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Updated: Sep 8, 2026
Evaluating the Effectiveness of Cancer Drug Sensitization In Vitro and In Vivo
Published on: February 6, 2015
Determinants of the sensitivity of human small-cell lung cancer cell lines to methotrexate
Abstract:
We have characterized the determinants of methotrexate (MTX) responsiveness in eight patient-derived cell lines of small-cell lung cancer (SCLC). Clonogenic survival was correlated with factors known to affect sensitivity to drug. NCI-H209 and NCI-H128 were most drug sensitive, with drug concentrations required to inhibit clonogenic survival by 50% with less than 0.1 microM MTX. Six cell lines (NCI-H187, NCI-H345, NCI-H60, NCI-H524, NCI-H146, and NCI-N417D) were relatively drug resistant. In all cell lines studied, higher molecular weight MTX-polyglutamates (MTX-PGs) with 3-5 glutamyl moieties (MTX-Glu3 through MTX-Glu5) were selectively retained. Relative resistance to low (1.0 microM) drug concentrations appeared to be largely due to decreased intracellular metabolism of MTX. Five of the six resistant lines were able to synthesize polyglutamates at higher (10 microM) drug concentrations, although one resistant cell line (NCI-N417D) did not synthesize higher molecular weight MTX-PGs, even after exposure to 10 microM drug. Two cell lines with resistance to 10 microM MTX (NCI-H146 and NCI-H524) synthesized and retained higher molecular weight MTX-PGs in excess of binding capacity after exposure to 10 microM drug. However, the specific activity of thymidylate synthase in these cell lines was low. MTX sensitivity in patient-derived cell lines of SCLC requires the ability of cells to accumulate and retain intracellular drug in the form of polyglutamate metabolites in excess of dihydrofolate reductase, as well as a high basal level of consumption of reduced folates in the synthesis of thymidylate.
Insights
Methotrexate (MTX) sensitivity in small-cell lung cancer (SCLC) cells depends on intracellular drug accumulation and retention as polyglutamates. High folate consumption for thymidylate synthesis is crucial for MTX responsiveness in SCLC.
Area of Science:
- Oncology
- Pharmacology
- Cancer Cell Biology
Background:
- Methotrexate (MTX) is a key chemotherapy agent.
- Understanding MTX responsiveness in small-cell lung cancer (SCLC) is critical for treatment optimization.
- Drug resistance mechanisms in SCLC limit therapeutic efficacy.
Purpose of the Study:
- To characterize the determinants of MTX responsiveness in patient-derived SCLC cell lines.
- To investigate the role of MTX polyglutamate formation and retention in drug sensitivity.
- To correlate cellular factors with MTX resistance in SCLC.
Main Methods:
- Culturing eight patient-derived SCLC cell lines.
- Assessing clonogenic survival after MTX exposure.
- Measuring intracellular MTX-polyglutamate (MTX-PG) levels.
- Evaluating thymidylate synthase activity.
Main Results:
- Two SCLC cell lines (NCI-H209, NCI-H128) were highly sensitive to MTX (<0.1 microM).
- Six SCLC cell lines exhibited relative resistance to MTX.
- Intracellular MTX-PG retention was observed in all cell lines, with higher molecular weight forms (MTX-Glu3-5) selectively retained.
- Resistance correlated with decreased MTX intracellular metabolism at low drug concentrations.
- Some resistant cell lines synthesized MTX-PGs at higher concentrations, but thymidylate synthase activity was low in two resistant lines (NCI-H146, NCI-H524).
Conclusions:
- MTX sensitivity in SCLC requires efficient intracellular accumulation and retention of MTX as polyglutamates, exceeding dihydrofolate reductase binding capacity.
- A high basal rate of reduced folate consumption for thymidylate synthesis is essential for MTX responsiveness.
- Variations in MTX metabolism and polyglutamation contribute to drug resistance in SCLC.
