Pentavalent antimony complexes, such as sodium stibogluconate and sodium antimony gluconate (SAG), are still the first choice for chemotherapy against various forms of leishmaniasis, including visceral leishmaniasis, or kala-azar. Although the requirement of a somewhat functional immune system for the antileishmanial action of antimony was reported previously, the cellular and molecular mechanism of action of SAG was not clear. Herein, we show that SAG induces extracellular signal-regulated kinase 1 (ERK-1) and ERK-2 phosphorylation through phosphoinositide 3-kinase (PI3K), protein kinase C, and Ras activation and p38 mitogen-activated protein kinase (MAPK) phosphorylation through PI3K and Akt activation. ERK-1 and ERK-2 activation results in an increase in the production of reactive oxygen species (ROS) 3 to 6 h after SAG treatment, while p38 MAPK activation and subsequent tumor necrosis factor alpha release result in the production of nitric oxide (NO) 24 h after SAG treatment. Thus, this study has provided the first evidence that SAG treatment induces activation of some important components of the intracellular signaling pathway, which results in an early wave of ROS-dependent parasite killing and a stronger late wave of NO-dependent parasite killing. This opens up the possibility of this metalloid chelate being used in the treatment of various diseases either alone or in combination with other drugs and vaccines.Visceral leishmaniasis, caused by Leishmania donovani, is fatal if left untreated. The pentavalent antimony (Sb V ) compound urea stibamine first emerged as an effective chemotherapeutic agent against Indian kala-azar (6). Although different forms of pentavalent antimony complexes (chelates, i.e., Sb V chelated to an organic backbone), namely, sodium stibogluconate (Pentostam) and meglumine antimoniate (Glucantime), are still the first choice for treatment of leishmaniases (21, 42), their mechanism of action is still largely unknown. Previous studies indicated that sodium antimony gluconate (SAG) failed to act in immunocompromised hosts, such as patients who are suffering from AIDS or receiving immunosuppressive agents (17, 38) and nude (36) and severe combined immunodeficient (SCID) mice (15). Several studies have shown that endogenous interleukin-2 (IL-2) (34), IL-4 (1, 43), and IL-12 (41) influence the effectiveness of chemotherapy with pentavalent antimony. These findings are inclined to indicate the requirement of a somewhat functional T-cell compartment for SAG action. Moreover, SAG has been found to inhibit selective protein tyrosine phosphatases (Src homology 2 domain-containing tyrosine phosphatase 1 [SHP1] and SHP2) in vitro and augment cytokine signaling and responses in hematopoietic cell lines (46), suggesting the role of phosphatases and possibly other signal transduction pathways in SAG-induced control of Leishmania infection. In addition, the dose of SAG that kills the axenic amastigotes in vitro is 50 times higher than the concentration of the drug required for killing the parasite w...

The emergence of antimony (Sb) resistance has jeopardized the treatment of visceral leishmaniasis in various countries. Previous studies have considered the part played by leishmanial parasites in antimony resistance, but the involvement of host factors in the clinical scenario remained to be investigated. Here we show that unlike infection with Sb-sensitive (Sb s ) Leishmania donovani, infection with Sb-resistant (Sb r ) L. donovani induces the upregulation of multidrug resistance-associated protein 1 (MRP1) and permeability glycoprotein (P-gp) in host cells, resulting in a nonaccumulation of intracellular Sb following treatment with sodium antimony gluconate (SAG) favoring parasite replication. The inhibition of MRP1 and P-gp with resistance-modifying agents such as lovastatin allows Sb accumulation and parasite killing within macrophages and offers protection in an animal model in which infection with Sb r L. donovani is otherwise lethal. The occurrence of a similar scenario in clinical cases is supported by the findings that unlike monocytes from SAG-sensitive kala-azar (KA) patients, monocytes from SAG-unresponsive KA patients overexpress P-gp and MRP1 and fail to accumulate Sb following in vitro SAG treatment unless pretreated with inhibitors of ABC transporters. Thus, the expression status of MRP1 and P-gp in blood monocytes may be used as a diagnostic marker for Sb resistance and the treatment strategy can be designed accordingly. Our results also indicate that lovastatin, which can inhibit both P-gp and MRP1, might be beneficial for reverting Sb resistance in leishmaniasis as well as drug resistance in other clinical situations, including cancer.The emergence of antimony-resistant (Sb r ) visceral leishmaniasis (VL) in various parts of the world (1,8,17,48) has severely compromised control of the disease. Among alternative drugs, pentamidine is toxic; amphotericin B is both expensive and toxic, with reported cases of resistance (8, 48); and oral miltefosine is limited by cost, contraindications, and emerging resistance (1,8,41,53). Therefore, an understanding of the mode of resistance and an identification of cost-effective therapeutic combinations have become major issues.ATP binding cassette (ABC) transporters have been widely reported to export xenobiotics (24, 55) and cause drug resistance in various diseases such as cancer (23). Earlier studies have reported the expression of analogs of ABC transporters on the surfaces of Sb r strains of Leishmania promastigotes (27, 35, 41), believed to efflux antimonials. However, the demonstration of these transporters in promastigotes may not be very relevant to clinical situations. There are a few reports available on the expression of similar transporters in laboratory isolates of in vitro-developed Sb r strains of leishmanial amastigotes (15) or on amastigotes from field isolates of Sb r L. donovani (10, 51). Although sodium antimony gluconate (SAG) kills leishmanial amastigotes directly at higher doses in vitro as reported previously (54), a much lower dose...

Multidrug resistance (MDR) is still a major threat to successful clinical application of cancer chemotherapy. Copper plays an important role in biological systems, and copper is also involved in carcinogenesis. In the present investigation, we addressed the question whether metal copper might be involved in drug resistance of murine and human tumors. By means of atomic absorption spectroscopy, we determined serum copper concentrations. We found that the blood serum of tumor-bearing mice contained higher amounts of copper than healthy mice with tumors. Secondly, mice bearing doxorubicin-resistant Ehrlich ascites carcinoma- or cyclophosphamide-resistant Lewis lung carcinoma contained more copper in their serum than mice bearing the corresponding drug-sensitive parental tumors. Furthermore, the analysis of patients with breast cancer, colon carcinoma or lung cancer showed that the serum copper contents were higher in patients not responding to chemotherapy when compared to patients whose tumors responded to treatment. The copper levels in serum of healthy volunteers were lower than in cancer patients irrespective of their response to chemotherapy. Our results imply that the level of serum copper may be considered as a biomarker for treatment response.

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Background: In search of a suitable GSH-depleting agent, a novel copper complex viz., copper N-(2-hydroxyacetophenone) glycinate (CuNG) has been synthesized, which was initially found to be a potential resistance modifying agent and later found to be an immunomodulator in mice model in different doses. The objective of the present work was to decipher the effect of CuNG on reactive oxygen species (ROS) generation and antioxidant enzymes in normal and doxorubicin-resistant Ehrlich ascites carcinoma (EAC/ Dox)-bearing Swiss albino mice.