Inhibition of RNA synthesis in Ehrlich tumor cells by the dialdehyde derivative of inosine (NSC 118994).

The dialdehyde derivative of inosine, INOX (NSC 118994), was studied for its effect on RNA synthesis in Ehrlich tumor cells. INOX inhibited the incorporation of [l4C]uridine into the RNA of intact tumor cells. Polyacrylamide gel electrophoresis and sucrose gradient centrifugation analysis of the RNA showed that the synthesis of preribosomal RNA and high-molecular-weight RNA was inhibited by INOX. The dialdehyde derivatives of adenosine 5 -triphosphate and inosine 5 -triphosphate inhibited RNA synthesis in isolated nuclei. The dialdehyde deriva tives of 5 -inosinic acid and inosine when they were added to isolated nuclei did not inhibit RNA synthesis. However, when tumor cells were incubated with INOX or the dialde hyde derivative of 5 -inosinic acid and the nuclei were then isolated, there was a marked decrease in RNA synthesis. This inhibition was both time dependent and concentration dependent. The inhibition of RNA synthesis in the nuclei from treated cells was not reversed by changing the culture medium. a-Amanitin and actinomycin D inhibited RNA polymerase activities in the nuclei from control cells to the same extent that they inhibited the residual activity in the nuclei from the treated cells. Nuclear extracts prepared from the INOX-treated cells did not show a decrease in RNA polymerase activity, indicat ing a reversal of the inhibition. The inhibition of RNA synthesis in the nuclei from INOX-treated cells was com pletely reversed by the addition of exogenous polydeoxyadenylate-deoxythymidylate as template, showing that the inhibition of RNA synthesis by INOX was not due to the inhibition of RNA polymerases but rather was due to chain termination of the growing RNA strand or impair ment of template function.