Abstract
Systemic administration of the highly potent anticancer therapeutic, tumour necrosis factor alpha (TNFα) induces high levels of toxicity and is responsible for serious side effects. Consequently, tumour targeting is required in order to confine this toxicity within the locality of the tumour. Bacteria have a natural capacity to grow within tumours and deliver therapeutic molecules in a controlled fashion. The non-pathogenic E. coli strain MG1655 was investigated as a tumour targeting system in order to produce TNFα specifically within murine tumours. In vivo bioluminescence imaging studies and ex vivo immunofluorescence analysis demonstrated rapid targeting dynamics and prolonged survival, replication and spread of this bacterial platform within tumours. An engineered TNFα producing construct deployed in mouse models via either intra-tumoural (i.t.) or intravenous (i.v.) administration facilitated robust TNFα production, as evidenced by ELISA of tumour extracts. Tumour growth was impeded in three subcutaneous murine tumour models (CT26 colon, RENCA renal, and TRAMP prostate) as evidenced by tumour volume and survival analyses. A pattern of pro-inflammatory cytokine induction was observed in tumours of treated mice vs. controls. Mice remained healthy throughout experiments. This study indicates the therapeutic efficacy and safety of TNFα expressing bacteria in vivo, highlighting the potential of non-pathogenic bacteria as a platform for restricting the activity of highly potent cancer agents to tumours.
Highlights
MG was administered to Balb/C mice bearing RENCA tumours i.t or CT26 tumours i.v. and monitored by whole-body bioluminescence imaging (BLI) over time
In order to qualitatively assess tumour targeting and proliferation of MG-TNFα, bacteria were administered to Balb/C mice bearing CT26 tumours (i.v.) and monitored by BLI and immunofluorescence (IF) over time
IF specific for E. coli confirmed bacterial presence within tumour tissue, and viable bacteria were recovered at all-time points examined
Summary
TNFerade is a serotype 5 adenovirus that expresses TNFα under the control of the early growth response gene (egr-1) promoter that responds to radiation, which has been examined in Phase 3 clinical trials for advanced prostate cancer [4,5,6,7] In this approach, while the biological delivery vehicle is not confined to tumours, TNFα production is restricted via physically targeted radiation induction of the egr-1 promoter to express the TNFα transgene. Unlike viral vectors, which induce agent production via transduction of cells followed by host cell expression of the delivered transgene, bacteria provide the option of host cell production (through employment of an invasive strain–aka ‘bactofection’ [10, 11]) or the bacterium can express the agent directly For the latter, non-pathogenic strains of bacteria may be used (e.g. probiotics), increasing the safety profile of the platform [12]. We demonstrate the utility of the naturally non-pathogenic E. coli MG1655 as a platform for safe and effective in situ biomolecule production, and the capacity to improve the safety profile of promising anticancer agents through employment of this platform
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