Tenidap, in contrast to several available nonsteroidal antiinflammatory drugs, potently inhibits the release of activated neutrophil collagenase

The in vitro free radical scavenging activity of tenidap, a new dual cyclo-oxygenase and 5-1ipoxygenase inhibitor

Tenidap, a new anti-inflammatory drug, is presently undergoing clinical studies as a treatment for rheumatoid arthritis (RA). Early pilot work has shown it to be of some benefit. Tenidap is a dual inhibitor of cyclo-oxygenase and 5-lipoxygenase enzymes. It has also been shown to modify white blood cell behaviour such as interleukin-1 production, monocyte differentiation and neutrophil degranulation. As free radicals (FRs) have been implicated in the pathogenesis of RA, we used an in vitro assay system developed by Misra and Fridovich to assess if tenidap has FR scavenging effects. Our study shows, for the first time, that tenidap has general FR scavenging effects although no effect on the superoxide anion (O2·-) could be demonstrated. This effect occurred in a dose-dependent manner at concentrations above 20 μg/ml (p < 0.005, Mann-Whitney U-test). As the therapeutic range of tenidap in serum is between 15 and 30 μg/ml such FR scavenging activity may be clinically relevant in the treatment of RA. Ex vivo confirmation of this possibility is underway.

Tenidap sodium inhibits secretory non-pancreatic phospholipase A(2) synthesis by foetal rat calvarial osteoblasts

Tenidap (TD) was initially defined as a dual inhibitor of cyclooxygenase and lipoxygenase. This study was designed to assess its inhibitory activity against proinflammatory phospholipase A(2). This study shows that TD inhibits the synthesis of pro-inflammatory secretory non-pancreatic phospholipase A(2) (sPLA(2)). Concentrations as low as 0.25 mug/ml (0.725 muM) reduced the release of sPLA(2) by 40% from foetal rat calvarial osteoblasts stimulated with IL-1beta and TNFalpha, whereas a concentration of 2.5 mug/ml (7.25 muM) reduced the release by over 80%. TD also markedly reduced the release of sPLA(2) from unstimulated cells. There was no direct inhibition of sPLA(2) enzymatic activity by TD in vitro. Northern blot analysis showed that TD did not affect the sPLA(2) mRNA levels; however, immunoblotting showed a dose-dependent reduction in sPLA(2) enzyme. These results, together with a marked reduction in sPLA(2) enzymatic activity, suggest that TD inhibits sPLA(2) synthesis at the post-transcriptional level. Therefore TD seems to inhibit the arachidonic acid cascade proximally to cyclooxygenase and lipoxygenase and its anti-inflammatory activity may be related at least in part to the inhibition of sPLA(2) synthesis.

Pharmacokinetic, distribution, metabolism, and excretion of (Z)-2-amino-1,5-dihydro-1-methyl-5-[4-(mesyl)benzylidene]-4H-imidazol-4-one mesilate (ZLJ-601) in Sprague-Dawley rats

(Z)-2-amino-1,5-dihydro-1-methyl-5-[4-(mesyl)benzylidene]-4H-imidazol-4-one mesilate (ZLJ-601) is an imidazolone COX/5-LOX inhibitor, which has excellent anti-inflammatory activity with an improved gastrointestinal safety profile. The purpose of this study was to evaluate the in vivo absorption, distribution, metabolism, and excretion of ZLJ-601 in Sprague-Dawley rats. After intravenous or intragastric administration to rats, the concentration of ZLJ-601 in plasma, bile, urine, feces and various types of tissues was detected by LC-MS. We also conducted the identification of metabolites using tandem mass spectrometry. After the intravenous administration, the t(1/2) ranged from 38.71 to 42.62 min and the AUC increased in a dose-proportional manner. After oral dosing, the plasma level of ZLJ-601 peaked at 28.33 min, having a C(max) value of 0.26 mg/l, and the bioavailability was only 4.92%. The highest tissue concentration of ZLJ-601 was observed in lung and kidney, but it was not found in brain. The majority of unchanged ZLJ-601 was excreted in urine (∼35.87%) within 36 h. Two main metabolites are the hydroxylation product and the glucuronide conjugate of the hydroxylation product.

Regulation of superoxide production in neutrophils: role of calcium influx

Upon stimulation, activation of NADPH oxidase complexes in neutrophils produces a burst of superoxide anions contributing to oxidative stress and the development of inflammatory process. Store-operated calcium entry (SOCE), whereby the depletion of intracellular stores induces extracellular calcium influx, is known to be a crucial element of NADPH oxidase regulation. However, the mechanistic basis mediating SOCE is still only partially understood, as is the signal-coupling pathway leading to modulation of store-operated channels. This review emphasizes the role of calcium influx in the control of the NADPH oxidase and summarizes the current knowledge of pathways mediating this extracellular calcium entry in neutrophils. Such investigations into the cross-talk between NADPH oxidase and calcium might allow the identification of novel pharmacological targets with clinical use, particularly in inflammatory diseases.

Tenidap, an anti-inflammatory agent, inhibits DNA and collagen syntheses, depresses cell proliferation, and lowers intracellular pH in cultured human gingival fibroblasts

The effect of tenidap [(+/-)-5-chloro-2,3-dihydro-3-(hydroxy-2-thienylmethylene)-2-oxo-1H-indole-1-carboxamide], a new anti-inflammatory agent, was investigated on DNA synthesis by means of [(3)H]thymidine incorporation, collagen synthesis by means of [(3)H]proline incorporation, cell proliferation, and intracellular pH in nicardipine-reactive human gingival fibroblasts. Tenidap significantly inhibited [(3)H]thymidine incorporation at concentrations greater than 20 microM on the 4th and 8th day of treatment. Tenidap also significantly inhibited [(3)H]proline incorporation at a concentration greater than 50 microM on the 4th day and at more than 20 microM on the 8th day of treatment. The presence of 1 microM nifedipine or 1 microM nicardipine did not alter the depressing effect of tenidap. Tenidap (20 microM) also lowered intracellular pH. These results suggest that tenidap might be effective for the prevention of gingival overgrowth caused by calcium channel blockers.

Can non-steroidal anti-inflammatory drugs act as metalloproteinase modulators? An in-vitro study of inhibition of collagenase activity

The in-vitro effects of some non-steroidal anti-inflammatory drugs and some analgesic drugs on collagenase activity were studied by use of a self-quenched fluorogenic esapeptide as substrate. The increased fluorescence signal arising as a result of peptide cleavage by collagenase was recorded and related to the inhibitory potency of the drugs. The effective concentrations in collagenase modulation were also correlated with the levels of the drugs in the plasma and synovial fluids of patients receiving therapeutic doses. Six of the tested drugs, nimesulide, piroxicam, tolmetin, meloxicam, sulindac and sodium meclofenamate, inhibited enzyme activity with IC50 values (concentrations resulting in 50% inhibition) ranging from 1.9 to 28.2 microM and Ki (apparent inhibition constant) ranging from 0.83 to 21.8 microM. Much of the activity was restored after dialysis of the enzyme-drug complex, demonstrating the reversibility of the effect. Although these results indicate that some anti-inflammatory drugs could modulate enzymatic activity involved in the degradation of the extracellular matrix, their possible pharmacological involvement as collagenase inhibitors in collagen degradative diseases remains to be assessed by clinical studies.

Tenidap decreases IL-8 and monocyte chemotactic peptide-1 (MCP-1) mRNA expression in the synovial tissue of rabbits with antigen arthritis and in cultured synovial cells

Since IL-8 and MCP-1 are chemoattractant proteins that participate in the recruitment of inflammatory cells into the arthritic joint, we examined the effects of tenidap, a new anti-inflammatory drug of the oxindole family, on IL-8 and MCP-1 expression in the joints of rabbits with acute antigen arthritis. The model was induced by injecting 5 mg/ml ovalbumin into the knees of 20 preimmunized rabbits. Animals were randomized into two groups: treated with tenidap (15 mg/kg per 12 h), or untreated. The effect of tenidap treatment was evaluated on chemokine production in synovial membranes of rabbits with arthritis and in cultured monocytic and synovial cells (SC). By immunoperoxidase staining, chemokines were localized in the synovial tissue. Chemokine messenger RNA levels in the synovial membranes and in cultured cells were analysed by reverse transcription-polymerase chain reaction (RT-PCR). At the end of the study, tenidap significantly reduced neutrophil infiltration into the joint cavity (27+/-4 x 10(6) cells/ml versus 45+/-6 x 10(6) cells/ml in untreated; P<0.05), and synovial effusion (134+/-15 microl versus 236+/-19 microl in untreated; P<0.005). Untreated rabbits showed synovial membrane up-regulation in mRNA expression of IL-8 and MCP-1 (11- and seven-fold versus healthy rabbits, respectively) that was markedly decreased by tenidap (two- and three-fold versus healthy rabbits, respectively). IL-8 and MCP-1 were localized in the synovial tissue in a perivascular pattern and areas of the interstitium and lining, mostly coinciding with cell infiltration. Tenidap also reduced the accumulation of IL-8 and MCP-1 proteins. In cultured synovial and monocytic cells, tumour necrosis factor-alpha (TNF-alpha) elicited an increase in gene expression of IL-8 (four- and nine-fold, respectively) and MCP-1 (nine- and four-fold, respectively) that was significantly reversed in both cell types by 10 microM tenidap. These results suggest that the beneficial effect of tenidap in acute antigen arthritis could be related to the down-regulation in gene expression and synthesis of IL-8 and MCP-1, two key chemokines involved in the recruitment of inflammatory cells.

Effects of tenidap on intracellular signal transduction and the induction of proinflammatory cytokines: a review

Tenidap is a novel, once-daily antirheumatic drug which has shown promising results against rheumatoid arthritis in extensive clinical trials. It combines NSAID-like cyclooxygenase inhibition with suppression of the acute phase response. In macrophages, tenidap inhibits the lipopolysaccharide-induced synthesis of interleukins-1 and -6, but it tends to potentiate the lipopolysaccharide-induced synthesis of tumor necrosis factor alpha, due to its cyclooxygenase inhibition. In macrophages, tenidap is a potent inhibitor of zymosan-induced responses, not only the induction of proinflammatory cytokines, but also arachidonate mobilization, protein phosphorylation, and inositol phosphate formation, possibly through interference with the receptor-mediated upregulation of phospholipase C. Tenidap also acts as an intracellular acidifier in many cell types, which may explain at least some of its other effects. Recent studies have indicated that, in addition to modulation of prostanoid and cytokine formation, tenidap has many other effects beneficial in rheumatic disease. It has been shown to inhibit bone resorption, neutrophil adhesion and degranulation, the interleukin-1-induced suppression of glycosaminoglycan synthesis, as well as the production of active metalloproteinases from chondrocytes.

Cyclooxygenase 1 and 2 in rheumatic disease: implications for nonsteroidal anti-inflammatory drug therapy

OBJECTIVES

Prostaglandin synthase (cyclooxygenase) is now known to exist in two separate isoforms, termed prostaglandin synthase 1 and 2 (or COX1 and COX2). This has prompted a dramatic increase in research regarding the contribution of these isoforms to inflammatory disease and their relationship to the efficacy and safety of nonsteroidal anti-inflammatory drugs (NSAIDs). The emerging picture is that COX1 is responsible for maintaining prostaglandin synthesis in the gastric mucosa, platelets, and kidney, whereas COX2 is responsible for prostaglandin production in inflamed tissues, including rheumatoid arthritis (RA) synovium. This review examines the validity of the hypothesis that NSAIDs exhibiting selectivity for COX2 demonstrate an improved safety and efficacy profile when compared with NSAIDs exhibiting selectivity for COX1.

METHODS

Literature on the efficacy and safety (gastric, renal, and hemostatic) of various NSAIDs are compared with published data on their relative COX1 and COX2 in vitro specificity.

RESULTS

No differences in clinical efficacy are evident between NSAIDs exhibiting preferential activity for either COX1 or COX2. NSAIDs representing the extremes in terms of selectivity for COX1 or COX2 do exhibit some differences with respect to gastric, renal, and hemostatic safety; those exhibiting a preferential action on COX2 are generally less toxic than those exhibiting a preferential activity on COX1. Exceptions do exist.

CONCLUSIONS

There is some support for the hypothesis that NSAIDs exhibiting a preferential action on COX2 are safer than those exhibiting a preferential activity on COX1, but there exists no support for improved efficacy. A strict correlation does not exist between the COX1 and COX2 specificity and the gastric, renal, and hemostatic toxicity of NSAIDs. This lack of correlation is believed to stem from the fact that both the safety and efficacy of NSAIDs may result from mechanisms distinct from prostaglandin inhibition. Preferential COX2 activity can reduce the level of toxicity for a given NSAID but may not be sufficient to overcome toxicities resulting from other mechanisms.

Differential effects of tenidap on the zymosan- and lipopolysaccharide-induced expression of mRNA for proinflammatory cytokines in macrophages

Tenidap is a novel antirheumatic drug that combines cyclooxygenase inhibition with cytokine modulating qualities. We demonstrate here that tenidap inhibits the zymosan-induced expression of both interleukin 1 and tumor necrosis factor alpha in macrophages, at the mRNA and protein levels. The concentration-dependence of the tenidap-induced inhibition of the expression of mRNA for these proinflammatory cytokines agrees with that of its inhibitory effects on zymosan-induced arachidonate mobilization and changes in phosphoprotein pattern. The effects of tenidap on the lipopolysaccharide-induced expression of these cytokines are more complex. Tenidap inhibits the induction of interleukin 1 by lipopolysaccharide or bacteria, but less potently than the interleukin 1-response induced by zymosan. In contrast, the drug markedly potentiates the lipopolysaccharide-induced expression of tumor necrosis factor alpha at both the mRNA and protein levels. The latter effect is demonstrated to be due to cyclooxygenase inhibition and is reversed by prostaglandin E2.

Pharmacological and functional properties of voltage-independent Ca2+ channels

During the last few years, considerable progress has taken place in our knowledge of the molecular and functional properties of the various voltage-independent Ca2+ channels. In addition to the ionotropic receptor-channels (ROCs), that are not discussed in the present review, these channels include the SMOCs, activated via second messengers or other transducing processes directly triggered by receptor activation; and the SOCCs, activated as a consequence of depletion of the rapidly exchanging Ca2+ stores in the cytoplasm. In parallel, a pharmacological approach to the study of these channels has been developed, based primarily on heterogeneous drugs already known for different biological effects, and subsequently recognized as voltage-independent Ca(2+)-channel blockers. From the systematic analysis of the effects of these drugs new information has emerged about SMOCs and SOCCs function. In addition, pharmacological blockade of these channels appears to have beneficial therapeutic effects in pathological conditions such as tumoral cell growth, inflammation and immunity. At the moment the field is rapidly evolving, with major developments expected in the years ahead.

Tenidap, a structurally novel drug for the treatment of arthritis: antiinflammatory and analgesic properties

Tenidap is a new anti-rheumatic agent which has clinical properties characteristic of a disease modifying drug combined with acute antiinflammatory and analgesic activity. This paper details tenidap's cyclooxygenase (COX) inhibitory activity and the resulting pharmacological properties in experimental animals. Tenidap inhibited calcium ionophore-stimulated prostaglandin D2 synthesis by rat basophilic leukemia cells (COX-1) with an IC50 of 20 nM. In two different in vitro human test systems, tenidap inhibited COX-1 activity more potently than COX-2, although the relative potency ratio (COX-1/COX-2) differed markedly between the two systems. Tenidap inhibited the COX pathway when added to human blood in vitro (IC50, 7.8 mu M) and when administered orally to monkeys, rats and dogs (at 5, 2.5 and 10 mg/kg p.o., respectively) and COX activity measured ex vivo in blood collected 2 to 4 hours post dose. After oral administration to rats, tenidap inhibited carrageenan-induced paw edema with an ED50 of 14 mg/kg and inhibited the glucocorticoid-resistant UV erythema in guinea pigs with an ED50 of 1.4 mg/kg. It retained antiinflammatory activity in adrenalectomized rats indicating that this property is independent of adrenal stimulation. Oral administration of tenidap inhibited the development of adjuvant-induced polyarthritis in the rat and exhibited antinociceptive activity in the murine phenylbenzoquinone and rat acetic acid abdominal constriction tests. These data indicate that tenidap is an effective antiinflammatory and analgesic agent in animal models. These cyclooxygenase-dependent pharmacologic activities do not explain tenidap's disease modifying anti-arthritic properties but add a useful symptom modifying component to its clinical profile.

Tenidap, but not nonsteroidal anti-inflammatory drugs, inhibits T-cell proliferation and cytokine induction

T-lymphocytes are involved in the inflammatory response that occurs in affected joints of patients with rheumatoid arthritis (RA). Some second-line disease modifying anti-rheumatic drugs used in the treatment of patients with RA are known to block T-cell activation. The present study assessed whether tenidap, an investigational anti-rheumatic drug, affects in vitro T-cell responses such as proliferation and cytokine production. It was found that tenidap, in contrast to several nonsteroidal anti-inflammatory drugs, inhibits anti-CD3 or IL-2 driven proliferative responses of cloned human T-cells. Furthermore, tenidap was found to inhibit IFN-gamma production as well as the induction of mRNA encoding IFN-gamma or TNF-alpha. The results indicate that tenidap may exert at least part of its anti-inflammatory activity via inhibition of T-cell function and cytokine production.

Innovative treatment approaches for rheumatoid arthritis. New cyclo-oxygenase and cytokine inhibitors

A need remains for the development of more effective therapies for the treatment of rheumatoid arthritis (both NSAIDs and DMARDs). The NSAIDs remain the cornerstone of symptomatic therapy, but concern remains about their safety, potential for the delay in commencing definitive therapy and theoretical pro-inflammatory effects. Each of the NSAIDs reviewed here do provide an advantage over therapies previously available and should prove to be useful additions to the rheumatologists' therapeutic armament.

Effects of tenidap on superoxide-generating enzymes. Non-competitive inhibition of xanthine oxidase

The anti-rheumatic drug tenidap has been shown previously to attenuate superoxide production by activated neutrophils. Given the importance of leukocyte as well as endothelial cell derived superoxide in mediating inflammatory responses, the effects of tenidap on mammalian enzymes capable of generating superoxide were determined. Tenidap had no effect on the generation of superoxide by NADPH oxidase reconstituted from fractionated neutrophil lysates. However, significant inhibition of superoxide production by mixtures of hypoxanthine and xanthine oxidase was observed in the presence of 3-30 micrograms/mL tenidap. The kientics of xanthine oxidase inhibition by tenidap were non-competitive; the Ki of tenidap for xanthine oxidase was 11 micrograms/mL (34 microM). No inhibition of xanthine oxidase was observed in the presence of other known inhibitors of cyclooxygenase. Inhibition of xanthine oxidase may be a heretofore unrecognized mechanism of the antirheumatic effects of tenidap.

Effects of tenidap on canine experimental osteoarthritis. I. Morphologic and metalloprotease analysis

OBJECTIVE

To examine the effects of tenidap and diclofenac on osteoarthritic lesions and metalloprotease activity in experimental osteoarthritis (OA).

METHODS

The anterior cruciate ligament of the right stifle joint of 25 mongrel dogs was sectioned by a stab wound. Seven dogs received no treatment, 6 were treated with oral omeprazole (20 mg/day), another 6 were treated with diclofenac (0.25 mg/kg/twice daily) plus omeprazole (20 mg/day), and 6 received oral tenidap (3 mg/kg/twice daily) plus omeprazole (20 mg/day). The dogs received medication for 8 weeks; all dogs were killed at the end of this period. Eight normal dogs were used as controls. Lesions were evaluated macroscopically for the incidence and size of osteophytes and the area and grade of cartilage erosions on the condyles and plateaus, along with histologic evaluation of the severity of the cartilage lesions and synovial inflammation. Stromelysin and collagenase activities and the collagenase messenger RNA (mRNA) level were measured in cartilage and synovial membrane.

RESULTS

Compared with the untreated or omeprazole-treated OA groups, the dogs treated with tenidap exhibited significant reduction in the incidence (P < or = 0.001) and size (P < or = 0.0001) of osteophytes. Tenidap also significantly decreased the size and grade of cartilage macroscopic lesions, as well as the histologic severity of cartilage lesions on both condyles and plateaus. The histologic severity of synovial inflammatory reaction was also significantly reduced (P < or = 0.003) in the tenidap group. Tenidap markedly decreased stromelysin and collagenase activity in both cartilage (stromelysin P < or = 0.003; collagenase P < or = 0.01) and synovial membrane (stromelysin P < or = 0.003; collagenase P < or = 0.005). Moreover, tenidap also decreased the collagenase mRNA level in cartilage (P < or = 0.005) and synovial membrane (P < or = 0.002). Diclofenac slightly reduced the incidence and size of osteophytes and cartilage lesions, but these changes were not statistically significant. Diclofenac had no effect on the severity of synovial inflammation, metalloprotease activity, or collagenase expression.

CONCLUSION

This study showed that tenidap had a more potent anti-osteoarthritic effect than diclofenac in this model. The effect of the drug in suppressing metalloprotease synthesis, a process known to play a major role in the pathophysiology of osteoarthritic lesions, may explain its mechanism of action.

The effects of Tenidap on cytokine induced proliferation of human synovial fibroblasts in vitro

OBJECTIVES

Tenidap, a new anti-rheumatic agent, is a lipoxygenase and cyclooxygenase inhibitor, and is reported to inhibit the production and action of interleukin 1 (IL-1). Since eicosanoids, IL-1, and other cytokines may influence the growth of fibroblasts in the joint synovium the study was carried out to determine the effects of Tenidap on cytokine induced proliferation of these cells in vitro.

METHODS

Cell cultures derived from patients with a variety of rheumatic diseases were cultured in different concentrations of Tenidap sodium, with or without IL-1, tumour necrosis factor alpha (TNF), IL-6, basic fibroblast growth factor (bFGF), or transforming growth factor beta (TGF beta). Cell proliferation was measured using a crystal violet colourimetric assay. Prostaglandin E2 levels in culture supernatants were measured by radioimmunoassay.

RESULTS

Tenidap at concentrations above 10 micrograms/ml inhibited cell growth, while at 1.25-5 micrograms/ml there was a small but significant increase in proliferation compared with controls. A further increase in growth was obtained when cells were incubated with Tenidap+IL-1, TNF or bFGF, and this was significantly higher than in the presence of any cytokine alone. Stimulation of IL-1 induced growth by Tenidap was reduced by addition of high levels of exogenous PGE2 (100 ng/ml) although growth was still higher than in IL-1 alone.

CONCLUSIONS

Depending on concentration, Tenidap may inhibit or stimulate synovial fibroblast growth. Our results suggest that augmentation of growth by low concentrations cannot be explained by inhibition of PGE2 production alone. Tenidap may directly stimulate cell growth or may block other fibroblast factors which are involved in control of cytokine induced proliferation.

Advances in anti-inflammatory therapy

Anti-inflammatory drugs are widely used in veterinary practice to provide symptomatic relief of acute and chronic inflammatory conditions. Whilst much is already known about the properties of corticosteroid and non-steroidal anti-inflammatory drugs, new findings on their biology and pharmacokinetics continue to emerge. These are discussed, together with some possible novel therapeutic applications. Recent evidence, suggesting that morphine-like analgesic drugs may possess anti-inflammatory activity, is additionally presented. Knowledge of the pathways of formation, actions and interactions of the diverse range of mediators responsible for the pathophysiological changes underlying the inflammatory process is also increasing. Compounds are being developed which act selectively to block the formation or actions of these mediators and the potential of such agents as anti-inflammatory drugs is discussed. Although such compounds do not, at present, have veterinary applications, when used either alone, or in combination, some may prove to be potent and effective therapeutic agents.

Tenidap: a novel cytokine-modulating antirheumatic drug for the treatment of rheumatoid arthritis

Tenidap is a novel, once-daily, cytokine modulating antirheumatic drug indicated for the treatment of rheumatoid arthritis (RA). In vitro, tenidap significantly inhibits the production of the pro-inflammatory cytokines, interleukin-1, interleukin-6 and tumour necrosis factor in human cell lines, and inhibits cytokine-mediated processes such as cartilage degradation, bone resorption, metalloprotease synthesis, endothelial cell adhesion and monocyte differentiation. Tenidap also inhibits cyclo-oxygenase. In RA patients, tenidap 120 mg/day is clinically equivalent to the combination of disease-modifying antirheumatic agents plus non-steroidal anti-inflammatory drugs (NSAIDs) and significantly more effective than NSAIDs. Tenidap also produces rapid, profound and sustained reductions in the serum levels of the acute phase proteins, C-reactive protein and serum amyloid A, an effect suggestive of disease modifying properties. In addition, tenidap reduces circulating levels of IL-6 in RA patients. Tenidap is well tolerated.

Tenidap: a novel inhibitor of calcium influx in a mast cell line

The anti-inflammatory agent tenidap has previously been shown to inhibit antigen-induced secretion in tumor mast cells. We have investigated the possibility that this effect is due to modulation of the Ca2+ response in mast cells and in particular that tenidap might be an inhibitor of the Ca2+ influx pathway or channel in these and other non-excitable cells. Tenidap inhibited the antigen-induced increase in intracellular Ca2+ measured both in cell suspensions and at the single cell level using digital imaging of Fura-2 fluorescence. Tenidap also inhibited both antigen- and thapsigargin-induced 45Ca influx across the plasma membrane at concentrations similar to those required for the inhibition of secretion. Somewhat unexpectedly, the compound itself caused some release of calcium from intracellular stores; however, this effect did not appear to be related to the inhibition of calcium influx or secretion. In mouse pituitary tumour (AtT-20) cells, tenidap inhibited depolarization-induced increases in intracellular Ca2+ suggesting that this compound also inhibits Ca2+ influx through voltage-sensitive calcium channels. We conclude that tenidap has a number of interesting effects on calcium handling which makes it a potentially valuable tool for the study of calcium movements particularly in non-excitable cells.

5-lipoxygenase inhibitors and their anti-inflammatory activities

A wide variety of agents have been reported as 5-LO inhibitors. The majority of the series appear to be lipophilic reducing agents, including phenols, partially saturated aromatics, and compounds containing heteroatom-heteroatom bonds. Many of these are not selective 5-LO inhibitors, but often affect CO and other LOs as well. In vivo systemic activity for many of these has been, in general, disappointing, probably because of poor bioavailability caused by lipophilicity and metabolic instability (oxidation, and conjugation of phenolic compounds). However, topically a number of agents have shown promise for skin inflammation, with Syntex's lonapalene the most advanced of these. Most results published to date appear more disappointing in the allergy/asthma field. More excitingly, a few structural types are selective 5-LO inhibitors which have shown systemic activity in vivo and in the clinic. Abbott's zileuton (136) appears to be one of the leading compounds in this category, along with other hydroxamates such as BW-A4C (129) from Burroughs-Wellcome. Recent selective non-reducing agents such as Wyeth-Ayerst's Wy-50,295 (143) and the similar ICI compounds such as ICI 216800 (145) also hold promise. The enantiospecific effects of (106) and (145) are especially interesting for the design of new inhibitors. If compounds like these validate the hypothesis that inhibition of 5-LO will have a significant anti-inflammatory effect, a redoubling of effort throughout the industry to find second- and third-generation selective agents may be expected. Part of the difficulty in interpreting and comparing the 5-LO literature is the plethora of test methods and activity criteria. As pointed out in the introduction, inhibition of product release from cells, often stimulated with A23187, has commonly been used to demonstrate 5-LO inhibition. However, this type of assay cannot be assumed to be diagnostic for 5-LO inhibition. Only if specificity for 5-LO product generation and (ideally) activity in cell-free enzymes is also shown should mechanistic interpretations be made. Recently, a new class of compounds was found at Merck which inhibited LT biosynthesis without inhibiting 5-LO, but apparently by a novel, specific mechanism. L-655,240 (169) and L-663,536 (MK-886) (170) were both active in human ISN, with IC50 values in the low micromolar range. Both also orally inhibited GPB (< 1 mg/kg). MK-886 was effective in Ascaris-induced asthma in squirrel monkeys, in rat carrageenan pleurisy, in rat Arthus pleurisy, and (topically) in guinea-pig ear oedema induced by A23187.(ABSTRACT TRUNCATED AT 400 WORDS)