Acquisition of the Q151M Mutation May Occur through a Q151L Intermediate but Requires the Presence of Specific Polymorphisms (S68G) in the Reverse Transcriptase (RT)

J. G. GARCIA LERMA*¹, P. GERRISH², A. WRIGHT¹, S. QARI¹, and W. HENEINE¹. ¹CDC, Atlanta, GA; and ²Los Alamos Natl. Lab., NM

Background: HIV-1-infected patients treated with AZT+ddC/ddI frequently develop AZT resistance mediated by the T215Y mutation. A small proportion (3%-16%) of patients, however, develop multiple dideoxynucleoside resistance (MDR) mediated by the Q151M mutation. The factors responsible for the low frequency of the Q151M mutation are not known.
Objective: To investigate whether replication of intermediates of the Q151M mutation (151L or 151K) is a limiting step for developing MDR, and to identify polymorphisms in the RT that may influence replication of these intermediates.
Methods: Recombinant viruses having Q, L, M, or K at codon 151 were generated with cloned RTs derived from either HIV-1_HXB2 or two patient-derived HIV-1 isolates obtained before (HIV-1_pre/Q151) or during (HIV-1_post/151M) therapy. Replication capacity and AZT susceptibility of these viruses were measured.
Results: HIV-1_post/151L replicated efficiently and had enzymatic resistance to AZT-TP similar to that of HIV-1_post/151M. In contrast, other viruses carrying the 151L mutation did not replicate (HIV-1_pre/151L) or replicated poorly (HIV-1_HXB2/151L). All viruses with the 151K mutation did not replicate. HIV-1_post/151L differed from HIV-1_pre/151L by having three mutations (V35I, S68G, and I178M). Introduction of S68G restored replication capacity to both HIV-1_pre/151L and HIV-1_HXB2/151L. Both HIV-1_pre and HIV-1_pre/S68G were sensitive to AZT and had similar replicative fitness.
Conclusions: Acquisition of the Q151M mutation is limited by the impaired replication of 151L or 151K intermediates. The ability of the S68G mutation to restore replication of HIV-1_151L suggests that 151L is a potential intermediate of Q151M. The dependence of 151L on other mutations such as S68G may explain the low frequency of the Q151M-mediated pathway of resistance.

Key Words: Fitness, Nucleoside analogs, Reverse transcriptas

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