title: Anticancer activity of a thymidine quinoxaline conjugate is modulated by cytosolic thymidine pathways.
abstract: BACKGROUND
  High levels of thymidine kinase 1 (TK1) and thymidine phosphorylase (TYMP) are key molecular targets by thymidine therapeutics in cancer treatment. The dual roles of TYMP as a tumor growth factor and a key activation enzyme of anticancer metabolites resulted in a mixed outcome in cancer patients. In this study, we investigated the roles of TK1 and TYMP on a thymidine quinoxaline conjugate to evaluate an alternative to circumvent the contradictive role of TYMP.
  
  
  METHODS
  TK1 and TYMP levels in multiple liver cell lines were assessed along with the cytotoxicity of the thymidine conjugate. Cellular accumulation of the thymidine conjugate was determined with organelle-specific dyes. The impacts of TK1 and TYMP were evaluated with siRNA/shRNA suppression and pseudoviral overexpression. Immunohistochemical analysis was performed on both normal and tumor tissues. In vivo study was carried out with a subcutaneous liver tumor model.
  
  
  RESULTS
  We found that the thymidine conjugate had varied activities in liver cancer cells with different levels of TK1 and TYMP. The conjugate mainly accumulated at endothelial reticulum and was consistent with cytosolic pathways. TK1 was responsible for the cytotoxicity yet high levels of TYMP counteracted such activities. Levels of TYMP and TK1 in the liver tumor tissues were significantly higher than those of normal liver tissues. Induced TK1 overexpression decreased the selectivity of dT-QX due to the concurring cytotoxicity in normal cells. In contrast, shRNA suppression of TYMP significantly enhanced the selective of the conjugate in vitro and reduced the tumor growth in vivo.
  
  
  CONCLUSIONS
  TK1 was responsible for anticancer activity of dT-QX while levels of TYMP counteracted such an activity. The counteraction by TYMP could be overcome with RNA silencing to significantly enhance the dT-QX selectivity in cancer cells.
authors.affiliation: Department of Nanomedicine & Biopharmaceuticals, National Engineering Research Center for Nanomedicine, Huazhong University of Science and Technology, Wuhan, Hubei, China. 429791916@qq.com.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Wei
authors.affiliation: Department of Nanomedicine & Biopharmaceuticals, National Engineering Research Center for Nanomedicine, Huazhong University of Science and Technology, Wuhan, Hubei, China. liuhaijuan1990@163.com.
authors.forename: Haijuan
authors.initials: H
authors.lastname: Liu
authors.affiliation: Hepatic Surgery Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China. 267411664@qq.com.
authors.forename: Honghao
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Department of Nanomedicine & Biopharmaceuticals, National Engineering Research Center for Nanomedicine, Huazhong University of Science and Technology, Wuhan, Hubei, China. 516043259@qq.com.
authors.forename: Dejun
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Hepatic Surgery Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China. zwzhang38@hotmail.com.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Nanomedicine & Biopharmaceuticals, National Engineering Research Center for Nanomedicine, Huazhong University of Science and Technology, Wuhan, Hubei, China. qibingzhou@hust.edu.cn.|Department of Medicinal Chemistry, Virginia Commonwealth University, Richmond, VA, USA. qibingzhou@hust.edu.cn.
authors.forename: Qibing
authors.initials: Q
authors.lastname: Zhou
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism* / Q000494:pharmacology* / Q000633:toxicity; D045744:Cell Line, Tumor; D003600:Cytosol / Q000378:metabolism; D004195:Disease Models, Animal; D015870:Gene Expression; D020868:Gene Silencing; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008297:Male; D053858:Metabolic Networks and Pathways; D051379:Mice; D009369:Neoplasms / Q000378:metabolism; D011810:Quinoxalines / Q000378:metabolism* / Q000494:pharmacology* / Q000633:toxicity; D013936:Thymidine / Q000378:metabolism*; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism; D013939:Thymidine Phosphorylase / Q000235:genetics / Q000378:metabolism; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D011810:Quinoxalines; D013939:Thymidine Phosphorylase; D013937:Thymidine Kinase; C092717:thymidine kinase 1; D013936:Thymidine