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An evaluation of thymidine phosphorylase as a means of preventing thymidine rescue from the thymidylate synthase inhibitor raltitrexed

Lookup NU author(s): Huw ThomasORCiD, Gordon Taylor, Professor Herbie Newell, Professor Alan Boddy


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The antitumour effect of thymidylate synthase inhibitors such as raltitrexed (RTX) may be reversed by salvage of thymidine (Thd). Since thymidine phosphorylase (TP) depletes Thd, the potential for tumour-selective depletion of Thd using antibody-mediated delivery of TP to tumours was investigated. In vitro studies demonstrated that 25 × 10-3 units/ml TP depleted extracellular Thd (3 μM) and restored sensitivity to the growth inhibitory effects of RTX in Lovo and HT29 cell lines. Thymidine concentrations in xenograft tumours were inversely proportional to the activity of TP in the tumour, and the presence of a subcutaneous Lovo xenograft reduced plasma Thd concentrations from 0.92 ± 0.07 to 0.37 ± 0.04 μM. Intravenous administration of native TP enzyme depleted plasma Thd to 5 nM, but following rapid elimination of TP, plasma Thd returned to pretreatment values. There was no effect on tumour TP or Thd. Conjugation of TP to the A5B7 F(ab)2 antibody fragment, which targets carcinoembryonic antigen (CEA) expressed on colorectal cell-lines such as Lovo, did result in selective accumulation of TP in the tumour. However, there was no tumour-selective depletion of Thd and there did not appear to be any potential benefit of combining antibody-targeted TP with RTX. © 2006 Springer-Verlag.

Publication metadata

Author(s): Graham-Cole C, Thomas HD, Taylor GA, Newell DR, Melton R, Hesp R, Boddy AV

Publication type: Article

Publication status: Published

Journal: Cancer Chemotherapy and Pharmacology

Year: 2007

Volume: 59

Issue: 2

Pages: 197-206

Print publication date: 01/02/2007

ISSN (print): 0344-5704

ISSN (electronic): 1432-0843


DOI: 10.1007/s00280-006-0258-x

PubMed id: 16721548


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