Chow M, Rubin H
Department of Molecular and Cell Biology and Virus Laboratory, 229 Stanley Hall, University of California, Berkeley, CA 94720-3206, USA.
Proc Natl Acad Sci U S A. 1998 Apr 14;95(8):4550-5. doi: 10.1073/pnas.95.8.4550.
Three sublines of NIH 3T3 cells had the properties of non-neoplastic, preneoplastic, and neoplastic cells, respectively. The closer the cells were to neoplastic behavior, characterized by continuing growth at high density, the slower they multiplied at lower density. Under the conditions of high population density and low calf serum concentration used in the assay for transformed focus formation, the transformed or neoplastic cells were much more sensitive to killing by methotrexate (MTX) than were non-neoplastic cells in the same culture. This differential sensitivity of neoplastic cells was far more pronounced in molecular, cellular, and developmental biology medium 402 (MCDB 402) than in DMEM. It is associated with the presence in MCDB 402 of folinic acid, known clinically as leucovorin, which is a reduced form of the folic acid present in DMEM. Although leucovorin had been shown to selectively spare normal bone marrow and intestine in animals from the killing effect of MTX on tumor cells, we demonstrate the preferential killing of neoplastic over non-neoplastic cells of the same derivation. Neither neoplastic nor non-neoplastic cells were killed once they had stopped multiplying at their respective saturation densities. The development of the light foci characteristic of the preneoplastic cells was less sensitive to MTX than the formation of the dense foci produced by the fully neoplastic cells. The system should serve as a valuable model to establish basic principles and optimal conditions for selective killing of neoplastic cells by chemotherapeutic drugs.
NIH 3T3细胞的三个亚系分别具有非肿瘤性、肿瘤前性和肿瘤性细胞的特性。细胞越接近以高密度持续生长为特征的肿瘤性行为，其在低密度下增殖就越慢。在用于转化灶形成检测的高细胞密度和低小牛血清浓度条件下，与同一培养物中的非肿瘤性细胞相比，转化或肿瘤性细胞对甲氨蝶呤（MTX）杀伤更为敏感。肿瘤性细胞的这种差异敏感性在分子、细胞和发育生物学培养基402（MCDB 402）中比在DMEM中更为明显。这与MCDB 402中存在亚叶酸有关，亚叶酸在临床上称为甲酰四氢叶酸，它是DMEM中存在的叶酸的还原形式。尽管已证明甲酰四氢叶酸可使动物的正常骨髓和肠道免受MTX对肿瘤细胞的杀伤作用，但我们证明了对同一来源的肿瘤性细胞比对非肿瘤性细胞有优先杀伤作用。一旦肿瘤性和非肿瘤性细胞在各自的饱和密度下停止增殖，它们都不会被杀死。肿瘤前性细胞特征性的淡色灶的形成对MTX的敏感性低于完全肿瘤性细胞产生的致密灶的形成。该系统应作为一个有价值的模型，用于确立化疗药物选择性杀伤肿瘤性细胞的基本原理和最佳条件。
