Introduction: To assess whether dihydrofolate reductase (DHFR) expression is correlated with the concentration of methotrexate (MTX) exposure and the resistance index during the establishment of MTX-resistant human choriocarcinoma JeG-3 cell line.

Methods: Two series of different MTX-resistant JeG-3 sublines were established by intermittent- and consecutive-inducing methods. Quantitative real-time reverse transcription polymerase chain reaction was used to measure DHFR messenger RNA expression in the sublines during different concentrations of MTX exposure. β-Human chorionic gonadotropin (β-HCG) secretion in these cell lines were detected by using chemoluminescence method.

Results: In the 2 series of MTX-resistant cell lines, the same dynamic profiling of β-HCG secretion and DHFR transcript level were found: At a certain range of concentration, the upward β-HCG secretion and the messenger RNA level of DHFR were correlated with the dose of MTX exposing. However, once the concentration of MTX exceeded this range, the expression would not increase but decrease sharply. According to the concentration of MTX exposure from low to high, the multiples of β-HCG increases were 1.86-, 5.15-, 8.38-, 64.17-, 2.6-, and 0.78-fold for intermittent induction and 22.05-, 6.12-, 5.80-, and 1.77-fold for continuous induction; the multiples of DHFR gene expression increases were 12.84-, 99.02-, 129.01-, 177.63-, 420.78-, and 86.09-fold for intermittent induction and 9.59-, 20.56-, 96.05-, and 58.72-fold for continuous induction.

Conclusions: The transcript level of DHFR gene only correlated with MTX drug resistance at a certain phase. It would be of limited use as a biomarker for the MTX-based chemoresistance prediction.