthly vaccinations. Patients with an OS > HPS were more likely to have decreased Treg function following vaccine. Larger studies to confirm and extend these findings are warranted.

Sipuleucel-T: harbinger of a new age of therapeutics for prostate cancer

Sipuleucel-T (Provenge) is the first therapeutic cancer vaccine approved by the US FDA. The approval heralds the long-awaited promise of improved patient survival with minimal toxicity by therapies designed to generate an active, specific anticancer immune response. The development of this first-in-class agent as well as other therapeutic vaccines in clinical evaluation has also led to a better understanding of relevant patient populations and end points for clinical trials. This article discusses the development and approval of sipuleucel-T in the context of other approved therapies for prostate cancer, as well as controversies and novel paradigms brought about by this new agent.

Type-1 polarized dendritic cells loaded with apoptotic prostate cancer cells are potent inducers of CD8(+) T cells against prostate cancer cells and defined prostate cancer-specific epitopes

BACKGROUND

In order to develop improved vaccines for patients with recurrent prostate cancer (PCa), we tested the feasibility of using type-1 polarized dendritic cells (αDC1s) to cross-present antigens from allogeneic PCa cells and to induce functional CD8(+) T cell responses against PCa cells and against defined MHC class I-restricted PCa-relevant epitopes.

METHODS

Monocyte-derived DCs from PCa patients were matured using the "standard" cytokine cocktail (IL-1β/TNFα/IL-6/PGE₂) or using the αDC1-polarizing cocktail (IL-1β/TNFα/IFNα/IFNγ/poly-I:C), loaded with UV-irradiated LNCaP cells, and used to sensitize autologous CD8(+) T cells.

RESULTS

αDC1s from PCa patients secreted 10-30 times higher levels of IL-12p70 than sDCs. Importantly this elevated capacity for IL-12p70 secretion was not inhibited by loading with apoptotic tumor cells. Compared to standard DCs, αDC1s induced higher numbers of CD8(+) T cells capable of recognizing both the original PCa cells as well as another PCa cell line, DU145, in MHC class I-restricted fashion. Furthermore, αDC1s induced higher numbers of CD8(+) T cells recognizing defined PCa-specific class I-restricted peptide epitopes of prostate-specific antigen and prostatic acid phosphatase: PAP(135-143) (average 49-fold higher), PAP(112-120) (average 24-fold), PSA(141-150) (average 5.5-fold), and PSA(146-154) (average 11-fold).

CONCLUSION

Type-1 polarization of GM-CSF/IL-4-generated DCs enhances their ability to present allogeneic tumor cells and to induce CD8(+) T cells recognizing different PCa cells and multiple defined PCa-specific epitopes. These observations help to develop improved immunotherapies of PCa for patients with different HLA types and lacking autologous tumor material.

The iSBTc/SITC primer on tumor immunology and biological therapy of cancer: a summary of the 2010 program

The Society for Immunotherapy of Cancer, SITC (formerly the International Society for Biological Therapy of Cancer, iSBTc), aims to improve cancer patient outcomes by advancing the science, development and application of biological therapy and immunotherapy. The society and its educational programs have become premier destinations for interaction and innovation in the cancer biologics community. For over a decade, the society has offered the Primer on Tumor Immunology and Biological Therapy of Cancer™ in conjunction with its Annual Scientific Meeting. This report summarizes the 2010 Primer that took place October 1, 2010 in Washington, D.C. as part of the educational offerings associated with the society's 25th anniversary. The target audience was basic and clinical investigators from academia, industry and regulatory agencies, and included clinicians, post-doctoral fellows, students, and allied health professionals. Attendees were provided a review of basic immunology and educated on the current status and most recent advances in tumor immunology and clinical/translational caner immunology. Ten prominent investigators presented on the following topics: innate immunity and inflammation; an overview of adaptive immunity; dendritic cells; tumor microenvironment; regulatory immune cells; immune monitoring; cytokines in cancer immunotherapy; immune modulating antibodies; cancer vaccines; and adoptive T cell therapy. Presentation slides, a Primer webinar and additional program information are available online on the society's website.

Novel approaches and future directions in castration-resistant prostate cancer

Recent advances in the treatment of castration-resistant prostate cancer (CRPC) have started to change the therapeutic landscape allowing clinicians to choose from a broad range of treatment options. Understanding the mechanisms that transform prostate cancer (PCA) into a castration-resistant state has enabled investigators to explore critical pathways involved in such process allowing for rational therapeutic design. These novel therapies complement the modest success that chemotherapy has demonstrated in recent years. In this review, we discuss the different mechanisms that render PCA castration resistant and elaborate on the nonchemotherapy approaches evolving in CRPC. These include agents targeting the epidermal growth factor receptor, endothelin receptor antagonists, angiogenesis inhibitors, immunomodulatory agents, immunotherapy, novel antiandrogens, and delivery of cytotoxic agents via therapeutic antibodies. This timely review coincides with the identification of newer therapies in this setting affirming our steady movement towards better disease control.

A phase I trial of preventive HIV vaccination with heterologous poxviral-vectors containing matching HIV-1 inserts in healthy HIV-uninfected subjects

We evaluated replication-defective poxvirus vectors (modified vaccinia Ankara [MVA] and fowlpox [FPV]) in a homologous and heterologous vector prime-boost vaccination regimen containing matching HIV inserts (MVA-HIV and FPV-HIV) given at months 0, 1, 3, 5 and 7 in 150 healthy HIV-negative vaccinia-naïve participants. FPV-HIV alone was poorly immunogenic, while the high dose (10(9)pfu/2 ml) of MVA-HIV alone elicited maximal responses after two injections: CD4+ and CD8+ T-cell responses in 26/55 (47.3%) and 5/60 (8.3%) of participants, respectively, and IFN-γ ELISpot responses in 28/62 (45.2%). The infrequent CD8+ T-cell responses following MVA-HIV priming were boosted only by the heterologous (FPV-HIV) construct in 14/27 (51.9%) of participants post 4th vaccination. Alternatively, HIV envelope-specific binding antibodies were demonstrated in approximately two-thirds of recipients of the homologous boosting regimen, but in less than 20% of subjects after the heterologous vector boost. Thus, a heterologous poxvirus vector prime-boost regimen can induce HIV-specific CD8+ T-cell and CD4+ T-cell responses, which may be an important feature of an optimal regimen for preventive HIV vaccination.