ANTIVIRAL METAL COMPLEXES compounds such as polyanionic compounds(polysulfates ...

20 Pages·2008·2.28 MB·English

ANTIVIRAL METAL COMPLEXES
ErikDe Clercq
RegaInstituteforMedicalResearch, Katholieke UniversiteitLeuven, B-3000Leuven, Belgium
Abstract
The initial events (virus adsorption and fusion with the cells) in the replicative cycle of
human immunodeficiencyvirus (HIV) can serve astargets forthe antiviral action ofmetal-binding
compounds such as polyanionic compounds (polysulfates, polysulfonates, polycarboxylates,
polyoxometalates, and sulfonated or carboxylated metalloporphyrins), bicyclams and G-octet-
forming oligonucleotides. The adsorption and fusion ofHIV with its target cells depends on the
interaction ofthe viral envelope glycoproteins (gpl20) with the receptors (CD4, CXCR4) at the
outer cell membrane. We are currently investigating how the aforementioned compounds interfere
withthese viral glycoproteins and/orcell receptor.
Introduction
There are ten steps in the replicative cycle of human immunodeficiency virus (HIV) that
could be considered as targets for chemotherapeutic interventions (Table 1) (1). The early events
in HIV infection, i.e. virus adsorption to the cells and virus cell fusion, have been shown to be the
points ofattack for some metal complexes or organic compounds containing metals. Here I will
discuss those compounds among the metal complexes that interfere with the virus adsorption
and/or virus cell fusion (i.e. polyanionic substances, bicyclam derivatives and G-octet-forming
oligonucleotides).
Table 1. HIV replicative cycle
Virus adsorptiontothe cells
2. Virus-cell fusion
3. Virus uncoating
4. Reversetranscription
5. Proviral DNA integration
6. Proviral DNAreplication
7. Proviral DNAtranscriptiontoviral mRNA
8. ViralmRNAtranslationto viralprecursorproteins
9. Maturation (proteolysis/myristoylation/glycosylation)
10. Budding(assembly/release)
The key molecule in the viral adsorption/fusion process is the viral envelope glycoprotein
gp120 (Fig. 1), which has a highly convoluted structure containing several regions referred to as
variable regions such as V3 and V4, which are assumed to interact with the corresponding
receptors atthe hostcell surface.
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Polyanionic substances
Foremost among the polyanionic substances that have been shown to interact with the
binding of HIV to the cells are the polysulfates such as dextran sulfate, dextrin sulfate, curdlan
sulfate, pentosan polysulfate, mannan sulfate, sulfoevernan, fucoidan, polyacetylal polysulfate
(PAPS) and polyvinylalcohol sulfate (PVAS) (Fig. 2) (2). These compounds inhibit HIV-induced
cytopathicity in cell cultures at an 50% effective concentration (EC0) ofabout 0.1 to pg/ml, that
is at a concentration which is 1,000- to more than 10,000-fold lower than the concentration
exhibiting cytotoxicity [50% cytotoxic concentration (CC0)] (Table 2).
In addition to the polysulfates, polysulfonates such as suramin, Evans blue,
bis(naphalenedisulfonate), polystyrene sulfonate (PSS), and polyvinyl sulfonate (PVS) (Fig. 3) and
polycarboxylates [in particularpolymerized aurintricarboxylic acid (ATA)] (Fig. 4) have also been
shown to inhibit HIV replicationwith EC0 values similarto those ofthe polysulfates (1).
Fig. 1. The HIV-1 envelope (surface)glycoprotein gpl20
A large series of polyoxometalates (Fig. 5), i.e. JM1590, which corresponds to
K3[Ce(SiWO39)2].26H20, are known to inhibitHIV replication atanEC0 of0.3 to 3 Mg/ml with
CCs0 values higher than 100 lg/ml (Table 3). Akin to the polysulfates and polysulfonates, the
polyoxometalates inhibitthe HIV replicative cycle atthe level ofvirus adsorptiontothe cells (3).
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ErikDe Clercq Metal-BasedDrugs
CH2OR CH2OR
0 O
H H H
H
OR R
R
H
Dextran Dextrin Curdlan
sulfate sulfate su--Glte
CH2OR TH2OR
O O O
H H H
H 01:1
Pentosan Mannan Sulfoevernan
polysulfate sulfate
CH2OR
--CH2-CH-O-CH-O- CH2 CH-CH2-CH-
CH2OR OR
OR H
Fucoidan PAPS PVAS
R SO3" or H
Fig. 2. Sulfatedpolysaccharides andpolymers
A new class, that ofthe anionic (sulfonated or carboxylated) metalloporphyrins, have been
recently shown to inhibit HIV replication (Table 4) (4). Metals (such as Fe or Ni) play an
important role in the selectivity of the compounds, for their presence significantly reduces
cytotoxicitywhile maintaining antiviral activity(Table 4).
An interesting feature of the polyanionic substances is that their antiviral activity is not
limited to HIV but also extends to various other enveloped viruses such as herpesviruses [herpes
simplex virus (HSV), cytomegalovirus (CMV)], influenza A virus, respiratory syncytial virus
(RSV), arenaviruses (Junin virus, Tacaribe virus) and rhabdoviruses [such as vesicular stomatitis
virus (VSV)] (Fig. 6). This broad spectrum antiviral action considerably enhances the therapeutic
potential ofthese compounds forthetreatmentofviral diseases.
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Table 2. Inhibitory effectofsulfated polysaccharides onthe cytopathicity ofHIV-l(III) inMT-4
cells
Compound ECs0 (lag/ml) CC50 (tg/ml) Selectivity index
(CCs0/ECs0)
Dextan sulfate (MW 5000) 0.5 > 2500 > 5000
Dextrin sulfate (MW 3000) 2.1 > 500 > 238
c-Cyclodextrin dodecasulfate 6.5 > 2500 > 385
13-Cyclodextrintetradecasulfate 0.8 > 2500 > 3125
qt-Cyclodextrin hexadecasulfate 0.2 > 2500 > 12500
Pentosan polysulfate (MW 3100) 0.19 > 2500 > 13150
Fucoidan 1.4 1060 757
Heparin (MW 11000) 0.58 > 2500 > 4310
-Carrageenan 0.54 > 625 > 1157
Mannan sulfate (MW 30000) 1.2 > 2500 > 2083
Sulfated E.coli K5 glycan 0.67 260 388
Periodate-treatedheparin 0.52 > 2500 > 4807
Polyacetal polysulfate (MW 30000) 0.4 > 2500 > 6250
Polyvinylalcohol sulfate (MW20000) 0.18 > 2500 > 13800
We have recently succeeded in obtaining mutants resistant to polyanionic substances after
passaging HIV in the presence of dextran sulfate (5). It thus appears possible for the virus to
develop resistance to these polyanionic substances (Fig. 7). The resistance mutations appear to be
located predominantly in the V3 loop ofthe gpl20 glycoprotein (Fig. 8) and render the overall
charge ofthe V3 loop less positive, thus resulting in a diminished electrostatic interaction with the
polyanionic compounds.
Polyanionic substances such as polyoxometalates (i.e. polyoxosilicotungstates) inhibit the
replication ofHIV, HSV and CMV atthe virus adsorption step. They inhibit influenza A virus and
RSV atthe virus-cell fusion step (6).
Little is known aboutthe therapeutic/prophylactic potential ofthe polyanionic substances in
the clinic. Protective effects with these compounds against HSV and influenza A virus infections
in vivo (mice) have been described with polyoxotungstates and polysulfonates when administered
systemically (intraperitoneally) or topically (intranasally), respectively (7,8). In particular, topical
administration ofthe polyanionic compounds, for instance as a vaginal formulation, seems to be
an attractive modality fortheprevention ofsexuallytransmittedHIV and HSV infections (9).
Bicyclams
The bicyclams (10) represent a new class of highly potent and selective HIV inhibitors.
They originated from the serendipitous discovery of anti-HIV activity in a monocyclam
preparation that contained bicyclam as contaminant. Starting from this lead compound, several
bicyclam derivatives were prepared that showed increased anti-HIV activity (Fig. 9) (11). The
most active ofthis series is the bicyclam JM3100 (Fig. 10) which has been found to inhibit HIV-
induced cytopathicity at a concentration ofa few nanograms per ml, while not being toxic to the
host cells at concentrations up to 500 tg/ml, thus achieving a selectivity index of 100,000 or
higher(Table 5) (12).
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ErikDe Clercq Metal-BasedDrugs
NH---
-03S NH--.CO..]l CO--- S03-
-------
-so CH H,C 03S--/-
3
NH NH
-03S so-
CO CO
NH--CO--NH Suramin
NH OH OH NH2
so-
so-
Evans Blue
SHO OHN--_SO S02S.--NHOOH:
2
03S 03S
Bis (naphtalenedisulfonafe)
so- so- so- so- so- so- so- so- so- so;
PSS (polystyrene sulfonate)
so- so- so- so- so- so- so- so- so- so-
PVS (po]yvnyl sulfonate)
Fig. 3. Sulfonatedpolymers
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HOcoo- OcoHo-
OH
C
coo-
OOC OH CH ( H CO
2
-OOC OH CHO2 HCOff
-OOC CO
coo
Fig. 4. Polycarboxylates" ATA (aurintricarboxylic acid)
Fig. 5. JM1590:K3[Ce(SiW1039)2].26 H20
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ErikDe Clercq Metal-BasedDrugs
Table 3. Anti-HIV activity ofpolyoxometalates
Compound ECso(tg/ml) CCo (lag/ml) Selectivity index
(CCso/ECso)
JM1583 Ks[BWO4o] 1.4 654 467
JM1590: Ks[Ce(SiWO39)].26HO 0.7 230 328
JM1591: KHPWOa8.24HO 0.3 339 1130
JM1596" Ko[PW8Zna(HO)O68].20HO 0.7 466 666
JM1809: K8HP2WsV306.34HO 1.1 293 266
JM2766" K6[BWGa(H20)O39] 2.8 > 500 > 178
JM2815" Ks[SiW(CsHs)TiO39] 1.9 > 500 > 263
JM2820: [MesNH]8[SiW8Nb6077] 3.2 > 500 > 156
Table 4. Anti-HIV activityofmetalloporphyrins
R M ECsoa(tg/ml) CC5ob (tg/ml) SIc
H3C SO3Na H2 4 4
\ / Mn 36 > 100 >2.8
Fe 4 > 100 >25
CH3
H3C SO3Na
H2 0.9 23 25
Fe 0.5 > 90 > 180
Ni > 90 > 9O
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Dextran sulfate PAPS PVAS
Herpes simplexvirus
Cytomegalovirus
Vacciniavirus
Polio/Coxsackie B virus
Sindbis virus
InfluenzaAvirus
InfluenzaB virus
Parainfluenzavirus
Respiratory syncytial virus
Junin/Tacaribevirus
Veicular stomatitis virus
Reovirus
Human immunodeficiencyvirus
Fig. 6. Antiviral activity spectrum ofpolysulthtes
Minimal effective concentration inthe range of0o1-1 tg/ml (ll), 1-10 (tg/ml (), 10--|00 (tg/ml) (El), or>
100 lag/ml (El)
5000
4000
aooo
2000
I000
0
0 2 4 6 8 10 12 14 16
Passage (n}
Fig. 7. Rate ofresistance developmentofHIVo NL4-3 to dextran sulfate (MW 5000)
MT-4 cells were infected with virus in the presence of 5 x the ECs0 (passage 0). Every 5 to 6 days
supematantofthe cell culturewasusedtore-infectfresh MT-4 cells inthe presence ofthe same or a2-to 5-
foldhighercompoundconcentration, dependingonthecytopathicityobserved.
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l(r#:De Clercq Metal,-BasedDrugs
Fig 8 Portion ofthe I]IV, envelope g!ycoprotein gp120 withthe mutations conferringresistance
to dextran sulfate
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HN NHHN
OM 1657 ,JM 2986
NH N N HN [....] [..
dM 2762 JM 3100
ENH N- FN HN-] EHN ENN3HNHNH
NHHN NHHNJ
,JM 2763 JM 3106
N/’N
ENH HN-
NH HN NH HN NH HN--J L-NH HN--J
JM 2849 JM 3109
Fig. 9. Bicyclams: bis(1,4,8,11-tetraazacyclotetradecane) derivatives
Time-of-addition experiments indicated that the bicyclams (i.e. JM2763) inhibit the HIV
replicative cycle at atime pointthat is situated between virus adsorption and reverse transcription
(Fig. 11). From these time-of-addition experiments we must conclude that the bicyclams interact
with the fusion/uncoating process (13). This process involves the removal ofthe envelope as well
as capsid proteins from the viral RNA genome so that the latter can be transcribed by the reverse
transcriptase. Theoretically, any of the viral envelope glycoproteins (gpl20, gp41) or capsid
proteins (plT, p24, p9, p7) could be considered as possible targets for the interaction with the
bicyclams (Fig. 12). Originally (13,14), we envisaged the capsid protein p7 (Fig. 13) as a possible
target for the bicyclams, as this protein contains two zinc fingers that could possibly make zinc-
coordination complexes withthe bicyclams.
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