Department of International Clinical Virology, 1 GlaxoSmithKline Inc., 5 Moore Drive, Research Triangle Park, NC 27709, USA; 2 GlaxoSmithKline Research and Development, Stevenage, Hertfordshire SG1 2NY, UK
Keywords: amprenavir, lopinavir, genotype, resistance, HIV
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Introduction |
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In vitro and in vivo resistance profiles for amprenavir and lopinavir |
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In vitro virus passage experiments using lopinavir (with or without ritonavir) have primarily selected either the I84V mutation in combination with L10F, M46I, T91S, V32I, I47V and gag cleavage site mutations or, less frequently, the I50V mutation with M46I.9,10 Clones with a V82A substitution have also been observed.9 The high plasma levels of lopinavir achieved in subjects treated with lopinavir/ritonavir mean that virological failure in antiretroviral-naive patients has been rarely accompanied by genotypic changes in the protease. Where genotypic changes were seen, these were secondary mutations.11,12 In PI-experienced patients, lopinavir/ritonavir treatment selects various different genotypic changes on the background of existing PI mutations, most often L10F, M46I, I54V and V82A and occasionally I50V.11
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The impact of specific mutations on cross-resistance and response to amprenavir and lopinavir in PI-experienced subjects |
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We have analysed two large sets of matched genotypic and phenotypic data in order to determine the genotypic correlates of cross-resistance to amprenavir and lopinavir in subjects previously treated with other PIs. The first data set comprised 271 plasma samples from a cohort of 207 HIV-1-infected subjects enrolled in the Pacific Oaks Clinic Population Study.16 These subjects had received one to four consecutive or concurrent non-boosted PIs for at least 4 months and had either failed to attain a virological response (defined as HIV-1 RNA < 400 copies/mL) or had attained a virological response and subsequently experienced virological rebound (defined as HIV-1 RNA > 1000 copies/mL after virological response). PIs in the regimens for these subjects included indinavir, ritonavir, saquinavir, amprenavir and nelfinavir. The second data set included a random selection of 233 samples from the VIRCO database.18 Samples were derived from PI-experienced patients but no detailed treatment history was available. Univariate analyses of these data sets identified several differences between the profiles of mutations significantly associated with two levels of reduced susceptibility to each drug (2.5-fold and
5-fold for amprenavir and
2.5-fold and
10-fold for lopinavir, Table 1). In both data sets, and at both levels of resistance, more mutations were associated with lopinavir resistance than with amprenavir resistance. The substitutions I54T or V and V82A were strongly associated with lopinavir resistance but were not associated with amprenavir resistance. In contrast, the relative incidence of M46I and I84V was higher in the amprenavir-resistant virus populations than in lopinavir-resistant viruses. Mutations L10I, M36I, M46I, G73S and L90M were associated with resistance to both drugs in at least one of the cohorts studied. D30N was associated with susceptibility to amprenavir and lopinavir in both data sets and V77I was significantly associated with susceptibility to lopinavir in one of the data sets. In several cases, discordance in the results between the two studies may have been because of a low incidence of the mutation in one or both data sets (e.g. L24I, L33F, G48V, F53L, I54T) or to low relative incidence values for mutations with a high incidence (e.g. L10I, G73S, L90M).
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Other studies have generally confirmed these observations identifying the I84V as a key determinant of reduced phenotypic susceptibility to amprenavir14,15,19 as well as some associations between amprenavir resistance and M46I/L and L90M.14,19 Univariate analysis from two different studies also reported a significant association between amprenavir resistance and mutations at codon 54, but did not differentiate between different amino acid substitutions (L, M or V).14,19 In our analysis I54V, the most commonly seen substitution at this position in PI-experienced patients, was not associated with amprenavir resistance. In vitro site-directed mutagenesis studies also show that the I54V has no affect on amprenavir susceptibility.3 In addition, treatment of PI-experienced patients with amprenavir during the CNA2007 study resulted in the replacement of 54V or I with either 54M, wild-type, or 54L in several cases.4
In a study carried out by researchers from VIRCO on 1300 samples derived from PI-experienced subjects, the mutations (in order of decreasing prevalence) L10I, A71V, V82A, L90M, I54V, M46I, I84V, G73S and K20R were more frequent in viruses demonstrating resistance to lopinavir (>10-fold).20 Researchers at Abbott Laboratories analysed the genotypic correlates of reduced phenotypic susceptibility to lopinavir in 112 clinical isolates from PI-experienced patients and identified 11 amino acid substitutions that appeared to be involved in lopinavir resistance (L10F/I/R/V, K20M/R, L24I, M46I/L, F53L, I54L/T/V, L63P, A71I/L/T/V, V82A/F/T, I84V and L90M).21 The number of substitutions from this list (referred to as the lopinavir mutation score) correlated with the reduction in susceptibility to lopinavir (R2 = 0.62) and a score of six or more gave a mean reduction in susceptibility of >10-fold. Kempf et al. have also applied the mutation score approach to correlate genotype with virological response.22 They examined the virological response of 50 multiple PI-experienced HIV-infected subjects over 72 weeks of treatment with lopinavir/ritonavir plus efavirenz and nucleoside reverse transcriptase inhibitors (study M98-957). A virological response to <400 HIV-1 RNA copies/mL was observed in 91% (21/23), 71% (15/21) and 33% (2/6) of subjects with baseline lopinavir mutation scores of 05, 67 and 8, respectively. Several studies carried out on PI-experienced patients treated with lopinavir/ritonavir as part of expanded access programmes have also aimed to identify mutations associated with reduced virological response to lopinavir. In the Canadian expanded access programme, a study of 167 PI-experienced patients treated with lopinavir/ritonavir identified L90M as an independent predictor of reduced response.23 However, this study only considered mutations included in the Abbott lopinavir mutation score. In a study of 700 patients in the French Drug Agency Temporary Authorisation for Use (ATU) a univariate analysis identified mutations at positions 54, 82, 10 and 46 as being statistically significantly (P < 0.01) associated with virological failure. In a stepwise logistic regression, mutations at the same four positions were determined to be independently associated with virological failure.24 The specific amino acid substitutions seen in this study were not given. A second ATU study, involving 68 patients, found that M46I, I54V and V82A were associated with a poor response (P < 0.25) in a univariate analysis.17 A multivariate analysis identified I54V and a lopinavir mutation score of greater than five as being independent predictors of virological failure. A high number of previous PIs, prior therapy with ritonavir or indinavir, absence of co-prescription of efavirenz, and a lower ex-posure to lopinavir or lower lopinavir trough concentrations were also independently correlated with poor response. Further analysis of the ATU data has led to the definition of an alternative mutation score that includes mutations at positions 10, 20, 24, 33, 36, 47, 48, 54, 82 and 84 (specific substitutions not specified).25 A stepwise logistic regression analysis of the ATU data and data from study M98-957 identified the ATU mutation score as being a better predictor of virologic response than the original lopinavir mutation score.25 The Clinic-Based Investigators Group26 also examined genotypic predictors of clinical response to lopinavir in a multicentre clinical cohort (n = 77), and found that mutations 20M, 36I, 46L, 54S/V, 71V, 73S and 82A were significant predictors of response (P < 0.05), with the specific mutations 46L, 71V and 82A being the strongest predictors. A weighted genotype score appeared to predict response better than summing mutations, although both the Abbott lopinavir mutation score and the ATU set were also tested and both were predictive of virological response over 24 weeks. Other unusual amino acid variants at resistance associated sites may also impact lopinavir response, as recent presentations have identified the less common V84A and V84C variants and the I47A variant as increasing resistance to lopinavir.27,28
Two groups have proposed mutation scores for the prediction of virological responses to amprenavir from genotypic data. Analysis of results from the ANRS088 (NARVAL) clinical trial suggested a mutation score for unboosted amprenavir comprising the substitutions L10I, V32I, M46I/L, I47V, I54V, G73S, V82A/F/T/S, I84V and L90M.29 A mutation score of 4 was associated with a reduced chance of achieving a
1 log10 reduction in viral load at week 12. In a substudy of 49 PI-experienced, amprenavir-naive patients in the Genophar trial, the substitutions L10F/I/V, K20M/R, E35D, R41K, I54V, L63P, V82A/F/T/S and I84V were associated with a response to ritonavir boosted amprenavir by univariate analysis and were included in a mutation score.30 In this case, a mutation score of
6 was associated with a reduced chance of achieving a
1 log10 reduction in viral load at week 12. The differences in the mutation score and the higher cut-off in the second study are probably partly the result of the use of ritonavir to boost the plasma concentrations of amprenavir to levels that can overcome a certain level of viral resistance. Indeed, in this study plasma amprenavir minimum concentrations at week 8 were also predictive of a response to treatment and a combination of the mutation score and the amprenavir concentration was more predictive than either of the two measures alone. Mutation scores for ritonavir-boosted GW433908, where plasma levels of amprenavir are higher, still need to be determined.
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Cross-resistance between amprenavir and lopinavir |
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Conclusions |
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Acknowledgements |
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Footnotes |
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Corresponding author. Tel: +1-919-483-6325; Fax: +1-919-315-0068; E-mail: lisa.l.ross{at}gsk.com
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References |
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