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The isolation and genetic analysis of V79-derived etoposide sensitive Chinese hamster cell mutants: two new
1School of Biological Sciences, Donnan Laboratories, University of Liverpool, Liverpool, UK.
Abstract:
Using a replica plating microwell method, three Chinese hamster V79-derived cell lines, designated ETO1, ETO2 and ETO3, which exhibit hypersensitivity to the non-intercalating topoisomerase II inhibitor etoposide have been isolated. Mutant lines ETO2 and ETO3 are cross-sensitive to the topoisomerase II inhibitors adriamycin and streptonigrin; however, neither mutant is sensitive to the topoisomerase I inhibitor camptothecin, the bifunctional alkylating agent mitomycin C, nor hydrogen peroxide. In contrast, ETO1 is cross-sensitive to camptothecin but displays only slight sensitivity to adriamycin, streptonigrin and hydrogen peroxide, and is not sensitive to mitomycin C. It has been established through extensive cell fusion studies that all three mutants are genetically distinct, and that ETO2 and ETO3 genetically complement all other known etoposide-sensitive Chinese hamster cell mutants (i.e., irs1, XR-1, xrs1, V3, BLM2, ADR1, ADR3, ADR4 and ADR5) thus defining two new complementation groups of etoposide sensitive mutants. Interestingly, the hybrids created by the fusion irs2TOR (thioguanine and ouabain resistant)xETO1 and the reciprocal cross ETO1TORxirs2 both exhibited a response to camptothecin intermediate with respect to V79 and ETO1. It has been hypothesised that this partial complementation may be the result of intragenic complementation and that both ETO1 and irs2 result from mutations in the gene XRCC8. This study indicates that cellular responses to topoisomerase II inhibitors are complex and hypersensitivity may result from mutations in many different genes.
Insights
Researchers isolated three Chinese hamster cell lines hypersensitive to etoposide, a topoisomerase II inhibitor. These mutants define new genetic groups, revealing the complex nature of cellular responses to DNA-damaging drugs.
Area of Science:
- Molecular Biology
- Genetics
- Drug Resistance
Background:
- Etoposide is a non-intercalating topoisomerase II inhibitor used in cancer therapy.
- Understanding cellular hypersensitivity to etoposide is crucial for developing effective treatments.
- Previous studies identified several etoposide-sensitive Chinese hamster cell mutants.
Purpose of the Study:
- To isolate and characterize novel Chinese hamster cell lines hypersensitive to etoposide.
- To investigate the genetic basis of etoposide hypersensitivity and cross-sensitivity patterns.
- To define new complementation groups for etoposide-sensitive mutants.
Main Methods:
- Isolation of etoposide-hypersensitive V79-derived cell lines (ETO1, ETO2, ETO3) using replica plating microwell method.
- Cross-sensitivity testing with various DNA-damaging agents including topoisomerase inhibitors, alkylating agents, and hydrogen peroxide.
- Extensive cell fusion studies to determine genetic distinctness and complementation groups.
Main Results:
- Three distinct etoposide-hypersensitive mutants (ETO1, ETO2, ETO3) were isolated.
- ETO2 and ETO3 showed cross-sensitivity to other topoisomerase II inhibitors but not topoisomerase I inhibitors or mitomycin C.
- ETO1 exhibited cross-sensitivity to camptothecin (a topoisomerase I inhibitor) and slight sensitivity to other agents, defining a new complementation group.
- ETO2 and ETO3 defined a second new complementation group, distinct from previously identified mutants.
- Fusion studies suggested ETO1 and irs2 may involve mutations in the XRCC8 gene, potentially exhibiting intragenic complementation.
Conclusions:
- Cellular responses to topoisomerase II inhibitors are complex, involving multiple genetic pathways.
- Hypersensitivity to etoposide can arise from mutations in various genes, defining new complementation groups.
- The characterization of ETO1, ETO2, and ETO3 provides new insights into DNA repair mechanisms and drug sensitivity.
