APC 366

APC 366 is a selective and competitive inhibitor of tryptase [1, 2, 3]. After about 4 h of incubation with human tryptase, APC 366 showed an inhibitory potential with a Ki value of 530 nM and an IC50 value of 1400 ± 240 nM [3].

Tryptase is a mast cell serine protease. It had been implicated in the allergic asthma pathophysiology [2].

It seemed that actions of tryptase were dependent on an intact catalytic site. APC 366 inhibited DNA synthesis and the proliferation of the smooth muscle cell (SMC) induced by tryptase. In this study, thymidine incorporation was reduced by APC 366 by 79%. Heating to inactivate enzymatic activity also abolished the ability of tryptase to stimulate SMC proliferation and DNA synthesis [4].

In urine in the control pigs, the concentration of histamine was immediately elevated after allergen challenge. But treatment with APC 366 markedly decreased this release [5]. In vivo in a sheep model, administration with APC 366 decreased allergen-induced early and late-phase bronchoconstriction and hyperresponsiveness [4]. In allergic sheep, APC 366 was administered by aerosol in all experiments. In vehicle control trials, antigen challenge caused peak early and late increases in specific lung resistance with values of 259 ± 30% and 183 ± 27% over baseline, respectively. 0.5 h before, 4 h after and 24 h after antigen challenge, treatment with APC 366 at 9 mg/3 ml H2O slightly decreased the peak early response (194 ± 41%) and significantly inhibited the late response (38 ± 6%, p < 0.05) [2].

References:
[1].  Krishna MT, Chauhan A, Little L, et al. Inhibition of mast cell tryptase by inhaled APC 366 attenuates allergen-induced late-phase airway obstruction in asthma. Journal of Allergy and Clinical Immunology, 2001, 107(6): 1039-1045.
[2].  Clark JM, Abraham WM, Fishman CE, et al. Tryptase inhibitors block allergen-induced airway and inflammatory responses in allergic sheep. American journal of respiratory and critical care medicine, 1995, 152(6): 2076-2083.
[3].  Hallgren J, Estrada S, Karlson U, et al. Heparin antagonists are potent inhibitors of mast cell tryptase. Biochemistry, 2001, 40(24): 7342-7349.
[4].  Berger P, Perng DW, Thabrew H, et al. Tryptase and agonists of PAR-2 induce the proliferation of human airway smooth muscle cells. Journal of Applied Physiology, 2001, 91(3): 1372-1379.
[5].  Sylvin H, Dahlbck M, Van Der Ploeg I, et al. The tryptase inhibitor APC-366 reduces the acute airway response to allergen in pigs sensitized to Ascaris suum. Clinical & Experimental Allergy, 2002, 32(6): 967-971.

The tryptase inhibitor APC-366 reduces the acute airway response to allergen in pigs sensitized to Ascaris suum.[Pubmed:12047446]

Clin Exp Allergy. 2002 Jun;32(6):967-71.

BACKGROUND: Tryptase is a mast cell serine protease that is released during mast cell degranulation. It has been implicated as an important enzyme in the pathophysiology of asthma, but its role in this disease is not fully elucidated. OBJECTIVE: In this study, we investigated the effects of a tryptase inhibitor, APC-366, on the acute allergic airway reaction in specific pathogen-free pigs sensitized to the antigen Ascaris suum. METHODS: APC-366 (5 mg in 1 mL of water, each dose) was given as an aerosol to seven pigs two times (t); at t = - 60 min and t = - 15 min Control pigs received water. Ascaris antigen (in 2 mL saline) was nebulized to the airways over approximately 5 min at t = 0. All aerosols were generated with an ultrasonic nebulizer. RESULTS: The allergen challenge caused an acute reaction with a significant increase in airway resistance (R(aw)) in the control pigs from 3.3 +/- 0.6 cmH20/l/s to 10.2 +/- 2.3 cmH20/l/s, while in the APC-366-treated pigs, the R(aw) increased from 2.6 +/- 0.4 cmH20/l/s to 4.5 +/- 0.7 cmH20/l/s (P < 0.05 compared to controls). The dynamic lung compliance (C(dyn)) decreased significantly in the control pigs, but not in the APC-366-treated animals. The histamine concentration in urine in the control pigs was elevated immediately after allergen challenge, while this release was markedly reduced in the APC-366-treated pigs. CONCLUSION: The tryptase inhibitor APC-366 reduces the acute airway response to allergen significantly. There is also a reduced elevation in urine histamine concentration after challenge in the treated pigs, compared to controls. These results indicate that inhibition of mast cell tryptase might be a useful anti-allergic treatment in asthma.

Inhibition of mast cell tryptase by inhaled APC 366 attenuates allergen-induced late-phase airway obstruction in asthma.[Pubmed:11398082]

J Allergy Clin Immunol. 2001 Jun;107(6):1039-45.

BACKGROUND: APC 366, a selective inhibitor of mast cell tryptase, has been shown to inhibit antigen-induced early asthmatic response (EAR), late asthmatic response (LAR), and bronchial hyperresponsiveness (BHR) in a sheep model of allergic asthma. OBJECTIVE: The purpose of this study was to investigate the effects of APC 366 on antigen-induced EAR, LAR, and BHR in mild atopic asthmatics not on any anti-inflammatory therapy. METHODS: Sixteen mild atopic asthmatics, each with a demonstrable antigen-induced EAR, LAR, and BHR to histamine, were recruited into this randomized, double-blinded, crossover study. APC 366 (5 mg)/placebo was administered by aerosol inhalation 3 times per day on treatment days 1 through 4. Allergen challenge was carried out on day 4. Histamine challenge was performed the following morning, 1 hour after final dosing. RESULTS: Subjects were shown to have a significantly smaller overall mean area under the curve for the LAR (P =.012) and mean maximum fall in FEV(1) for the LAR (P =.007) after pretreatment with APC 366 in comparison with placebo. No significant effects on BHR were demonstrable. Although the EAR was reduced by 18% after treatment with APC 366 in comparison with placebo, this was not statistically significant. CONCLUSION: Short-term repeated administration of APC 366 significantly reduced the magnitude of antigen-induced LAR in atopic asthmatics, which supports the role of mast cell tryptase in the pathophysiology of the LAR.

Tryptase inhibitor APC 366 prevents hepatic fibrosis by inhibiting collagen synthesis induced by tryptase/protease-activated receptor 2 interactions in hepatic stellate cells.[Pubmed:24735816]

Int Immunopharmacol. 2014 Jun;20(2):352-7.

Protease-activated receptor (PAR) 2 is a G-protein-coupled receptor that is activated by mast cell tryptase. PAR-2 activation augments profibrotic pathways through the induction of extracellular matrix proteins. PAR-2 is widely expressed in hepatic stellate cells (HSCs), but the role of tryptase/PAR-2 interaction in liver fibrosis is unclear. We studied the development of bile duct ligation (BDL)-induced hepatic fibrosis in rats treated with mast cell tryptase inhibitor APC 366, and showed that APC 366 reduced hepatic fibrosis scores, collagen content and serum biochemical parameters. Reduced fibrosis was associated with decreased expression of PAR-2 and alpha-smooth muscle actin (alpha-SMA). Our findings demonstrate that mast cell tryptase induces PAR-2 activation to augment HSC proliferation and promote hepatic fibrosis in rats. Treatment with tryptase antagonists may be a novel therapeutic approach to prevent fibrosis in patients with chronic liver disease.

Inhibitors of tryptase as mast cell-stabilizing agents in the human airways: effects of tryptase and other agonists of proteinase-activated receptor 2 on histamine release.[Pubmed:14722328]

J Pharmacol Exp Ther. 2004 Apr;309(1):119-26.

Tryptase, the major secretory product of human mast cells, is emerging as a new target for therapeutic intervention in allergic airways disease. We have investigated the ability of tryptase and inhibitors of tryptase to modulate histamine release from human lung mast cells and have examined the potential contribution of proteinase-activated receptor 2 (PAR2). The tryptase inhibitor APC366 [N-(1-hydroxy-2-naphthoyl)-L-arginyl-L-prolinamide hydrochloride] was highly effective at inhibiting histamine release stimulated by anti-IgE antibody or calcium ionophore from enzymatically dispersed human lung cells. A concentration of APC366 as low as 10 microM was able to inhibit anti-IgE-dependent histamine release by some 50%. Addition of leupeptin or the tryptic substrate N-benzoyl-D,L-arginine-p-nitroanilide also inhibited IgE-dependent histamine release. Purified tryptase in the presence of heparin stimulated a small but significant release of histamine from lung cells, suggesting that tryptase may provide an amplification signal from activated cells that may be susceptible to proteinase inhibitors. Trypsin was also able to induce histamine release apparently by a catalytic mechanism. Moreover, pretreatment of cells with metabolic inhibitors or with pertussis toxin reduced responses, indicating a noncytoxic pertussis toxin-sensitive G protein-mediated signaling process. Addition to cells of the PAR2 agonists SLIGKV-NH(2) or tc-LIGRLO-NH(2) or appropriate control peptides were without effect on histamine release, and PAR2 was not detected by immunohistochemistry in tissue mast cells. The potent actions of tryptase inhibitors as mast cell-stabilizing agents could be of value in the treatment of allergic inflammation of the respiratory tract, possibly by targeting the non-PAR2-mediated actions of tryptase.

Tryptase mediates hyperresponsiveness in isolated guinea pig bronchi.[Pubmed:9877219]

Life Sci. 1998;63(26):2295-303.

Hyperresponsiveness of airway smooth muscle to allergens and environmental factors has long been associated with the pathophysiology of asthma. Tryptase, a serine protease of lung mast cells, has been implicated as one of the mediators involved in the induction of hyperresponsiveness. As a consequence, tryptase inhibitors have become the subject of study as potential novel therapeutic agents for asthma. Secretory leukocyte protease inhibitor (SLPI) is a naturally occurring protein of human airways which exhibits anti-tryptase activity. To assess the potential therapeutic utility of SLPI in asthma, its effects were evaluated using in vitro and ex vivo models of airway hyperresponsiveness and compared with the effects of the small molecule tryptase inhibitor APC-366. Our results demonstrate that SLPI inhibits tryptase-mediated hyperresponsiveness in vitro and attenuates the hyperresponsiveness observed in airway smooth muscle from antigen-sensitized animals subjected to antigen exposure. The small molecule tryptase inhibitor APC-366 has a similar inhibitory effect. Thus, tryptase appears to be a significant contributor to the development of hyperresponsiveness in these models. To the extent that tryptase contributes to the development and progression of asthma, SLPI may possess therapeutic potential in this disease setting.

A role for tryptase in the activation of human mast cells: modulation of histamine release by tryptase and inhibitors of tryptase.[Pubmed:9655871]

J Pharmacol Exp Ther. 1998 Jul;286(1):289-97.

Tryptase, the most abundant protein product of human mast cells is emerging as an important mediator and target for therapeutic intervention in allergic disease. We have investigated the potential of tryptase and inhibitors of tryptase to modulate histamine release from human mast cells. Addition of purified human tryptase in concentrations ranging from 1 to 100 mU/ml stimulated a concentration-dependent release of histamine from cells dispersed from tonsil, although not from skin tissue. The reaction dependent on an intact catalytic site being inhibited by heat inactivation of the enzyme, or by preincubating with the tryptase inhibitors APC366 or leupeptin or the tryptic substrate N-benzoyl-DL-arginine-p-nitroanilide (BAPNA). Tryptase-induced histamine release took approximately 6 min to reach completion, appeared to require exogenous calcium and magnesium, and on the basis of inhibition by antimycin A and 2-deoxy-D-glucose, seemed to be a noncytotoxic process. Pre-incubation of cells with tryptase at concentrations that were suboptimal for histamine release had little effect on their responsiveness to anti-immunoglobulin (Ig) E or to calcium ionophore A23187, but at higher concentrations their subsequent activation was inhibited. APC366 significantly inhibited histamine release induced by anti-IgE or calcium ionophore from both tonsil and skin cells, with up to 90% inhibition being observed at a concentration of 100 microM with skin. IgE-dependent histamine release was inhibited also by leupeptin, benzamidine and BAPNA. Tryptase may act as an amplification signal for mast cell activation, and this could account at least partly for the potent mast cell stabilizing properties of tryptase inhibitors.