Plasma Protein Binding of Nine Antisense Oligonucleotides by Ultrafiltration

Plasma protein binding (PPB) data are known to be important for understanding the pharmacokinetic (PK) and pharmacodynamic (PD) behaviors of antisense oligonucleotides (ASOs). However, ASOs present unique challenges in fraction unbound determination through traditional techniques considering their properties such as relatively high molecular weight, linear structure, and nonspecific binding. We described an accurate and reliable ultrafiltration (UF) method combined with LC-MS/MS analysis for determining the PPB of ASOs using 9 commercially available ASO compounds. Results showed high equilibrium rate and low nonspecific binding, with the fraction unbound in plasma being consistent with the previously reported data. The ultracentrifugation (UC) performance was also evaluated and discussed in this study.