Next Generation Gold Drugs and Probes: Chemistry and Biomedical Applications.

The gold drugs, gold sodium thiomalate (Myocrisin), aurothioglucose (Solganal), and the orally administered auranofin (Ridaura), are utilized in modern medicine for the treatment of inflammatory arthritis including rheumatoid and juvenile arthritis; however, new gold agents have been slow to enter the clinic. Repurposing of auranofin in different disease indications such as cancer, parasitic, and microbial infections in the clinic has provided impetus for the development of new gold complexes for biomedical applications based on unique mechanistic insights differentiated from auranofin. Various chemical methods for the preparation of physiologically stable gold complexes and associated mechanisms have been explored in biomedicine such as therapeutics or chemical probes. In this Review, we discuss the chemistry of next generation gold drugs, which encompasses oxidation states, geometry, ligands, coordination, and organometallic compounds for infectious diseases, cancer, inflammation, and as tools for chemical biology via gold-protein interactions. We will focus on the development of gold agents in biomedicine within the past decade. The Review provides readers with an accessible overview of the utility, development, and mechanism of action of gold-based small molecules to establish context and basis for the thriving resurgence of gold in medicine.

Effects of aurothiomalate treatment on canine osteosarcoma in a murine xenograft model.

Osteosarcoma is a highly fatal cancer, with most patients ultimately succumbing to metastatic disease. The purpose of this study was to evaluate the effects of the antirheumatoid drug aurothiomalate on canine and human osteosarcoma cells and on canine osteosarcoma growth and metastasis in a mouse xenograft model. We hypothesized that aurothiomalate would decrease osteosarcoma cell survival, tumor cellular proliferation, tumor growth, and metastasis. After performing clonogenic assays, aurothiomalate or a placebo was administered to 54 mice inoculated with canine osteosarcoma. Survival, tumor growth, embolization, metastasis, histopathology, cell proliferation marker Ki67, and apoptosis marker caspase-3 were compared between groups. Statistical analysis was carried out using the Kaplan-Meier method with the log-rank test and one-way analysis of variance with the Tukey's test or Dunn's method. Aurothiomalate caused dose-dependent inhibition of osteosarcoma cell survival (P<0.001) and decreased tumor growth (P<0.001). Pulmonary macrometastasis and Ki67 labeling were reduced with low-dose aurothiomalate (P=0.033 and 0.005, respectively), and tumor emboli and pulmonary micrometastases were decreased with high-dose aurothiomalate (P=0.010 and 0.011, respectively). There was no difference in survival, tumor development, ulceration, mitotic indices, tumor necrosis, nonpulmonary metastases, and caspase-3 labeling. Aurothiomalate treatment inhibited osteosarcoma cell survival and reduced tumor cell proliferation, growth, embolization, and pulmonary metastasis. Given aurothiomalate's established utility in canine and human medicine, our results suggest that this compound may hold promise as an adjunctive therapy for osteosarcoma. Further translational research is warranted to better characterize the dose response of canine and human osteosarcoma to aurothiomalate.

Gold(I) ion and the phosphine ligand are necessary for the anti-Toxoplasma gondii activity of auranofin.

Auranofin, an FDA-approved drug for rheumatoid arthritis, has emerged as a promising antiparasitic medication in recent years. The gold(I) ion in auranofin is postulated to be responsible for its antiparasitic activity. Notably, aurothiomalate and aurothioglucose also contain gold(I), and, like auranofin, they were previously used to treat rheumatoid arthritis. Whether they have antiparasitic activity remains to be elucidated. Herein, we demonstrated that auranofin and similar derivatives, but not aurothiomalate and aurothioglucose, inhibited the growth of Toxoplasma gondii in vitro. We found that auranofin affected the T. gondii biological cycle (lytic cycle) by inhibiting T. gondii's invasion and triggering its egress from the host cell. However, auranofin could not prevent parasite replication once T. gondii resided within the host. Auranofin treatment induced apoptosis in T. gondii parasites, as demonstrated by its reduced size and elevated phosphatidylserine externalization (PS). Notably, the gold from auranofin enters the cytoplasm of T. gondii, as demonstrated by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).IMPORTANCEToxoplasmosis, caused by Toxoplasma gondii, is a devastating disease affecting the brain and the eyes, frequently affecting immunocompromised individuals. Approximately 60 million people in the United States are already infected with T. gondii, representing a population at-risk of developing toxoplasmosis. Recent advances in treating cancer, autoimmune diseases, and organ transplants have contributed to this at-risk population's exponential growth. Paradoxically, treatments for toxoplasmosis have remained the same for more than 60 years, relying on medications well-known for their bone marrow toxicity and allergic reactions. Discovering new therapies is a priority, and repurposing FDA-approved drugs is an alternative approach to speed up drug discovery. Herein, we report the effect of auranofin, an FDA-approved drug, on the biological cycle of T. gondii and how both the phosphine ligand and the gold molecule determine the anti-parasitic activity of auranofin and other gold compounds. Our studies would contribute to the pipeline of candidate anti-T. gondii agents.

Phase I dose escalation study of the PKCι inhibitor aurothiomalate for advanced non-small-cell lung cancer, ovarian cancer, and pancreatic cancer.

Protein kinase C iota (PKCι) is overexpressed in non-small-cell lung cancer, ovarian, and pancreatic cancers, where it plays a critical role in oncogenesis. The gold compound aurothiomalate (ATM) has been shown to inhibit PKCι signaling and exerts potent antitumor activity in preclinical models. We sought to determine the maximum tolerated dose (MTD) of ATM. We conducted a phase I dose escalation trial of ATM in patients with non-small-cell lung cancer, ovarian or pancreatic cancer. Patients received ATM intramuscularly weekly for three cycles (cycle duration 4 weeks) at 25, 50, or 75 mg in a 3+3 design. The dose was not escalated for individual patients. Blood samples were analyzed for elemental gold levels. Patients were evaluated every 4 weeks for toxicity and every 8 weeks for response. Fifteen patients were enrolled in this study. Six patients were treated at 25 mg, seven at 50 mg, and two at 75 mg. There was one dose-limiting toxicity at 25 mg (hypokalemia), one at 50 mg (urinary tract infection), and none at 75 mg. There were three grade 3 hematologic toxicities. The recommended MTD of ATM is 50 mg. Patients received treatment for a median of two cycles (range 1-3). There appeared to be a dose-related accumulation of steady-state plasma concentrations of gold consistent with linear pharmacokinetics. In summary, this phase I study was successful in identifying ATM 50 mg intramuscularly weekly as the MTD. Future clinical investigations targeting PKCι are currently in progress.

Conditional pharmacology/toxicology V: ambivalent effects of thiocyanate upon the development and the inhibition of experimental arthritis in rats by aurothiomalate (Myocrysin®) and metallic silver.

This article discusses the bizarre and contrary effects of thiocyanate, the major detoxication product of hydrogen cyanide inhaled from tobacco smoke or liberated from cyanogenic foods, e.g. cassava. Thiocyanate both (1) promotes inflammatory disease in rats and (2) facilitates the anti-inflammatory action of historic metal therapies based on gold (Au) or silver (Ag) in three models of chronic polyarthritis in rats. Low doses of nanoparticulate metallic silver (NMS) preparations, i.e. zerovalent silver (Ag°) administered orally, suppressed the mycobacterial ('adjuvant')-induced arthritis (MIA) in rats. Similar doses of cationic silver, Ag(I), administered orally as silver oxide or soluble silver salts were inactive. By contrast, NMS only inhibited the development of the collagen-induced arthritis (CIA) and pristane-induced arthritis (PIA) in rats when thiocyanate was also co-administered in drinking water. These (a) arthritis-selective and (b) thiocyanate-inducible effects of Ag° were also observed in some previous, and now extended, studies with the classic anti-arthritic drug, sodium aurothiomalate (ATM, Myocrisin(®)) and its silver analogue (STM), administered subcutaneously to rats developing the same three forms of polyarthritis. In the absence of either Ag° or ATM, thiocyanate considerably increased the severity of the MIA, CIA and PIA, i.e. acting as a pro-pathogen. Hitherto, thiocyanate was considered relatively harmless. This may not be true in rats/people with immuno-inflammatory stress and concomitant leukocyte activation. Collectively, these findings show how the drug action of a xenobiotic might be determined by the nature (and severity) of the experimental inflammation, as an example of conditional pharmacology. They also suggest that an incipient toxicity, even of normobiotics such as thiocyanate, might likewise be modulated beneficially by well-chosen xenobiotics (drugs, nutritional supplements, etc.), i.e. conditional toxicology (Powanda 1995). Thus, both the disease and the environment may determine (1) the therapeutic action and/or (2) adverse effect(s) of xenobiotics--and even some normobiotics.

Effect of NF-κB inhibitor aurothiomalate on local inflammation in experimental Th1- and Th2-type immune response.

We compared the effect of NF-κB inhibitor aurothiomalate and voltaren on local inflammation in different types of immune response. Both substances reduced edema caused by sheep erythrocytes (Th1-type immune response) and local immediate-type hypersensitivity response induced with ovalbumin (Th2-dependent response). The anti-inflammatory effects of aurothiomalate were similar to those of voltaren during Th1-type immune response.

Aurothiomalate-Based Drugs as Potentially Novel Agents Against Leishmania major: A Mini Review.

PURPOSE: Leishmaniasis is a major public health problem worldwide in many parts of the world. Current anti-leishmanial drugs have only limited clinical efficacy. Aurothiomalate derivatives are useful for treating rheumatoid arthritis, but have emerged as a promising therapeutic candidate for leishmaniasis. This paper gives a review of the literature about the usefulness of aurothiomalate derivatives against leishmaniasis. METHODS: In this study, we reviewed the proposed mechanisms of action of aurothiomalate and related compounds on the metabolism of L. major and collected data by searching relevant articles. RESULTS: Aurothiomalate-based drugs could be effective against leishmaniasis through two direct and indirect mechanisms: first, cytotoxic effects on parasites via thiomalate's false substrate role in the citric acid cycle against malate; and second, immunosuppressive and anti-inflammatory effects of aurothiomalate derivatives with prostaglandin production inhibitory effects. CONCLUSIONS: The current study documented that aurothiomalate-based drugs could be effective against leishmaniasis through two direct and indirect mechanisms of action. Gold thiomalate as a promising hit should be evaluated against L. major in vitro and in vivo conditions in the future.

Gold sodium thiomalate for the treatment of rheumatoid arthritis in a patient with hepatitis B.

OBJECTIVE: To describe a case of gold sodium thiomalate use for the treatment of rheumatoid arthritis (RA) in a patient with hepatitis B. CASE SUMMARY: A 53-year-old Korean American woman with mild RA and chronic hepatitis B infection was treated for worsening RA symptoms with subcutaneous injections of gold sodium thiomalate for 21 months, with the dosage decreased from the initial 40 mg per week to 40 mg every 3 weeks after 51 weeks of successful treatment. She had undergone treatment for hepatitis B in the past with lamivudine; however, she had not received that medication for at least 1 year prior to initiating treatment with gold sodium thiomalate injections. During the treatment period she achieved remission of RA without a significant elevation of her liver enzyme levels or reactivation of hepatitis B. DISCUSSION: Two main factors influence drug product selection when considering the subset of RA patients with chronic hepatitis B infection: severity of liver function compromise and treatment status of chronic hepatitis B. Our patient did not demonstrate significant liver function compromise, but was not receiving viral suppressive treatment for hepatitis B; therefore, the use of many first-line nonbiologic disease-modifying antirheumatic drugs (DMARDs) was contra-indicated based on current guideline recommendations. Additionally, because the patient had refused viral suppressive therapy, there was great concern with the use of biological DMARDs and potential reactivation of hepatitis B. In the past, gold salts were the standard of care in treating RA until the development of the newer agents and there was some evidence that gold sodium thiomalate could be used with minimal risk of hepatotoxicity. CONCLUSIONS: Gold sodium thiomalate proved to be a safe and effective treatment option in a patient with RA and hepatitis B.

Study of anti-inflammatory action of aurothiomalate, an inhibitor of NF-κB.

We compared the effects of NF-κB inhibitor aurothiomalate and voltaren on NO production by mouse macrophages in vitro, their ability to cause local edema at the site of injection, and their effect on carrageenan-induced inflammation. High concentrations of aurothiomalate reduced NO production, while in low concentrations both aurothiomalate and voltaren stimulated this process. When injected into mouse footpad, aurothiomalate in a dose >1 mM and voltaren in a dose >1.6 µM induce paw edema. Both compounds suppressed carrageenan-induced inflammation, but the efficacy of aurothiomalate 2-fold exceeded that of voltaren.

Successful treatment of juvenile pemphigus foliaceus in a Nigerian Dwarf goat.

CASE DESCRIPTION-A 2-month-old female Nigerian Dwarf goat was evaluated for a generalized crusting dermatitis; signs of depression; and fever of 1 month's duration. CLINICAL FINDINGS-Histologic evaluation of skin biopsy specimens revealed subcorneal pustules and rafts of acantholytic cells. No etiologic agents were detected in the biopsy material, and bacterial culture of skin biopsy specimens yielded no growth of pathological organisms. A diagnosis of pemphigus foliaceus was made. TREATMENT AND OUTCOME-Remission was achieved with a combination of SC administration of dexamethasone and IM administration of gold sodium thiomalate. The goat remained free of clinical signs for at least 26 months after discontinuation of all medications. No clinically apparent adverse effects of treatment were evident. CLINICAL RELEVANCE-This report represents the first description of successful treatment of juvenile pemphigus foliaceus in a goat by use of a novel protocol involving dexamethasone and gold sodium thiomalate.

Disability measured by the modified health assessment questionnaire in early rheumatoid arthritis: prognostic factors after two years of follow-up.

OBJECTIVE: To analyze the rate and baseline prognostic factors of disability measured by the modified HAQ (MHAQ), in a series of patients with early rheumatoid arthritis (RA) after two years of therapy with a structured algorithm using disease-modifying anti-rheumatic drugs (DMARDs). METHODS: One hundred and five patients (81% female) with early RA (disease duration <2 years) treated with the same therapeutic protocol using gold salts and methotrexate in a step-up strategy, together with methylprednisolone (4 mg/day), were followed up for two years. The outcome was the absence of disability (MHAQ=0) after two years of DMARD therapy. Clinical, biological, immunogenetic and radiographic data (Larsen score) were analyzed at study entry and at 12 and 24 months of follow-up. RESULTS: The MHAQ decreased significantly at 6 months after initiation of DMARD therapy and the reduction was maintained at 24 months (mean+/-SD: 0.97+/-0.56 at baseline, 0.51+/- 0.57 at month 6 and 0.45+/-0.5 at month 24). No disability (MHAQ=0) was observed in 26.6% of patients after two years of follow-up. Age, MHAQ>0.5, DAS28>5.1, VAS pain, positive rheumatoid factor and ESR at baseline were associated with disability in the univariate analysis. In the logistic regression analysis, only age (OR: 1.058, 95%CI 1.017; 1.101 p<0.006), rheumatoid factor status (OR: 3.772 95%CI 1.204; 11.813, p<0.02) and MHAQ>0.5 (OR:4.023, 95%CI 1.373; 11.783, p<0.02) were associated with disability (MHAQ>0) at two years. CONCLUSION: In a series of early RA patients treated with a structured algorithm using DMARDs and very low doses of glucocorticoids, no disability was observed in a quarter of patients after two years. Age, rheumatoid factor positivity and MHAQ>0.5 were independent predictors of disability at two years.

Pivotal advance: inhibition of HMGB1 nuclear translocation as a mechanism for the anti-rheumatic effects of gold sodium thiomalate.

Gold compounds such as gold sodium thiomalate (GST) can reduce the symptoms of rheumatoid arthritis (RA), although their mechanism of action is not well defined. As the proinflammatory mediator high mobility group box chromosomal protein 1 (HMGB1) may play a role in the pathogenesis of RA, we have performed in vitro studies to investigate whether GST inhibits HMGB1 release as the basis of its mode of action. Murine RAW 264.7 or human THP-1 macrophage cells were stimulated in culture with agents causing extracellular HMGB1 release, including LPS, IFN-gamma, polyinosinic:polycytidylic acid, IFN-beta, or NO in the presence of GST, ranging from 0 microM to 250 microM. Secretion and intracellular location of HMGB1 were assessed by Western blotting, HMGB1-specific ELISPOT assay, and immunofluorescent staining. In parallel, TNF and IFN-beta levels were analyzed by ELISPOT and/or ELISA. Supernatant NO production was analyzed by the Griess method. At pharmacologically relevant doses, GST inhibited the extracellular release of HMGB1 from activated macrophages and caused the nuclear retention of this protein; in contrast, no effects were observed on the secretion or production of TNF. Release of the key endogenous mediators of HMGB1 translocation, IFN-beta and NO, was inhibited by GST. This inhibition required gold, as sodium thiomalate did not affect the responses measured. Furthermore, gold chloride also inhibited release of HMGB1. Together, these results suggest a new mechanism for the anti-rheumatic effects of gold salts in RA and the potential of drugs, which interfere with intracellular HMGB1 transport mechanisms, as novel agents to treat RA.

[Effect of disease modifying anti-rheumatic drugs on radiographic progression in rheumatoid arthritis].

Because of a paradigm shift in the therapeutic strategy of RA by biologics, the goal of RA therapy became not only the clinical remission, but also the imaging remission. From the results of randomized controlled clinical trials of disease modifying anti-rheumatic drugs (DMARDs), decreased radiographic progression has been documented. In particular, methotrexate (MTX) is described as "anchor drug" of RA therapy because inhibitory effects of MTX on radiographic progression are proved by many clinical trials. Although DMARDs can slow down the radiographic progression with the achievement of clinical remission in RA, some patients still have subclinical synovitis detected by imaging technique. Such subclinical inflammation may explain the observed discrepancy between disease activity and radiographic progression in RA during DMARD therapy.

Prognostic markers of clinical remission in early rheumatoid arthritis after two years of DMARDs in a clinical setting.

OBJECTIVE: To analyze the rate and baseline prognostic factors of clinical remission in a series of patients with early rheumatoid arthritis (RA) after 2 years of therapy based on a structured algorithm using disease-modifying anti-rheumatic drugs (DMARDs) in a clinical setting. To determine whether a good therapeutic response at 6 months of therapy is associated with remission at 2 years. METHODS: One hundred and five patients (81% female) with early RA (disease duration < 2 years) treated with the same therapeutic protocol using gold salts and methotrexate in a step-up strategy, together with methylprednisolone (4 mg/day), were followed up for 2 years. The outcome variable was clinical remission after 2 years of DMARD therapy using the 28-joint disease activity score (DAS28 < 2.6). Clinical, biological, immunogenetic and radiographic data (Larsen score) were analyzed at study entry and after 6, 12, 18 and 24 months of follow-up. Therapeutic response was analyzed using the ACR and EULAR criteria. RESULTS: Remission was observed in 34 patients (32.4%) after 2 years of follow-up. A baseline DAS28 score < 5.1 (p = 0.004), hemoglobin (p = 0.04) and male gender (p = 0.02) were associated with remission in the univariate analysis. In the multivariate logistic regression analysis, only a DAS28 < 5.1 was associated with remission at 2 years (OR 4.1, 95% CI: 1.56;10.77, p = 0.004). The percentage of ACR50 responses after 6 months was significantly higher in patients with remission at 2 years than in those without (66.7% vs 43.3%; p = 0.04). Similar results were obtained when analyzing the good EULAR response (50% vs 20.9%; p = 0.003). Furthermore, when the therapeutic response at 6 months was included in the logistic regression model, only an ACR50 response (OR 3.9, 95% CI 1.14;13.38, p = 0.03) and a good EULAR response (OR 6.23, 95% CI 1.61; 24.04, p = 0.008), but not an ACR20 response or a whole EULAR response were significantly associated with remission. CONCLUSION: In a series of early RA patients treated using a structured algorithm with DMARDs and very low doses of glucocorticoids, clinical remission was observed in one-third of patients after 2 years. Low or moderate disease activity (DAS28 < 5.1) at baseline and a good therapeutic response during the first months of therapy predicts clinical remission at 2 years.

Liposome encapsulated aurothiomalate reduces collagen-induced arthritis in DBA/1J mice.

Collagen-induced arthritis (CIA) generated in rats or mice has long been a model system for the study of rheumatoid arthritis in humans. In particular, this system has been used to study the mechanisms and effects of anti-arthritic drugs in the treatment of the disease. Sodium aurothiomalate (ATM) is an agent often used to treat rheumatoid arthritis in humans; however, it possesses inherent toxicities which limits its usefulness. Liposome-encapsulated drugs are currently being developed to minimize the toxicities associated with a variety of potentially beneficial drugs. We have chosen to encapsulate ATM into small unilamellar vesicles (SUVs) to determine whether greater efficacy would be achieved in treating CIA with SUV ATM as compared to using the free drug. SUVs were prepared from hydrogenated egg phosphatidylcholine and cholesterol. These SUVs were very stable. Vesicles stored at 4 degrees C lost only 0.09% of encapsulated ATM (SUV ATM) after 14 days and were able to reduce collagen-induced arthritis in these mice. Animals treated by i.m. injections of SUV ATM exhibited a 50% reduction in symptoms. More importantly, histological examination of knee joints of the affected animals verified that SUV ATM treatment prevented cellular infiltration of lymphocytes into the synovia of the collagen-sensitized mice. Conditioned media from spleen cell cultures was assayed for the presence of inflammatory lymphokines that might be affected by SUV ATM to account for the success in suppressing collagen-induced arthritis.

Ankylosing spondylitis and rheumatoid arthritis in a patient with Paget's disease. Differential effects of indomethacin, D-penicillamine, or gold sodium thiomalate in the respective arthritides.

A patient developed both ankylosing spondylitis and rheumatoid arthritis, each of which responded to D-penicillamine or gold sodium thiomalate and indomethacin, respectively. The patient was both HLA-B27 and -DR4 positive. In addition, he was found to have Paget's disease of bone, which has required no treatment.

[Pemphigus foliaceus in a Haflinger gelding]. / Pemphigus foliaceus bei einem Haflingerwallach.

A 10-year-old Haflinger gelding was presented with severe generalized chronic dermatitis characterized by scales, crusts and widespread alopecia with a partially diffuse and partially circumscribed pattern. Pemphigus foliaceus was diagnosed based on history, clinical signs and histological examination of skin biopsies. Typical histological findings were subcorneal pustules with accumulations of intact neutrophil granulocytes and acantholytic keratinocytes. The gelding was treated with glucocorticoids and gold salts. The skin lesions resolved completely after 8 weeks of treatment. No recurrence was observed within 1 year.

The quantitative distribution of gold in skin during chrysotherapy.

Gold concentrations in epidermis, dermis, and whole skin were measured by neutron activation analysis after formation of suction bullae in 8 patients who had received protracted cyrysotherapy. Epidermis contained 3% (median) of the gold content of whole skin. A direct correlation between cumulative gold dose and skin gold level was noted. These findings suggest that apparent gold concentrations in skin are influenced by the depth of the biopsy, that keratinous tissues have little affinity for gold, and that the gold storage capability of skin is not saturated by large cumulative doses of gold. The beneficial effect of gold in pemphigus may not be mediated at the site of blister formation.