Prediction of Abacavir Resistance from Genotypic Data: Impact of Zidovudine and Lamivudine Resistance In Vitro and In Vivo

Abstract

Abacavir is frequently used in antiretroviral combination therapies as a potent nucleoside reverse transcriptase inhibitor (NRTI). Four mutations are selected for by abacavir in vitro and in vivo: K65R, L74V, Y115F, and M184V. Abacavir resistance has also been observed in NRTI multidrug-resistant samples. Furthermore, abacavir resistance has been described in the context of zidovudine resistance. To evaluate the genetic basis of abacavir resistance, the viral genotype and phenotypic resistance were analyzed for 307 patient samples. Lowand high-level resistances were defined as 2.5-to 5.5-fold-and >5.5-fold-reduced susceptibility, respectively. If all samples with abacavir-selected and NRTI multidrug resistance-associated mutations were scored as resistant, 27.6% of the samples were misclassified, mainly due to samples falsely scored as susceptible. Therefore, the relative frequencies of other mutations were evaluated. Mutations at codons 44 and 118 were rarely detected in abacavir-susceptible samples but were overrepresented in resistant samples. Site-directed mutagenesis of E44D, V118I, and M184V resulted in low-level resistance for the double mutant 44/184 and the triple mutant. Low-level abacavir resistance was also detected for a viral clone carrying zidovudine mutations only. Additional insertion of M184V into the zidovudine background doubled the resistance, whereas 44/118 did not lead to a further increase. Incorporating combinations of zidovudine mutations and M184V into the scoring system markedly reduced the number of misclassified samples, whereas 44/118 did not improve the prediction. In conclusion, the combination of M184V with zidovudine mutations gives rise to high-level abacavir resistance, which may be clinically relevant. Thus, options for useful sequential combinations of NRTI are limited.

Mechanistic Studies to Understand the Progressive Development of Resistance in Human Immunodeficiency Virus Type 1 Reverse Transcriptase to Abacavir

“…The elevated rate of CBVMP removal may be related to the association between AZT resistance mutations and decreased abacavir activity in vitro (70) and in vivo (71). Interestingly, RT Q151M also showed an elevated rate of ATP-mediated removal of dGMP; however, it was slightly slower than RT WT at removing CBVMP.…”

Tenofovir Resistance and Resensitization

“…Viral clones were constructed by insertion of the following mutations into the HXB2 backbone: M41L; K70R; M184I; M184V; T215F; T215Y; M41L and K70R; M41L and M184V; M41L and T215F; M41L and T215Y; K70R and M184V; K70R and T215Y; M184V and T215Y; M41L, K70R, and T215Y; M41L, M184V, and T215Y; K70R, M184V, and T215Y; and M41L, K70R, M184V, and T215Y. Construction of viral clones with mutations within the NL4-3 backbone (mutations M184V; M184V and T215Y; L210W and T215Y; M184V, L210W, and T215Y; M41L, L210W, R211K, and T215Y; and M41L, M184V, L210W, R211K, and T215Y) was described previously (27). For the mutagenesis of positions 62 and 65 of the RT, the following sense (s) and antisense (as) primers were used: A65A-K65K-s (5Ј-CCAGTATTTGCCATAA AGAAAAAAAATA-3Ј), A62A-K65K-as (5Ј-ATTTTTTTTCTTTATGGCAAA TACTGGA-3Ј), A62V-K65K-s (5Ј-CCAGTATTTGTAATAAAGAAAAAAAA-3Ј), A62V-K65K-as (5Ј-TTTTTTTCTTTATTACAAATACTGGA-3Ј), A62A-K65R-s (5Ј-CCAGTATTTGCCATAAAGAGAAAAAA-3Ј), and A62A-K65R-as (5Ј-TTTTTCTCTTTATGGCAAATACTGGA-3Ј).…”

Impact of Novel Human Immunodeficiency Virus Type 1 Reverse Transcriptase Mutations P119S and T165A on 4′-Ethynylthymidine Analog Resistance Profile

“…The M184V mutation and the triple mutation (M184V/P119S/T165A) conferred 3-to 5-fold and 130-fold resistance to 4Ј-Ed4T, respectively. The M184V mutation, which is in a highly conserved motif (YMDD) of the polymerase active site of RT, is known to confer high-level resistance to 3TC and low-level resistance to zalcitabine, didanosine, and abacavir (13,44). Moreover, the M184V mutation has been reported to diminish viral fitness, reduce RT processivity, increase RT fidelity, and diminish the rescue of viral DNA synthesis in the presence of RT inhibitors (10,27,43).…”