title: Pathways for the emergence of multi-dideoxynucleoside-resistant HIV-1 variants.
abstract: OBJECTIVE
  To investigate the mechanism by which the Q151M mutation in reverse transcriptase (RT) that confers multi-dideoxynucleoside resistance on HIV-1 and that requires a two base change (CAG-->ATG) develops, and to understand the reason for the relatively lengthy period of time required for its emergence under therapy with multiple nucleoside RT inhibitors (NRTI).
  
  
  METHODS
  Propagation assays and competitive HIV-1 replication assays were used to evaluate the fitness of various infectious clones, including two putative intermediates (HIV-1(Q151K(AAG)) and HIV-(1Q151L(CTG))) for HIV-1(Q151M(ATG)), in terms of sensitivity to zidovudine and didanosine. Steady-state kinetic constants of recombinant RT were also determined.
  
  
  RESULTS
  HIV-1(Q151L) replicated relatively poorly while HIV-1(Q151K) failed to replicate. When HIV-1(Q151L) was propagated further, it took three pathways in continuing to replicate: (i) HIV-1(Q151L) changed to HIV-1(Q151M) in eight of 16 experiments; (ii) HIV-1(Q151L) reverted to wild-type HIV-1 (HIV-1(WT)) in four of 16 experiments; and (iii) HIV-1(Q151L) acquired an additional mutation M230I in four of 16 experiments improving HIV-1 fitness. The relative order of replicative fitness without drugs was: HIV-1(Q151M) > HIV-1(WT) > HIV-1(Q151L/M230I) > HIV-1(M230I) >> HIV-1(Q151L) >>> HIV-1(Q151K), HIV-1(Q151K/M230I). HIV-1(Q151M) was less susceptible to drugs, while HIV-1(Q151L/M230I) was as sensitive as HIV-1(WT). Enzymatic assays corroborated that HIV-1(Q151L) is more replication-competent than HIV-1(WT) and HIV-1(Q151K) in the presence of drugs.
  
  
  CONCLUSIONS
  HIV-1(Q151M) probably develops through a poorly replicating HIV-1(Q151L); however, it is also possible that it occurs through two concurrent base changes. The present data should explain the mechanism by which HIV-1(Q151M) emerges after long-term chemotherapy with NRTI.
authors.affiliation: The Experimental Retrovirology Section, HIV and AIDS Malignancy Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Shintaro
authors.initials: S
authors.lastname: Matsumi
authors.forename: Pope
authors.initials: P
authors.lastname: Kosalaraksa
authors.forename: Hsinyi
authors.initials: H
authors.lastname: Tsang
authors.forename: Mark F
authors.initials: MF
authors.lastname: Kavlick
authors.forename: Shigeyoshi
authors.initials: S
authors.lastname: Harada
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Mitsuya
mesh_terms: D019380:Anti-HIV Agents / Q000494:pharmacology*; D016049:Didanosine / Q000494:pharmacology; D015224:Dideoxynucleosides / Q000494:pharmacology*; D024921:Drug Resistance, Multiple, Viral; D054303:HIV Reverse Transcriptase / Q000235:genetics*; D015497:HIV-1 / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D006801:Humans; D009154:Mutation; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology; D014779:Virus Replication / Q000187:drug effects; D015215:Zidovudine / Q000494:pharmacology
chemical_list: D019380:Anti-HIV Agents; D015224:Dideoxynucleosides; D018894:Reverse Transcriptase Inhibitors; D015215:Zidovudine; D054303:HIV Reverse Transcriptase; D016049:Didanosine