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PATRÍCIA MUNERATO
A RESISTÊNCIA AOS ANTI-RETROVIRAIS E A DIVERSIDADE
GENÉTICA DO HIV-1 NO BRASIL
Tese apresentada à Universidade Federal de
São Paulo – Escola Paulista de Medicina,
para obtenção do Título de Doutor em
Ciências.
SÃO PAULO
2008
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PATRÍCIA MUNERATO
A RESISTÊNCIA AOS ANTI-RETROVIRAIS E A DIVERSIDADE
GENÉTICA DO HIV-1 NO BRASIL
Orientador: Prof. Dr. Ricardo Sobhie Diaz
Co-Orientador: Prof. Dr Luiz Mário Ramos Janini
Tese apresentada à Universidade Federal de
São Paulo – Escola Paulista de Medicina,
para obtenção do Título de Doutor em
Ciências.
SÃO PAULO
2008
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Munerato, Patrícia
A RESISTÊNCIA AOS ANTI-RETROVIRAIS E A DIVERSIDADE
GENÉTICA DO HIV-1 NO BRASIL/Patrícia Munerato – São Paulo, 2008.
Tese (Doutorado) – Universidade Federal de São Paulo. Escola Paulista de
Medicina. Programa de Pós-Graduação da Disciplina de Doenças
Infecciosas e Parasitárias.
Antiretrovirals resistance and HIV-1 genotypic diversity in Brazil.
1. antiretroviral resistance 2.resistance mutation 3.resistance pathway 4.
phenotypic resistance 5.genotypic diversity
Dedicatória
A minha mãe, Luiza Zerlin Munerato, que pacientemente esperou 34 anos
até que eu entendesse o significado completo do seu papel em minha vida.
Ao meu pai, Vercy Antonio Munerato, por sempre apoiar e incentivar as
minhas escolhas.
Ao meu irmão, Roger Munerato, por compartilhar a minha história de vida e,
por este motivo, ser o meu porto seguro, mesmo que distante.
Ao meu marido, Júlio Cesar R. Cordeiro, por compreender e apoiar sempre
a minha busca por mais, mesmo tendo menos a minha presença. Por me
amar de uma forma tão sublime e me fazer tão feliz.
A minha filha Isabela, a quem, embora esteja apenas no seu primeiro ano de
vida, espero ter dado exemplo de determinação.
Ao Prof. Dr. e Ser Humano Ricardo Sobhie Diaz.
!
"
#$ %
%& !
Alice no País das Maravilhas
Lewis Carroll
Agradecimentos
Esta tese representa a concretização de um esforço efetivo de diversas
instituições, profissionais, amigos e familiares, aos quais gostaria de
agradecer especialmente:
Ao meu orientador, Prof. Dr. Ricardo Sobhie Diaz, por compartilhar comigo
seu conhecimento, por ser paciente e generoso. Pela compreensão silenciosa
dos momentos difíceis pelos quais passei, permitindo que meu trabalho
fluísse, respeitosamente.
À Márcia Perez Oliveros, pela contribuição inestimável a este trabalho, pela
disponbilidade irrestrita para discussões e análises estatísticas e pelo
profissionalismo exemplar.
Aos Prof(s). Dr(s). Amilcar Tanuri e Rodrigo Brindeiro, por me receberem no
laboratório de Virologia do Departamento de Genética da Universidade
Federal do Rio de Janeiro para realização de experimentos de cultura de
células, contribuindo e muito para minha formação científica.
A Alexandre Calazans, pela preciosa contribuição técnica e científica, pela
disponibilidade em me ensinar na prática o que os livros e publicações não
mencionan.
À Prof. Dra. Luciana Jesus da Costa, pelo apoio, amizade e carinho durante
todas as etapas do desenvolvimento deste trabalho.
Ao Prof. Dr. Marcelo Soares, da UFRJ, que gentilmente colaborou com a
realização do projeto de análise de resistência fenotípica, cedendo amostras
de HIV-1 do subtipo C.
A Antonio Charlys da Costa, secretário da pós gradução, pela prestatividade e
pró-atividade nas questões burocráticas deste trabalho. Pela amizade e
incentivo e pelo bom papo de final de tarde.
Aos amigos do Laboratório de Retrovirologia: Sandra, Graziela, Cecília,
Dercy, Erika, Dani, Beth, Mario, Shirley, Michele, Wagner e Cristiano pelo
convívio prazeroso e boas recordações...
Aos amigos do laboratório de Virologia do departamento de genética da
UFRJ: Helena, Renato, Celina, Adriana, Monica, Ana Flávia e Angélica por
tornarem minha estada no Rio de Janeiro tão agradável e proveitosa.
À família Applied Biosystems por compreender a importância deste trabalho
na minha vida pessoal e profissional e, assim, permitir que eu o concluísse.
À Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP) pelo
apoio e suporte financeiro para realização deste trabalho.
A Deus, por me abençoar em todos os caminhos que trilhei.
Sumário
1. Introdução.........................................................................................página 01
2. Objetivos...........................................................................................página 06
Artigo 1: Profiling resistance-related mutations according to the clade
assignment in a Brazilian population……………………...……………...página 07
Artigo 2: Decreased Phenotypic Susceptibility to Reverse Transcriptase
Inhibitors in the Absence of Known Resistance Mutations in Clades C, F, and
B/F Recombinant Antiretroviral Naïve HIV-1
Strains………………...……………………………………………………..página 41
3. Conclusões…………………………………………………………..…..página 62
4. Referências Bibliográficas………………………………………….…..página 64
1
1. Introdução
O Vírus da Imunodeficiência Humana Tipo 1 (HIV-1) é um exemplo
clássico dos retrovírus e, como tal, sofre mutações numa velocidade
alarmante. Substituições nucleotídicas, tais como, insersões, deleções e
recombinações são comuns durante o curso da infecção por este agente.
1
Neste contexto de geração de diversidade, o HIV-1 está classificado em três
grupos distintos e altamente divergentes: M (major), O (outlier) e N (new), os
quais podem representar três introduções separadas do Vírus da
Imunodeficiência Símia (SIV) aos seres humanos. A grande maioria das
variantes genéticas do HIV-1 está inseridas no grupo M, o qual está
subdividido em 9 subtipos (A, B, C, D, F, G, H, J e K) e inúmeras Formas
Recombinantes Circulantes (CRFs) que têm sido descritas num número cada
vez maior de publicações.
2,3,4
As CRFs são fruto da ocorrência de eventos de
recombinação entre dois subtipos distintos e contribuem para o processo
dinâmico de expansão e heterogeneidade da epidemia.
Atualmente, os 33,2 milhões de indivíduos infectados pelo HIV estão
espalhados pelos 5 continentes, porém a distribuição de subtipos não é
homogênea (http://www.unaids.org/en/KnowledgeCentre/HIVData). A África,
berço da pandemia, abriga todos os subtipos do HIV-1, tendo o C como
predominante. Porém, na América do Norte e Europa Ocidental o vírus do
subtipo B circula quase que com exclusividade, embora outras variantes
venham sendo descritas nos últimos anos.
5,6,7,8,9,10,11,12
No Brasil, a
diversidade é um pouco maior, onde cerca de 85% dos vírus são B e 25%
subtipo F em locais como São Paulo e Rio de Janeiro, com uma proporção
significativa de recombinantes B/F. No sul do país há uma alta prevalência do
subtipo C, que chega a 50% no estado do Rio Grande do Sul, enquanto a
prevalência do subtipo F aumenta em direção ao norte do país.
13
2
Recentemente, as CRFs 28 e 29, recombinantes entre as clades B e F, foram
caracterizadas e descritas no estado de São Paulo, corroborando o fato da
ocorrência de eventos de recombinação onde mais de um subtipo co-circula.
14
Avaliar os diferentes subtipos e CRFs do HIV-1 é de importância crucial
para o entendimento da tendência da pandemia. Mais do que isso, a
diversidade do HIV-1 pode afetar testes diagnósticos, principalmente aqueles
baseados em manipulação dos ácidos nucléicos.
15,16,17
O mesmo pode
acontecer com a eficácia dos anti-retrovirais atuais, que foram inicialmente
testados em pacientes infectados pelo vírus B, podendo ter desempenho
diferente frente aos vírus não-B, além destes últimos poderem apresentar
padrões de resistência e vias mutacionais distintas.
A maioria dos testes de susceptibilidade a anti-retrovirais foram também
desenhados e desenvolvidos principalmente para o subtipop B, haja vista que
este é o subtipo mais prevalente nos países desenvolvidos, onde concentram-
se os grandes centros de pesquisa e desenvolvimento farmacêuticos. No
entanto, com o aumento global de subtipos não-B, surge a necessidade de
investigar o desempenho dos ensaios de resistência aos medicamentos em
relação a outros subtipos que não o B. Estes testes se tornaram uma
ferramenta importante no acompanhamento de pacientes infectados pelo HIV
sob terapia anti-retroviral.
18
Tanto métodos genotípicos (genotipagem) quanto
fenotípicos (fenotipagem) parecem ser igualmente úteis na determinação da
susceptibilidade aos anti-retrovirais.
19
Enquanto a genotipagem identifica as
posições das mutações e/ou dos polimorfismos no genoma do HIV associados
à resistência aos anti-retrovirais, a fenotipagem examina a susceptibilidade
relativa do vírus em questão às diferentes concentrações de medicamentos in
vitro.
Não existem dados conclusivos até o momento, se mutações ou vias
mutacionais específicas de resistência são selecionadas em subtipos não-B.
3
Da mesma forma, não se sabe com certeza se os polimorfismos presentes nos
demais subtipos influenciam a susceptibilidade às drogas. Polimorfismos que
ocorrem naturalmente no gene pol, o qual codifica enzimas que são alvos de
medicamentos anti HIV (protease, transcriptase reversa (TR) e integrase),
resultam da alta taxa de replicação viral, que atinge 10
9
a 10
10
virions por dia,
e da baixa fidelidade da enzima TR, que possui taxa de erro de 3 x 10
-5
por
base por ciclo replicativo.
20
Tais mudanças genéticas são freqüentemente relatadas em indivíduos
virgens de tratamento infectados por subtipos não-B.
21,22,23,24,25,26,27,28
Algumas destas mudanças, tais como K20I, M36I e V82A, estão associadas à
resistência aos inibidores da protease (IPs) e são consideradas mutações
secundárias ou acessórias, ou seja, emergem naturalmente e, via de regra,
recuperam o fitness perdido pelo aparecimento de mutações principais, além
de poderem propiciar perda modesta de susceptibilidade aos anti-retrovirais.
29
De modo geral, a alteração genética M36I na protease pode ser considerada
um marcador genético de subtipos não-B do grupo M,
29
e a substituição K20I
aparece quase exclusivamente em seqüências da protease pertencentes ao
subtipo G.
29
Outro polimorfismo da protease, o L89M, comumente presente
nos vírus clade F, já foi associado à perda de susceptibilidade ao Nelfinavir.
30
Por outro lado, o polimorfismo L93I, presente no subtipo C, foi descrito por
causar hipersusceptibilidade deste vírus ao Lopinavir.
31
A L93I também está
presente nos vírus do subtipo F, porém seu afeito nesta clade não foi
demonstrado.
É interessante notar, com relação às vias mutacionais para a
resistência aos anti-retrovirais, que quando existe a pressão seletiva do
inibidor de protease Nelfinavir sobre os vírus dos subtipos não-B, a mutação
que emerge quase exclusivamente é a L90M, sendo muito rara a via pela
D30N.
32
A razão para existência de uma via preferencial divergente entre o B e
os não-B parece ser a presença do poliformfismo L89M nestes últimos, a qual
representa uma barreira para seleção da D30N.
33
Essa é uma das evidências
4
de que as vias mutacionais têm relação com a estrutura do vírus em questão e
não ocorrem de maneira puramente aleatória. O entendimento sobre as vias
mutacionais seguidas por cada subtipo viral tem relevância no sentido de que
algumas delas podem implicar em resistência cruzada e, conseqüentemente,
impedir o sucesso de determinados tratamentos.
Outro exemplo de padrão de resistência diferenciado entre os subtipos
é em relação aos Inibidores não-nucleosídeos da Transcriptase Reversa
(ITRNN), onde a seleção da mutação V106M pelo vírus do subtipo C
possibilita a rápida resistência a esta classe de medicamentos.
34
Normalmente
no subtipo B, a mutação de resistência relacionada a este códon é a V106A
(substituição de GTG por GCA) ou V106I (GTG por ATT, ATC ou ATA), que
não emerge com facilidade. A mutação V106M (substituição de GTG por ATG)
ocorre rapidamente nos vírus do subtipo C, levando a alto nível de resistência
aos ITRNN.
35
Alguns estudos retrospectivos sobre a relevância clínica destes
polimorfismos basais mostraram que indivíduos infectados por vírus da clade F
apresentaram comprometimento na resposta aos anti-retrovirais quando
comparados a indivíduos infectados pela clade B.
36
Sugerem ainda, que a
presença de grande número de substituições em posições associadas à
resistência pode, de alguma maneira, colocar em risco o sucesso do
tratamento.
35,37,38,39
Por outro lado, outros estudos sustentam a idéia de que a
resposta aos anti-retrovirais parece ser independente do subtipo.
40
De acordo com o cenário exposto acima, fica implícita a importância de
se realizar mais estudos sobre a diversidade genética e sua correlação com a
resposta aos anti-retrovirais e os padrões de resistência oriundos do
tratamento.
Para o Brasil, onde a epidemia é composta por três subtipos (B, C e F)
e seus recombinantes e que foi o primeiro país a ter um programa
governamental gratuito para controle da Síndrome da Imunodeficiência
Humana Adquirida (AIDS), atendendo atualmente mais de 180 mil pessoas,
5
seria importantíssimo estudos a partir de amostras brasileiras representando a
diversidade genética local que pudessem jogar luz acerca de padrões de
resistência a resposta aos anti-retrovirais.
6
2. Objetivos
As propostas dos dois trabalhos apresentados a seguir foram:
1. Delinear o perfil mutacional de resistência aos anti-retrovirais para
os subtipos de HIV-1 que compõem a epidemia nacional.
2. Analisar a resposta fenotípica aos antiretrovirais de vírus
circulantes no Brasil frente a um teste de fenotipagem.
7
Profiling HIV-1 antiretroviral drug resistance mutations by
subtype in a Brazilian population
Running head: HIV-1 resistance mutations in Brazil
Patricia Munerato
a
, Maria Cecilia A. Sucupira
a
, Márcia P. R. Oliveros
b
,
Denise F. C. de Souza
c
, Anderson A. Pereira
c
, Lilian A. Inocencio
c
, Ricardo S.
Diaz
a,
*
From the
a
Federal University of São Paulo, São Paulo, Brazil, the
b
University of São Paulo, São
Paulo, Brazil, and the
c
National STD/AIDS Program of the Brazilian National Ministry of Health,
Brasília, Brazil
*
Correspondence to Ricardo S. Diaz, Rua Pedro de Toledo, 781, 16 andar, CEP
04039-032, São Paulo, SP, Brazil
Tel/fax: +55 11 5571 2130; e-mail: [email protected]
Financial support: This study received financial support in the form of grants from
the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Foundation
for the Support of Research in the State of São Paulo) and from the Brazilian National
Ministry of Health Programa Nacional de DST/AIDS (PNDST/AIDS, National
Sexually Transmitted Diseases/AIDS Program).
8
Abstract
Objectives: In Brazil, where three distinct HIV-1 subtypes (B, F, and C) co-circulate, a
significant portion of the HIV-infected population has been exposed to antiretroviral
drugs. This study analyzes the antiretroviral resistance profiles of HIV-1-infected
individuals failing antiretroviral therapy.
Methods: We analyzed the genotypic resistance profiles of 2,474 patients presenting
virologic failure to antiretroviral therapy in the city of São Paulo, Brazil.
Results: We detected high levels of resistance to a variety of antiretroviral classes:
resistance mutations to protease inhibitors and nucleoside reverse transcriptase inhibitors
were less common in subtype C viruses, whereas non-nucleoside reverse transcriptase
inhibitor resistance mutations were less common in subtype F viruses. The thymidine
analog mutation pathway known as pathway 1 was more prevalent in subtype B viruses
than in subtype C viruses, whereas pathway 2 was more prevalent in subtype C viruses.
Selected resistance mutations varied according to subtype for all three classes of
antiretrovirals. We describe two pathways of non-nucleoside reverse transcriptase
inhibitor resistance (to nevirapine and efavirenz). Although cross-resistance to etravirine
should occur more frequently among individuals failing nevirapine treatment, the
prevalence of cross-resistance to etravirine, darunavir, and tipranavir was found to be low.
We found that increases in the number of resistance mutations will be related to increases
in the viral load.
9
Conclusions: Special attention should be given to resistance profiles in non-B subtype
viruses. The accumulation of knowledge regarding such profiles in the developing world
is desirable.
Keywords: drug resistance, multiple, viral/genetics, anti-retroviral agents,
HIV-1/drug effects, anti-HIV agents/therapeutic use
10
Introduction
Understanding the genetic basis for antiretroviral resistance might be particularly
important for predicting cross-resistance to new antiretrovirals within a given population.
In developing countries such as Brazil, which provides HIV-infected patients with full and
free access to all U.S. Food and Drug Administration-approved antiretrovirals, the issue of
antiretroviral resistance could be especially critical. Given the sequential use of
antiretrovirals in many patients in Brazil and the extensive use of unboosted protease
inhibitors (PIs) in the recent past, it is assumed that a high proportion of patients
experience virologic failure. One study showed that the time to virologic failure after the
first treatment regimen is only 9 months in Brazil [1]. The rate of virologic failure after an
initial 48 weeks of successful viral suppression is 82.5% [2], and it can be expected that
extensive resistance will emerge in this population. Another repercussion of antiretroviral
failure with secondary resistance is the high rate of transmission of antiretroviral-resistant
HIV, which can be as high as 36% among recently infected individuals in some areas of
Brazil [3]. The HIV-1 epidemic in Brazil is concentrated around the city of São Paulo,
which harbors more than 20% of all AIDS cases in the country (www.aids.gov.br). In this
region, as in many other areas of Brazil, subtype F and subtype C viruses, as well as B/F
recombinant viruses, co-circulate with subtype B viruses.
There are many unresolved issues regarding HIV-1 behavior in relation to its genetic
diversity. It is conceivable that the genetic diversity of the virus impairs immune
responses to candidate vaccines, causes false-negative results in diagnostic/monitoring
11
laboratory tests (especially those involving nucleic acids) [4, 5], and alters disease
progression [6, 7]. Most of the resistance mutation profiles described to date has been in
subtype B HIV-1 viruses. However, in non-B subtypes subjected to the selective pressure
exerted by antiretroviral therapy, specific resistance mutations or pathways can be
selected. For instance, some thymidine analog mutations (TAMs), as well as some PI
resistance mutations, are more frequently selected in subtype B viruses than in non-B
subtypes [8, 9]. Emerging in vitro data suggest that some natural polymorphisms in the
pol gene interfere with antiretroviral efficacy. For instance, in subtype C viruses, the
V106M mutation is related to lower activity of non-nucleoside reverse transcriptase
inhibitors (NNRTIs) [10], and the I93L mutation increases susceptibility to lopiinavir [11].
In addition, subtype C viruses, due to a silent polymorphism, also have a lower genetic
barrier to tenofovir resistance [12]. In the present study, we sought to analyze the
secondary resistance among HIV-1-infected individuals failing antiretroviral therapy in
the city of São Paulo, Brazil in a cohort of patients for whom information related to
previous antiretroviral exposure was available, with a special emphasis on how well
subtype correlates with resistance and with resistance pathway.
12
Patients and methods
Population
Samples from 2,474 patients were collected between 2002 and 2006. Samples were
processed at the Federal University of São Paulo, in São Paulo, Brazil. All participating
patients gave written informed consent.
Viral load and number of mutations
The number of resistance mutations was calculated as the sum of all nucleoside reverse
transcriptase inhibitor (NRTI), NNRTI, and major PI resistance mutations (minor PI
resistance mutations were excluded). Means, standard deviations, and medians were
calculated for viral load in each group of patients. Analysis of variance was performed in
order to identify statistically significant differences.
The same analyses were performed using the proportion test based on binominal
distribution to determine the number of patients in each group presenting a viral load
100,000 copies/mL. All groups were compared to an antiretroviral-naïve group of 194
individuals, in which 0.19% of the patients had a viral load 100,000 copies/mL. Values
of P 0.05 were considered statistically significant.
13
Genotypic resistance analysis
All samples were sequenced using ViroSeq v2.0 (Celera Diagnostics, Alameda,
California, USA). Resistance mutations were identified according to the IAS mutations
list [13]. Statistical analyses were performed using Minitab Release 14 Statistical
Software.
The prevalence of mutations in subtype B viruses was compared with that observed for
subtype F and C viruses using chi-square tests and tests of proportion based on a binomial
distribution.
HIV-1 subtype analysis
The nucleotide sequences of pol gene were subtyped using BLAST analysis
(http://hivdb6.stanford.edu).
14
Results
Patient characteristics
2,474 consecutive patients were enrolled in this study. All were being treated with
antiretroviral drugs, and all were experiencing virologic failure: for the first time (17%);
for the second time (33%); or for the third or subsequent time (50%). The mean viral load
was 123,845 copies/mL.
Sample characteristics
Only 1.2% of strains presented no antiretroviral drug resistance mutations. The subtyping
analysis showed that 78.3% (1,938) of the viruses belonged to subtype B, 4.3% (106)
belonged to subtype C, and 8.6% (214) belonged to subtype F. In addition, 0.5% (12)
were B/C recombinants, and 8.2% (204) were B/F recombinants. According to the
analysis of individual fragments, the prevalence of protease and reverse transcriptase
subtype B was, respectively, 79.6% and 85.8%, compared with 4.3% and 4.8% for
subtype C, and 16.1% and 9.5% for subtype F.
Genotypic resistance patterns
Mutations were identified in the following proportions: 54.3% (major PI resistance
mutations); 89.7% (NRTI resistance mutations); and 62.5% (NNRTI resistance
15
mutations). The prevalence of antiretroviral resistance by drug class and by HIV-1
subtype is presented in Table 1. Overall, 21% of individuals presented resistance to one
antiretroviral class, 44.8% presented resistance to two classes, and 34% presented
resistance to all three classes. As can be seen, there was a differential acquisition of
resistance mutations by subtype, which was not explained by antiretroviral exposure (data
not shown). Considering only major PI resistance mutations, the prevalence of PI
resistance was lower in subtype C than in the other subtypes. Additionally, subtype C
viruses accumulated fewer NRTI resistance mutations than did subtype B or subtype F
viruses. Subtype F viruses presented significantly fewer NNRTI resistance mutations than
did subtype B viruses.
Analysis of PI resistance mutations
Of the major PI resistance mutations, L90M, M46I/L, N88D/S, and D30N were the most
frequently observed, whereas G48V and I50V/L were the rarest (Figure 1A). Individuals
failing nelfinavir as the first PI were evaluated. Among those infected with subtype B (n =
168) the following resistance pathways were identified: D30N in 52.5%; L90M in 38.3%;
and the D30N-L90M combination in 9.6%. Among those infected with subtype F (n = 48),
30.4% presented the D30N pathway, and 47.8% presented the L90M pathway. Using end-
point PCR, we generated 10 clones from 5 individuals that presented the D30N-L90M
combination and observed that the D30N or L90M mutations never co-existed in the same
viral clone (data not shown). At the time of plasma sample collection from this group of
16
patients, there had been no exposure to tipranavir or darunavir. Of the samples evaluated,
2.21% harbored three or more darunavir resistance mutations: V11I (1.18%); V32I
(3.51%); L33F (3.55%); I47V (2.75%); I50V (1.07%); I54M (0.61%); G73S (5.57.8%);
L76V (2.10%); I84V (7.44%); and L89V (1.49%). In addition, 22.15% of samples
harbored 3 or more tipranavir resistance mutations: L10V (12.21%); I13V (30.46%);
K20M/R (10.50%); L33F (6.49%); E35G (1.34%); M36I (49.43%); K43T (4.31%); M46L
(5.73%); I47V (2.75%); I54A/M/V (2.60%); Q58E (5.31%); H69K (7.86%); T74P
(2.21%); V82L/T (3.09%); N83D (0.84%); and I84V (7.52%). Of the individuals
evaluated, 0.38% harbored viruses with three or more mutations associated with resistance
to tipranavir and darunavir, 18.9% harbored viruses with three or more mutations
associated with resistance to tipranavir, but not to darunavir, and 1.8% harbored viruses
with three or more mutations associated with resistance to darunavir, but not to tipranavir.
Although exposure to different PIs or to the number of previous PIs did not vary among
the different subtypes, there were differences in the prevalence of primary and secondary
PI resistance mutations. In subtype B viruses, resistance mutations at codons 33, 34, 58,
63, 73, 71, 77, and 84 were more common than in subtype F or C viruses, whereas those at
codons 20, 36, and 89 were less common. In subtype F and C viruses, resistance mutations
at codons 20, 36, and 89 were more common. In subtype F viruses, resistance mutations
were more common at codons 10, 35, 48, 74, 57, and 82, whereas they were less common
at codons 47 and 93. In subtype C viruses, the frequency of resistance mutations was
higher at codon 93 and lower at codons 10, 30, 43, 46, and 74 (P < 0.05 for all).
17
Analysis of NRTI resistance mutations
The NRTI resistance mutation M184V/I was present in 66.3% of patients (Figure 1B),
whereas 3.5% harbored viruses with multiple NRTI resistance mutations related to the
Q151M complex and to the codon 69 insertion. The K65R mutation was found in only 1%
of patients. The NRTI resistance selected by the TAMs M41L, D67N, K70R, L210W,
T215Y/F, and K219Q/E was 70%. Of the individuals evaluated, 13.31% presented one
TAM, 22.35% presented two TAMs, 17.09% presented three TAMs, 12.13% presented
four TAMs, 2.48% presented five TAMs and 1.37% presented six TAMs. Interestingly the
TAM pathway 1, which includes mutations at codons 41, 210, and 215, was most
prevalent among subtype B viruses, whereas pathway 2, which includes mutations at
codon 67, 70, and 219, was most prevalent among subtype C viruses (Figure 2). In
subtype F viruses, pathway 1 and pathway 2 were equally distributed.
In subtype B viruses, resistance mutations other than TAMs were most often observed at
codons 75 and 151; in subtype C viruses, such mutations were least common at codons 44
and 118 (P < 0.05 for all).
Analysis of NNRTI resistance mutations
The prevalence of individual NNRTI resistance mutations is presented in Figure 1C. An
interesting new pathway of NNRTI resistance was detected in this study. Individuals
failing efavirenz presented K103N as a key selected mutation, whereas those failing
nevirapine presented the Y181C mutation (Figure 3A). In addition, mutations L100I and
18
P225H were strongly associated with the K103N mutation, whereas mutations K101E and
G190A were strongly associated with the Y181C mutation (P < 0.000 for all). Therefore,
we were able to describe two pathways of NNRTI resistance: one in which failing
nevirapine is most often related to mutations Y181C, K101E, and G190A; and one in
which failing efavirenz is most often related to mutations K103N, L100I, and P225H
(Figure 3B). Potential cross-resistance to etravirine was evaluated, and 1.06% of the
individuals presented three or more resistance mutations to this new antiretroviral drug:
A98G (9.00%); L100I (5.40%); K101P/E (7.20%); V106I (5.30%); V179E/F/I (9.84%);
Y181C/I/V (9.36%); G190A/S (15.4%); and M230L (0.90%).
Resistance mutations at codon 106 were most prevalent in subtype C viruses, resistance
mutations at codon 190 were less prevalent in subtype F viruses, and resistance mutations
at codon 225 were less prevalent in subtype B viruses (P < 0.05 for all).
Viral load and number of resistance mutations
Figure 4 shows the mean viral load according to the number of resistance mutations
accumulated during antiretroviral treatment. The results for all groups were compared
with those obtained for the treatment-naïve group, which consisted of 194 patients with
recent HIV-1 infection, as determined using the serologic testing algorithm for recent HIV
seroconversion [14]. Viral loads analyzed for each individual patient in this group of naïve
patients were chosen after the viral load set point (6 months after inclusion in the cohort).
Initially, viral load decreased in parallel with the increase in the number of resistance
19
mutations, after which it increased as the number of resistance mutations peaked and
stabilized (Figure 4).
The variance test results did not show statistical significance for the mean viral load
among groups with different numbers of resistance mutations. Therefore, the proportion
test based on binomial distribution was used in order to analyze the groups stratified
according to the number of mutations in terms of the distribution of patients with viral
loads greater than 100,000 copies/mL. When all resistance mutations were analyzed, the
proportion of individuals with viral loads greater than 100,000 copies/mL was
significantly higher in the groups with eight or more resistance mutations than in the
treatment-naïve group. There was also a higher proportion of individuals with viral loads
greater than 100,000 copies/mL in the groups with at least one NNRTI resistance mutation
than in the treatment-naïve group.
20
Discussion
This study enabled us to profile genotypic resistance to antiretrovirals in a large group of
patients failing antiretroviral therapy and for whom information related to previous
treatment was available. It can be seen that the majority of individuals failing
antiretroviral treatment in this region of Brazil, where genotyping was requested by the
attending physician, had extensive antiretroviral exposure, and 50% were failing their
third or subsequent antiretroviral regimen. This extensive antiretroviral exposure and
failure, consequences of, among other factors, long term treatment with suboptimal
antiretroviral schemes, leads to extensive antiretroviral resistance. Of these patients, 34%
harbored resistance to all three classes of antiretrovirals, a scenario that has been
associated with a high risk of mortality [15].
In the present study, resistance to NRTIs revealed the extensive exposure to thymidine
analogs and lamivudine. Rare resistance mutations related to didanosine (codon 74), and
stavudine (codon 75) were also prevalent in our patient sample, with a prevalence of
approximately 10%. We observed a differential prevalence of resistance mutations among
HIV-1 subtypes without any difference in the previous antiretroviral exposure. Subtype B
viruses presented more NRTI resistance mutations than did subtype C or F viruses.
Another recent report also showed that, among infected individuals failing antiretroviral
therapy, those infected with subtype C viruses present less accumulation of resistance
mutations to NRTIs than do those infected with subtype B viruses [16]. The reasonable
explanation for this differential acquisition of antiretroviral drug resistance mutations is
21
related to the current ignorance regarding the genotypic correlates of viral resistance
among HIV-1 subtypes other than subtype B. Alternatively, and perhaps less likely,
resistance to NRTIs in these non-B subtypes could be related to resistance mutations to
other as yet uninspected HIV genomic regions, such as RNaseH [17, 18]. A similar
explanation could be given for the fact that NRTI resistance mutations were more
frequently acquired in subtype B viruses than in subtype F viruses. We found less
acquisition of protease mutations in subtype C viruses than in subtype B or F viruses.
Indeed, previous studies have also produced the same results comparing subtype C and B
only [16]. However, it must be borne in mind that some natural polymorphisms, such as
the L89M substitution present in subtype F viruses, might be sufficient to decrease the
susceptibility to a number of PIs [19], perhaps underscoring the importance of using
boosted PIs for the treatment of subtype F-infected individuals [20].
Identifying pathways of antiretroviral resistance is considered important for predicting
cross-resistance to antiretrovirals. The term antiretroviral resistance pathway refers to the
group of resistance mutations selected in vivo or in vitro by a given antiretroviral agent.
One likely explanation for these resistance pathways is the genetic structure of the virus.
This insight comes from the observation that subtype B viruses exposed in vivo or in vitro
to nelfinavir will typically select the D30N mutation, whereas non-B viruses will select
the L90M mutation [21]. Supposedly, the D30N mutation rarely co-exists with the L90M
mutation. In confirmation of this, we found that, in the few cases in which these two
resistance mutations occurred concomitantly, they arose in different genomes. We also
found that the L90M mutation was present in subtype B-infected individuals at a higher
22
proportion than that previously reported, in 47.9% of our patients, including the viruses
containing the D30N-L90M combination. This indicates that cross-resistance to nelfinavir
was higher than expected in this population, since cross-resistance to other PIs is lower
among D30N-containing viruses. In addition and in contrast of what has been generally
speculated, we found D30N mutations in 30.4% of the subtype F-infected individuals in
our sample.
Another important pathway for resistance described more recently refers to the TAM
profile of resistance mutations. The initial selection of TAMs has been shown to occur
either within pathway 1, which includes resistance mutations at codons 41, 210, and 215,
or within pathway 2, which includes resistance mutations at codons 67, 70, and 219. The
practical implication of this is cross-resistance to tenofovir, where resistance mutations at
codon 41 or codon 210 in a total of three TAMs will result in a marked decrease in the
activity of this adenosine analog [22]. Although it has been demonstrated that pathway 1
and pathway 2 present an approximately equal risk of initiating resistance [23, 24], we
found that both of these pathways correlated strongly with the viral subtype. Clearly, the
prevalence of acquired resistance mutations related to pathway 1 would be higher among
subtype B-infected individuals, whereas that of those related to pathway 2 would be
higher among subtype C-infected individuals. In this sense, cross-resistance to Tenofovir
would be more prevalent in subtype B-infected individuals than in subtype C-infected
individuals. Therefore, although the results of in vitro studies have suggested that the
genetic barrier to tenofovir resistance is lower in subtype C viruses due to rapid selection
of the K65R mutation [12], we can speculate that salvage therapy with tenofovir is more
23
effective among subtype C-infected individuals, especially in view of the possibility that
K65R will not emerge in the presence of TAMs, since TAMs and K65R rarely co-exist
[25, 26]. It is of note that, in the present study, subtype F viruses were intermediate
between subtype B and C viruses in terms of the pathway 1- and pathway 2-selected
TAMs, suggesting that, in subtype F viruses, the chance of pathway 1 TAMs being
selected is approximately the same as that of pathway 2 TAMs being selected.
In the present study, we also detected two distinct pathways to NNRTI resistance, one
related to the selective pressure of efavirenz and other to that of nevirapine. The most
common mutation related to efavirenz resistance is the K103N mutation, whereas the most
common mutation related to nevirapine resistance is the Y181C mutation. It is noteworthy
that mutations K101E and G190A were associated with the Y181C mutation and with
nevirapine exposure, whereas mutations L100I and P225H were associated with the
K103N mutation and with efavirenz exposure. All three mutations associated with
nevirapine exposure are related to etravirine cross-resistance, whereas, among those
associated with efavirenz exposure, only the L100I mutation is related to etravirine cross-
resistance. Therefore, nevirapine failure might impair future salvage therapy with
etravirine, which was designed to be active against NNRTI-resistant HIV strains.
Nevertheless, cross-resistance to etravirine appears to be low (1.06% of samples presented
three or more related mutations), and etravirine might be a good option for salvage
therapy in this population (those failing other NNRTIs). Similarly, darunavir and
tipranavir might also be good options for salvage therapy, since cross-resistance to both
seems to be equally low in this population. Since strains resistant to darunavir will
24
sometimes remain sensitive to tipranavir and vice versa, the availability of both drugs will
be important in such cases.
A well-defined paradigm related to the accumulation of antiretroviral drug resistance
mutations is the concomitant decrease in the replicative capacity of a virus, which will
ultimately decrease viral fitness. Some experts even suggest that the presence of a
resistant virus will lead to a more modest decrease in CD4 T-cell counts [27], as well as to
less pronounced cell activation [28], thereby potentially delaying disease progression. It
has been established that the viral load can be a surrogate marker of viral fitness [29]. On
the basis of this assumption, we attempted to draw a correlation between the number of
resistance mutations accumulated and the viral load in order to infer the impact of that the
accumulation of resistance mutations has on viral fitness. We found that, as the number of
resistance mutations increases, there is in fact a drop in the mean viral load. However,
after the number of resistance mutations reaches a certain threshold, the viral load begins
to increase in direct proportion to the number of resistance mutations. We therefore
speculate that the replicative capacity of the virus is restored after a virus has accumulated
a large number of resistance mutations, and that this explains the more rapid disease
progression seen in individuals presenting more extensive resistance [15]. Another
possible explanation for viral load increasing in parallel with the number of resistance
mutations is that, since all of our patients were receiving antiretroviral therapy, there was
less residual activity. Nevertheless, it is undeniable that the strains containing a high
number of resistance mutations and producing high viral loads also present high fitness.
Since the probability of accumulating antiretroviral drug resistance mutations over time is
25
directly proportional to the magnitude of the residual viral replication in cases of treatment
failure [30], it would be reasonable to pursue a viral load that would be as low as possible,
even in patients harboring resistant viruses, in order to minimize the chances of
accumulating additional resistance mutations.
In conclusion, it is becoming clear that special attention should be given to the resistance
profile selected in non-B subtypes, and further studies along this line are warranted.
26
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31
Figure Legends
Fig. 1. Prevalence of codons with antiretroviral resistance mutations according to
HIV-1 subtype (B, F and C). Panel A shows the major PI resistance mutations, Panel
B shows the NRTI resistance mutations, and Panel C shows the NNRTI resistance
mutations.
Fig. 2. Prevalence of TAMs by subtype. Pathway 1 TAMs are represented by reverse
transcriptase codons 41 and 210, and pathway 2 TAMs are represented by codons 67
and 219. Statistical analyses were performed using chi-square tests, and P values are
shown for each subtype comparison.
Fig. 3. Analysis of 798 patients failing NNRTIs as the most recent treatment
regimen. Panel A shows the prevalence of NRTI resistance mutations in patients
treated with nevirapine (NVP) or efavirenz (EFV). Panel B shows the association
between mutations related to K103N, which was the mutation most often selected by
EFV, and Y181C, which was the mutation most often selected by NVP.
Fig. 4. Mean viral load according to the number of antiretroviral drug resistance
mutations: Number of NRTI, NNRTI, and PI resistance mutations (panel A); Number
of NRTI and PI resistance mutations (panel B); and Number of NNRTI resistance
mutations (panel C).
32
Table 1. Prevalence of resistance to different classes of antiretrovirals by HIV-1
subtype.
Antiretroviral class Subtype
Resistance
mutations, n %
Subtypes
compared P
B 1076 54.6
B vs. F NS
F 226 57.0 P = 0.00 B vs. C 0.00
PI*
C 41 39.0
F vs. C 0.00
B 1914 90.1
B vs. F NS
F 212 90.5 P = 0.00 B vs. C 0.00
NRTI
C 94 79.6
F vs. C 0.01
B 1347 63.5
B vs. F 0.00
F 126 53.8 P = 0.01 B vs. C NS
NNRTI
C 73 61.8
F vs. C NS
*PI mutations included in the analysis were L23I, L24I, D30N, V32I, V33F, M46I/L, I47V/A, G48V/M,
I50L/V, F53F/V, I54V/T/A/L/M, G73S/T, L76L/V, V82A/F/T/S, I84V/A/C, N88T/S and L90M. PI, protease
inhibitor; NRTI, nucleoside reverse transcriptase inhibitor; NNRTI, non-nucleoside reverse transcriptase
inhibitor.
33
Prevalence of PI Major Mutations
0% 5% 10% 15% 20% 25% 30% 35%
50
48
47
32
84
33
30
88
54
82
46
90
Mutation Codons
Prevalence
Prevalence
Prevalence subtype B
Prevalence subtype C
Prevalence subtype F
Figure 1, panel A.
34
Prevalence of NRTI Mutations
0% 10% 20% 30% 40% 50% 60% 70% 80%
ins69
115
116
77
65
62
151
74
75
70
210
219
67
41
215
184
Mutation codons
Prevalence
Prevalence
Prevalence Subtype B
Prevalence Subtype C
Prevalence Subtype F
Figure 1, panel B.
35
Prevalence of NNRTI Mutations
0% 10% 20% 30% 40% 50%
236
230
227
106
100
188
225
108
98
181
179
101
190
103
Mutation Codons
Prevalence
Prevalence
Prevalence Subtype B
Prevalence Subtype C
Prevalence Subtype F
Figure 1, panel C.
36
Fig. 2.
Mutation
B vs.
F
B vs.
C
F vs.
C
M41L 0.001 0.000 0.013
D67N 0.036 0.387 0.055
K70R 0.278 0.001 0.026
L210W 0.000 0.000 0.215
T215Y/F 0.063 0.003 0.095
K219Q/E 0.572 0.529 0.795
M41L/L210W 0.000 0.000 0.321
D67N/K219Q/
E
0.573 0.015 0.104
Prevalence of TAMs by subtype
0
10
20
30
40
50
60
70
M41L D67N K70R L210W T21Y/F5 K219Q/E TAMs 1 TAMs 2
TAM codons
%
B F C
37
Figure 3. Panels A and B.
(A)
0%
5%
10%
15%
20%
25%
30%
35%
A98G 100I K101E V106M/A V108I Y188L G190A P225H F227L
NNRTI mutations
Prevalence
K103N
Y181C
Mutations related to K103N or Y181C
(confirmed by
phi
)
38
(B)
0%
10%
20%
30%
40%
50%
60%
70%
80%
A98G L100I K101E K103N V106M/A V108I Y181C Y188L G190A P225H F227L Zero
Mutation Codons
NVP
EFV
*
*
*
*
*
Codons selected by nevirapine or efavirenz
* = p<0.01
39
Figure 4, Panes A, B, and C.
(A)
(B)
0
50.000
100.000
150.000
200.000
250.000
0 1 2 3 4 5 6 7 8 9 10 to
12
13
number of mutation to NRTI, NNRTI and PI
Mean Viral Load (copies/ml)
n 109 92 118 146 175 166 173 190 143 124 247 153
0
50000
100000
150000
200000
250000
0 1 2 3 4 5 6 7 8 9 10 11 12
Number of mutations to NRTI and PI without mutations to NNRTI
Mean of Viral Load (copies/ml)
n 155 195 153 158 166 211 167 144 126 100 76 68 117
40
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
0 1 2 3 4
Number of mutations to NNRTI
Mean of Viral Load (copies/ml)
n 742 383 446 188 77
(C)
41
Decreased Phenotypic Susceptibility to Reverse
Transcriptase Inhibitors in the Absence of Known
Resistance Mutations in Clades C, F, and B/F
Recombinant Antiretroviral Naïve HIV-1 Strains
Patricia Munerato
1
, Maria Cecília A Sucupira
1
, Jussara Silveira
2
, André F.
Santos
3
, Marcelo A. Soares
3,4
, Ricardo Sobhie Diaz
1
1
Universidade Federal de São Paulo, UNIFESP, Brazil
2
Fundação Universidade Federal do Rio Grande, Rio Grande, Brazil
3
Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
4
Instituto Nacional de Câncer, Rio de Janeiro, Brazil
Running title: phenotypic susceptibility in non-B HIV-1
42
Abstract
The impact of clade-specific polymorphisms on HIV antiretroviral susceptibility is
not completely understood. To evaluate the antiretroviral phenotypic susceptibility
of wild-type HIV-1 strains circulating in Brazil, samples from 32 antiretroviral-naïve
individuals infected with non-B subtypes C (n = 16), F (n = 9), or B/F (n = 7)
where RT is B and protease is F, were phenotyped. Reduced susceptibility to
protease inhibitors (PIs) was observed in three F and one C isolates. None of
these strains presented any known resistance mutation correlated to PI. BR43
was the only strain containing the Y59H substitution, and presented Saquinavir
resistance. The fold change in susceptibility to one or more PIs was above the
cut-off value in 3.1% of clade F isolate and 1.0% of C isolates. Phenotypic
resistance to at least one nucleoside reverse transcriptase inhibitor (NRTI) was
found for one B/F isolate, three C, and three F isolates. The fold change in
susceptibility to NRTIs was above the cut-off value in 6.2% of clade C isolates,
compared with 4.8% for clade F and 2.0% for clade B. The fold change in non-
NRTI (NNRTI) susceptibility was above the cut-off in 21.9% of C isolates,
whereas none of F isolates presented such susceptibility. Only two of these
sixteen C samples presented a known resistance mutation. Surprisingly, the
NNRTI susceptibility fold change was above the cut-off value in 21.4% of Brazilian
B/F recombinants, presenting clade B reverse transcriptase. In HIV-1 clades F
and C, PI and NRTI susceptibility is apparently preserved, whereas NNRTI
susceptibility should be better investigated in clade C and B/F recombinants.
43
Introduction
Drug resistance testing has become an important tool in the management of HIV-
infected individuals undergoing antiretroviral therapy.
1
Genotyping and
phenotyping methods appear to be equally useful for determining the
susceptibility of HIV-1 to antiretroviral drugs.
2
Genotyping identifies mutations in
the HIV genome associated with antiretroviral resistance, whereas phenotyping
examines the relative susceptibility of viruses to different antiretroviral
concentrations in vitro. Drug susceptibility tests have been designed for subtype B
strains and are performed mainly on those strains. However, the increasing global
prevalence of non-B subtypes creates the need to determine the performance of
commercial drug resistance assays testing HIV-1 subtypes other than B, since it
is conceivable that the genetic diversity of HIV-1 influences the susceptibility to
antiretroviral drugs. Furthermore, it is not well known whether specific mutations
or pathways are differently selected by antiretrovirals among HIV-1 clades. Some
retrospective results suggest that individuals infected with clade F strains respond
more poorly to antiretroviral therapy than do clade B-infected individuals.
3
It has
also been suggested that the L89M polymorphism, which is highly prevalent in the
clade F protease, plays a role in the antiretroviral response, since this
polymorphism decreases the susceptibility of viruses to most protease inhibitors
(PIs).
4
In contrast, it has been also speculated that the I93L polymorphism
increases the susceptibility of clade C strains to lopinavir.
5
Although the I93L
polymorphism is also common in clade F viruses, its effect in that subtype has not
44
been determined. Moreover, a study conducted with subtypes B and C-infected
patients in southern Brazil has shown that the latter acquires less drug resistance
mutations under treatment exposure, particularly to nucleoside analogues and
protease inhibitors. In Brazil, HIV-1 clades B, C, and F co-circulate, B/F
recombinants accounting for a significant proportion.
6
In the present study, we
evaluated the mutation profile and in vitro antiretroviral response in strains
isolated from antiretroviral-naïve Brazilian patients infected with subtypes C, F, or
B/F. In order to assess the natural susceptibility of the C and F HIV subtypes to
PIs, as well as to nucleoside and non-nucleoside reverse transcriptase inhibitors
(NRTIs and NNRTIs), we evaluated the phenotypic susceptibility and genotypic
correlates of resistance in antiretroviral-naïve strains.
Materials and Methods
Isolates from 32 antiretroviral-naïve Brazilian patients were evaluated: 16 were
subtype C, 9 were subtype F1, and 7 were B/F recombinant strains, all of which
carried a F1 protease and a B reverse transcriptase. Viruses from plasma
samples were genotyped at the Federal Universities of Sao Paulo and Rio de
Janeiro, Brazil, using the ViroSeq
®
System (Celera Diagnostics, Alameda, CA,
USA). Sequences were analyzed using an ABI 3100 sequencer (Applied
Biosystems, Foster City, CA, USA). All genotyping was performed based on an
analysis of a portion of the pol gene sequence profile, spanning reverse
45
transcriptase and protease regions. Samples identified as recombinants were
analyzed using the SimPlot program, version 3.5.1
7
and confirmed by
bootscanning analysis. The basic principle of bootscanning is that mosaicism is
suggested when one observes high levels of phylogenetic relatedness between a
query sequence and more than one subtype reference sequence in different
genomic regions.
8
Sample sets were subjected to antiretroviral phenotypic
analysis using the Antivirogram
TM
Assay (Virco, Mechelen, Belgium). This
phenotyping assay uses HIV-1 genomes generated by recombination between
PCR amplified pol products derived from patient viruses and a subtype B proviral
clone with deletion of protease and reverse transcriptase regions. Recombinant
viral production and detection methods were conducted as previously
described.
9,10
For clade C, clade F and B/F recombinant isolates obtained from
treatment-naïve subjects, the mean, median, and interquartile range of fold
change values for each drug, as determined using the Antivirogram
TM
assay,
were compared to the same parameters for clade B isolates in the Virco
database. The mutation patterns associated with reduced susceptibility to one or
more drugs in clade C, clade F, and B/F isolates were evaluated and compared to
genotypic correlates of drug resistance described for clade B isolates.
46
Results
Sample identification, protease/reverse transcriptase subtypes,
polymorphisms/mutations at codons associated to resistance, and fold change in
susceptibility to PIs, NRTIs and NNRTIs, as well as the mean fold change by
subtype, are shown in Tables 1A and 1B.
As in any diagnostic test that produces a quantitative result, the Antivirogram
TM
HIV-1 fold change values are interpreted using cut-off values that separate viral
strains that are considered to be highly susceptible to antiretrovirals from those
that are considered to present low antiretroviral susceptibility. Biological cut-off
values are derived from in vitro experiments and mark the upper limit of natural
variation in phenotypic susceptibility among wild-type viruses, which includes
97.5% of strains after two standard deviations to the right of the normal
distribution.
11
Since these biological cut-off values were typically calculated using
clade B strains, we analyzed the percentage of viruses from clades C, F and
Brazilian B/F recombinant that remained above the biological cut-off value. For PI
susceptibility, 1.0% of the isolates from clade C and 3.1% from clade F presented
fold change values above the upper limit of the biological cut-off values. For NRTI
susceptibility, 6.2% of fold change values were above the biological cut-off for
clade C isolates, compared with 4.8% for clade F and 2.0% for B/F isolates. The
phenotyping results for NNRTIs susceptibility showed 21.9% of fold change
values above the biological cut-off value in clade C isolates. None of clade F
47
isolates showed decreased susceptibility to NNRTIs. Most importantly, clade C
samples did not present any known mutation to correlate with NRTI resistance,
and only two samples presented mutation that correlates with NNRTI resistance,
A98G and K103N (samples BR76 and BR87, respectively, Table 1B).
Surprisingly, 21.4% of the Brazilian clade B/F isolates presented fold change that
was above the biological cut-off value for NNRTI susceptibility.
All but four viral strains were fully susceptible to all six PIs tested (Table 1A).
Three strains belonging to subtype F (BR38, BR43, and BR44) presented
reduced susceptibility to PIs. The first strain, BR38, presented a fold change of
1.8 for saquinavir and carried the following protease polymorphisms/mutations:
V3I, I15V, E35D, M36I, S37N, R41K, R57K, D60E, Q61E, L63P, K70T, and V77I.
The BR43 isolate also presented decreased susceptibility to saquinavir, with a
fold change of 2.1, and carried the protease polymorphisms/mutations V3I, L10V,
I13V, I15V, G16E, K20M, E35D, M36I, S37N, R41K, R57K, Y59H, Q61N, I72T,
and L89M. The BR44 isolate presented a fold change of 2.3 for lopinavir,
containing the amino acid substitutions V3I, I15V, G17E, K20R, E35D, M36I,
S37N, R57K, Q61N, L63T, E65D, and I72V. Only one clade C isolate (BR86)
presented a low level of resistance, with a 0.1 fold change above the biological
cut-off value. This isolate contained the following amino acid substitutions: V3I,
I15V, M36I, S37K/N, R41N, L63I/P/S/T, H69K, V82I/V, L89M, and I93L. As can
be seen in Table 1A, these four viruses presented fold changes discreetly above
the biological cut-off values for each respective drug
11
. Since other strains
48
displayed the same mutation profile without reduced PI susceptibility, direct
involvement of those amino acid changes with drug resistance could not be
speculated. One exception was the mutation Y59H, which was only detected in
the BR43 isolate, which showed a loss of susceptibility to saquinavir. All twenty-
eight of the remaining isolates (13 of subtype F and 15 of subtype C) were fully
susceptible to all PIs tested. The mean fold change in antiretroviral susceptibility
per subtype sample set was nearly 1.0, which is comparable to that found for
subtype B wild-type strains.
Amino acid substitutions that were considered accessory mutations and
correlated with selective pressure from antiretroviral drugs among subtype B
strains, including substitutions at codons 10, 20, 36, 63, 77, and 82, were
detected in the protease region of non-B strains isolated from antiretroviral-naïve
individuals. Changes were found at various rates: L10I (12.5% in subtype F and
6.2% in subtype C), L10V (18.7% in subtype F and 6.2% in subtype C), K20R
(43.7% in subtype F and 12.5% in subtype C), M36I (87.5% in subtype F and 81.2
in subtype C), M36T (12.5% in subtype C), L63P (12.5% in subtype F and
subtype C), L63A/G/H/I/L/Q/S/T/V (31.2% in subtype F and 43.7% in subtype C),
V77I (18.7% in subtype F) and V82I (6.2% in subtype F and 31.2% in subtype C).
The L89M polymorphism did not have any impact on PI susceptibility among
clade F strains, which presented fold change less than or equal to 1.0. Nor did the
I90L polymorphism have any impact on PI susceptibility among clade C strains,
for which the mean fold change in susceptibility to lopinavir was 1.0. Although
49
previous studies have shown that the L89M polymorphism has an impact on
saquinavir, nelfinavir, ritonavir, amprenavir and lopinavir susceptibility,
4,12
we
found no data to support a consistent change in PI susceptibility related to this
polymorphism. It has also previously been reported that susceptibility to lopinavir
increases in the presence of the I93L substitution in clade C strains, and that the
poor response to PI therapy is empowered by I93L.
5,13
In contrast, we found I93L
in all subtype C strains analyzed, and the mean fold change value for clade C
samples set was very close to 1.0 (0.8) and the susceptibility to other PI was not
compromised. The remaining polymorphisms are of uncertainly significance. As
previously described,
14
100% of the clade F isolates carried V3I, and R57K;
81.2% carried S37N, R41K, and Q61N; 62.5% carried E35D; 56.2% carried I15V;
and 50% carried L89M. For clade C, 100% of the isolates carried S37K, R41N,
H69K, I89M, and I93L; 87.5% carried I15V; and 31.2% carried G16A/E. It is of
note that, whereas subtype F isolates presented S37N, R41K, and R57K
polymorphisms, subtype C isolates presented S37K, R41N, and H69K
polymorphisms in all samples. When different substitutions at amino acid
positions known to be related to PI resistance in clade B, such as K20I, M36V/L,
and L63S/A/T/F, were taken into account, all but two subtype F strains (87.5%)
carried two to four mutations. Nearly 62% of subtype C strains carried one to
three of those mutations.
We also analyzed the susceptibility of clades C and F to reverse transcriptase
inhibitors. Seven NRTIs and two NNRTIs were tested for Brazilian isolates: 7 from
50
subtype B/F reverse transcriptase, 16 from subtype C and 9 from subtype F
reverse transcriptase (Table 1B). Decreased susceptibility to at least one of the
reverse transcriptase inhibitors tested was observed in 10 viral strains: 2 clade
B/F (BR36 and BR39), 3 clade F (BR43, BR44 and BR46) and 6 clade C (BR76,
BR82, BR86, BR87, BR94, and BR99; Table 1B). Since clades C and F carried
many reverse transcriptase polymorphisms, Table 1B shows only amino acid
substitutions known to be related to drug resistance. In the analysis of clade F
samples set, the BR43 presented decreased susceptibility to ddI with 0.1 fold
change above the cut-off value, BR44 and BR46 presented decreased
susceptibility to zidovudine with 0.2 and 0.5 fold changes above the cut-off
values, respectively. These three clade F samples presented loss of susceptibility
without any amino acid substitutions previously described to be related to
antiretroviral resistance. Into clade C samples set, the BR76 sample presented
A98G and a 20.7 fold change in susceptibility to nevirapine, compared with 18.7
and 61.6 fold changes in susceptibility to efavirenz and nevirapine, respectively,
presented by BR87 sample, which was found to carry K103N. The BR86 strain
presented decreased susceptibility to abacavir, zidovudine and efavirenz, with
only one NRTI resistance-related codon previously described, although with a
different amino acid substitution: E40D. In contrast, BR43 from clade F presented
the same amino acid change, but no decreased susceptibility was observed. The
other four subtype C strains that presented decreased susceptibility to NNRTIs
did not show any known resistance mutations. The mean fold change values for
51
clade F samples were comparable to those found for clade B in all reverse
transcriptase inhibitors tested. For the clade C sample set, the mean fold change
values were also near 1.0, except those for susceptibility to efavirenz and
nevirapine, which were 2.6 and 7.1, respectively.
52
Discussion
Despite the fact that genetic polymorphisms at positions associated with PI
resistance were found at a higher rate in the two non-B subtypes isolated from
antiretroviral-naïve subjects, no phenotypic decrease in PI susceptibility was
identified in this set of samples. In contrast, some level of decrease in the
susceptibility to NRTIs and NNRTIs was found among strains belonging to these
non-B HIV-1 viruses. Strikingly, only two of the twelve samples revealed known
resistance mutations related to reverse transcriptase inhibitors, suggesting that
the genotypic correlates of decreased susceptibility among clade C, clade F and
BF recombinants are yet obscure. One recent study demonstrated that the rates
of resistance-related mutation acquisition among clade C strains might be inferior
to those of clade B strains
15
. One reasonable explanation for the fact that the
prevalence of mutations is lower among clade C-infected individuals than among
clade B-infected individuals is again the fact that the correlates of genotypic
resistance in HIV-1 clade C might be unknown.
Another hypothetical explanation for the lack of mutations known to confer
resistance to reverse transcriptase inhibitors in the presence of a low level of
resistance is that genetic mutations outside the reverse transcriptase catalytic
region could be influencing susceptibility to certain reverse transcriptase
inhibitors. In fact, there is mounting data that mutations in the RT connection and
RNase H regions lead to either NRTI or NNRTI resistance.
16,17
Resistance
53
mutations outside the reverse transcriptase region might explain the lack of
resistance mutations found, since B/F recombinant strains cluster with clade B in
the reverse transcriptase region, although one sample showed resistance to
NRTIs and two samples presented resistance to NNRTIs. Sequencing outside the
protease and reverse transcriptase catalytic regions was not performed, and we
are therefore unable to assign the outside regions to any particular HIV-1 subtype.
Although all clade C strains tested here presented the I93L polymorphism in the
protease region, we were unable to confirm previous results suggesting that this
natural polymorphism causes in vitro hypersusceptibility to lopinavir
5
. In fact, the
I93L substitution has been related to lower in vivo susceptibility to indinavir and
nelfinavir among clade B-infected individuals
18
. Likewise, we were unable to
confirm that the L89M present in clade F strains would compromise the natural
susceptibility to PIs, as previously described
4
. However, it can be argued that the
high number of clade-related polymorphism found in non-B strains contributes to
decreasing the genetic barrier to PI resistance, even in the absence of baseline
resistance to PIs, as described in the present study. It has been reported that the
polymorphisms found at positions 10 and 36 are the strongest predictors of
virologic failure, appearing in nearly 40% of antiretroviral-naïve subjects in whom
PI-based therapies failed.
19
It is of note that the M36I mutation was present in
87.5% of the F and 75.0% of C subtype proteases in our study, and that the
phenotypic assays did not recognize any significant loss in PI susceptibility.
54
Although previously antiretroviral-naïve individuals treated with boosted PIs do not
typically present PI mutations or virologic resistance,
20,21,22,23
one recent study
revealed genetic progression in five patients treated with boosted lopinavir
monotherapy, two infected with a clade B strain and three infected with
CRF02_AG strains
24
. Although no phenotypic resistance was confirmed in these
two clade B strains, it has been confirmed in two CRF02_AG strains with the
emergence of mutation L76V, as well as other mutations. It can be speculated
that, in those cases, the high number of polymorphisms present in non-B strains
allows genetic evolution resulting in selective pressure of PIs.
Another point of great interest is the relationship between the genetic diversity of
HIV and response to treatment. An unrecognized level of risk of antiretroviral
failure might be related to a high number of natural polymorphisms present in
non-B strains, and, although the results of some studies indicate that the level of
response is lower among patients infected with non-B HIV,
3
other studies have
shown the opposite
25
.
We recognize that the small size of the sample analyzed here is a major limitation
of this study, and that further studies are needed in order to confirm our results.
Nevertheless, we believe that, until better correlates of genotypic resistance
become available, phenotypic tests for non-B clades should be more widely
accessible.
55
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59
TABLE 1A. Results of phenotypic susceptibility to protease inhibitors (PIs) using Antivirogram
TM
Assay and protease genotypic profile from HIV-1 Brazilian samples
from clades F and C.
APV AZT IDV LPV NFV SQV
(1.8) (2.0) (2.1) (1.6) (2.3) (1.7)
BR29 F 1.1 0.7 0.5 1.6 1.4 0.8 V3I R41K R57K Q61N K70R L89M
BR35 F 1 1 0.7 0.6 0.8 0.4 V3I L10I I13V L33V E35D M36I S37N R41K R57K D60E Q61N G68E L89M
BR36 F 0.7 1.1 1 1.6 0.7 1.5 V3I G17D K20R E35D M36I S37N R41K K43R R57K Q61N I72R
BR37 F 0.8 1.1 1 0.6 0.9 0.5 V3I T12I I13V M36I S37N R41K R57K Q61H/N L89M
BR38 F 1.4 0.9 0.7 1.2 1.7
1.8
V3I I15V E35D M36I S37N R41K R57K D60E Q61E L63P K70T V77I
BR39 F 0.3 0.2 1.4 0.7 0.6 0.3 V3I T12K I15V L19I E35D M36I S37N R41K R57K Q61N E65D I72T
BR40 F 0.6 0.5 0.9 0.9 1 1 V3I L10V I13V G17E K20R M36I S37E R57K Q61N L63A/V K70R
BR31 F 0.9 1 0.8 0.6 0.8 0.5 V3I I13I/V I15I/L M36I S37N R41K R57K Q61N H69Y L89M
BR43 F 1.2 1.3 0.7 1.1 1.2
2.1
V3I L10V I13V I15V G16E K20M E35D M36I S37N R41K R57K Y59H Q61N I72R L89M
BR44 F 0.6 0.4 0.6
2.3
1.4 0.6 V3I I15V G17E K20R E35D M36I S37N R57K Q61N L63T E65D I72V
BR46 F 1.1 1.5 0.5 1.3 1.4 0.9 V3I I15V K20R E35D M36I S37N P39Q R41K R57K D60E Q61D L63P/S L89M
BR48 F 0.3 0.1 0.2 0.7 1.1 0.2 V3I L10V I15V S37E R57K Q61N L63A I64L I72V V77I I93L
BR50 F 1.3 0.7 0.7 1.1 0.5 0.5 V3I L10I T12S I13V K14R G16E K20R E35D M36I S37N R41K R57K Q61N L63V I72T
BR51 F 0.3 0.6 1.5 0.9 1 0.9 V3I I15V E35D M36I S37N P39Q R41K R57K Q61N V77I L89M
BR52 F 0.3 0.4 0.3 0.5 0.3 0.4 V3I I15V K20R M36I/L S37K R41N H69K V82I L89M I93L
BR53 F 0.4 0.3 0.2 0.7 0.8 0.3 V3I I15V E35D M36I S37N R41K R57K Q61N L63S E65D I72T
0.8 0.7 0.7 1 0.9 0.8
BR76 C 0.2 0.5 0.3 0.7 0.4 0.5 V3I I15V G16A M36I S37K R41N H69K L89M I93L
BR78 C 0.2 0.6 0.3 0.6 0.4 0.5 V3I I15V G16E M36I S37K R41N H69K L89M I93L
BR79 C 0.6 0.8 0.5 0.9 1.4 0.5 V3I I15V M36I S37K R41N L63T H69K L89M I93L
BR80 C 0.7 0.8 0.4 0.6 0.4 0.9 V3I I15V M36I S37K R41N L63T H69K V82I L89M I93L
BR81 C 0.2 0.1 0.2 0.7 0.7 0 V3I I15V M36I S37K R41N L63G/V H69K L89M I93L
BR82 C 0.7 0.6 0.2 1.2 1 0.6 V3I G16E M36I S37K R41N L63H/L/Q/V I64L H69K L89M I93L
BR83 C 0.5 0.6 0.8 1 1.1 0.9 V3I I15V L19I M36I S37K R41N M46V H69K V82I L89M I93L
BR84 C 0.4 0.9 0.8 0.7 0.5 0.7 V3I T12P I15V M36T S37K R41N L63T H69K L89M I93L
BR86 C 1.3 1.1 0.8 1.2 1.6 1.8 V3I I15V M36I S37K/N R41N L63I/P/S/T H69K V82I/V L89M I93L
BR87 C 0.9 1 1.8 0.6 0.5 1.4 V3I I15V L19I S37K R41I D60E H69K L89M I93L
BR88 C 0.3 0.3 0.2 0.8 1.3 0.8 V3I T12N I15V M36I S37N R41K H69K L89M I93L
BR89 C 0.5 0.6 0.6 0.7 1.1 0.7 V3I L10I/V I13V K14R M'36I/T S37K R41N L63P H69K L89M I93L
BR91 C 0.8 1.1 0.3 1 1.3 0.5 V3I I15V G16E K20R E35D M36I S37K P39S R41N/S H69K L89M I93L
BR92 C 0.2 0.4 0.2 0.3 0.2 0.3 V3I T12K K14R I15V M36I S37K R41N H69K V82I L89M I93L
BR94 C 0.6 0.4 0.3 0.6 0.6 0.5 V3I I15V S37K R41N L63V H69K V82I L89M I93L
BR99 C 0.8 1.2 1.7 1.4 1.2 0.7 V3I K14R I15V G16E K20R M36I S37K P39S R41N H69K L89M I93L
0.6 0.7 0.6 0.8 0.9 0.7Mean FC
Protease polymorphisms/mutations
Mean FC
Virco biological cut-off value*
Sample ID
Protease
Subtype
FC in PI susceptibility vs. wild-type
FC, fold change; PI, protease inhibitor; APV, amprenavir; AZT, zidovudine; IDV, indinavir; LPV, lopinavir; NFV, nelfinavir; SQV, saquinavir.
*Values refer to the second generation Virco biological cut-off values.
11
60
TABLE 1B. Results of phenotypic susceptibility to reverse transcriptase inhibitors (NRTIs and NNRTIs) using
Antivirogram
TM
Assay and reverse transcriptase related resistance codons from HIV-1 Brazilian samples.
ABC NVP
(2.2)
(5.5)
BR29 B/F 0.7 0.7
BR35 B/F 0.5 2.8
BR36 B/F 0.5
7.2
BR37 B/F 1.1 1.2
BR38 B/F 0.7 1.1
BR39 B/F 0.8 1.6
BR40 B/F 0.5 0.9
Mean FC
0.7
2.2
BR31 F 0.8 1.7
BR43 F 0.2 1.1
E40D
BR44 F 1.7 0.8
BR46 F 0.8 1.8
BR48 F 0.2 0.5
I50V
BR50 F 1 0.9
BR51 F 1.6 0.7
G333D
BR52 F 0.3 0.2
BR53 F 0.5 0.2
Mean FC
0.7
1.5
BR76 C 0.4
20.7
A98G
BR78 C 0.4 1.2
BR79 C 0.4 0.8
BR80 C 0.6 4.7
A98S
BR81 C 0.2 0.5
BR82 C 0.6
6.3
BR83 C 0.5 0.9
BR84 C 0.4 0.4
BR86 C
2.7
0.8
E40D
BR87 C 1.9
61.6
K103N
BR88 C 0.2 0.7
BR89 C 0.8 0.7
BR91 C 1.3 0.5
BR92 C 0.3 0.3
BR94 C 0.5
6.1
BR99 C 1.2
7.2
Mean FC
0.8
7.1
2.4
2.3 3
0.9 1.1 1.1 1.0 1.1 1.2 2.6
2.4
1.1
2.6 4
0.2 0.7 0.5
0.7 0.1 0.6 0.6 0.8 0.4 0.5
0.3 0.6 0.8 0.3
0.6 0.9 0.6
1 0.9 1.2 1 0.5 1.2 0.9
0.5 1.4 0.8 0.4
1.4 2.6 18.7
0.3 0.3 0.7 0.3 1.6 0.5 0.5
1.8 2.2 1.1 2.1
0.8 0.6 2.3
1.4 2 2 1.5 3.4 3.9
1.3 0.5 1.6 0.3
1 1.1 2
1.2 1.3 0.8 0.6 1.4 0.9 2.2
1.8 1.5 1.6 2.6
0.8 1.9 2.1
0.2 0.1 0.7 0.2 0.6 0.2 0.5
0.4 3.3 0.6 0.4
0.9 0.6 0.2
0.8 1.7 1.2 0.5 1.4 0.5 2.2
0.9 1 0.9 0.4
0.8 1.3 1.4
0.5 0.7 1 0.3 1.4 0.8 1.9
0.9 1.1 0.8 1.0
0.4 1.8 0.9
0.2 0.3 0.6 0.2 0.5 0.4 0.2
0.5 0.9 1.1 0.7
1.4 1.2 1.1
0.3 0.5 0.6 0.3 0.3 0.3 0.2
0.7 1.4 0.9 1.3
0.5 3.2 0.7
0.2 0.1 0.4 0.2 0.6 0.2 0.5
1.1 1 0.7 2.2
1 0.6 0.7
0.7 1.3 0.6 1.5 0.6
2.9
1.2
2.3
0.4 1.1 1.5
0.9 1.3 2.0
0.9 0.7 0.5 1.3 0.8 1.2 1.5
1.1 1.4 0.9 1.0
0.7 0.7 3.8
0.6 1.1 1.1 0.8 0.4 1.9 0.2
2.1 3.6 0.6 0.4
1 1.2 2.6
1.9 0.9 1.4 1.8 1.7 0.7 1
1 0.7 1.1 1.1
0.4 1.2 0.9
1.1 1.2 0.7 1.6 1 0.7 4.1
0.7 2 0.7 0.6
(2.1) (2.7) (3.4)
0.5 0.4 0.8 0.4 1 2.7 1.6
(2.2) (3.5) (2.4) (2.3)
RT
resistance
mutation
codons
Virco biological cut-off value* Virco biological cut-off value*
ddI FTC 3TC d4T TDF AZT
Sample ID
RT
Subtype
FC susceptibility vs. wild-type
NRTIs NNRTIs
EFV
FC, fold change; NRTIs, nucleoside reverse transcriptase inhibitors; NNRTIs, non-nucleoside reverse transcriptase inhibitors; RT, reverse transcriptase; ABC, abacavir; ddI,
didanosine; FTC, emtricitabine; 3TC, lamivudine; d4T, stavudine; TDF, tenofovir; AZT, zidovudine; EFV, efavirenz; NVP, nevirapine.
*Values refer to the second generation Virco biological cut-off values.
11
61
1. IDS. 2001 Aug 17;15(12):1493-502.
62
3. Conclusões
1. Altos níveis de resistência anti-retroviral, incluindo resistência a múltiplas
classes, foram encontradas na população analisada neste estudo. Mutações de
resistência relacionadas aos inibidores da protease e inibidores da transcriptase
reversa análogos aos nucleosídeos foram menos frequentes no subtipo C,
enquanto as mutações relacionadas aos inibidores não-nucleosídeos da
transcriptase reversa foram menos frequentes no F.
2. Os virus do subtipo B seguem, preferencialmente, a via 1 no acúmulo de
mutações aos análogos de timidina (TAM1), enquanto os virus C seguem mais
frequentemente a via 2 (TAM2). Os virus do subtipo F ocupam uma posição
intermediária quando comparados aos subtipos B e C.
3. A seleção de mutações de resistência varia de acordo com os subtipos do
HIV-1 analisados para as três classes de anti-retrovirais (IP, ITRN, ITRNN).
4. Duas vias mutacionais de resistência foram descritas para os inibidores não
nucleosídeos da transcriptase reversa nevirapina e efavirenz. A substituição de
aminoácido K103N é mais frequentemente selecionada em esquemas utilizando
efavirenz, enquanto Y181C é mais selecionada pela nevirapina. Uma alta
correlação positiva foi encontrada entre as mutações K103N, L100I, P225H,
caracterizando assim a via mutacional relacionada ao efavirenz. Por outro lado,
63
Y181C esteve fortemente associada com K101E e G190A, caracterizando a via
da nevirapina.
5. De acordo com as vias mutacionais de resistência descritas, pode-se
antecipar que resistência cruzada à etravirina ocorrerá mais frequentemente
entre os indivíduos sob falha terapêutica da nevirapina.
6. Usando valores de carga viral plasmática como um marcador substitutivo de
fitness viral, pode-se demonstrar uma tendência de restabelecimento do fitness
após um determinado número de mutações de resistência acumuladas.
7. A susceptibilidade aos inibidores de protease e análogos aos nucleosídeos
parece estar preservada nos virus dos subtipos F e C. Porém, a susceptibilidade
aos inibidores não nucleosídeos da TR merece ser mais bem investigada para
os subtipos C e recombinantes B/F brasileiros.
64
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