Substituted pyridopyrrolopyrimidine ribonucleosides of general formula I, wherein R is as described in the independent claim, preferably R is selected from the group comprising thiophen-3-yl, furan-2-yl, furan-3-yl, benzofuran-2-yl, methylsulfanyl, methoxy, amino, dimethylamino, methyl; and pharmaceutically acceptable salt thereof, their optical isomers and mixtures of such optical isomers. Compounds according to the invention show strong cytostatic and cytotoxic effects on cell lines of tumor origin in a wide variety of diseases including tumors of different histogenetic origin.