Clinical experience with CTLA-4 blockade for cancer immunotherapy: From the monospecific monoclonal antibody ipilimumab to probodies and bispecific molecules targeting the tumor microenvironment

The immune checkpoint cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is an inhibitory regulator of T-cell mediated responses that has been investigated as target of monoclonal antibodies (mAbs) for cancer immunotherapy. The anti-CTLA-4 mAb ipilimumab represents the first immune checkpoint inhibitor that significantly improved overall survival in patients with unresectable/metastatic melanoma. The subsequent approved indications (often in the first-line setting) for melanoma and other advanced/metastatic solid tumors always require ipilimumab combination with nivolumab, an anti-programmed cell death protein 1 (PD-1) mAb. However, the improved clinical efficacy of the mAb combination is associated with increased immune-related adverse events, which might require treatment discontinuation even in responding patients. This drawback is expected to be overcome by the recent development of anti-CTLA-4 probodies proteolitycally activated in the tumor microenvironment and bispecific molecules targeting both CTLA-4 and PD-1, whose co-expression is characteristic of tumor-infiltrating T cells. These molecules would preferentially stimulate immune responses against the tumor, reducing toxicity toward normal tissues.

Immunologic checkpoints blockade in renal cell, prostate, and urothelial malignancies

Genitourinary (GU) tumors, and in particular renal cell and prostate cancer, represent one of the most dynamic areas in oncology from the scientific point of view. One of the most recent treatment approaches for GU tumors has focused on a series of molecules known as immune checkpoints and the possibility of manipulating immune responses against tumor cells by blocking these molecules with monoclonal antibodies (mAbs). Cytotoxic T lymphocyte antigen-4 (CTLA-4), and the immune checkpoint inhibitor mAbs ipilimumab and tremelimumab, represent the prototypes of this new growing class of agents called immunomodulating antibodies, while programmed death/ligand 1 (PD-1/PD-L1) also has garnered a significant interest as a new immune checkpoints to target in urothelial cancer, with the anti-PD-1/PD-L1 inhibitor mAbs nivolumab, MPDL-3280, and BMS-936559 as the first agents tested. Here we report the encouraging initial data observed in GU cancers with this new class of agents, which have reinforced the interest of investigating the therapeutic potential of the immune checkpoint modulators in large controlled trials.

Sequencing therapy in advanced prostate cancer: focus on sipuleucel-T

Immunotherapies such as sipuleucel-T present new and unique challenges for the optimal timing and sequencing of therapies for metastatic castration-resistant prostate cancer (mCRPC). Key considerations for the sequencing of sipuleucel-T are its unique proposed mechanism of action, the time required to generate a clinically relevant immune response, and the observed efficacy in Phase III trials in 'early' or asymptomatic or minimally symptomatic mCRPC. There are three broad timing and sequencing options for sipuleucel-T in patients with rising prostate-specific antigen and radiologic evidence of disease: immediately after androgen-deprivation therapy failure, after failure of secondary hormonal maneuvers, or after chemotherapy. There are several other agents in Phase III development in mCRPC and any future approvals will impact on the current treatment algorithm, and raise further questions regarding how to optimize sequencing and timing of therapies for better clinical outcomes.

Evolving Personalized Therapy for Castration-Resistant Prostate Cancer

With advances in molecular biologic and genomic technology, detailed molecular mechanisms for development of castration-resistant prostate cancer (CRPC) have surfaced. Metastatic prostate cancer (PCa) no longer represents an end stage, with many emerging therapeutic agents approved as effective in prolonging survival of patients from either pre- or post-docetaxel stage. Given tumor heterogeneity in patients, a one-size-fits-all theory for curative therapy remains questionable. With the support of evidence from continuing clinical trials, each treatment modality has gradually been found suitable for selective best-fit patients: e.g., new androgen synthesis inhibitor arbiraterone, androgen receptor signaling inhibitor enzalutamide, sipuleucel-T immunotherapy, new taxane carbazitaxel, calcium-mimetic radium-223 radiopharmaceutical agent. Moreover, several emerging immunomodulating agents and circulating tumor cell enumeration and analysis showed promise in animal or early phase clinical trials. While the era of personalized therapy for CRPC patients is still in infancy, optimal therapeutic agents and their sequencing loom not far in the future.

Perspectives on immunotherapy in prostate cancer and solid tumors: where is the future?

The goals of any cancer therapy are to improve disease control, palliate pain and improve overall survival. We are fortunate to have in our cancer armamentarium two new immune-directed therapies which not only impact on disease control but also on overall survival. The first, sipuleucel-T, a cellular-based vaccine, was approved for prostate cancer and was shown to be safe with minimal toxicity. The second, ipilimumab, a monoclonal antibody directed to an immunologic checkpoint molecule, showed a survival benefit in patients with advanced melanoma. Benefit appeared to correlate in some cases with the development of autoimmune events, signaling that the immune system is in overdrive against the cancer. Where we are and where we will likely go are the topics to be discussed in this review.

Unmet needs in the prediction and detection of metastases in prostate cancer

The therapeutic landscape for the treatment of advanced prostate cancer is rapidly evolving, especially for those patients with metastatic castration-resistant prostate cancer (CPRC). Despite advances in therapy options, the diagnostic landscape has remained relatively static, with few guidelines or reviews addressing the optimal timing or methodology for the radiographic detection of metastatic disease. Given recent reports indicating a substantial proportion of patients with CRPC thought to be nonmetastatic (M0) are in fact metastatic (M1), there is now a clear opportunity and need for improvement in detection practices. Herein, we discuss the current status of predicting the presence of metastatic disease, with a particular emphasis on the detection of the M0 to M1 transition. In addition, we review current data on newer imaging technologies that are changing the way metastases are detected. Whether earlier detection of metastatic disease will ultimately improve patient outcomes is unknown, but given that the therapeutic options for those with metastatic and nonmetastatic CPRC vary, there are considerable implications of how and when metastases are detected.

Immunotherapy for prostate cancer enters its golden age

In the United States, prostate cancer is the most frequent malignancy in men and ranks second in terms of mortality. Although recurrent or metastatic disease can be managed initially with androgen ablation, most patients eventually develop castration-resistant disease within a number of years, for which conventional treatments (eg, chemotherapy) provide only modest benefits. In the last few years, immunotherapy has emerged as an exciting therapeutic modality for advanced prostate cancer, and this field is evolving rapidly. Encouragingly, the US Food and Drug Administration (FDA) has recently approved two novel immunotherapy agents for patients with advanced cancer: the antigen presenting cell-based product sipuleucel-T and the anti-CTLA4 (cytotoxic T-lymphocyte antigen 4) antibody ipilimumab, based on improvements in overall survival in patients with castration-resistant prostate cancer and metastatic melanoma, respectively. Currently, a number of trials are investigating the role of various immunological approaches for the treatment of prostate cancer, many of them with early indications of success. As immunotherapy for prostate cancer enters its golden age, the challenge of the future will be to design rational combinations of immunotherapy agents with each other or with other standard prostate cancer treatments in an effort to improve patient outcomes further.

Metastatic castrate-resistant prostate cancer: dawn of a new age of management

What's known on the subject? and What does the study add? Metastatic castrate-resistant prostate cancer (mCRPC) was historically considered to be an aggressive disease resistant to conventional anticancer therapy. Within the last decade the outlook has changed beyond recognition; docetaxel chemotherapy is now firmly established as a well-tolerated treatment with significant survival benefits. Building on this, more recently there have been several landmark developments using various approaches in patients whose disease has progressed despite previous chemotherapy. Cabazitaxel chemotherapy offers survival and health-related quality of life (HRQL) improvements in this setting, as does the CYP inhibitor abiraterone acetate. Significant clinical benefits are also seen with novel radioisotope and immunotherapeutic approaches. There have been many developments in the management of this condition within the last 2 years, with several landmark studies showing new treatments that offer survival and HRQL benefits even in the setting of advanced disease, which has been heavily pretreated. This review article summarises these important developments and gives the reader an overview of current practice, recent changes and future directions. With current and forthcoming developments in the treatment of metastatic castrate-resistant prostate cancer (mCRPC) post-docetaxel, we are embarking on an age of potential 'chronic' management of this disease. It is hoped that the survival benefits associated with the various treatments, cytotoxic, hormonal and immunotherapeutic, will prove to be additive, providing a multimodal continuum of care. If so, it will be necessary to determine the optimal sequence and timing of the new treatments. One key factor in this regard is likely to be the patient's performance status and hence his eligibility for cytotoxic intervention. If chemotherapy is offered early in the post-docetaxel pathway, the patient may still be able to benefit from non-chemotherapeutic options subsequently. However, if this stage of management begins with a non-chemotherapeutic option, there is a risk that the patient's performance status will decline before he has an opportunity to benefit from chemotherapy. Further studies and ongoing clinical experience are likely to clarify this important issue, and help clinicians to maximise the survival of men with mCRPC post-docetaxel.

Immune response to sipuleucel-T in prostate cancer

Historically, chemotherapy has remained the most commonly utilized therapy in patients with metastatic cancers. In prostate cancer, chemotherapy has been reserved for patients whose metastatic disease becomes resistant to first line castration or androgen deprivation. While chemotherapy palliates, decreases serum prostate specific antigen and improves survival, it is associated with significant side effects and is only suitable for approximately 60% of patients with castrate-resistant prostate cancer. On that basis, exploration of other therapeutic options such as active secondary hormone therapy, bone targeted treatments and immunotherapy are important. Until recently, immunotherapy has had no role in the treatment of solid malignancies aside from renal cancer and melanoma. The FDA-approved autologous cellular immunotherapy sipuleucel-T has demonstrated efficacy in improving overall survival in patients with metastatic castrate-resistant prostate cancer in randomized clinical trials. The proposed mechanism of action is reliant on activating the patients' own antigen presenting cells (APCs) to prostatic acid phosphatase (PAP) fused with granulocyte-macrophage colony stimulating factor (GM-CSF) and subsequent triggered T-cell response to PAP on the surface of prostate cancer cells in the patients body. Despite significant prolongation of survival in Phase III trials, the challenge to health care providers remains the dissociation between objective changes in serum PSA or on imaging studies after sipleucel-T and survival benefit. On that basis there is an unmet need for markers of outcome and a quest to identify immunologic or clinical surrogates to fill this role. This review focuses on the impact of sipuleucel-T on the immune system, the T and B cells, and their responses to relevant antigens and prostate cancer. Other therapeutic modalities such as chemotherapy, corticosteroids and GM-CSF and host factors can also affect immune response. The optimal timing for immunotherapy, patient selection and best sequencing with other prostate cancer therapies remain to be determined. A better understanding of immune response may help address these issues.

Unmasking the immune recognition of prostate cancer with CTLA4 blockade

Although cancer cells can be immunogenic, tumour progression is associated with the evasion of immunosurveillance, the promotion of tumour tolerance and even the production of pro-tumorigenic factors by immune cells. Cytotoxic T lymphocyte-associated antigen 4 (CTLA4) represents a crucial immune checkpoint, the blockade of which can potentiate anti-tumour immunity. CTLA4-blocking antibodies are now an established therapeutic approach for malignant melanoma, and clinical trials with CTLA4-specific antibodies in prostate cancer have also shown clinical activity. This treatment may provide insights into the targets that the immune system recognizes to drive tumour regression, and could potentially improve both outcome and toxicity for patients with prostate cancer.

New and emerging agents for the treatment of castration-resistant prostate cancer

Most men with recurrent prostate cancer (CaP) initially respond to androgen deprivation therapy but eventually develop metastatic castration-resistant prostate cancer (CRPC). Over the last decade, new therapeutic targets have been identified in CRPC and several new drugs have reached advanced stages of clinical development. In 2010, the Food and Drug Administration (FDA) approved sipuleucel-T and cabazitaxel, and in 2011, abiraterone for patients with metastatic CRPC based on phase 3 trials showing improved survival. Although not yet available for clinical use, a press release in June 2011 announced that radium 223 also demonstrated a survival advantage in men with metastatic CRPC. Emerging therapies in advanced stages of clinical development in CRPC include the hormonal therapies MDV3100 and TAK 700, and the immunotherapy ipilimumab. Results are also pending on phase 3 studies comparing docetaxel plus prednisone with docetaxel given with the novel agents aflibercept, dasatinib, lenalidomide, and custirsen. In addition to these new and emerging therapeutic agents, denosumab was approved for the prevention of skeletal complications in patients with bone metastases due to solid tumor malignancies, providing an alternative to zoledronic acid. While the addition of these new treatment options is a great advance for men with metastatic CRPC, there are many new questions arising regarding sequencing of these treatments with each other, with previously existing therapies, and with the emerging agents now in clinical trials. Furthermore, there are concerns that on-going phase 3 trials may be contaminated if patients go off study treatment to start 1 of the newly approved agents or take the agent subsequently. These realities make clinical trial design more challenging than ever.

Current and emerging treatment options for castration-resistant prostate cancer: a focus on immunotherapy

BACKGROUND

Castration-resistant prostate cancer is a disease with limited treatment options. However, the ongoing elucidation of the mechanisms underlying this disease continues to support the development of not only novel agents, but also innovative approaches. Among these therapies, immunotherapy has emerged as a promising strategy.

DESIGN

This review article summarizes the most recent data from investigations of immunotherapies in castration-resistant prostate cancer (literature and congress searches current as of August 2011).

RESULTS

Immunotherapeutic strategies such as passive immunization, vaccines, and particularly checkpoint blockade have demonstrated some efficacy as single agents. Elucidation of effective combinations of agents and drug regimens is ongoing but will require continued careful investigation, including the standardization of surrogate endpoints in clinical trials.

CONCLUSIONS

It is hypothesized that the combination of immunotherapeutic agents with traditional and novel chemotherapeutics will potentiate the efficacy of the chemotherapeutics while maintaining manageable toxicity.

Castration-resistant prostate cancer: new science and therapeutic prospects

There is a growing number of new therapies targeting different pathways that will revolutionize patient management strategies in castration-resistant prostate cancer (CRPC) patients. Today there are more clinical trial options for CRPC treatment than ever before, and there are many promising agents in late-stage clinical testing. The hypothesis that CRPC frequently remains driven by a ligand-activated androgen receptor (AR) and that CRPC tissues exhibit substantial residual androgen levels despite gonadotropin-releasing hormone therapy, has led to the evaluation of new oral compounds such as abiraterone and MDV 3100. Their results, coupled with promising recent findings in immunotherapy (eg sipuleucel-T) and with agents targeting angiogenesis (while awaiting the final results of the CALGB trial 90401) will most probably impact the management of patients with CRPC in the near future. Other new promising agents need further development. With our increased understanding of the biology of this disease, further trial design should incorporate improved patient selection so that patient populations are those who may be most likely to benefit from treatment.

Ipilimumab: a novel immunostimulatory monoclonal antibody for the treatment of cancer

Ipilimumab (Yervoy, developed by Medarex and Bristol-Myers Squibb) is a fully human monoclonal IgG1κ antibody against the cytotoxic T-lymphocyte antigen-4 (CTLA-4), an immune-inhibitory molecule expressed in activated T cells and in suppressor T regulatory cells. Interaction of the monoclonal antibody with CTLA-4 blocks inhibitory signals generated through this receptor and enhances T cell activation, leading to increased antitumor responses. Ipilimumab has been approved by FDA in March 2011 as monotherapy (3mg/kg every 3 weeks for 4 doses) for the treatment of advanced (unresectable or metastatic) melanoma both in pre-treated or chemotherapy naïve patients. Four months later, ipilimumab has received a rapid approval by the European Commission, after a positive opinion from the Committee for Medicinal Products for Human Use. However, the indication in the EU is limited to previously-treated patients with advanced melanoma. Ipilimumab is the first agent that has demonstrated to improve overall survival in patients with metastatic melanoma, which has a very poor prognosis, in randomized phase III clinical trials. The patterns of tumour response to ipilimumab differ from those observed with cytotoxic chemotherapeutic agents, since patients may have a delayed yet durable response and obtain long-term survival benefit despite an initial tumour growth. The major draw-back of ipilimumab is the induction of immune-related adverse effects; the latter can be life-threatening, unless promptly managed with immunosuppressive agents (most frequently corticosteroids) according to specific guidelines. Further development of ipilimumab includes its use in the neoadjuvant or adjuvant high-risk melanoma setting and for the treatment of other refractory and advanced solid tumours, either as single agent or in combination with additional immunostimulating agents or molecularly targeted therapies.

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.

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.

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.

CTLA-4 blockade increases antigen-specific CD8(+) T cells in prevaccinated patients with melanoma: three cases

BACKGROUND

Anti-cytotoxic T-lymphocyte antigen-4 (CTLA-4) antibodies, such as ipilimumab, have generated measurable immune responses to Melan-A, NY-ESO-1, and gp100 antigens in metastatic melanoma. Vaccination against such targets has potential for immunogenicity and may produce an effector-memory T-cell response.

METHODS

To determine the effect of CTLA-4 blockade on antigen-specific responses following vaccination, in-depth immune monitoring was performed on three ipilimumab-treated patients prevaccinated with gp100 DNA (IMF-24), gp100(209-217) and tyrosinase peptides plus GM-CSF DNA (IMF-32), or NY-ESO-1 protein plus imiquimod (IMF-11); peripheral blood mononuclear cells were analyzed by tetramer and/or intracellular cytokine staining following 10-day culture with HLA-A*0201-restricted gp100(209-217) (ITDQVPFSV), tyrosinase(369-377) (YMDGTMSQV), or 20-mer NY-ESO-1 overlapping peptides, respectively. Tumors from IMF-32 were analyzed by immunohistochemistry to help elucidate mechanism(s) underlying tumor escape.

RESULTS

Following vaccination, patients generated weak to no CD4(+) or CD8(+) T-cell response specific to the vaccine antigen but demonstrated increases in effector-memory (CCR7(lo)CD45RA(lo)) tetramer(+)CD8(+) T cells. After ipilimumab induction, patients experienced a robust, although sometimes transient, antigen-specific response for gp100 (IMF-32 and IMF-24) or NY-ESO-1 (IMF-11) and produced polyfunctional intracellular cytokines. Primary and metastatic tumors expressed tyrosinase but not gp100 or class I/II MHC molecules.

CONCLUSION

Vaccination induced a measurable antigen-specific T-cell response that increased following CTLA-4 blockade, potentially "boosting" the vaccine-primed response. Tumor escape may be related to antigen loss or lack of MHC expression necessary for immune activity. These results in a limited number of patients support the need for further research into combining vaccination with ipilimumab and provide insight into mechanisms underlying tumor escape.

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.

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.

Clinical studies with anti-CTLA-4 antibodies in non-melanoma indications

Available medical treatments have limited impact on the survival of patients with advanced cancer; therefore, new therapeutic strategies able to generate more effective host's immune responses against neoplastic cells are being actively pursued. Among these, a recent approach involves targeting of cytotoxic T-lymphocyte antigen-4 (CTLA-4), a key immune checkpoint molecule, by monoclonal antibodies (mAbs). Ipilimumab and tremelimumab represent the prototypes of this new class of immunomodulating mAb and have been extensively tested in metastatic melanoma with highly promising results. The clinical activity observed in melanoma has served as a model to exploit the therapeutic potential of CTLA-4 blockade in a variety of human malignancies. Along this line, early-phase trials with anti-CTLA-4 mAbs have been completed or are ongoing in tumors of different histotype. Results are demonstrating the feasibility, safety, and activity of these agents, thus suggesting a promising therapeutic role to be further investigated in phase II/III trials in a wide range of tumors. This review summarizes the main trials with ipilimumab and tremelimumab in tumors of different histotypes, excluding cutaneous melanoma, which is extensively described in other chapters of this issue of Seminars in Oncology.

Ipilimumab: unleashing the power of the immune system through CTLA-4 blockade

Malignant melanoma is rising faster in incidence than any other malignancy. Long-term remission or "cure" is rare and is almost exclusively limited to therapies that stimulate an immune antitumor response. Ipilimumab is a novel targeted human immunostimulatory monoclonal antibody that blocks cytotoxic T-lymphocyte antigen4 (CTLA-4), an immune-inhibitory site expressed on activated T cells. Ipilimumab is well tolerated as an outpatient infusion therapy. Multiple studies have confirmed significant antimelanoma activity. A randomized trial has documented a survival benefit when ipilimumab was compared to a gp-100 vaccine only arm. The unique mechanism of action of ipilimumab makes assessment of response by conventional criteria difficult. Benefit from ipilimumab can occur after what would be considered progression with World Health Oganization (WHO) or Response Evaluation Criteria in Solid Tumors (RECIST) criteria. New immune response criteria have been proposed. Therapeutic responses peak between 12 and 24 weeks, with slow responses continuing up to and beyond 12 months. The major drug- related adverse side effects (10%-15% grade 3 or above) are immune-related and consist most commonly of rash, colitis, hypophysitis, thyroiditis, and hepatitis. Colonic perforation can occur and patients with diarrhea have to be monitored carefully with strict adherence to treatment algorithms. Algorithms for the treatment of other adverse side effects have been developed. The treatment of immune-related side effects with immunosuppressive agents, such as corticosteroids, does not appear to impair antitumor response. With proper monitoring and management of side effects, ipilimumab is an extremely safe drug to administer. The benefits of ipilimumab will most certainly extend to other malignancies in the near future.

Update on castrate-resistant prostate cancer: 2010

PURPOSE OF REVIEW

Prostate cancer remains a medical dilemma and a major cause of morbidity and mortality in many western countries. It represents the most common cancer in US men, with an estimated 192 280 new cases diagnosed in 2009. The median survival for men with metastatic castrate-resistant prostate cancer is 1-2 years, with improvements in survival seen primarily with docetaxel-based therapies. The purpose of this article is to discuss developments of novel agents in the field of metastatic castration-resistant prostate cancer (CRPC), including new cytotoxic agents, immune-based therapies, circulating tumor markers and targeting agents.

RECENT FINDINGS

During this past year, several promising approaches yielded disappointing results in the phase III setting (GVAX); nonetheless, expectations for other agents (Abiraterone, MDV3100, Zibotentan, immunotherapy agents) still remain high.

SUMMARY

Systemic therapy options are limited in CRPC and survival benefit remains to be seen with the new therapies. Circulating tumor cells continue to provide important prognostic information and will likely become an important aspect of future clinical decision-making.

Immune regulatory antibodies: are they the next advance?

During the past decade, new insights into the mechanisms by which T-cell activation and proliferation are regulated have led to the identification of checkpoint proteins that either up- or down-modulate T-cell reactivity. In the presence of active malignancy, pathophysiologic inhibition of T-cell activity may predominate over stimulation. A number of antibodies have been generated that can block inhibitory checkpoint proteins or promote the activity of activating molecules. In murine models, their use alone or with a vaccine strategy has resulted in regression of poorly immunogenic tumors and cures of established tumors. The prototypical immune regulatory antibodies are those directed against cytotoxic T-lymphocyte antigen-4, a molecule present on activated T cells. In this review, the preclinical rationale and clinical experience with 2 anticytotoxic T-lymphocyte antigen-4 antibodies are extensively discussed, demonstrating that abrogation of an immune inhibitory molecule can result in significant regression of tumors and long-lasting responses. The unique kinetics of antitumor response and the characteristic immune-related side effects of ipilimumab are also discussed. This clinical efficacy of this promising antitumor agent has been evaluated in 2 randomized phase III trials, whose results are eagerly awaited. Programmed death (PD)-1 is another immune inhibitory molecule against which an abrogating human antibody has been prepared. Initial preclinical testing with anti-PD-1 and anti-PD-L1 has shown encouraging results. Stimulatory molecules such as CD40, 41-BB, and OX-40 are also targets for antibody binding and activation, not blockade, and early dose ranging trials with antibodies against all 3 have shown that they can mediate regression of tumors, albeit with their own spectrum of side effects that are different from those that occur with abrogation of immune inhibition.