In vitro antimicrobial activity of T-91825, a novel anti-MRSA cephalosporin, and in vivo anti-MRSA activity of its prodrug, TAK-599.

TAK-599 is a water-soluble prodrug of a cephalosporin compound, T-91825. In vitro and in vivo antibacterial activities of T-91825 and TAK-599, respectively, were examined. T-91825 was active against both gram-positive and gram-negative bacteria, unlike vancomycin and linezolid, which are inactive against gram-negative bacteria. The 90% minimum inhibitory concentration of T-91825 against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) was 2 micro g/ml. This activity was comparable to those of vancomycin, linezolid, teicoplanin, and arbekacin. T-91825 was similarly active against vancomycin-intermediate S. aureus. In a time-kill study, T-91825 showed more rapid and distinct decrease of viable cells of two MRSA strains than did vancomycin and linezolid in vitro. The effect of TAK-599 against systemic infection caused by clinical isolates of MRSA in mice was comparable or superior to that of vancomycin, linezolid, teicoplanin, and arbekacin. In addition, TAK-599 at a dose of 20 mg/kg significantly decreased bacterial counts in lungs of mice in an experimental pneumonia model caused by MRSA in which vancomycin and linezolid were totally ineffective at the same dose. These results suggest the usefulness of TAK-599 in the treatment of MRSA infections in humans.

Synthesis and anti-Helicobacter pylori activity of pyloricidin derivatives II. The combination of amino acid residues in the dipeptidic moiety and its effect on the anti-Helicobacter pylori activity.

The novel natural antibiotics pyloricidin A, B and C, consisting of a common (2S,3R,4R,5S)-5-amino-2,3,4,6-tetrahydroxyhexanoyl-beta-D-phenylalanine moiety and a terminal peptidic moiety (pyloricidin A: L-valine-L-valine-L-leucine; pyloricidin B: L-valine-L-leucine; pyloricidin C: L-leucine), exhibit potent and highly selective anti-Helicobacter pylori activity. In order to develop more potent compounds and to investigate structure activity relationships for the peptidic moiety with regard to the combination of amino acids, a series of derivatives with various dipeptidic moieties were prepared and evaluated for their anti-H. pylori activity. The combination of the two amino acids in the moiety was found to have a significant effect on the activity; the compound with Nva-Abu showed excellent anti-H. pylori activity with an MIC value of 0.013 microg/ml against H. pylori TN2. In addition, this compound was found to show 60% clearance of H. pylori from infected Mongolian gerbils upon repetitive oral administration (10 mg/kg, b. i. d. for 7 days).

Adherence of Helicobacter pylori to gastric epithelial cells and mucosal inflammation.

Adherence of Helicobacter pylori to the gastric epithelium is believed to be an important step in the induction of active inflammation of the mucosal layer. However, structural evidence showing a quantitative relationship between the adherence of H. pylori and severity of gastric mucosal inflammation is lacking. We therefore investigated the correlations between severity of gastritis and adherence of morphologically different forms of H. pylori. Fifty-seven biopsy specimens from the gastric bodies of patients with H. pylori-induced gastritis were examined. The severity of gastritis and the adherence and structure of H. pylori were determined with the use of light and scanning electron microscopy. We also investigated the ability of H. pylori organisms with different structural features to induce interleukin-8 secretion by human gastric adenocarcinoma (AGS) cells in vitro because production of interleukin-8 is related to H. pylori-associated gastritis. Furthermore, serum pepsinogen concentrations and cytotoxin-associated protein status in relation to adherence of H. pylori to the epithelial surface were examined. The results indicated that H. pylori organisms, which adhered firmly to the epithelial surface, were consistently long, tightly coiled bacilli. Histologically, those gastric mucosa samples with H. pylori firmly attached showed severe gastritis. H. pylori bacilli of greater length induced higher levels of interleukin-8 secretion. The serum pepsinogen I/II ratio showed a significant negative correlation with the grade of H. pylori adhesion (r = -0.401, P <.01). We also noted a significant correlation between cytotoxin-associated protein status and the adherence of H. pylori (r = 0.344, P <.05). A quantitative correlation was found between adherence of H. pylori and gastric inflammation. Both adherence and the induction of inflammation were found to be related to the structure of H. pylori.

Total synthesis of novel antibiotics pyloricidin A, B and C and their application in the study of pyloricidin derivatives.

The novel natural antibiotics pyloricidin A, B and C, which possess potent and highly selective anti-Helicobacter pylori activity, were synthesized from D-galactosamine as a chiral template for the common (2S,3R,4R,5S)-5-amino-2,3,4,6-tetrahydroxyhexanoic acid moiety. The synthetic strategy, using 2-amino-2-deoxyuronic acid derivatives as key intermediates, was also useful to prepare a series of derivatives modified at the beta-D-phenylalanine and with altered stereochemistry on the 5-amino-2,3,4,6-tetrahydroxyhexanoic acid moiety. From the drastic decrease of their anti-H. pylori activity, it was clear that the beta-D-phenylalanine part and the stereochemistry of the 5-amino-2,3,4,6-tetrahydroxyhexanoic acid moiety were significant for the activity.

Synthesis and anti-Helicobacter pylori activity of pyloricidin derivatives I. Structure-activity relationships on the terminal peptidic moiety.

The novel natural antibiotics pyloricidin A, B and C possess potent and highly selective antibacterial activity against Helicobacter pylori. In order to investigate the structure activity relationships for the terminal peptidic moiety, a series of pyloricidin B and pyloricidin C derivatives, bearing various amino acids in the moiety, were prepared and evaluated for their anti-H. pylori activity. The derivatives bearing alpha-D-, beta- and gamma-amino acids or peptidemimetics showed drastically decreased activity. On the other hand, the derivatives with a-L-amino acids were found to maintain the activity. Among the derivatives prepared in this work, the allylglycine derivative 2s showed the most potent anti-H. pylori activity, with an MIC value of less than 0.006 microg/ml against H. pylori NCTC11637, which is 60-fold greater than the activity of the lead compound pyloricidin C.