Differential removal of thymidine nucleotide analogues from blocked DNA chains by human immunodeficiency virus reverse transcriptase in the presence of physiological concentrations of 2 '-deoxynucleoside triphosphates

Removal of 2',3'-didehydro-3'-deoxythymidine-5'-monophosphate (d4TMP) from a blocked DNA chain can occur through transfer of the chain-terminating res idue to a nucleotide acceptor by human immunodeficiency virus type 1 (HIV-1 ) reverse transcriptase (RT). ATP-dependent removal of either d4TMP or 3'-a zido-3'-deoxythymidine-5'-monophosphate (AZTMP) is increased in AZT resista nt HIV-1 RT (containing D67N/K70R/T215F/K219Q mutations). Removal of d4TMP is strongly inhibited by the next complementary deoxynucleoside triphosphat e (50% inhibitory concentration [IC50] of similar to0.5 muM), whereas remov al of AZTMP is much less sensitive to this inhibition (IC50 of >100 muM). T his could explain the lack of cross-resistance by AZT-resistant HIV-1 to d4 T in phenotypic drug susceptibility assays.