Anaerobic bacteria as a delivery system for cancer gene therapy: in vitro activation of 5-fluorocytosine by genetically engineered clostridia

Certain species of anaerobic bacteria have been shown to localise and germinate specifically in the hypoxic regions of tumours, resulting in tumour lysis. We propose an innovative approach to cancer gene therapy in which genetically engineered anaerobic bacteria of the genus Clostridium are used to...

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Bibliographic Details
Published inGene therapy Vol. 3; no. 2; p. 173
Main Authors Fox, M E, Lemmon, M J, Mauchline, M L, Davis, T O, Giaccia, A J, Minton, N P, Brown, J M
Format Journal Article
LanguageEnglish
Published England 01.02.1996
Subjects
Animals
Antimetabolites, Antineoplastic
Base Sequence
Carcinoma - therapy
Cell Survival - drug effects
Cloning, Molecular
Clostridium - genetics
Cytosine Deaminase
Escherichia coli - enzymology
Flucytosine - toxicity
Fluorouracil
Gene Transfer Techniques
Genetic Therapy - methods
Mammary Neoplasms, Experimental - therapy
Mice
Molecular Sequence Data
Nucleoside Deaminases - genetics
Nucleoside Deaminases - metabolism
Prodrugs - toxicity
Transformation, Bacterial
Tumor Cells, Cultured
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Summary:Certain species of anaerobic bacteria have been shown to localise and germinate specifically in the hypoxic regions of tumours, resulting in tumour lysis. We propose an innovative approach to cancer gene therapy in which genetically engineered anaerobic bacteria of the genus Clostridium are used to achieve tumour-specific gene delivery. Our strategy involves enzyme/prodrug therapy, in which the Escherichia coli enzyme cytosine deaminase is used to convert the non-toxic prodrug 5-fluorocytosine to the active chemotherapeutic agent 5-fluorouracil. The E. coli gene encoding cytosine deaminase has been cloned into a clostridial expression vector and transformed into Clostridium beijerinckii, resulting in constitutive expression of cytosine deaminase and significant levels of active enzyme in the bacterial medium. When added to an in vitro clonogenic survival assay, supernatant from clostridia expressing cytosine deaminase increased the sensitivity of murine EMT6 carcinoma cells to 5-fluorocytosine approximately 500-fold. This high level of prodrug activation, combined with the specificity of clostridia for hypoxic regions of tumours, indicates a potential use in cancer gene therapy.
ISSN:0969-7128