Immunotherapy for prostate cancer: biology and therapeutic approaches

The role of regulatory T cells in the pathogenesis and treatment of prostate cancer

Despite developments in the treatment of various cancers, prostate cancer is one of the deadliest diseases known to men. Systemic therapies such as androgen deprivation, chemotherapy, and radiation therapy have not been very successful in treating this disease. Numerous studies have shown that there is a direct relationship between cancer progression and inhibition of anti-tumor immune responses that can lead to progression of various malignancies, including prostate cancer. Interestingly, CD4⁺CD25⁺FoxP3⁺ regulatory T cells significantly accumulate and increase in draining lymph nodes and PBMCs of patients with prostate cancer and other solid tumors. In vivo and in vitro studies have shown that Tregs can suppress anti-tumor responses, which is directly related to the increased risk of cancer recurrence. Tregs are essential for preserving self-tolerance and inhibiting extra immune responses harmful to the host. Since the tumor-related antigens are mainly self-antigens, Tregs could play a major role in tumor progression. Accordingly, it has discovered that prostate cancer patients with higher Tregs have poor prognosis and low survival rates. However, anti-tumor responses can be reinforced by suppression of Tregs with using monoclonal antibodies against CD25 and CTLA-4. Therefore, depleting Tregs or suppressing their functions could be one of the effective ways for prostate cancer immunotherapy. The purpose of this review is to investigate the role of Treg cells in the progression of prostate cancer and to evaluate effective strategies for the treatment of prostate cancer by regulating Treg cells.

Gas-blasting nanocapsules to accelerate carboplatin lysosome release and nucleus delivery for prostate cancer treatment

To improve therapeutic effect and reduce severely side effects of carboplatin (CBP), the gas-generating nanocapsules were developed to accelerate CBP lysosome release and nucleus delivery. CBP/SB-NC was prepared by co-loading CBP and NaHCO₃ (SB) in nanocapsules using w/o/w emulsification solvent evaporation. They exhibited vesicle-like spherical morphology, uniform particle size and negative zeta potential. Reaching the tumor site with a relatively high concentration is the first step for CBP delivery and the results showed that CBP/SB-NC could effectively increase drug accumulation at tumor site. After that, the drug delivery carriers need to be internalized into tumor cells and the in vitro cellular uptake ability results showed CBP/SB-NC could be internalized into RM-1 cells more efficient than CBP solution. After internalized by RM-1 cells, the gas-blasting release process was tested in acid environment. It was demonstrated that 5 mg/ml NaHCO₃ was optimal to achieve pH-responsive gas-blasting release. In vitro release results showed that CBP significantly rapid release in acid environment (pH 5.0) compared to neutral pH (pH 7.4) (P < 0.05). Meanwhile, TEM and the change of the concentration of H⁺ results exhibited that the explosion of CBP/SB₅-NC was more easily happened in lysosome acid environment (pH 5.0). The blasting release can accelerate CBP lysosome release to cytoplasm. Furthermore, the nucleus delivery results showed CBP/SB₅-NC can promote pH-triggered rapid nucleus delivery. And the results of Pt-DNA adduct assay showed that the binding efficiency between CBP and DNA of CBP/SB₅-NC was higher than CBP solution. At last, in vitro and in vivo anti-tumor efficacy proved that CBP/SB₅-NC could enhance anti-tumor activity for prostate cancer therapy. CBP/SB₅-NC also showed superior safety in vitro and in vivo by hemolysis assay and histopathological study. All of the results demonstrate that CBP/SB₅-NC would be an efficient gas-blasting release formulation to enhance prostate cancer treatment.

The Immune Landscape of Prostate Cancer and Nomination of PD-L2 as a Potential Therapeutic Target

BACKGROUND

Immunotherapy has been less successful in treating prostate cancer than other solid tumors. We sought to better understand the immune landscape in prostate cancer and identify immune-related biomarkers and potential therapeutic targets.

METHODS

We analyzed gene expression data from 7826 prospectively collected prostatectomy samples (2013-2016), and 1567 retrospective samples with long-term clinical outcomes, for a total of 9393 samples, all profiled on the same commercial clinical platform in a CLIA-certified lab. The primary outcome was distant metastasis-free survival (DMFS). Secondary outcomes included biochemical recurrence-free survival (bRFS), prostate cancer-specific survival (PCSS), and overall survival (OS). All statistical tests were two-sided.

RESULTS

Unsupervised hierarchical clustering of hallmark pathways demonstrated an immune-related tumor cluster. Increased estimated immune content scores based on immune-specific genes from the literature were associated with worse bRFS (hazard ratio [HR] = 1.26 [95% confidence interval [CI] = 1.12 to 1.42]; P < .001), DMFS (HR = 1.34 [95% CI = 1.13 to 1.58]; P < .001), PCSS (HR = 1.53 [95% CI = 1.21 to 1.92]; P < .001), and OS (HR = 1.27 [95% CI = 1.07 to 1.50]; P = .006). Deconvolution using Cibersort revealed that mast cells, natural killer cells, and dendritic cells conferred improved DMFS, whereas macrophages and T-cells conferred worse DMFS. Interestingly, while PD-L1 was not prognostic, consistent with its low expression in prostate cancer, PD-L2 was expressed at statistically significantly higher levels (P < .001) and was associated with worse bRFS (HR = 1.17 [95% CI = 1.03 to 1.33]; P = .01), DMFS (HR = 1.25 [95% CI = 1.05 to 1.49]; P = .01), and PCSS (HR = 1.45 [95% CI = 1.13 to 1.86]; P = .003). PD-L2 was strongly associated with immune-related pathways on gene set enrichment analysis suggesting that it is playing an important role in immune modulation in clinical prostate cancer samples. Furthermore, PD-L2 was correlated with radiation response pathways, and also predicted response to postoperative radiation therapy (PORT) on multivariable interaction analysis (P = .03).

CONCLUSION

In the largest study of its kind to date, these results illustrate the complex relationship between the tumor-immune interaction, prognosis, and response to radiotherapy, and nominate PD-L2 as a potential novel therapeutic target in prostate cancer, potentially in combination with radiotherapy.

A Bayesian Phase I/II Trial Design for Immunotherapy

Immunotherapy is an innovative treatment approach that stimulates a patient's immune system to fight cancer. It demonstrates characteristics distinct from conventional chemotherapy and stands to revolutionize cancer treatment. We propose a Bayesian phase I/II dosefinding design that incorporates the unique features of immunotherapy by simultaneously considering three outcomes: immune response, toxicity and efficacy. The objective is to identify the biologically optimal dose, defined as the dose with the highest desirability in the risk-benefit tradeoff. An Emax model is utilized to describe the marginal distribution of the immune response. Conditional on the immune response, we jointly model toxicity and efficacy using a latent variable approach. Using the accumulating data, we adaptively randomize patients to experimental doses based on the continuously updated model estimates. A simulation study shows that our proposed design has good operating characteristics in terms of selecting the target dose and allocating patients to the target dose.

Morphological changes induced by intraprostatic PSA-based vaccine in prostate cancer biopsies (phase I clinical trial)

Immunotherapy is a novel treatment for many tumors including prostate cancer. Little is known about the histological changes in prostate biopsies caused by the prostate-specific antigen (PSA)-based vaccine. This study evaluated the histopathological effects in prostate biopsies of recombinant fowlpox (rF) virus-based vaccine engineered to present the PSA and 3 costimulatory molecules (collectively labeled as PSA-TRICOM). This vaccine has shown that it can break tolerance of the PSA, and its administration directly into a tumor enables the affected tumor cells to act as antigen-presenting cells activating new T cells and broadening the immune response to recognize and kill tumor. We studied 10 patients with recurrent prostate cancer who had failed radiation therapy and/or androgen-deprivation therapy. Pre- and posttreatment biopsies were compared. Posttreatment biopsies induced 8 cases with residual adenocarcinoma despite evidences of treatment effect and inflammation, 2 cases did not show any residual tumor, and 1 one case did not have any inflammatory infiltrate or any evidence of treatment effect. The inflammatory infiltrate varied from mild to severe and was composed of mononuclear cells. Greater numbers of infiltrating CD8+ lymphocytes were identified around prostatic glands and within the epithelial lining. The most remarkable feature was the presence of increased eosinophils around the glands and stroma. Three cases showed areas of necrosis surrounded by lymphocytes and palisading epithelioid macrophages arranged in granuloma-like pattern with multinucleated giant cells. This description of these morphological changes induced by the PSA-TRICOM will help to interpret the results of future intratumoral vaccine therapy trials.

Neoadjuvant therapy for localized prostate cancer: Examining mechanism of action and efficacy within the tumor

OBJECTIVES

Efforts to improve the clinical outcome for patients with localized high-risk prostate cancer have led to the development of neoadjuvant systemic therapies. We review the different modalities of neoadjuvant therapies for localized prostate cancer and highlight emerging treatment approaches including immunotherapy and targeted therapy.

METHODS

We performed a PubMed search of clinical trials evaluating preoperative systemic therapies for treating high-risk prostate cancer published after 2000, and those studies with the highest clinical relevance to current treatment approaches were selected for review. The database at clinicaltrials.gov was queried for neoadjuvant studies in high-risk prostate cancer, and those evaluating novel targeted therapies and immunotherapies are spotlighted here.

RESULTS

Neoadjuvant chemotherapy has become standard of care for treating some malignancies, including breast and bladder cancers. In prostate cancer, preoperative hormonal therapy or chemotherapy has failed to demonstrate improvements in overall survival. Nevertheless, the emergence of novel treatment modalities such as targeted small molecules and immunotherapy has spawned neoadjuvant clinical trials that provide a unique vantage from which to study mechanism of action and biological potency. Tissue-based biomarkers are being developed to elucidate the biological efficacy of these treatments. With targeted therapy, these can include phospho-proteomic signatures of target pathway activation and deactivation. With immunotherapies, including sipuleucel-T and ipilimumab, recruitment of immune cells to the tumor microenvironment can also be used as robust markers of a biological effect. Such studies can provide insight not only into mechanism of action for these therapies but can also provide paths forward to improving clinical efficacy like with rationally designed combinations and dose selection.

CONCLUSIONS

The use of neoadjuvant androgen-deprivation therapy and chemotherapy either singly or in combination before radical prostatectomy is generally safe and feasible while reducing prostate volume and tumor burden. However, pathologic complete response rates are low and no long-term survival benefit has been observed with the addition of neoadjuvant therapies over surgery alone at present, and therefore preoperative therapy is not the current standard of care in prostate cancer treatment.

Anti-tumor effect of the alphavirus-based virus-like particle vector expressing prostate-specific antigen in a HLA-DR transgenic mouse model of prostate cancer

The goal of this study was to determine if an alphavirus-based vaccine encoding human Prostate-Specific Antigen (PSA) could generate an effective anti-tumor immune response in a stringent mouse model of prostate cancer. DR2bxPSA F1 male mice expressing human PSA and HLA-DRB1(*)1501 transgenes were vaccinated with virus-like particle vector encoding PSA (VLPV-PSA) followed by the challenge with Transgenic Adenocarcinoma of Mouse Prostate cells engineered to express PSA (TRAMP-PSA). PSA-specific cellular and humoral immune responses were measured before and after tumor challenge. PSA and CD8 reactivity in the tumors was detected by immunohistochemistry. Tumor growth was compared in vaccinated and control groups. We found that VLPV-PSA could infect mouse dendritic cells in vitro and induce a robust PSA-specific immune response in vivo. A substantial proportion of splenic CD8 T cells (19.6 ± 7.4%) produced IFNγ in response to the immunodominant peptide PSA(65-73). In the blood of vaccinated mice, 18.4 ± 4.1% of CD8 T cells were PSA-specific as determined by the staining with H-2D(b)/PSA(65-73) dextramers. VLPV-PSA vaccination also strongly stimulated production of IgG2a/b anti-PSA antibodies. Tumors in vaccinated mice showed low levels of PSA expression and significant CD8+ T cell infiltration. Tumor growth in VLPV-PSA vaccinated mice was significantly delayed at early time points (p=0.002, Gehan-Breslow test). Our data suggest that TC-83-based VLPV-PSA vaccine can efficiently overcome immune tolerance to PSA, mediate rapid clearance of PSA-expressing tumor cells and delay tumor growth. The VLPV-PSA vaccine will undergo further testing for the immunotherapy of prostate cancer.

Overcoming tumor-mediated immunosuppression

Mechanisms of tumor-mediated immunosuppression have been described for several solid and hematological tumors. Tumors inhibit immune responses by attraction of immunosuppressive lymphocytic populations, secretion of immunosuppressive cytokines or expression of surface molecules, which inhibit immune responses by induction of anergy or apoptosis in tumor-infiltrating lymphocytes. This tumor-mediated immunosuppression represents a major obstacle to many immunotherapeutic or conventional therapeutic approaches. In this review we discuss how tumor-mediated immunosuppression interferes with different immunotherapeutic approaches and then give an overview of strategies to overcome it. Particular emphasis is placed on agents or approaches already transferred into clinical settings. Finally the success of immune checkpoint inhibitors targeting CTLA-4 or the PD-1 pathway highlights the enormous therapeutic potential of an effective overcoming of tumor-mediated immunosuppression.

Challenges of managing elderly men with prostate cancer

The incidence of prostate cancer increases with age. Current evidence suggests that prostate cancer is under treated in patients aged ≥70 years, despite evidence of efficacy and acceptable toxicity. Radical cystectomy and definitive radiotherapy are often denied owing to fears of post-operative complications and radiotherapy-associated gastrointestinal and genitourinary toxicity. However, modern radical prostatectomy techniques provide excellent clinical outcomes with low perioperative morbidity. Moreover, volume-restricted intensity-modulated radiation therapy is a significant improvement over previous 2D conformal radiotherapy with similar efficacy and lower toxicity. Androgen-deprivation therapy is also under-prescribed among the elderly, owing to concerns of increases in cardiac deaths and osteoporosis acceleration. However, prospective trials have not identified any increase in cardiovascular mortality among elderly men receiving androgen-deprivation therapy compared to age-matched controls. Most patients on androgen deprivation eventually progress to a castration-resistant state. At this stage, the disease still responds to newer agents that target the androgen pathway and to chemotherapy. Among the elderly, chemotherapy is under-prescribed even though it has been demonstrated to be palliative and improve survival. We describe the trends in prostate cancer management in the elderly and the importance of assessing comorbidity status, tumour characteristics, and health status, including a complete geriatric evaluation, before making treatment recommendations.

Development of thyroglobulin antibodies after GVAX immunotherapy is associated with prolonged survival

Cancer immunotherapy induces a variety of autoinflammatory responses, including those against the thyroid gland, which can be exploited to predict clinical outcomes. Considering the paucity of information about thyroid autoimmunity in patients receiving cancer vaccines, we designed our study to assess the development of thyroglobulin antibodies (TgAbs) in patients treated with GVAX (vaccine made of a tumor cell type transfected with GM-CSF) and/or ipilimumab and correlated seroconversion with survival. Using both in house and commercial ELISA assays, we measured TgAbs in patients with pancreatic (No. = 53), prostate (No. = 35) or colon (No. = 8) cancer, before and after treatment with GVAX only (No. = 34), GVAX plus ipilimumab (No. = 42) or ipilimumab (No. = 20), and correlated their levels with patient's survival, disease status and T-cell surface markers. Antibodies to thyroperoxidase, myeloperoxidase, proteinase 3, insulin and actin were also measured. TgAbs specifically developed after GVAX, independent of the underlying cancer (81% in prostate, 75% colon cancer and 76% pancreatic cancer) and co-administration of ipilimumab (75% in GVAX only and 78% in GVAX plus ipilimumab). This TgAbs seroconversion could be detected mainly by the in house assay, suggesting that the thyroglobulin epitopes recognized by the antibodies induced by GVAX are different from the epitopes seen in the classic form of Hashimoto thyroiditis. Notably, TgAbs seroconversion was associated with significantly prolonged survival (p = 0.01 for pancreas and p = 0.005 for prostate cancer). In conclusion, GVAX immunotherapy induces the appearance of TgAbs that recognize a unique antigenic repertoire and associate with prolonged survival.

Immunotherapy for prostate cancer: lessons from responses to tumor-associated antigens

Prostate cancer (PCa) is the most common cancer in men and the second most common cause of cancer-related death in men. In recent years, novel therapeutic options for PCa have been developed and studied extensively in clinical trials. Sipuleucel-T is the first cell-based immunotherapeutic vaccine for treatment of cancer. This vaccine consists of autologous mononuclear cells stimulated and loaded with an immunostimulatory fusion protein containing the prostate tumor antigen prostate acid posphatase. The choice of antigen might be key for the efficiency of cell-based immunotherapy. Depending on the treatment strategy, target antigens should be immunogenic, abundantly expressed by tumor cells, and preferably functionally important for the tumor to prevent loss of antigen expression. Autoimmune responses have been reported against several antigens expressed in the prostate, indicating that PCa is a suitable target for immunotherapy. In this review, we will discuss PCa antigens that exhibit immunogenic features and/or have been targeted in immunotherapeutic settings with promising results, and we highlight the hurdles and opportunities for cancer immunotherapy.

CD8+ T-cell responses rapidly select for antigen-negative tumor cells in the prostate

Stimulation of patients' immune systems for the treatment of solid tumors is an emerging therapeutic paradigm. The use of enriched autologous T cells for adoptive cell therapy or vaccination with antigen-loaded dendritic cells have shown clinical efficacy in melanoma and prostate cancer, respectively. However, the long-term effects of immune responses on selection and outgrowth of antigen-negative tumor cells in specific tumor types must be determined to understand and achieve long-term therapeutic effects. In this study, we have investigated the expression of a tumor-specific antigen in situ after treatment with tumor-specific CD8(+) T cells in an autochthonous mouse model of prostate cancer. After T-cell treatment, aggregates of dead antigen-positive tumor cells were concentrated in the lumen of the prostate gland and were eventually eliminated from the prostate tissue. Despite the elimination of antigen-positive tumor cells, prostate tumor continued to grow in T-cell-treated mice. Interestingly, the remaining tumor cells were antigen negative and downregulated MHC class I expression. These results show that CD8(+) T cells are effective in eliminating antigen-bearing prostate tumor cells but they also can select for the outgrowth of antigen-negative tumor cells. These findings provide insights into the requirements for an effective cancer immunotherapy within the prostate that not only induces potent immune responses but also avoids selection and outgrowth of antigen-negative tumor cells.

Melanoma of non-sun exposed skin in a man with previous prostate cancer: recognition of a recently confirmed association

Background

The association of an increased risk to develop melanoma in patients with prostate cancer has recently been confirmed.

Purpose

The postulated etiologic relationship between prostate cancer and the subsequent occurrence of melanoma is discussed.

Methods

A man with previous prostate cancer who developed melanoma on the plantar surface of his left great toe is described and the possibility of high levels of endogenous androgens promoting not only prostate cancer, but also increased risk of melanoma are reviewed.

Results

Modification of the host immune response, alteration of chromosome telomere length, and/or imbalance of androgen level (presenting as severe teenage acne) are potential mechanisms whereby high levels of endogenous androgens may contribute to the association between prostate cancer and risk of melanoma.

Conclusions

An increased surveillance for melanoma should be considered in prostate cancer patients. Complete skin examination in men who have had prostate cancer—especially in those individuals diagnosed with prostate cancer prior to age 68 years—should regularly be performed.

Electronic supplementary material

The online version of this article (doi:10.1007/s13555-014-0045-2) contains supplementary material, which is available to authorized users.

Molecular alterations and emerging targets in castration resistant prostate cancer

Prostate cancer is the most common malignancy in Western Europe, of which approximately 10-20% presents with advanced or metastatic disease. Initial response with androgen deprivation therapy is almost universal, but progression to castration resistant prostate cancer (CRPC), an incurable disease, occurs in approximately 2-3 years. In recent years, the novel taxane cabazitaxel, the hormonal agents abiraterone and enzalutamide, the immunotherapeutic agent sipuleucel-T and the radiopharmaceutical radium-223 have been shown to prolong survival in large randomised trials, thus widely increasing the therapeutic armamentarium against the disease. Despite these advances, the median survival in the first-line setting of metastatic castration-resistant prostate cancer (mCRPC) is still up to 25 months and in the post-docetaxel setting is about 15-18 months. There is an urgent need for the development of biomarkers of treatment response, and for a deeper understanding of tumour heterogeneity and the molecular biology underlying the disease. In this review, we attempt to provide insight into the novel molecular targets showing promise in clinical trials.

Personal history of prostate cancer and increased risk of incident melanoma in the United States

PURPOSE

Steroid hormones, particularly androgens, play a major role in prostatic carcinogenesis. Personal history of severe acne, a surrogate for higher androgen activity, has been associated with an increased risk of prostate cancer (PCa), and one recent study indicated that severe teenage acne was a novel risk factor for melanoma. These findings suggest a possible relationship between PCa and risk of melanoma. We prospectively evaluated this association among US men.

METHODS

A total of 42,372 participants in the Health Professionals' Follow-Up Study (HPFS; 1986 to 2010) were included. Biennially self-reported PCa diagnosis was confirmed using pathology reports. Diagnosis of melanoma and nonmelanoma skin cancer (NMSC) was self-reported biennially, and diagnosis of melanoma was pathologically confirmed. We sought to confirm the association in 18,603 participants from the Physicians' Health Study (PHS; 1982 to 1998).

RESULTS

We identified 539 melanomas in the HPFS. Personal history of PCa was associated with an increased risk of melanoma (multivariate-adjusted hazard ratio [HR], 1.83; 95% CI, 1.32 to 2.54). Although we also detected a marginally increased risk of NMSC associated with PCa (HR, 1.08; 95% CI, 0.995 to 1.16), the difference in the magnitude of the association between melanoma and NMSC was significant (P for heterogeneity = .002). We did not find an altered risk of melanoma associated with personal history of other cancers. The association between PCa and risk of incident melanoma was confirmed in the PHS (HR, 2.17; 95% CI, 1.12 to 4.21).

CONCLUSION

Personal history of PCa is associated with an increased risk of melanoma, which may not be entirely a result of greater medical scrutiny.

Novel therapeutic approaches for the treatment of castration-resistant prostate cancer

Prostate cancer is a leading cause of cancer death in men in developed countries. Once the tumor has achieved a castration-refractory metastatic stage, treatment options are limited with the average survival of patients ranging from two to three years only. Recently, new drugs for treatment of castration-resistant prostate cancer (CRPC) have been approved, and others are in an advanced stage of clinical testing. In this review we provide an overview of the new therapeutic agents that arrived in the clinical praxis or are tested in clinical studies and their mode of action including hormone synthesis inhibitors, new androgen receptor blockers, bone targeting and antiangiogenic agents, endothelin receptor antagonists, growth factor inhibitors, novel radiotherapeutics and taxanes, and immunotherapeutic approaches. Results and limitations from clinical studies as well as future needs for improvement of CRPC treatments are critically discussed.

Prostate cancer vaccines

In 2010, the US FDA approved the first therapeutic cancer vaccine for the treatment of castration refractory prostate cancer - sipuleucel-T. Prostate cancer is an ideal model for cancer vaccine development based on the ready demonstration of humoral and cellular immunity to a range of cancer antigens as well as often slow progression which means that patients who are otherwise well may have a radiologically evaluable minor progression, after conventional treatment and can undergo vaccine therapy over sufficient periods of time, so as to allow the generation of a robust antitumor response. The association of prostate cancer with one of the few serum cancer biomarkers in general use has also allowed assessment of response and risk stratification of patients. In this review, we will examine key aspects of the evolution of prostate cancer vaccines, which provides an accurate prototype for other cancers, and the challenges we face.

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.

Reciprocal complementation of the tumoricidal effects of radiation and natural killer cells

The tumor microenvironment is a key determinant for radio-responsiveness. Immune cells play an important role in shaping tumor microenvironments; however, there is limited understanding of how natural killer (NK) cells can enhance radiation effects. This study aimed to assess the mechanism of reciprocal complementation of radiation and NK cells on tumor killing. Various tumor cell lines were co-cultured with human primary NK cells or NK cell line (NK-92) for short periods and then exposed to irradiation. Cell proliferation, apoptosis and transwell assays were performed to assess apoptotic efficacy and cell viability. Western blot analysis and immunoprecipitation methods were used to determine XIAP (X-linked inhibitor of apoptosis protein) and Smac (second mitochondria-derived activator of caspase) expression and interaction in tumor cells. Co-culture did not induce apoptosis in tumor cells, but a time- and dose-dependent enhancing effect was found when co-cultured cells were irradiated. A key role for caspase activation via perforin/granzyme B (Grz B) after cell-cell contact was determined, as the primary radiation enhancing effect. The efficacy of NK cell killing was attenuated by upregulation of XIAP to bind caspase-3 in tumor cells to escape apoptosis. Knockdown of XIAP effectively potentiated NK cell-mediated apoptosis. Radiation induced Smac released from mitochondria and neutralized XIAP and therefore increased the NK killing. Our findings suggest NK cells in tumor microenvironment have direct radiosensitization effect through Grz B injection while radiation enhances NK cytotoxicity through triggering Smac release.

Is there a role for immune checkpoint blockade with ipilimumab in prostate cancer?

Treatment for advanced prostate cancer has and will continue to grow increasingly complex, owing to the introduction of multiple new therapeutic approaches with the potential to substantially improve outcomes for this disease. Agents that modulate the patient's immune system to fight prostate cancer - immunotherapeutics - are among the most exciting of these new approaches. The addition of antigen-specific immunotherapy to the treatment of castration-resistant prostate cancer (CRPC) has paved the way for additional research that seeks to augment the activity of the immune system itself. The monoclonal antibody ipilimumab, approved in over 40 countries to treat advanced melanoma and currently under phase 2 and 3 investigation in prostate cancer, is thought to act by augmenting immune responses to tumors through blockade of cytotoxic T-lymphocyte antigen 4, an inhibitory immune checkpoint molecule. Ipilimumab has been studied in seven phase 1 and 2 clinical trials that evaluated various doses, schedules, and combinations across the spectrum of patients with advanced prostate cancer. The CRPC studies of ipilimumab to date suggest that the agent is active in prostate cancer as monotherapy or in combination with radiotherapy, docetaxel, or other immunotherapeutics, and that the adverse event profile is as expected given the safety data in advanced melanoma. The ongoing phase 3 program will further characterize the risk/benefit profile of ipilimumab in chemotherapy-naïve and -pretreated CRPC.

Over-expressing transporters associated with antigen processing increases antitumor immunity response in prostate cancer

As we know, prostate cancer down-regulates expression of HLA-1 Antigen Processing Machinery (APM) and has defects in the antigen presentation pathway. In vitro, the prostate cancer cell (PC-3 cells) infected with Lentivirus TAP1 can efficiently over-express TAP1 and Tapasin, and HLA-1 was also up-regulated on the surface of the infected cells. The lentivirus TAP1 infection increased the apoptosis rate of PC-3 cells. In addition, with the co-cluture PC-3 cells and lymphocytes, TAP1 augmented the expression of CD3⁺CD8⁺CD38⁺ T cell. Importantly, administration of Lentivirus TAP1 to prostate cancer cells in a xenograft mouse model can prolong survival and increase the CD4⁺ T cells, and CD8⁺ T cells as well as decrease Foxp3⁺ T cells in the tumor microenvironment. In summary, a recombinant lentivirus expressing TAP1 can effectively increase prostate cancer tumor-specific immune response.

Quality of life during dendritic cell vaccination against metastatic renal cell carcinoma

Patients with metastatic renal cell carcinoma (RCC) undergoing cytokine or targeted therapies may show a remarkable decline in quality of life (QoL). We wanted to evaluate QoL in patients with metastatic RCC undergoing therapeutic vaccination with dendritic cells (DCs). In a cross-sectional analysis, QoL was therefore assessed in RCC patients participating in three consecutive clinical trials of DC vaccination. Before the first and after the third vaccination with DCs, patients completed a QoL questionnaire (EORTC QLQ-C30, version 3). Data were transformed into scale scores and analysed using SPSS 12.0 software. Mean values of the resulting scores obtained before and after DC vaccination were compared using students t test and Wilcoxon rank-sum test. P < 0.05 was considered statistically significant. The questionnaire was completed by 55 of 71 patients (compliance rate, 77.5%) who had a median age of 58.7 years (from 30 to 75 years). No significant reductions in functioning scales including physical, emotional and social criteria as well as symptom scores, which assess typical symptoms of tumour therapies, were observed indicating that QoL remained high during DC vaccination. Significant correlations were found between overall survival and functional as well as symptom scores. Our data indicate that DC vaccination, which is a personalised treatment modality, maintains QoL and thus represents an attractive nontoxic treatment option for patients with metastatic RCC. It will be important to identify the most effective conditions of DC vaccination including combinations with other therapeutics to maximise clinical efficacy while still preserving QoL.

In situ vaccination with CD204 gene-silenced dendritic cell, not unmodified dendritic cell, enhances radiation therapy of prostate cancer

Given the complexity of prostate cancer progression and metastasis, multimodalities that target different aspects of tumor biology, for example, radiotherapy in conjunction with immunotherapy, may provide the best opportunities for promoting clinical benefits in patients with high-risk localized prostate cancer. Here, we show that intratumoral administration of unmodified dendritic cells (DC) failed to synergize with fractionated radiotherapy. However, ionizing radiation combined with in situ vaccination with DCs, in which the immunosuppressive scavenger receptor A (SRA/CD204) has been downregulated by lentivirus-mediated gene silencing, profoundly suppressed the growth of two mouse prostate cancers (e.g., RM1 and TRAMP-C2) and prolonged the lifespan of tumor-bearing animals. Treatment of subcutaneous tumors with this novel combinatorial radioimmunotherapeutic regimen resulted in a significant reduction in distant experimental metastases. SRA/CD204-silenced DCs were highly efficient in generating antigen or tumor-specific T cells with increased effector functions (e.g., cytokine production and tumoricidal activity). SRA/CD204 silencing-enhanced tumor cell death was associated with elevated IFN-γ levels in tumor tissue and increased tumor-infiltrating CD8(+) cells. IFN-γ neutralization or depletion of CD8(+) cells abrogated the SRA/CD204 downregulation-promoted antitumor efficacy, indicating a critical role of IFN-γ-producing CD8(+) T cells. Therefore, blocking SRA/CD204 activity significantly enhances the therapeutic potency of local radiotherapy combined with in situ DC vaccination by promoting a robust systemic antitumor immunity. Further studies are warranted to test this novel combinatorial approach for translating into improved clinical outcomes in patients with prostate cancer.

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.

Tumor-associated antigens for specific immunotherapy of prostate cancer

Prostate cancer (PCa) is the most common noncutaneous cancer diagnosis and the second leading cause of cancer-related deaths among men in the United States. Effective treatment modalities for advanced metastatic PCa are limited. Immunotherapeutic strategies based on T cells and antibodies represent interesting approaches to prevent progression from localized to advanced PCa and to improve survival outcomes for patients with advanced disease. CD8⁺ cytotoxic T lymphocytes (CTLs) efficiently recognize and destroy tumor cells. CD4⁺ T cells augment the antigen-presenting capacity of dendritic cells and promote the expansion of tumor-reactive CTLs. Antibodies mediate their antitumor effects via antibody-dependent cellular cytotoxicity, activation of the complement system, improving the uptake of coated tumor cells by phagocytes, and the functional interference of biological pathways essential for tumor growth. Consequently, several tumor-associated antigens (TAAs) have been identified that represent promising targets for T cell- or antibody-based immunotherapy. These TAAs comprise proteins preferentially expressed in normal and malignant prostate tissues and molecules which are not predominantly restricted to the prostate, but are overexpressed in various tumor entities including PCa. Clinical trials provide evidence that specific immunotherapeutic strategies using such TAAs represent safe and feasible concepts for the induction of immunological and clinical responses in PCa patients. However, further improvement of the current approaches is required which may be achieved by combining T cell- and/or antibody-based strategies with radio-, hormone-, chemo- or antiangiogenic therapy.

[Immunotherapy for metastatic prostate cancer: do we really need this?]

Following the approval of Sipuleucel-T, the development of new immunomodulatory approaches such as ipilimumab and tasquinimod, and the development of new antihormonal drugs (abiraterone acetate, MDV3100, TAK-700), treatment of castration-resistant prostate cancer is finally reaching a new era of management. Docetaxel based chemotherapy remains the standard treatment of choice for patients with a high tumour burden, rapidly progressiong castration resistant prostate cancer, and poorly differentiated prostate cancer. Sipuleucel-T might be an option in the pre-docetaxel management of castration-resistant prostate cancer resulting in a 4-months improvement of overall survival. However, as with all other modalities of immunotherapy patients with good prognostic factors such as minimal tumour burden, slow PSA doubling time, Gleason score ≤ 7, and a long survival probability of > 1 year might be the best candidates taking into account that immunomodulatory approaches demonstrate positive responses after 4-6 months of therapy. Ipilimumab and tasqunimod as inhibitors of the immune checkpoints are additional, promising therapeutic agents with high clinical potential. It is the aim of the current article to critically review the current options of immune therapy in men with castration resistant prostate cancer.

Current vaccination strategies for prostate cancer

CONTEXT

The first therapeutic cancer vaccine demonstrating effectiveness in a phase 3 study was approved by the US Food and Drug Administration on 29 April 2010. The pivotal trial demonstrated overall survival (OS) benefit in patients treated with antigen-loaded leukapheresis cells compared with a control infusion. Results of other prostate cancer (PCa) vaccination strategies are awaited, as this approach may herald a new era in the care for patients with advanced PCa.

OBJECTIVE

Consider effectiveness and safety of vaccination strategies in the treatment of PCa.

EVIDENCE ACQUISITION

We searched three bibliographic databases (January 1995 through October 2010) for randomised phase 2 and 3 studies of vaccination strategies for PCa based on predetermined relevant Medical Subject Heading terms and free text terms.

EVIDENCE SYNTHESIS

Data from 3 randomised phase 3 and 10 randomised phase 2 vaccination trials are discussed with respect to clinical outcome in terms of progression-free survival and OS, toxicity, prostate-specific antigen (PSA) response, and immunologic response. Three phase 3 trials (D9901, D9902A, and D9902B) that enrolled a total of 737 patients, all controlled and double-blinded, tested the efficacy of sipuleucel-T. The largest of these three trials, called Immunotherapy for Prostate Adenocarcinoma Treatment (IMPACT), has demonstrated safety and effectiveness of sipuleucel-T (now marketed as Provenge) as measured by prolonged survival of 512 asymptomatic patients with metastatic castration-resistant PCa (mCRPC). The study showed a 4.1-mo median survival benefit in the sipuleucel-T vaccine-treated group compared with the control group (25.8 vs 21.7 mo; hazard ratio [HR]: 0.78; 95% confidence interval [CI], 0.62-0.98; p=0.032) and extended 3-yr survival (31.7% vs 23.0%). In contrast, two phase 3 vaccination trials with a whole-tumour-cell mixture of two PCa cell lines (GVAX) and testing GVAX either alone or in combination with chemotherapy versus chemotherapy alone (VITAL1 and 2) were terminated prematurely based on futility and increased deaths. Other phase 2 vaccination trials testing different types of vaccines in castration-resistant PCa patients have been reported with variable outcomes. Notably, a controlled, double-blind, randomised phase 2 vaccine trial of PROSTVAC-VF, a recombinant viral vector containing complementary DNA encoding PSA, in 125 patients with chemotherapy-naïve, minimally symptomatic mCRPC also demonstrated safety but no significant effect on the time to disease progression. In comparison with controls (n=40), PROSTVAC-VF-treated patients (n=82) experienced longer median survival of 8.5 mo (25.1 vs 16.6 mo; HR: 0.56; 95% CI, 0.37-0.85; p=0.0061) and extended 3-yr survival (30% vs 17%). In general, PCa vaccines are perceived to have less toxicity compared with current cytotoxic or targeted therapies. Evaluation of clinical efficacy of different vaccination strategies (eg, protein-, peptide- and DNA-based vaccines) in the context of properly designed and controlled phase 3 studies is warranted.

CONCLUSIONS

Cancer vaccines represent a new paradigm in the treatment of PCa. The IMPACT trial showed improved survival but no difference in time to disease progression in mCRPC patients with minimal tumour burden. Observations in phase 2 and 3 trials pave the way for other vaccination approaches for this disease, raise questions regarding the most appropriate clinical trial designs, and underscore the importance of identifying biomarkers for antitumour effect to better implement such therapies.