Discovery of novel 3,6-disubstituted 2-pyridinecarboxamide derivatives as GK activators

A novel class of 3,6-disubstituted 2-pyridinecarboxamide derivatives was designed based on X-ray analysis of the 2-aminobenzamide lead class. Subsequent chemical modification led to the discovery of potent GK activators which eliminate potential toxicity concerns associated with an aniline group of the lead structure. Compound 7 demonstrated glucose lowering effect in a rat OGTT model.     

Discovery and structure–activity relationships of a novel class of quinazoline glucokinase activators

We describe design, syntheses and structure–activity relationships of a novel class of 4,6-disubstituted quinazoline glucokinase activators. Prototype quinazoline leads (4 and 5) were designed based on the X-ray analyses of the previous 2-aminobenzamide lead classes. Modifications of the quinazoline leads led to the identification of a potent GK activator (21d).     

N-terminal domain of the murine coronavirus receptor CEACAM1 is responsible for fusogenic activation and conformational changes of the spike protein

The mouse hepatitis virus (MHV) receptor (MHVR), CEACAM1, has two different functions for MHV entry into cells: binding to MHV spike protein (S protein) and activation of the S protein to execute virus-cell membrane fusion, the latter of which is accompanied by conformational changes of the S protein. The MHVR comprising the N-terminal and fourth domains [R1(1,4)] displays these two activities, and the N domain is thought to be critical for binding to MHV. In this study, we have addressed whether or not the N domain alone is sufficient for these activities. We examined three types of soluble form MHVR (soMHVR), one consisting of the N domain alone [soR1(1)], one with the N and second domains [soR1(1,2)], and one [soR1(1,4)] expressed by recombinant baculoviruses. We assessed the abilities of these three types of soMHVR to bind to MHV, activate fusogenicity, and induce conformational changes of the S protein. All three types of soMHVR similarly bound to MHV, as examined by a solid-phase binding assay and neutralized MHV infectivity. They also activated S protein fusogenicity and induced its conformational changes with similar levels of efficiency. However, R1(1) expressed on the BHK cell surface failed to serve as a receptor in spite of a sufficient level of expression. The inability of expressed R1(1) to work as a receptor was due to the inaccessibility of virions to R1(1); however, these were accessible using the MHVR-specific monoclonal antibody CC1. These results collectively indicated that the N domain retains all biological activities necessary for receptor function.     

Discovery of potent and orally active 3-alkoxy-5-phenoxy-N-thiazolyl benzamides as novel allosteric glucokinase activators

Identification and synthesis of novel 3-alkoxy-5-phenoxy-N-thiazolyl benzamides as glucokinase activators are described. Removal of an aniline structure of the prototype lead (2a) and incorporation of an alkoxy or phenoxy substituent led to the identification of 3-Isopropoxy-5-[4-(methylsulfonyl)phenoxy]-N-(4-methyl-1,3-thiazol-2-yl)benzamide (27e) as a novel, potent, and orally bioavailable GK activator. Rat oral glucose tolerance test indicated that 27e exhibited a glucose-lowering effect after 10 mg/kg oral administration.     

The design and optimization of a series of 2-(pyridin-2-yl)-1H-benzimidazole compounds as allosteric glucokinase activators

The optimization of a series of benzimidazole glucokinase activators is described. We identified a novel and potent achiral benzimidazole derivative as an allosteric GK activator. This activator was designed and synthesized via removal of the chiral center of the lead compound, 6-(N-acylpyrrolidin-2-yl)benzimidazole. The activator exhibited good PK profiles in rats and dogs, and significant hypoglycemic efficacy at 1 mg/kg po dosing in a rat OGTT model. The binding site and binding mode of the benzimidazole class of GKA with GK protein was confirmed by X-ray crystallographic analysis.     

Impaired processing and presentation of cytotoxic-T-lymphocyte (CTL) epitopes are major escape mechanisms from CTL immune pressure in human immunodeficiency virus type 1 infection

Investigating escape mechanisms of human immunodeficiency virus type 1 (HIV-1) from cytotoxic T lymphocytes (CTLs) is essential for understanding the pathogenesis of HIV-1 infection and developing effective vaccines. To study the processing and presentation of known CTL epitopes, we prepared Epstein-Barr virus-transformed B cells that endogenously express the gag gene of six field isolates by adopting an env/nef-deletion HIV-1 vector pseudotyped with vesicular stomatitis virus G protein and then tested them for the recognition by Gag epitope-specific CTL lines or clones. We observed that two field variants, SLFNTVAVL and SVYNTVATL, of an A*0201-restricted Gag CTL epitope SLYNTVATL, and three field variants, KYRLKHLVW, QYRLKHIVW, and RYRLKHLVW, of an A24-restricted Gag CTL epitope KYKLKHIVW escaped from being killed by the CTL lines, despite the fact that they were recognized when the synthetic peptides corresponding to these variant sequences were exogenously loaded onto the target cells. Thus, their escape is likely due to the changes that occur during the processing and presentation of epitopes in the infected cells. Mutations responsible for this mode of escape were located within the epitope regions rather than the flanking regions, and such mutations did not influence the virus replication. The results suggest that the impaired antigen processing and presentation often occur in HIV-1 field isolates and thus are one of the major mechanisms that enable HIV-1 to escape from CTL recognition. We emphasize the importance of testing HIV-1 variants in an endogenous expression system.     

Identification of novel and potent 2-amino benzamide derivatives as allosteric glucokinase activators

The identification and structure–activity-relationships (SARs) of novel 2-amino benzamide glucokinase activators are described. Compounds in this series were developed to be potent GK activators, and their binding mode to the GK protein was determined by crystal structure analysis. In vivo pharmacokinetic and acute in vivo efficacy studies of compound 18 are also described.     

Role of Mouse Hepatitis Virus (MHV) Receptor Murine CEACAM1 in the Resistance of Mice to MHV Infection: Studies of Mice with Chimeric mCEACAM1a and mCEACAM1b

Although most inbred mouse strains are highly susceptible to mouse hepatitis virus (MHV) infection, the inbred SJL line of mice is highly resistant to its infection. The principal receptor for MHV is murine CEACAM1 (mCEACAM1). Susceptible strains of mice are homozygous for the 1a allele of mCeacam1, while SJL mice are homozygous for the 1b allele. mCEACAM1a (1a) has a 10- to 100-fold-higher receptor activity than does mCEACAM1b (1b). To explore the hypothesis that MHV susceptibility is due to the different MHV receptor activities of 1a and 1b, we established a chimeric C57BL/6 mouse (cB61ba) in which a part of the N-terminal immunoglobulin (Ig)-like domain of the mCeacam1a (1a) gene, which is responsible for MHV receptor function, is replaced by the corresponding region of mCeacam1b (1b). We compared the MHV susceptibility of these chimeric mice to that of SJL and B6 mice. B6 mice that are homozygous for 1a are highly susceptible to MHV-A59 infection, with a 50% lethal dose (LD₅₀) of 10^2.5 PFU, while chimeric cB61ba mice and SJL mice homozygous for 1ba and 1b, respectively, survived following inoculation with 10⁵ PFU. Unexpectedly, cB61ba mice were more resistant to MHV-A59 infection than SJL mice as measured by virus replication in target organs, including liver and brain. No infectious virus or viral RNA was detected in the organs of cB61ba mice, while viral RNA and infectious virus were detected in target organs of SJL mice. Furthermore, SJL mice produced antiviral antibodies after MHV-A59 inoculation with 10⁵ PFU, but cB61ba mice did not. Thus, cB61ba mice are apparently completely resistant to MHV-A59 infection, while SJL mice permit low levels of MHV-A59 virus replication during self-limited, asymptomatic infection. When expressed on cultured BHK cells, the mCEACAM1b and mCEACAM1ba proteins had similar levels of MHV-A59 receptor activity. These results strongly support the hypothesis that although alleles of mCEACAM1 are the principal determinants of mouse susceptibility to MHV-A59, other as-yet-unidentified murine genes may also play a role in susceptibility to MHV.Differences in susceptibility to a number of viral infections have been documented among inbred mouse strains (20). These differences have been studied as models for the various degrees of susceptibility of individual humans to some viral infections. Numerous host factors have been found to be involved in such differences (2, 15). For example, allelic variations in the virus receptor and coreceptor for HIV-1 are important host factors influencing susceptibility to HIV-1 infection (36).A virus receptor is a molecule with which the virus interacts at an initial step of infection. Therefore, receptors are crucial host determinants of virus susceptibility (15, 16). A variety of receptor proteins has been identified for many different viruses, including the murine coronavirus mouse hepatitis virus (MHV) (12, 50). The principal receptor for MHV is murine carcinoembryonic antigen-related cell adhesion molecule 1 (mCEACAM1; previously called Bgp or MHVR [3]), which is in the immunoglobulin (Ig) superfamily (12, 50). Four isoforms of mCEACAM1a (1a) are expressed on the plasma membranes of a variety of murine cells and tissues (14). The two mCEACAM1 isoforms with a molecular mass of 100 to 120 kDa are composed of four Ig-like ectodomains, a transmembrane (TM) domain, and either a long or a short cytoplasmic tail (Cy) (3, 22). Two other isoforms consist of two Ig-like domains, with either long or short Cy (3, 22). The N-terminal (N) domain is responsible for virus binding (10, 24), the induction of conformational changes in the viral spike protein (S), and membrane fusion during virus entry and syncytium formation (13, 24). The replacement of the N-terminal domain of mCEACAM1a with that of the murine homolog of the poliovirus receptor (PVR) yields a functional receptor for MHV (10), and Ceacam1a-knockout mice are completely resistant to infection with the hepatotropic A59 strain of MHV (17, 25).Wild mice have two alleles of the mCeacam1 gene, called mCeacam1a and mCeacam1b. Inbred mouse strains that are homozygous for mCeacam1a, including BALB/c, C57BL/6 (B6), C3H, and A/J mice, etc., are highly susceptible to infection with strains of MHV. In contrast, the SJL line of inbred mice, which is resistant to death from MHV infection, is homozygous for the mCeacam1b allele (5, 11, 50). The most extensive differences in amino acid sequence between mCEACAM1a and mCEACAM1b are found in the N-terminal domain, where the virus-binding region is located (21, 22, 32). It was initially reported by Boyle et al. that mCEACAM1a proteins had MHV-A59 virus-binding activity in a virus overlay protein blot, while mCEACAM1b did not (5). Those authors speculated that the different viral affinities of these mCEACAM1 proteins may account for the various MHV-A59 susceptibilities of BALB/c mice compared to those of SJL mice (49). However, Yokomori and Lai (53) and Dveksler et al. (11) previously showed that when recombinant CEACAM1a and CEACAM1b proteins are expressed at high levels on cultured cells, both proteins have MHV-A59 receptor activity. Yokomori and Lai suggested that the difference in MHV susceptibility between BALB/c and SJL mice does not depend solely upon the interaction of the virus with mCEACAM1 proteins (52, 53). Dveksler et al. suggested that small differences in MHV-A59 receptor activity between mCEACAM1a and mCEACAM1b could result in very large biological differences during multiple cycles of infection in in vivo infection (11). We then quantitatively showed that recombinant mCEACAM1a expressed in BHK cells has 10- to 30-times-higher MHV-binding activity than mCEACAM1b (31). Similar results were observed in other laboratories (7, 32). Because the mCeacam1 gene is located on chromosome 7 (34) and the gene controlling MHV-A59 susceptibility and the resistance of BALB/c mice versus SJL mice is also located on chromosome 7 close to the mCeacam1 gene (40), we speculated that the mCeacam1 gene is identical to the gene that determines the susceptibility and/or resistance of mice to MHV-A59 and MHV-JHM infection.To examine the above-described hypothesis, we used progeny mice produced by crossing BALB/c and SJL mice. F₂ mice and F₁ mice backcrossed to SJL mice were examined for the mCeacam1 genotype and for MHV-JHM susceptibility (30). Mice homozygous for mCeacam1a (1a/1a) and heterozygous mice (1a/1b) were susceptible to lethal MHV-JHM infection, while mice homozygous for mCeacam1b (1b/1b) were not killed by inoculation with MHV-JHM. These data are consistent with the hypothesis that the susceptibility of mice to MHV is determined by the mCeacam1a allele (30). However, this classical genetic analysis could not prove that mCeacam1 alone determines the susceptibility or resistance of mice to MHV-JHM infection, because this methodology cannot rule out the possibility that a different unknown host gene located close to mCeacam1 on chromosome 7 could also affect MHV-JHM susceptibility. Therefore, we used gene replacement in B6 embryonic stem (ES) cells to create a mouse strain in which the exon encoding the N-terminal part of the N-terminal Ig domain of mCeacam1a was replaced with the corresponding region of mCeacam1b from SLJ mice. We bred the chimeric mCeacam1 gene on the B6 background (called B6 chimeric mCeacam1ba, or cB61ba). We compared these mice, wild-type B6 mice, and SJL mice for their susceptibilities to MHV-A59 infection. We confirmed that the expression of mCEACAM1a makes mice susceptible to lethal infection with MHV-A59. However, surprisingly, we found that cB61ba mice were profoundly resistant to MHV-A59 infection, while the virus could replicate at low levels in SJL mice in a self-limited, unapparent infection. Our results suggest that one or more as-yet-unidentified murine genes may also contribute to murine susceptibility and/or resistance to MHV-A59 infection.     

Formation and characterization of kinesin.ADP.fluorometal complexes

Recent crystallographic studies of motor proteins showed that the structure of the motor domains of myosin and kinesin are highly conserved. Thus, these motor proteins, which are important for motility, may share a common mechanism for generating energy from ATP hydrolysis. We have previously demonstrated that, in the presence of ADP, myosin forms stable ternary complexes with new phosphate analogues of aluminum fluoride (AlF(4)(-)) and beryllium fluoride (BeF(n)), and these stable complexes mimic the transient state along the ATPase kinetic pathway [Maruta et al. (1993) J. Biol. Chem. 268, 7093-7100]. In this study, we examined the formation of kinesin.ADP.fluorometals ternary complexes and analyzed their characteristics using the fluorescent ATP analogue NBD-ATP (2'(3')-O-[6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoyl]-ADP). Our results suggest that these ternary complexes may mimic transient state intermediates in the kinesin ATPase cycle. Thus, the kinesin.ADP.AlF(4)(-) complex resembles the kinesin.ADP state, and the kinesin.ADP.BeF(n) complex mimics the kinesin.ADP.P(i) state.