MOUSE CANCER MODELS--INACTIVATION OF TUMOR SUPPRESSOR GE

过去二十年的研究为人类癌症提供了重要的新见解。视网膜母细胞瘤基因（RB）和p53的突变与大约70%的人类癌症有关。这些基因，以及另外两个肿瘤抑制基因BRCA1和BRCA2，在乳腺癌易感家族中发生突变，似乎也与前列腺癌有关。我们有兴趣开发具有与人类相似的病因和发病机制的小鼠乳腺和前列腺肿瘤模型。由于胚胎致死性和幼鼠中常见的致死性肿瘤类型的发展，先前具有上述四种基因的模型在癌症研究中的应用受到限制。为了规避这些限制，我们在本应用中表明，使用一种新的方法可以在小鼠中实现肿瘤抑制基因的时间、空间和细胞类型特异性失活，该方法将Cre-loxP重组酶的表达置于四环素二元基因控制系统的调控下。该方法已被应用于通过条件失活Rb、p53、Brca1和Brca2来生成小鼠癌症模型。这些小鼠将用于：(A)测试特定肿瘤抑制因子单独或组合在肿瘤形成中的特异性，并通过病理和分子分析验证其肿瘤与人类癌症的相似性。(B)评价磁共振图像分析对早期发现癌症的敏感性。(C)研究环境因素，如低剂量辐射在肿瘤形成中的作用。(D)测试激素治疗或热量限制在预防肿瘤形成方面的作用。(E)评价抗癌药物和肿瘤抑制基因靶向治疗小鼠乳腺癌和前列腺癌的疗效。为了实现这一目标，我们提出了以下四个总体目标：(1)培养具有肿瘤抑制基因的小鼠，包括p53、Rb、Brca1和Brca2，这些基因的关键外显子整合了侧翼loxP （floxed）位点。(2)利用四环素二元体系调控Cre-重组酶的表达，建立具有时间、空间和细胞类型特异性DNA切除的转基因小鼠。(3)将Aims 1和2中的小鼠进行杂交，以产生所需的转基因/絮束小鼠。(4)在多种抑癌基因单独或联合失活的情况下，研究这些小鼠乳腺和前列腺肿瘤的形成和进展。通过与该联盟其他成员的合作，这些肿瘤抑制基因在其他类型癌症中的作用也将得到研究。此外，具有调控的crer -重组酶的转基因小鼠，无论是普遍表达的还是细胞类型特异性表达的，都可以供该联盟的其他研究人员与他们的固定小鼠杂交，从而大大扩大位点特异性敲除的范围。这些有价值的小鼠模型将对癌症研究人员非常有用。

Studies in the last two decades have provided a significant new insights into human cancer. Mutations of the retinoblastoma gene (RB) and p53 are involved in about 70 percent of human cancer. These genes, as well as two other tumor suppressor genes, BRCA1 and BRCA2, that are mutated in families predisposed to breast cancer, appear to be also implicated in prostate cancer. We are interested to develop mouse mammary and prostate models of tumorigenesis with an etiology and pathogenesis similar to humans. Due to embryonic lethality and the development of a prevalent type of lethal tumor in young mice, previous models with the above four genes were restricted in their use for cancer research. To circumvent these limitations, we show in this application that the temporal, spatial, and cell-type-specific inactivation of tumor suppressor genes can be achieved in mice using a novel method that places expression of the Cre-loxP recombinase under the regulation of the tetracycline binary system of gene control. This approach has been applied to generate mouse cancer models by conditional inactivation of Rb, p53, Brca1, and Brca2. These mice will be used to: (A) test the specificity of a given tumor suppressor singly or in combination in tumor formation, and to validate the similarity of their tumors to human cancer by pathological and molecular analyses. (B) evaluate the sensitivity of magnetic resonance image analysis for early detection of cancer. (C) investigate environmental factors, such as low dose radiation in tumor formation. (D) test hormone treatments or caloric restriction in preventing tumor formation. (E) evaluate the efficacy of anti-cancer drugs and targeted therapy using tumor suppressor genes in the treatment of breast and prostate cancer in mice. To achieve this goal, four overall specific aims are proposed as follows: (1) To generate mice with tumor suppressor genes, including p53, Rb, Brca1 and Brca2, whose critical exon(s) have integrated flanking loxP (floxed) sites. (2) To establish transgenic mice that demonstrate temporal, spatial and cell-type- specific DNA excision by regulating the expression of the Cre- recombinase with the tetracycline binary system for gene control. (3) To cross mice in Aims 1 and 2 to produce the desired transgenic/floxed mice. (4) To characterize breast and prostate tumor formation and progression in these mice under a variety of settings where tumor suppressor genes, either singly or in combination, are inactivated. In collaboration with other members of the consortium, the involvement of these tumor suppressor genes in other types of cancer could be investigated. In addition, the transgenic mice with regulated Cre-recombinase, either ubiquitously or cell-type- specifically expressed, would be available to other investigators in the consortium to cross with their floxed mice to greatly expand the repertoire of site-specific knock-outs. These valuable mouse models will be extremely useful for the general community of cancer researchers.