Inhibition of reverse transcriptase activity by 2′,3′-dideoxythymidine 5′-triphosphate and its derivatives modified on the 3′ position

Inhibitory effects of 2′,3′-dideoxythymidine 5′-triphosphate (ddTTP) and its three derivatives modified on the 3′ position of ribose moiety [3′-azido-2′,3′-dideoxythymidine 5′-triphosphate (3′-N 3-ddTTP), 3′-amino-2′,3′-dideoxythymidine 5′-triphosphate (3′-NH 2-ddTTP) and 2′-deoxyxylofuranosylthymine 5′-triphosphate (dXTP)] on the activity of the reverse transcriptase purified from Rauscher murine leukemia virus were examined and compared with each other. When (rA) n•(dT) 12–18 was used as the template · primer in the presence of manganese ion, all these compounds except 3′-NH 2-ddTTP inhibited the reverse transcriptase activity in competitive fashion with respect to the dTTP substrate. The inhibition potentials of these compounds are ordered as follows: 3′-N 3-ddTTP (Ki = 1.8 μM)>ddTTP (Ki = 9.3 μM)>dXTP (Ki = 16.3 μM), and the Ki values of these inhibitors are smaller than the Km of dTTP (30 μM). The observed inhibitions were mainly due to competition between the dTTP substrate and inhibitor rather than chain-termination of the elongating DNAs caused by incorporation of these dideoxy compounds.