Synthesis and evaluation of 1-arylsulfonyl-3-piperazinone derivatives as factor Xa inhibitor

Intravascular clot formation is an important factor in a number of cardiovascular diseases. Therefore, the prevention of blood coagulation has become a major target for new therapeutic agents. One attractive approach is the inhibition of factor Xa (FXa), which is a key enzyme in coagulation cascade responsible for the generation of thrombin by limited proteolysis of its zymogen, prothrombin. We have investigated 1-arylsulfonyl-3-piperazinone derivatives, containing a 4-(piperidino)pyridine group in place of guanidino and/or amidino groups, and discovered compound M55113 (30a: 4-[(6-Chloro-2-naphthalenyl)sulfonyl]-1-[[1-(4-pyridinyl)-4-piperidinyl]methyl]piperazinone), as a potent inhibitor of FXa (IC50=0.06 microM) with high selectivity for FXa over trypsin and thrombin.

Six missense mutations associated with type I and type II protein C deficiency and implications obtained from molecular modelling

The molecular basis of protein C deficiency was studied in three type I and three type II heterozygotes. Three probands showed thrombotic complications. All the exons and intron/exon junctions of the protein C gene were studied using a strategy combining by the polymerase chain reaction (PCR) amplification, single-strand conformational polymorphism (SSCP) analysis, and DNA sequencing of the PCR-amplified fragments. Six missense mutations were identified, including three novel ones. One was located in exon II, in which the initiating translation codon (ATG) encoding for Met at position -42 was replaced by ACG encoding for Thr. The other five were located in exon IX, and included TAC(Tyr399)-->CAC(His), CCG(Pro327)-->CTG(Leu), GAC(Asp359)-->AAC(Asn) in two cases, and GGG(Gly350)-->AGG(Arg). Four of the six missense mutations occurred in CG dinucleotide. Sequence analysis of the other exons excluded additional mutations. By restriction enzyme analysis, co-segregation of the mutation with protein C deficiency was observed in four families. The other two mutations at amino acid positions -42 and 350 were also considered to be associated with protein C deficiency due to the absence of these mutations in 50 normal individuals. A structural model of the protease domain of mutant activated protein C was constructed by the chimeric modelling method, and the resultant model suggested conformational changes due to each missense mutation identified in protein C deficiency. The present data also provide some evidence regarding the genetic heterogeneity of protein C deficiency.

Factor IX Bm Kiryu: a Val-313-to-Asp substitution in the catalytic domain results in loss of function due to a conformational change of the surface loop: evidence obtained by chimaeric modelling

Factor IX Kiryu is a naturally occurring mutant of factor IX that has 2.5% coagulant activity, even though normal plasma levels of factor IX antigen are detected. Factor IX Kiryu was purified from a patient's plasma by immunoaffinity chromatography with a calcium-dependent anti-factor IX monoclonal antibody column. It was cleaved normally by factor XIa in the presence of Ca2+, yielding a two-chain factor IXa. However, the resulting factor IXa showed only 1.5% of the normal factor IXa in terms of factor X activation in the presence of factor VIII, phospholipids, and Ca2+, and had 20% of the normal esterase activity for Z-Arg-p-nitrobenzyl ester. Therefore factor IXa Kiryu showed the defect of the catalytic triad or primary substrate binding site as well as defective interaction with factors VIII/X. Single-strand conformational polymorphism analysis and DNA sequencing of the amplified DNA revealed a missense point mutation, a T-to-A substitution at nucleotide number 31,059 of the factor IX Kiryu gene. This mutation resulted in the amino acid substitution of Val-313 by Asp in the catalytic domain. Restriction enzyme analysis of the amplified DNA showed that the mutation was inherited from the patient's mother. The chimaeric method was employed to construct a model of the serine protease domain of factor IXa, and the resultant model suggested that the Val-313 to Asp substitution altered the conformation of the substrate-binding site. These data combined with our previous findings on a Gly-311-to-Glu mutant of factor IX suggest that the loop conformation from Gly-311 to ARg-318 is important for the expression of coagulant activity.

Design of variants of the second domain of urinary trypsin inhibitor (R-020) with increased factor Xa inhibitory activity

The second domain (R-020) of human urinary trypsin inhibitor (UTI) exerts similar inhibitory activities on trypsin, alpha-chymotrypsin, leukocyte elastase, and plasmin to those of UTI itself, and additionally inhibits coagulation factor Xa (FXa) and plasma kallikrein, on both of which UTI has no inhibitory effect. In the present study, we attempted to increase this FXa-inhibitory activity by modeling the structure of R-020-FXa complex and substituting one or two amino acids in R-020 using recombinant DNA technology. Molecular modeling of R-020 and FXa was performed with reference to X-ray analysis of the complex of bovine pancreatic trypsin inhibitor (BPTI) and bovine trypsin to determine the site of amino acid modification. The expression plasmids into which R-020 genes with base substitution were inserted were prepared and introduced into Escherichia coli to express R-020 variants. The resulting variants were purified and their enzyme inhibitory activities were measured. The FXa-inhibitory activity was increased in four variants with single amino acid substitution. With another four variants having two amino acid substitutions involving combinations of the above single amino acid substitutions, the FXa-inhibitory activity was further increased. Because the electrostatic interaction within R-020-FXa complex seemed stronger in these R-020 variants, this increase in FXa-inhibitory effect was speculated to be a consequence of more potent binding between the enzyme and the inhibitor.

Novel factor Xa and plasma kallikrein inhibitory-activities of the second Kunitz-type inhibitory domain of urinary trypsin inhibitor

Urinary trypsin inhibitor is a glycoprotein with a structure in which two Kunitz-type inhibitory domains are linked in a row. We isolated two genes encoding the 70 amino acid sequence from the 78th amino acid (Thr) to the C-terminal and the 68 amino acid sequence from the 80th (Ala) to the C-terminal of human urinary trypsin inhibitor, both which correspond to the second Kunitz-type inhibitory domain, and then constructed expression plasmids by ligating it to the E. coli alkaline phosphatase signal peptide gene. These plasmids under the control of the tryptophan promoter expressed the second domain in E. coli strain JE5505 which lacks the membrane lipoprotein. The recombinant second domain purified from the culture supernatant of the transformant inhibited trypsin, plasmin, leukocyte elastase and chymotrypsin which are known to be inhibited by urinary trypsin inhibitor. In addition it inhibited blood coagulation factor Xa and plasma kallikrein in a concentration dependent and competitive manner, and significantly prolonged the plasma-based activated partial thromboplastin time (APTT). The truncated natural counterpart obtained by a limited degradation of human urinary trypsin inhibitor also revealed the identical inhibitory activities.