Sohn Kyoung-Jin, Croxford Ruth, Yates Zoe, Lucock Mark, Kim Young-In
Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
J Natl Cancer Inst. 2004 Jan 21;96(2):134-44. doi: 10.1093/jnci/djh015.
Although single nucleotide polymorphisms may be potentially important pharmacogenetic determinants of cancer therapy, functional evidence regarding their relevance is currently lacking. The C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with changes in cellular composition of folates. We hypothesized that this polymorphism may modulate the cytotoxic effect of 5-fluorouracil (5FU) and methotrexate (MTX), two commonly used chemotherapeutic agents for colon and breast cancers, because the modes of action of 5FU and MTX are critically dependent on cellular composition of folates.
Human HCT116 colon and MDA-MB-435 breast cancer cells were stably transfected with wild-type or mutant 677T human MTHFR cDNA. MTHFR enzyme activity and thermolability, intracellular folate composition, growth rate, and catalytic thymidylate synthase activity were determined. In vitro chemosensitivity to 5FU and MTX was determined using the sulforhodamine B assay. In vivo chemosensitivity of HCT116 cells to 5FU was determined in nude mice.
Compared with cells expressing the wild-type MTHFR, HCT116 and MDA-MB-435 cells expressing the mutant 677T MTHFR had decreased MTHFR activity, MTHFR thermolability, changed intracellular folate distribution, accelerated cellular growth rate, and increased thymidylate synthase activity. The MTHFR 677T mutation increased chemosensitivity of colon and breast cancers to 5FU, but decreased chemosensitivity of breast cancer cells to MTX. In nude mice, xenografts expressing the mutant 677T MTHFR grew faster, but were more sensitive to 5FU, than xenografts expressing the wild-type protein.
Our data provide evidence that the MTHFR C677T polymorphism affects the concentration and intracellular distribution of folates and changes the growth and chemosensitivity of colon and breast cancer cells. The MTHFR C677T polymorphism may be a useful pharmacogenetic determinant for providing rational and effective tailored chemotherapy.
尽管单核苷酸多态性可能是癌症治疗中潜在重要的药物遗传学决定因素，但目前缺乏关于其相关性的功能证据。亚甲基四氢叶酸还原酶（MTHFR）基因中的C677T多态性与叶酸的细胞组成变化有关。我们推测，这种多态性可能会调节5-氟尿嘧啶（5FU）和甲氨蝶呤（MTX）的细胞毒性作用，这两种药物是结肠癌和乳腺癌常用的化疗药物，因为5FU和MTX的作用方式严重依赖于叶酸的细胞组成。
将野生型或突变型677T人MTHFR cDNA稳定转染至人HCT116结肠癌细胞和MDA-MB-435乳腺癌细胞。测定MTHFR酶活性和热稳定性、细胞内叶酸组成、生长速率以及催化胸苷酸合成酶活性。使用磺酰罗丹明B试验测定对5FU和MTX的体外化学敏感性。在裸鼠中测定HCT116细胞对5FU的体内化学敏感性。
与表达野生型MTHFR的细胞相比，表达突变型677T MTHFR的HCT116和MDA-MB-435细胞的MTHFR活性降低、MTHFR热稳定性降低、细胞内叶酸分布改变、细胞生长速率加快且胸苷酸合成酶活性增加。MTHFR 677T突变增加了结肠癌和乳腺癌对5FU的化学敏感性，但降低了乳腺癌细胞对MTX的化学敏感性。在裸鼠中，表达突变型677T MTHFR的异种移植物比表达野生型蛋白的异种移植物生长更快，但对5FU更敏感。
我们的数据提供了证据表明MTHFR C677T多态性影响叶酸的浓度和细胞内分布，并改变结肠癌细胞和乳腺癌细胞的生长及化学敏感性。MTHFR C677T多态性可能是提供合理有效个体化化疗的有用药物遗传学决定因素。
