2.3. PASylation Strongly Prolongs Tα1 Pharmacokinetics in Rats
To mimic the clinically approved route of Zadaxin™ administration, the N-acetylated Tα1-PAS was injected subcutaneously into the dorsal area of rats (N = 5). The injected dose of 3.4 mg/kg Tα1-PAS was well tolerated without any drug-related adverse events or significant changes in body weight. The Tα1-PAS plasma levels at various sampling times were analyzed using a quantitative sandwich ELISA developed to detect only Tα1-PAS and no endogenous rat Tα1, which shares 100% sequence identity with the human peptide. The pharmacokinetic (PK) profile of Tα1-PAS (Figure 4) exhibited a typical curve according to the Bateman function [40], with a Cmax of 25.6 ± 4.4 mg/L at tmax = 22.7 ± 1.1 h. Curve fitting with the WinNonlin software revealed a drastically extended terminal half-life of 15.9 ± 0.9 h, which is more than 8-fold longer than the one for the native peptide (τ1/2 = 1.9 h) published for rats [41]. The strong impact of PASylation on the PK profile is also reflected by other parameters such as the large area under the curve (AUC) and slow clearance (CL) (Table 1).