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Decreasing sensitivity to cytotoxic agents parallels increasing tumorigenicity in human fibroblasts
1Paterson Institute for Cancer Research, Christie Hospital and Holt Radium Institute, Manchester, United Kingdom.
Abstract:
Human embryo fibroblasts of common genetic origin but exhibiting a range of phenotypes from normal to aggressively tumorigenic have been used to study resistance to the cytotoxic drugs methotrexate and N-(phosphonacetyl)-L-aspartate. Measurement of the intrinsic sensitivities of these cells to the two drugs in standard survival assays, in normal fetal bovine serum, showed increasing resistance to parallel increasing tumor-igenicity. Tumor cells were totally resistant to 10 mM N-(phosphonacetyl)-L-aspartate whereas the 50% lethal dose for methotrexate for the tumor cells was 500 nM compared with 50 nM for the normal diploid parent cell line. The difference in resistance between the immortal and tumorigenic cell lines was eliminated for both methotrexate and N-(phosphonacetyl)-L-aspartate, when the experiments were repeated in the presence of dialyzed fetal bovine serum, but could be restored by the addition of either hypoxanthine (100 microM) or uridine (10 microM). This suggested an important role for the salvage pathways of purine and pyrimidine biosynthesis in the increased resistance of the more tumorigenic cell lines. The implications of these data in relation to cancer chemotherapy will be discussed.
Insights
Tumorigenic cells show increased resistance to methotrexate and N-(phosphonacetyl)-L-aspartate. This resistance is linked to purine and pyrimidine salvage pathways, impacting cancer chemotherapy strategies.
Area of Science:
- Biochemistry
- Cancer Biology
- Cell Biology
Background:
- Human embryo fibroblasts display varying tumorigenic phenotypes.
- Cytotoxic drug resistance is a significant challenge in cancer chemotherapy.
Purpose of the Study:
- To investigate the differential resistance of human fibroblasts to methotrexate and N-(phosphonacetyl)-L-aspartate.
- To elucidate the role of purine and pyrimidine salvage pathways in drug resistance.
Main Methods:
- Standard survival assays were performed on fibroblasts with varying tumorigenicity.
- Drug sensitivity was measured in the presence of normal and dialyzed fetal bovine serum.
- Restoration of drug sensitivity was assessed by adding hypoxanthine or uridine.
Main Results:
- Tumorigenic fibroblasts exhibited significantly higher resistance to both drugs compared to normal cells.
- Resistance was abolished in dialyzed serum but restored by hypoxanthine or uridine supplementation.
- N-(phosphonacetyl)-L-aspartate resistance was complete in highly tumorigenic cells.
Conclusions:
- Purine and pyrimidine salvage pathways play a critical role in the cytotoxic drug resistance of tumorigenic cells.
- These findings have implications for optimizing cancer chemotherapy regimens.
- Targeting salvage pathways could be a strategy to overcome drug resistance in cancer.