Immunotherapy for prostate cancer

Immunodiagnostics and Immunotherapy Possibilities for Prostate Cancer

Despite significant progress in early detection and improved treatment modalities prostate cancer remains the second leading cause of cancer death in American men which results in about 30,000 deaths per year in the USA. An aggressive phenotype leading to 2.58% risk of dying from prostate cancer still exists and immunotherapy has offered new possibilities to treat metastatic prostate cancer that cannot be treated by other modalities. Cancer immunotherapy is a rapidly growing field of research aimed at identifying biomarkers in immunodiagnosis and to develop new therapies by enabling the immune system to detect and destroy cancer cells. Immunotherapy falls into three different broad categories which are checkpoint inhibitors, cytokines, and vaccine immunotherapy. While immunotherapy to treat prostate cancer is still limited progress has been made; for treatment of advanced prostate cancer sipuleucel-T has been administered to patients in personalized doses to destroy prostate cancer cells which is promising and invites further research to determine immunotherapies for advanced prostate cancer. Antibody-based targeted immunotherapy and dendritic-cell-based vaccination are among the therapies that are currently being evaluated as promising approaches to treat prostate cancer. Combination immunotherapies include prostate cancer vaccines and radiotherapy for castration resistant prostate cancer. Microbial vectors for prostate cancer immunotherapy have been developed and bacterial strains have been engineered to express cancer-specific antigens, cytokines, and prodrug-converting cytokines. These approaches are addressed in the present review.

Cell-based Hyper-interleukin 6 or Hyper-interleukin 11 secreting vaccines combined with low dose cyclophosphamide in an orthotopic murine prostate cancer model

Background

Cell based vaccines encoding Hyper-IL-6 (H6) and Hyper-IL-11 (H11) present high activity in murine melanoma and renal cancer model. We evaluated the efficacy of cellular vaccines modified with H6 or H11 combined with cyclophosphamide in orthotopic murine prostate cancer model.

Material and methods

TRAMP cells were transduced with H6 and H11 cDNA (TRAMP-H6 and TRAMP-H11). An orthotopic TRAMP model based on the implantation of TRAMP cells into the dorsolateral lobe of the prostate of C57BL6/J mice was employed. The efficacy of TRAMP-H6 and TRAMP-H11 vaccines evaluated in the therapeutic setting was compared with the TRAMP cells modified with a mock transduced E1-deleted adenoviral vector (TRAMP-AdV) and non-modified irradiated TRAMP cells (TRAMP IRR) in relation to naive (non-immunized) mice. In the next experimental groups mice vaccinated with TRAMP-H6 and TRAMP-H11 received cyclophosphamide (CY). Detection of immune cells in the spleen in mice receiving vaccines combined with CY was evaluated.

Results

Modification of TRAMP cells with H6 increased the efficacy of TRAMP-based whole-cell vaccine. The highest response rate was observed in mice receiving TRAMP-H6 alone and combined with CY. Vaccination with TRAMP-H6 alone and combined with CY and TRAMP H11 combined with CY extended median OS of mice bearing orthotopic TRAMP tumors in therapeutic setting. Low dose CY administered alone demonstrated some antitumor activity in employed model. TRAMP-H6 or TRAMP-H11 combined with CY strongly augmented generation of CD8+, CD4+ T lymphocytes and memory T cells. Immunization with TRAMP combined with or without CY suppressed generation of T regulatory cells.

Conslusions

Prostate cancer vaccines modified with H6 or H11 induce prostate tumour regression and increase mice survival by stimulating the immune system. Cyclophosphamide added to modified TRAMP vaccines demonstrated clinical benefit of treated mice and enhanced anti-tumour immune response.

Cancer immunotherapy: a paradigm shift for prostate cancer treatment

Prostate cancer remains a significant health problem for men in the Western world. Although treatment modalities are available, these do not confer long-term benefit and are accompanied by deleterious side effects. Immunotherapy represents a valuable alternative to conventional treatments by inducing tumour-specific immune responses that control the growth of cancer cells. Sipuleucel-T is approved by the FDA as an immunotherapeutic agent for the treatment of patients with asymptomatic or minimally symptomatic castration-resistant prostate cancer (CRPC). Although this approval has raised cost-versus-benefit issues, it has provided proof of concept for the therapeutic potential of active immunotherapy approaches for metastatic CRPC. Numerous clinical studies have demonstrated clinical benefit using immunotherapy compared to traditional chemotherapy and several active immunotherapy approaches (at various developmental stages)have demonstrated the potential to change the face of prostate cancer treatment.

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.

Novel targeted agents on the horizon for castration-resistant prostate cancer

Androgen deprivation treatment in prostate cancer patients is well established; however, resistance to such treatment manifests itself by progression to castration-resistant prostate cancer (CRPC). Despite significant advances in treatment options for patients with CRPC, their prognosis remains poor. Resistance results from multiple processes that facilitate cancer cell growth and survival. Mechanisms underlying the shift to castrate resistance have been attributed to a complex interplay of clonal selection, reactivation of the androgen receptor axis despite castrate levels of serum testosterone, stress-induced prosurvival genes and cytoprotective chaperone networks and alternative mitogenic growth factor pathways. This article discusses several pathways involved in the development of CRPC, with a particular focus on those mechanisms that have led to the development of new targeted therapies.

Prostate cancer as a model for tumour immunotherapy

Advances in basic immunology have led to an improved understanding of the interactions between the immune system and tumours, generating renewed interest in approaches that aim to treat cancer immunologically. As clinical and preclinical studies of tumour immunotherapy illustrate several immunological principles, a review of these data is broadly instructive and is particularly timely now that several agents are beginning to show evidence of efficacy. This is especially relevant in the case of prostate cancer, as recent approval of sipuleucel-T by the US Food and Drug Administration marks the first antigen-specific immunotherapy approved for cancer treatment. Although this Review focuses on immunotherapy for prostate cancer, the principles discussed are applicable to many tumour types, and the approaches discussed are highlighted in that context.

Immunotherapy for prostate cancer: an emerging treatment modality

This article examines prostate cancer as a target for immunotherapy and investigates active immunotherapy for prostate cancer, combining conventional therapy with active immunotherapy, immune modulators (brakes and accelerators), and monoclonal antibodies.

Cyclophosphamide augments antitumor immunity: studies in an autochthonous prostate cancer model

To study the immune response to prostate cancer, we developed an autochthonous animal model based on the transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse in which spontaneously developing tumors express influenza hemagglutinin as a unique, tumor-associated antigen. Our prior studies in these animals showed immunologic tolerance to hemagglutinin, mirroring the clinical situation in patients with cancer who are generally nonresponsive to their disease. We used this physiologically relevant animal model to assess the immunomodulatory effects of cyclophosphamide when administered in combination with an allogeneic, cell-based granulocyte-macrophage colony-stimulating factor-secreting cancer immunotherapy. Through adoptive transfer of prostate/prostate cancer-specific CD8 T cells as well as through studies of the endogenous T-cell repertoire, we found that cyclophosphamide induced a marked augmentation of the antitumor immune response. This effect was strongly dependent on both the dose and the timing of cyclophosphamide administration. Mechanistic studies showed that immune augmentation by cyclophosphamide was associated with a transient depletion of regulatory T cells in the tumor draining lymph nodes but not in the peripheral circulation. Interestingly, we also noted effects on dendritic cell phenotype; low-dose cyclophosphamide was associated with increased expression of dendritic cell maturation markers. Taken together, these data clarify the dose, timing, and mechanism of action by which immunomodulatory cyclophosphamide can be translated to a clinical setting in a combinatorial cancer treatment strategy.

CD8+ Foxp3+ regulatory T cells mediate immunosuppression in prostate cancer

PURPOSE

Although elevated proportions of CD4(+)CD25(+) regulatory T (Treg) cells have been shown in several types of cancers, very little is known about the existence and function of CD8(+) Treg cells in prostate cancer. In this study, we investigated prostate tumor-derived CD8(+) Treg cells and their function.

EXPERIMENTAL DESIGN

Tumor-infiltrating lymphocytes (TIL) from fresh tumor specimens of patients with prostate cancer were generated and subjected to phenotypic and suppressive function analyses. In particular, we investigated the role and function CD8(+) Treg cells in prostate cancer.

RESULTS

We show that high percentages of CD4(+)CD25(+) T cells are probably present in the majority (70%) of prostate TILs. Remarkably, both CD4(+) and CD8(+) T-cell subpopulations possessed potent suppressive activity. T-cell cloning and fluorescence-activated cell sorting analyses showed the presence of CD8(+)CD25(+) Treg cell clones that expressed FoxP3 and suppressed naïve T-cell proliferation, in addition to the previously known CD4(+)CD25(+) Treg cells. These CD8(+) Treg cells suppressed naïve T-cell proliferation mainly through a cell contact-dependent mechanism. Importantly, the suppressive function of CD8(+) Treg cells could be reversed by human Toll-like receptor 8 (TLR8) signaling.

CONCLUSION

Our study shows that like CD4(+)CD25(+) Treg cells, CD8(+) Foxp3(+) Treg cells present in prostate tumor-derived TILs suppress immune responses and that their suppressive function can be regulated by TLR8 ligands, raising the possibility that the manipulation of Treg cell function by TLR8 ligands could improve the efficacy of immunotherapy for prostate cancer patients.

SPAS-1 (stimulator of prostatic adenocarcinoma-specific T cells)/SH3GLB2: A prostate tumor antigen identified by CTLA-4 blockade

Discovery of immunologically relevant antigens in prostate cancer forms the basis for developing more potent active immunotherapy. We report here a strategy using the transgenic adenocarcinoma of mouse prostate (TRAMP) model, which allows for the functional identification of immunogenic prostate tumor antigens with relevance for human immunotherapy. Using a combination of active tumor vaccination in the presence of CTL-associated antigen 4 (CTLA-4) in vivo blockade, we elicited tumor-specific T cells used to expression clone the first T cell-defined TRAMP tumor antigen, called Spas-1 (stimulator of prostatic adenocarcinoma specific T cells-1). Spas-1 expression was increased in advanced primary TRAMP tumors. We show that the immunodominant SPAS-1 epitope SNC9-H(8) arose from a point mutation in one allele of the gene in TRAMP tumor cells, and that immunization with dendritic cells pulsed with SNC9-H(8) peptide resulted in protection against TRAMP-C2 tumor challenge. In humans, the Spas-1 ortholog SH3GLB2 has been reported to be overexpressed in prostate cancer metastases. Additionally, we identified a nonmutated HLA-A2-binding epitope in the human ortholog SH3GLB2, which primed T cells from healthy HLA-A2(+) individuals in vitro. Importantly, in vitro-primed T cells also recognized naturally processed and presented SH3GLB2. Our findings demonstrate that our in vivo CTLA-4 blockade-based T cell expression cloning can identify immunogenic cancer antigens with potential relevance for human immunotherapy.

Prostate cancer: genes, environment, immunity and the use of immunotherapy

Prostate cancer remains the most prevalent noncutaneous cancer, leading to almost 30,000 deaths every year in men in the United States. A large body of knowledge emphasizes a strong influence of epidemiological factors such as lifestyle, environment and diet, on the development of prostate cancer. Although risk reduction of prostate cancer has been somewhat successful, effective prevention is still lacking. Immunotherapeutic approaches, although moderately complicated, remain promising in an effort to control the progression and development of the disease. Taken together, the parameters of epidemiological studies and immunotherapeutic regimens might eventually be the most effective and preventive approach for prostate cancer. This review highlights some of the events associated with the development and prevention of prostate cancer.