Immunopharmacological profile of a novel isoxazol derivative, HWA 486, with potential antirheumatic activity--I. Disease modifying action on adjuvant arthritis of the rat

Isoxazole compounds: Unveiling the synthetic strategy, in-silico SAR & toxicity studies and future perspective as PARP inhibitor in cancer therapy

Latest developments in cancer treatment have shed a light on the crucial role of PARP inhibitors that enhance the treatment effectiveness by modifying abnormal repair pathways. PARP inhibitors, such as Olaparib, Rucaparib, Niraparib, and Talazoparib have been approved in a number of cancers including BRCA 1/BRCA2 associated malignancies although there are many difficulties as therapeutical resistance. Besides the conventional synthetic drugs, natural compounds such as flavones and flavonoids have been found to be PARP inhibitors but only in preclinical studies. Isoxazole is very important class of potential candidates for medicinal chemistry with anti-cancer and other pharmacological activities. At present, there are no approved PARP inhibitors of isoxazole origin but their ability to hit many pathways inside the cancer cells points out on its importance for future treatments design. In drug development, isoxazoles are helpful because of the molecular design flexibility that may be enhanced using various synthetic approaches. This review highlights the molecular mechanisms of PARP inhibition, importance of isoxazole compounds and present advances in their synthetic strategies that demonstrate promise for these agents as new anticancer drugs. It emphasizes that isoxazole-based PARP inhibitors compounds could be novel anti-cancer drugs. Through this review, we hope to grow a curiosity in additional explorations of isoxazole-based PARP inhibitors and their applications in the trends of novel insights towards precision cancer therapy.

Is Target-Based Drug Discovery Efficient? Discovery and "Off-Target" Mechanisms of All Drugs

Target-based drug discovery is the dominant paradigm of drug discovery; however, a comprehensive evaluation of its real-world efficiency is lacking. Here, a manual systematic review of about 32000 articles and patents dating back to 150 years ago demonstrates its apparent inefficiency. Analyzing the origins of all approved drugs reveals that, despite several decades of dominance, only 9.4% of small-molecule drugs have been discovered through "target-based" assays. Moreover, the therapeutic effects of even this minimal share cannot be solely attributed and reduced to their purported targets, as they depend on numerous off-target mechanisms unconsciously incorporated by phenotypic observations. The data suggest that reductionist target-based drug discovery may be a cause of the productivity crisis in drug discovery. An evidence-based approach to enhance efficiency seems to be prioritizing, in selecting and optimizing molecules, higher-level phenotypic observations that are closer to the sought-after therapeutic effects using tools like artificial intelligence and machine learning.

Epigenetic landscape of drug responses revealed through large-scale ChIP-seq data analyses

Background

Elucidating the modes of action (MoAs) of drugs and drug candidate compounds is critical for guiding translation from drug discovery to clinical application. Despite the development of several data-driven approaches for predicting chemical–disease associations, the molecular cues that organize the epigenetic landscape of drug responses remain poorly understood.

Results

With the use of a computational method, we attempted to elucidate the epigenetic landscape of drug responses, in terms of transcription factors (TFs), through large-scale ChIP-seq data analyses. In the algorithm, we systematically identified TFs that regulate the expression of chemically induced genes by integrating transcriptome data from chemical induction experiments and almost all publicly available ChIP-seq data (consisting of 13,558 experiments). By relating the resultant chemical–TF associations to a repository of associated proteins for a wide range of diseases, we made a comprehensive prediction of chemical–TF–disease associations, which could then be used to account for drug MoAs. Using this approach, we predicted that: (1) cisplatin promotes the anti-tumor activity of TP53 family members but suppresses the cancer-inducing function of MYCs; (2) inhibition of RELA and E2F1 is pivotal for leflunomide to exhibit antiproliferative activity; and (3) CHD8 mediates valproic acid-induced autism.

Conclusions

Our proposed approach has the potential to elucidate the MoAs for both approved drugs and candidate compounds from an epigenetic perspective, thereby revealing new therapeutic targets, and to guide the discovery of unexpected therapeutic effects, side effects, and novel targets and actions.

Amelioration of complete Freund’s adjuvant-induced arthritis by Calotropis procera latex in rats

Background

Rheumatoid arthritis is the most common cause of disability, affecting 0.3–1% of the adult population worldwide. The latex of Calotropis procera possesses potent anti-inflammatory as well as analgesic properties. In light above facts, the present study was designed to evaluate anti-arthritic activity of Calotropis procera latex in complete Freund's adjuvant (CFA)-induced arthritis in Wistar albino rats. Complete Freund's adjuvant was injected into the left hind paw on day 0, and treatment of prednisolone and Calotropis procera latex was given from day 0 to 28. Various biochemical, hematological and functional parameters as well as radiological and histopathological changes of joint along with body weight and paw volume were measured.

Results

Calotropis procera treatment significantly lowered paw volume in CFA-induced arthritic rats. Significant improvement was observed in functional, biochemical and hematological parameters in Calotropis procera-treated rats. However, the body weight remained unaffected. Histological and radiographical examination of synovial joints in Calotropis procera-treated animals exhibited less synovial hyperplasia, infiltration and accumulation of inflammatory cell in synovial fluid, cartilage and bone erosion and joint space narrowing.

Conclusion

Calotropis procera latex possesses anti-arthritic activity, which is facilitated by modulation in the level of inflammatory mediators and oxidative stress. The improvement in hematological as well as biochemical parameters might be reflected on functional, histopathological, radiological changes and thereby disease progression.

DHODH and cancer: promising prospects to be explored

Human dihydroorotate dehydrogenase (DHODH) is a flavin-dependent mitochondrial enzyme catalyzing the fourth step in the de novo pyrimidine synthesis pathway. It is originally a target for the treatment of the non-neoplastic diseases involving in rheumatoid arthritis and multiple sclerosis, and is re-emerging as a validated therapeutic target for cancer therapy. In this review, we mainly unravel the biological function of DHODH in tumor progression, including its crucial role in de novo pyrimidine synthesis and mitochondrial respiratory chain in cancer cells. Moreover, various DHODH inhibitors developing in the past decades are also been displayed, and the specific mechanism between DHODH and its additional effects are illustrated. Collectively, we detailly discuss the association between DHODH and tumors in recent years here, and believe it will provide significant evidences and potential strategies for utilizing DHODH as a potential target in preclinical and clinical cancer therapies.

Leflunomide an immunomodulator with antineoplastic and antiviral potentials but drug-induced liver injury: A comprehensive review

Leflunomide (LF) represents the prototype member of dihydroorotate dehydrogenase (DHODH) enzyme inhibitors. DHODH is a mitochondrial inner membrane enzyme responsible for catalytic conversion of dihydroorotate into orotate, a rate-limiting step in the de novo synthesis of the pyrimidine nucleotides. LF produces cellular depletion of pyrimidine nucleotides required for cell growth and proliferation. Based on the affected cells the outcome can be attainable as immunosuppression, antiproliferative, and/or the recently gained attention of the antiviral potentials of LF and its new congeners. Also, protein tyrosine kinase inhibition is an additional mechanistic benefit of LF, which inhibits immunological events such as cellular expansion and immunoglobulin production with an enhanced release of immunosuppressant cytokines. LF is approved for the treatment of autoimmune arthritis of rheumatoid and psoriatic pathogenesis. Also, LF has been used off-label for the treatment of relapsing-remitting multiple sclerosis. However, LF antiviral activity is repurposed and under investigation with related compounds under a phase-I trial as a SARS CoV-2 antiviral in cases with COVID-19. Despite success in improving patients' mobility and reducing joint destruction, reported events of LF-induced liver injury necessitated regulatory precautions. LF should not be used in patients with hepatic impairment or in combination with drugs elaborating a burden on the liver without regular monitoring of liver enzymes and serum bilirubin as safety biomarkers. This study aims to review the pharmacological and safety profile of LF with a focus on the LF-induced hepatic injury from the perspective of pathophysiology and possible protective agents.

Leflunomide ameliorates experimental autoimmune myasthenia gravis by regulating humoral and cellular immune responses

Leflunomide, an immunosuppressive disease-modifying anti-rheumatic drug (DMARD), is widely used in the treatment of rheumatoid arthritis (RA), psoriatic arthritis (PA) as well as multiple sclerosis. However, its role in myasthenia gravis (MG) has not yet been clearly explored. Here, we investigated the effect of leflunomide on experimental autoimmune myasthenia gravis (EAMG) in vivo and in vitro. The results demonstrated that leflunomide alleviated the severity of EAMG associated with reduced serum total anti-acetylcholine receptor (AChR) IgG levels. During the development of EAMG, the increase of follicular helper T cells (Tfh) 1, Tfh 17 cells and decrease of follicular regulatory T cells (Tfr) were reversely altered after leflunomide administration. Our work further found that leflunomide might inhibit Tfh cells through the IL-21/STAT3 pathway to reduce the secretion of antibodies by B cells. In addition, leflunomide rebuilt the balance of Th1/Th2/Th17/Treg subsets. These results suggested that leflunomide ameliorated EAMG severity by regulating humoral immune responses and Th cell profiles thereby providing a novel effective treatment strategy for MG.

Diacetylcurcumin: Its Potential Antiarthritic Effect on a Freund's Complete Adjuvant-Induced Murine Model

The present study aims to evaluate the antiarthritic activity of diacetylcurcumin (DAC), a synthetic derivative where the free phenolic groups of curcumin are derivatized by acetylation, thereby conferring greater lipophilicity to the parent molecule and partially overcoming the limited systemic bioavailability of curcumin. Antiarthritic activity was evaluated on a Freund’s complete adjuvant (FCA)-induced murine model of arthritis. Oral administration of DAC (60 and 120 mg/kg) resulted in a significant inhibition of inflammation in the acute and chronic phases, respectively, demonstrating an improved and sustained anti-inflammatory effect, comparable to that of curcumin (150 mg/kg) in the chronic stage at a lower dose. Phenylbutazone (80 mg/kg) was used as a reference drug. The pharmacological consequence of DAC or curcumin treatment is the prevention of secondary lesions commonly associated with this biological model.

Isoxazole Derivatives as Regulators of Immune Functions

In this review, we present reports on the immunoregulatory properties of isoxazole derivatives classified into several categories, such as immunosuppressive, anti-inflammatory, immunoregulatory, and immunostimulatory compounds. The compounds were tested in various models using resident cells from rodents and humans, cell lines, and experimental animal disease models corresponding to human clinical situations. Beneficial features of the described isoxazole derivatives include low toxicity and good bioactivity at low doses. In a majority of studies, the activities of investigated compounds were comparable or even higher than registered reference drugs. Whenever possible, a plausible mechanism of action of the investigated compounds and their potential therapeutic utility were proposed. Among the described compounds, particular attention was paid to the class of immune stimulators with a potential application in chemotherapy patients.

Facile and highly diastereo and regioselective synthesis of novel octahydroacridine-isoxazole and octahydroacridine-1,2,3-triazole molecular hybrids from citronella essential oil

A novel and highly efficient synthetic approach for the expedite construction of new octahydroacridine-isoxazole- and octahydroacridine-1,2,3-triazole-based molecular hybrids is first reported. Rapid access to the octahydroacridine core was achieved in a highly diastereoselective fashion via cationic Povarov reaction of N-propargyl anilines and citronella essential oil (Cymbopogon nardus). The subsequent 1,3-dipolar and Cu (I) catalyzed alkyne-azide cycloaddition reaction of the terminal alkyne fragment with the corresponding oxime or azide affords the desired 3,5-isoxazoles and 1,2,3-triazoles, respectively, as interesting molecular hybrid models for pharmacological studies.

From Leflunomide to Teriflunomide: Drug Development and Immunosuppressive Oral Drugs in the Treatment of Multiple Sclerosis

BACKGROUND

Immunosuppressive drugs have been used in the treatment of multiple sclerosis (MS) for a long time. Today, orally available second generation immunosuppressive agents have been approved or are filed for licensing as MS therapeutics. Due to semi-selective targeting of cellular processes, these second-generation immunosuppressive compounds might rather be immunomodulatory. For example, Teriflunomide inhibits the de novo pyrimidine synthesis and thus only targets rapidly proliferating cells, including lymphocytes. It is used as first line disease modifying therapy (DMT) in relapsing-remitting MS (RRMS).

METHODS

Review of online content related to oral immunosuppressants in MS with an emphasis on Teriflunomide.

RESULTS

Teriflunomide and Cladribine are second-generation immunosuppressants that are efficient in the treatment of MS patients. For Teriflunomide, a daily dose of 14 mg reduces the annualized relapse rate (ARR) by more than 30% and disability progression by 30% compared to placebo. Cladribine reduces the ARR by about 50% compared to placebo but has not yet been licensed due to unresolved safety concerns. We also discuss the significance of older immunosuppressive compounds including Azathioprine, Mycophenolate mofetile, and Cyclophosphamide in current MS therapy.

CONCLUSION

Teriflunomide has shown a favorable safety and efficacy profile in RRMS and is a therapeutic option for a distinct group of adult patients with RRMS.

Methods for Testing Immunological Factors

Hypersensitivity reactions can be elicited by various factors: either immunologically induced, i.e., allergic reactions to natural or synthetic compounds mediated by IgE, or non-immunologically induced, i.e., activation of mediator release from cells through direct contact, without the induction of, or the mediation through immune responses. Mediators responsible for hypersensitivity reactions are released from mast cells. An important preformed mediator of allergic reactions found in these cells is histamine. Specific allergens or the calcium ionophore 48/80 induce release of histamine from mast cells. The histamine concentration can be determined with the o-phthalaldehyde reaction.

Risk stratification and mitigation multiple sclerosis

The increasing availability of new agents to treat multiple sclerosis poses new challenges for clinicians who seek therapies that are both safe and effective for their patients. The introduction of additional effective therapies has been accompanied by the recognition of serious side effects. The clinician now must weigh both the benefits and risks of therapies to help patients decide which treatment best fits each patient׳s risk/benefit profile. An optimal selection of therapies relies on a complete understanding of the risks of therapies and the factors that may help evaluate and mitigate those risks. An individualized treatment approach that incorporates patient and disease factors is needed for each patient. In this review we present risk stratification and mitigation strategies of disease modifying agents for multiple sclerosis.

Teriflunomide for oral therapy in multiple sclerosis

Teriflunomide, the active metabolite of an approved antirheumatic drug, is an emerging oral therapy for multiple sclerosis (MS). Next to the inhibition of pyrimidine biosynthesis and proliferation of activated lymphocytes, it seems to have multiple anti-inflammatory and immunomodulating effects. Phase II and III clinical trials in relapsing MS demonstrated favorable safety and tolerability of the drug, as well as clinical efficacy, with a significant reduction of relapse rate, comparable with those of the available injectable immunomodulatory agents. While multiple other studies with teriflunomide are currently ongoing, its exact place in future treatment algorithms for MS is difficult to predict. It may be a good alternative for patients wishing to have an oral treatment with relatively large data regarding long-term safety.

An update of teriflunomide for treatment of multiple sclerosis

There are a number of oral agents emerging as potential disease-modifying agents in multiple sclerosis (MS). Among these investigational agents, teriflunomide has shown promise in large, multicenter, phase III clinical trials with respect to safety and efficacy in relapsing MS patients, and is the latest disease-modifying agent approved for use in MS patients in the United States. This review will summarize teriflunomide’s historical development, clinical pharmacology, studies in animals, clinical trials, and safety data, and will end with a discussion of the role of teriflunomide in MS in the context of existing treatment options.

Differentiation and function of human monocyte-derived dendritic cells under the influence of leflunomide

Leflunomide is an immunosuppressive drug effective in experimental models of transplantation and autoimmune diseases and in the treatment of active rheumatoid arthritis (RA). Having in mind that it has been shown that some other immunosuppressive drugs (glucocorticoids, mycophenolate mofetil, sirolimus etc.) impair dendritic cell (DC) phenotype and function, we investigated the effect of A77 1726, an active metabolite of leflunomide, on the differentiation and function of human monocyte-derived dendritic cells (MDDC) in vitro. Immature MDDC were generated by cultivating monocytes in medium supplemented with GM-CSF and IL-4. To induce maturation, immature MDDC were cultured for 2 additional days with LPS. A77 1726 (100 ?M) was added at the beginning of cultivation. Flow cytometric analysis showed that MDDC differentiated in the presence of A77 1726 exhibited an altered phenotype, with a down-regulated surface expression of CD80, CD86, CD54 and CD40 molecules. Furthermore, the continuous presence of A77 1726 during differentiation and maturation prevented successful maturation, judging by the decreased expression of maturation marker CD83, costimulatory and adhesive molecules on A77 1726-treated mature MDDC. In addition, A77 1726-pretreated MDDC exhibited a poor stimulatory capacity of the allogeneic T cells and a low production of IL-10 and IL-18. These data suggest that leflunomide impairs the differentiation, maturation and function of human MDDC in vitro, which is an additional mechanism of its immunosuppressive effect.

Leflunomide in the treatment of rheumatoid arthritis

Rheumatoid arthritis is a chronic and highly morbid disease affecting approximately 1% of the world's population. With the advent of disease-modifying antirheumatic drugs, patients are increasingly able to maintain control of their arthritis and prevent joint destruction. However, not all patients respond adequately to any single disease-modifying antirheumatic drug, and many newer parenteral therapies are cost prohibitive. Leflunomide, an inhibitor of pyrimidine biosynthesis, is the first oral disease-modifying antirheumatic drug to have been approved for rheumatoid arthritis in the USA in the last 15 years, and is now widely used in over 70 countries around the world. Leflunomide is efficacious when used as monotherapy or in combination with methotrexate to treat patients with rheumatoid arthritis, and is generally well tolerated. As clinical use increases, new ways to use leflunomide in order to minimize toxicity and maximize efficacy are being explored.

1-[(E)-(3,4-Dimethylisoxazol-5-yl)iminomethyl]-2-naphthol

The title Schiff base compound, C₁₆H₁₄N₂O₂, has been synthesized by the reaction of 5-amino-3,4-dimethyl­isoxazole and 2-hydr­oxy-1-naphthaldehyde. The dihedral angle between the isoxazole ring and the napthyl ring system is 3.29 (7)°. The mol­ecule adopts an E configuration about the central C=N double bond. Intra­molecular O—H⋯N hydrogen bonding generates an S(6) ring motif. In the crystal structure, π–π inter­actions are observed involving the isoxazole ring and the substituted benzene ring of the naphthyl unit, with centroid–centroid distances of 3.5200 (10) Å.

Leflunomide induces immunosuppression in collagen-induced arthritis rats by upregulating CD4+CD25+ regulatory T cells

This study was to investigate the effect of leflunomide on the immunosuppressive CD4+CD25+ regulatory T cells (CD4+CD25+ Tregs) in collagen-induced arthritis (CIA) rats. CIA was induced by collagen type II in Wistar rats. Immunofluorescence flow cytometry and RT-PCR were used to determine the proportion of CD4+CD25+ Tregs and the expression of Foxp3 mRNA, respectively. Proliferation of T lymphocytes was assayed with MTT reagent, and the level of transforming growth factor β1 (TGF-β1) in the supernatant of concanavalin A (Con A)-induced T lymphocytes was determined by ELISA kit. Our investigations demonstrated that inhibition of arthritis by leflunomide was related to changes in CD4+CD25+ Tregs. In addition, A771726, which is the active metabolite of leflunomide, promoted the differentiation of spleen lymphocytes into CD4+CD25+ Tregs, increased antiinflammatory cytokine TGF-β1 secretion, and adjusted the activity of Con A-induced lymphocytes in vitro.

Disease-Modifying Antirheumatic Drug Use in the Elderly Rheumatoid Arthritis Patient

During the 10-year period since the last review was done by Gardner and Furst, studies have furthered the knowledge of the use of disease-modifying antirheumatic drugs (DMARDs) in the elderly rheumatoid arthritis (RA) patient. This article briefly reviews the clinical pharmacology of humans as they age, and details the effects of aging on the specific pharmacokinetics and responses to commonly used DMARDs. There has been some progress in understanding the elderly RA patient; however, data are insufficient to provide much confidence in DMARDs effects in the elderly.

High-turnover osteoporosis is induced by cyclosporin A in rats

Cyclosporin A (CsA) is used widely as an immunosuppressive agent, but it induces osteoporosis as a prominent side effect. To elucidate the mechanisms involved in CsA-induced osteoporosis, the effects of CsA on bone metabolism were investigated in a rat experimental model. Fifteen-day-old rats were fed a powdered diet containing or lacking CsA for 8-30 days. Analysis was performed by micro-computed tomography (muCT) and light microscopy to examine histomorphometric changes in rat tibiae on days 8, 16, and 30. Plasma parathyroid hormone (PTH) and osteocalcin (OCN) levels were determined by enzyme-linked immunosorbent assay (ELISA) on days 8, 16, and 30. The expression of OCN, osteopontin (OPN), and cathepsin K mRNAs in tibial bone marrow was examined by Northern blot analysis on days 8 and 16. Although no significant differences were observed in tibial length during the experimental periods, or in histomorphometric parameters on day 8, an apparent decrease in bone volume was observed in the CsA-treated group after day 16. Histologic analysis showed that the number of osteoblasts and osteoclasts on the surface of trabecular bone in the CsA-treated group had increased significantly on day 16. Plasma PTH and OCN levels in CsA-treated rats were significantly higher than those in control animals on day 8. Northern blot analysis revealed that the CsA-treated group showed an increase in the expression of OCN, OPN, and cathepsin K mRNAs on day 8 compared with the controls. These findings suggest that bone resorption in CsA-treated rats is induced by high-turnover osteoporosis and that bone remodeling activity may be activated by PTH.

Disease-modifying antirheumatic drug use in the elderly rheumatoid arthritis patient

During the 10-year period since the last review was done by Gardner and Furst, studies have furthered our knowledge of use of disease-modifying antirheumatic drugs (DMARDs) in the elderly rheumatoid arthritis (RA) patient. This article will briefly review the clinical pharmacology of human as they age, and detail the effects of aging on the specific pharmacokinetics and responses to commonly used DMARDs. There has been some progress in understanding the elderly RA patient, however, there is insufficient data for much confidence in DMARDs effects in the elderly.

2005 Dr. Gary J. Becker Young Investigator Award: Periprocedural Oral Administration of the Leflunomide Analogue FK778 Inhibits Neointima Formation in a Double-injury Rat Model of Restenosis

PURPOSE

To test the efficacy of limited oral administration of the new leflunomide analogue FK778 for suppression of neointima proliferation in a double-injury restenosis model in the rat.

MATERIALS AND METHODS

For induction of aortic lesions, silicon cuffs were placed operatively around the infrarenal aortas of Lewis rats. After 21 days, the aortic cuffs were removed and the lesions were dilated with 2-F Fogarty catheters inserted via the left common carotid artery. The novel immunosuppressant FK778 was administered at a dose of 5 mg/kg body weight (group 1) or 15 mg/kg body weight (group 2) in a total of 38 animals. For both doses, three different periinterventional time periods, each with a 5-day course of oral FK778, were defined as follows: (i) days -2 to 2, (ii) days 1-5, and (iii) days 7-11, with six or seven rats in each group. After 3 weeks, intima/media ratios were assessed morphometrically and immunohistochemistry for quantification of intimal alpha-actin expression was performed.

RESULTS

In both dose groups, there was a trend toward inhibition of neointima formation when the 5-day course of FK778 was started before or 1 day after the intervention. However, in the lower-dose group, inhibition of neointima was not statistically significant regardless of the time frame of treatment (groups 1a-c). With the higher dose, suppression of intimal hyperplasia was significant when FK778 was administered between days 1 and 5 after angioplasty (group 2b; P<.01). Expression of alpha-actin in the intima of FK778-treated rats was significantly reduced when the drug was started 2 days before angioplasty in group 1a (P<.05) or 1 day after angioplasty in both dosage groups (group 1b, P<.01; group 2b, P<.05).

CONCLUSION

In the double-injury rat model presented, balloon-mediated proliferation of smooth muscle cells in the intima with consecutive intimal thickening was influenced by FK778 in a dose-dependent manner. However, long-term studies are needed to exclude a delay of vascular healing in this particular model.

Leflunomide and malononitriloamides

Leflunomide is a new immunomodulatory drug effective in experimental models of autoimmune diseases and allo- or xenotransplantation. In a Phase II clinical trial leflunomide has shown high tolerability and efficacy in patients with advanced rheumatoid arthritis. The immunomodulatory activity of leflunomide is attributed to its primary metabolite, A77 1726, a malononitriloamide. The in vitro and in vivo mechanisms of action of this class of compounds remain to be completely defined. A77 1726 and several malononitriloamide analogues inhibit T- and B-cell proliferation, suppress immunoglobulin production, and interfere with cell adhesion. While no one central molecular mechanism of action has been proposed to explain all the effects of the malononitriloamides, inhibition of de novo pyrimidine biosynthesis and inhibition of cytokine- and growth factor-receptor associated tyrosine kinase activity are leading hypotheses for the effects of A77 1726 on T- and B-cell proliferation and function. Leflunomide is effective when administered at daily doses of 10 and 25 mg to patients with active rheumatoid arthritis. The improved efficacy at the 25 mg dose is associated with a higher incidence of adverse effects (gastrointestinal symptoms, weight loss, allergic reactions, skin rash, and reversible alopecia). Due to the long plasma half-life of A77 1726 (11-16 days), loading doses are required to achieve steady-state concentrations. Phase III randomised, placebo-controlled trials using daily doses of 10 or 20 mg are underway in the US and Europe to confirm and extend the results of the Phase II study. Malononitriloamide analogues of A77 1726 are being evaluated for immunosuppressive efficacy in preclinical models of transplantation, because these compounds have a shorter half-life in animals than A77 1726. If these analogues show efficacies similar to leflunomide in these models and have shorter half-lives than A77 1726 in Phase I trials, the preclinical and Phase I data will be used to select the analogues for Phase II trials in organ transplant recipients.

Leflunomide protects from T-cell-mediated liver injury in mice through inhibition of nuclear factor kappaB

Leflunomide is a novel immunosuppressive and anti-inflammatory agent for the treatment of autoimmune disease. The aim of this study was to investigate whether leflunomide protects from liver injury induced by concanavalin A (Con A), a T-cell-dependent model of liver damage. BALB/c mice were injected with 25 mg/kg Con A in the presence or absence of 30 mg/kg leflunomide. Liver injury was assessed biochemically and histologically. Levels of circulating cytokines and expressions of cytokine messenger RNA (mRNA) in the liver and the spleen were determined. Treatment with leflunomide markedly reduced serum transaminase activities and the numbers of dead liver cells. Leflunomide significantly inhibited increases in plasma tumor necrosis factor alpha (TNF-alpha) and interleukin 2 concentrations, and also reduced TNF-alpha mRNA expression in the liver after administration of Con A. These findings were supported by the results in which leflunomide administration decreased the number of T lymphocytes infiltrating the liver as well as inhibiting their production of TNF-alpha. Activation of nuclear factor kappaB (NF-kappaB), which regulates TNF-alpha production, was inhibited in the liver of mice treated with leflunomide, resulting in a reduction of TNF-alpha production from lymphocytes infiltrating the liver. In conclusion, leflunomide is capable of regulating T-cell-mediated liver injury in vivo and that this event may depend on the decrease of TNF-alpha production in the liver through inhibition of NF-kappaB activation caused by leflunomide.

Peroral TAS-202 reduced vessel density in rats with adjuvant-induced arthritis

The present study was designed to investigate blood vessel density interpreted as an indirect measurement of angiogenesis following 4-(3,4,5-trimethoxyphenyl)-6-(2,4,5-trimethoxyphenyl)-2-diethylamino-pyrimidine (TAS-202) treatment in a rat model of arthritis. Male Lewis rats were inoculated intradermally with Mycobacterium butyricum into the hind paw and the arthritic responses were evaluated by measuring the changes in paw volume. Both peroral TAS-202 (10 or 30 mg/kg/day) and indomethacin (1 mg/kg/day) inhibited the autoimmune phase of the arthritic response. However, while the increase in blood vessel density in the synovial tissue was significantly inhibited by TAS-202 (10 and 30 mg/kg/day), indomethacin did not exert this effect (1 mg/kg/day). These results, together with the observation that TAS-202 in combination with indomethacin or prednisolone maintained its ability to exert an antiangiogenic effect, indicate that TAS-202 may offer promise as an oral pro-drug for the treatment of rheumatoid arthritis, through its inhibitory effect on angiogenesis at the inflammation site.

Application of LC/MS/MS in the quantitation of SU101 and SU0020 uptake by 3T3/PDGFr cells

SU101 or leflunomide, has been studied extensively because of its anti-cancer and immunomodulating properties. The parent isoxazole compound is converted in vitro and metabolized in vivo to an open ring isomeric form, SU0020. Several pharmacological activities have been reported for the parent and metabolite compounds including inhibition of platelet-derived growth factor (PDGF)-mediated signaling for the parent compound and inhibition of de novo pyrimidine biosynthesis for the metabolite. The inhibition of PDGF-mediated signaling and the anti-tumor properties have been ascribed to the parent compound. In spite of its short plasma half-life of the parent molecule, SU101 can be administered intermittently in animal tumor models and retain efficacy. Therefore, the relationship between plasma levels of SU101 and its efficacy in tumor-implanted immuno-compromised mice is not well established. This study was conducted to assess the concentration of SU101 in 3T3/PDGFr alpha and beta cells (NIH3T3 mouse fibroblasts engineered to overexpress human PDGFr alpha or beta) to better understand the cellular levels of SU101 and SU0020. Two strains of 3T3/PDGFr cells (alpha and beta) were incubated with 1, 25, and 100 microM concentrations of SU101 for 1, 6, 24, and 48 hours. Quantitation of SU101 and SU0020 in these cell lines was achieved by a specific and sensitive liquid chromatography-tandem mass spectrometry (LC/MS/MS) method. Interestingly, in both alpha and beta cell lysates SU101 was much more concentrated than SU0020. The greater concentration of SU101 versus SU0020 that was observed may be due to the preferential partitioning of SU101 into the cells and this shows that significant levels of the parent drug can reach the pharmacological site of action for inhibition of PDGF receptors. The data suggest that the conversion of SU101 to SU0020 is much slower in these cells than in the incubation media.

Leflunomide for the treatment of rheumatoid arthritis and autoimmunity

Leflunomide, a new oral immunomodulatory agent, is effective for the treatment of rheumatoid arthritis. Its mechanism of action in suppressing inflammation is based in its inhibition of dihydroorotate dehydrogenase, an enzyme responsible for de novo synthesis of pyrimidine containing ribonucleotides. It is the first disease-modifying antirheumatic drug approved for treatment of rheumatoid arthritis with an indication for retardation of joint damage by radiography. Side effects are generally mild and include diarrhea, rashes, reversible alopecia, and elevation of hepatic transaminases. Despite the concern about hepatotoxicity, combination use with methotrexate in treating patients with rheumatoid arthritis has been shown to be safe. Other autoimmune diseases in which leflunomide has been used successfully include Felty syndrome, vasculitis, Sjogren syndrome, Wegener granulomatosis, and bullous pemphigoid.

Differential effect of FR122047, a selective cyclo-oxygenase-1 inhibitor, in rat chronic models of arthritis

We investigated the effects of FR122047 (1-[(4,5-bis(4-methoxyphenyl)-2-thiazoyl)carbonyl]-4-methylpiperazine hydrochloride), a selective cyclo-oxygenase (COX)-1 inhibitor, in rat type II collagen-induced arthritis (CIA) and adjuvant-induced arthritis (AIA). Using an ex vivo rat whole blood assay, FR122047 (0.032 - 3.2 mg kg(-1)) inhibited COX-1-derived thromboxane (TX) B(2) production with ED(50) value of 0.059 mg kg(-1), indicating that it was orally active, but did not inhibit lipopolysaccharide-induced prostaglandin (PG) E(2) production derived by COX-2. Oral administration of FR122047 showed a dose-dependent anti-inflammatory effect in rat CIA with ED(50) value of 0.56 mg kg(-1). This drug also dose dependently suppressed the levels of PGE(2) and TXB(2) in CIA rat paws with ED(50) values of 0.24 and 0.13 mg kg(-1), respectively. FR122047 had no effect in rat AIA model. In contrast, indomethacin, a non-selective COX inhibitor, was anti-inflammatory and reduced the formation of PGs in AIA rat paws. Unlike indomethacin, chronic treatment of FR122047 did not damage the stomach mucosa in CIA rats. These results demonstrate that COX-1 contributes to the oedema and the formation of PGE(2) and TXB(2) in rat CIA model, but not in rat AIA model. We conclude that FR122047 has an orally active and anti-inflammatory effect mediated by inhibition of PGE(2) and TXB(2) produced by COX-1 at a site of inflammation induced by type II collagen and it may be a useful tool for studying the involvement of COX-1 in various in vivo models of inflammation.

Leflunomide-mediated suppression of antiviral antibody and Tcell responses: differential restoration by uridine

BACKGROUND

Leflunomide is an isoxazol derivative with immunosuppressive capacities in various experimental allo- and xenotransplantation models. Two main mechanisms of action have been described: Inhibition of pyrimidine de novo synthesis and impairment of tyrosine phosphorylation of different tyrosine kinases involved in receptor signaling via B cell and cytokine receptors.

MATERIALS AND METHODS

Interference of Leflunomide with the IgM antibody responses to vesicular stomatitis virus (VSV, T-independent type 1), IgM to recombinant VSV glycoprotein (T-independent type 2), and IgG to lymphocytic choriomeningitis virus (LCMV, T-dependent) were analyzed whereas the cytotoxic T cell (CTL) response was examined after LCMV infection. Interference with the CD8+ T cell-mediated autoimmune diabetes in a transgenic mouse expressing the LCMV-glycoprotein in the pancreatic islets was studied as a model for T cell-mediated autoimmune diseases. Uridine substitution experiments were performed to differentiate between the above mentioned two mechanisms of action on different functions of the immune system in vivo.

RESULTS

Leflunomide at 35 mg/kg/day suppressed the humoral immune response against all antigens tested. Similar effects on T-independent compared to T-dependent antibody responses required two to four times higher drug doses. CTL responses to LCMV were considerably impaired. Uridine substitution prevented lethal VSV encephalitis under Leflunomide treatment by restoring the neutralizing IgM and IgG responses. However, the inhibition of LCMV specific CTLs and suppression of CD8+ T cell-mediated autoimmune diabetes remained unaffected by additional uridine treatment.

CONCLUSIONS

Leflunomide-mediated suppression of B cell and T helper cell activity but not of CTLs largely depends on inhibition of pyrimidine de novo synthesis.

Old and new drugs used in rheumatoid arthritis: a historical perspective. Part 2: the newer drugs and drug strategies

After a 20-year hiatus, drug development for rheumatoid arthritis resumed in the early 1980s with cyclosporine, continuing in the 1990s with minocycline, leflunomide, and the tumor necrosis factor-alpha antagonists, infliximab and etanercept. Unlike the older disease-modifying antirheumatic drugs (apart from the cytotoxics), the newer drugs were designed with strict reference to proven pathophysiology in rheumatoid arthritis and, apart from minocycline, the intended action of these agents is highly likely the explanation for the observed efficacy. The evidence for the evolution of more rational drug development in rheumatoid arthritis has not altered the fact that efficacy versus toxicity still remains the major determinant in the practical use of these agents, as well as in the use of other, experimental agents briefly discussed. Action, efficacy, and toxicity also determine the rational chronologic use of these drugs alone and, in particular, in combination.

From oncogene to drug: development of small molecule tyrosine kinase inhibitors as anti-tumor and anti-angiogenic agents

The confluence of two distinct but related activities in the past 10 years has dramatically accelerated efforts towards the discovery and development of novel drugs to treat cancer. The first is a rapidly emerging understanding that a number of distinct tyrosine kinases play roles in diverse but fundamentally important aspects of tumor progression (growth, survival, metastasis and angiogenesis). The second is the discovery that small molecule compounds have the capacity to potently and selectively inhibit the biochemical function of tyrosine kinases by competing for ATP binding at the enzyme catalytic site. These observations have been conjoined in major efforts to bring forward into clinical development novel cancer drugs with the potential to provide both clinical efficacy and improved tolerability. The focus of this review is on the development of small molecule tyrosine kinase inhibitors, and does not extend to other approaches that could be applied to disrupt the same pathways in clinical tumors (receptor and/or ligand-competitive antibodies, intrabodies, antisense ribonucleotides, ribozymes, phosphatase inhibitors or SH2/SH3-directed agents). Selected tyrosine kinase inhibitors, known or believed to be in development in cancer treatment trials, are summarized as are some of the key issues that must be addressed if these compounds are to be developed into clinically useful cancer chemotherapeutic agents.

Leflunomide suppresses TNF-induced cellular responses: effects on NF-kappa B, activator protein-1, c-Jun N-terminal protein kinase, and apoptosis

Leflunomide is a pyrimidine biosynthesis inhibitor that has recently been approved for treatment of rheumatoid arthritis. However, the mechanism of leflunomide's antiarthritis activity and is not fully understood. The critical role that TNF plays in rheumatoid arthritis led us to postulate that leflunomide blocks TNF signaling. Previously, we have demonstrated that leflunomide inhibits TNF-induced NF-kappaB activation by suppressing I-kappaBalpha (inhibitory subunit of NF-kappaB) degradation. We in this study show that leflunomide also blocks NF-kappaB reporter gene expression induced by TNFR1, TNFR-associated factor 2, and NF-kappaB-inducing kinase (NIK), but not that activated by the p65 subunit of NF-kappaB, suggesting that leflunomide acts downstream of NIK. Leflunomide suppressed TNF-induced phosphorylation of I-kappaBalpha, as well as activation of I-kappaBalpha kinase-beta located downstream to NIK. Leflunomide also inhibited TNF-induced activation of AP-1 and the c-Jun N-terminal protein kinase activation. TNF-mediated cytotoxicity and caspase-induced poly(ADP-ribose) polymerase cleavage were also completely abrogated by treatment of Jurkat T cells with leflunomide. Leflunomide suppressed TNF-induced reactive oxygen intermediate generation and lipid peroxidation, which may explain most of its effects on TNF signaling. The suppressive effects of leflunomide on TNF signaling were completely reversible by uridine, indicating a critical role for pyrimidine biosynthesis in TNF-mediated cellular responses. Overall, our results suggest that suppression of TNF signaling is one of the possible mechanisms for inhibitory activity of leflunomide against rheumatoid arthritis.

Leflunomide: mode of action in the treatment of rheumatoid arthritis

Leflunomide is a selective inhibitor of de novo pyrimidine synthesis. In phase II and III clinical trials of active rheumatoid arthritis, leflunomide was shown to improve primary and secondary outcome measures with a satisfactory safety profile. The active metabolite of leflunomide, A77 1726, at low, therapeutically applicable doses, reversibly inhibits dihydroorotate dehydrogenase (DHODH), the rate limiting step in the de novo synthesis of pyrimidines. Unlike other cells, activated lymphocytes expand their pyrimidine pool by approximately eightfold during proliferation; purine pools are increased only twofold. To meet this demand, lymphocytes must use both salvage and de novo synthesis pathways. Thus the inhibition of DHODH by A77 1726 prevents lymphocytes from accumulating sufficient pyrimidines to support DNA synthesis. At higher doses, A77 1726 inhibits tyrosine kinases responsible for early T cell and B cell signalling in the G(0)/G(1) phase of the cell cycle. Because the immunoregulatory effects of A77 1726 occur at doses that inhibit DHODH but not tyrosine kinases, the interruption of de novo pyrimidine synthesis may be the primary mode of action. Recent evidence suggests that the observed anti-inflammatory effects of A77 1726 may relate to its ability to suppress interleukin 1 and tumour necrosis factor alpha selectively over their inhibitors in T lymphocyte/monocyte contact activation. A77 1726 has also been shown to suppress the activation of nuclear factor kappaB, a potent mediator of inflammation when stimulated by inflammatory agents. Continuing research indicates that A77 1726 may downregulate the glycosylation of adhesion molecules, effectively reducing cell-cell contact activation during inflammation.

Pharmacodynamics of immunosuppressive drugs

The inability to measure the effects of immunosuppressive drugs on immune cells in vivo has always severely limited preclinical drug development, the design and interpretation of clinical trials and the optimal clinical use of this drug class in transplantation. Now, new technologies using microliter samples of whole blood and exploiting the specificity, sensitivity and versatility of flow cytometry have been developed. These novel techniques not only are illuminating the 'black box' that has obscured the pharmacodynamic effects of immunosuppressants but also are uncovering new mechanisms of action of these drugs. Pharmacodynamic assays measure biologically relevant events in vivo, since changes in lymphocyte functions in blood collected from immunosuppressed graft recipients faithfully reflect histopathologic events within allograft tissue.

Anti-inflammatory effect of FR140423, a novel selective cyclo-oxygenase-2 inhibitor, in rat adjuvant arthritis without gastrointestinal side effects

We investigated the effect of FR140423 (3-(difluoromethyl)-1-(4-methoxyphenyl)-5-[4-(methylsulphinyl)phen yl]pyrazole), a novel and selective cyclo-oxygenase (COX)-2 inhibitor, in rat adjuvant arthritis. The results were compared with that of indomethacin. We tested the inhibitory effects of FR140423 on paw oedema and the formation of the arachidonic acid metabolites prostaglandin (PG) E2 and leukotriene (LT) B4 in inflamed paws immunized with heat-killed and dried Mycobacterium tuberculosis. Oral administration of FR140423 showed a dose-dependent anti-inflammatory effect. This effect was two- to threefold more potent than that of indomethacin. The increase of PGE2 and LTB4 in inflamed paws was associated with the development of paw swelling. FR140423 and indomethacin dose-dependently suppressed the level of PGE2 but not LTB4 in arthritic paws. Unlike indomethacin, FR140423 did not induce gastric lesions even at doses up to 10 mgkg(-1) in arthritic rats. FR140423 has a potent anti-inflammatory effect mediated by inhibition of PGE2 produced by COX-2 in inflamed tissues. The safety profile of FR140423 appears to be an improvement on the safety profile of indomethacin.

Leflunomide: an immunomodulatory drug for the treatment of rheumatoid arthritis and other autoimmune diseases

Leflunomide (Arava) has recently been approved by the Food and Drug Administration for the treatment of rheumatoid arthritis (RA). The drug, due to its protective effects on structural joint damage, has been classified as a disease modifying anti-rheumatic drug (DMARD). Leflunomide is structurally dissimilar from other drugs currently used to treat RA and exhibits a different mechanism of action. It has shown to be protective in a variety of animal models of arthritis and autoimmunity based on its immunomodulatory activity. Leflunomide is rapidly converted in vivo to its pharmacologically active metabolite A77 1726. This metabolite is a potent non-cytotoxic inhibitor of the enzyme dihydroorotate dehydrogenase (DHODH), a key enzyme in the de novo synthesis of uridine monophosphate (UMP). Activated lymphocytes depend on the pyrimidine de novo syntheses to fulfill their metabolic needs for clonal expansion and terminal differentiation into effector cells. De novo synthesis of pyrimidines is not only essential to provide precursors for new RNA and DNA synthesis, but also for phospholipid synthesis and the pyrimidine sugars necessary for protein glycosylation, which support the massive expansion in membrane biosynthesis to form daughter cells. This mechanism likely contributes to leflunomide's action as a DMARD in RA and other autoimmune diseases. This review is a summary of current in vivo and in vitro data, focussing primarily on the mechanism of action of leflunomide in RA.

The use of leflunomide in the treatment of rheumatoid arthritis: an experimental and clinical review

Leflunomide, the newest disease-modifying antirheumatic drug (DMARD) for the treatment of rheumatoid arthritis (RA), acts by inhibiting dihydroorotate dehydrogenase, the rate-limiting enzyme in the pathway for pyrimidine production. The drug thus limits T-cell proliferation, a process thought to be a key step in the pathogenesis of RA. In placebo-controlled trials, leflunomide was superior to placebo and comparable to sulfasalazine and methotrexate for improving the signs and symptoms of RA; and superior to placebo, sulfasalazine, and methotrexate for improving health-related quality of life. In the same trials, leflunomide was also superior to methotrexate and comparable to sulfasalazine for slowing radiographically assessed progression of RA. When used in combination therapy in an open-label trial, leflunomide resulted in improvement for over half of a group of RA patients who had failed to respond to methotrexate alone. The most common adverse events associated with leflunomide treatment were gastrointestinal symptoms, allergic reactions, alopecia, and elevated liver enzyme levels. Adverse events were generally mild to moderate in severity and resolved without sequelae. Clinical trial results indicate that leflunomide is an efficacious and safe addition to the roster of therapeutic agents used to treat RA.

Mechanism of action for leflunomide in rheumatoid arthritis

Leflunomide (Arava) has recently been approved by the Food and Drug Administration for the treatment of rheumatoid arthritis (RA). This approval was based on data from a double-blind, multicenter trials in the United States (leflunomide versus methotrexate versus placebo) in which leflunomide was superior to placebo and similar to methotrexate (Strand et al., Arch. Intern. Med., in press, 1999). In a multicenter European trial, leflunomide was similar to sulfasalazine in efficacy and side effects (Smolen et al., Lancet 353, 259-266, 1999). Both methotrexate and leflunomide retarded the rate of radiolographic progression, entitling them to qualify as disease-modifying agents (Strand et al., Arch. Intern. Med., in press, 1999). Leflunomide is an immunomodulatory drug that may exert its effects by inhibiting the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH), which plays a key role in the de novo synthesis of the pyrimidine ribonucleotide uridine monophosphate (rUMP). The inhibition of human DHODH by A77 1726, the active metabolite of leflunomide, occurs at levels (approximately 600 nM) that are achieved during treatment of RA. We propose that leflunomide prevents the expansion of activated and autoimmune lymphocytes by interfering with the cell cycle progression due to inadequate production of rUMP and utilizing mechanisms involving p53. The relative lack of toxicity of A77 1726 on nonlymphoid cells may be due to the ability of these cells to fulfill their ribonucleotide requirements by use of salvage pyrimidine pathway, which makes them less dependent on de novo synthesis.

Leflunomide, a novel immunomodulator for the treatment of active rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic disease affecting 0.8% of the population. Nonsteroidal anti-inflammatory drugs reduce the pain and inflammation of RA and improve mobility but do not slow the progression of joint damage. Disease-modifying antirheumatic drugs (DMARDs), which limit potentially irreversible joint damage, may influence the course of disease progression. This review describes the recently approved DMARD leflunomide, an isoxazole-based immunomodulator. Unlike other DMARDs, leflunomide arrests the growth of activated lymphocytes by inhibiting the enzyme dihydroorotate dehydrogenase, a critical link in the production of uridine monophosphate. Leflunomide is rapidly metabolized to the active major metabolite A77 1726, which is responsible for the drug's pharmacologic activity. Leflunomide has exerted inhibitory activity in animal models of RA. Its clinical efficacy has been demonstrated in a number of controlled trials. In two multinational 52-week studies and two 24-week studies, all leflunomide-treated patients received an initial loading dose of 100 mg for 3 days, followed by 20 mg/d. The effects on the signs and symptoms of RA were evaluated using the American College of Rheumatology (ACR) 20 responder index, tender and swollen joint counts and scores, patients' and physician's global assessments, and pain intensity index. Erosions and joint-space narrowing were assessed by radiography. Compared with placebo, leflunomide significantly improved the signs and symptoms of RA (41%-64% improvement) by ACR 20 responder criteria (P < 0.001). Leflunomide, methotrexate, and sulfasalazine were equally effective in terms of symptom outcomes. In terms of retarding the progression of disease, leflunomide was significantly superior to placebo, with no consistent difference from methotrexate or sulfasalazine. In a trial using a combination of leflunomide and methotrexate therapy, 53% of patients were responders by ACR 20 criteria. Adverse effects in RA patients receiving leflunomide included diarrhea, elevated liver enzymes, alopecia, and rash. Additional adverse events occurring with a frequency >5% included allergic reaction, asthenia, abdominal pain, back pain, and hypertension, among others. Thus leflunomide may be used in selected RA patients (ie, those starting RA therapy for the first time or failing earlier DMARD therapy). However, the product labeling requires monthly monitoring of liver enzymes until stable concentrations are reached. Other labeled warnings include a risk of immunosuppression and an increased risk of fetal death or teratogenic effects in pregnant women. Methotrexate, which is also hepatotoxic, is usually the initial DMARD recommended for use in patients with aggressive RA.

Methotrexate and leflunomide: biochemical basis for combination therapy in the treatment of rheumatoid arthritis

OBJECTIVES

Methotrexate is currently one of the most widely prescribed disease-modifying antirheumatic drugs (DMARDs) for the treatment of rheumatoid arthritis (RA). Combination therapy of methotrexate with other DMARDs increases the clinical success of low-dose methotrexate treatment. Leflunomide is a new DMARD that may have a high potential for success in combination therapy with methotrexate. This review compares the mode of action of methotrexate and leflunomide and speculates on how this contributes to therapeutic efficacy in RA when these agents are used singly or in combination.

METHODS

A literature review of the biochemical mechanisms considered to be the basis for the therapeutic efficacy of methotrexate and leflunomide in treating RA is presented.

RESULTS

Low-dose methotrexate inhibits cytokine production, purine biosynthesis, and, in an animal model, causes the release of adenosine, a potent antiinflammatory agent. Leflunomide, through inhibition of de novo pyrimidine biosynthesis, can regulate lymphocyte proliferation.

CONCLUSIONS

The biochemical mechanisms underlying the therapeutic efficacy of low-dose methotrexate and leflunomide in the treatment of RA are quite different. The potentially complementary mechanisms of action of these two effective DMARDs should provide a rationale for their use in combination therapy for patients whose condition no longer responds to methotrexate alone.

Newer immunosuppressive drugs: a review

In recent years, many new immunosuppressive drugs have been discovered and developed for clinical use in transplantation. This review focuses on those drugs (leflunomide, mycophenolate mofetil, sirolimus, tacrolimus) that have been shown to have immunosuppressive activity in patients. Different anti-interleukin-2 receptor antibodies are also reviewed as an example of a resurgence of development in the area of monoclonal antibodies. The price for reducing the incidence of allograft rejection by improved immunosuppression was thought to be a proportional increase in the incidence of infection and malignancy. Data from Phase III clinical trials of new immunosuppressants, however, show a statistically significant reduction in the incidence of acute rejection produced by these new drugs, which has not been accompanied by increases in infection and malignancy rates. The wide array of new drugs offers the opportunity to use combinations that block different pathways of immune activation while at the same time selecting drug combinations with nonoverlapping toxicity profiles so that doses of each single drug can be reduced below toxicity levels. The immunosuppressive therapy for patients can be tailored according to their individual needs.