Direct thrombin inhibitors built on the azaphenylalanine scaffold provoke degranulation of mast cells.
The main structural feature of direct thrombin inhibitor LK-732 responsible for the appropriate interaction at the thrombin active site is a strong basic group. A possibility that a strong basic group of LK-732 might contribute to the mast cell degranulation effect and consequent reduction of tracheal air flow (TAF) and fall of mean arterial blood pressure (MAP) in rats was investigated in the present study. At doses up to 5 mg/kg (i.v.), LK-732 did not cause significant changes of TAF and MAP. At 7 mg/kg (i.v.), a sudden reduction of TAF and a fall of MAP was observed within 5 min after LK-732 administration (75% mortality, p = 0.007). A less basic direct thrombin inhibitor LK-658 (21 mg/kg, i.v.) did not significantly disturb TAF and MAP. A reduction of TAF and a fall of MAP caused by LK-732 (7 mg/kg, i.v.) was almost completely abolished in rats with degranulated mast cells (0% mortality, p = 0.008). LK-732 concentration-dependently degranulated rat peritoneal mast cells in vitro (pEC(50) = 1.92 +/- 0.05 muM). A structure-activity relationship (SAR) study revealed that the terminal basic groups attached to the aromatic ring are responsible for the mast cell degranulation effect. A good correlation was observed between mast cell degranulation and pK(b) of analogues of LK-732 (R(2) = 0.49), but not between mast cell degranulation and thrombin K(i) (R(2) = 0.23). LK-732-induced reduction of TAF, the fall of MAP and high mortality originate from LK-732-induced mast cell degranulation. As judged by the SAR study, this effect could be overcome by reducing the basicity of LK-732.
Peternel
Luka
L
Drug Discovery, Lek Pharmaceuticals d.d., Verovskova 57, 1526 Ljubljana, Slovenia. luka.peternel@sandoz.com
Stempelj
Mateja
M
Cerne
Manica
M
Zega
Anamarija
A
Obreza
Ales
A
Oblak
Marko
M
Drevensek
Gorazd
G
Budihna
Metka V
MV
Stanovnik
Lovro
L
Urleb
Uros
U
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D015550:Cell Degranulation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D008407:Mast Cells / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity; D012123:Pulmonary Ventilation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013329:Structure-Activity Relationship; D015996:Survival Rate; D013917:Thrombin / Q000037:antagonists & inhibitors*
C493947:azaphenylalanine; D010649:Phenylalanine; D013917:Thrombin