Thaker Ameet I, Shaker Anisa, Rao M Suprada, Ciorba Matthew A
Division of Gastroenterology, Washington University School of Medicine, USA.
J Vis Exp. 2012 Sep 11(67):4100. doi: 10.3791/4100.
Individuals with inflammatory bowel disease (IBD), such as Crohn's disease (CD) or ulcerative colitis (UC) are at increased risk of developing colorectal cancer (CRC) over healthy individuals. This risk is proportional to the duration and extent of disease, with a cumulative incidence as high as 30% in individuals with longstanding UC with widespread colonic involvement. Colonic dysplasia in IBD and colitis associated cancer (CAC) are believed to develop as a result of repeated cycles of epithelial cell injury and repair while these cells are bathed in a chronic inflammatory cytokine milieu. While spontaneous and colitis-associated cancers share the quality of being adenocarcinomas, the sequence of underlying molecular events is believed to be different. This distinction argues the need for specific animal models of CAC. Several mouse models currently exist for the study of CAC. Dextran sulfate sodium (DSS), an agent with direct toxic effects on the colonic epithelium, can be administered in drinking water to mice in multiple cycles to create a chronic inflammatory state. With sufficient duration, some of these mice will develop tumors. Tumor development is hastened in this model if administered in a pro-carcinogenic setting. These include mice with genetic mutations in tumorigenesis pathways (APC, p53, Msh2), as well as mice pre-treated with genotoxic agents (azoxymethane [AOM], 1,2-dimethylhydrazine [DMH]). The combination of DSS with AOM as a model for colitis associated cancer has gained popularity for its reproducibility, potency, low price, and ease of use. Though they have a shared mechanism, AOM has been found to be more potent and stable in solution than DMH. While tumor development in other models generally requires several months, mice injected with AOM and subsequently treated with DSS develop adequate tumors in as little as 7-10 weeks. Finally, AOM and DSS can be administered to mice of any genetic background (knock out, transgenic, etc.) without cross-breeding to a specific tumorigenic strain. Here, we demonstrate a protocol for inflammation-driven colonic tumorigenesis in mice utilizing a single injection of AOM followed by three seven-day cycles of DSS over a 10 week period. This model induces tumors with histological and molecular changes closely resembling those occurring in human CAC and provides a highly valuable model for the study of oncogenesis and chemoprevention in this disease.
患有炎症性肠病（IBD）的个体，如克罗恩病（CD）或溃疡性结肠炎（UC），相较于健康个体，患结直肠癌（CRC）的风险更高。这种风险与疾病的持续时间和范围成正比，在患有广泛性结肠受累的长期溃疡性结肠炎患者中，累积发病率高达30%。炎症性肠病中的结肠发育异常和结肠炎相关癌（CAC）被认为是在上皮细胞反复经历损伤和修复周期的过程中发生的，而这些细胞处于慢性炎症细胞因子环境中。虽然自发性癌症和结肠炎相关癌症都具有腺癌的特征，但据信其潜在分子事件的序列是不同的。这种差异表明需要建立特定的结肠炎相关癌动物模型。目前有几种小鼠模型用于研究结肠炎相关癌。硫酸葡聚糖钠（DSS）是一种对结肠上皮具有直接毒性作用的试剂，可以通过饮水多次给予小鼠，以建立慢性炎症状态。如果持续时间足够长，其中一些小鼠会发生肿瘤。在致癌环境中给予该试剂，此模型中的肿瘤发生会加速。这些致癌环境包括在肿瘤发生途径（APC、p53、Msh2）中具有基因突变的小鼠，以及预先用基因毒性试剂（氧化偶氮甲烷[AOM]、1,2 - 二甲基肼[DMH]）处理过的小鼠。DSS与AOM联合作为结肠炎相关癌的模型因其可重复性、有效性、低成本和易于使用而受到欢迎。尽管它们有共同的机制，但已发现AOM在溶液中比DMH更有效且更稳定。在其他模型中，肿瘤发生通常需要几个月时间，而注射AOM后再用DSS处理的小鼠在短短7 - 10周内就能长出足够的肿瘤。最后，AOM和DSS可以给予任何遗传背景（基因敲除、转基因等）的小鼠，无需与特定的致瘤品系进行杂交。在此，我们展示了一种在小鼠中通过炎症驱动结肠肿瘤发生的方案，即在10周内单次注射AOM，随后进行三个为期七天的DSS处理周期。该模型诱导产生的肿瘤在组织学和分子变化上与人类结肠炎相关癌极为相似，为研究该疾病的肿瘤发生和化学预防提供了一个非常有价值的模型。
