, Volume 25, Issue 5, pp 417-423
Date: 30 May 2007

In vitro chemosensitivity of freshly explanted tumor cells to pemetrexed is correlated with target gene expression

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Aim of the study

mRNA expression of genes involved in the mechanism of action of pemetrexed was correlated with in vitro chemosensitivity of freshly explanted human tumor specimens.

Experimental design

Chemosensitivity to pemetrexed was studied in soft-agar. Multiplex rtPCR experiments for reduced folate carrier (RFC), folate receptor-α (FR-α), folylpolyglutamate synthetase (FPGS), thymidylate synthase (TS), dihydrofolate reductase (DHFR), glycinamide ribonucleotide formyl transferase (GARFT), mrp4, and mrp5 were performed in parallel. Correlations, threshold optimization, sensitivity, specificity, and efficiency were analyzed using the appropriate statistical methodologies.


In 61 samples, low levels of TS, GARFT, DHFR, and mrp4 gene expression significantly correlated with chemosensitivity to pemetrexed. Optimization analyses demonstrated threshold values of 144 copies for TS and six copies for mrp4 relative to 104 copies of β-actin.


These results form a rational basis for the design of clinical trials to evaluate the expression of these enzymes as predictors for treatment outcome.

Axel-Rainer Hanauske and Ulrike Eismann have contributed equally to this project.