Related Experiment Videos
Characterization of difluoromethylornithine-resistant mouse and human tumour cell lines
A Hirvonen1, T Eloranta, T Hyvönen
1Department of Biochemistry, University of Kuopio, Finland.
Abstract:
Four mouse and two human tumour cell lines resistant to alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), were analysed for the activities of polyamine-biosynthetic and -biodegradative enzymes as well as for cellular polyamine contents. In all but one of these cell lines the resistance to DFMO was based on an overproduction of ODC. In a human myeloma cell line the resistance was based on a greatly enhanced arginase activity. Except for one L1210 variant cell line, all the resistant cell lines contained elevated S-adenosylmethionine decarboxylase activity. Similarly, all the resistant mouse, but not human, cell lines displayed enhanced spermidine and spermine synthase activities. Arginase activity was detected only in human cell lines. In both DFMO-resistant cell lines the activity of arginase was strikingly elevated. Of the biodegradative enzymes, polyamine oxidase activity was readily detectable in all mouse cells, but no measurable activity was found in the human cells. Spermidine/spermine N1-acetyltransferase activity was elevated in three out of four resistant mouse cell lines. Even though the concentration of spermidine was usually lower in the overproducer cells, this was compensated by an increased content of spermine. The two resistant human myeloma cells contained intracellular ornithine concentrations that were from more than 5 to more than 20 times higher than those in the parental cells.
Insights
Drug resistance in cancer cells can arise from altered polyamine metabolism. This study reveals that resistance to alpha-difluoromethylornithine (DFMO) in tumor cells is often due to increased ornithine decarboxylase (ODC) or arginase activity.
Area of Science:
- Biochemistry
- Cancer Biology
- Pharmacology
Background:
- Polyamines are essential for cell growth and proliferation.
- Alpha-difluoromethylornithine (DFMO) is a potent inhibitor of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis.
- Tumor cell resistance to DFMO poses a significant challenge in cancer therapy.
Purpose of the Study:
- To investigate the mechanisms of DFMO resistance in mouse and human tumor cell lines.
- To analyze the activities of enzymes involved in polyamine metabolism and cellular polyamine content in resistant cells.
- To identify key enzymatic alterations contributing to DFMO resistance.
Main Methods:
- Analysis of polyamine-biosynthetic and -biodegradative enzyme activities.
- Quantification of cellular polyamine content.
- Comparison of enzyme activities and polyamine levels between DFMO-resistant and parental cell lines.
Main Results:
- DFMO resistance was primarily associated with ODC overproduction in most cell lines.
- A human myeloma cell line exhibited resistance due to significantly enhanced arginase activity.
- Elevated S-adenosylmethionine decarboxylase activity was observed in most resistant cell lines.
- Mouse cell lines showed increased spermidine and spermine synthase activities.
- Human cell lines displayed strikingly elevated arginase activity upon DFMO resistance.
- Polyamine oxidase was detectable in mouse cells, but not human cells.
- Spermidine/spermine N1-acetyltransferase activity increased in resistant mouse cells.
- Resistant human myeloma cells had significantly higher intracellular ornithine concentrations.
Conclusions:
- DFMO resistance mechanisms in tumor cells are diverse, involving ODC overproduction or enhanced arginase activity.
- Alterations in multiple polyamine metabolic enzymes contribute to drug resistance.
- Understanding these mechanisms is crucial for developing effective cancer treatment strategies targeting polyamine metabolism.