Vaccines as treatment strategies for relapsed prostate cancer: approaches for induction of immunity

Prostate-Specific Membrane Antigen Vaccines: Naked DNA and Protein Approaches

Prostate-specific membrane antigen (PSMA) is a relatively omnipresent molecule with a multiplicity of functions and has been shown to be a reasonable target for immunologic approaches such as vaccines or more directed therapy with radioactively labeled monoclonal antibodies against PSMA. Given the abundance of various glycoprotein and carbohydrate antigens expressed on the surface of prostate cancer cells and cell lines, PSMA stands out as another self-antigen that is not only expressed on cancer cells but also on neovasculature. Although vaccines are varied in their design and target goal, recent technology has afforded researchers the opportunity to induce recruitment of multiple effector cell populations, cytokines, and factors that can elicit cellular and humoral responses. This review serves to present unique approaches in vaccine development that can induce immunologic responsiveness to PSMA with potential impact on disease progression.

Targeting novel antigens for prostate cancer treatment: focus on prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA) is a relatively omnipresent, but unique Type II dimeric transmembrane protein with a multiplicity of functions and has been shown to be a reasonable target for immunological approaches such as vaccines or more directed therapy with radioactively labelled monoclonal antibodies against PSMA. Given the abundance of various glycoprotein and carbohydrate antigens expressed on the surface of prostate cancer cells and cell lines, PSMA stands out as another 'self' antigen which is not only expressed on cancer cells, but on neovasculature. Although vaccines are varied in their design and target goal, recent technology has afforded researchers the opportunity to induce recruitment of multiple effector cell populations, cytokines and factors which can elicit both cellular and humoral responses. This review serves to present unique approaches in vaccine development which can induce immunological responsiveness with potential impact on disease progression and to introduce PSMA as a potential target for multimodality therapies.

Immune-based therapies for prostate cancer

Prostate cancer is a leading cause of cancer morbidity and mortality in the United States. Animal and clinical studies performed four decades ago suggested that immunological approaches might be useful for the treatment of prostate cancer. The wealth of information that has been learned over the last two decades has suggested many new directions to the immune-based therapy of prostate cancer, including passive and active immunotherapy approaches. The findings from current trials, and the likely combination of current immunotherapy approaches with conventional therapies, portends a hopeful future for the treatment of prostate cancer.

Androgen deprivation for minimal metastatic disease: Threshold for achieving undetectable prostate-specific antigen

OBJECTIVES

To develop objective measures to select systemic therapies for study in large-scale trials for patients with lesser tumor burdens, we explored prostate-specific antigen (PSA) changes after androgen ablation in patients with disease progression after treatment of localized disease. Long-term follow-up of trials incorporating androgen-deprivation with local therapy have shown improved survival relative to local therapy alone. This suggests that the benchmark for treatment of minimal metastatic disease can be cure.

METHODS

Patients with a rising PSA level with or without clinical metastases after local therapy who received androgen deprivation at Memorial Sloan-Kettering Cancer were identified from two institutional databases. The primary outcome was the proportion achieving an undetectable PSA level, and the pretreatment parameters associated with this endpoint were evaluated.

RESULTS

A total of 130 patients who received androgen ablation and were followed up at Memorial Sloan-Kettering Cancer Center were identified. Overall, 31 (57%) of 54 (95% confidence interval 44% to 71%) patients with a rising PSA level alone and 28 (37%) of 76 (95% confidence interval 26% to 47%) patients with a rising PSA level and clinical metastases achieved an undetectable PSA level after androgen ablation (P = 0.02). The PSA level at the start of androgen ablation and the presence of metastases were the most significant predictive factors.

CONCLUSIONS

The probability of achieving an undetectable PSA level varied inversely with the disease extent. Although achieving an undetectable PSA level does not mean that a patient has been cured, it does establish an endpoint that can be used to identify approaches worthy of study in the Phase III setting.

Novel approaches to treat asymptomatic, hormone-naive patients with rising prostate-specific antigen after primary treatment for prostate cancer

Biochemical-only recurrent prostate cancer presents the ideal setting for assessing novel agents or approaches for prostate cancer treatment. There is no clear evidence that delay in initiation of more definitive androgen-deprivation therapy is harmful, and a simple blood test--the prostate-specific antigen (PSA) level--is readily available to screen for potential antineoplastic activity. Current novel approaches include vaccines, cyclooxygenase-2 (COX-2) inhibitors, selective apoptotic antineoplastic drugs, endothelin-A receptor antagonists, chemotherapy, vitamin D, and peroxisome proliferator-activated receptor-gamma agonists. In this screening process, certain therapies have emerged as delaying PSA progression or decelerating PSA velocity. These therapies, such as the COX-2 inhibitors, will need to proceed to phase 3 trials to answer the more important question of whether this change in PSA dynamics translates into improved survival. Patients enrolling in these trials need to be clearly informed of the limited expectations of these novel exploratory approaches.

DC therapy for prostate cancer

The wide range of currently available treatments for metastatic prostate cancer have demonstrated a modest palliative effect, but none to date has shown an increase in overall survival. The immune system has evolved to protect against infection, however, the modulation of this system represents the possibility of allowing it to identify and destroy cancer cells. The immune system is capable of inciting a powerful immune response against tissues, in the form of transplant rejection, and the potential exists to harness these powers to fight against tumors. Modest clinical responses have been seen in patients with metastatic prostate cancer treated with DC therapies; however, no increase in overall survival has been demonstrated. The current state of DC immunotherapy for prostate cancer is reviewed.

Immunotherapy of dendritic cells transfected with mRNA of gastric cancer cells in carried-tumor mice

AIM: To probe into the possibility of dendritic cells (DC) in preventing solid carcinomas such as gastric cancer (GC).

METHODS: Immunotherapy was proformed by DC sensitized by mRNA of gastric cancer cells.

RESULTS: The indices such as the production rate of ascites of mice (75%), the metastasis rate of tumor (25%), the survival rate of animals (75%) and the average weight of tumor (2.04±0.33 g) showed that the condition of the mice treated by DC was better than that in the control group (P< 0.01). And the level of gene expression of IL-12, IFN and IL-18 in local tumor tissue was significantly raised (P < 0.01) and the amount of local CD₄⁺ (0.71±0.25/m²) and CD₈⁺ (0.67±0.22/m²) cells was increased (P < 0.05) and the cytotoxicity of TIL was remarkably enhanced.

CONCLUSION: DC transfected with mRNA isolated from mouse tumor cells may effectively control the growth of tumor and ameliorate the symptoms, suggesting that a certain therapeutic efficiency for mice carrying tumor can be realized.

Inhibition of prostate cancer cell growth by activated eosinophils

BACKGROUND

Host Immune response to prostate cancer primarily involves the CTL and NK effector cells. Recent immunotherapeutic strategies incorporating cytokine genes into the tumor cell and/or dendritic cells have had encouraging results. In this study, we describe the inhibitory activity of a third potential effector cell, the eosinophil, against DU 145 and PC-3 prostate tumor cells growth in vitro.

METHODS

Subconfluent monolayer cultures of DU 145 and PC-3 cells were incubated with peripheral blood eosinophils from allergic or asthmatic individuals and also with eosinophil cultured supernatants. Newly established eosinophil cell lines were also studied. After harvesting, the plates were washed and stained with Hematoxylin/eosin (H/E) then photographed. The combination of monolayer cell growth inhibition and colony formation inhibition assays were used to evaluate eosinophil inhibitory activity. In the colony formation inhibition assay one hundred cells per well in 6-well plates were incubated overnight, after which peripheral blood eosinophils, conditioned media and cytokines, IL-4 and TNF-alpha were added. The plates were harvested after 10 days incubation period. Colonies were stained and counted.

RESULTS

Hypo- and hyperdense peripheral blood eosinophils from allergic and asthmatic individuals as well as eosinophil cell lines established from these subpopulations inhibited both DU 145 and PC-3 cell growth at 58-78% and 10-38%, respectively. IL-5 up-regulated eosinophil cell line activity by 21-24%. The conditioned media which contained the released mediators of activated eosinophils were potent in their actions on both DU 145 and PC-3, inhibiting colony formation by as much as 90-100%.

CONCLUSION

These results clearly demonstrate the inhibitory potential of activated eosinophils and their released "soup" of mediators and therefore support the hypothesis that eosinophils may participate in host response to prostate cancer together with CTLs and NK cells. Furthermore, this study offers insights into possible strategies for enhancing eosinophilic activity in prostate cancer.

Optimizing targeted therapy and developing novel outcome measures for patients with advanced prostate cancer at Memorial Sloan-Kettering Cancer Center

Hormonal therapy and chemotherapy, though active treatments for prostate cancer, are not curative for patients with metastatic disease. Targeted therapy has the potential to control, if not eradicate, cells resistant to castration and chemotherapy. Despite several years of development, however, a biologic approach with clear clinical benefits has yet to emerge from a crowded field. This review outlines the approaches being studied at Memorial Sloan-Kettering Cancer Center to optimize biologic therapy. Trials of targeted therapy are designed on the basis of a clinical states model that describes both patient clinical risks and tumor biology. Drugs that act on multiple pathways are being developed, and targets that are expressed across all phases of the disease are selected. New molecular imaging techniques permit assessments of the target before, during, and after treatment. High-throughput preclinical assays of gene expression are being developed to enhance selection of drug sequences and combinations for clinical testing.

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Pharmacological treatments for prostate cancer

Recently, chemotherapy for prostate cancer has been primarily reserved for the palliation of symptoms secondary to prostate cancer. Chemotherapy regimens and new approaches are being developed that offer new hope of response and improved survival to men with prostate cancer. This paper discusses pharmacological strategies that are under investigation: cytotoxic agents and biological or targeted therapies, including the microtubule inhibitors (taxane/taxoids, vinorelbine) alone and in novel combinations with other experimental agents such calcitriol, thalidomide or flavopiridol (cell-cycle inhibitor) and treatment with epothilone analogues; endothelin receptor antagonists; other novel strategies such as vaccine therapy (GVAX; Cell Genesys) and prostate-specific membrane antibodies; and bisphosphonates.