Bradyzide, a potent non-peptide B₂ bradykinin receptor antagonist with long-lasting oral activity in animal models of inflammatory hyperalgesia

1. Bradyzide is from a novel class of rodent-selective non-peptide B₂ bradykinin antagonists (1-(2-Nitrophenyl)thiosemicarbazides). 2. Bradyzide has high affinity for the rodent B₂ receptor, displacing [³H]-bradykinin binding in NG108-15 cells and in Cos-7 cells expressing the rat receptor with K(I) values of 0.51 ± 0.18 nM (n = 3) and 0.89 ± 0.27 nM (n = 3), respectively. 3. Bradyzide is a competitive antagonist, inhibiting B₂ receptor-induced ⁴⁵Ca efflux from NG108-15 cells with a pK(B) of 8.0 ± 0.16 (n = 5) and a Schild slope of 1.05. 4. In the rat spinal cord and tail preparation, bradyzide inhibits bradykinin-induced ventral root depolarizations (IC₅₀ value; 1.6 ± 0.05 nM (n = 3)). 5. Bradyzide is much less potent at the human than at the rodent B₂ receptor, displacing [³H]-bradykinin binding in human fibroblasts and in Cos-7 cells expressing the human B₂ receptor with K(I) values of 393 ± 90 nM (n = 3) and 772 ± 144 nM (n = 3), respectively. Bradyzide inhibits bradykinin-induced [³H]-inositol trisphosphate (IP₃) formation with IC₅₀ values of 11.6 ± 1.4 nM (n = 3) at the rat and 2.4 ± 0.3 mM (n = 3) at the human receptor. 6. Bradyzide does not interact with a range of other receptors, including human and rat B₁ bradykinin receptors. 7. Bradyzide is orally available and blocks bradykinin-induced hypotension and plasma extravasation. 8. Bradyzide shows long-lasting oral activity in rodent models of inflammatory hyperalgesia, reversing Freund's complete adjuvant (FCA)-induced mechanical hyperalgesia in the rat knee joint (ED₅₀, 0.84 mmol kg^-1; duration of action > 4 h). It is equipotent with morphine and diclofenac, and 1000 times more potent than paracetamol, its maximal effect exceeding that of the non-steroidal anti-inflammatory drugs (NSAIDs). Bradyzide does not exhibit tolerance when administered over 6 days. 9. In summary, bradyzide is a potent, orally active, antagonist of the B₂ bradykinin receptor, with selectivity for the rodent over the human receptor.