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Biochem Pharmacol. 2018 Dec;158:192-200. doi: 10.1016/j.bcp.2018.10.020. Epub 2018 Oct 21.

Evaluating the abilities of diverse nitroaromatic prodrug metabolites to exit a model Gram negative vector for bacterial-directed enzyme-prodrug therapy.

Author information

1
School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand; Centre for Biodiscovery, Victoria University of Wellington, Wellington 6012, New Zealand.
2
School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand; Centre for Biodiscovery, Victoria University of Wellington, Wellington 6012, New Zealand; Michael Smith Laboratories, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
3
Auckland Cancer Society Research Centre, School of Medical Sciences, University of Auckland, Auckland 1023, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, School of Biological Sciences, University of Auckland, Auckland 1010, New Zealand.
4
School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand; Centre for Biodiscovery, Victoria University of Wellington, Wellington 6012, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, School of Biological Sciences, University of Auckland, Auckland 1010, New Zealand. Electronic address: david.ackerley@vuw.ac.nz.

Abstract

Gene-directed enzyme-prodrug therapy (GDEPT) employs tumour-tropic vectors including viruses and bacteria to deliver a genetically-encoded prodrug-converting enzyme to the tumour environment, thereby sensitising the tumour to the prodrug. Nitroreductases, able to activate a range of promising nitroaromatic prodrugs to genotoxic metabolites, are of great interest for GDEPT. The bystander effect (cell-to-cell transfer of activated prodrug metabolites) has been quantified for some nitroaromatic prodrugs in mixed multilayer human cell cultures, however while these provide a good model for viral DEPT (VDEPT) they do not inform on the ability of these prodrug metabolites to exit bacterial vectors (relevant to bacterial-DEPT (BDEPT)). To investigate this we grew two Escherichia coli strains in co-culture; an activator strain expressing the nitroreductase E. coli NfsA and a recipient strain containing an SOS-GFP DNA damage responsive gene construct. In this system, induction of GFP by reduced prodrug metabolites can only occur following their transfer from the activator to the recipient cells. We used this to investigate five clinically relevant prodrugs: metronidazole, CB1954, nitro-CBI-DEI, and two dinitrobenzamide mustard prodrug analogues, PR-104A and SN27686. Consistent with the bystander efficiencies previously measured in human cell multilayers, reduced metronidazole exhibited little bacterial cell-to-cell transfer, whereas nitro-CBI-DEI was passed very efficiently from activator to recipient cells post-reduction. However, in contrast with observations in human cell multilayers, the nitrogen mustard prodrug metabolites were not effectively passed between the two bacterial strains, whereas reduced CB1954 was transferred efficiently. Using nitroreductase enzymes that exhibit different biases for the 2- versus 4-nitro substituents of CB1954, we further showed that the 2-nitro reduction products exhibit substantially higher levels of bacterial cell-to-cell transfer than the 4-nitro reduction products, consistent with their relative bystander efficiencies in human cell culture. Overall, our data suggest that prodrugs may differ in their suitability for VDEPT versus BDEPT applications and emphasise the importance of evaluating an enzyme-prodrug partnership in an appropriate context for the intended vector.

KEYWORDS:

BDEPT; Bystander effect; Cancer gene therapy; GDEPT; Nitroreductase

PMID:
30352235
DOI:
10.1016/j.bcp.2018.10.020
[Indexed for MEDLINE]

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