The present proposal seeks to develop a novel anti-prostate specific antigen (PSA) IgE antibody for the treatment of prostate cancer (PCA) with the goal to induce a hypersensitivity reaction to the tumor. The objective of this proposal is to generate the anti-PSA IgE and to demonstrate that this anti-PSA IgE will target the tumor by two parallel pathways: a) by mediating bystander antibody-dependent cell-mediated cytotoxicity (ADCC) and phagocytosis (ADCP) effects in the tumor microenvironment and b) by activating PSA- specific T and B cells due to uptake of immune complexes (IC) composed of anti-PSA IgE and soluble PSA antigen by antigen-presenting cells (APCs). Together, these mechanisms can result in an acute inflammation of the tumor microenvironment with subsequent tumor destruction. This will initially be investigated in in vitro systems, followed by studies in relevant animal models and clinical trials in hormone refractory PCA. Specific Aims: To accomplish our goal we propose three specific aims: 1) to construct, test and produce at small-scale the human/mouse chimeric anti-PSA IgE antibody, 2) to biochemically and biologically characterize the anti-PSA IgE in vitro, and 3) to assess the direct anti-tumor effector mechanisms of the anti-PSA IgE. Study Design: The anti-PSA IgE will be constructed by genetically fusing the cDNA encoding the variable regions of the anti-PSA MAb-AR47.47 to the DNA encoding the human kappa and epsilon constant regions and transfecting the construct into murine myeloma cells. To evaluate the properties of the anti-PSA IgE in vitro, we will evaluate the antibody's ability to bind antigen of different sources. Binding to human Fc receptor will be studied by flow cytometry, using cell lines, isolated human DCs and monocytes. Antigen-presentation studies with PSA and PSA-anti-PSA-IgE IC pulsed human DCs will be used to detect T helper CTL responses by intracellular cytokine staining for IL-4 and IL-5 vs. interferon- by CD8+ and CD4+ T cells and by confocal microscopy. Finally, we will evaluate the ability of the IgE to mediate ADCC of LNCaP tumor cells by eosinophils and test for mast cell degranulation. More elaborate in vivo studies are planned for Phase II using a human IgE/human Fc receptor transgenic mouse model. The anti-tumor activity will then be studied in this model crossed to PSA-transgenic mice bearing syngeneic human PSA expressing tumor cells. Relevance: The relevance of this project relates to the limitations of current treatment options for metastatic, hormone-refractory prostate cancer and prostate cancer in African-American men. The anti-PSA IgE will be a novel molecule capable of a two-pronged attack against cancer cells, through direct elimination of tumor cells by mast cells and eosinophils and through an adaptive anti-tumor immune response. The proposed approach is expected to significantly contribute to a decrease in the human and economic cost associated with prostate cancer and to address an unmet medical need for treatment of hormone-refractory cancer.
Public Health Relevance: With an estimated 186,320 new cases in the US for 2008, Prostate Cancer is the most frequently diagnosed cancer and the second leading cause of cancer deaths in American men. Incidence rates and death rates are significantly higher in African American men than in white men. Although the 5-year survival rate for all stages combined has increased due to earlier diagnosis, patients with metastatic disease, which account for approximately 15% of patients, often cannot be cured by chemotherapy and palliative radiotherapies once patients become refractory to androgen ablation, thus the need to develop innovative modalities of treatment.
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