DHFR and glioblastoma: Using quantitative western blot analysis of lysates from CRSPR/Cas9-mediated glioblastoma ID-1-knockout cells (ID-1−/−U251.1, ID-1−/−U251.1) (U251-ID-1-null), we found lower expression of DHFR and MTHFD2 in U251-ID-1-null, compared to their parental controls (Fig. 2-A/B).