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Differential methotrexate toxicity between two human oral squamous carcinoma cell lines
1Department of Otolaryngology, University of Western Ontario, Canada.
Abstract:
Methotrexate is often used for induction or palliative therapy of advanced head and neck squamous cell carcinoma (HNSCC). However, resistance to this drug is a common clinical problem, which may be conferred by several mechanisms, including: i) decreased level of folate transport proteins, required for entry of methotrexate into cells, and ii) increase in amount of dihydrofolate reductase (DHFR), the target enzyme of this drug. Two established, clonal cell lines of HNSCC, having equal growth rates, differed 9-fold in sensitivity to methotrexate. Cellular accumulation of radiolabelled methotrexate was measured, and did not differ between the two lines when corrected for the different volume of the cells. This suggested that the difference in drug sensitivity was not due to differential uptake. This was confirmed by the finding of a 22-fold difference in sensitivity to piritrexin, a lipophilic antifolate which enters cells by simple diffusion, and, unlike methotrexate, is not polyglutamated. These results suggest that a quantitative difference in DHFR between the two cell lines probably accounts for the differential sensitivity to antifolates. Screening of patient tumors for DHFR content and drug uptake may provide a basis upon which to recommend whether methotrexate treatment is indicated.
Insights
Drug resistance in head and neck cancer is common. This study suggests higher dihydrofolate reductase (DHFR) levels, not drug uptake, likely explain varying methotrexate sensitivity in head and neck squamous cell carcinoma (HNSCC) cells.
Area of Science:
- Oncology
- Pharmacology
- Molecular Biology
Background:
- Methotrexate is a key drug for advanced head and neck squamous cell carcinoma (HNSCC).
- Drug resistance, often due to altered folate transport or increased dihydrofolate reductase (DHFR), limits treatment efficacy.
- Understanding resistance mechanisms is crucial for optimizing HNSCC therapy.
Purpose of the Study:
- To investigate the mechanisms underlying differential sensitivity to methotrexate in HNSCC cell lines.
- To determine if drug uptake or enzyme levels explain variations in methotrexate response.
Main Methods:
- Compared methotrexate sensitivity in two HNSCC cell lines with equal growth rates.
- Measured cellular accumulation of radiolabeled methotrexate.
- Assessed sensitivity to piritrexin, an antifolate entering cells via diffusion.
Main Results:
- A 9-fold difference in methotrexate sensitivity was observed between the cell lines.
- Methotrexate uptake did not differ significantly between the cell lines, suggesting uptake is not the primary resistance factor.
- A 22-fold difference in piritrexin sensitivity indicated that intracellular enzyme levels, likely DHFR, are responsible for differential antifolate sensitivity.
Conclusions:
- Differential sensitivity to antifolates in HNSCC is likely due to quantitative variations in dihydrofolate reductase (DHFR) levels.
- Assessing DHFR content and drug uptake in patient tumors could guide methotrexate treatment decisions.
- This research may lead to more personalized therapeutic strategies for HNSCC.