Plant thymidine kinase 1: a novel efficient suicide gene for malignant glioma therapy.

The prognosis for malignant gliomas remains poor, and new treatments are urgently needed. Targeted suicide gene therapy exploits the enzymatic conversion of a prodrug, such as a nucleoside analog, into a cytotoxic compound. Although this therapeutic strategy has been considered a promising regimen for central nervous system (CNS) tumors, several obstacles have been encountered such as inefficient gene transfer to the tumor cells, limited prodrug penetration into the CNS, and inefficient enzymatic activity of the suicide gene. We report here the cloning and successful application of a novel thymidine kinase 1 (TK1) from the tomato plant, with favorable characteristics in vitro and in vivo. This enzyme (toTK1) is highly specific for the nucleoside analog prodrug zidovudine (azidothymidine, AZT), which is known to penetrate the blood-brain barrier. An important feature of toTK1 is that it efficiently phosphorylates its substrate AZT not only to AZT monophosphate, but also to AZT diphosphate, with excellent kinetics. The efficiency of the toTK1/AZT system was confirmed when toTK1-transduced human glioblastoma (GBM) cells displayed a 500-fold increased sensitivity to AZT compared with wild-type cells. In addition, when neural progenitor cells were used as delivery vectors for toTK1 in intracranial GBM xenografts in nude rats, substantial attenuation of tumor growth was achieved in animals exposed to AZT, and survival of the animals was significantly improved compared with controls. The novel toTK1/AZT suicide gene therapy system in combination with stem cell-mediated gene delivery promises new treatment of malignant gliomas.
AuthorsZahidul Khan, Wolfgang Knecht, Mette Willer, Elzbieta Rozpedowska, Peter Kristoffersen, Anders Ranegaard Clausen, Birgitte Munch-Petersen, Per M Almqvist, Zoran Gojkovic, Jure Piskur, Tomas J Ekström
JournalNeuro-oncology (Neuro Oncol) Vol. 12 Issue 6 Pg. 549-58 (Jun 2010) ISSN: 1523-5866 [Electronic] United States
PMID20154339 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • Plant Proteins
  • Thymidine Kinase
  • thymidine kinase 1
  • Animals
  • Cell Line, Tumor
  • Genes, Transgenic, Suicide (genetics)
  • Genetic Therapy (methods)
  • Glioma (genetics, pathology, therapy)
  • Humans
  • Lycopersicon esculentum (enzymology, genetics)
  • Plant Proteins (genetics, therapeutic use)
  • Rats
  • Rats, Nude
  • Thymidine Kinase (genetics, therapeutic use)
  • Xenograft Model Antitumor Assays (methods)

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