PSMA, Nutritional Target for Prostate Cancer Prevention

描述（由申请人提供）： 前列腺特异性膜抗原（PSMA）是一种在人体内高度表达的前列腺抗原，在大多数人前列腺癌中表达增加。我们发现PSMA是一种独特的叶酸水解酶。除了是对多γ-谷氨酸化叶酸具有高亲和力的叶酸水解酶之外，PSMA还经历内化并被转运至溶酶体区室，因此也可以在多γ-谷氨酸化叶酸的结合和转运中发挥作用。叶酸在DNA和RNA的合成中提供甲基。叶酸缺乏与染色体损伤和致癌作用中对致癌物的敏感性增加有关，叶酸还可以改变表达与癌症发展相关的突变基因的转基因模型中癌症的发展。PSMA的小鼠同源物在小鼠前列腺中不表达。正常小鼠前列腺也具有低的前列腺癌发病率。我们产生了在PSA启动子/增强子的控制下在其前列腺中强烈表达PSMA的小鼠。我们发现，在这些小鼠的前列腺增生和PIN的发生率很高，在约9个月的年龄，特别是在腹侧前列腺和侧前列腺。表达缺乏叶酸水解酶活性的PSMA形式的转基因动物不表现出这些变化。我们假设PSMA作为叶酸水解酶的功能是导致前列腺异常组织学结构增加的原因，我们提出了一些研究来确定在何种程度上膳食叶酸的调节会加重或减弱这些组织学变化。 前列腺是一种低水平增殖的组织。叶酸的变化被认为对细胞增殖有重要影响。最近在人类前列腺中的研究表明，诸如前列腺上皮内萎缩（PIA）的病症实际上是高度增殖性的。因为还没有建立小鼠前列腺PIA的模型，我们将使用具有驱动增殖的主导作用基因的转基因动物，如大T抗原或c-Myc。这两种动物都在合理的时间范围内发展肿瘤，我们将确定PSMA表达和叶酸调节对这些前列腺肿瘤模型中肿瘤形成的影响程度。在我们提出的研究中，我们将利用表达PSMA、大T抗原或c-Myc的转基因动物，有或没有饮食叶酸操纵，有或没有给予高度特异性的高亲和力PSMA抑制剂。我们将测量血清、RBC和组织叶酸，以及多γ-谷氨酸化程度、SAM/SAH、放射性标记叶酸的比率和组织摄取和保留。我们将确定组织病理学的变化，并通过阵列分析确定小鼠前列腺中PSMA表达对前列腺基因表达的影响。将验证表现出最大变化的那些变化，并通过原位杂交确定表现出这些变化的前列腺细胞。由于PSMA可能会增强前列腺对癌症的易感性，这些研究可能表明PSMA抑制剂或叶酸操纵是否可以提供一种方法来减少PSMA作为异常前列腺生长因素的影响。

DESCRIPTION (provided by applicant): Prostate-Specific Membrane Antigen, PSMA is a highly expressed prostate antigen in human, which is increased in expression in the majority of human prostate cancers. We discovered that PSMA is a unique folate hydrolase. In addition to being a folate hydrolase with high affinity for polygammaglutamated folates, PSMA undergoes internalization and is transported to the lysosomal compartment, and thus may play a role in the binding and transport of polygammaglutamated folates as well. Folates provide methyl groups in the synthesis of DNA and RNA. Folate deficiencies are associated with chromosomal damage and increased sensitivity to carcinogens in carcinogenesis and folate can also alter the development of cancer in transgenic models expressing mutant genes associated with the development of cancers. The mouse homolog of PSMA is not expressed in the mouse prostate. The normal mouse prostate also has a low incidence of prostate cancer. We generated mice that strongly express PSMA in their prostates under the control of the PSA promoter/enhancer. We find a high incidence of hyperplasia and PIN in the prostates of these mice at about 9 months of age, especially in the ventral prostate and lateral prostate. Transgenic animals made to express a form of PSMA that lack the folate hydrolase activity do not demonstrate these changes. We hypothesize that PSMA's function as a folate hydrolase is responsible for the increased abnormal histologic architecture in the prostate and we propose a number of studies to determine to what extent manipulation of dietary folate will accentuate or attenuate these histologic changes. The prostate is a tissue with a low level of proliferation. Changes in folate are thought to have their major impact in cells that are proliferating. Recent studies in the human prostate suggest that conditions such as prostate intraepithelial atrophy, PIA, are in fact highly proliferative. Because a way to model PIA is not established for the mouse prostate, we will use transgenic animals which have dominate acting genes which drive proliferation, such as the large T antigen, or c-Myc. Both of these animals develop tumors in a reasonable time frame and we will determine the extent PSMA expression and folate modulation impact tumor formation in these prostate tumor models. In our proposed studies we will utilize transgenic animals that express PSMA, large T antigen, or c-Myc with or without dietary folate manipulation, with or without administration of highly specific high affinity inhibitors of PSMA. We will measure serum, RBC, and tissue folates, and extent of polygammglutamation, SAM/SAH, ratios and tissue uptake and retention of radio labeled folate. We will determine the changes in tissue histopathology and determine the effect of PSMA expression in the mouse prostate on prostate gene expression by array analysis. Those changes exhibiting the greatest changes will be verified and the cells of the prostate demonstrating those changes determined by in-situ hybridization. As PSMA may be enhancing the prostates susceptibility to develop cancer, these studies may indicate whether either PSMA inhibitors or folate manipulation may provide an approach to reducing the impact of PSMA as a factor in abnormal prostate growth.