It should be noted, however, that this glioma cell line is only partially resistant to MTX (Figure 3); therefore, aberrations, downstream to MTX entry, such as the decrease in thymidylate synthase activity [32], a moderate elevation in the intracellular level of DHFR [33], or a decrease in the binding affinity of MTX to DHFR [23], might take place as well. This evidence concerns the gene DHFR and central nervous system cancer.