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. Levels of SHP-1 substrates (pSTAT1, pSTAT3, pLck and pSlp76) were increased (up to 3x) in peripheral blood cells following SSG with no potentiation by combination with IFN-α2b. Representative ISGs in peripheral blood were induced after IFN-α2b at 4 and 24 hrs with selective modulations by combination. The median time on trials was 2.3 months (10-281d) with no objective regression of disease. Alive at 1y were 17/40 (43%) patients and after 2y were 8/40 (20%) following treatment initiation. These data demonstrate that SSG impacted signal molecules consistent with PTP inhibition and was tolerated in combination with IFN-α2b. Phase II investigations of SSG could safely utilize doses of up to 1200 mg/m2 of SSG for up to 10d alone or in combination with IFN-α2b with or without chemotherapy.

Sodium stibogluconate is a potent inhibitor of protein tyrosine phosphatases and augments cytokine responses in hemopoietic cell lines.

Using in vitro protein tyrosine phosphatase (PTPase) assays, we found that sodium stibogluconate, a drug used in treatment of leishmaniasis, is a potent inhibitor of PTPases Src homology PTPase1 (SHP-1), SHP-2, and PTP1B but not the dual-specificity phosphatase mitogen-activated protein kinase phosphatase 1. Sodium stibogluconate inhibited 99% of SHP-1 activity at 10 micrograms/ml, a therapeutic concentration of the drug for leishmaniasis. Similar degrees of inhibition of SHP-2 and PTP1B required 100 micrograms/ml sodium stibogluconate, demonstrating differential sensitivities of PTPases to the inhibitor. The drug appeared to target the SHP-1 domain because it showed similar in vitro inhibition of SHP-1 and a mutant protein containing the SHP-1 PTPase domain alone. Moreover, it forms a stable complex with the PTPase: in vitro inhibition of SHP-1 by the drug was not removed by a washing process effective in relieving the inhibition of SHP-1 by the reversible inhibitor suramin. The inhibition of cellular PTPases by the drug was suggested by its rapid induction of tyrosine phosphorylation of cellular proteins in Baf3 cells and its augmentation of IL-3-induced Janus family kinase 2/Stat5 tyrosine phosphorylation and proliferation of Baf3 cells. The augmentation of the opposite effects of GM-CSF and IFN-alpha 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.

Sodium stibogluconate (pentostan) overdose in a patient with acquired immunodeficiency syndrome.

A 32-year-old man with acquired immunodeficiency syndrome (AIDS) admitted to the hospital for treatment of visceral leishmaniasis was inadvertently given 10 times the prescribed first dose of sodium stibogluconate ([Sb] 6.5 g instead of 0.65 g). He experienced no immediate major toxicity during the first 48 hours, but a significant rise of pancreatic enzyme activities was observed (amylase at 10 times the upper limit of normal, lipase at 50 times the upper limit of normal) without clinical signs or indications on computed tomography (CT) of pancreatitis. The third day after the overdose, he developed appendicitis, which appeared coincidental; he recovered uneventfully from surgery. Most of the overdose of Sb was eliminated within the first few hours. Pharmacokinetics remained linear; the rapid, long elimination half-lives (2.7 hours and 54 hours, respectively) were similar to those in previously published results. The administration of a chelating agent, dimercaptosuccinic acid (DMSA), 72 hours after the Sb overdose did not modify the pharmacokinetics of the medication.

An experimental model system for leishmaniasis. An ultrastructural study on cultured macrophages exposed to Leishmania parasites and sodium stibogluconate.

To facilitate studies on the effect of chemotherapeutic agents on the host-parasite interaction in leishmaniasis, we have developed an experimental model for infecting mouse peritoneal macrophages in culture with recently-isolated Leishmania donovani promastigotes. As the drug action is often dependent on concentration, the distribution of sodium stibogluconate, which is the commonly used drug for treatment of leishmaniasis, was studied in various parts of the macrophages by energy dispersive X-ray microanalysis. The drug was found to accumulate in secondary lysosomes. The ultrastructural examination, using TEM and SEM, of macrophages, whose secondary lysosomes had been preloaded with gold particles, showed that leishmania parasites are phagocytosed and finally located in secondary lysosomes. Using flameless atomic absorption spectrophotometry, the concentration of Mn, Fe and Cu in promastigotes of Leishmania donovani, Leishmania aethiopica, Leishmania crithidia, Leishmania major and their culture media was estimated. Of the three transition metals, the parasites accumulated only Mn from the medium, which they may use in a primitive defense mechanism against reactive oxygen metabolites produced by macrophages during the respiratory burst associated with phagocytosis.

Immunochemotherapy for intracellular Leishmania donovani infection: gamma interferon plus pentavalent antimony.

To determine if the macrophage-activating T cell lymphokine gamma interferon (IFN-gamma) can enhance the effect of conventional chemotherapy against intracellular Leishmania donovani, we treated human macrophages in vitro with both recombinant (r) IFN-gamma and sodium stibogluconate (Pentostam). After pretreatment with a nonactivating dose of rIFN-gamma (10 U/mL), ineffective concentrations of Pentostam (1 and 5 micrograms/mL) were converted to leishmanistatic concentrations, and a leishmanistatic dose (10 micrograms/mL) was converted to uptake of Pentostam. In a model of visceral leishmaniasis, infected mice were treated with ineffective concentrations of rIFN-gamma (10(4) U) plus suboptimal doses of Pentostam (10 or 50 mg/kg). With combination therapy, the doses of Pentostam required to achieve 50% inhibition or killing of visceral L. donovani were reduced by 10-fold and fourfold, respectively. These results suggest that IFN-gamma therapy may be a useful adjunct in visceral leishmaniasis and illustrate one potential role for IFN-gamma in the treatment of systemic intracellular infections.