Library Volume 2, Issue 2:
Resistance Reporter© 6th European HIV Drug
Resistance Workshop
Selections from the 6th European HIV Drug Resistance Workshop (EHDRW);
26-28 March, 2008; Budapest, Hungary.
Select presentations concerning resistance
to antiretroviral drugs and clinical implications
Combined PI and NNRTI Resistance Analysis of the
Pooled DUET Trial: Towards a Regimen-Based Resistance Interpretation
EHDRW Abstract 46, Schapiro J et al.
Assessing drug resistance in relation to an
entire antiretroviral regimen may be a better predictor of virologic
response than assessing resistance to individual regimen components.
This concept was explored using pooled data from the DUET studies,
parallel randomized phase 3 trials which compared the safety and
efficacy of etravirine with that of placebo, each combined with a
darunavir/ritonavir-containing optimized background regimen (OBR), in a
total of 1,203 treatment-experienced patients with resistance to NNRTIs
and PIs, and HIV-1 RNA > 5,000 copies/mL at baseline. The proportion of
patients with HIV-1 RNA < 50 copies/mL at Week 48 was higher in the
etravirine arm in an intent-to-treat time-to-loss-of-virologic-response
(ITT-TLOVR) analysis (61% versus 40%, P < .0001). Schapiro and
colleagues conducted a subanalysis designed to evaluate the combined
effect of 13 predefined etravirine resistance-associated mutations (RAMs)
and 11 predefined darunavir RAMs on virologic response. Patients were
ineligible if their OBR included de novo enfuvirtide or they had
stopped treatment for causes excluding virologic failure. Data from 406
individuals were included. Patients with HIV-1 RNA < 50 copies/mL at
Week 24 were considered to be virologic responders. Response rates
decreased in line with an increasing number of combined baseline RAMs.
Among patients with an absence of baseline RAMs, 77.8% had HIV-1 RNA <
50 copies/mL at Week 24, compared with 14.3% of patients with > 7
baseline RAMs. Response rates among patients with no more than 1 RAM to
each drug ranged between 66.7% and 81.8%. For those patients with no
more than 2 RAMs to each drug, response rates ranged from 56.3% to
100.0%. Rates of response fell below 60% in patients with 2 or more RAMs
to each drug.
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The efficacy of etravirine following failure
of a prior NNRTI-based regimen has been demonstrated in DUET-1 and -2,
parallel randomized phase 3 trials that compared etravirine with
placebo, each combined with a darunavir/ritonavir-containing OBR, in a
total of 1,203 viremic patients with resistance to NNRTIs and PIs at
baseline. At Week 48, 61% of patients receiving etravirine had HIV-1 RNA
< 50 copies/mL compared with 40% of placebo-treated patients by ITT-TLOVR
analysis (P < .0001). Tambuyzer and colleagues performed a subanalysis
of these DUET studies in order to identify RAMs that emerge following
virologic failure on etravirine. Virologic failure, defined as confirmed
HIV-1 RNA increase ≥ 0.5 log10
copies/mL from nadir following a confirmed decrease
≥ 1.0 log10 copies/mL from
baseline, occurred in 91 of 599 (15%) etravirine-treated DUET patients
by Week 48, compared with 28% of placebo-treated patients. Among the 91
etravirine failures, 75 individuals had genotypic and phenotypic data
available from baseline and at endpoint, defined as the last on-study
visit. Patients who experienced virologic failure on etravirine
exhibited greater phenotypic resistance to etravirine and darunavir at
baseline than etravirine-treated patients who remained virologic
responders. Median baseline fold change (FC) in failures versus
responders was 3.3 versus 1.6 for etravirine, and 14.0 versus 5.3 for
darunavir, respectively. Virologic failure was associated with increased
phenotypic resistance to etravirine and darunavir. Median FC at failure
rose to 34.2 (from 3.3) for etravirine, and to 70.6 (from 14.0) for
darunavir, respectively. Four NNRTI RAMs emerged in
≥ 10% of patients failing etravirine: V179F
in 17%, V179I in 17%, Y181C in 12%, and V108I in 11%. In most cases,
these mutations emerged alongside other NNRTI RAMs. Y181C and V179F are
known etravirine RAMs. By site-directed mutagenesis, Y181C produced an
increase in etravirine phenotypic resistance (FC = 3.9). V179F was
detected only in the presence of Y181C, and the combined impact of these
two mutations increased etravirine FC to 187.0. V179I and V108I had no
discernible impact on virologic response or etravirine FC, and were not
therefore considered to be etravirine RAMs.
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MOTIVATE 1 and 2 were parallel randomized
phase 3 studies that demonstrated the efficacy of the CCR5 antagonist
maraviroc in treatment-experienced patients with CCR5- HIV-1, who
received a concomitant optimized background regimen (OBR). Failure of
maraviroc in the MOTIVATE studies has been associated either with
emergence of CXCR4-using variants (undetected at screening due to assay
insensitivity) or with evolution of CCR5-using variants that exhibit
maraviroc resistance. Phenotypic resistance to maraviroc is evidenced by
a plateauing in maximal percentage inhibition (MPI) at < 95%, whereas
genotypic markers of maraviroc resistance have yet to be clearly
identified. To this end, Mori and colleagues selected patients who
experienced virologic failure on maraviroc with CCR5-using virus by Week
24 in the MOTIVATE studies. Among the 36 patients identified, 15
displayed phenotypic maraviroc resistance at failure. Most individuals
(9 of 15) who failed with maraviroc-resistant virus were receiving an
OBR that contained no active agents. Failure without maraviroc-resistant
virus was associated with suboptimal maraviroc exposure. Among the 21
patients with maraviroc-sensitive virus at failure, 15 were observed to
have undetectable or low maraviroc levels in plasma, indicative of
nonadherence. Sequencing of env clones from patients with maraviroc-resistant
virus identified various amino acid changes within the V3 loop. No clear
pattern of mutations emerged, although mutations occurred largely within
the stem and tip of the V3 loop, with the base region generally
remaining conserved. Mutations in gp120 were found outside the V3 loop,
but with no recognizable pattern.
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Optimal use of CCR5 antagonists is dependent
on the availability of screening tools able to identify patients with
non-R5-utilizing variants, as these strains are not susceptible to
agents from this drug class. Coakley and colleagues compared the
performance of two tropism detection techniques, the plasma-based
TrofileTM assay (Monogram Biosciences, California) and the
peripheral blood mononuclear cell (PBMC)-based MT-2 assay (Academic
Medical Center, Amsterdam, Netherlands) using a panel of clinical HIV-1
isolates obtained from the Amsterdam HIV/AIDS Cohort. Tropism data were
collected for a subset of HAART-naïve cohort members every 3 months
using the MT-2 assay: The current analysis included tropism data
recorded at 5 or 6 time points per patient close to the time of
conversion to syncytium-inducing (SI) virus (CXCR4-using virus) as
determined by the MT2 assay. For 21 biological HIV-1 clones derived from
2 patients the two assays reported concordant results for 20 of 21
clones (95%). For 42 MT-2 cell culture derived supernatants obtained
from 4 patients, assay results were concordant in 39 of 42 samples
(93%). For 20 MT-2 cell culture derived cells from 4 patients, the
assays provided concordant results in 19 of 20 (95%). Finally, in 67
consecutive plasma samples obtained from 10 patients (with corresponding
PBMC samples available), TrofileTM detected a switch to
non-R5-utilizing virus at the same time or before SI detection by the
MT-2 assay in 5 of 10 patients (50%). The time lapse between SI
detection and subsequent detection of non-R5-utilizing virus by TrofileTM
for the remaining 5 patients was 3, 3, 6, 6, and 15 months,
respectively. When this last analysis was repeated using a novel TrofileTM
assay with enhanced sensitivity, non-R5-utilizing virus was detected at
or before the detection of SI virus by the MT-2 assay in 9 of 10
patients (90%).
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Select presentations concerning integrase
inhibitor resistance and resistance testing
Assays currently used to monitor
antiretroviral resistance in clinical settings do not assess resistance
to integrase inhibitors. With the approval of the first agent from this
class, raltegravir, modification of current assays to include the
integrase region of the HIV-1 genome is required. Van Eygen and
colleagues used a genotyping technique to assess sequence variability
within the reverse transcriptase (RT) connection domain, RNAseH, and
integrase (IN) gene regions in 220 clinical HIV-1 isolates derived from
integrase inhibitor-naive individuals. The study aimed to draw
associations between thymidine analogues mutations (TAMs) and other
amino acid changes. The following RT mutations were defined as TAMs:
M41L, D67N, K70R, L210W, T215Y/F, and K219Q/E. Samples were classified
as either TAM-containing (n = 95), TAM-negative but other RAMs detected
(n = 29), or RAM-negative (n = 96). In addition, samples were subtyped
and found to be predominantly subtype B (65.5%), with 11.8% of samples
subtype C, 6.8% subtype A, 5.5% subtype CRF02-AG, and 10.5% other
subtypes. The dataset did not include variants in which major IN
mutations were present. Several secondary IN mutations were detected,
and their presence was correlated with the presence of TAMs. The IN
mutations M154I, M154L, and K156N were detected in 7.4%, 4.3% and 16.0%
of TAM-positive samples, compared with 1.0%, 1.0% and 4.2% of
RAM-negative samples, respectively. In samples containing other RAMs but
no TAMs, M154I also occurred at a higher frequency (6.5%) than in the
RAM-negative group. Two mutations found in RNAseH from TAM-positive
variants, T57S (8.6%) and Q72T (5.4%) were not detected in samples from
either TAM-negative subgroup. In addition, two further mutations found
in RT from TAM-positive variants, R284K (10.8%) and N348I (10.8%) were
either absent or present at lower frequency in the TAM-negative groups.
A few things to note:
(1) R248K is in the tail end of the polymerase domain of RT, and N348I
is in the connection domain (the part between the polymerase and RNaseH
domains),
(2) these mutations have nothing to do with integrase,
(3) the clinical significance of these mutations is uncertain.
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EHDRW Abstract 79, Marlowe N et al.
Marlowe and colleagues reported data on a
prototype IN genotyping assay designed to enhance the scope of the
ViroSeq HIV-1 Genotyping System (Celera Diagnostics, California). A
panel of 84 HIV-1 isolates were obtained from donors in Cameroon,
Brazil, Thailand and the United Kingdom. Samples were taken between 2001
and 2006. Samples were categorized by HIV-1 subtype as either subtype A
(n = 10), subtype B (n = 24), subtype C (n = 10), subtype D (n = 6),
subtype F (n = 6), subtype G (n = 6), subtype CRF01_AE (n = 10), or
CRF02_AG (n = 12). Using the prototype technique, the IN region was
amplified effectively, and the complete
IN gene (aa 1-288) sequenced, in 83 of 84 (98.8%) samples. A
bidirectional sequence of the key catalytic core domain (aa 50-240) in
the IN gene that is the site of known integrase inhibitor RAMs was
obtained for 82 samples (98.8%). Polymorphisms associated with
resistance to the FDA-approved integrase inhibitor, raltegravir, were
detected at L74I (9.6%), L74M (4.8%), T97A (3.6%), V151I (2.4%), I203M
(1.2%), S230R (1.2%), and N232D (97.6%). Polymorphisms associated with
resistance to, elvitegravir, another integrase inhibitor in development,
were detected at Q95K (2.4%), E157Q (4.8%), and N232D (97.6%). Several
integrase inhibitor mutations were not found within this dataset: H51Y,
T66I, L74A, E92Q, F121Y, E138A/K, G140A/S, Y143C/H/R, Q146P, S147G,
Q148H/K/R, S153Y, N155H, G163R, H183P, Y226D/F/H, and R263K. The author
noted that this prototype assay provides the foundation for the
development of a commercial assay for IN genotyping.
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RELATED ARTICLES:
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Madruga JV, Cahn P, Grinsztejn B, et al.
Efficacy and safety of TMC125 (etravirine) in treatment-experienced
HIV-1-infected patients in DUET-1: 24-week results from a
randomised, double-blind, placebo-controlled trial. Lancet.
2007;370(9581):29-38.
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Lazzarin A, Campbell T, Clotet B, et al.
Efficacy and safety of TMC125 (etravirine) in treatment-experienced
HIV-1-infected patients in DUET-2: 24-week results from a
randomised, double-blind, placebo-controlled trial. Lancet.
2007;370(9581):39-48.
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Hardy D, Reynes J, Konourina I, et al.
Efficacy and safety of maraviroc plus optimized background therapy
in treatment-experienced patients infected with CCR5-tropic HIV-1:
48-week combined analysis of the MOTIVATE studies. Program and
abstracts of the 15th Conference on Retroviruses and Opportunistic
Infections; February 3-6, 2008; Boston, Massachusetts. Abstract 792.
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Westby M, Lewis M, Whitcomb J, et al.
Emergence of CXCR4-using human immunodeficiency virus type 1 (HIV-1)
variants in a minority of HIV-1-infected patients following
treatment with the CCR5 antagonist maraviroc is from a pretreatment
CXCR4-using virus reservoir. J Virol. 2006;80(10):4909-4920.
-
Westby M, Smith-Burchnell C, Mori J, et
al.
Reduced maximal inhibition in phenotypic susceptibility assays
indicates that viral strains resistant to the CCR5 antagonist
maraviroc utilize inhibitor-bound receptor for entry. J Virol.
2007;81(5):2359-2371.
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