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Influence of thiols on inhibition of ribonucleic acid synthesis in vitro by a 1-nitro-9-aminoalkylacridine derivative, C-283.

1-Nitro-9,3- N,N -dimethylaminopropylaminoacridine (C-283) is of pharmacological interest as a potent inhibitor of tumor growth and RNA synthesis in vivo . Its effect on RNA synthesis directed by Escherichia coli RNA polymerase is strongly influenced by sulfhydryl compounds. Its maximal inhibitory effect requires simultaneous mixing of a sulfhydryl compound, such as mercaptoethanol, dithiothreitol, or α-thioglycerol, with DNA and drug at pH 8.0 prior to addition of the enzyme. Very slight inhibition was observed with the nitroacridine in the absence of a thiol. The influence of sulfhydryl compounds has been ascribed to reaction of the template with the 1-nitro group of the dye. Among the DNA-interacting dyes so far investigated, only 1-nitro analogues of C-283 enhance inhibition in the presence of sulfhydryl compounds. There are indications that the metabolite rather than the nitroacridine itself is responsible for the inhibitory effect in vivo .