In Vitro Characterization of the Bacteria-derived Hypoxia-selective Cytotoxin BE-43547

Morten Busk*, Peter P Eggertsen, Jens Overgaard, Michael R Horsman, Thomas Tørring, Kristian M Jacobsen, Thomas B Poulsen

*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

Abstract

BACKGROUND/AIM: Hypoxia-activated pro-drugs, such as TH-302, may kill hypoxic treatment-resistant tumor cells, but have failed in clinical trials. This may be related to variable levels of drug-activating reductases. Compounds such as bacteria-derived BE-43547, which target hypoxic cells independently of reductases, may be beneficial. This study characterized the in vitro potency and hypoxia selectivity of BE-43547 and TH-302.

MATERIALS AND METHODS: Tumor cells were exposed to different oxygenation levels in the presence/absence of drug, and survival was quantified using total cell number (BE-43547) or clonogenic survival (BE-43547 and TH-302) assays. Half-maximal inhibitory concentration (IC 50) values and the hypoxia-cytotoxicity-ratio (HCR: normoxic IC 50/hypoxic IC 50) were determined from dose-response curves. Finally, both drugs were tested in spheroids exposed to 20% or 0% O 2 for 24 h followed by assessment of clonogenic survival.

RESULTS: BE-43547 was highly potent and displayed little inter-cell line variability. Strongly enhanced cytotoxicity was observed under oxygen-restricted conditions with HCR's of ~100 and ~20 after 24 h of treatment with 0 or 0.5% O 2, respectively. Reducing treatment time somewhat reduced hypoxia selectivity. Hypoxia selectivity was observed regardless of whether the drug was added before or during the hypoxic challenge. TH-302 IC 50 values varied 10-fold under oxic conditions, whereas those of the anoxic-to-normoxic HCR varied from 15 to 88. Both BE-43547 and TH-302 were unable to completely sterilize anoxic incubated spheroids.

CONCLUSION: BE-43547 is highly hypoxia-selective, and unlike TH-302, displayed minimal variability between cell lines, suggesting that BE-43547 targets a fundamental feature/target that is only present, or of survival importance, during hypoxia. Spheroid experiments suggested inadequate tissue penetrability, which may be overcome by designing novel drug analogs.

Original languageEnglish
JournalAnticancer Research
Volume43
Issue12
Pages (from-to)5319-5329
Number of pages11
ISSN0250-7005
DOIs
Publication statusPublished - Dec 2023

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