Multiple actions of the leukotriene B4 receptor antagonist SC-41930.

7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8- propyl-2H-1-benzopyran-2-carboxylic acid (SC-41930), a leukotriene B4 (LTB4) receptor antagonist with anti-inflammatory activity in animal models of colitis, was evaluated for effects on superoxide, LTB4 and prostaglandin E2 production. SC-41930 inhibited human neutrophil (PMN) superoxide generation maximally stimulated by f-Met-Leu-Phe (IC50 4 microM) and C5a (IC50 approximately 12 microM). Moreover, postreceptor stimulation of superoxide production by NaF (a G protein activator), but not by phorbol myristate acetate, was significantly inhibited by SC-41930, indicating that SC-41930 may act via attenuation of a G protein-mediated signal transduction. SC-41930 also inhibited A23187-stimulated LTB4 production (IC50 5.3 microM) in human PMN as well as LTB4 (IC50 2.1 microM) and prostaglandin E2 (IC50 2.9 microM) production in HL-60 cells. When coinjected intradermally (400 micrograms/site), SC-41930 inhibited A23187-stimulated increases in LTB4 levels in guinea pig skin. SC-41930 inhibited human synovial phospholipase A2 (IC50 72 microM), A23187-stimulated 5-hydroxy-eicosatetranoic acid production in human PMN (IC50 8.5 microM), and rat peritoneal leukotriene A4 hydrolase (IC50 20 microM), but not ram seminal vesical cyclooxygenase. The results suggest that the anti-inflammatory activity of SC-41930 could be attributed to postreceptor inhibition of inflammatory mediator production by PMN and other cells in addition to antagonism of PMN LTB4 receptors.     

Molecular genetics and epidemiology of the NAT1 and NAT2 acetylation polymorphisms.

The focus of this review is the molecular genetics, including consensus NAT1 and NAT2 nomenclature, and cancer epidemiology of the NAT1 and NAT2 acetylation polymorphisms. Two N-acetyltransferase isozymes, NAT1 and NAT2, are polymorphic and catalyze both N-acetylation (usually deactivation) and O-acetylation (usually activation) of aromatic and heterocyclic amine carcinogens. Epidemiological studies suggest that the NAT1 and NAT2 acetylation polymorphisms modify risk of developing urinary bladder, colorectal, breast, head and neck, lung, and possibly prostate cancers. Associations between slow NAT2 acetylator genotypes and urinary bladder cancer and between rapid NAT2 acetylator genotypes and colorectal cancer are the most consistently reported. The individual risks associated with NAT1 and/or NAT2 acetylator genotypes are small, but they increase when considered in conjunction with other susceptibility genes and/or aromatic and heterocyclic amine carcinogen exposures. Because of the relatively high frequency of some NAT1 and NAT2 genotypes in the population, the attributable cancer risk may be high. The effect of NAT1 and NAT2 genotype on cancer risk varies with organ site, probably reflecting tissue-specific expression of NAT1 and NAT2. Ethnic differences exist in NAT1 and NAT2 genotype frequencies that may be a factor in cancer incidence. Large-scale molecular epidemiological studies that investigate the role of NAT1 and NAT2 genotypes and/or phenotypes together with other genetic susceptibility gene polymorphisms and biomarkers of carcinogen exposure are necessary to expand our current understanding of the role of NAT1 and NAT2 acetylation polymorphisms in cancer risk.     

The pharmacokinetics and metabolism of SC-53228, a specific leukotriene B4 receptor antagonist

Inflammation Research -     

Inflammation of guinea pig dermis

Neutrophil (PMNL) infiltration is a prominent feature of human psoriasis. Psoriatic skin lesions contain abnormally high amounts of leukotriene B₄ (LTB₄), itself a potent PMNL chemoattractant both in vivo and in vitro. SC-41930 {7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8-propyl-2H-1-benzo-pyran-2-carboxylic acid}, an orally active LTB₄ receptor antagonist, was tested topically in models of skin inflammation induced by 200 nmol of the calcium ionophore A23187 or 200g phorbol-12-myristate-13-acetate (PMA) applied topically to the guinea pig ear as assessed by ear weight, levels of the PMNL marker enzyme myeloperoxidase (MPO), and histological examination (PMA model) at 4 and 18 h respectively. When coapplied topically with A23187 or PMA, SC-41930 significantly inhibited epidermal inflammation with ED₅₀ values of 0.6 and 4 mg, respectively. SC-41930 treatment also was associated with lowered dermal LTB₄ levels in both models. The PMA-induced skin inflammation model also was assessed histologically and revealed acanthosis, edema, PMNL infiltration, and rete ridge prominence as long as 96 h after a single application that was completely inhibited by SC-41930 topical coapplication. Furthermore, oral treatment (40 mg/kg) significantly reduced edema and inflammatory cell infiltration in both models. These models possess many of the characteristics of human psoriasis, and agents such as SC-41930 that demonstrate activity in these models may well have therapeutic utility in the treatment of human psoriasis.     

Inflammatory mediator changes in cotton-top tamarins (CTT) after SC-41930 anti-colitic therapy

Use of the CTT model provides insight into the inflammatory mediator contribution in the pathogenesis of idiopathic colitis. To evaluate anti-colitic efficacy, the leukotriene B₄ receptor antagonist and anti-inflammatory agent, SC-41930, was administered (10 mg/kg BW by gavage BID) for 8 weeks to CTTs with histologically confirmed persistent and defined active colitis. The inflammatory mediators LTB₄, PGE₂, TXB₂, and PAF were assayed in colonic dialysate that was collected after 11/2 h from four CTTs pre-, mid-, and post-treatment, frozen at −70°C, and analyzed by RIA after HPLC purification. LTB₄ levels were lower at mid- and post-treatment and had little inter-animal variation post-treatment. PGE₂ and PAF levels were elevated during SC-41930 treatment, but there was a trend towards lower thromboxane B₂ levels. Reduced LTB₄ (PMN degranulation and chemotaxis) and increased PGE₂ (mucosal-protective effect) may, in part, explain the observed efficacy of SC-41930 in active tamarin colitis.

     

The design and synthesis of second generation leukotriene B4 (LTB4) receptor antagonists related to SC-41930

SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid, is a selective, orally active, LTB₄ receptor antagonist currently in clinical trials for psoriasis and ulcerative colitis. Exhaustive SAR studies found a potential backup compound, SC-50605, which was 7–16 times more potent than SC-41930 in LTB₄ receptor binding, chemotaxis and degranulation assays. SC-50605 also inhibited LTB₄-induced intradermal chemotaxis in cavine skin at an oral dose of 0.10 mg/kg and displayed good activity in animal models of colitis and epidermal inflammation both orally and topically.     

Effects of the prostaglandin analogue misoprostol on inflammatory mediator release by human monocytes

The effect of misoprostol (M) on IL-1, TNF-, and lipid mediator release (assessed by RIA) by adherent (assessed by electron microscopy) human monocytes were studiedin vitro. Human monocytes stimulated with E. Coli-derived lipopolysaccharide showed an increase in both IL-1 and TNF- release. Incubation of the monocytes with LPS and M (18 hrs.), resulted in a reduction of both IL-1 and TNF- levels. Leukotriene B₄ levels did not increase in response to LPS or M. LPS also caused an increase in thromboxane (TXB₂).M decreased TXB₂ levels. 6-keto PGF1 (6KP). Incubation with LPS and M stimulated release. LPS caused an increase in PGE₂ levels. M (100 M) caused an increase in PGE₂ levels, M (1 M) had no effect on PGE₂. These data suggest a possible immunomodulatory role for misoprostol in inflammatory diseases.     

Prostate-specific human N-acetyltransferase 2 (NAT2) expression in the mouse.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic amine identified in the human diet and in cigarette smoke that produces prostate tumors in the rat. PhIP is bioactivated by cytochrome P-450 enzymes to N-hydroxylated metabolites that undergo further activation by conjugation enzymes, including the N-acetyltransferases, NAT1 and NAT2. To investigate the role of prostate-specific expression of human N-acetyltransferase 2 (NAT2) on PhIP-induced prostate cancer, we constructed a transgenic mouse model that targeted expression of human NAT2 to the prostate. Following construction, prostate, liver, lung, colon, small intestine, urinary bladder, and kidney cytosols were tested for human NAT1- and NAT2-specific N-acetyltransferase activities. Human NAT2-specific N-acetyltransferase activities were 15-fold higher in prostate of transgenic mice versus control mice, but were equivalent between transgenic mice and control mice in all other tissues tested. Human NAT1-specific N-acetyltransferase activities did not differ between transgenic and control mice in any tissue tested. Prostate cytosols from transgenic and control mice did not differ in their capacity to catalyze the N-acetylation of 2-aminofluorene, the O-acetylation of N-hydroxy-2-aminofluorene and N-hydroxy-PhIP or the N,O-acetylation of N-hydroxy-2-acetylaminofluorene. Transgenic and control mice administered PhIP did not differ in PhIP-DNA adduct levels in the prostate. This study is the first to report transgenic expression of human NAT2 in the mouse. The results do not support a critical role for bioactivation of heterocyclic amine carcinogens by human N-acetyltransferase-2 in the prostate. However, the lack of an effect may relate to the level of overexpression achieved and the presence of endogenous mouse acetyltransferases and/or sulfotransferases.