Application of Transgenic Models for Toxicological Characterization

确定潜在人类致癌物的主要测试方法仍然是为期两年的啮齿动物生物测试，其中近亲繁殖的小鼠和大鼠被用作人类风险的潜在替代品。我们已经建议用在选定的转基因小鼠模型中进行的短期生物检测来补充为期两年的癌症生物检测。随着对肿瘤分子认识的快速发展和对直接参与肿瘤发生的基因的识别，人们对控制细胞增殖、抑制肿瘤表型的基因或这些基因的调控因子之间的关系有了明确的认识。今天使用的转基因模型主要集中在这些领域。为此，将P53基因缺失(P53+/-)和zetaglobin v-Ha-ras(Tg.AC)转基因小鼠模型与传统的两种啮齿动物致癌物生物检测的结果进行了比较。这些研究的结果已经显示了一些确定的能力来识别选定的一组已知的人类致癌物，并且转基因模型的结果提供了对化学物质作用的直接机制洞察。例如，P53+/-模型已经证明了遗传毒性/致突变致癌物的优先识别，在这种模型中，可以证明野生型等位基因的分子变化，并与化学暴露直接相关。此外，在合作实验中，已经有可能证明通过植入用于动物识别的应答器来诱导皮下肉瘤。随后对这些肿瘤的分子分析表明，特异性的P53等位基因丢失。Tg.AC模型已显示出对非遗传毒性致癌物的优先反应。在与传统的两阶段启动/促进模型平行的研究中，已经获得的数据表明，两阶段模型和Tg.AC转基因模型都能够在比传统生物检测更短的时间内识别潜在的非遗传毒性致癌物和肿瘤促进剂。此外，使用促癌模型对长期获得的数据进行分析和长期生物测定分析表明，促癌特性是完全非遗传毒性致癌物的一个组成部分。因此，化学物质在Tg.AC模型中的作用机制是优先诱导转基因表达，从而导致皮肤乳头状瘤的报告表型的发展。在传统的啮齿动物生物检测中进行的研究与这些转基因模型进行的直接前瞻性比较表明，转基因模型并不是“超敏感”的，因为它们没有检测到在小鼠或大鼠身上引起优先物种特异性效应的药物。许多关键问题仍有待回答，以促进关于使用这些转基因株系识别潜在人类致癌物的科学共识，但迄今开发的数据表明，这些模型可以在化学和药物安全性评估中发挥重要作用。

The primary testing method for the identification of potential human carcinogens remains the two-year rodent bioassay where in-bred mice and rats are used as potential surrogates for human risk. We have proposed to supplement the two-year cancer bioassays with short-term bioassays conducted in selected transgenic mouse models. The rapid progress in the molecular understanding of cancer and the identification of genes that are directly involved in neoplasia have provided specific insights into the relationship between genes which control cell proliferation, suppression of tumor phenotype or modulators of these genes. The transgenic models utilized today are focused in these areas. To this end, the haploinsufficient p53 knockout (p53+/-) and zetaglobin v-Ha-ras (Tg.AC) transgenic mouse models have been compared with the results of conventional, two rodent species carcinogen bioassays. The results of these studies have shown some definitive capacity to identify a selected group of known human carcinogens, and that the results from the transgenic models provide direct mechanistic insights into the action of chemicals. For example, the p53+/- model has demonstrated the preferential identification of genotoxic/mutagenic carcinogens in which molecular changes in the wildtype allele can be demonstrated and associated directly with chemical exposure. In addition, in collaborative experiments, it has been possible to demonstrate the induction of subcutaneous sarcomas by implantation of transponders used for animal identification. Subsequent molecular analysis of these tumors has demonstrated specific p53 allelic loss. The Tg.AC model has demonstrated preferential responsive to nongenotoxic carcinogens. In studies in parallel with the conventional two-stage initiation/promotion model, data have been obtained to suggest that both the two-stage model and the Tg.AC transgenic model have the capacity to identify potential nongenotoxic carcinogens and tumor promoters in a much shorter period of time than conventional bioassays. In addition, the analysis of data obtained over a long period of time with tumor promotion models and analysis of long-term bioassays suggests that the property of tumor promotion is one component of complete nongenotoxic carcinogens. Thus, the mechanism of action of chemicals in the Tg.AC model is the preferential induction of transgene expression which leads to the development of a reporter phenotype of skin papillomas. Direct prospective comparison of studies conducted in conventional rodent bioassays with these transgenic models has demonstrated that the transgenic models are not "supersensitive" in that they do not detect agents which cause preferential species-specific effects in either mice or rats. Many critical questions remain to be answered in order to promote a scientific consensus on the use of these transgenic lines for the identification of potential human carcinogens, but the data developed to date suggests that these models can play an important role in chemical and drug safety assessments.