On the inhibition of the RNA polymerase-catalysed synthesis of RNA by daunomycin. Interference of the inhibitor with elongation and pre-longation steps

Enhancement of the Antiviral Activity of Poly (A-U) by Adriamycin and Daunomycin

The role of adriamycin (ADR) and daunomycin (DMN) in modulating the antiviral activity of poly (adeylate-uridylate) (poly (A-U)) was examined using a human foreskin fibroblast – vesicular stomatitis virus (HSF-VSV) bioassay in which the concentration of poly (A-U) was fixed at 0.05 mm or 0.2 mm while the ADR or DMN concentration was varied to produce ADR (or DMN)/ribonucleotide ratios ranging from 1:16 to 2:1. Poly (A-U), ADR and DMN were not efficacious antiviral agents when tested individually at the concentrations employed in the ADR (or DMN)/poly (A-U) combinations. When the ADR or DMN was combined with the poly (A-U) to produce ADR (or DMN)/poly (A-U) ratios of 1/6, the 50% effective doses (ED50) of the poly (A-U), ADR and DMN decreased 18, 104, and 185-fold, respectively. However, when ADR or DMN was combined with polyriboinosinic-polyribocytidylic acid [poly (I) · poly (C)], the ED50 of the ADR, DMN and the poly (I) · poly (C) were not affected. Interferon neutralization studies indicated that ADR, DMN, poly (A-U) and the ADR (or DMN)/poly (A-U) combination induced the production of interferon-beta (IFN-β). The amount of IFN produced by the ADR (or DMN)/poly (A-U) combinations was equal to the sum of the IFN prduced by their constituents. These results indicate that the ADR and DMN potentiate the antiviral activity of the poly (A-U) without affecting the amount of IFN induced. The direct viral inactivation study demonstrated that ADR, DMN, poly (A-U) and the ADR (or DMN)/poly (A-U) combinations do not inactivate the VSV at concentrations near the ED50.

RNA–Intercalating Agent Interactions: in vitro Antiviral Activity Studies

Twenty intercalating agents were tested to examine the effects of intercalating dye-induced perturbations upon the antiviral activity of poly (adenylate–uridylate) [poly (A-U)]. Neither poly (A-U) alone nor each intercalative dye was an efficacious antiviral agent. When poly (A-U) was combined with major groove intercalating dyes (acridine orange or proflavine), no synergism was observed. When poly (A-U) was combined with minor groove intercalating dyes [ethidium (EB), propidium (PI), adriamycin (ADR) or daunomycin (DMN)] or minor/major groove intercalating dyes [9-aminoacridine (9-AA), N2-methyl-9-hydroxy-ellipticine (NMHE) or N2,N6-dimethyl-9-hydroxy-ellipticine (DMHE)] the 50% effective doses (ED50) of the poly (A-U), 9-AA, ADR, DMHE, DMN, EB, NMHE and PI decreased 18-, 22-, 60-, 274-, 61-, 154-, 113- and 299-fold, respectively. When poly (A-U) was combined individually with 11 dyes whose mode of intercalation was not known, the ED50 of ametantrone (HAQ), chloroquine (CHL), mitoxantrone (DHAQ) and quinine (QUI) decreased 125-, 65-, 251- and 32-fold, respectively. These results suggest that the four dyes may intercalate into poly (A-U) from the minor groove. Ten (ADR, CHL, DMN, DHAQ, DMHE, EB, HAQ, NMHE, PI, QUI) of the 20 dyes evaluated exhibited significant synergism with poly (A-U), as quantified by the fractional inhibitory concentration index. Interferon (IFN) neutralization assays demonstrated that the IFN-inducing capability of the dye/poly (A-U) combinations approximated the sum of the capabilities of the poly (A-U) and the dyes employed. These results suggest that the majority of the dyes tested potentiate the antiviral activity of poly (A-U) without affecting the amount of IFN induced.

Drug inhibitors of RNA polymerase II transcription

Transcription by RNA polymerase II occurs after formation of a transcription complex. This complex is assembled in stages by the interaction of transcription factors with the template and/or with each other. We report on the ability of six drugs to inhibit the assembly of the RNA polymerase II transcription complex. Assembly of the complex on the adenovirus major late promoter requires several transcription factors. The normal assembly process requires that the DNA first interact with TFIIA, then with TFIID, and finally with at least four additional transcription factors (one of which is RNA polymerase II). We observed that streptolydigin (10 micrograms/ml) inhibits association of ILA and IID, and at higher concentrations (100 micrograms/ml) inhibits that IIA/IID complex from binding to DNA. Streptovaricin (100 micrograms/ml) appears to inhibit the IIA/IID interaction with DNA and prevents reinitiation (at 500 micrograms/ml). Adriamycin (1 microgram/ml) inhibits the interaction of TFIID with the IIA/DNA complex and inhibits an additional event immediately prior to, or during, elongation. Daunorubicin may be an elongation inhibitor. Heparin at 10 micrograms/ml inhibits further assembly after the IIA/IID/DNA complex has formed, and at 100 micrograms/ml also inhibits a late event in the assembly process and blocks reinitiation. Rifamycin AF/013 (100 micrograms/ml) inhibits the early events necessary to form the IIA/IID/DNA complex and (at 10 micrograms/ml) an assembly event following formation of the IIA/IID/DNA complex. Therefore, these compounds should be useful as probes for further examination of the assembly process.

In vitro DNA strand scission and inhibition of nucleic acid synthesis in L1210 leukemia cells by a new class of DNA complexers, the anthra[1,9-cd]pyrazol-6(2H)-ones (anthrapyrazoles)

CI-937 and CI-942 belong to a new class of DNA complexers, the anthra[1,9-cd]pyrazol-6(2H)-ones (anthrapyrazoles), and are being further developed as antitumor drugs based on their curative properties against murine solid tumour models. The biochemical effects of these agents were studied in L1210 leukemia in relation to other clinically used intercalators. After a 1-hr exposure, CI-937 and CI-942 reduced the cloning efficiency of L1210 cells by 50% at 3.0 X 10(-8) and 1.5 X 10(-7) M respectively. Based on an ethidium displacement assay, these drugs bound strongly to DNA, reducing the fluorescence of an ethidium-DNA complex by 50% at concentrations of 23 and 33 nM for CI-937 and CI-942 respectively. This was comparable to mitoxantrone at 15 nM, but much more potent than Amsacrine which required over 1.3 microM. A distinct property of the anthrapyrazoles was a much more potent inhibitory effect on whole cell DNA synthesis than on RNA synthesis. After L1210 cells were exposed to drug for 2 hr the concentration needed to inhibit DNA synthesis by 50% was 0.33 and 0.57 microM for CI-937 and CI-942, respectively, whereas 2.0 and 11.3 microM were required to inhibit RNA synthesis by the same extent. This was in contrast to Adriamycin and mitoxantrone which inhibited both activities equally at similar concentrations. It was apparent that the inhibition of these processes was not due to substrate depletion since intracellular ribonucleoside and deoxyribonucleoside triphosphates either remained constant or were elevated after a 2-hr exposure to 1 or 10 microM drug. A similar discriminatory effect was observed on DNA and RNA polymerase in permeabilized cells, and the inhibition of nucleic acid synthesis in this system could be reversed by exogenously added DNA. Since the high incidence of cardiotoxicity associated with the administration of anthracyclines has been related to the formation of reactive oxygen species, the ability of the anthrapyrazoles to augment superoxide dismutase sensitive oxygen consumption was observed in a rat liver microsomal system. CI-937 and CI-942 induced 5- and 10-fold less oxygen consumption than Adriamycin, producing rates of 12.4, 24.2 and 138.9 nmoles/min/mg microsomal protein, respectively, at a drug concentration of 0.5 mM.(ABSTRACT TRUNCATED AT 400 WORDS)