A picogram BA-ELISA quantification assay for rLj-RGD3, a platelet fibrinogen receptor antagonist, in the rat plasma and its application to a pharmacokinetic study.

rLj-RGD3, a new member of the RGD (Arginine-Glycine-Aspartate)-motif toxin protein family obtained from Lampetra japonica by means of recombinant DNA techniques, has been demonstrated to be a platelet fibrinogen receptor antagonist and holds potential as a drug candidate for a specific indication. The present article reports an innovative validated highly sensitive and specific biotin-avidin enzyme linked immunosorbent assay (BA-ELISA) to provide a bio-analytical method for pharmacokinetic (PK) studies of rLj-RGD3. The concentration of picogram level rLj-RGD3 in rat plasma was measured using the developed double sandwich BA-ELISA assay, which used two mouse anti-rLj-RGD3 monoclonal antibodies that recognize different epitopes for capture and detection. This method was verified to be highly specific (blank plasma did not interfere with detection), precise (RSD <15%), and accurate (86%-113%). Absolute recovery was in the 94%-119% range. The calibration curve showed good linearity within the 50 to 1600 pg/mL range. The LOQ was as low as 50 pg/mL. The above validated assay was successfully employed to assess PK of rLj-RGD3 in rats. After i.v. and s.c. dosing with 30 μg/kg, the rLj-RGD3 plasma concentration declined bi-exponentially with time. This decay was best fitted to a two-compartment model. In conclusion, the BA-ELISA method described here meets all requirements for PK studies of rLj-RGD3 with an effective pharmacological dose in the μg/kg BW range.