Effects of anticancer drugs on transcription in vitro

The effects of DNA interacting drugs on: (1) total RNA synthesis catalyzed by E.coli and T7 RNA polymerase; (2) synthesis of the initiating dinucleoti de (pppApU) by E.coli RNA polymerase ("abortive initiation"); (3) elongatio n of RNA chains synthesized by T7 RNA polymerase on pT7-7 plasmid DNA beari ng T7 RNA polymerase promoter phi 10 with human Cu/Zn superoxide dismutase coding sequence, (4) interaction of transcription factor Sp1 and its bindin g site were studied. Intercalating ligands which form quickly dissociating complexes with DNA (anthracyclines, proflavine, ethidium bromide) are compa red with the slowly dissociating drug of d(G . C) specificity (actinomycin D), the non-intercalating, d(A . T) specific pyrrole antibiotics (netropsin and distamycin A) and covalently binding to DNA 1-nitroacridine derivative (nitracrine). The obtained results indicate that rapidly dissociating liga nds, proflavine and ethidium bromide, inhibit total RNA synthesis in vitro and the abortive initiation to a similar extent while they do not induce di screte elongation stops of RNA polymerase. Actinomycin D and nitracrine exh ibit a high inhibitory effect on total RNA synthesis and induce stops of RN A polymerase while not affecting abortive initiation. Pyrrole antibiotics p rimarily inhibit the initiation, while no elongation stops are induced. Act inomycin D inhibits complex formation between nuclear proteins and the Sp1 binding site. Netropsin, ethidium bromide, proflavine and other intercalati ng acridines do not affect Sp1 binding. The results indicate that the effec ts primarily depend on sequence specificity and secondarily on the dissocia tion rate of ligands from their complexes with DNA.