Related Experiment Videos
The relationship between intrinsic thymidylate synthase expression and sensitivity to THYMITAQ in human leukaemia and
E J Estlin1, K Balmanno, A H Calvert
1Department of Paediatric Oncology, Sir James Spence Institute of Child Health, Royal Victoria Infirmary, Newcastle upon Tyne, UK.
Abstract:
Thymidylate synthase (TS) expression has been characterized for a panel of eight human colorectal carcinoma and five human leukaemia cell lines, to relate differences in intrinsic TS activity, protein and mRNA levels to growth inhibition caused by continuous exposure to THYMITAQ, a specific non-classical antifolate TS inhibitor. Although a 20-fold variation in sensitivity to THYMITAQ was found within the colorectal cell line panel (IC50 0.12-2.7 microM), sensitivity was not related to TS activity, TS protein or TS mRNA levels. For the leukaemic cell lines, only a twofold range in sensitivity to THYMITAQ was observed (IC50 0.87-2.3 microM), and this did not correlate with TS activity, TS protein or TS mRNA levels. Across all of the cell lines, TS activity was linearly related to TS protein levels (r2 = 0.87, P < 0.0001). However, for both the colorectal and leukaemia cell line panels, no relationship was found between TS mRNA/18S rRNA ratios and either TS activity or TS protein, consistent with the importance of post-transcriptional mechanisms in regulating TS activity. Two of the colorectal cell lines (BE and HCT116) and one of the human leukaemic cell lines (HL60), were intrinsically resistant to THYMITAQ (IC50 > 2 microM) in the absence of TS overexpression, suggesting that, subsequent to TS inhibition, events such as DNA repair and tolerance to apoptotic stimuli are also important determinants of sensitivity to THYMITAQ.
Insights
Sensitivity to THYMITAQ, a thymidylate synthase (TS) inhibitor, varied in colorectal and leukaemia cell lines. Resistance was not solely linked to TS levels, suggesting other cellular mechanisms influence drug response.
Area of Science:
- Oncology
- Pharmacology
- Molecular Biology
Background:
- Thymidylate synthase (TS) is a key enzyme in DNA synthesis and a target for antifolate drugs.
- Understanding the relationship between TS expression and drug sensitivity is crucial for cancer therapy.
Purpose of the Study:
- To investigate the correlation between thymidylate synthase (TS) expression (activity, protein, mRNA) and sensitivity to THYMITAQ, a non-classical antifolate TS inhibitor.
- To explore factors contributing to intrinsic resistance to THYMITAQ in colorectal and leukaemia cell lines.
Main Methods:
- Characterization of TS expression levels (activity, protein, mRNA) in eight human colorectal carcinoma and five human leukaemia cell lines.
- Assessment of growth inhibition (IC50) upon continuous exposure to THYMITAQ.
- Statistical analysis to determine correlations between TS parameters and drug sensitivity.
Main Results:
- A 20-fold variation in THYMITAQ sensitivity was observed in colorectal cell lines, but not correlated with TS activity, protein, or mRNA levels.
- Leukaemia cell lines showed a twofold range in sensitivity, also not correlating with TS expression.
- TS activity was linearly related to TS protein levels, but TS mRNA/18S rRNA ratios did not correlate with TS activity or protein, indicating post-transcriptional regulation.
Conclusions:
- Intrinsic resistance to THYMITAQ in some cell lines was not explained by TS overexpression.
- Factors beyond TS inhibition, such as DNA repair and apoptotic tolerance, are critical determinants of THYMITAQ sensitivity.