Peters G J, Bijnsdorp I V, Fukushima M
Department of Medical Oncology, VU University Medical Center, Amsterdam, the Netherlands.
Nucleic Acids Symp Ser (Oxf). 2008(52):629. doi: 10.1093/nass/nrn318.
Thymidine phosphorylase (TP) has emerged as a promising target for antiangiogenesis treatment of cancer. Angiogenesis, the formation of blood vessels, is essential for tumors to grow in order to be supplied with nutrients and oxygen. The association of TP with angiogenesis was demonstrated in several clinical studies in various tissue types. It has been postulated that the angiogenic effect of TP is related to its enzymatic activity, which catalyzes the breakdown of thymidine to thymine and deoxyribose-1-phosphate (dR-1-P). The latter, in its parent form or in its sugar form, deoxyribose, may play a role in angiogenesis. It may interfere in cellular energy metabolism or be substrate in a chemical reaction generating reactive oxygen species. L-deoxyribose and a specific TP inhibitor, TPI, can reverse these effects, supporting the role of the enzymatic reaction and that of the sugar. Although TP is usually high in the tumor, we also observed a high expression in tumor-associated stromal cells and macrophages. In order to elucidate the mechanism of TP induced angiogenesis we have investigated the association of TP with angiogenesis, the effect of thymidine and its metabolites on angiogenic parameters (e.g. invasion), the modulation by TPI, the formation and retention of the sugar metabolites of thymidine, and the potential signalling pathways involved in the angiogenic process. We used cell lines without/low TP expression (Colo320 and RT112) and TP transfected variants (Colo320TP1 and RT112/TP). Intrinsic TP expression in cancer cells did not stimulate these cells to invade more. On the other hand, Colo320 and Colo320TP1 cells could attract endothelial cells to a high extent, but Colo320TP1 did not attract them to a higher extent. RT112/TP cells attracted more endothelial cells than RT112 (2 fold). The difference between the RT112's and Colo320's may be related to different formation of sugars. Exposure of tumor cells to thymidine resulted in a rapid formation of dR-1-P, which was rapidly degraded to deoxyribose and further metabolized to other sugar derivatives. Of the possible sugars that can be produced by the conversion of TdR, dR-5-P seems to accumulate the most. dR accumulated 3 fold higher extent in RT112/TP than in Colo320/TP1 cells. dR could be converted to advanced glycation endproducts (AGE), however this was to a lower extent than ribose. Thymidine also induced several signalling pathways in the cells, involved in migration and invasion, such as the Focal adhesion kinase (FAK), which subsequently stimulated p70/S6 phosphorylation. The latter is a downstream kinase of rapamycin and its phosphorylation is inhibited by rapamycin, an mTOR inhibitor. The association between rapamycin and TP was shown by the protection by thymidine of rapamycin induced cytotoxicity, while TPI inhibited the effect of thymidine addition. These studies clearly show a mechanistic link between TP, signalling pathways, and cell migration.
胸苷磷酸化酶（TP）已成为癌症抗血管生成治疗的一个有前景的靶点。血管生成，即血管的形成，对于肿瘤生长以获取营养和氧气至关重要。TP与血管生成的关联在多种组织类型的多项临床研究中得到了证实。据推测，TP的血管生成作用与其酶活性有关，该酶催化胸苷分解为胸腺嘧啶和脱氧核糖 - 1 - 磷酸（dR - 1 - P）。后者，以其母体形式或糖形式（脱氧核糖），可能在血管生成中发挥作用。它可能干扰细胞能量代谢或作为产生活性氧的化学反应的底物。L - 脱氧核糖和一种特定的TP抑制剂（TPI）可以逆转这些效应，支持酶促反应及其糖的作用。尽管TP在肿瘤中通常含量很高，但我们也观察到其在肿瘤相关基质细胞和巨噬细胞中高表达。为了阐明TP诱导血管生成的机制，我们研究了TP与血管生成的关联、胸苷及其代谢产物对血管生成参数（如侵袭）的影响、TPI的调节作用、胸苷糖代谢产物的形成和保留以及血管生成过程中涉及的潜在信号通路。我们使用了无/低TP表达的细胞系（Colo320和RT112）以及TP转染变体（Colo320TP1和RT112/TP）。癌细胞中的内源性TP表达并未刺激这些细胞更多地侵袭。另一方面，Colo320和Colo320TP1细胞在很大程度上可以吸引内皮细胞，但Colo320TP1并没有在更高程度上吸引它们。RT112/TP细胞比RT112吸引更多的内皮细胞（2倍）。RT112和Colo320之间的差异可能与糖的不同形成有关。肿瘤细胞暴露于胸苷会导致dR - 1 - P的快速形成，其迅速降解为脱氧核糖并进一步代谢为其他糖衍生物。在由胸苷转化产生的可能糖中，dR - 5 - P似乎积累最多。dR在RT112/TP中的积累程度比在Colo320/TP1细胞中高3倍。dR可以转化为晚期糖基化终产物（AGE），然而其程度低于核糖。胸苷还诱导了细胞中的几种信号通路，参与迁移和侵袭，如粘着斑激酶（FAK），其随后刺激p70/S6磷酸化。后者是雷帕霉素的下游激酶，其磷酸化被雷帕霉素（一种mTOR抑制剂）抑制。雷帕霉素与TP之间的关联通过胸苷对雷帕霉素诱导的细胞毒性的保护作用得以体现，而TPI抑制了添加胸苷的作用。这些研究清楚地表明了TP、信号通路和细胞迁移之间的机制联系。
