Immunopharmacology of gold sodium thiomalate and auranofin (SK&F D-39162): effects on cell-mediated immunity

Recent Advances of Gold Compounds in Anticancer Immunity

In recent years, gold compounds have gained more and more attentions in the design of new metal anticancer drugs. Numerous researches have reported that gold compounds, in addition to their widely studied cytotoxic antitumor effects, also reverse tumor immune escape and directly facilitate the functions of immune cells, leading to enhanced anticancer effects. This review mainly summarizes our current understandings of antitumor effects of gold drugs and their relationships with various aspects of antitumor immunity, including innate immunity, adaptive immunity, immunogenic cell death, and immune checkpoints, as well as their roles in adverse effects. Some recent examples of anticancer gold compounds are highlighted. The property of gold compounds is expected to combine with anticancer immunotherapy, such as immune checkpoint inhibitors, to develop new anticancer therapeutic strategies.

Seleno-auranofin (Et3PAuSe-tagl): synthesis, spectroscopic (EXAFS, 197Au Mössbauer, 31P, 1H, 13C, and 77Se NMR, ESI-MS) characterization, biological activity, and rapid serum albumin-induced triethylphosphine oxide generation

Seleno-auranofin (SeAF), an analogue of auranofin (AF), the orally active antiarthritic gold drug in clinical use, was synthesized and has been characterized by an array of physical techniques and biological assays. The Mössbauer and extended X-ray absorption fine structure (EXAFS) parameters of the solid compound demonstrate a linear P-Au-Se coordination environment at a gold(I) center, analogous to the structure of auranofin. The (31)P, (13)C, and (1)H NMR spectra of SeAF in chloroform solution closely resemble those of auranofin. The (77)Se spectrum consists of a singlet at 481 ppm, consistent with a metal-bound selenolate ligand. The absence of (2)J(PSe) coupling in the (31)P and (77)Se spectra may arise from dynamic processes occurring in solution or because the (2)J(PSe) coupling constants are smaller than the observed bandwidths. Electrospray ionization mass spectrometry (ESI-MS) spectra of SeAF in 50:50 methanol-water exhibited strong signals for [(Et(3)P)(2)Au](+), [(Et(3)PAu)(2)-mu-Se-tagl](+), and [Au(Se-tagl)(2)](-), which arise from ligand scrambling reactions. Three assays of the anti-inflammatory activity of SeAF allowed comparison to AF. SeAF exhibited comparable activity in the topically administered murine arachadonic acid-induced and phorbol ester-induced anti-inflammatory assays but was inactive in the orally administered carrageenan-induced assay in rats. However, in vivo serum gold levels were comparable in the rat, suggesting that differences between the in vivo metabolism of the two compounds, leading to differences in transport to the inflamed site, may account for the differential activity in the carrageenan-induced assay. Reactions of serum albumin, the principal transport protein of gold in the serum, demonstrated formation of AlbSAuPEt(3) at cysteine 34 and provided evidence for facile reduction of disulfide bonds at cysteine 34 and very rapid formation of Et(3)P=O, a known metabolite of auranofin.

Suplatast tosilate (IPD), a new immunoregulator, is effective in vitiligo treatment

The major type of vitiligo is considered to be an autoimmune disorder. Anti-melanocyte antibodies are frequently detected in sera of patients with this disease. Interleukin (IL)-4 released from Th2 cells is an important factor in stimulating autoantibody production by B-cells. In this study, seven patients with vitiligo treated with suplatast tosilate (IPD), three showed repigmentation and improvement of their lesions after administration of the drug. IPD halted the continuous spread of the lesions in three of the other patients, and, in two of them, also reduced microsome test and thyroid test titers. The efficacy of IPD in treating vitiligo was thought to be due to the suppressive effect of this drug on IL-4 production. No side effect was observed. Thus IPD may represent a new alternative in vitiligo treatment due to its inhibition of autoimmunity by the suppression of IL-4.

Auranofin-induced suppression of autoimmune antibody production and inflammation in genetically autoimmune-prone mice

The gold compound auranofin and lobenzarit (CCA) were compared in regard to effects on development of an autoimmune-like disease in MRL/1 mice, which normally develop elevated levels of serum anti-DNA antibodies and rheumatoid factor as well as joint lesions similar to those seen in patients with rheumatoid arthritis. MRL/1 mice, which are genetically prone to development of autoimmune disease, were given auranofin or lobenzarit by gavage for 15 weeks, starting at 6 weeks of age. Mice were examined periodically for immunological abnormalities as well as histologic changes in articular joints. The auranofin-treated mice showed marked diminution in development of anti-DNA antibodies and serum rheumatoid factor as compared to control animals. Although higher than in the auranofin-treated animals, CCA-treated mice also had lower levels of serum autoantibodies than those seen in the control animals. Examination of limb joints for histopathologic changes indicated that the auranofin-treated animals developed only the slightest evidence of lesions as compared to control animals. CCA-treated mice also had a lessening of lesion development compared to control animals, but lesions were more developed than in auranofin-treated mice. This study indicates that auranofin is more effective than CCA in diminishing development of autoimmunity in MRL/1 mice.

Control of oxidative damage in rheumatoid arthritis by gold(I)-thiolate drugs

The roles of anti-arthritic gold(I)-thiolate drugs such as disodium aurothiomalate ('Myocrisin') in the modulation or promotion of oxygen radical-mediated oxidative damage in vivo are reviewed. In particular, the precise molecular mechanisms by which these novel second-line agents exert their therapeutic effects are discussed in terms of (i) the direct and indirect control of enzymes involved in the generation or scavenging of reactive oxygen species (ROS) such as superoxide ion, hydrogen peroxide and hydroxyl radical, (ii) the protection of proteins and relevant enzyme systems against attack by ROS and (iii) their direct involvement in the production (at appropriate 'target' sites) or scavenging of ROS in vivo. In addition, the role of the orally-effective gold(I)-phosphine complex auranofin in the control of oxidative damage in rheumatoid arthritis is also discussed.

The in vivo effect of triethylphosphine gold (auranofin), sodium aurothiomalate and azathioprine on lymphocyte subsets of patients with rheumatoid arthritis

The percentages of CD5+ (pan T), CD8+ (mainly T suppressor) and CD4+ (mainly T helper) cells were studied in 80 patients with rheumatoid arthritis (RA), grouped according to medication into four groups: 1) controls, not receiving remission-inducing therapy, 2) patients on oral gold (triethylphosphine gold, auranofin), 3) patients on parenteral gold (sodium aurothiomalate) and 4) patients on azathioprine. The total number of lymphocytes was not influenced by treatment with auranofin or sodium aurothiomalate, while the number of lymphocytes was depressed in the azathioprine-treated group (P less than 0.01). Neither treatment with azathioprine or parenteral gold, nor treatment with azathioprine influenced the CD4+/CD8+ ratio.

Benign lymphoplasia of the earlobes induced by gold earrings: immunohistologic study on the cellular infiltrates

We report three patients with peculiar nodules of the earlobes that developed a few months after the wearing of pierced-type gold earrings. Biopsy specimens showed dense infiltration of lymphoid cells in the dermis and subcutaneous tissue associated with the formation of lymphoid follicles. The clinical and histologic pictures were similar to those of lymphocytoma cutis. Immunohistologically, the nodular lesions were characterized by the proliferation of T cells, mainly suppressor/cytotoxic T cells, and the presence of histiocytic cells displaying Leu-3a antigens on the surface. Patch tests of aqueous gold compound induced a strong skin reaction. A histologic study of the patch test reaction sites revealed a picture of ordinary allergic contact dermatitis showing that T cells, including both helper and suppressor T cells, invaded the spongiotic epidermis and the papillary dermis. Eosinophils and a few Langerhans cells were also present in the dermal infiltrates. These findings suggest that pierced-type gold earrings induced a long-term dermal response that resulted in producing benign lymphoplasia in the sensitized individuals.

Initial experience with oral gold salts in the treatment of rheumatoid arthritis in patients followed up for one year

Fifteen patients, eight males and seven females, suffering from classic or definite rheumatoid arthritis were treated for 1 year with Auranofin, a new gold salt active by the oral route, different from parenteral gold as far as dosage, mechanism of action and toxicity are concerned. Patients received a dosage of 3 mg twice daily, equivalent to 0.85 mg of elemental gold, in order to evaluate the therapeutic efficacy and tolerability of this new compound. Subjective and objective parameters were monitored during the trial and serum gold levels were assayed every 2 months by atomic absorption spectrophotometry. Our study, which is on-going, shows the therapeutic efficacy of Auranofin which seems better tolerated than parenteral gold salts and will probably become a widely used drug in the long-term treatment of rheumatoid arthritis.

Auranofin. A preliminary review of its pharmacological properties and therapeutic use in rheumatoid arthritis

Auranofin is the first orally active gold compound for the treatment of rheumatoid arthritis. Like other chrysotherapeutic agents, its exact mechanism of action is unknown, but it probably acts via immunological mechanisms and alteration of lysosomal enzyme activity. Although long term clinical experience with auranofin is limited, its efficacy appears to approach that of sodium aurothiomalate. Further comparative studies with aurothioglucose, hydroxychloroquine and D-penicillamine are required before definitive statements can be made regarding the relative efficacy of auranofin and these agents. While patients have demonstrated clinical remission of rheumatoid arthritis in response to auranofin therapy, radiological studies have been inconclusive regarding its effect on the occurrence or progression of erosive lesions. Auranofin is relatively well tolerated in most patients, but diarrhoea, skin rash, and pruritus are sometimes troublesome, and thrombocytopenia and proteinuria are potentially serious side effects which may occur during therapy. Whereas mucocutaneous side effects are more frequent with injectable gold compounds, gastrointestinal reactions are the most common adverse effect seen with auranofin. The frequency of side effects has been similar with auranofin and sodium aurothiomalate, but they are generally less severe with auranofin. While some of the side effects are controlled by a reduction in dosage, temporary or permanent withdrawal of auranofin may be necessary. Auranofin is clearly a useful addition to the limited list of agents with disease-modifying potential presently available for the treatment of rheumatoid arthritis. It will doubtless generate much interest as its final place in therapy becomes better defined through additional well-designed studies and wider clinical experience.

Auranofin: a unique oral chrysotherapeutic agent

Auranofin is a chemically unique gold coordination complex with demonstrated antiarthritic properties on oral administration. Its pharmacokinetic and immunologic profiles are distinct from injectable gold compounds. When auranofin is added to a regimen of salicylates and/or a nonsteroidal antiinflammatory drug for the treatment of RA, significant additional therapeutic benefit is observed. Published studies indicate that auranofin given 6 mg per day approaches the efficacy of parenteral gold salts in the treatment of rheumatoid disease. Noticeable improvement in clinical and laboratory parameters of disease activity has been observed by the third month of auranofin therapy. Further benefit occurs in some patients during the remainder of the first year of treatment. In the more than 3,000 patients treated with auranofin, the most frequently reported side effects were gastrointestinal (mainly diarrhea) and mucocutaneous. Most side effects were mild in nature and the withdrawal rate due to all adverse reactions averaged 11%. Auranofin differs from injectable gold by producing more gastrointestinal but fewer mucocutaneous reactions. The severity of these reactions is less with auranofin and causes fewer withdrawals from therapy.

Comparative investigations of various immunoregulatory substances in the delayed type hypersensitivity test of the mouse

The substances D-penicillamine, auranofin, chloroquine, levamisole, BM 41.332, azimexone, bestatin, methisoprinol (inosiplex), thymosine (fraction 5), indomethacin and cyclophosphamide were examined comparatively in the delayed type hypersensitivity test after oxazolone sensitisation in mice. It was found, that only the basal antirheumatic drugs D-penicillamine, auranofin, chloroquine and levamisole and also BM 41.332 led to a potentiation of the DTH reactions. Methisoprinol, bestatin, azimexone, thymosine fraction 5 and indomethacin had no effect on the DTH, whilst the immunosuppressant cyclophosphamide led to an inhibition of the DTH reaction. It is concluded that this pharmacological model is suitable for screening of new basal drugs for rheumatoid arthritis.

Biologic actions and pharmacokinetic studies of auranofin

The preclinical profiles of auranofin (Ridaura), an oral chrysotherapeutic agent, parenteral gold sodium thiomalate, gold thioglucose, and their respective ligands were compared. Auranofin was more effective than gold sodium thiomalate in suppressing inflammation and stimulating cell-mediated immunity. In contrast to gold sodium thiomalate and gold thioglucose, auranofin inhibited cellular release of lysosomal enzymes, antibody-dependent cellular cytotoxicity, production of antibodies in adjuvant arthritic rats, and antibodies involved in cytotoxicity reactions. The respective ligands were without significant biologic activity. In rats, a higher fraction of gold was associated with blood cells after auranofin administration than after gold sodium thiomalate. The absorption, distribution, metabolism, and excretion of auranofin are uniquely different from other gold compounds.

Mechanism of action, pharmacology, clinical efficacy and side effects of auranofin. An orally administered organic gold compound for the treatment of rheumatoid arthritis

The mechanism of action of auranofin, an oral organic gold compound used in the treatment of rheumatoid arthritis, is probably similar to the previously available parenteral gold compounds. Auranofin affects polymorphonuclear cells and monocytes at lower concentrations than gold sodium thiomalate and generally affects humoral and cell-mediated immunity in the same direction as the latter drug. The pharmacokinetics of auranofin are different from the intramuscular gold compounds. Auranofin is 20-25% orally absorbed and has less total body retention, greater fecal excretion, and less urinary excretion than gold sodium thiomalate. This may be due in part to its differing chemistry, including its lipophilicity and monomeric structure (at least in vitro). While many clinical studies are not yet complete, auranofin (6 mg/day) is clearly more effective than placebo for treating rheumatoid arthritis. Its efficacy relative to gold sodium thiomalate is not clear. Auranofin may be slightly less effective than gold sodium thiomalate, but because it is generally less toxic than intramuscular gold compounds, its therapeutic index may be more favorable.

The pharmacological profile of auranofin, an orally active gold compound

Auranofin (AF; ' Ridaura '), an oral chrysotherapeutic agent, parenteral gold sodium thiomalate (GST) and gold thioglucose (GTG) were evaluated in order to compare their preclinical profiles. AF was found to be more effective than GST and GTG in suppressing inflammation and stimulating cell-mediated immunity. In contrast to GST, AF inhibited cellular release of lysosomal enzymes, antibody-dependent cellular cytotoxicity, production of antibodies in adjuvant arthritic rats, and antibodies involved in cytotoxicity reactions. In pharmacokinetic studies, plasma gold in rats following AF administration, exhibited greater cell association than after GST administration. In conclusion, the pharmacological profile of AF is markedly different from those of GST and GTG and this suggests potential for improvements in chrysotherapy.

Effect of selected immunoregulatory agents on low-grade contact sensitivity

The effect of selected compounds with known immunoregulatory activity was examined in a 45-h sensitization period oxazolone contact-sensitivity reaction. Oxazolone sensitivity was induced by applying 0.1 ml of 5% oxazolone in absolute ethanol to the shaved abdomen of C57Bl/6 mice on day 0. Challenge with oxazolone followed 45 h later and was accomplished by painting a 5% solution of oxazolone in absolute ethanol on the left hindpaw. The response at 24 h was determined plethysmographically. Histamine (0.062-1.0 mg/kg, subcutaneously, twice a day), concanavalin A (0.31-5.0 mg/kg intravenously), penicillamine (6.25-25 mg/kg, subcutaneously), chloroquine (6.25-25 mg/kg, subcutaneously), and thymosin fraction 5 (0.125-1.25 mg/kg subcutaneously) all stimulated the oxazolone reaction when administered on day 0. These data suggest that the low-grade oxazolone response may be a useful assay to detect immunostimulatory activity.

Prevention of peroxidase mediated inhibition of neutrophil motility and lymphocyte transformation by levamisole, OMPI, sodium aurothiomalate, indomethacin and tolmetin in vitro

The effects of sodium aurothiomalate, levamisole, its active metabolite OMPI and the anti-inflammatory agents indomethacin and tolmetin on neutrophil motility and post-phagocytic hexose monophosphate shunt activity, superoxide and H2O2 generation and myeloperoxidase (MPO) mediated iodination of Candida albicans were investigated in vitro. All five agents caused stimulation of neutrophil random motility and migration towards the leucoattractants f-met-met-phe and EAS. Only levamisole caused inhibition of H2O2 and superoxide production, which was associated with inhibition of HMS activity and not related to superoxide scavenging activity. All five agents caused inhibition of MPO mediated iodination of C. albicans. The relationship between inhibition of peroxidase mediated iodination and enhanced motility was further investigated using the horseradish peroxidase (HRP) H2O2/iodide system. Incubation of neutrophils with this system caused inhibition of neutrophil motility. However in the presence of the various drugs neutrophils were protected from inhibition of motility by the HRP/H2O2/iodide system. Further experiments showed that lymphocyte transformation to mitogens was also inhibited by the HRP/H2O2/iodide system. Incubation of lymphocytes with the various drugs prior to exposure to HRP/H2O2/iodide protected the lymphocyte mitogenic responsiveness.

Immunomodulation of delayed hypersensitivity to methylated bovine serum albumin (MBSA) in mice using subliminal and normal sensitization procedures

Delayed hypersensitivity (DH) was induced in the footpads of mice sensitized to methylated bovine serum albumin (MBSA). The magnitude of this DH response increased with increasing sensitizing concentration of MBSA. Levamisole administered 1 hr prior to MBSA challenge stimulated the DH response and this was optimal using subliminal sensitizing concentrations of antigen. A number of antirheumatic agents, immunomodulators mediator antagonists and antiallergics were subsequently examined using the subliminal sensitizing concentration of MBSA. The same drugs were also evaluated using a normal sensitizing procedure. These studies indicate that the sensitizing concentration of antigen is critical in establishing whether a drug will stimulate or suppress a DH response.

Assessment of immune response during chrysotherapy. Comparison of gold sodium thiomalate vs. auranofin

Auranofin (AF) differs significantly from gold sodium thiomalate (GST) in formulation, i.e., aurous gold is stabilized by dual sulfur and phosphorus ligands, has hydrophobic rather than hydrophilic characteristics, and lacks ionic charge. These attributes facilitate: oral absorption of AF, plasma membrane penetration, increase in intracellular lymphocyte gold concentration and perhaps thereby influence lymphocyte function. AF therapy was observed to affect primarily T rather than B lymphocyte function in 16 RA subjects receiving 6 mg of AF per day for an average of 45 weeks (range 20-74 weeks) compared with GST-treated RA subjects. Lymphocytes from AF-treated subjects manifested prompt and sharp declines in mitogen-induced lymphoproliferative response (LPR); suppressed response to skin testing with dinitrochlorobenzene (DNCB); and blebbing of lymphocyte membranes as shown by scanning electron microscopy. Suppression of LPR with AF was approximately 60% after the first week and 80% after 20 weeks of therapy, contrasting with 0% and 30% for the respective intervals in GST-treated subjects. DNCB skin testing of AF patients, indicated 11 of 14, failed to respond, whereas all GST patients responded. Local or systemic fungal, bacterial and/or opportunistic infections were not encountered. The effect of AF on B cell effector function, e.g., suppression of immunoglobulins and rheumatoid factor titer, was less marked when contrasted with GST therapy in RA subjects, as previously reported.

Effect of auranofin on antibody-dependent cellular cytotoxicity (ADCC) mediated by rat peripheral blood polymorphonuclear leukocytes and mononuclear cells

Auranofin and other clinically used gold compounds were evaluated in vitro for effects on antibody-dependent cellular cytotoxicity (ADCC) of L929 fibroblast target cells mediated by adjuvant rat peripheral blood PMNs or mononuclear cells. Auranofin (10 microM) was found to be a potent inhibitor of PMNADCC. In contrast, gold sodium thiomalate (10-100 microM), gold thioglucose (10-1000 microM), and nongold substructures of auranofin (10 microM) were not inhibitory.. In continuous culture, gold sodium thiomalate and relatively low concentrations of auranofin (smaller than or equal to microM) significantly enhanced PMNADCC. Results of pretreatment studies indicate that auranofin's inhibitory activity of PMNADCC is caused by a noncytotoxic effect on PMN function which is not associated with alteration of PMN-target cell contact. In contrast to its inhibitory activity on PMNADCC, auranofin pretreatment of mononuclear cells resulted in enhanced target cell destruction which appeared to correlate with increased mononuclear cell-target cell contact.

Action of gold salts in some inflammatory and immunological models

Several gold salts were compared in kaolin-induced rat paw oedema, u.v. erythema in guinea pigs, delayed type hypersensitivity and humoral immunity in mice, and adjuvant-induced arthritis in the rat. In the latter the additional parameters of serum gold and copper levels and lysosomal enzyme activity were determined. In addition, the in vitro inhibition of several lysosomal enzymes derived from mouse macrophages was studied. The gold compounds examined were aurothiomalate, aurothioglucose, triethylphosphine gold chloride (SK & F 36914) and its glucopyranoside derivative (SK & F D-39162), triphenylphosphine gold chloride and sodium gold chloride dihydrate. SK & F 36914 and SK & F D-39162 has significant activity after oral dosage upon paw kaolin and u.v. erythema in rats and guinea pigs, respectively. Gastric swelling also occurred. In Wistar rats, adjuvant arthritis was little affected by the gold salts but in the Lewis rats there was suppression. In both strains there was less elevation in serum copper levels with treatment by SK & F 36914 and SK & F D-39162, but not by aurothiomalate. None of the compounds had any measurable effect on delayed hypersensitivity or humoral antibody levels in mice. The in vitro activities of cathepsin B1 and cathepsin D were inhibited by all the gold compounds. Reactivity of gold compounds with glutathione and cysteine in vitro was dependent on compound solubility and the nature of the gold ligand. Considerable differences exist between the profiles of activity for the different gold salts evaluated. These observations indicate that some gold salts do possess anti-inflammatory activity with a potency similar to that of indomethacin.