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Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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on TF-1 cell growth by the
drug indicated its broad activities in the signaling of various
cytokines. These data represent the first evidence that sodium
stibogluconate inhibits PTPases and augments cytokine responses. Our
results provide novel insights into the pharmacological effects of the
drug and suggest potential new therapeutic
applications. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Thus far, few specific inhibitors of protein tyrosine phosphatases (PTPases)3 have been reported despite extensive efforts in the last decade to identify them (5). Although a number of chemicals that broadly inhibit PTPases are known, including sodium orthovanadate and iodoacetic acid, their usefulness as therapeutic agents is severely limited due to their general toxicity in vivo. Recently, it has been reported that suramin, a polysulfonated naphthylurea compound, can act in vitro as a competitive and reversible inhibitor of several protein tyrosine phosphatases (6). Such an inhibitory activity of suramin against PTPases is consistent with its activity in augmenting tyrosine phosphorylation of cellular proteins and may explain its antitumor activity and its therapeutic effect in treating trypanosomiasis and onchocerciasis (6).
Src homology PTPase-1 (SHP-1) is a PTPase that plays a pivotal role in down-regulating signaling in hemopoietic cells (7, 8). Deficiency of the phosphatase due to mutations in the SHP-1 gene associates with heightened signaling in hemopoietic cells (9, 10, 11) and leads to hyperresponsiveness of hemopoietic cells to a variety of extracellular stimuli, including cytokines (12), hemopoietic growth factors (13, 14, 15, 16, 17, 18), and Ags (19, 20, 21, 22). Thus, drugs targeting the enzyme may effectively modulate activation, proliferation. and immune responses of hemopoietic cells for therapeutic purposes.
We have screened chemical reagents by in vitro phosphatase assays to
identify inhibitors of the SHP-1 phosphatase. Here we report that
sodium stibogluconate (also known as sodium antimony gluconate,
Stibanate, Dibanate, Stihek, Solustibostam, Solyusurmin, or Pentostam),
a pentavalent antimonial used for the treatment of leishmaniasis
(23), is a potent in vitro inhibitor of PTPases, including
SHP-1. The SHP-1 phosphatase activity in vitro was almost completely
inhibited by the drug at 10 µg/ml, a concentration less than or equal
to the peak serum level obtained in human beings treated for
leishmaniasis (24, 25). The inhibitory activity of the
drug against PTPases in vivo was indicated by its enhancement of
tyrosine phosphorylation of distinct cellular proteins in Baf3 cells
and by its augmentation of Baf3 proliferation induced by the
hemopoietic growth factor IL-3. Importantly, we demonstrated that
sodium stibogluconate augmented the opposite ffects of GM-CSF and
IFN- on TF-1 cell growth, suggesting broad activities of the drug in
enhancing the signaling of various cytokines. These data provide novel
insights into the pharmacological mechanism of sodium stibogluconate
and suggest new therapeutic applications.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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PTPase assay kits and GST fusion protein of PTP1B were purchased from Upstate Biotechnology (Lake Placid, NY). Suramin and potassium antimonyl tartrate was purchased from Sigma (St. Louis, MO). Sodium stibogluconate (its Sb content is 100 mg/ml and used to designate SS concentrations hereafter) was a gift from Dr. Xiaosu Hu (Sichuan Medical College, Sichuan, China). GST fusion proteins of SHP-1 (26) and SHP-2 (27) have been described previously and were prepared following established protocols (28). The GST fusion protein of SHP-1cata was purified from DH5a bacteria transformed with a pGEX construct containing the coding region of the PTPase catalytic domain (aa 202–554) of murine SHP-1 (26), derived by PCR from the murine SHP-1 cDNA. The GST fusion protein of mitogen-activated protein kinase phosphatase 1 (MKP1) was purified from DH5a bacteria transformed with a pGEX construct containing the coding region of MKP1 cDNA derived by RT-PCR with the following primers (MKP1/5, 5'-ctggatcctgcgggggctgctgcaggagcgc; MKP1/3, 5'-aagtcgacgcagcttggggaggtggtgat).
Murine IL-3 (29), recombinant human GM-CSF
(30), and recombinant human IFN- (31) have
been described previously. Abs against phosphotyrosine (4G10; Upstate
Biotechnology), 
-actin (Amersham, Arlington Heights, IL),
phosphotyrosine Stat5 (New England BioLab, Beverly, MA) and Janus
family kinase 2 (Jak2; Affinity BioReagents, Golden, CO) were purchased
from commercial sources.
In vitro PTPase assays
In vitro PTPase activities were measured using the commercial PTPase assay kit (Upstate Biotechnology) following established procedures (28). This assay measures the in vitro dephosphorylation of a synthetic phosphotyrosine peptide (R-R-L-I-E-D-A-E-pY-A-A-R-G). Briefly, 0.01 µg GST/PTPase fusion proteins was incubated in 50 µl Tris buffer (10 mM Tris, pH 7.4) containing different concentrations of inhibitors or chemicals (0–1000 µg/ml) at 22°C for 10 min, followed by addition of 0.2 mM phosphotyrosine peptide and incubation at 22°C for 18 h; 100 µl Malachite Green solution were added and incubated for 5 min, and OD660 was measured after 5 min.
To assess the reversibility of inhibition of SHP-1 by PTPase inhibitors, GST/SHP-1 fusion proteins bound on glutathione beads were preincubated in cold Tris buffer or Tris buffer containing the PTPase inhibitors at 4°C for 30 min. The beads were then either washed three times in Tris buffer or not washed before in vitro PTPase assays.
Cells, cell culture, and cell proliferation assays.
The murine hemopoietic cell line Baf3 was maintained in RPMI 1640 supplemented with 10% FCS and murine IL-3 (20 U/ml) as described previously (32). Human myeloid cell line TF-1 was maintained in RPMI 1640 supplemented with 10% FCS and 40 ng/ml recombinant human GM-CSF as described previously (30). For cell proliferation assays, cells were washed in 10% FCS medium twice, resuspended in 10% FCS medium, incubated at 37°C for 16 h, and then cultured at 37°C in 10% FCS medium containing various amounts of cytokines, sodium stibogluconate, or potassium antimonyl tartrate for 3–6 days as indicated. The cell numbers in proliferation assays were determined by an MTT assay (18) or by microscopic cell counting as indicated.
Induction of cellular protein phosphorylation and Western blotting
For induction of cellular protein phosphorylation by sodium stibogluconate or pervanadate (33), Baf3 cells were incubated in 0.1% FCS-RPMI 1640 at 37°C for 16 h. The cells were then washed twice in RPMI 1640 and incubated with sodium stibogluconate or pervanadate (0.1 mM) for various times before termination by lysing cells in cold lysis buffer (50 mM Tris (pH 7.4), 150 mM NaCl, 0.2 mM Na3VO4; 20 mm NaF, 1% Nonidet P-40, 2 mM PMSF; 20 µg/ml aprotinin, and 1 mM sodium molybdic acid). To determine the effect of sodium stibogluconate or potassium antimonyl tartrate on IL-3-induced Jak/Stat phosphorylation, Baf3 cells were deprived of the growth factor for 16 h in 0.1% FCS RPMI 1640 and then incubated with or without sodium stibogluconate or potassium antimonyl tartrate for 10 min. IL-3 was next added to the cell suspension and incubated for various times. The cells were then harvested and lysed in cold lysis buffer at 4°C for 45 min. Total cell lysates (TCL) were separated in SDS-PAGE gels, blotted onto nitrocellulose membrane (Schleicher & Schuell, Keene, NH), probed with specific Abs, and detected using an enhanced chemiluminescence kit (ECL; Amersham, Arlington Heights, IL).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Through screening various chemical compounds by in vitro PTPase
assays, we identified sodium stibogluconate as an inhibitor of PTPases.
The dephosphorylation of a synthetic phosphotyrosine peptide by the
GST/SHP-1 fusion protein was almost completely blocked (99%) by sodium
stibogluconate at 10 µg/ml (Fig. 1
A). Sodium stibogluconate
also inhibited SHP-2 and PTP1B (Fig. 1A). However,
10-fold higher concentrations of the drug (100 µg/ml) were
required to achieve a similar degree (99%) of inhibition of the two
PTPases (Fig. 1A). Inhibition of SHP-1 by the known PTPase
inhibitor suramin was less effective under comparable conditions (Fig. 1B). The drug showed no obvious inhibitory activity against
MKP1 (34), a dual-specificity protein tyrosine phosphatase
(Fig. 1C). Under the experimental conditions, the GST fusion
proteins of SHP-1, SHP-2, PTP1B, and MKP1 showed similar PTPase
activities against the peptide substrate (OD660
0.6 above background (0.03)) in the absence of inhibitors.
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Substrate dephosphorylation is mediated by the PTPase catalytic
domain, the activity of which is often regulated by flanking N-terminal
and C-terminal regions (5). To define whether sodium
stibogluconate inhibits PTPases through targeting the PTPase catalytic
domain or via the flanking regulatory regions, we compared the effect
of sodium stibogluconate on the GST/SHP-1 fusion protein and the
GST/SHP-1cata fusion protein which contains the PTPase catalytic domain
but has the Src homology 2 (SH2) domains and the C-terminal region
deleted (Fig. 2A). Sodium
stibogluconate showed similar activities in inhibiting the two proteins
in their dephosphorylation of the phosphotyrosine peptide substrate in
vitro (Fig. 2B), demonstrating that inhibition of SHP-1
PTPase activity by sodium stibogluconate does not require the SHP-1 SH2
domains and the C-terminal region. These results provide strong
evidence that sodium stibogluconate directly targets the SHP-1 PTPase
catalytic domain.
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). In contrast, the
inhibition of the phosphatase by suramin was almost completely removed
by the washing process (Fig. 3), consistent with a previous report
(6).
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It is expected that the inhibition of PTPases in vivo will
increase tyrosine phosphorylation of cellular protein substrates. To
determine whether sodium stibogluconate functions as a PTPase inhibitor
in vivo, we examined its effect on cellular protein tyrosine
phosphorylation in the murine IL-3-dependent cell line Baf3. Treatment
of Baf3 cells with sodium stibogluconate induced protein tyrosine
phosphorylation (Fig. 4A) that
was modest and transient in comparison with those induced by
pervanadate (Fig. 4B). Increased tyrosine phosphorylation of
cellular proteins of 55 and 32 kDa was apparent in cells incubated
with the drug for 5 min (Fig. 4, lanes 1-3). This induction
of cellular protein tyrosine phosphorylation was dose dependent with
more marked induction occurring at the higher drug concentration (Fig. 4, comparing lanes 2 and 3). Heightened
phosphorylation of these proteins was also detected with prolonged
treatment of 10, 30, or 60 min but at more modest levels (Fig. 4, lanes 4-12). This increased protein tyrosine
phosphorylation was not due to variations in the protein samples as
indicated by the similar amounts of -actin protein in these samples
(Fig. 4A, bottom). The drug showed no obvious
effect on several other phosphotyrosine cellular proteins in the TCL
samples (Fig. 4), suggesting certain specificity of the drug in
induction of protein tyrosine phosphorylation. The identities of the
55- and 32-kDa proteins have not been determined. The weaker
phosphorylation signal of p32 band in lane 1 of Fig. 4
compared with those of lanes 4, 7, and
10 was not consistently detected.
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). Baf3 cells deprived of IL-3 were
incubated with or without the drug for 10 min and then stimulated with
IL-3 for various times. IL-3 induced tyrosine phosphorylation of Jak2
and Stat5 in Baf3 cells in the presence or absence of the drug.
However, the phosphotyrosine levels of Jak2 and Stat5 in the presence
of the drug were about twice those in cells without drug treatment as
determined by densitometry analysis (Fig. 5; compare lanes
2–6 with lanes 8–12).
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, lanes 1 and 7). Prolonged incubation with the
drug alone at 37°C for 16 h also failed to induce Jak2/Stat5
tyrosine phosphorylation (data not shown). Sodium stibogluconate augments IL-3-induced cell proliferation of Baf3 cells
SHP-1 down-regulates cytokine signaling as demonstrated by the
hyperresponsiveness of SHP-1-deficient cells to various cytokines,
including IL-3 (18, 29). The inhibitory activity of sodium
stibogluconate against SHP-1 predicted that the drug would augment
IL-3-induced proliferation of Baf3 cells. Indeed, IL-3-induced Baf3
proliferation was increased in the presence of sodium stibogluconate at
0.3–200 µg/ml with the maximal effect concentration 40 µg/ml
(Fig. 6A). This modest
increase was consistently detected in two separate experiments (data
not shown). At a higher concentration (1000 µg/ml), the drug
suppressed IL-3-induced Baf3 growth (Fig. 6A). This
growth-promoting activity of the drug was apparent at suboptimal (3.3
or 10 U/ml), but not optimal (30 U/ml), amounts of IL-3 (Fig. 6B). In the absence of IL-3, sodium stibogluconate failed to
support cell proliferation or maintain cell viability on day 3 of
culture (Fig. 6B). Whether the drug has a delaying effect on
the onset of apoptosis on a shorter time course has not been
determined.
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on the proliferation of TF-1 cells
The Jak/Stat signaling pathways transduce signals initiated by
cytokines that often have opposite effects on cell growth. The human
myeloid leukemia cell line TF-1 responds to both GM-CSF, which promotes
proliferation, and IFN-, which inhibits cell growth. To determine
whether the effect of the PTPase inhibitor is unique for the
IL-3-initiated signaling events or affects other cytokines, we examined
the growth responses of TF-1 cells to GM-CSF and IFN- in the
presence or absence of sodium stibogluconate.
Proliferation of TF-1 cells was induced by suboptimal concentrations of
GM-CSF (5–40 ng/ml) in a dose-dependent manner (Fig. 7A). This proliferation of
TF-1 cells was augmented in the presence of sodium stibogluconate at 50
µg/ml (Fig. 1A). No viable cells were detected in the
cultures lacking GM-CSF in the presence or absence of the drug (Fig. 7A). These results demonstrated that sodium stibogluconate
augmented the growth-promoting activity of GM-CSF in TF-1 cells but
could not substitute the growth factor for maintaining cell viability
or promoting growth under the experimental conditions.
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, GM-CSF-induced proliferation of TF-1 cells
was suppressed (Fig. 7B). Further reduction of
GM-CSF-induced cell growth was detected in cultures containing both
IFN- and sodium stibogluconate (50 µg/ml; Fig. 7, B and
C), indicating that the growth inhibition activity of
IFN- was enhanced in the presence of the drug. Because the enhanced
growth inhibition of IFN- by the drug occurred in the presence of
GM-CSF, it indicated the dominance of the synergy between IFN- and
the drug over the activity of the drug in augmenting GM-CSF mitogenic
signaling under the experimental conditions.
As shown in Fig. 7D, the activity of sodium stibogluconate
in augmenting GM-CSF-induced TF-1 proliferation was dose dependent,
with the optimal activity at 50 µg/ml. In contrast, more dramatic
growth inhibition in the presence of IFN- occurred at higher
concentrations of the drug (Fig. 7E). Because the drug at
low doses (12.5–50 µg/ml) showed no negative effect on
GM-CSF-induced cell growth, its effect at such doses in augmenting
IFN--induced growth inhibition was likely resulted from specific
enhancement of IFN- signaling. In contrast, nonspecific toxicity of
drug at higher doses in combination with IFN- might have contributed
to the more dramatic growth inhibition.
The Sb(III) form of potassium antimonyl tartrate lacks inhibitory activity against PTPases
Sodium stibogluconate is of Sb(V) form which transforms inside cells into Sb(III) form that can affect Leishmania growth (38). We therefore determined the activity of potassium antimonyl tartrate of Sb(III) form in inhibiting PTPases in vitro and in vivo.
Unlike sodium stibogluconate, potassium antimonyl tartrate at 1–1000
µg/ml showed no detectable inhibition of PTPases SHP-1 and PTP1B in
vitro (Fig. 8A). It also
failed to enhance IL-3-induced Stat5 phosphorylation (Fig. 8B) or IL-3-induced proliferation of Baf3 cells (Fig. 8C), indicating its lack of inhibitory activity against
PTPases in vivo. Interestingly, it showed marked toxicity against Baf3
cells. The results together indicate that only the Sb(V) form acts as a
PTPase inhibitor which is inactivated when transformed into the
Sb(III) form.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Our data provide the first evidence that sodium stibogluconate is a
potent inhibitor of PTPases in vitro and in vivo. Sodium stibogluconate
inhibited the dephosphorylation of a synthetic phosphotyrosine peptide
substrate by PTPases (SHP-1, SHP-2, and PTP1B) in in vitro PTPase
assays (Fig. 1). The dephosphorylation of p-nitrophenyl
phosphate (Sigma) by these PTPases in vitro was also similarly
inhibited by the drug (data not shown). The inhibitory activity of the
drug against PTPases in vivo was indicated by the rapid induction of
protein tyrosine phosphorylation of the two yet unidentified 56- and
32-kDa cellular proteins in Baf3 cells (Fig. 4). Interestingly,
proteins of similar molecular mass had been found to be
hyperphosphorylated in SHP-1-deficient cells in previous studies
(29). Induced cellular protein tyrosine phosphorylation
was less dramatic with prolonged drug incubation (Fig. 4), suggesting
that the drug may be unstable under the experimental conditions or that
the drug may sequentially inactivate PTPases with opposite effects on
the phosphorylation of the cellular proteins. In this regard, it is
interesting that PTPases were inhibited by the Sb(V) form of sodium
stibogluconate which is known to transform in cells to the Sb(III) form
that failed to show PTPase-inhibitory activity (Fig. 8). The
intracellular transformation therefore could result in inactivation of
the PTPase inhibitor and may account for the modest and transient
induction of tyrosine phosphorylation by the drug and its modest effect
on cell proliferation. This may have a beneficial side because it may
be related to the lower toxicity of the drug in comparison to other
PTPase inhibitors that allows its clinical application.
The inhibitory activity of sodium stibogluconate against PTPases in vivo was further indicated by the augmentation of IL-3-induced Jak2/Stat5 phosphorylation and IL-3-induced proliferation of Baf3 cells. We and others showed previously that SHP-1 dephosphorylates the Jak family kinases to down-regulate signaling initiated by cytokines (12, 16, 18, 35, 36, 37). Among the Jak kinases, IL-3 specifically activates the Jak2 kinase that phosphorylates the Stat5 protein to regulate gene expression (39). The observation that sodium stibogluconate augmented IL-3-induced Jak2/Stat5 tyrosine phosphorylation and IL-3-induced proliferation of Baf3 cells is therefore consistent with inhibition of SHP-1 by the drug in vivo. However, it remains possible that the effect of the drug on IL-3-induced Jak2/Stat5 phosphorylation and cell proliferation involves additional PTPases (e.g., the CD45 PTPase) that participate in dephosphorylating the Jak kinases (40). Indeed, sodium stibogluconate augmented G-CSF-induced Tyk2/Stat3 tyrosine phosphorylation in SHP-1-deficient cells (our unpublished data). The enhancement of IL-3-induced Jak2/Stat5 tyrosine phosphorylation by the drug was more substantial in later time points post-IL-3 stimulation, indicating induction of an extended period of phosphorylation by the drug. Such an effect of the drug suggests its targeting of PTPases recruited to Jak2/Stat5 at the later time points post-IL-3 stimulation to inactivate the signaling molecules.
Inhibition of PTPases in vivo by sodium stibogluconate was also
consistent with the observation that the drug augmented the opposite
effects of GM-CSF and IFN- on TF-1 cell proliferation (Figs. 7 and 8). In particular, the observation suggested that the drug targeted
PTPases that dephosphorylate shared signaling molecules (e.g., the Jak
family kinases) used by both GM-CSF and IFN-. Such a putative
mechanism would explain the cytokine-dependent effects of the drug; its
inhibition of PTPases leads to amplification of both mitogenic and
growth inhibitory signals initiated by GM-CSF and IFN-,
respectively. It also suggests that drug may have broad activities in
augmenting the signaling of various cytokines. SHP-1 has been shown in
previous studies to down-regulate the signaling of GM-CSF
(18) and IFN- (12). It was reported
(18) that macrophages from SHP-1-deficient mice show
2-fold increase of GM-CSF-induced cell growth in comparison with
controls. This level of growth increase is similar to the increase of
GM-CSF-induced TF-1 cell growth in the presence of sodium
stibogluconate, consistent with inhibition of SHP-1 by the drug. In
light of the pathogenic effect of SHP-1-deficient monocytes/macrophages
in the fatal motheaten phenotype (10), it is possible that
the apparently modest effect of the drug on GM-CSF-induced cell growth
could have significant biological consequences in vivo.
Our results also suggest that inhibition of PTPases by sodium
stibogluconate at therapeutic concentrations to increase Jak/Stat
phosphorylation and cellular responses to cytokines may be a major
factor responsible for the pharmacological effect of the drug in the
treatment of leishmaniasis. Among the cytokines that depend on Jak/Stat
pathways for signal transduction (41), IFN-
plays an
important role in eliminating intracellular Leishmania
(42). Moreover, impaired IFN- signaling was detected in
Leishmania-infected macrophages and was associated with
activation of SHP-1 by the parasite (43, 44, 45, 46). Therefore,
it could be postulated that sodium stibogluconate may augment IFN-
signaling in macrophages via inhibiting SHP-1 (and other PTPases) and
contribute to the clearance of intracellular Leishmania.
Thus anti-Leishmania activity of sodium stibogluconate
may derive both from augmenting cell signaling by Sb(V) and from
parasite killing by Sb(III) transformed from Sb(V) inside cells.
Further studies using Leishmania-infected macrophage cell
lines will help to verify this hypothesis. Such a functional mechanism,
nevertheless, is consistent with previous observations that modulation
of host PTPases with specific inhibitors can effectively control the
progression of Leishmania infection by enhancing cytokine
signaling in macrophages (47, 48, 49). In light of the
observation that anti-Leishmania drug sodium arsenite
inhibits LPS-induced MAP kinase signaling in macrophages
(50), modulation of cellular signaling could be a common
mechanism of anti-Leishmania drugs.
The mechanism through which the drug inhibits PTPases is likely by
targeting the PTPase catalytic domain of the enzymes. The drug was
effective in inhibiting both the wild-type SHP-1 and the SHP-1 mutant
containing the PTPase domain without the flanking N-terminal SH2
domains or the C-terminal region that regulate SHP-1 activity (Fig. 2).
This mechanism is also consistent with the observation that the drug
inhibited PTP1B which, except for its PTPase catalytic domain, has no
apparent structure similarity with SHP-1 and SHP-2 (34).
In this regard, it is not unexpected that the drug showed no obvious
activity against MKP1 because the amino acid sequence and structure of
the catalytic domain of dual-specificity phosphatases are substantially
different from those of the tyrosine-specific PTPases
(34). Such a mechanism also suggests that the drug may
have inhibitory activities against all tyrosine-specific PTPases that
have the conserved PTPase catalytic domain. Although our results
indicated that the drug formed a stable complex with SHP-1 in vitro
that was resistant to a washing process, it is not clear at present
whether this was due to docking of the drug into a pocket structure in
the PTPase domain or involved the formation of covalent bonds. In the
former case, it is likely that subtle differences in the putative
pocket structure of PTPases may be responsible for the different
sensitivities of the enzymes to the inhibitor in vitro. It also
suggests the feasibility of developing chemical derivatives of the drug
with more specific and potent activities against individual PTPases.
Further studies to resolve the crystal structures of PTPases complexed
with the drug will provide definitive answers in the future.
Demonstrated differential sensitivities of PTPases to the drug in vitro suggest similar differential sensitivities of PTPases in vivo, which may explain the dose-dependent effect of the drug on IL-3-induced cell proliferation and the known clinical side effect of the drug at higher dosages. Sodium stibogluconate augmented IL-3-induced Baf3 proliferation at therapeutic concentrations and suppressed cell growth at higher dosages. In clinical applications, sodium stibogluconate at therapeutic dosages was well tolerated but is known at higher dosages to have side effects that include reversible nonspecific ECG changes and renal defects (25). Effects of the drug at higher dosages may be related to inhibition of PTPases that are sensitive to the drug only at higher concentrations.
Importantly, our finding that sodium stibogluconate was a potent inhibitor of PTPases and an enhancer of cytokine signaling suggests potential novel clinical applications for the drug in a variety of situations in which increased cytokine responses are beneficial. It is tempting to speculate coadministration of the drug with cytokines will improve the efficacy of existing cytokine therapies and reduce side effects and costs associated with cytokine therapies. Moreover, the drug by itself may have therapeutic effects through inhibiting PTPases to change the balance of intracellular tyrosine phosphorylation that controls cell proliferation, differentiation and functional activities. Suramin is presently being evaluated in clinical trials for the treatment of prostate cancer and other solid tumors (51). Because sodium stibogluconate appeared to be a more efficient inhibitor of PTPases than suramin, it has the potential to become a better drug for effective treatment of these diseases.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Taolin Yi, Department of Cancer Biology, Lerner Research Institute, NB4-67, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195. E-mail address: yit{at}ccf.org
3 Abbreviations used in this paper: PTPase, protein tyrosine phosphatase; SH2, Src homology 2 domain; SHP-1, Src homology PTPase-1; Jak2, Janus family kinase 2; TCL, total cell lysate; SHP-1cata, SHP-1 catalytic domain; MKP1, mitogen-activated protein kinase phosphatase 1.
Received for publication April 18, 2001. Accepted for publication July 17, 2001.
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K. Fan, M. Zhou, M. K. Pathak, D. J. Lindner, C. Z. Altuntas, V. K. Tuohy, E. C. Borden, and T. Yi Sodium Stibogluconate Interacts with IL-2 in Anti-Renca Tumor Action via a T Cell-Dependent Mechanism in Connection with Induction of Tumor-Infiltrating Macrophages J. Immunol., November 15, 2005; 175(10): 7003 - 7008. [Abstract] [Full Text] [PDF]
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 F. Krotz, B. Engelbrecht, M. A. Buerkle, F. Bassermann, H. Bridell, T. Gloe, J. Duyster, U. Pohl, and H.-Y. Sohn The Tyrosine Phosphatase, SHP-1, Is a Negative Regulator of Endothelial Superoxide Formation J. Am. Coll. Cardiol., May 17, 2005; 45(10): 1700 - 1706. [Abstract] [Full Text] [PDF]
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 I. K. Lund, H. S. Andersen, L. F. Iversen, O. H. Olsen, K. B. Moller, A. K. Pedersen, Y. Ge, D. D. Holsworth, M. J. Newman, F. U. Axe, et al. Structure-based Design of Selective and Potent Inhibitors of Protein-tyrosine Phosphatase {beta} J. Biol. Chem., June 4, 2004; 279(23): 24226 - 24235. [Abstract] [Full Text] [PDF]
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R. Mukhopadhyay, Y. Zhou, and B. P. Rosen Directed Evolution of a Yeast Arsenate Reductase into a Protein-tyrosine Phosphatase J. Biol. Chem., June 27, 2003; 278(27): 24476 - 24480. [Abstract] [Full Text] [PDF]
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M. Ghosh, C. Pal, M. Ray, S. Maitra, L. Mandal, and S. Bandyopadhyay Dendritic Cell-Based Immunotherapy Combined with Antimony-Based Chemotherapy Cures Established Murine Visceral Leishmaniasis J. Immunol., June 1, 2003; 170(11): 5625 - 5629. [Abstract] [Full Text] [PDF]
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D. Nandan, T. Yi, M. Lopez, C. Lai, and N. E. Reiner Leishmania EF-1alpha Activates the Src Homology 2 Domain Containing Tyrosine Phosphatase SHP-1 Leading to Macrophage Deactivation J. Biol. Chem., December 13, 2002; 277(51): 50190 - 50197. [Abstract] [Full Text] [PDF]
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 M. K. Pathak, D. Dhawan, D. J. Lindner, E. C. Borden, C. Farver, and T. Yi Pentamidine Is an Inhibitor of PRL Phosphatases with Anticancer Activity Mol. Cancer Ther., December 1, 2002; 1(14): 1255 - 1264. [Abstract] [Full Text] [PDF]
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T. Yi, M. K. Pathak, D. J. Lindner, M. E. Ketterer, C. Farver, and E. C. Borden Anticancer Activity of Sodium Stibogluconate in Synergy with IFNs J. Immunol., November 15, 2002; 169(10): 5978 - 5985. [Abstract] [Full Text] [PDF]
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 C. R. Engwerda, M. Ato, S. E. J. Cotterell, T. L. Mynott, A. Tschannerl, P. M. A. Gorak-Stolinska, and P. M. Kaye A Role for Tumor Necrosis Factor-{alpha} in Remodeling the Splenic Marginal Zone during Leishmania donovani Infection Am. J. Pathol., August 1, 2002; 161(2): 429 - 437. [Abstract] [Full Text] [PDF]
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