| Summary: | Inhibition of DNA repair enzymes tyrosyl-DNA phosphodiesterase 1 and poly(ADP-ribose)polymerases 1 and 2 in the presence of pyrimidine nucleoside derivatives was studied here. New effective Tdp1 inhibitors were found in a series of nucleoside derivatives possessing 2′,3′,5′-tri-<i>O</i>-benzoyl-<span style="font-variant: small-caps;">d</span>-ribofuranose and 5-substituted uracil moieties and have half-maximal inhibitory concentrations (IC<sub>50</sub>) in the lower micromolar and submicromolar range. 2′,3′,5′-Tri-<i>O</i>-benzoyl-5-iodouridine manifested the strongest inhibitory effect on Tdp1 (IC<sub>50</sub> = 0.6 μM). A decrease in the number of benzoic acid residues led to a marked decline in the inhibitory activity, and pyrimidine nucleosides lacking lipophilic groups (uridine, 5-fluorouridine, 5-chlorouridine, 5-bromouridine, 5-iodouridine, and ribothymidine) did not cause noticeable inhibition of Tdp1 (IC<sub>50</sub> > 50 μM). No PARP1/2 inhibitors were found among the studied compounds (residual activity in the presence of 1 mM substances was 50–100%). Several <i>O</i>-benzoylated uridine and cytidine derivatives strengthened the action of topotecan on HeLa cervical cancer cells.
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