Journal of Virology, February 1999, p. 1719-1723, Vol. 73, No. 2
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
T134, a Small-Molecule CXCR4 Inhibitor, Has No
Cross-Drug Resistance with AMD3100, a CXCR4 Antagonist with a
Different Structure
Rieko
Arakaki,1
Hirokazu
Tamamura,2
Mariappan
Premanathan,1
Kenji
Kanbara,1
Sivasundaram
Ramanan,1
Katsura
Mochizuki,3
Masanori
Baba,4
Nobutaka
Fujii,2 and
Hideki
Nakashima1,*
Department of Microbiology and Immunology,
Kagoshima University Dental School, 8-35-1 Sakuragaoka, Kagoshima
890-8544,1
Graduate School of
Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto
606-8501,2
Department of Chemistry,
Faculty of Science and Graduate School of Integrated Science, Yokohama
City University, Seto 22-2, Kanazawa-ku, Yokohama
236-0027,3 and
Center for Chronic Viral
Diseases, Faculty of Medicine, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8520,4 Japan
Received 10 August 1998/Accepted 15 October 1998
 |
ABSTRACT |
T22, an analog of polyphemusin II (18 amino acid residues), was
found to block T-tropic human immunodeficiency virus type 1 (HIV-1)
entry into target cells as a CXCR4 inhibitor. We synthesized T134, a
small analog (14 amino acid residues) of T22 with reduced positive
charges. T134 exhibited highly potent activity and significantly less
cytotoxicity in comparison to that of T22. T134 prevents the anti-CXCR4
monoclonal antibody from binding to peripheral blood mononuclear cells
but has no effect on the binding of anti-CCR5 monoclonal antibodies.
Since T134 inhibits the binding of stromal cell-derived factor-1
(SDF-1) to MT-4 cells, it seems that T134 prevents HIV-1 entry by
binding to CXCR4. The bicyclam AMD3100 has also been shown to block
HIV-1 entry via CXCR4 but not via CCR5. Both T134 and AMD3100 are CXCR4
antagonists and low-molecular-weight compounds but have different
structures. Our results indicate that T134 is active against wild-type
T-tropic HIV-1 strains and against AMD3100-resistant strains.
 |
TEXT |
For anti-human immunodeficiency
virus (anti-HIV) chemotherapy, the virus-cell fusion process is an
attractive target. If specific drugs can inhibit the stage of
virus-cell fusion, HIV type 1 (HIV-1) proviral DNA cannot be integrated
into the cell genome, which prevents the spread of infection. For entry
into target cells, HIV-1 requires a primary receptor, CD4, and
coreceptors such as chemokine receptors. CXC chemokine receptor 4 (CXCR4) is a coreceptor for the entry of T-cell-line-tropic (T-tropic)
strains of HIV-1 (15), and the CC chemokine receptor 5 (CCR5) serves as a coreceptor for macrophage tropic (M-tropic) strains
of HIV-1 (1, 6, 11, 14). Therefore, compounds which interact
with the chemokine receptors may be the ultimate hope for anti-HIV
drugs. The ligands identified for these receptors, stromal cell-derived
factor-1 (SDF-1) for CXCR4 (3, 22) and RANTES, macrophage
inflammatory protein-1
(MIP-1
), and MIP-1
for CCR5
(7), were shown to be potent competitive inhibitors of HIV-1
entry into cells expressing the appropriate coreceptor.
We previously found that a synthetic peptide of T22
([Tyr5,12, Lys7]-polyphemusin II), which
consists of 18 amino acid residues and is an analog of polyphemusin II
isolated from the hemocyte debris of American horseshoe crabs
(Limulus polyphemus), showed strong anti-HIV activity in
vitro (21, 28, 31). Recently, it was also found that T22
blocked T-tropic HIV-1 entry into target cells via CXCR4, not via CCR5
(19). In a series of investigations in the search for more
active anti-HIV derivatives, we synthesized two smaller analogs, TW70
(des-[Cys8,13,
Tyr9,12]-[D-Lys10,
Pro11]-T22) and T134
(L-citrulline16-TW70 substituted for
the C-terminal amide by a carboxylic acid), which have 14 amino acid
residues and reduced basic amino acid residues less than T22
(27). TW70 and T134 showed more pronounced anti-HIV-1
activity than T22.
The bicyclam AMD3100 {octahydrochloride dihydrate of
1,1' - [1,4 - phenylene - bis - (methylene)] - bis - 1,4,8,11 - tetra - azacyclotetradecane
with a molecular weight of 830} has also been shown to block HIV-1
entry and membrane fusion via CXCR4 but not via CCR5 (13,
26). The structure of AMD3100 is different from that of T134
(10, 27), but both compounds function via CXCR4 to block
HIV-1 entry into target cells. This investigation shows that T134 is a
CXCR4 antagonist and attempts to clarify the cross-resistance observed
between T134 and AMD3100, by using AMD3100-resistant HIV-1 prepared
previously from a clinical HIV-1 isolate (2).
We first studied the anti-HIV-1 activity of T22 and its derivatives,
TW70 and T134. Table 1 summarizes the
amino acid sequence of each test compound and their anti-HIV activities
and cytotoxicities in MT-4 cells by the MTT
[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide]
method (21, 23). We have already investigated the structure-activity relationship of more than 140 analogs of T22 (27, 30). These investigations showed that the analogs that were small in size and contained reduced basic amino acids exhibited highly potent activity and low cytotoxicity. Table 1 shows that T134
exhibited much higher potency and lower cytotoxicity than T22 and TW70,
and therefore it was more suitable for further analysis in the
investigation of the mechanism of these types of compounds.
The possibility that T134 inhibits T-tropic HIV-1 but not M-tropic
HIV-1 infection as exhibited by T22 was investigated with the
multinuclear activation of the galactosidase indicator (MAGI) assay in
MAGI-CCR5 cells (17). Table 2
demonstrates that T134 and its derivatives inhibited only T-tropic
HIV-1 strains such as HIV-1IIIB and not the M-tropic HIV-1
strains such as HIV-1JR-FL. This data suggests that T134
and other derivatives of T22 inhibit the T-tropic HIV-1 infection
mediated by CXCR4 but not the M-tropic HIV-1 infection mediated by
CCR5.
We used anti-CXCR4 and -CCR5 monoclonal antibodies (MAbs) to examine
whether T134 interacted with these chemokine receptors. Preincubation
of peripheral blood mononuclear cells (PBMC) with T134 caused binding
inhibition of 12G5 (R & D Systems Inc., Minneapolis, Minn.). This
binding inhibition was also observed for our synthesized SDF-1[1-67]
(29) and AMD3100 (4). As shown in Fig.
1, T134, AMD3100, and SDF-1 inhibited the
binding activity of 12G5 to PBMC; however, none of these compounds
affected the binding of anti-CCR5 MAb (2D7; NIH AIDS Research and
Reference Reagent Program) to PBMC and only MIP-1
inhibited the
binding of 2D7 to PBMC. T134 and AMD3100 had no effect on the binding
of anti-CD4 MAbs to PBMC. These findings show that T134 interacts
specifically with CXCR4 to prevent both 12G5 binding and coreceptor
activity. The specific interaction of T134 with CXCR4 was also
confirmed in other human T-cell lines such as MT-4 (data not shown). To
investigate the interaction of T134 with the binding of CXCR4 and
its ligand SDF-1
, a binding inhibition experiment was
performed. Figure 2 demonstrates that
T134 inhibits the binding of 125I-labeled SDF-1
(0.02 nM; DuPont-NEN, Boston, Mass.) to MT-4 cells and complete
inhibition was observed at a concentration of 0.8 nM; AMD3100
inhibition of SDF-1
binding was observed at the same concentration.
These results reveal that T134 directly blocks the interaction of
virus, anti-CXCR4 MAb, or SDF-1 with CXCR4. Our results suggest that
the structure of T134 mimics the region of SDF that is involved in
binding to CXCR4. In fact, the CXC chemokines have a core structure
consisting of three antiparallel
-sheets (16) and T134 is
also comprised of an antiparallel
-sheet structure similar to that
of T22 and TW70 (27). Our results were also supported by
Murakami and colleagues, who demonstrated that cellular signal
transduction induced by SDF-1 binding to CXCR4, detected by using
Ca2+ mobilization, was inhibited by T22 (19).
Several variants isolated from patients with one class of protease
inhibitor exhibited cross-resistance to other structurally diverse
protease inhibitors (8, 9, 24). This type of
cross-resistance is frequently observed in non-nucleoside reverse
transcriptase inhibitors (5, 18), and it creates a
disadvantage for clinical use of the same class antiviral drugs in
combination therapy. AMD3100 was found to function in the same manner
as T134. However, the chemical structures of these compounds were
extremely different (10, 27). Therefore, we were interested
in investigating whether cross-resistance like that found with protease
inhibitors or non-nucleoside reverse transcriptase inhibitors would
occur in these two anti-HIV-1 compounds. AMD3100-resistant HIV-1 was
generated from a clinical HIV-1 isolate (A018A) after several passages
of the virus in cell culture in the presence of AMD3100 (2).
The anti-HIV-1 activity of AMD3100 was assessed by using the MAGI-CCR5
assay for wild-type clinically isolated HIV-1 and AMD3100-resistant
HIV-1 strains. Table 3 demonstrates that
the concentration of AMD3100 required to achieve 50% antiviral
activity in AMD3100-resistant strains was 20- to 27-fold higher than
that needed for the wild type (strain A018A). However, approximately
equal concentrations of T134 were needed to achieve 50% effective
concentrations (EC50s) in both the wild-type and
AMD3100-resistant strains. This suggests that both T134 and AMD3100
inhibit HIV-1 infection via CXCR4, but these two compounds have no
cross-resistance to each other. Cross-resistance was also not exhibited
when zidovudine, 1-ethoxymethyl-5-ethyl-6-(phenylthio)-uracil (E-EPU), or dextran sulfate was tested against AMD3100-resistant strains (data not shown).
We had also intended to prepare HIV-1 strains resistant to T22 or T134
by the cell culture methods used to generate AMD3100-resistant HIV-1.
However, we were unable to prepare T134-resistant strains for more than
25 passages. T22 and T134 may not induce resistant viruses easily. De
Clercq and colleagues reported that a mutant of HIV-1NL4-3
with decreased sensitivity to AMD3100 has multiple amino acid
substitutions in env glycoprotein 120 (gp120), most of them
within, or in proximity to, the V3 loop (12). But they also
reported that it was difficult to obtain a completely resistant AMD3100
virus (12, 25). This information may show the potential of
these CXCR4 antagonists as therapeutic drugs. It was reported that
SDF-1
-resistant HIV-1NL4-3, which was more easily
prepared than AMD3100-resistant HIV-1NL4-3, had been
produced. Of the nine mutations detected in gp120 of the
SDF-1
-resistant virus, four were located in the V3 domain and all
four were also detected in the AMD3100-resistant virus (25).
The SDF-1
-resistant virus became resistant to SDF-1
and to
anti-CXCR4 MAbs. However, AMD3100 was still active against the
SDF-1
-resistant virus. Although HIV-1NL4-3 with complete
resistance to AMD3100 was not obtained, it was shown that a larger
number of mutations were present in the gp120 of the AMD3100-resistant
virus than in the gp120 of SDF-1
-resistant virus. AMD3100 and T134
may not induce resistant virus easily in comparison with SDF-1
.
These results may show that these compounds have a much stronger
interaction with CXCR4 than the natural ligand SDF-1 itself, a finding
which is also reflected by the fact that T134 and AMD3100 compete with
SDF-1 at much lower concentrations (under 1 pM) than that for
125I-SDF-1
(20 pM). Since T134 and AMD3100 are much
smaller in size than SDF-1, these compounds may be able to interact
with CXCR4 at a higher affinity than SDF-1. It was reported that
knocking out the SDF-1 gene in mice creates a lethal phenotype. Thus,
SDF-1 might be a necessary chemokine for prenatal viability, B
lymphopoiesis, bone marrow myelopoiesis, and cardiac ventricular septal
formation (20). However, the biological importance of CXCR4
for T lymphocyte function and whether blocking of the function of CXCR4
is detrimental to the adult host are not clear.
In our present study, we can conclude that T134 has anti-HIV-1 activity
against not only the wild type but also AMD3100-resistant strains.
We produced two different CXCR4 antagonists, which, should HIV-1
acquire resistance to one of the inhibitors, would allow for the use of
another inhibitor to suppress the resistant strain. This observation
indicates the potential for using these inhibitors as preventive and/or
therapeutic drugs for HIV infections.
This work was supported by a Grant-in-Aid for Scientific Research
from the Ministry of Education, Science and Culture of Japan and a
Research Grant from the Human Science Foundation. M.P. is grateful to
the Japanese Foundation for AIDS Prevention, Tokyo, Japan, for a fellowship.
Anti-CCR5 MAb (2D7) and MAGI-CCR5 cells were obtained through the AIDS
Research and Reference Reagent Program, Division of AIDS, NIAID, NIH,
with 2D7 from LeukoSite, Inc., and MAGI-CCR5 from Julie Overbaugh.
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