A comparison of DNA-binding drugs as inhibitors of E2F1- and Sp1-DNA complexes and associated gene expression

In this study, we examined how DNA-binding drugs prevented formation of transcription factor-DNA complexes and influenced gene transcription from the hamster dihydrofolate reductase promoter, which is regulated by E2F1 and Spl. Gel mobility shift assay data showed that GC-binding drugs (e.g., mitoxantrone) inhibited the DNA binding of both E2F1 and Spl. In contrast, AT-binding drugs (e.g., distamycin) interfered only with E2F1-DNA complex formation. In an in vitro transcription assay using HeLa nuclear extracts, inhibition of transcription was observed when mitoxantrone or distamycin was added either before or after assembly of the transcription complex on the DNA, although for the latter, higher drug concentrations were needed. Mitoxantrone, which was a stronger inhibitor of transcription factor-DNA complex, was more effective than distamycin at preventing transcript formation. Time course transcription in a cell-free assay with addition of various drug concentrations indicated that high drug concentrations of either mitoxantrone or distamycin completely blocked transcription, while low drug concentrations could delay the synthesis of transcripts.