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Radiosensitization of gliomas by intracellular generation of 5-fluorouracil potentiates prodrug activator gene therapy with a retroviral replicating vector

Cancer Gene Therapy volume 21, pages 405–410 (2014)Cite this article

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Abstract

A tumor-selective non-lytic retroviral replicating vector (RRV), Toca 511, and an extended-release formulation of 5-fluorocytosine (5-FC), Toca FC, are currently being evaluated in clinical trials in patients with recurrent high-grade glioma (NCT01156584, NCT01470794 and NCT01985256). Tumor-selective propagation of this RRV enables highly efficient transduction of glioma cells with cytosine deaminase (CD), which serves as a prodrug activator for conversion of the anti-fungal prodrug 5-FC to the anti-cancer drug 5-fluorouracil (5-FU) directly within the infected cells. We investigated whether, in addition to its direct cytotoxic effects, 5-FU generated intracellularly by RRV-mediated CD/5-FC prodrug activator gene therapy could also act as a radiosensitizing agent. Efficient transduction by RRV and expression of CD were confirmed in the highly aggressive, radioresistant human glioblastoma cell line U87EGFRvIII and its parental cell line U87MG (U87). RRV-transduced cells showed significant radiosensitization even after transient exposure to 5-FC. This was confirmed both in vitro by a clonogenic colony survival assay and in vivo by bioluminescence imaging analysis. These results provide a convincing rationale for development of tumor-targeted radiosensitization strategies utilizing the tumor-selective replicative capability of RRV, and incorporation of radiation therapy into future clinical trials evaluating Toca 511 and Toca FC in brain tumor patients.

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Acknowledgements

We thank Dr Christopher R Logg for advice and suggestions, and the UCLA Vector Core & Shared Resource Facility (supported by P30 DK041301 and P30 CA016042) for assistance with lentiviral vector production, and the UCLA Virology Core for assistance with p24 enzyme-linked immunosorbent assay. This work was supported in part by NIH grant no. U01 NS059821 and a research award from Tocagen. This work was also enabled by support to Tocagen from Accelerate Brain Cancer Cure, National Brain Tumor Society, American Brain Tumor Association, Musella Foundation and Voices Against Brain Cancer.

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Author notes

  1. M Takahashi and G Valdes: Co-first authors owing to their equal participation in this study.

Authors and Affiliations

  1. Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, University of California Los Angeles (UCLA), Los Angeles, CA, USA

    M Takahashi, K Hiraoka, A Inagaki, S Kamijima & N Kasahara

  2. Department of Radiation Oncology, David Geffen School of Medicine, University of California Los Angeles (UCLA), Los Angeles, CA, USA

    G Valdes, E Micewicz, W H McBride & K S Iwamoto

  3. Tocagen, San Diego, CA, USA

    H E Gruber, J M Robbins & D J Jolly

  4. Departments of Cell Biology and Pathology, Miller School of Medicine, University of Miami, Miami, FL, USA

    N Kasahara

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  1. M Takahashi
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  2. G Valdes
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  3. K Hiraoka
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  7. H E Gruber
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  10. W H McBride
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  11. K S Iwamoto
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Corresponding author

Correspondence to N Kasahara.

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Competing interests

HEG, JMR and DJJ are employees and/or shareholders of Tocagen. NK is a consultant, has ownership interest and is the recipient of a research grant from Tocagen. The research conducted under this grant award has been reviewed and approved by the UCLA Conflict of Interest Review Committee.

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Takahashi, M., Valdes, G., Hiraoka, K. et al. Radiosensitization of gliomas by intracellular generation of 5-fluorouracil potentiates prodrug activator gene therapy with a retroviral replicating vector. Cancer Gene Ther 21, 405–410 (2014). https://doi.org/10.1038/cgt.2014.38

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  • DOI: https://doi.org/10.1038/cgt.2014.38

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