AntiTNF-alpha agents in the treatment of inflammation

Tumour necrosis factor/cachecin (TNF-alpha) and lymphotoxin (LTalpha / TNF-alpha), 2 members of the TNF family of cytokines, have numerous biological functions, such as induction of apoptosis, cytotoxicity, inflammation, immunoregulation, proliferation and antiviral responses. Although TNF-alpha is produced by many cell types, the majority comes from activated macrophages. The related molecule, LT-alpha is produced mainly by activated lymphocytes and shares many of TNF's properties. TNF-alpha is active in both of its molecular forms, a secreted 17 kDa mature form and a transmembrane 26 kDa precursor. It induces activity by stimulating 2 distinct receptor subtypes, TNFR1 (55 kDa) and TNFR2 (75 kDa). The activation of TNFR1 is generally thought to trigger the majority of inflammatory and apoptotic effects, although TNFR2 has recently been shown to play more of a role in signal transduction than was initially thought. TNF-alpha is responsible for the induction of apoptosis in certain cell types, where it plays a pivotal role in the induction of cytotoxicity, killing of neoplastic cells and deletion of autoreactive T-cell clones. This cytokine, and in particular, its overproduction, has been implicated in the pathogenesis of a variety of immunologically mediated inflammatory diseases, including endotoxic shock, inflammatory bowel disease (IBD), multiple sclerosis (MS) and rheumatoid arthritis (RA). Currently, there is an intense effort underway to regulate TNF-alpha production and activity, in order to treat diseases where TNF-alpha is thought to be pathologically indicated. To achieve this goal, the pharmaceutical industry is currently pursuing a 2 pronged strategy: a) testing biological agents such as antibodies against TNF-alpha or soluble TNF-alpha receptor constructs, and b) identifying small molecular inhibitors directed against targets such as phosphodiesterase-IV (PDE-IV) and TNF-alpha converting enzyme (TACE), a subgroup of the matrix metalloproteinases (MMP). The main difficulties in the clinical implementation of the biological agents are: development of immunogenicity, lack of oral availability and the high cost of production. The currently available small molecular compounds exhibit poor bio-availability and low selectivity, resulting in unacceptable side effects and a low therapeutic index. Despite these hurdles, numerous companies are actively pursuing agents that inhibit TNF-alpha.

Pharmacokinetics and immunological effects of exogenously administered recombinant human B lymphocyte stimulator (BLyS) in mice

B lymphocyte stimulator (BLyS; also known as TNFSF20, BAFF, TALL-1, zTNF4, and THANK), a tumor necrosis factor ligand family member, has recently been identified as a factor that promotes expansion and differentiation of the B cell population, leading to increases in serum immunoglobulin levels. Here, pharmacokinetic parameters for BLyS administered i.v. and s.c. to mice are described, and the effects of different dosing regimens on serum and salivary immunoglobulin levels as well as splenic cell populations are reported. The pharmacokinetics of BLyS following i.v. injection are monophasic with a half-life of 160 min, a clearance of 0.22 ml/min-kg, and a volume of distribution of 53 ml/kg. Systemic administration of BLyS to mice resulted in increased serum IgG, IgA, IgM, and IgE and salivary IgA as well as splenic B cell population expansion and differentiation. The i.v. and s.c. routes of administration were pharmacologically equivalent, even though s.c. bioavailability of BLyS is only 25%. BLyS (s.c.) dramatically elevated serum IgG and IgA levels, and the duration of the responses after cessation of treatment (t(1/2) = 4.4 and 1.3 days, respectively) are similar to the half-lives of endogenous IgG and IgA in mice. The IgM response is more modest than that of IgG and IgA but lasts longer (t(1/2) = 7.0 days) than the half-life of endogenous IgM. A linear pharmacodynamic response was identified between days of dosing x log(dose), and increases in serum IgG, IgA, and IgM indicating that the response is more sensitive to the duration of dosing than to the cumulative dose. The implications of these findings for therapeutic administration of BLyS are discussed.

Caspase-1 processes IFN-gamma-inducing factor and regulates LPS-induced IFN-gamma production

Interferon-gamma-inducing factor (IGIF, interleukin-18) is a recently described cytokine that shares structural features with the interleukin-1 (IL-1) family of proteins and functional properties with IL-12. Like IL-12, IGIF is a potent inducer of interferon (IFN)-gamma from T cells and natural killer cells. IGIF is synthesized as a biologically inactive precursor molecule (proIGIF). The cellular production of IL-1beta, a cytokine implicated in a variety of inflammatory diseases, requires cleavage of its precursor (proIL-1beta) at an Asp-X site by interleukin-1beta-converting enzyme (ICE, recently termed caspase-1). The Asp-X sequence at the putative processing site in proIGIF suggests that a protease such as caspase-1 might be involved in the maturation of IGIF. Here we demonstrate that caspase-1 processes proIGIF and proIL-1beta with equivalent efficiencies in vitro. A selective caspase-1 inhibitor blocks both lipopolysaccharide-induced IL-1beta and IFN-gamma production from human mononuclear cells. Furthermore, caspase-1-deficient mice are defective in lipopolysaccharide-induced IFN-gamma production. Our results thus implicate caspase-1 in the physiological production of IGIF and demonstrate that it plays a critical role in the regulation of multiple proinflammatory cytokines. Specific caspase-1 inhibitors would provide a new class of anti-inflammatory drugs with multipotent action.

A canine model for determination of the therapeutic index of cytokine inhibitors

Using tumor necrosis factor (TNF) inhibition in dog blood as a measure of efficacy, and canine emesis as a measure of toxicity, we were able to assign a therapeutic index to rolipram, a prototypic anti-inflammatory compound. Because both assays were performed in the same species, the ambiguities associated with comparing the physiologic effects of drugs on various species was avoided. Rolipram, a standard phosphodiesterase type IV inhibitor, was a prototypic test compound characterized by a number of cardiovascular and central nervous system side effects, as well as its in vitro and in vivo inhibition of TNF. Initial experiments with canine whole blood incubated with lipopolysaccharide resulted in nanogram-per-milliliter concentrations of TNF that could be significantly reduced by in vitro addition of a 0.03 microM concentration of rolipram. Because rolipram inhibited canine TNF production in vitro, a protocol was devised in which TNF inhibitory activity was measured in a series of blood samples from dogs infused with increasingly high doses of rolipram. This yielded the efficacy half of the therapeutic index, whereas the emetogenic dose represented the side effect portion of the index. Rolipram was infused stepwise into conscious dogs at gradually increasing doses. The infusion was stopped when vomiting occurred, and the cumulative dose was reported as the emetic dose. Rolipram caused emesis in dogs at a cumulative dose of 0.1 mg/kg. At each dose of rolipram, blood was collected. The whole blood was incubated in vitro with lipopolysaccharide to induce TNF production, which in turn was quantified by the L929 bio-assay. Theoretically, if the rolipram infusion raised blood values high enough, the rolipram in whole blood would inhibit TNF production and be reflected by a lack of TNF activity in the L929 assay. In this assay system, rolipram's 50% effective dose in the TNF assay was always at least 33-fold lower than its emetic dose of 0.1 mg/kg. This gave rolipram a therapeutic index of at least 33:1 (0.003 versus 0.1 mg/kg) on the basis of its activity in a canine efficacy model (TNF inhibition) and a toxicity model (emesis induction). Experimental compounds were tested for their emetic dose as well as TNF 50% effective dose, with the goal of obtaining a therapeutic index better than that of rolipram. Thus the coupling of cytokine activity with overt toxicity was used to arrive at the therapeutic index of a compound. The therapeutic index was used to rank compounds as to their efficacy/toxicity profile. This ranking was used to eliminate several anti-inflammatory compounds that had a therapeutic index less than that of rolipram.

Inhibition of cartilage and bone destruction in adjuvant arthritis in the rat by a matrix metalloproteinase inhibitor

Considerable evidence has associated the expression of matrix metalloproteinases (MMPs) with the degradation of cartilage and bone in chronic conditions such as arthritis. Direct evaluation of MMPs' role in vivo has awaited the development of MMP inhibitors with appropriate pharmacological properties. We have identified butanediamide, N4-hydroxy-2-(2-methylpropyl)-N1-[2-[[2-(morpholinyl)ethyl]-,[S- (R*,S*)] (GI168) as a potent MMP inhibitor with sufficient solubility and stability to permit evaluation in an experimental model of chronic destructive arthritis (adjuvant-induced arthritis) in rats. In this model, pronounced acute and chronic synovial inflammation, distal tibia and metatarsal marrow hyperplasia associated with osteoclasia, severe bone and cartilage destruction, and ectopic new bone growth are well developed by 3 wk after adjuvant injection. Rats were injected with Freund's adjuvant on day 0. GI168 was was administered systemically from days 8 to 21 by osmotic minipumps implanted subcutaneously. GI168 at 6, 12, and 25 mg/kg per d reduced ankle swelling in a dose-related fashion. Radiological and histological ankle joint evaluation on day 22 revealed a profound dose related inhibition of bone and cartilage destruction in treated rats relative to rats receiving vehicle alone. A significant reduction in edema, pannus formation, periosteal new bone growth and the numbers of adherent marrow osteoclasts was also noted. However, no significant decrease in polymorphonuclear and mononuclear leukocyte infiltration of synovium and marrow hematopoietic cellularity was seen. This unique profile of antiarthritic activity indicates that GI168 is osteo- and chondro-protective, and it supports a direct role for MMP in cartilage and bone damage and pannus formation in adjuvant-induced arthritis.

Anti-inflammatory activity of phosphodiesterase (PDE)-IV inhibitors in acute and chronic models of inflammation

Inhibitors of cyclic nucleotide phosphodiesterases are known to suppress lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) production in vitro in human monocytes. The most potent of these have selectivity for type IV PDEs, suggesting that this class of PDE is the major type involved in the regulation of human TNF-alpha production. Using compounds of two distinct chemical structural classes, a quinazolinedione (CP-77059) and a 4 arylpyrrolidinone (rolipram), we show here that PDE-IV-specific inhibitors are also potent in suppressing LPS-induced TNF-alpha production in vitro in sodium periodate-elicited murine macrophages (IC50s of 1 and 33, respectively). We then report the in vivo anti-inflammatory effect of PDE-IV inhibition in five murine models of inflammation: (i) elevation of serum TNF-alpha induced by a sublethal LPS injection; (ii) LPS-induced endotoxic shock; (iii) LPS/galactosamine-induced endotoxic shock; (iv) carrageenan-induced paw oedema; and (v) adjuvant arthritis. Following a sublethal (5 micrograms/mouse) injection of LPS, serum TNF-alpha levels in mice peaked sharply, reaching concentrations of 3-12 ng/ml 90 min after injection. In this sublethal LPS assay, CP-77059 was about 30 times more potent than rolipram, with a minimum effective dose of 0.1 mg/kg versus 3 mg/kg for rolipram. This rank order is in keeping with the relative in vitro IC50s for CP-77059 and rolipram, as well as their relative Ki against the human PDE-IV enzyme (46 nM and 220 nM, respectively). In LPS-induced endotoxic shock, rolipram and CP-77059 at relatively high doses of 30 and 10 mg/kg, respectively, significantly reduced serum TNF-alpha levels, and also inhibited mortality 66%. In the LPS/galactosamine shock model, in which mice are rendered exquisitely sensitive to LPS by co-injection with galactosamine, only 0.1 microgram of LPS/mouse is necessary for serum TNF-alpha elevation and death. Both rolipram and the CP-77059 caused dose-dependent reduction of serum TNF-alpha and lethality. In the carrageenan-induced paw oedema model, in which there is a pronounced local TNF-alpha response (without a serum TNF-alpha elevation), rolipram significantly inhibited paw swelling as well as localized TNF-alpha levels in the paw. In the adjuvant arthritis model, a chronic model of inflammation also possessing localized TNF-alpha elevation in the inflamed paw, rolipram and CP-77059 suppressed ankle swelling and radiological evidence of joint damage. These data are consistent with a major role for PDE-IV in regulation of TNF-alpha production and inflammatory responses in murine systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Anti-inflammatory activity of salmeterol: down-regulation of cytokine production

Elevation of intracellular cAMP levels has been shown previously to inhibit cytokine secretion by various cell types in vitro. Since salmeterol is a beta 2-agonist which activates adenylate cyclase, its ability to inhibit cytokine production was evaluated. Though salmeterol, and the related drug albuterol, did not inhibit IL-1 beta production in vitro, both drugs did inhibit tumour necrosis factor-alpha (TNF-alpha) secretion by lipopolysaccharide (LPS)-activated THP-1 cells with similar IC50s of approximately 0.1 microM. This inhibition was effectively reversed by the beta 2-antagonist oxprenolol, indicating that the inhibition was mediated through the beta 2-adrenergic receptor. A strikingly different reactivity profile was seen with T cells. Salmeterol was able to inhibit the activation of both mouse and human T cells, as measured by proliferation and IL-2 secretion in response to anti-CD3 antibody, whereas albuterol was completely inactive in these assays. This T cell inhibition by salmeterol was about 10-fold less potent than that for TNF-alpha production, and was not reversed by a beta 2-antagonist, indicating that a different mechanism was involved in the effect of salmeterol on T cells. Paralleling the TNF-alpha inhibitory activity in vitro, oral dosing of salmeterol and albuterol inhibited LPS-induced increase in murine serum TNF level in vivo, with ED50s of approximately 0.1 mg/kg. This inhibition could be abrogated by dosing orally with the beta-blocker propranolol. The long-acting pharmacological profile of salmeterol was apparent in that it maintained its efficacy for 3 h, while albuterol had a much shorter duration of action. Salmeterol also had some protective effects in the galactosamine/LPS model of endotoxic shock, which is dependent upon TNF-alpha production. Though salmeterol inhibited serum TNF-alpha levels by up to 94% in this assay, it protected less than 50% of the animals from the lethal effects of the LPS/galactosamine mixture. This observation suggests that functional levels of TNF-alpha localized in tissues may not be accurately reflected by serum levels.

Evaluation of the significance of elevated levels of systemic and localized tumor necrosis factor in different animal models of inflammation

Elevated tumor necrosis factor (TNF) levels have been reported in various models of acute and chronic inflammation and used by many investigators to determine the stage of disease and effectiveness of treatment. Because of the documented involvement of TNF in the mechanism of septic shock, experiments were done to determine whether serum TNF levels paralleled the pathology in endotoxic shock and other models of inflammation. When mice received an intraperitoneal injection of lipopolysaccharide, serum TNF levels increased dramatically, peaking 90 minutes after injection. In a dose-response experiment with lipopolysaccharide alone, we found no correlation between serum levels of TNF and survival rate of mice. All three lipopolysaccharide concentrations resulted in comparable elevations of serum TNF, yet only in the high-dose group did the animals die. In a second model of endotoxic shock, TNF-alpha levels in serum were again compared with the survival rate of mice receiving lipopolysaccharide plus galactosamine. As in the first model, we found no relationship between the level of TNF in mouse serum and mouse survival rate. The two lowest concentrations of lipopolysaccharide/galactosamine induced identically low levels of serum TNF, yet in one group all of the animals survived and in the other all died. Discrepancies between serum TNF level and mortality rate were also seen in drug treatment experiments. GI 147404X, a standard phosphodiesterase type IV inhibitor, inhibited lipopolysaccharide/galactosamine-induced elevation of serum TNF by 90% at doses of 1 and 10 mg/kg. However, the high dose resulted in 66% protection while the low dose afforded no protection.(ABSTRACT TRUNCATED AT 250 WORDS)