Kerbel R S, Cornil I, Theodorescu D
Division of Cancer Research, Sunnybrook Health Science Centre, Toronto, Ontario, Canada.
Cancer Metastasis Rev. 1991 Oct;10(3):201-15. doi: 10.1007/BF00050792.
Assessment of the function of putative dominantly-acting oncogenes or recessive tumor-suppressor genes in human tumor development and progression must ultimately involve xenografting experiments using immune deficient animals such as nude mice. Most human tumor xenograft experiments have employed conventional subcutaneous injection procedures. However, despite the simplicity of this procedure, it poses some serious potential drawbacks as most types of human tumor will not readily grow or metastasize from a subcutaneous ('ectopic') site of injection. In contrast, 'orthotopic' injection procedures will often enhance the tumorigenic and/or metastatic ability of tumor cell populations. An example of this is summarized in the context of human malignant melanoma where the effects of subcutaneous versus subdermal injection are compared. Despite the seeming subtle and minor change in injection site, superior growth of human melanomas can be obtained by the latter, orthotopic-like, route of injection. It therefore follows that induction of tumorigenic or metastatic properties in a given human cell population by gene transfection may not be detected if the transfected cells are assayed in vivo only by subcutaneous injection procedures. An example of this is provided by experiments involving transfection of normal or mutated ras genes into a low-grade, well-differentiated human bladder carcinoma cell line, called RT-4. Thus overexpression of normal or mutated (valine 12) c-H-ras resulted in acquisition of a clinical-like invasive phenotype. However, this was clearly seen only if the cells were injected into the bladders (i.e. 'intravesically') of nude mice. In contrast, conventional subcutaneous injection of the high ras expressing transfected RT-4 cell lines did not reveal acquisition of invasive properties: all cell lines grew locally as well-encapsulated tumor masses. It is argued that similar orthotopic injection procedures should be employed when assessing the suppressive effects of various wild-type tumor-suppressor genes on human tumor growth in vivo. Utilization of subcutaneous injection procedures may grossly exaggerate the growth suppressive effects of such genes. This could explain the paradox of why, on the one hand, alterations involving many different genes (including different suppressor genes) appear to be involved in human carcinoma tumorigenesis while on the other hand, complete suppression of tumorigenicity can be caused by transfer of a single wild-type suppressor gene. Such complete suppressions might be observed only after ectopic (usually subcutaneous) injection procedures.
评估推定的显性癌基因或隐性肿瘤抑制基因在人类肿瘤发生和发展中的功能，最终必须涉及使用免疫缺陷动物（如裸鼠）进行异种移植实验。大多数人类肿瘤异种移植实验采用传统的皮下注射方法。然而，尽管该方法简单，但它存在一些严重的潜在缺点，因为大多数类型的人类肿瘤在皮下（“异位”）注射部位不易生长或转移。相比之下，“原位”注射方法通常会增强肿瘤细胞群体的致瘤和/或转移能力。在人类恶性黑色素瘤的背景下总结了一个例子，其中比较了皮下注射与皮内注射的效果。尽管注射部位看似细微的变化，但通过后者类似原位的注射途径可以获得人类黑色素瘤更好的生长效果。因此，如果仅通过皮下注射方法在体内检测转染细胞，那么在给定的人类细胞群体中通过基因转染诱导的致瘤或转移特性可能无法被检测到。涉及将正常或突变的ras基因转染到一种低级别、高分化的人类膀胱癌细胞系（称为RT - 4）中的实验提供了一个这样的例子。因此，正常或突变（缬氨酸12）的c - H - ras的过表达导致获得临床样侵袭表型。然而，只有当细胞注射到裸鼠的膀胱（即“膀胱内”）时才能清楚地看到这一点。相比之下，对高表达ras的转染RT - 4细胞系进行传统的皮下注射并没有显示出侵袭特性的获得：所有细胞系都作为包膜良好的肿瘤块在局部生长。有人认为，在评估各种野生型肿瘤抑制基因对人类肿瘤体内生长的抑制作用时，应采用类似的原位注射方法。使用皮下注射方法可能会严重夸大此类基因的生长抑制作用。这可以解释为什么一方面涉及许多不同基因（包括不同的抑制基因）的改变似乎参与了人类癌的肿瘤发生，而另一方面，单个野生型抑制基因的转移却可以导致肿瘤发生性的完全抑制。这种完全抑制可能只有在异位（通常是皮下）注射方法后才会观察到。
