Phosphatase inhibitor, sodium stibogluconate, in combination with interferon (IFN) alpha 2b: phase I trials to identify pharmacodynamic and clinical effects.

Since sodium stibogluconate (SSG) inhibited phosphatases including SHP-1 and augmented anti-tumor actions of IFN-α2b in vitro and in mice, two Phase I trials of SSG/IFN-α2b combination were undertaken to evaluate safety and target inhibition. Escalating doses of SSG (200-1200 mg/m2) and fixed doses of IFN-α2b (3x106 units/m2) with or without chemotherapy (dacarbazine, vinblastine, cisplatin) were evaluated for side effects and impact on SHP-1 phospho-substrates and IFNα-stimulated-genes (ISGs) in peripheral blood in 40 patients with metastatic melanoma, soft tissue sarcomas, gastrointestinal stromal tumors, and breast or colorectal carcinomas who did not have other established treatment options. Common adverse events were bone marrow suppression, fatigue, gastrointestinal upset, and asymptomatic lipase elevation (n=13); the latter was dose related and mostly after 10d of SSG/IFN-α2b in combination.

Tyrosine phosphatase inhibitor-3 sensitizes melanoma and colon cancer to biotherapeutics and chemotherapeutics.

Drug resistance is a major obstacle in cancer treatments and diminishes the clinical efficacy of biological, cytotoxic, or targeted therapeutics. Being an antiapoptotic mediator of chemoresistance in breast and lung cancer cells, MKP1 phosphatase might be targeted for overcoming chemoresistance and improving therapeutic efficacy. In this work, tyrosine phosphatase inhibitor-3 (TPI-3) was identified as a novel small molecule inhibitor of MKP1 and was capable of sensitizing tumors to bio- and chemotherapeutics in mice as a tolerated oral agent.

Novel SHP-1 inhibitors tyrosine phosphatase inhibitor-1 and analogs with preclinical anti-tumor activities as tolerated oral agents.

Src homology region 2 domain-containing phosphatase 1 (SHP-1) has been implicated as a potential cancer therapeutic target by its negative regulation of immune cell activation and the activity of the SHP-1 inhibitor sodium stibogluconate that induced IFN-gamma(+) cells for anti-tumor action. To develop more potent SHP-1-targeted anti-cancer agents, inhibitory leads were identified from a library of 34,000 drug-like compounds. Among the leads and active at low nM for recombinant SHP-1, tyrosine phosphatase inhibitor-1 (TPI-1) selectively increased SHP-1 phospho-substrates (pLck-pY394, pZap70, and pSlp76) in Jurkat T cells but had little effects on pERK1/2 or pLck-pY505 regulated by phosphatases SHP-2 or CD45, respectively.

PRL-2 increases Epo and IL-3 responses in hematopoietic cells.

Dual specificity protein tyrosine phosphatase PRL-2 is overexpressed in pediatric acute myeloid leukemia (AML) and is located at human chromosome 1p35, a region often rearranged or amplified in malignant lymphoma and B-cell chronic lymphocytic leukemia (B-CLL). Little is known of the significance of PRL-2 expression in hematopoietic malignancies. Herein we demonstrated that ectopic expression of PRL-2 in murine pre-B-cell line Baf3ER and mouse bone marrow cells induced key features associated with malignant progression and metastasis.

Interferon-gamma is induced in human peripheral blood immune cells in vitro by sodium stibogluconate/interleukin-2 and mediates its antitumor activity in vivo.

Sodium stibogluconate (SSG), an inhibitor of SHP-1 that negatively regulates cytokine signaling and immunity, suppressed growth of murine Renca tumors in combination with interleukin-2 (IL-2) via a T-cell-dependent mechanism. The ability of SSG to interact with IL-2 in activating primary human immune cells was evaluated herein by assessing its induction of interferon (IFN)-gamma(+) TH1 cells in human peripheral blood in vitro. The significance of IFN-gamma(+) cells was also investigated by assessing SSG/IL-2 antitumor activity in wild-type and IFN-gamma(-/-) mice.

The role and target potential of protein tyrosine phosphatases in cancer.

Protein tyrosine phosphatases (PTPases) are attractive targets for developing novel cancer therapeutics. Activated via gain-of-function point mutations or overexpression, several PTPases have been identified as critical oncogenic molecules in human malignancies that may be targeted with small chemical inhibitors as a therapeutic strategy. Tumor suppressor PTPases have also been discovered as contributing factors in cancer development that may be targeted via intervention of downstream signaling events for therapeutic purposes.

Efficacy of SSG and SSG/IFNalpha2 against human prostate cancer xenograft tumors in mice: a role for direct growth inhibition in SSG anti-tumor action.

Background: Pre-clinical activity of SSG against melanoma and renal cancer has been identified recently although the drug's mechanism of action and activity against tumors of additional histological-types remain undefined.

Methods: The effects of SSG and SSG combination with other agents on DU145 human prostate carcinoma xenograft tumors in mice and on DU145 cell subpopulations of differential SSG sensitivities were evaluated.

Results: DU145 tumor growth was inhibited by SSG (69%), IFNalpha2 (33%) or the combination (80%) that induced complete regression of WM9 human melanoma tumors.

SHP-1 inhibits LPS-mediated TNF and iNOS production in murine macrophages.

Several lines of evidence have suggested that protein tyrosine phosphatases, including CD45 and SHP-1, regulate macrophage activation. Macrophages from mice lacking SHP-1 (motheaten mice) are hyper-responsive to many stimuli, suggesting that SHP-1 may negatively regulate macrophage activation. Herein we report that the repressible/inducible over-expression of wild-type SHP-1 in a subclone of RAW 264.

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.

IL-2 therapy results in 10-20% response rates in advanced renal cell carcinoma (RCC) via activating immune cells, in which the protein tyrosine phosphatase Src homology 2 domain-containing phosphatase 1 (SHP-1) is a key negative regulator. Based on finding that sodium stibogluconate (SSG) inhibited SHP-1, the anti-RCC potential and action mechanism of SSG and SSG/IL-2 in combination were investigated in a murine renal cancer model (Renca). Despite its failure to inhibit Renca cell proliferation in cultures, SSG induced 61% growth inhibition of Renca tumors in BALB/c mice coincident with an increase (2-fold) in tumor-infiltrating macrophages (Mphi).

Novel growth and death related interferon-stimulated genes (ISGs) in melanoma: greater potency of IFN-beta compared with IFN-alpha2.

Interferon (IFN)-dependent cellular effects are mediated by transcriptional induction of responsive genes, collectively referred to as IFN-stimulated genes (ISGs). Which ISGs regulate the potent antiviral, antiproliferative, apoptosis-inducing, antiangiogenic, and immunologic effects of IFNs remains largely undetermined. To identify genes that might be useful for predicting or targeting apoptosis induction in response to IFNs, WM9 melanoma cells were assessed.

Cells previously desensitized to type 1 interferons display different mechanisms of activation of stat-dependent gene expression from naïve cells.

Over the past decade, a wealth of knowledge has been obtained concerning the mechanisms by which interferons (IFNs) and other cytokines activate or down-regulate immediate early genes via the Jak/Stat pathway. In contrast, little information is available on interferon-activated gene expression in naïve cells compared with cells that have been desensitized and subsequently resensitized to the actions of these cytokines. In naïve cells, the ISG54 gene is activated via IFN beta-stimulated formation of ISGF3, a heterotrimeric DNA binding complex consisting of p48 (IRF9) and tyrosine-phosphorylated Stat1 and Stat2.

Molecular cloning, biochemical and structural analysis of elongation factor-1 alpha from Leishmania donovani: comparison with the mammalian homologue.

The Src-homology 2 domain containing protein tyrosine phosphatase-1 (SHP-1) is involved in the pathogenesis of infection with Leishmania. Recently, we identified elongation factor-1 alpha (EF-1 alpha) from Leishmania donovani as a SHP-1 binding and activating protein [J. Biol.

Identification of Shp-2 as a Stat5A phosphatase.

Stat5A, a member of the signal transducers and activators of transcription (Stat) family, is activated upon a single tyrosine phosphorylation. Although much is known about the activation process, the mechanism by which the tyrosine-phosphorylated Stat5A proteins are inactivated is largely unknown. In this report, we demonstrate that down-regulation of the tyrosine-phosphorylated Stat5A was via dephosphorylation.

Pentamidine is an inhibitor of PRL phosphatases with anticancer activity.

The PRL family oncogenic phosphatases are attractive targets for developing inhibitors as anticancer therapeutics given their potentially pathogenic role in human malignancies. Herein we demonstrate that pentamidine, an anti-protozoa drug with an unknown mechanism of action, is an inhibitor of PRLs with anticancer potential. Pentamidine at its therapeutic doses inhibited recombinant PRL phosphatases in vitro and inactivated ectopically expressed PRLs in NIH3T3 transfectants with an effective duration more than 24 h after a pulse cell treatment.

Difference in DNA sequences in SSU rDNA variable regions among pathogens isolated from different epidemic foci of visceral leishmaniasis in China.

Objective: To confirm the existence of point mutations in the SSU rDNA variable regions of 5 Leishmania donovani (L.d.) isolates from different epidemic foci in China.

Anticancer activity of sodium stibogluconate in synergy with IFNs.

Cancer cell resistance limits the efficacy of IFNs. In this study, we show that sodium stibogluconate (SSG) and IFN-alpha synergized to overcome IFN-alpha resistance in various human cancer cell lines in culture and eradicated IFN-alpha-refractory WM9 human melanoma tumors in nude mice with no obvious toxicity. SSG enhanced IFN-alpha-induced Stat1 tyrosine phosphorylation, inactivated intracellular SHP-1 and SHP-2 that negatively regulate IFN signaling, and induced cellular protein tyrosine phosphorylation in cancer cell lines.

Leishmania EF-1alpha activates the Src homology 2 domain containing tyrosine phosphatase SHP-1 leading to macrophage deactivation.

The human leishmaniasis are persistent infections of macrophages caused by protozoa of the genus Leishmania. The chronic nature of these infections is in part related to induction of macrophage deactivation, linked to activation of the Src homology 2 domain containing tyrosine phosphatase-1 (SHP-1) in infected cells. To investigate the mechanism of SHP-1 activation, lysates of Leishmania donovani promastigotes were subjected to SHP-1 affinity chromatography and proteins bound to the matrix were sequenced by mass spectrometry.

SHP-1 regulates Fcgamma receptor-mediated phagocytosis and the activation of RAC.

Fcgamma receptor-mediated phagocytosis is a complex process involving the activation of protein tyrosine kinases, events that are potentially down-regulated by protein tyrosine phosphatases. We used the J774A.1 macrophage cell line to examine the roles played by the protein tyrosine phosphatase SHP-1 in the negative regulation of Fcgamma receptor-mediated phagocytosis.

A bipartite NLS at the SHP-1 C-terminus mediates cytokine-induced SHP-1 nuclear localization in cell growth control.

SHP-1 protein tyrosine phosphatase is a critical regulator of signaling in hematopoietic cells as illustrated by the lethal hematopoietic disorders in SHP-1-deficient mice. We and others have shown in previous studies that SHP-1 regulates membrane receptor signaling: it binds via its N-terminal region SH2 domains to tyrosine phosphorylated membrane receptors to dephosphorylate key substrates in the receptor complexes. Here we demonstrate that the SHP-1 C-terminal region contains a bipartite NLS that mediates SHP-1 nuclear localization in response to cytokines.

Absence of CD5 dramatically reduces progression of pulmonary inflammatory lesions in SHP-1 protein-tyrosine phosphatase-deficient 'viable motheaten' mice.

Mice homozygous for the viable motheaten (Hcph(me-v)) mutation are deficient in SHP-1 protein-tyrosine phosphatase, resulting in severe systemic autoimmunity and immune dysfunction. A high percentage of B-cells in viable motheaten mice express the cell surface glycoprotein CD5, in contrast to wild type mice that express CD5 on only a small percentage of B-cells. CD5(+) B-cells have been associated with autoantibody production.