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3TC Residual Antiviral Activity Despite M184V Resistance
Reported by Jules Levin
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At the Resistance Workshop (June 10-14, 2003, Cabos, Mexico) there was an interesting abstract on 3TC that has potentially important effect for patients. Remember the old days when it was first suggested that despite 3TC resistance with the M184V mutation it may be beneficial to continue taking 3TC because it might slow HIV replication and might increase AZT sensitivity. The first study discussed below addresses that question in patients. 4 patients with 3TC resistance and the M184V mutation who were taking 3TC stopped taking it. Within 12 weeks HIV viral load increased in all 4 patients. Since HIV viral load increased after 3TC was discontinued, this suggests that retaining 3TC in the regimen despite 3TC resisistance was beneficial: viral load was lower when 3TC was still in the regimen but increased after 3TC was discontinued. This was accompanied by increased replication capacity. In 2 patients AZT susecptibility decreased. The authors say 3TC has antiviral activity when 3TC resistance and the M184V mutation are present, and this supports the notion of using 3TC in salvage situations when multi-drug resistance is present and when 3TC resistance is present.
In the second study below GSK researchers examine the effect of 3TC (M184V) resistance on resistance to other NRTIs in the laboratory (in vitro). They examined patient isolates (blood samples) in the laboratory. Sensitivity to all NRTIs was observed when a single TAM was present without M184V except for zidovudine with K70R (2.8-fold reduced susceptibility), T215Y (5.6-fold) or T215F (6.3-fold). The T215Y/F mutations, without M184V, were also associated with increases in FC values to stavudine (1.4- to 1.5-fold) and TDF (1.2- to 1.3-fold), but were below reduced-susceptibility cut-offs. The presence of the M184 3TC mutation reduced the fold-change (resistance) to these NRTIs. Researchers report that the M184V plus K70R, T215Y/F was significantly associated with lower fold-change to zidovudine, stavudine or tenofovir compared to viruses without M184V. Susceptibility (FC<1.7) was maintained to didanosine with M184V plus any single TAM. Since we are unsure of the significance of the phenotypic cut-offs used by resistance testing companies, I'm unsure how to interpret the clinical significance of these findings and the fold-changes reported in this study.
They report finding that in the presence of 3TC resistance M184V, re-sensitization to some drugs is observed despite the presence of a single TAM (thymidine analogue mutation). These findings suggest that retaining lamivudine in those treatment regimens where TAMs can be selected may provide therapeutic benefit by maintaining M184V and concomitant sup-pression of resistance to zidovudine, stavudine and tenofovir.
In the third study below researchers take a look at the NRTI-associated resistance mutation V118I. They characterize the phenotypic and virological characteristics of V118I arising from different NRTI regimens. Previous recent data suggest this mutation may be associated with d4T, AZT and ddI but not 3TC. The mutation could be associated with NRTI cross-resistance. The study reviews resistance and virologic findings related to V118I in the context of several NRTI combinations.
Antiviral activity of lamivudine in persons infected with HIV-1 that
has M184V and multiple thymidine analogue mutations
TB Campbell 1 , RK Young, SC Johnson, ER Lanier and DR Kuritzkes
1 University of Colorado Health Sciences Center, Denver, Col., USA
BACKGROUND: M184V in HIV-1 reverse transcriptase (RT) confers >1000-fold resistance to lamivudine (3TC), increased thymidine analogue [zidovudine
(ZDV) and stavudine (d4T)] susceptibility and decreased replicative fitness. Thus, maintenance of M184V may be an important component of treatment
strategies for multidrug-resistant HIV-1 infection. This study tested the hypothesis that continued 3TC treatment provides antiviral benefit by maintaining M184V, and that reversion to wild-type (184V M) is associated with increased plasma HIV RNA.
METHODS: This was an open-label pilot study of 3TC interruption in patients failing 3TC-containing regimens. Entry criteria included plasma HIV-1 RNA
>1000 copies/ml, use of 3TC, and ZDV or d4T in the current regimen. Persons taking abacavir, didanosine or zalcitabine were excluded. M184V, at least three
thymidine analogue mutations and mutations associated with resistance to all other drugs in the current anti-retroviral regimen were required at study entry.
Subjects stopped 3TC but continued all other anti-retrovirals.
RESULTS: Four subjects were enrolled (entry CD4 count range: 163-517 cells/mm 3 ; entry plasma HIV-1 RNA range: 4.26-5.53 log 10 copies/ml). All subjects were on three-drug antiretroviral regimens that included an HIV-1 protease inhibitor, in addition to d4T or ZDV, and 3TC at study entry. Three subjects completed 24 weeks of follow-up and one subject completed 20 weeks. Within 12 weeks after 3TC withdrawal, plasma HIV-1 RNA increased >0.5 log 10 copies/ml above baseline in all subjects. Increased plasma HIV-1
RNA occurred concomitantly with 184V M in one subject, but occurred prior to 184V M in two subjects who had either complete or partial 184V M
during 3TC withdrawal. One subject had increased plasma HIV-1 RNA despite continued M184V. Increased 3TC susceptibility (>34-fold increase above
baseline) and increased replicative capacity (1.2- to 2.7-fold increase above baseline) occurred in the three subjects who had 184V M. In two of three subjects with 184V M, ZDV susceptibility decreased nine-and 10-fold from baseline. CD4 lymphocyte counts were stable during the period of 3TC withdrawal in the three subjects with 184V M, but decreased 97 cells/mm 3
(19%) in the subject who did not have 184V M. M184V reappeared after reinitiation of 3TC in all three subjects who had 184V M, but plasma HIV-1
RNA did not return to baseline values in two subjects. Additional resistance mutations in protease and decreased lopinavir susceptibility occurred in two subjects during 3TC interruption.
CONCLUSIONS: 3TC contributes to partial suppression of HIV-1 replication despite presence of the 184V mutation. Although maintenance of decreased virus replication fitness and increased thymidine analogue susceptibility contribute to the persistent antiviral activity of 3TC in the presence of M184V, there is also residual direct antiviral activity of 3TC in this setting. These data support the use of 3TC in salvage therapy of multidrug-resistant HIV-1 infection even when M184V is present.
The impact of the HIV reverse transcriptase M184V mutation in combination with single thymidine analogue mutations on nucleoside reverse transcriptase inhibitor resistance in clinical samples from a large patient database
L Ross 1 , N Parkin 2 , M Bates 2 , R Fisher 1 , M St Clair 1 , M Tisdale 3 and R Lanier 1 1 GlaxoSmithKline, RTP, NC, USA; 2 ViroLogic, Inc., Calif., USA; and 3 GlaxoSmithKline, Stevenage, UK
BACKGROUND: Previous studies have assessed the impact on multiple thymidine analogue mutations (TAMs) in specific combinations on phenotypic sensitivity
and have demonstrated for some nucleoside reverse transcriptase inhibitors (NRTIs), a re-sensitization of the virus in the presence of the M184V mutation.
However, assessment of the impact of the M184V mutation in combination with single TAMs on phenotypic susceptibility to NRTIs may be useful in devising
rules for genotypic-based drug resistance algorithms.
METHODS: Approximately 10000 HIV clinical samples containing matching genotypes and phenotypes were queried to identify samples with a single TAM
(M41L, D67N, K70R, L210W, T215F or Y, and K219E, H, N, Q or R). Samples with mixtures at queried positions, more than one TAM, or any other
NRTI resistance-associated mutation other than M184I or V were excluded. Samples were divided into those with or without M184I or V, in addition to a specific TAM. The median fold-change (FC) for each NRTI was compared with predictions made by several genotypic algorithms for HIV drug resistance using the Stanford HIValg Resistance Algorithm Comparison version 3.1.1.
RESULTS: Sensitivity to all NRTIs was observed for any single TAM without M184V except for zidovudine with K70R (2.8-fold reduced susceptibility), T215Y
(5.6-fold) or T215F (6.3-fold). The T215Y/F mutations, without M184V, were also associated with increases in FC values to stavudine (1.4- to 1.5-fold, Mann-Whitney P<0.0001 vs wild-type) and TDF (1.2- to 1.3-fold; P<0.01 vs wild-type), but were below reduced-susceptibility cut-offs.
However, M184V plus K70R, T215Y/F was significantly associated with lower FC to zidovudine, stavudine or tenofovir compared to viruses without M184V (P<0.05). Reduced susceptibility to abacavir (FC>4.5) was only seen with
less common T215F+M184V (4.6-fold), and the FC to abacavir was 4.3-fold when T215Y/F+M184V were analysed together. Susceptibility (FC<1.7) was maintained to didanosine with M184V plus any single TAM. When genotypic algorithms were compared for the same mutation patterns, concordance across all algorithms (ANRS, HIVDB, RCG, REGA, VGI and GeneSeq) was not observed. Most algorithms predicted decreased susceptibility to zidovudine for every
TAM pattern and did not account for the presence of M184V, which decreased phenotypic resistance for zidovudine below the cut-off for all groups. Most algorithms predicted decreased susceptibility to abacavir for M184V and any TAM. Over-prediction of reduced susceptibility was also observed for didanosine and zalcitabine.
CONCLUSIONS: In vivo, individual TAMs do not have an equivalent impact on NRTI resistance. Concordance across algorithms for these mutation patterns
was not observed. In the presence of the M184V, re-sensitization to some drugs is observed despite the presence of a single TAM. These findings suggest that
retaining lamivudine in those treatment regimens where TAMs can be selected may provide therapeutic benefit by maintaining M184V and concomitant sup-pression of resistance to zidovudine, stavudine and tenofovir.
Implications of lamivudine use and the M184V mutation in V118I-related multidrug resistance
BG Brenner 1 , M Oliveira 1 , V Micheli 2 , D Moisi 1 , A Cargnel 2 , M Petrella 1 and MA Wainberg 1. 1 McGill University AIDS Centre Montreal, Quebec, Canada; and 2 L Sacco Hospital, Milan, Italy
BACKGROUND: A new pattern of mutations involving V118I with or without E44D/A can confer moderate resistance to lamivudine (3TC), as well as cross
resistance to other nucleoside reverse transcriptase inhibitors (NRTIs). Recent studies suggest that thymidine analogues (ZDV/d4T) and didanosine (ddI), but
not 3TC, promote development of this V118I resistance pathway. We characterized the phenotypic and virological characteristics of V118I arising from different NRTI regimens.
METHODS: Genotypic analysis of plasma viral RNA was monitored in 559 individuals having viraemia >1000 copies/ml. Prevalence of V118I with or without other NRTI mutations was related to usage of zidovudine (ZDV), stavudine (d4T), ddI, abacavir (ABC) and/or 3TC. NRTI mutations included M184V, TAMs (M41L, D67N, K70R, L210W, T215Y/F, K219E/Q), NAMs (Q151M, F77L, F116Y, A62V, V75I), as well as V118I (ħE44A/V and TAMs). Clinical viral isolates were amplified from select patients with known therapeutic
histories. Cell-based phenotypic assays were used to determine IC 50 values of viruses with V118I. These viruses were grown in varying doses of 3TC or
tenofovir (TFV) to confirm drug susceptibility.
RESULTS: A high prevalence of viruses harbouring M184V, V118I and both mutations were observed in individuals undergoing treatment failure (37.7, 6.4 and 11.7% of cases, respectively). Of note, viraemia was significantly lower in the M184V group than the M184V/V118I group, with even higher viraemia in the
V118I and wild-type groups (P>0.001, ANOVA analy-sis). The presence of V118I in the absence of M184V was restricted to those individuals receiving d4T
and/or ddI without 3TC. The combination of V118I and M184V was more prevalent in 3TC-treated individuals receiving d4T and/or ddI (n=39) than those
receiving ZDV (n=14). A subset of the samples were isolated and five distinct V118I phenotypic patterns were observed: 1) V118I alone without TAMs/M184V
in untreated patients (n=2) did not result in resistance to NRTIs, including 3TC; 2) V118I/M184V without TAMs in a rare ZDV/3TC-treated patient was resistant
to 3TC, but sensitive to all other NRTIs; 3) V118I with TAMs in d4T-treated patients (not receiving 3TC) (n=2) showed ZDV, ABC and TFV resistance but
remained sensitive to 3TC; 4) V118I/M184V/TAMs in d4T/3TC-treated patients showed resistance to 3TC/ABC (n=4) but retained varying degrees of sensitivity
to ZDV and TFV; 5) V118/184V/TAMs in ZDV/3TC-treated patients (n=2) showed cross resistance to all NRTIs.
CONCLUSIONS: V118I without M184V is generally associated with use of d4T and/or ddI, conferring resistance to all NRTIs except 3TC. The presence of
V118I/184V/TAMs in d4T/ddI-experienced patients receiving 3TC conferred 3TC resistance but also facil-itated retention of ZDV/TFV sensitivity. In contrast,
V118I with M184V, arising in ZDV failure, rendered viruses resistant to all NRTIs. V118I appears to arise as a compensatory mutation that improves fitness of multi-NRTI-resistant viruses.
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