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Journal of Virology, January 2001, p. 589-594, Vol. 75, No. 2
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.2.589-594.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Human Immunodeficiency Virus Type 1 Protease
Cleavage Site Mutations Associated with Protease Inhibitor
Cross-Resistance Selected by Indinavir, Ritonavir, and/or
Saquinavir
Hélène C. F.
Côté,
Zabrina L.
Brumme, and
P. Richard
Harrigan*
British Columbia Centre for Excellence in
HIV/AIDS, St. Paul's Hospital, Vancouver, British Columbia, Canada
V6Z 1Y6
Received 18 May 2000/Accepted 11 October 2000
 |
ABSTRACT |
We examined the prevalence of cleavage site mutations, both within
and outside the gag region, in 28 protease inhibitor (PI) cross-resistant patients treated with indinavir, ritonavir, and/or saquinavir compared to control patients treated with reverse
transcriptase inhibitors. Three human immunodeficiency virus protease
cleavage sites within gag (p2/NC, NC/p1, and NC/TFP) showed
considerable in vivo evolution before and after therapy with indinavir,
ritonavir, and/or saquinavir. Another gag cleavage site
(p1/p6gag) showed a trend compared to matched
controls. The other eight recognized cleavage sites showed relatively
little difference between PI-resistant cases and controls. An A
V
substitution at the P2 position of the NC/p1 and NC/TFP cleavage sites
was the most common (29%) change selected by the PIs used in this study.
| |
INTRODUCTION |
The human immunodeficiency virus
(HIV) protease must recognize and cleave up to 12 sites, each with a
different amino acid sequence, in the Gag and Gag-Pol precursor
polypeptides (18) and in Nef (9, 10).
Protease inhibitor (PI)-resistant or cross-resistant isolates (1,
5) with impaired replication or Gag and Gag-Pol processing
(3, 17, 23) can partially compensate by acquiring amino
acid substitutions at gag cleavage sites in HIV culture
(2, 8) and in vivo (17, 24). There is
surprisingly little data (17, 24) published on the
frequency and nature of cleavage site mutations in the clinical HIV
population, particularly for those mutations situated away from the
protease gene. This case control study is an attempt to determine the
prevalence of mutations at all 12 recognized protease cleavage sites
within a population of highly PI cross-resistant HIV-infected patients (n = 28) compared to a matched control group who
received antiretroviral therapy that did not include PIs.
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MATERIALS AND METHODS |
Selection and characteristics of study and control groups.
Clinical isolates (n = 28) with >4-fold increases in
the 50% inhibitory concentration (IC50) for indinavir,
ritonavir, saquinavir, and nelfinavir were identified by Virco
Antivirogram (11). All patients with an available pre-PI
therapy sample which could be amplified by PCR (n = 28)
were included in this study. No patient had experience with PIs other
than saquinavir, ritonavir, or indinavir at the time of this study or
with non-nucleoside reverse transcriptase (RT) inhibitors. Each case
was individually matched with a control patient treated with nucleoside
analogue RT inhibitors (NRTIs), but not PIs or non-nucleosides.
Matching was based upon (i) length of time on therapy, (ii) plasma
viral load prior to PI or NRTI therapy, and (iii) plasma viral load of
the post-therapy sample. For each control, a sample collected prior to
any antiretroviral therapy was also retrieved.
Genotypic analysis of protease cleavage site mutations.
Plasma HIV RNA was amplified by nested reverse transcription-PCR and
analyzed by automated sequence analysis using conditions described
elsewhere (14) with primers chosen to amplify regions surrounding the protease cleavage sites (primer sequences available upon request). For the purpose of this analysis, a "mutation" is
defined as any change in the HIV RNA nucleotide sequence between the
pre- and post-therapy samples resulting in an inferred amino acid substitution.
Statistical analyses.
The frequency of patients developing
at least one HIV mutation resulting in an amino acid change within the
10 codons surrounding the 12 protease cleavage sites was compared by
using the Fisher's exact test adjusted for multiple comparisons (a
significant association was found if P < 0.004). The
association of the AV substitution with protease mutations at
positions 10, 36, 46, 48, 82, 84, and 90 was compared similarly, with
an adjustment for multiple comparison. In this instance, patient 19 (with the valine present at baseline) (see Table 3) was included in the analysis.
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RESULTS |
Patient and viral characteristics.
The PI-resistant and
control groups were very similar for most parameters, except CD4 counts
(Tables 1 and
2). The duration on PI or NRTI regimens
ranged between 3 and 22 months and, within a matched pair, the length
of time on this therapy differed by a maximum of 3 months (Table 2). By
definition, all viruses had >4-fold increased IC50s for
indinavir, ritonavir, saquinavir, and nelfinavir, with a very high
median fold resistance (29-, 33-, 30-, and 41-fold, respectively). In
fact, all but one PI sample showed >10-fold resistance to at least
three of these four PIs.
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TABLE 1.
Characteristics of the highly PI-resistant patients (PI
group) versus the NRTI-treated patients (control group)
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TABLE 2.
Protease inhibitors received, cleavage site mutations,
and number of protease gene mutations appearing during PI therapy
(PI) or NRTI therapy (control)
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Prevalence and patterns of cleavage site mutations.
Mutations
at protease cleavage sites were selected far more often during PI
therapy than during NRTI therapy (Fig.
1). Following therapy, 93% (26 of 28) of
the patients in the PI group harbored HIV with a mutation(s) at one or
more cleavage sites compared to 61% of the patients from the control
group (Table 2). The majority of patients (61% [17 of 28]) on PI
therapy exhibited mutations at 
2 cleavage sites (including 11 instances where two or more amino acids were substituted within a given
cleavage site) versus only 14% in the control group. Mutations at up
to six different cleavage sites could be selected together after as
little as 3 months of PI therapy (Table 2).
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FIG. 1.
Frequency of amino acid substitution at all the
potential protease cleavage sites within HIV-1 during PI therapy
(above) versus NRTI therapy (below).
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In the PI group, mutations were observed in both HIV reading frames at
all potential cleavage sites (Fig.
1 and
2). For the
control group, mutations
occurred at TFP/p6
pol, NEF, p2/NC, NC/TFP,
p6
pol/protease, and protease/RT, with no
substitutions observed at
other sites. A total of 52, 32, or 39% of PI
cases had mutations
at the p2/NC, NC/p1, or NC/TFP sites, versus 14, 0, or 11%, respectively,
in the controls (
P < 0.004).
Mutations at a fourth site, p1/p6
gag, were
present in 6 of 28 of the PI-treated group versus 0 of
28 in the
control group, though this was not statistically significant
after an
adjustment was made for multiple comparisons (
P = 0.01).
Mutations at other cleavage sites were either relatively
uncommon
or observed at nearly equal frequencies in controls (Fig.
1
and
3).
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FIG. 2.
Amino acid substitutions observed during therapy. The
identity and the number of times each substitution occurred is
indicated above the HIV-1 HXB2 "consensus" cleavage site sequence
for the PI group (n = 28) and below the sequence for
the control group (n = 28).
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FIG. 3.
Polymorphism observed in both groups. The identity and
the number of patients harboring HIV-1 with each polymorphism is
indicated above the HIV-1 HXB2 "consensus" cleavage site sequence
for the PI group (n = 28) and below the sequence for
the control group (n = 28).
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The substitution QAN/F
QVN/F at the P2 position of the NC/p1 and
NC/TFP sites was the single most common and specific adaptation
observed, occurring in 8 of 28 (29%) of PI-resistant cases but
in none
of the control group. Surprisingly, the L
F substitution
at position
P1' of the p1/p6
gag cleavage site (
8,
17,
24) was not detected in this study,
although proline, valine,
and isoleucine were all observed at
that position (Fig.
3).
Prevalence and patterns of cleavage site polymorphisms.
In
this report, we define a "polymorphism" as an amino acid that
differed from the HXB2 sequence at baseline and did not change during
the course of treatment (Fig. 3). Several were common: a VI change
at position P3' of the p6pol/PR cleavage site,
an RK change at position P3' of the p2/NC cleavage site, and an
LP change at position P1' of the TFP/p6pol
site, as well as a DN change at position P4 (which is also the P5'
position of NC/TFP), an NS change at position P2' of the p6pol/PR site, and an AD change at position
P4 of the NEF cleavage site. Two positions within the transframe (TFP)
region of Gag-Pol (16) were highly polymorphic: the
aspartate shared between the NC/TFP and the
TFP/p6pol sites and the lysine in position P4'
of the TFP/p6pol site (Fig. 3). In addition, the
results showed that several positions were consistently occupied by an
amino acid different from that found in HXB2.
Prevalence of protease mutations.
Consistent with their
phenotypes, genotypic analysis indicated that the highly PI-resistant
isolates had far more "primary" and "secondary" protease
mutations (as defined in reference 12) than the
control group (43 versus 0 and 110 versus 35, respectively [data not
shown]). The number of protease mutations remained relatively stable
during treatment within the control group but increased significantly
under PI therapy, a result consistent with the large body of literature
on PI resistance development (for a review, see reference
12). Two individuals (one in each group) had virus with an M46I change at baseline, and one from the PI group had a V82T
mutation at the onset. The M46I mutation from the control group
reverted to M46 during the study.
Relationship between protease and cleavage site mutations.
There was no obvious relationship between the number of protease
mutations and the number of cleavage site changes observed during PI
therapy (data not shown), nor was there an obvious relationship between
specific cleavage site mutations and the degree of PI resistance or the
duration of PI therapy (data not shown). However, the AV
substitution in NC/p1 was associated with the M46I or L substitution in
the protease (P < 0.007) (Table
3). In fact, the only patient with HIV
harboring a valine residue at that position prior to PI therapy was
also the only one to show a M46I mutation before therapy. V82A/T
mutations were present in six of nine patients with AV-substituted
HIV (including two of the three that did not have a mutation at M46)
but were also found in six of the other patients of the PI group
(P = 0.243).
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TABLE 3.
Protease genotypes before and after PI therapy from the
nine patients with virus harboring the AV substitution within
the NC/p1 cleavage site
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DISCUSSION |
The data presented are consistent with previous observations that
mutations in the HIV protease and at Gag protease cleavage sites are
specifically selected during PI therapy. The inclusion in this study of
a control group of patients who did not receive any PI therapy enabled
the assessment of the contribution of PI exposure (and resistance) to
the selection of cleavage site mutations versus nonspecific changes.
The Gag p2/NC and NC/p1 and the Gag-Pol NC/TFP cleavage sites were the
only protease cleavage sites for which a statistically significant
association between the mutations and the development of high-level PI
cross-resistance could be demonstrated in this study. Changes at sites
outside Gag were either rare or not significantly more common in those
patients who had received PI therapy than in those who did not.
The sites observed to mutate most frequently flanked the
nucleocapsid protein (NC). The NC/p1 and NC/TFP are cleaved most slowly
within the Gag and Gag-Pol precursors (7, 15, 16, 18, 22).
This likely represents a rate-limiting step in the processing of NC, a
protein required for the formation of mature infectious particles.
These sites may therefore evolve relatively quickly under small
selective pressures. Interestingly, the amino acids in
positions P1 and P1' of these two sites also differ considerably from
the more common pattern of an aromatic amino acid opposite a leucine or
a proline.
One implication of these results is that the specificity of the HIV
protease is not greatly altered despite the development of high-level
PI cross-resistance or that the amino and carboxyl termini of
structural proteins can more easily tolerate amino acid substitutions
than can the enzymatic proteins. Indeed, 
1% of all protease
sequences in an HIV database including both PI-naive and -experienced
viruses (19) show a difference from the most common
residue at amino acids 1 to 5 and amino acids 95 to 99 of protease,
residues involved in the dimerization of the enzyme (21).
Similarly, the amino termini of the RT, RNase H, and integrase are also highly conserved among different HIV clades and isolates (13). Although cleaved Nef is found in virus
particles (20), the proteolysis of Nef does not seem to
influence the infectivity of HIV in culture (4). It is
unlikely that the few changes observed in the NEF site in this study
play a specific role in the development of PI resistance.
To evaluate the relevance of cleavage site mutations,
consideration should be given to naturally occurring
polymorphisms. Indeed, these clinical isolates showed baseline
protease cleavage site sequences that sometimes differed considerably
from the "consensus sequences" after which HIV protease
peptide substrates are often designed. Some of the most frequently
mutated positions under PI therapy also happen to be more polymorphic
(e.g., positions P2 to P5 and P3' of the p2/NC cleavage site or
position P3 of the p66/INT site). Polymorphisms and mutations in the
p6pol/protease site were strikingly confined to
the P side of the site, and several different amino acids could be
accommodated in the P2 position, which is normally quite restrictive
(18). There was no evidence of PI-selected evolution
within the transframe peptide, though almost half of the patients
harbored a polymorphism within the E-D-L tripeptide sequence postulated
to influence protease activity (15).
The mutation with the highest prevalence in the PI-treated group
encoded the AV substitution shared by the NC/p1 and NC/TFP cleavage
sites within Gag and Gag-Pol. This mutation has been observed before in
HIV culture (2, 6, 8) and clinical (17, 24)
isolates, correcting defects in NC processing by the mutant protease
(17) and producing a better substrate for mutant protease
(8). Previously, a large genotypic study of PI- resistant
HIV-1 found that 16% (55 of 300) of the samples harbored this
mutation, in close association with the protease V82 mutations, and
that the level of phenotypic resistance was not influenced by the
presence or absence of this mutation in recombinant viruses (B. A. Larder, S. Bloor, K. Hertogs, C. Van den Eynde, and R. Pauwels, Abstr.
2nd Int. Workshop on HIV Drug Resist. Treatment Strategies, abstr. 23, 1998). Although much smaller, this study also found this mutation to be
the most common and specific to PI therapy, developing in 32% (9 of
28) of the PI cases, usually associated with the M46I/L protease
genotype. In contrast to observations made in vitro with another PI,
ABT-378 (2), we did not observe the AV substitution in
conjunction with another at the p1/p6gag site or
with the I47V-to-A protease genotype.
Isolates in this study are likely more drug resistant than those in
most other studies, as we selected the most phenotypically PI-resistant
isolates available to us. It should also be noted that these results
were obtained only from patients taking indinavir, saquinavir, and/or
ritonavir and that results from individuals receiving other, newer PIs
could differ. The specific limitations of this study include the fact
that only 28 cases and controls could be examined, in part due to the
large number of sequencing reactions required to examine all of the
sites before and after therapy and to the absence of pretherapy samples
in many cases. It is therefore possible that some mutations failed to
achieve statistical significance here, even though their effects were biologically significant. Finally, mutant protease could potentially use new cleavage sites altogether (3), which would not be
detected here.
| |
ACKNOWLEDGMENTS |
We thank Kurt Hertogs and Brendan Larder (Virco) for performing
the phenotypic analyses; Mark Whaley, Winnie Dong, and Keith Chan (B.C.
Centre for Excellence in HIV/AIDS) for assistance with plasma HIV RNA
extractions and data analysis; and Michael Murphy (Department of
Microbiology and Immunology, University of British Columbia) for help
with the protease structural examinations.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: B.C. Centre for
Excellence in HIV/AIDS, St. Paul's Hospital, 613-1081 Burrard St., Vancouver, BC V6Z 1Y6, Canada. Phone: (604) 806-8281. Fax: (604) 806-8464. E-mail: lab{at}hivnet.ubc.ca.
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REFERENCES |
| 1.
|
Boden, D., and M. Markowitz.
1998.
Resistance to human immunodeficiency virus type 1 protease inhibitors.
Antimicrob. Agents Chemother.
42:2775-2783[Free Full Text].
|
| 2.
|
Carrillo, A.,
K. D. Stewart,
H. L. Sham,
D. W. Norbeck,
W. E. Kohlbrenner,
J. M. Leonard,
D. J. Kempf, and A. Molla.
1998.
In vitro selection and characterization of human immunodeficiency virus type 1 variants with increased resistance to ABT-378, a novel protease inhibitor.
J. Virol.
72:7532-7541[Abstract/Free Full Text].
|
| 3.
|
Carron de la Carrière, L. C.,
S. Paulous,
F. Clavel, and F. Mammano.
1999.
Effects of human immunodeficiency virus type 1 resistance to protease inhibitors on reverse transcriptase processing, activity, and drug sensitivity.
J. Virol.
73:3455-3459[Abstract/Free Full Text].
|
| 4.
|
Chen, Y.-L.,
D. Trono, and D. Camur.
1998.
The proteolytic cleavage of human immunodeficiency virus type 1 Nef does not correlate with its ability to stimulate virion infectivity.
J. Virol.
72:3178-3184[Abstract/Free Full Text].
|
| 5.
|
Condra, J. H.,
W. A. Schleif,
O. M. Blahy,
L. J. Gabryelski,
D. J. Graham,
J. C. Quintero,
A. Rhodes,
H. L. Robbins,
A. Rothy,
M. Shivaprakash,
D. Titus,
T. Yang,
H. Teppler,
K. E. Squires,
P. J. Deutsch, and E. A. Emini.
1995.
In vivo emergence of HIV-1 variants resistant to multiple protease inhibitors.
Nature
374:569-571[CrossRef][Medline].
|
| 6.
|
Croteau, G.,
L. Doyon,
D. Thibeault,
G. McKercher,
L. Pilote, and D. Lamarre.
1997.
Impaired fitness of human immunodeficiency virus type 1 variants with high-level resistance to protease inhibitors.
J. Virol.
71:1089-1096[Abstract].
|
| 7.
|
Darke, P. L.,
R. F. Nutt,
S. F. Brady,
V. M. Garsky,
T. M. Ciccarone,
C. H. Leu,
P. K. Lumma,
R. M. Freidinger,
D. F. Veber, and I. S. Sigal.
1988.
HIV-1 protease specificity of peptide cleavage is sufficient for processing of Gag and Pol polyproteins.
Biochem. Biophys. Res. Commun.
156:297-303[CrossRef][Medline].
|
| 8.
|
Doyon, L.,
G. Croteau,
D. Thibeault,
F. Poulin,
L. Pilote, and D. Lamarre.
1996.
Second locus involved in human immunodeficiency virus type 1 resistance to protease inhibitors.
J. Virol.
70:3763-3769[Abstract].
|
| 9.
|
Freund, J.,
R. Kellner,
J. Konvalinka,
V. Wolber,
H.-G. Kräusslich, and H. R. Kalbitzer.
1994.
A possible regulation of negative factor (Nef) activity of human immunodeficiency virus type 1 by the viral protease.
Eur. J. Biochem.
223:589-593[Medline].
|
| 10.
|
Gaedigk-Nitschko, K.,
A. Schön,
G. Wachinger,
V. Erfle, and B. Kohleisen.
1995.
Cleavage of recombinant and cell derived human immunodeficiency virus 1 (HIV-1) Nef protein by HIV-1 protease.
FEBS Lett.
357:275-278[CrossRef][Medline].
|
| 11.
|
Hertogs, K.,
M.-P. de Béthune,
V. Miller,
T. Ivens,
P. Schel,
A. Van Cauwenberge,
C. Van Den Eynde,
V. Van Gerwen,
H. Azijn,
M. Van Houtte,
F. Peeters,
S. Staszewski,
M. Conant,
S. Bloor,
S. Kemp,
B. Larder, and R. Pauwels.
1998.
A rapid method for simultaneous detection of phenotypic resistance to inhibitors of protease and reverse transcriptase in recombinant human immunodeficiency virus type 1 isolates from patients treated with antiretroviral drugs.
Antimicrob. Agents Chemother.
42:269-276[Abstract/Free Full Text].
|
| 12.
|
Hirsch, M. S.,
B. Conway,
R. T. D'Aquila,
V. A. Johnson,
F. Brun-Vezinet,
B. Clotet,
L. M. Demeter,
S. M. Hammer,
D. M. Jacobsen,
D. R. Kuritzkes,
C. Loveday,
J. W. Mellors,
S. Vella, and D. D. Richman.
1998.
Antiretroviral drug resistance testing in adults with HIV infection: implications for clinical management. International AIDS Society USA Panel.
JAMA
279:1984-1991[Abstract/Free Full Text].
|
| 13.
| Kuiken, C. L., B. Foley, B. Hahn, B. Korber, F. McCutchan, P. A. Marx, J. W. Mellors, J. I. Mullins, J. Sodroski, and S. Wolinksy (ed.). Human retroviruses and AIDS 1999:
a compilation and analysis of nucleic acid and amino acid sequences.
Theoretical Biology and Biophysics Group, Los Alamos National
LaboratoryLos Alamos, N.Mex.
|
| 14.
|
Larder, B. A.,
S. Kemp, and P. R. Harrigan.
1995.
Potential mechanism for sustained antiretroviral efficacy of AZT-3TC combination therapy.
Science
269:696-699[Abstract/Free Full Text].
|
| 15.
|
Louis, J. M.,
F. Dyda,
N. T. Nashed,
A. R. Kimmel, and D. R. Davies.
1998.
Hydrophilic peptides derived from the transframe region of Gag-Pol inhibit the HIV-1 protease.
Biochemistry
37:2105-2110[CrossRef][Medline].
|
| 16.
|
Louis, J. M.,
E. M. Wondrak,
A. R. Kimmel,
P. T. Wingfield, and N. T. Nashed.
1999.
Proteolytic processing of HIV-1 protease precursor, kinetics and mechanism.
J. Biol. Chem.
274:23437-23442[Abstract/Free Full Text].
|
| 17.
|
Mammano, F.,
C. Petit, and F. Clavel.
1998.
Resistance-associated loss of viral fitness in human immunodeficiency virus type 1: phenotypic analysis of protease and gag coevolution in protease inhibitor-treated patients.
J. Virol.
72:7632-7637[Abstract/Free Full Text].
|
| 18.
|
Pettit, S. C.,
S. F. Michael, and R. Swanstrom.
1993.
The specificity of the HIV-1 protease.
Perspect. Drug Discov. Des.
1:69-83[CrossRef].
|
| 19.
|
Shafer, R. W.,
D. Stevenson, and B. Chan.
1999.
Human immunodeficiency virus reverse transcriptase and protease sequence database.
Nucleic Acids Res.
27:348-352[Abstract/Free Full Text].
|
| 20.
|
Welker, R.,
H. Kottler,
H. R. Kalbitzer, and H. G. Krausslich.
1996.
Human immunodeficiency virus type 1 Nef protein is incorporated into virus particles and specifically cleaved by the viral proteinase.
Virology
219:228-236[CrossRef][Medline].
|
| 21.
|
Wlodawer, A.,
M. Miller,
M. Jaskólski,
B. K. Sathyanarayana,
E. Baldwin,
I. T. Weber,
L. M. Selk,
L. Clawson,
J. Schneider, and S. B. H. Kent.
1989.
Conserved folding in retroviral proteases: crystal structure of a synthetic HIV-1 protease.
Science
245:616-621[Abstract/Free Full Text].
|
| 22.
|
Wondrak, E. M.,
J. M. Louis,
H. de Rocquigny,
J. C. Chermann, and B. P. Roques.
1993.
The Gag precursor contains a specific HIV-1 protease cleavage site between the NC (p7) and p1 proteins.
FEBS Lett.
333:21-24[CrossRef][Medline].
|
| 23.
|
Zennou, V.,
F. Mammano,
S. Paulous,
D. Mathez, and F. Clavel.
1998.
Loss of viral fitness associated with multiple Gag and Gag-Pol processing defects in human immunodeficiency virus type 1 variants selected for resistance to protease inhibitors in vivo.
J. Virol.
72:3300-3306[Abstract/Free Full Text].
|
| 24.
|
Zhang, Y. M.,
H. Imamichi,
T. Imamichi,
H. C. Lane,
J. Falloon,
M. B. Vasudevachari, and N. P. Salzman.
1997.
Drug resistance during indinavir therapy is caused by mutations in the protease gene and in its Gag substrate cleavage sites.
J. Virol.
71:6662-6670[Abstract].
|
Journal of Virology, January 2001, p. 589-594, Vol. 75, No. 2
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.2.589-594.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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[Full Text]
-
van der Hoek, L., Back, N., Jebbink, M. F., de Ronde, A., Bakker, M., Jurriaans, S., Reiss, P., Parkin, N., Berkhout, B.
(2005). Increased Multinucleoside Drug Resistance and Decreased Replicative Capacity of a Human Immunodeficiency Virus Type 1 Variant with an 8-Amino-Acid Insert in the Reverse Transcriptase. J. Virol.
79: 3536-3543
[Abstract]
[Full Text]
-
Johnston, E., Winters, M. A., Rhee, S.-Y., Merigan, T. C., Schiffer, C. A., Shafer, R. W.
(2004). Association of a Novel Human Immunodeficiency Virus Type 1 Protease Substrate Cleft Mutation, L23I, with Protease Inhibitor Therapy and In Vitro Drug Resistance. Antimicrob. Agents Chemother.
48: 4864-4868
[Abstract]
[Full Text]
-
Prabu-Jeyabalan, M., Nalivaika, E. A., King, N. M., Schiffer, C. A.
(2004). Structural Basis for Coevolution of a Human Immunodeficiency Virus Type 1 Nucleocapsid-p1 Cleavage Site with a V82A Drug-Resistant Mutation in Viral Protease. J. Virol.
78: 12446-12454
[Abstract]
[Full Text]
-
Tamiya, S., Mardy, S., Kavlick, M. F., Yoshimura, K., Mistuya, H.
(2004). Amino Acid Insertions near Gag Cleavage Sites Restore the Otherwise Compromised Replication of Human Immunodeficiency Virus Type 1 Variants Resistant to Protease Inhibitors. J. Virol.
78: 12030-12040
[Abstract]
[Full Text]
-
Gonzalez, L. M. F., Brindeiro, R. M., Aguiar, R. S., Pereira, H. S., Abreu, C. M., Soares, M. A., Tanuri, A.
(2004). Impact of Nelfinavir Resistance Mutations on In Vitro Phenotype, Fitness, and Replication Capacity of Human Immunodeficiency Virus Type 1 with Subtype B and C Proteases. Antimicrob. Agents Chemother.
48: 3552-3555
[Abstract]
[Full Text]
-
Gonzalez, R., Masquelier, B., Fleury, H., Lacroix, B., Troesch, A., Vernet, G., Telles, J. N.
(2004). Detection of Human Immunodeficiency Virus Type 1 Antiretroviral Resistance Mutations by High-Density DNA Probe Arrays. J. Clin. Microbiol.
42: 2907-2912
[Abstract]
[Full Text]
-
Charpentier, C., Dwyer, D. E., Mammano, F., Lecossier, D., Clavel, F., Hance, A. J.
(2004). Role of Minority Populations of Human Immunodeficiency Virus Type 1 in the Evolution of Viral Resistance to Protease Inhibitors. J. Virol.
78: 4234-4247
[Abstract]
[Full Text]
-
Myint, L., Matsuda, M., Matsuda, Z., Yokomaku, Y., Chiba, T., Okano, A., Yamada, K., Sugiura, W.
(2004). Gag Non-Cleavage Site Mutations Contribute to Full Recovery of Viral Fitness in Protease Inhibitor-Resistant Human Immunodeficiency Virus Type 1. Antimicrob. Agents Chemother.
48: 444-452
[Abstract]
[Full Text]
-
Goodenow, M. M., Rose, S. L., Tuttle, D. L., Sleasman, J. W.
(2003). HIV-1 fitness and macrophages. J. Leukoc. Biol.
74: 657-666
[Abstract]
[Full Text]
-
de Oliveira, T., Engelbrecht, S., Janse van Rensburg, E., Gordon, M., Bishop, K., zur Megede, J., Barnett, S. W., Cassol, S.
(2003). Variability at Human Immunodeficiency Virus Type 1 Subtype C Protease Cleavage Sites: an Indication of Viral Fitness?. J. Virol.
77: 9422-9430
[Abstract]
[Full Text]
-
Simon, V., Padte, N., Murray, D., Vanderhoeven, J., Wrin, T., Parkin, N., Di Mascio, M., Markowitz, M.
(2003). Infectivity and Replication Capacity of Drug-Resistant Human Immunodeficiency Virus Type 1 Variants Isolated during Primary Infection. J. Virol.
77: 7736-7745
[Abstract]
[Full Text]
-
Karlsson, A. C., Deeks, S. G., Barbour, J. D., Heiken, B. D., Younger, S. R., Hoh, R., Lane, M., Sallberg, M., Ortiz, G. M., Demarest, J. F., Liegler, T., Grant, R. M., Martin, J. N., Nixon, D. F.
(2003). Dual Pressure from Antiretroviral Therapy and Cell-Mediated Immune Response on the Human Immunodeficiency Virus Type 1 Protease Gene. J. Virol.
77: 6743-6752
[Abstract]
[Full Text]
-
Gordon, M., De Oliveira, T., Bishop, K., Coovadia, H. M., Madurai, L., Engelbrecht, S., Janse van Rensburg, E., Mosam, A., Smith, A., Cassol, S.
(2003). Molecular Characteristics of Human Immunodeficiency Virus Type 1 Subtype C Viruses from KwaZulu-Natal, South Africa: Implications for Vaccine and Antiretroviral Control Strategies. J. Virol.
77: 2587-2599
[Abstract]
[Full Text]
-
Watkins, T., Resch, W., Irlbeck, D., Swanstrom, R.
(2003). Selection of High-Level Resistance to Human Immunodeficiency Virus Type 1 Protease Inhibitors. Antimicrob. Agents Chemother.
47: 759-769
[Abstract]
[Full Text]
-
Matsuoka-Aizawa, S., Sato, H., Hachiya, A., Tsuchiya, K., Takebe, Y., Gatanaga, H., Kimura, S., Oka, S.
(2002). Isolation and Molecular Characterization of a Nelfinavir (NFV)-Resistant Human Immunodeficiency Virus Type 1 That Exhibits NFV-Dependent Enhancement of Replication. J. Virol.
77: 318-327
[Abstract]
[Full Text]
-
Resch, W., Ziermann, R., Parkin, N., Gamarnik, A., Swanstrom, R.
(2002). Nelfinavir-Resistant, Amprenavir-Hypersusceptible Strains of Human Immunodeficiency Virus Type 1 Carrying an N88S Mutation in Protease Have Reduced Infectivity, Reduced Replication Capacity, and Reduced Fitness and Process the Gag Polyprotein Precursor Aberrantly. J. Virol.
76: 8659-8666
[Abstract]
[Full Text]
-
Maguire, M. F., Guinea, R., Griffin, P., Macmanus, S., Elston, R. C., Wolfram, J., Richards, N., Hanlon, M. H., Porter, D. J. T., Wrin, T., Parkin, N., Tisdale, M., Furfine, E., Petropoulos, C., Snowden, B. W., Kleim, J.-P.
(2002). Changes in Human Immunodeficiency Virus Type 1 Gag at Positions L449 and P453 Are Linked to I50V Protease Mutants In Vivo and Cause Reduction of Sensitivity to Amprenavir and Improved Viral Fitness In Vitro. J. Virol.
76: 7398-7406
[Abstract]
[Full Text]
-
Shafer, R. W.
(2002). Genotypic Testing for Human Immunodeficiency Virus Type 1 Drug Resistance. Clin. Microbiol. Rev.
15: 247-277
[Abstract]
[Full Text]
-
Yusa, K., Song, W., Bartelmann, M., Harada, S.
(2002). Construction of a Human Immunodeficiency Virus Type 1 (HIV-1) Library Containing Random Combinations of Amino Acid Substitutions in the HIV-1 Protease due to Resistance by Protease Inhibitors. J. Virol.
76: 3031-3037
[Abstract]
[Full Text]
-
Dauber, D. S., Ziermann, R., Parkin, N., Maly, D. J., Mahrus, S., Harris, J. L., Ellman, J. A., Petropoulos, C., Craik, C. S.
(2002). Altered Substrate Specificity of Drug-Resistant Human Immunodeficiency Virus Type 1 Protease. J. Virol.
76: 1359-1368
[Abstract]
[Full Text]
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Abstract
Introduction
