The ability of hypoxia to modify the gene expression of thymidylate synthase in tumour cells in vivo

Purpose: Hypoxic cells in tumours are resistant to 5-fluorouracil (5-FU). This in vivo study investigated the ability of hypoxia to regulate the gene expression of thymidylate synthase (TS), the target enzyme of 5-FU. Materials and methods: C3H mammary carcinomas, grown in the feet of female CDF1 mi...

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Bibliographic Details
Published in:International journal of radiation biology 1999, Vol.75 (7), p.885-891
Main Author: EHRNROOTH, H. VON DER MAASE, B. S. SORENSEN, J. HJELM POULSEN, M. R. HORSMAN, E.
Format: Article
Language:English
Subjects:
Animals
Antimetabolites, Antineoplastic - pharmacology
Antineoplastic agents
Base Sequence
Biological and medical sciences
DNA Primers - genetics
Drug Resistance
Female
Fluorouracil - pharmacology
Gene Expression
General aspects
Hypoxia - enzymology
Hypoxia - genetics
Mammary Neoplasms, Experimental - enzymology
Mammary Neoplasms, Experimental - genetics
Mammary Neoplasms, Experimental - therapy
Medical sciences
Mice
Pharmacology. Drug treatments
RNA, Messenger - genetics
RNA, Messenger - metabolism
RNA, Neoplasm - genetics
RNA, Neoplasm - metabolism
Thymidylate Synthase - genetics
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Summary:Purpose: Hypoxic cells in tumours are resistant to 5-fluorouracil (5-FU). This in vivo study investigated the ability of hypoxia to regulate the gene expression of thymidylate synthase (TS), the target enzyme of 5-FU. Materials and methods: C3H mammary carcinomas, grown in the feet of female CDF1 mice, were used for all experiments. Mice were placed in a 10% oxygen environment for various time periods and the tumour oxygen status was determined with an Eppendorf oxygen electrode. The animals were then injected with BrdU (100mg/kg, i.p.). Tumours were excised and immediately frozen (-80 C) until isolation of total RNA. The mRNA was reversibly transcribed to complementary DNA and the resulting cDNA amplified in a multiplex PCR reaction, with beta-actin as the internal reference gene. Results: One hour of low oxygen breathing made tumours significantly more hypoxic. This increase was maintained for a maximum incubation period of 48h. In the same tumours, no change in TS gene expression was seen with up to 3h of low oxygen breathing. At longer times it decreased, reaching significance at 12-24h and remaining at this lower level for up to 48h. BrdU labelling was significantly reduced after breathing low O2 for 24h (p=0.001). Conclusion: Hypoxia-induced down-regulation of TS gene expression was observed. This would be expected to make hypoxic tumour cells more sensitive to 5-FU. Other mechanisms must be responsible for the previously reported resistance to this drug.
ISSN:0955-3002
1362-3095
DOI:10.1080/095530099139944