To obtain an extinction promotor for nucleic acid base hydroxide useful for cancer therapies such as radiotherapy, optical therapy, chemotherapy, etc., comprising a specific heterocyclic aromatic compound and having excellent extinction promoting action for nucleic acid base hydroxide.

This extinction promoter for a nucleic acid base hydroxide comprises a heterocyclic aromatic compound preferably expressed by formula I [R is CH2OCH(CH2OH)CHOHCH2OH, CH2(CO)NHCH2CH2OH, CH2CF2(CO) NHCH2CH2OH, CH2CH(OH) CH2NHCH2CH2Br] and having a straight chain, a branched chain or a cyclic alkyl group as a side chain and a nitro group. As the compound of formula I, 1-(2,3-dihydroxy-1- hydroxymethylpropyloxymethyl)-2-nitroimidazole of formula II can be preferably cited. The compound of formula I can be obtained by usual methods. The extinction promoter for a nucleic acid base hydroxide comprising the compound can promote the extinction of, e.g. 8-hydroxyguanine.